Course Code: MSE 456
Materials Quality Control,
Assurance and Selection
Dr. Emmanuel Kwesi Arthur
Department of Materials Engineering,
Kwame Nkrumah University of Science and Technology,
Kumasi, Ghana
Email: ekarthur2005@yahoo.com
Phone #: +233541710532
©2019
1
Goal and Objectives
Goals: This course is a required course in Metallurgical and Materials
Engineering. The major goal is to provide an introduction to materials
selection in relation to the design process. It also focuses on materials
quality control and assurance.
There are several objectives for this course:
1.) To introduce the parameters that are important to design, to understand
how they are interrelated, to understand how they relate to the materials
selection process, and to use these concepts in engineering design.
2.) To develop the ability to use modern software (CES EduPack) in the
materials selection and design process.
3.) To develop the ability to obtain materials property and processing data
needed in the materials selection and design process from both handbooks
and electronic sources.
4.) To provide an introduction to team-oriented projects that introduce basic
approaches to product design and materials selection
5.) To introduce the common material quality control and assurance methods
used in materials manufacturing industries.
Resources:


Text
:

―Materials: engineering, science, processing and design‖
by M.F. Ashby, H.R. Shercliff and D. Cebon, Butterworth
Heinemann, Oxford 2007, Chapters 1 and 2

―Materials Selection in Mechanical Design‖, 4th edition
by M.F. Ashby, Butterworth Heinemann, Oxford, 2006,
Chapters 1 - 3.
Computer Software:

CES EduPack 2013 Design Software (grantadesign.com).
We will be using this software throughout the semester.
It can be used as a materials database, a processing
database, and a materials selection tool. It will be
installed on students‘ computers for practice.
Syllabus:

Attendance is your job – come to class!
Or our regularly scheduled time
(Tues. 4:00-6:00 pm & Thurs. 8:00 – 9:00 am)

Homeworks
 There will be homework in the form of problem sets and projects. The
projects will focus on materials selection and design and will frequently
include using the materials selection software, or library and web
research.
 The homework will typically be shorter assignments related to the
material being covered in lecture.
 Don‘t copy from others; don‘t plagiarize – its just the right thing to do!!

Tutorials – by Fuseini Abdullah (TA)

Grading
 Class Attendance, Pop Quizzes and Assignments – (5% of your
grade!)
 Mid Semester Exams – (15%)
 Group Project and Presentation (10%)
 End of Semester Exams (70%)

Homework: Homework problems will be uploaded on my website.
Each student will turn in homework to the TA one week after it
is assigned. On the day homework is due, students will be
randomly selected to solve selected homework problems,
explaining to the class how each problem is worked. Students are
encouraged to work together on homework. Students will be
evaluated on both the quality of their written answers and board
presentations.

Design Presentation: The class will be divided evenly into groups
for a materials selection in design projects. Projects for each
group will be assigned by the lecturer. Each group will write a
report on their respective project, as well as make an oral
presentation to the class.

Exams: Exams will be based on homework and information
provided in lecture, tutorials and assigned reading. All exams will
be closed book. The final will be cumulative. Relevant materials
selection charts, etc. will be provided.
Suggestions for success in this class:
1. Read the relevant material in the Ashby book (preferably before
the lecture topic)
2. Review and understand the examples given in the book.
3. Do the assigned homework. If you are having difficulty with a
particular concept, work additional problems given in the book on
that topic that have the answers given in the back of the book.
4. Seek help: tutors, etc.
Academic success is directly proportional to the amount of time
devoted to study.
Credits: 3 Credit Hours –Lecture
Prerequisite: No prerequisite, however, knowledge in strength of
materials and core materials courses is plus.
Office Hours:
I have an open door policy. If I am in my office, feel free to stop in
and ask questions about the class or any other materials questions you
may have. If you would like to meet at another time, please send me
an email with several available times.
Academic Dishonesty: In general, academic dishonesty will not be
tolerated. You will be practicing engineers in a few months. Integrity
and competence are critical to your professional success. Developing
bad habits in university will hinder your professional development and
will weaken the prestige of your degree.
Design Stage
Unit Objective...
Introduce fundamental design concepts in
Materials Selection
You will learn about:
• design
• how structure dictates properties
• how processing can change structure
This unit will help you to:
• use materials properly
• realize new design opportunities with materials
8
MATERIALS SELECTION
Introduction

Materials selection is an important part of a larger process of
creating new solutions to problems. This larger process is called
――Engineering Design‖‖

Design of engineering components is limited by the available
materials, and new designs are made possible by new materials

To see how important is the material selection in the design, consider
the definition of ――engineering‖‖ used by ABET in the U.S.A
According to Accreditation Board for Engineering and Technology
(ABET), Engineering is the profession in which a knowledge of the
mathematical and natural sciences gained by study, experience, and
practice is applied with judgement to develop ways to utilise
economically the materials and forces of nature for the benefit of
mankind
Materials Selection
Materials Selection
Why Materials Selection

An incorrectly chosen material may lead not
only to part failure, but also unnecessary
life-cycle cost.

Selection of material is also related with
processing of material.

Hence, the designer must seek for the best
combination of design-material-process.
Functional Requirements

For satisfying the need, designer must determine essential and desirable
features of the design.

They are expressed in the form of ―functional requirements‖ concerning
performance characteristics of materials (i.e. material properties).

As it is impossible to satisfy all requirements to the same degree, they are
arranged in the order of importance to identify the areas of compromise.
Design Limitations

Furthermore, a design must be in compliance with inevitable ―design
limitations‖.

Such requirements are expressed by means of 3M rule:
Manufacturing, Money, Maintenance

Manufacturing requirements are logically the first to be considered.
Hence, the designer must consider functional merits of the material
as well as its , ability to be machined, shaped, formed, cast, welded,
and so on.

Money (economic) requirements are based on the final product cost,
which is composed of raw material cost and production costs with
overheads. The cost of any product should be as high as the
customers can pay for it.

Finally, maintenance (service life) requirements will define whether
replacement or repair is required. They depend upon size of the part,
extent of possible damage, facilities of the customers, and the
acceptable level of costs.
Failure of Materials

Failure happens when a design is no longer able to satisfy any of functional requirements.

Failures not only cause costly damage, but also may lead to loss of lives as in airplane
crashes.

In most design problems, primary concern is to minimize the possibility of a premature
failure in service. The service life can be in seconds (in case of space applications) or
many years (in case of bridges).

Possible failure modes during service are as follows:

Excessive deformation: yielding, buckling, stress rupture (creep)

Fracture: sudden brittle, fatigue (progressive), time dependent (creep)

Inordinate wear: abrasion

Deterioration: chemical (corrosion or oxidation), embrittlement (ductile to brittle
transition), irradiation, natural (fungus, other growths)

In practice, it is impossible to predict failure mode of a part under severe service
conditions.

Some failures happen soon after the part is in service, which are covered by a factor of
safety.

However, time dependent failures are difficult or even impossible to avoid by applying
factor of safety. In such cases, parts are withdrawn from service and tested for
reliability. Such specific data are not found in general reference books.
Materials Selection
Classification of Engineering Materials
Machine Elements
18
Materials Selection
MATERIALS SELECTION
MATERIALS SELECTION IN DESIGNBASICS
Intro Lecture. Design Stage:
the first steps of optimised
selection
The design process and material search space
Market need
Material & process needs
Problem statement
Material search space
Choice of material family
(metals, ceramics, polymers..)
Concept
Choice of material class
(Steel, Al-alloy, Ni-alloy…..)
Embodiment
Screen
Screen
Rank
Choice of single material
(Al-2040, Al-6061, Al-7075…..)
All materials
Detail
Product specification
Increasing
constraints
Final choice
Need – Concept -- Embodiment
Concepts
Need
Embodiments
Direct pull
Levered pull
Geared pull
Spring assisted pull
Embodiment -- Detail
Methods of Material Selection

The common methods of material selection are as follows:
1. Performance indices (including the use of Ashby charts)
2. Decision matrices
– Pugh selection method
– Weighted property index
3. Selection with Artificial Intelligence tools (i.e. Expert Systems)
4. Selection with Computer-Aided Databases
5. Value analysis
6. Failure analysis
7. Benefit-cost analysis

We will be focusing on computer-Aided Databases, performance indices
and weighted property index.
The decision-making strategy
Normative information
Factual information
Material attributes
Process attributes
Design requirements
including prompts for
Constraints and
Objectives
expressed as
Intuitive estimation
Methodic information
Comparison engine
 Screening
 Ranking
 Documentation
Final selection
Translation to create Normative information
Translation: “express design requirements as constraints”
Design requirements
Function
A label
Constraints
What essential conditions must it meet ?
Objectives
What measure of performance is to
be maximized or minimized ?
Free variables
 Be strong enough
 Conduct electricity
 Tolerate 250 oC
 Be able to be cast
What does the component do ?
Which design variables are free ?




Cost
Weight
Volume
Eco-impact
Choice of
material
QUESTIONS
Translation: a heat sink for power electronics
Power micro-chips get hot.
They have to be cooled to
prevent damage.
Design requirements
Keep chips below 200 C
without any electrical
coupling.
Translation
Function
Constraints
Heat sink
1. Max service temp > 200 C
2. “Good electrical insulator”
3. “Good thermal conductor”
(or T-conduction > 25 W/m.K)
Free variable
Choice of material
Screening using a LIMIT STAGE
Screening: “Eliminate materials that can’t do the job”
Browse
Select
Search
Print
1. Selection data
Search web
A Limit stage
Edu Level 2: Materials
Mechanical properties
2. Selection Stages
Graph
Limit
Tree
Thermal properties
Maximum service temperature
Thermal conductivity
Min.
Max
200
25
Specific heat
Results
Ranking
X out of 95 pass Prop 1
Prop 2
Material 1
Material 2
Material 3
Material 4
etc...
113
300
5.6
47
2230
2100
1950
1876
C
W/m.K
J/kg.K
Electrical properties
Electrical conductor
or insulator?
Good conductor
Poor conductor
Semiconductor
Poor insulator
Good insulator
Screening using a GRAPH STAGE
File
Edit
View
Browse
Select
Select
Tools
Search
Print
Search web
1. Selection data
WC
Edu Level 2: Materials
Steel
Copper
2. Selection Stages
Graph
Limit
Alumina
CFRP
2000C
PEEK
Tree
Aluminum
Zinc
Glass
PP
PTFE
GFRP
Fibreboard
Lead
Results
Ranking
X out of 95 pass Prop 1
Material 1
Material 2
Material 3
Material 4
etc...
2230
2100
1950
1876
Prop 2
113
300
5.6
47
Don’t need
numbers!
T-conductivity (W/m.s)
Metals
Polymers
Ceramics
Composites
1000
Ceramics
Metals
100
10
Polymers &
elastomers
Composites
1
0.1
Foams
0.01
1
1010
1020
Electrical resistivity (.cm)
1030
Screening using a TREE STAGE
Browse
Select
Search
1. Selection data
Print
Search web
Tree stage for material
Edu Level 2: Materials
2. Selection Stages
Graph
Limit
Results
Tree
Material
Ceramics
Steels
Hybrids
Al alloys
Metals
Cu alloys
Polymers
Ni alloys...
Tree stage for process
X out of 95 pass
Material 1
Material 2
Material 3
Material 4
etc...
Join
Process
Shape
Surface
Cast
Deform
Mold
Composite
Powder
Prototype
Stacking selection stages
Browse
Select
Search
Print
Search web
Stacked stages
1. Selection data
Edu Level 2: Materials
Join
Process
2. Selection Stages
Graph
Limit
Tree
Shape
Surface
Min
Ranking
X out of 95 pass Prop 1
Prop 2
Material 1
Material 2
Material 3
Material 4
etc...
113
300
5.6
47
2230
2100
1950
1876
Property
Results
Density
Modulus
Strength
T-conduction
Cast
Deform
Mold
Composite
Powder
Prototype
Max
2
200
100
10
Translation: a CD case, an example of redesign
CD cases are made of polystyrene
(PS). They crack and scratch the
disks. Find a better material.
Translation
Design requirements
 Injection-moldable
 Contain and protect CD
better than the PS case.
 As transparent as PS
 Recylable
Function
CD enclosure
Constraints
1. Can be injection molded
2. Toughness K1c > that of PS
3. Optically clear
4. Can be recycled
Free variable
Choice of material
The CD case: the whole story
Select Level 2: Materials
2
Translation
Function
CD enclosure
Constraints
Tree stage: injection mold
Fracture toughness
1
Keep these!
Polystyrene
Optical properties
1. Can be injection molded
Transparency
2. Toughness K1c > that of PS

Transparent
3
3. Optically clear
Translucent
Eco properties
Opaque
4. Can be recycled
Free variable
Material
Optical quality
Recycle

Documentation: the pedigree
Documentation: “now that the number of candidates is small, explore their
character in depth”
Handbooks
Trade
associations
Suppliers’
data sheets
Material
portals
Documentation:
the “pedigree” of surviving candidates
Granta’s Web Portal (http://matdata.net) gives
indexed access to information providers’ web sites.

Quiz 1
1)
The cases in which most CDs are sold have an
irritating way of cracking and breaking. Which
design-limiting property has been neglected in
selecting the material of which they are
made?
2) State
two reasons why proper materials
selection procedure should be used in choosing
suitable material for a given application
Documentation with CES
Browse
Select
Search
Print
Search web
1. Selection data
Matdata.net
Edu Level 2: Materials
Searches information sources
for selected record
2. Selection Stages
Graph
Limit
Tree
Age hardening ALUMINUM ALLOYS
The material
The high-strength aluminum alloys rely
on age-hardening: a sequence of heat
treatment steps that causes the precipitation
of a nano-scale dispersion of intermetallics
that impede dislocation motion and impart strength.
Results
X out of 94 pass
Material 1
Material 2
Material 3
Material 4
Material 5
………..
Open the record
General properties
Density
Price
2500 - 2900
1.423 - 2.305
kg/m^3
USD/kg
68
95
180
1
60
57
21
GPa
MPa
MPa
%
HV
MPa
MPa.m^1/2
Mechanical properties
Young's modulus
Elastic limit
Tensile strength
Elongation
Hardness - Vickers
7
Fatigue strength at 10 cycles
Fracture toughness
-
80
610
620
20
160
210
35
Thermal properties
Thermal conductor or insulator?
Thermal conductivity
Good conductor
118 - 174
W/m.K
The main points
The four steps of selection:
1. Translation, giving constraints and objectives
2. Screening , using constraints
3. Ranking, using objectives
4. Documentation in CES, and http://matdata.net
CES allows Screening using
• Limit stages,
• Graph stages
• Tree stages and
• All three in any number and sequence
These are
often enough !
Pause for demo
Exercise: Stage 1, a tree stage
3.1 A material is required for a molded electrical
enclosure that may be used outdoors. There are
requirements on
 Processing (this Stage)
 Properties (Stage 2)
 Price (Stage 3)
Browse
Select
Search
1. Selection data
Edu
Edu Level
Level2:
2: Materials
Materials
2. Selection Stages
Graph
Limit
Tree
Apply Stage 1 – a Tree Stage





Tree stage
ProcessUniverse
Shaping
Molding -- Insert
OK
Now add Stage 2 – next page
Select from
materials or
process tree
Exercise: Stage 2, a limit stage
3.2 The material of the enclosure must have




Hardness - Vickers
Be a good electrical insulator
Have dielectric strength
Be able to be recycled
> 8 HV
> 10 MV/m
Browse
Select
Search
1. Selection data
Edu
Edu Level
Level2:
2: Materials
Materials
2. Selection Stages
Graph
Limit
Mechanical properties
Hardness - Vickers
8
HV
Enter
limits
Electrical properties
Good conductor
Conductor or insulator?
Poor conductor
Poor insulator
Good insulator
Dielectric strength
10
Eco properties
Recycle
Now add Stage 3 – next page
MV/m
Tree
Exercise: Stage 3, a graph stage
3.3 The material of the enclosure should be as cheap
as possible. Find the four materials meeting all the
previous constraints that have the lowest price per kg.



Graph stage – Y-axis – Price
Hide all materials failing previous stages
Rank the final Results list by Price
Browse
3. Results: 15 of 95 pass
Price (USD/kg)
Polypropylene (PP)
Soda-lime glass
Polystyrene (PS)
Polyvinylchloride (tpPVC)
Polyethylene terephthalate (PET)
Polyethylene (PE)
Polyoxymethylene (Acetal, POM)
Polymethyl methacrylate
Acrylonitrile butadiene styrene (ABS)
Polyamides (Nylons, PA)
Polycarbonate (PC)
Polylactide (PLA)
Polyurethane (tpPUR)
Cellulose polymers (CA)
Polyetheretherketone (PEEK)
1.41 - 1.62
1.41 - 1.659
1.476 - 1.574
1.6 - 2.2
1.608 - 1.769
1.718 - 1.89
2.203 - 2.732
2.335 - 2.569
2.511 - 2.952
3.194 - 3.569
3.6 - 4.47
3.667 - 4.584
3.723 - 4.45
3.921 - 4.313
99.14 - 109
Search
1. Selection data
Edu
Edu Level
Level2:
2: Materials
Materials
2. Selection Stages
Graph
Choose
Y-axis
Name
Select
Limit
Tree
Assignment 1
1) What is meant by the design-limiting properties of a material in a
given application?
2) There have been many attempts to manufacture and market plastic
bicycles. All have been too flexible. Which design-limiting property is
insufficiently large?
3) What, in your judgement, are the design-limiting properties for the
material for the blade of a knife that will be used to cut fish?
4) What, in your judgement, are the design-limiting properties for the
material of an oven glove?
5) What, in your judgement, are the design-limiting properties for the
material of an electric lamp filament?
6) A material is needed for a tube to carry fuel from the fuel tank to
the carburetor of a motor mower. The design requires that the tube
can bend and that the fuel be visible. List what you would think to be
the design-limiting properties.
Assignment 1
7) A material is required as the magnet for a magnetic soap holder. Soap
is mildly alkaline. List what you would judge to be the design-limiting
properties.
8) List three applications that, in your judgement, need high stiffness
and low weight.
10) List three applications that, in your judgement, need optical quality
glass.
Exercise 1
Exploring design using CES
1)
Designers need to be able to find data quickly and reliably. That is where
the classifications come in. The CES system uses the classification scheme
described in this unit. Before trying these exercises, open the Materials
Universe in CES and explore it. The opening screen offers options—take
the Edu Level 2: Materials.
2)
Use the ‗Browse‘ facility in Level 2 of the CES Software to find the record
for Copper. What is its thermal conductivity? What is its price?
3)
Use the ‗Browse‘ facility in Level 2 of the CES Software to find the record
for the thermosetting polymer Phenolic. Are they cheaper or more
expensive than Epoxies?
4)
Use the ‗Browse‘ facility to find records for the polymer-shaping processes
Rotational molding. What, typically, is it used to make?
5)
Use the ‗Search‘ facility to find out what Plexiglas is. Do the same for
Pyroceram.
6)
Use the ‗Search‘ facility to find out about the process Pultrusion. Do the
same for TIG welding. Remember that you need to search the Process
Universe, not the Material Universe.
Quiz 2
1)
Compare Young‘s modulus E (the stiffness property) and
thermal conductivity λ (the heat transmission
property) of aluminum alloys (a non-ferrous metal),
alumina (a technical ceramic), polyethylene (a
thermoplastic polymer) and neoprene (an elastomer) by
retrieving values from CES Level 2. Which has the
highest modulus? Which has the lowest thermal
conductivity?
End of Unit 3
Lecture 4. Ranking:
refining the choice
Outline

Selection has 4 basic steps
Step 1
Translation: express design requirements as constraints
and objectives
Step 2
Screening: eliminate materials that cannot do the job
Step 3
Ranking: find the materials that do the job best
Step 4 Documentation: explore pedigrees of top-ranked
candidates

Exercises
More info:
• “Materials: engineering, science, processing and design”, Chapter 3, 4 and 6
• “Materials Selection in Mechanical Design”, Chapters 5 and 6
Unit 3
This
Unit
Unit 3
Analysis of design requirements
Express design requirements as constraints and objectives
Bike frame
Design requirements
Function
A label
What does the
component do ?
Constraints What essential
conditions must be met ?
Objectives
Free variable
What is the criterion
of excellence ?
What can be
varied ?
Choice of
material
Must be
 Stiff enough
 Strong enough
 Tough enough
 Able to be welded
Minimize
 Cost
 Weight
 Volume
 Eco-impact
Common constraints and objectives
Case Study – Material Selection

Problem: Select suitable material for
bicycle frame and fork.
Steel and
alloys
Wood
Low cost but
Heavy. Less
Corrosion
resistance
Light and
strong. But
Cannot be
shaped
Carbon fiber
Aluminum
Reinforced
alloys
plastic
Ti and Mg
alloys
Very light and Light, moderately Slightly better
strong. No
Strong. Corrosion
Than Al
corrosion.
Resistance.
alloys. But much
Very expensive
expensive
expensive
Cost important? Select steel
Properties important? Select CFRP
The CD case, with an objective
Translation
Function
CD enclosure
Constraints
Design requirements
1. Can be injection molded
 Injection-moldable
2. Optically clear
 Contain and protect CD
better than the PS case.
3. Toughness K1c > that of PS
 As transparent as PS
4. Can be recycled
OBJECTIVE
Minimise material cost
Free variable
Choice of material
 Eco-friendly
 As cheap as possible
Screening and ranking: the CD case
Select Level 2: Materials
Minimise material cost C
Volume of material in case, V, fixed
Density , cost per unit mass Cm
Keep these!
C = V Cm 
Material cost/case
Polystyrene
Rank on this index
Surviving materials
Polycarbonate
Optical properties
 Optical quality
Transparent
Transparency
3
Translucent
Opaque
Eco properties
Recycle

Cost metric Cm 
2
Tree stage: injection mold
Fracture toughness
1
OBJECTIVE
Cellulose acetate
3
PMMA
2
1
Ranking
Polystyrene
Advanced ranking: modelling performance
The method:
1. Identify function, constraints, objective and free variables
(list simple constraints for screening).
2. Write down equation for objective -- the “performance equation”.
If the performance equation involves a free variable (other than
the material):

Identify the constraint that limits it.

Use this to eliminate the free variable in performance equation.
3. Read off the combination of material properties that
maximises performance -- the material index
4. Use this for ranking
Selection Procedure
Example 1: strong, light tie-rod
Strong tie of length L and minimum mass
Function
Tie-rod
F
F
Area A
Constraints
Objective
L
• Length L is specified
• Must not fail under load F
Equation for constraint on A:
F/A < y
(1)
Minimize mass m:
m = AL
Free variables
• Material choice
• Section area A.
Performance
metric m
  
mFL  
 y 
 
m = mass
A = area
L = length
 = density
 y= yield strength
(2)
Eliminate A in (2) using (1):
Chose materials with smallest
(or maximize σ y / ρ )





ρ 
σ y 
Demo
The chart-management tool bar
Zoom
Add text
Cancel
selection
Box selection
tool
Line selection
tool
Un-zoom
Add
envelopes
Black and white
chart
Grey failed
materials
Hide failed
materials
Exercise: selecting light, strong materials (1)
Browse
Select
Search
1. Selection data
Edu
Edu Level
Level2:
2: Materials
Materials
2. Selection Stages
Graph
Strength  y
4.1 The material index for selecting
light strong materials is
M = y / 
where  y is the yield strength and 
the density.
 Make a Graph stage with these
two properties as axes
 Impose a selection line (slope 1)
to find materials with the highest
values of M.
 Add a Limit stage to impose the
additional constraint:
Elongation > 10%
High
Limit
Min
y
Density

Modulus
1
Strength
Elongation
etc
Density 
Results:




Tree
Age-hardening wrought Al-alloys
Nickel-based superalloys
Titanium alloys
Wrought magnesium alloys
10
Max
Exercise: selecting light, strong materials (2)
4.2 Repeat the selection of 4.1, but use the
Advanced facility to make a bar-chart with
the index
Browse
Edu
Edu Level
Level2:
2: Materials
Materials
Index y /
on the Y-axis.
 Impose a Box selection to find materials
with the highest values of M.
2. Selection Stages
Graph
Limit
y

Add a Limit stage to impose the additional
constraint:
Elongation > 10%

Search
1. Selection data
M = y / 
High
Select
Tree
Min
Density
Yield strength /
Density
+
-
/
*
^
(
List of properties




Density
Modulus
Yield strength
etc
Modulus
)
Strength
Elongation
etc
10
Max
Exercise: selecting materials for springs (1)
4.3 A material is required for a spring that may be
exposed to shock loading, and must operate in
fresh and salt water.
Browse
Edu
Edu Level
Level2:
2: Materials
Materials
2. Selection Stages
Graph
y
Elastic energy
2
1
1 y
y y 
2
2 E
Strain 
Make a graph with
 Young’s modulus E on the X-axis
 Yield strength  y on the Y-axis
 Put on a line of slope 0.5 (corresponding to power 2)
 Select materials above the line
 Add the other constraints using a limit stage
Strength  y
E
Stress
 2y
Search
1. Selection data
Constraints:
 Fracture toughness > 15 MPa.m1/2
 Very good durability in fresh and salt water
Objective:
 Maximise stored elastic energy
The best materials for
springs are those with the
greatest value of
the index
Select
High
Limit
Tree
Min
 2y
Max
Density
E
0.5
Modulus E
Fr. toughness 15
etc
Fresh water
v. good
Salt water
v. good
Exercise: selecting materials for springs (2)
4.4 Repeat the selection of 4.3, but use the
Advanced facility to make a bar-chart with
the index
 2y / E
on the Y-axis.
1. Selection data
.Plot the bar chart
Edu
Edu Level
Level2:
2: Materials
Materials
Browse
Index y2 /E
 Use a box selection to select the materials
with high values of the index
High
Select
Search
2. Selection Stages
Graph
 2y
Limit
E
Min
(Yield strength^2)/
Young’s modulus
+
-
/
*
^
(
List of properties
 Add the other constraints using a limit stage
Results:
 CFRP, epoxy matrix (isotropic)
 Nickel-based superalloys
 Titanium alloys
Tree




Density
Modulus
Yield strength
etc
)
Max
Density
Fr. toughness 15
etc
Fresh water
v. good
Salt water
v. good
Quiz 3
1. Use the modulus–density chart to find, from among the
materials that appear on it:
(a) The material with the highest density.
(b) The metal with the lowest modulus.
(c) The polymer with the highest density.
(d) The approximate ratio of the modulus of woods
measured parallel to the grain and perpendicular to
the grain.
(e) The approximate range of modulus of elastomers.
Quiz 3
Exercise 2
1)
Make an E–ρ chart using the CES software. Use a box
selection to find three materials with densities between
1000 and 3000 kg/m3 and the highest possible modulus.
2)
Data estimation. The modulus E is approximately
proportional to the melting point Tm in Kelvin (because
strong inter-atomic bonds give both stiffness and
resistance to thermal disruption). Use CES to make
an E–Tm chart for metals and estimate a line of slope 1
through the data for materials. Use this line to estimate
the modulus of cobalt, given that it has a melting point of
1760 K.
3)
Sanity checks for data. A text reports that nickel,
with a melting point of 1720 K, has a modulus of 5500
GPa. Use the E–Tm correlation of the previous question to
check the sanity of this claim. What would you expect it
to be?
Exercise 3
1)
Explore the potential of PP–SiC (polypropylene–silicon
carbide) fiber composites in the following way. Make
a modulus–density (E–ρ) chart and change the axis
ranges so that they span the range 1 < E <1000 GPa and
500 < ρ < 5000 kg/m3 . Find and label PP and SiC, then
print it. Retrieve values for the modulus and density of
PP and of SiC from the records for these materials
(use the means of the ranges).
2)
Use a ‗Limit‘ stage to find materials with modulus E >
180 GPa and price Cm < 3 $/kg.
3)
Use a ‗Limit‘ stage to find materials with modulus
E > 2 GPa, density ρ < 1000 kg/m3 and Price < 3/kg.
Exercise 4
1)
Make a bar chart of modulus, E. Add a tree stage to limit the
selection to polymers alone. Which three polymers have the
highest modulus?
2)
Make a chart showing modulus E and density ρ. Apply a selection
line of slope 1, corresponding to the index E/ρ positioning the line
such that six materials are left above it. Which are they and what
families do they belong to?
3)
A material is required for a tensile tie to link the front and back
walls of a barn to stabilize both. It must meet a constraint on
stiffness and be as cheap as possible. To be safe the material of
the tie must have a fracture toughness K1c > 18 MPa.m1/2. The
relevant index is
Assignment 2
1)
Construct a chart of E plotted against Cm ρ. Add the
constraint of adequate fracture toughness, meaning
K1c > 18 MPa.m1/2, using a ‗Limit‘ stage. Then plot an
appropriate selection line on the chart and report
the three materials that are the best choices for the
tie.
Example 2: Stiff & Light Tension Members
Example 2: Stiff & Light Tension Members
Assignment 3
1)
List the six main classes of engineering materials. Use your own
experience to rank them approximately:`
(a) By stiffness (modulus, E).
(b) By thermal conductivity (λ).
1)
What are the steps in developing an original design?
2)
Describe and illustrate the ‗translation‘ step of the material
selection strategy.
3)
What is meant by an objective and what by a constraint in the
requirements for a design? How do they differ?
4)
You are asked to design a fuel-saving cooking pan with the goal of
wasting as little heat as possible while cooking. What objective
would you choose, and what constraints would you think must be
met?
Assignment 4
Bikes come in many forms, each aimed at a particular sector of the market:
a)
Sprint bikes.
b)
Touring bikes.
c)
Mountain bikes.
d)
Shopping bikes.
e)
Children‘s bikes.
f)
Folding bikes.
Use your judgement to identify the primary objective and the
constraints that must be met for each of these.
Quiz 4
Examine the material property chart of modulus versus density.
By what factor are polymers less stiff than metals? Is wood
denser or less dense than polyethylene (PE)?
Example 3: Cheap Stiff Column

A column supports compressive
loads e.g. legs of a table or pillars

The goal is to identify the cheapest
materials that will support the load
without failing
77
Cheap Stiff Column

The objective function is cost

The buckling constraint is given by (safe design)

Noting that I = r4/4 = A2/4 and eliminating the
variable A gives

The material index for a low cost column that resists
buckling is
Performance of Stiff but Cost Effective Column
Slope=2
Quiz 5
1)
Use the modulus–relative cost chart to find, from among
the materials that appear on it:
(a) The cheapest material with a modulus greater than
1 GPa.
(b) The cheapest metal.
(c) The cheapest polymer.
(d) Whether magnesium alloys are more or less expensive
than aluminum alloys.
(e) Whether PEEK (a high-performance engineering
polymer) is more or less expensive than PTFE.
Quiz 5
Assignment 5
Pick any three engineering applications and answer the
following:
1.
Determine required properties:
electrical, thermal,
magnetic, optical, deteriorative.
ex:
mechanical,
2. Express the design requirements into functions and
objectives.
3. Properties: identify candidate materials
4. Material: identify required Processing
Processing: changes structure and overall shape
ex: casting, sintering, vapor deposition, doping
forming, joining, annealing.
QUESTIONS
Example 4: Selecting a Slender but strong Table Leg
Anita Ama Yentumi, furniture designer, conceives of a lightweight table of
simplicity, with a flat toughened glass top on slender, unbraced, cylindrical legs.
For attractiveness, legs must be solid [to be thin] and light as possible [to make
table easy to move]. Legs must support table top and load without buckling.
What material would you recommend to Anita?
I = r4/4
A light-weight table with slender cylindrical legs. Lightness and
slenderness are independent design goals, both constrained by the
requirement that the legs must not buckle when the table is loaded.
Example 4: (cont)
Polymers are out: they are not stiff enough; metals too: they are too heavy (even magnesium alloys, which
are the lightest).
The Selection
 The choice is further narrowed by the requirement that, for slenderness, E must be
large. A horizontal line on the diagram links materials with equal values of E; those
above are stiffer. Placing this line at M1=100 GPa eliminates woods and GFRP. If the
legs must be really thin, then the short-list is reduced to CFRP and ceramics: they give
legs that weigh the same as the wooden ones but are barely half as thick.
 Ceramics, we know, are brittle: they have low values of fracture toughness.
 Table legs are exposed to abuse—they get knocked and kicked; common
sense suggest that an additional constraint is needed, that of adequate
toughness.
 We then eliminate ceramics, leaving CFRP.
 The cost of CFRP may cause Anita to reconsider her design, but that is
another matter: she did not mention cost in her original specification.
Quiz 6
1)
What is meant by a material index?
2)
Derive a material index for a light and stiff panel
with a square cross section.
3)
Plot the index for a light, stiff panel on a copy of
the modulus–density chart, positioning the line
such that six materials are left above it. What
classes do they belong to?
Assignment 6
1)
The speed of longitudinal waves in a material is proportional to sqrt
[E/ρ]. Plot contours of this quantity onto a copy of an E–ρ chart
allowing you to read off approximate values for any material on the
chart. Which metals have about the same sound velocity as steel?
Does sound move faster in titanium or glass?
2)
A material is required for a cheap column with a solid circular crosssection that must support a load F crit without buckling. It is to
have a height L. Write down an equation for the material cost of the
column in terms of its dimensions, the price per kg of the material, C
m , and the material density ρ. The cross-section area A is a free
variable—eliminate it by using the constraint that the buckling load
must not be less than F crit (equation (5)). Hence read off the index
for finding the cheapest tie. Plot the index on a copy of the
appropriate chart and identify three possible candidates.
Example 5: stiff, light beam
Stiff beam of length L and minimum mass
Function
Beam
b
Constraints
• Length L is specified
• Must have bending stiffness > S*
Equation for constraint on A:
S
Objective
Free variables
Performance
metric m
CEI

3
L
CE A2
3
12 L
Minimize mass m:
m = AL
• Material choice
• Section area A.
1/ 2
 12 L5 S* 

m
 C



(1)
(2)
L
Square
section,
area
A = b2
m = mass
A = area
L = length
 = density
E = Young’s modulus
I = second moment of area
(I = b4/12 = A2/12)
C = constant (here, 48)
Eliminate A in (2) using (1):
  
 1/ 2 
E 
Chose materials
with smallest
 ρ 
 1/2 
E 
Optimized selection using charts

1/ 2
E
Light stiff beam:
1000
Ceramics
E1/2
Rearrange:
E  ρ2 / M2
Take logs:
Log E = 2 log  - 2 log M
Contours of constant
M are lines of slope 2
on an E- chart
Young’s modulus E, (GPa)
Index M 
ρ
C
100
Decreasing
M
Composites
Woods
10
Metals
1
2
Slope 2
Polymers
0.1
0.01
0.1
Elastomers
Foams
10
1
3
Density (Mg/m )
100
Optimized selection using charts

E1/ 2
C
Example 5: STRONG & LIGHT TORSION MEMBERS
• Bar must carry a moment, Mt ;
must have a length L.
-- Strength relation:
 f 2Mt

N R3
-- Mass of bar:
M  R2 L
• Eliminate the "free" design parameter, R:
2 /3

M  2  NM t
L
2f / 3

specified by application

minimize for small M
• Maximize the Performance Index: P 
(strong, light torsion members)
2f / 3

6
Example 5: Torsionally stressed shaft
Example 5: Torsionally stressed shaft
Example 5: Torsionally stressed shaft
Other Material Indices: Cost factor
Material “indices”
Each combination of
FUNCTION
Function
Constraint
Objective
Free variable
has a
characterising
material index
Tie
CONSTRAINTS
Minimise this!
Beam
Stiffness
specified
Shaft
Column
Mechanical,
Thermal,
Electrical...
OBJECTIVE
Minimum cost
Strength
specified
Minimum
weight
Fatigue limit
Geometry
specified
Minimum
volume
Minimum
eco- impact
INDEX
  
M   1/ 2 
E 
Demystifying material indices
A material index is just the combination of material properties that
appears in the equation for performance (eg minimizing mass or cost).


Sometimes a single property

Sometimes a combination
Example:
Objective -minimise mass
Function
Either is a material index
Constraints
Stiffness
Strength
Tension (tie)
ρ/E
ρ/σ y
ρ/E1/2
ρ/σ 2/3
ρ/E1/3
ρ/σ1/2
y
Bending (beam)
Performance
metric = mass
y
Bending (panel)
Minimize these!
(Or maximize
reciprocals)
Summary of Some Materials Indices
Assignment
Selecting a beam material for minimum cost

A simply supported beam of rectangular cross section of
length 1 meter, width 100 mm, and no restriction on the
depth is subjected to a load of 20 kN in its middle. The main
design requirement is that the beam should not suffer
plastic deformation as a result of load application. Select the
least expensive material for the beam
Single Property Ranking Example
Overhead Transmission Cable

Single Property Ranking Example
Overhead Transmission Cable
Overhead Transmission Cable
End of Unit 4
WEIGHTED
PROPERTY
INDEX
Weighted Property Method
 In most applications, the selected material should
satisfy more than one functional requirement
 In this method each material requirement (or
property) is assigned a certain weight (which depends
on its importance to the performance of the design)
 This method attempts to:
1. Quantify how important each desired requirement
is by determining a weighting factor (α)
2. Quantify how well a candidate material satisfies
each requirement by determining a scaling factor (β)
MATERIALS
Since different properties have widely different numerical values.
Each property must be so scaled that the largest value does not
exceed 100
Weighted Properties Method
Scaled Factor
 For properties that should have maximum values [strength, toughness …],
the scaling factor [β] for a given candidate material is
For properties such that it is more desirable to have low values, e.g.,
density, corrosion loss, cost and electrical resistance, the scale
factor is formulated as follows
 The relative importance is shown by using a point scale that does
not exceed 100 points
 e.g; if strength is 4 times as important as cost, it will be
represented by an 80 / 20 division
 For properties that are not readily expressed in numerical
values, e.g., weldability and wear resistance, some kind of
subjective rating is required. For example
 The best material may either have the largest value of the given
property or the smallest
 For example High strength is given 100
 Low density or low corrosion rates are given 100
113
Weighted Property Index
 It is calculated by multiplying the scaling factor by the weight
factor. Then the summed for the criteria
 The material performance index γ is
where i is summed over all the properties, and n is the number of properties
under consideration
There are two general schemes for working with
the weighting factors
The most
common one is
to set
such that
The other is to
let w take on a
range of values,
with the largest
value denoting
the property of
greatest
importance
Weighted Point Method
 Step 1- List all the essential and desirable properties of the
material. Eg. Availability, shape and size, cost, corrosion
resistance, weldability, forgibility, density, etc.
 Step 2- Categorize these properties into two groups. a] GoNo-Go parameters- are constraints, b] Discriminating
parameters- can be assigned values. For example, in the case of
connecting rod endurance strength is given number 5 and cost
is given number 1. Here in weightage point method, #1 means
poor weightage and #5 means high priority.
 Step 3- The quantitative values or weightage depends upon
the importance of that particular property in the given
application
 Step 4- Calculation of weightage contribution and decision
making
Weighting factors- Example
Weight is 4 times as important as strength, strength is 4 times as
important as cost, corrosion is 2 /3 as importance as strength, etc
Weighting of attributes
We can also use the Digital Logic Method
Digital Logic Approach

When many material properties are used to specify
performance, it may be difficult to establish the
weighting factors

One way to do so is to use a digital logic approach

Each property is listed and is compared in every
combination, taken two at a time to make the comparison

The property that is considered to be the more
important of the two is given a 1 and the less important
property is given a 0
118
The total number of
 possible combinations is


If the total number of possible decisions for
each property is m, then:
119
where n is the number of
 properties under consideration

 The number of attributes that should be listed vary between 5 - 10
 This method combine properties with different units. This
limitation is overcome by the use of a ―scaling factor‖
 The relative merit of each property of the candidate material may
be incorporated by assigning the value of 100 (%) to the best
material in that property category
Example
 Select a suitable material by weighted point method. There are four
materials selected on the basis of design requirement which are i] stainless
steel 301, ii] aluminium 2014-T6, iii] Ti-6Al-4V and iv] Inconel 718. The
material is to be used for a cryogenic storage tank for transporting liquid
nitrogen at -196oC.
Mechanical Properties
 On the basis of importance of these properties they are ranked on the
scale of 1 to 5 [1 stands for the poorest and 5 for the best].
 As the tank is to be used in -198oC, toughness should be at the top and
to reduce the weight, density has to be assigned to the second place.
Hence, toughness is assigned 5 points, density 4 points and so on. These
are listed below-
Assignment of Weighted Index
 The calculation of percentage contribution of each property is illustrated
below.
 The percentage contribution of toughness of Al-2024-T6 is obtained as
 Since weight index for toughness is 5, the material performance index for
Al-2024-T6 is
 Similarly, material performance index for other materials are obtained and
included in Table below
Summary of Calculations
Properties of Sample Candidate Materials
Use of Digital Logic Method in the Cylinder Example
Weighted Factors for the Cylinder Example
Scaled Values of Properties and Calculated
Weighted Property Index
Calculation of Performance Index Property
Class Test
The material selection for a cryogenic storage
vessel for liquefied propane gas is being
evaluated on the basis of
1) low-temperature fracture toughness, 2) elastic
modulus, 3) specific gravity,
4) thermal expansion and 5) yield strength.
Determine the weighting factors for these
properties with the aid of a digital logic table.
Class Test
The material selection for a cryogenic storage vessel for
liquefied propane gas is being evaluated on the basis of
1) low-temperature fracture toughness, 2) elastic modulus,
3) specific gravity, 4) thermal expansion and 5) yield
strength.
Determine the weighting factors for these properties with
the aid of a digital logic table. Select the best material
from the following candidate materials
Class Test

The material for the shaft of an automobile is being evaluated on
the basis Fatigue strength, Fracture toughness, stiffness, thermal
expansion and cost. Determine the weighting factors for these
properties with the aid of a digital logic table. Hence or otherwise,
select the best material from the following candidate materials: A.
Unalloyed DI; B. Ni- alloyed DI; C. Cr-alloyed DI; D. NiCr-Alloyed DI
Fatigue strength
Candidate Materials
A
B
C
D
0
100
90
90
Fracture Toughness
50
100
10
30
Stiffness
45
100
45
90
Thermal Expansion
100
5
100
90
Cost
100
10
100
30
129
Property
The material selection for the legs of a table is being evaluated on the
basis of the following properties: (1) density, (2) stiffness, (3) cost, (4)
production energy, and (5) CO2 production.
What information do we need?
Alternatives
– Bamboo, Cast iron, Low carbon steel, and Oak
• Property Values (see handout)
• Weighting Factors (How do we determine these?)
– Your/design team‘s intuition (good)
– Pair-wise comparison (better)
Materials Quality Control and
Assurance
131
Contents

Concepts of quality control

Objectives of quality control

Consequences of quality control

Costs associated with quality control

The economics of quality control

Control chats; types of control chats

Inspection of finished products and the economics of quality
control
Materials Quality Control

Questions to answer in this module…

Why is Quality Control important in materials
manufacturing?

What can go wrong in quality control?

How are materials quality controlled?
What does the word “quality” mean to you?

Think about a product you bought. How can you
define its ―quality‖?
Terminology
 Every product possesses a number of elements that jointly describe
what the user or consumer thinks of as quality
 These parameters are often called quality characteristics
 Sometimes these are called critical-to-quality [CTQ] characteristics
 Quality characteristics may be of several types
o Physical- length, weight, viscosity
o Sensory- taste, appearance, color
o Time Orientation- reliability, durability, serviceability
135
Dimensions of Quality
Garvin (1987)

1.
Performance:

2.
Reliability:

3.
How often does the product fail?
Durability:

4.
Will the product do the intended job?
How long does the product last?
Serviceability:

How easy to repair the product to solve the
problems in service?
Dimensions of Quality
5.
Aesthetics:

6.
Features:

7.
What does the product do/ service give?
Perceived Quality:

8.
What does the product look/smell/sound/ feel like?
What is the reputation of the company or its
products/services?
Conformance to Standards:

Is the product/service made exactly as the
designer/standard intended?
What is Quality?

―The degree to which a system, component, or process
meets
(1) specified requirements, and
(2) customer or users needs or expectations‖ – IEEE

Degree to which a set of inherent characteristics fulfils
requirements – ISO 9000:2000
The word Quality does not mean the Quality of
manufactured product only. It may refer to the
Quality of the process (i.e., men, material,
machines) and even that of management.
What is Quality?


Quality means those features of products which meet
customer needs and thereby provide customer
satisfaction.

In this sense, the meaning of quality is oriented to
income

The purpose of such higher quality is to provide
greater customer satisfaction and one hopes to
increase income
Quality means freedom from deficiencies

In this sense, the meaning of quality is oriented to
costs, and higher quality usually costs less
More about Quality

Quality begins with the design of a product in accordance with the
customer specification.

Further it involves the established measurement standards, the
use of proper material, selection of suitable manufacturing process
and the necessary tooling to manufacture the product. It also
involve the performance of the necessary manufacturing operations
and the inspection of the product to check the manufacturing
operations and the inspection of the product to check on
performance with the specifications.

Quality characteristics can be classified as follows :
(1) Quality of design
(2) Quality of conformance with specifications
(3) Quality of performance.
Modern Importance of Quality

―The first job we have is to turn out quality
merchandise that consumers will buy and keep on
buying. If we produce it efficiently and
economically, we will earn a profit.‖
- William Cooper Procter
141
Factors Affecting Quality
(1) Men, Materials and Machines
(2) Manufacturing conditions
(3) Market research in demand of purchases
(4) Money in capability to invest
(5) Management policy for quality level
(6) Production methods and product design
(7) Packing and transportation
What is Quality Control?

Quality Control (QC) is the implementation of regular
testing procedures against your definitions of quality
and more specifically the refinement of these
procedures
 Formal use of testing

Acting on the results of your tests

Requires planning, structured tests, good
documentation

Relates to output - Quality Circle

Standards - ISO 9000 & BS5750
Quality Control (QC) process evaluates actual performance, compares
actual performance to goal and takes action on the difference
Objectives of Quality Control
(1) To decide about the standard of Quality of a product that
is easily acceptable to the customer.
(2) To check the variation during manufacturing.
(3) To prevent the poor quality products reaching to customer.
144
Quality Control

The process through which the standards are established and met
with standards is called control. This process consists of observing
our activity performance, comparing the performance with some
standard and then taking action if the observed performance is
significantly to different from the standards.

The control process involves a universal sequence of steps as
follows :
(1) Choose the control subject.
(2) Choose a unit of measure.
(3) Set a standard value i.e., specify the quality characteristics
(4) Choose a sensing device which can measure.
(5) Measure actual performance.
(6) Interpret the difference between actual and standard.
(7) Taking action, if any, on the difference.
The Feedback Loop

Quality control takes place by use of the
feedback loop. A generic form of the feedback
loop is shown below
ISO As A Data Quality Management System

ISO 9004-1: General quality guidelines to implement a quality system.

ISO 9004-4: Guidelines for implementing continuous quality
improvement within the organisation, using tools and techniques based
on data collection and analysis.

ISO 10005: Guidance on how to prepare quality plans for the control
of specific projects.

ISO 10011-1: Guidelines for auditing a quality system.

ISO 10011-2: Guidance on the qualification criteria for quality
systems auditors.

ISO 10011-3: Guidelines for managing quality system audit
programmes.

ISO 10012: Guidelines on calibration systems and statistical controls
to ensure that measurements are made with the intended accuracy.

ISO 10013: Guidelines for developing quality manuals to meet specific
needs.
Source: http://www.iso.ch/
Materials Quality Control

Quality Control is conducted by a team…

Design engineer

Materials/Metallurgical engineer

Stress engineer

Raw materials producer

Production Planner

Technician

Quality Assurance Inspector
Statistical Quality Control (SQC)

Statistica1 quality control (SQC) is the term used to describe the
set of statistical tools used by quality professionals. Statistical
quality control can be divided into three broad categories:
1)
Descriptive statistics are used to describe quality
characteristics and relationships. Included are statistics such
as the mean, standard deviation, the range, and a measure of
the distribution of data.
2)
Statistical process control (SPC) involves inspecting a random
sample of the output from a process and deciding whether the
process is producing products with characteristics that fall
within a predetermined range. SPC answers the question of
whether the process is functioning properly or not.
3)
Acceptance sampling is the process of randomly inspecting a
sample of goods and deciding whether to accept the entire lot
based on the results. Acceptance sampling determines
whether a batch of goods should be accepted or rejected
SQC

A Quality control system performs inspection, testing
and analysis to conclude whether the quality of each
product is as per laid quality standard or not.

It‘s called ‗‗Statistical Quality Control‘‘ when
statistical techniques are employed to control quality
or to solve quality control problem.

SQC makes inspection more reliable and at the same
time less costly.

It controls the quality levels of the outgoing
products.

SQC should be viewed as a kit of tools which may
influence related to the function of specification,
production or inspection.
DESCRIPTIVE STATISTICS

Descriptive statistics can be helpful in describing
certain characteristics of a product and a process. The
most important descriptive statistics are measures of
central tendency such as the

The Mean

The Range and Standard Deviation
DESCRIPTIVE STATISTICS
 Normal distributions with varying
standard deviations
 Differences between symmetric
and skewed distributions

When a distribution is symmetric, there are the same
number of observations below and above the mean

When a disproportionate number of observations are
either above or below the mean, we say that the data
has a skewed distribution.
Developing Control Charts

A control chart (also called process chart or quality
control chart) is a graph that shows whether a sample
of data falls within the common or normal range of
variation.

A control chart has upper and lower control limits that
separate common from assignable causes of variation.

We say that a process is out of control when a plot of
data reveals that one or more samples fall outside the
control limits.
Control Charts

The center line (CL) of the control chart is the mean, or average, of
the quality characteristic that is being measured.

The upper control limit (UCL) is the maximum acceptable variation
from the mean for a process that is in a state of control.

Similarly, the lower control limit (LCL) is the minimum acceptable
variation from the mean for a process that is in a state of control.
Control Chart

We say that a process is out of control when a plot of
data reveals that one or more samples fall outside the
control limits.

You can see that if a sample of observations falls
outside the control limits we need to look for
assignable causes.

Assignable causes of variation involves variations
where the causes can be precisely identified and
eliminated.

Examples of this type of variation are poor quality in
raw materials, an employee who needs more training,
or a machine in need of repair.
CONTROL CHARTS FOR VARIABLES

Control charts for variables monitor characteristics that
can be measured and have a continuous scale, such as
height, weight, volume, or width

When an item is inspected, the variable being monitored
is measured and recorded.

For example, if we were producing candles, height might
be an important variable. We could take samples of
candles and measure their heights.

Mean (x-Bar) Charts: A control chart used to monitor
changes in the mean value of a process.

Range (R) Charts: A control chart that monitors
changes in the dispersion or variability of process.
Constructing a Mean (x-Bar) Chart


The center line of the chart is then computed as the mean of all
sample means, where is the number of samples:
To construct the upper and lower
control limits of the chart, we use
the following formulas:
Constructing a Mean (x-Bar) Chart from the
Sample Range
 Another way to construct the control limits is to use the sample
range as an estimate of the variability of the process.
 The spread of the range can tell us about the variability of the
data.
 In this case control limits would be constructed as follows:
Notice that A2 is a factor that includes three standard deviations of
ranges and is dependent on the sample size being considered.
Factors for three-sigma control limits of and R-charts
Factors for three-sigma control limits of and R-charts
EXAMPLE : Constructing a Mean (x-Bar) Chart

A quality control inspector at the Cocoa Fizz soft drink
company has taken twenty-five samples with four
observations each of the volume of bottles filled. The
data and the computed means are shown in the table. If
the standard deviation of the bottling operation is 0.14
ounces, use this information to develop control limits of
three standard deviations for the bottling operation.
Test Data
Continuation of Test Data
Solution
Resulting Control Chart
EXAMPLE 6.2 Constructing a Mean (x-Bar)
Chart from the Sample Range
Range (R) Charts
 Range (R) charts are another type of control chart for variables.
Whereas x-bar charts measure shift in the central tendency of the
process, range charts monitor the dispersion or variability of the
process.
 The method for developing and using R-charts is the same as that
for x-bar charts.
 The center line of the control chart is the average range, and the
upper and lower control limits are computed as follows:
where values for D4 and D3 are obtained from Table 6-1.
Constructing a Range (R) Chart
The quality control inspector at Cocoa Fizz would like to develop a
range (R) chart in order to monitor volume dispersion in the bottling
process. Use the data from Example 6.1 to develop control limits for
the sample range.
The resulting control chart is:
CONTROL CHARTS FOR ATTRIBUTES
 Control charts for attributes are used to measure quality
characteristics that are counted rather than measured.
 Attributes are discrete in nature and entail simple yes-orno decisions.
 For example, this could be the number of nonfunctioning
lightbulbs, the proportion of broken eggs in a carton, the
number of rotten apples, the number of scratches on a
tile, or the number of complaints issued.
 Two of the most common types of control charts for
attributes are p-charts and c-charts.
 P-charts are used to measure the proportion of items
in a sample that are defective..
 C-charts count the actual number of defects.
Problem-Solving Tip:
 The primary difference between using a p-chart and a
c-chart is as follows.
 A p-chart is used when both the total sample size
and the number of defects can be computed.
 A c-chart is used when we can compute only the
number of defects but cannot compute the
proportion that is defective.
P-Charts
 P-charts are used to measure the proportion that is defective in
a sample.
 The center line is computed as the average proportion defective in
the population, 𝑃.This is obtained by taking a number of samples of
observations at random and computing the average value of p
across all samples.
 To construct the upper and lower control limits for a p-chart, we
use the following formulas:
z is selected to be either 2 or 3
standard deviations, depending
on the amount of data we wish to
capture in our control limits. Usually,
however, they are set at 3.
The sample standard deviation is computed as follows:
where n is the sample size.
Constructing a p-Chart
A production manager at a tire manufacturing plant has inspected the
number of defective tires in twenty random samples with twenty
observations each. Following are the number of defective tires found in
each sample:
Constructing a p-Chart
Construct a three-sigma control chart
Construct a three-sigma control chart (z = 3) with this information.
Solution
The center line of the chart is
In this example the lower control limit is negative, which sometimes occurs
because the computation is an approximation of the binomial distribution. When
this occurs, the LCL is rounded up to zero because we cannot have a negative
control limit.
Resulting Control Chart
The resulting control chart is as follows:
C-CHARTS
 C-charts are used to monitor the number of defects per unit.
 Examples are the number of returned meals in a restaurant, the
number of trucks that exceed their weight limit in a month, the
number of discolorations on a square foot of carpet, and the number
of bacteria in a milliliter of water.
 Note that the types of units of measurement we are considering are
a period of time, a surface area, or a volume of liquid.
 The average number of defects, 𝐶 , is the center line of the control
chart.
 The upper and lower control limits are computed as follows:
Computing a C-Chart
The number of weekly customer complaints are monitored at a large
hotel using a c-chart. Complaints have been recorded over the past
twenty weeks. Develop three-sigma control limits using the following
data:
As in the previous example, the LCL is negative and should be
rounded up to zero. Following is the control chart for this example:
Resulting Control Chart
Before You Go On
 We have discussed several types of statistical quality control
(SQC) techniques.
 One category of SQC techniques consists of descriptive
statistics tools such as the mean, range, and standard deviation.
 These tools are used to describe quality characteristics and
relationships.
 Another category of SQC techniques consists of statistical
process control (SPC) methods that are used to monitor changes
in the production process.
 To understand SPC methods you must understand the differences
between common and assignable causes of variation.
 Common causes of variation are based on random causes that
cannot be identified.
 You should also understand the different types of quality control
charts that are used to monitor the production process: x-bar
charts, R-range charts, p-charts, and c-charts.
Statistical Quality Control (SQC)

A successful SQC programme is expected to yield the
following results :
(1) Improvement of quality.
(2) Reduction of scrap and rework.
(3) Efficient use of men and machines.
(4) Economy in use of materials.
(5) Removing production bottle-necks.
(6) Decreased inspection costs.
(7) Reduction in cost/unit.
(8) Scientific evaluation of tolerance.
(9) Scientific evaluation of quality and production.
(10) Quality consciousness at all levels.
(11) Reduction in customer complaints.
Advantages and Limitations of SPC


Advantages
1)
Emphasis on early detection -An advantage of SPC over other
methods of quality control, such as "inspection", is that it
emphasizes early detection and prevention of problems, rather than
the correction of problems after they have occurred.
2)
Increasing rate of production -In addition to reducing waste, SPC
can lead to a reduction in the time required to produce the product.
SPC makes it less likely the finished product will need to be
reworked or scrapped.
Limitations
1)
SPC is applied to reduce or eliminate process waste. This, in turn,
eliminates the need for the process step of post-manufacture
inspection. The success of SPC relies not only on the skill with which
it is applied, but also on how suitable or amenable the process is to
SPC. In some cases, it may be difficult to judge when the
application of SPC is appropriate.
What is Quality Assurance?

What is Quality?
Quality is the ability of your product to be able to
satisfy your users

What is Quality Assurance?
Quality Assurance is the process that demonstrates
your product is able to satisfy your users

What is the aim of Quality Assurance?
o
When good Quality Assurance is implemented there
should be improvement in usability and performance
and lessening rates of defects
The Relation to Quality Assurance

Quality control and quality assurance have much in
common. These may include
1)
2)
3)

Each evaluate performance
Each compares performance to goals
Each acts on the difference
However they also differ from each other. Thus for
quality control
1)
2)
3)
4)
It has its primary purpose to maintain control
Performance is evaluated during operations, and performance
is compared to goals during operations
The resulting information is provided to both the operating
forces and others who have a need to know
Others may include plant, functional, or sector management,
corporate staff, regulatory bodies, customers, and the general
public
Quality Assurance vs. Quality Control

The difference is that Quality Assurance is process
oriented and focuses on defect prevention, while
quality control is product oriented and focuses on
defect identification.

Testing, therefore is product oriented and thus is in
the QC domain. Testing for quality
isn't assuring quality, it's controlling it.

Quality Assurance makes sure you are doing the right
things, the right way.

Quality Control makes sure the results of what you've
done are what you expected.
What does QA give?

Quality’ means your product is ‗useful‘ without ‘quality’ you may have little to offer

‘Quality’ can help to future-proof products

But ‗quality assurance’ needs documented standards
and best practices to be meaningful

‘Quality’ & ‘Best Practice’ can be considered in terms
of being ‘Fit for Purpose’
Inspection

Inspection is the most common method of attaining
standardisation, uniformity and quality of workmanship.

It is the cost art of controlling the product quality
after comparison with the established standards and
specifications.

It is the function of quality control.

If the said item does not fall within the zone of
acceptability it will be rejected and corrective measure
will be applied to see that the items in future conform
to specified standards.

It helps to control quality, reduces manufacturing
costs, eliminate scrap losses and assignable causes of
defective work.
Objectives of Inspection
(1) To collect information regarding the performance of
the product with established standards for the use of
engineering production, purchasing and quality control
etc.
(2) To sort out poor quality of manufactured product and
thus to maintain standards.
(3) To establish and increase the reputation by
protecting customers from receiving poor quality
products.
(4) Detect source of weakness and failure in the finished
products and thus check the work of designer
Purpose of Inspection
(1) To distinguish good lots from bad lots
(2) To distinguish good pieces from bad pieces.
(3) To determine if the process is changing.
(4) To determine if the process is approaching the
specification limits.
(5) To rate quality of product.
(6) To rate accuracy of inspectors.
(7) To measure the precision of the measuring
instrument.
(8) To secure products – design information.
(9) To measure process capability.
Stages of Inspection
(1)
Inspection of incoming material
o
It consists of inspecting and checking of all the purchased
raw materials and parts that are supplied before they are
taken on to stock or used in actual manufacturing. It may
take place either at supplier‘s end or at manufacturer‘s gate.
If the incoming materials are large in quantity and involve
huge transportation cost it is economical to inspect them at
the place of vendor or supplier.
(2) Inspection of production process
o
The work of inspection is done while the production process
is simultaneously going on. Inspection is done at various work
centres of men and machines and at the critical production
points. This had the advantage of preventing wastage of time
and money on defective units and preventing delays in
assembly.
Stages of Inspection
(3) Inspection of finished goods.
o
This is the last stage when finished goods are
inspected and carried out before marketing to
see that poor quality product may be either
rejected or sold at reduced price.
Inspection Procedures

There are three ways of doing inspection. They are Floor inspection, Centralised
inspection and Combined inspection.

Floor Inspection
It suggests the checking of materials in process at the machine or in the
production time by patrolling inspectors. These inspectors moves from machine to
machine and from one to the other work centres. Inspectors have to be highly
skilled. This method of inspection minimise the material handling, does not disrupt
the line layout of machinery and quickly locate the defect and readily offers field
and correction.
Advantages
Disadvantages
o
(1) Encourage co-operation of inspector and
foreman.
(2) Random checking may be more successful
than batch checking.
(1) Difficult in inspection due to
vibration.
(2) Possibility of biased inspection
because of worker.
(3) Does not delay in production.
(3) Pressure on inspector.
(4) Saves time and expense of having to more
(4) High cost of inspection because
of numerous sets of inspections
and skilled inspectors.
batches of work for inspection.
(5) Inspectors may see and be able to report
on reason of faculty work.
Centralised Inspection

Materials in process may be inspected and checked at centralised
inspection centre which are located at one or more places in the
manufacturing industry.

Advantages


(1) Better quality checkup.

(2) Closed supervision.

(3) Absence of workers pressure.

(4) Orderly production flow and low inspection cost.
Disadvantages

(1) More material handling.

(2) Delays of inspection room causes wastage of time.

(3) Work of production control increases.

(4) Due to non-detection of machining errors in time, there may
be more spoilage of work.
Combined Inspection

Combination of two methods what ever may be the
method of inspection, whether floor or central. The
main objective is to locate and prevent defect which
may not repeat itself in subsequent operation to see
whether any corrective measure is required and finally
to maintained quality economically.
Methods of Inspection

There are two methods of inspection. They are 100%
inspection and Sampling inspection.

100% Inspection
o
o
This type will involve careful inspection in detail of
quality at each strategic point or stage of manufacture
where the test involved is non-destructive and every
piece is separately inspected. It requires more number
of inspectors and hence it is a costly method. There is
no sampling error. This is subjected to inspection error
arising out of fatigue, negligence, difficulty of
supervision etc. Hence complete accuracy of influence is
seldomly attained.
It is suitable only when a small number of pieces are
there or a very high degree of quality is required.
Example : Jet engines, Aircraft, Medical and Scientific
equipment.
Sampling Inspection

In this method randomly selected samples are inspected. Samples
taken from different batches of products are representatives. If
the sample prove defective. The entire concerned is to be
rejected or recovered. Sampling inspection is cheaper and quicker.
It requires less number of Inspectors. Its subjected to sampling
errors but the magnitude of sampling error can be estimated. In
the case of destructive test, random or sampling inspection is
desirable. This type of inspection governs wide currency due to
the introduction of automatic machines or equipment which are
less susceptible to chance variable and hence require less
inspection, suitable for inspection of products which have less
precision importance and are less costly.

Example: Electrical bulbs, radio bulbs, washing machine etc.
o

Destructive tests conducted for the products whose
endurance or ultimate strength properties are required.
Example: Flexible strength, resistance capacity, compressibility
etc.
Drawbacks of Inspection

(1) Inspection adds to the cost of the product but not
for its value.

(2) It is partially subjective, often the inspector has to
judge whether a product passes or not.
o
Example : Inspector discovering a slight burnish on a
surface must decide whether it is bad enough to
justify rejection even with micrometers a tight or
loose fit change measurement by say 0.0006 inches.
The inspectors design is important as he enforces
quality standards.

(3) Fatigue and Monotony may affect any inspection
judgement.

(4) Inspection merely separates good and bad items. It is
no way to prevent the production of bad items.
Materials Quality Control Techniques
Materials
property verification

Destructive Testing

Non-destructive Testing
Materials Quality Control Techniques
Destructive
Testing

Corrosion Testing

Tensile Testing

Impact Testing
Materials Quality Control Techniques

Non-destructive Testing

Liquid penetrant Testing

Radiograhic Testing

Impulse Excitation Testing

Ultrasonic Testing

Electromagnetic Testing

Acoustic Emission Testing

Positive Material Identification

Hardness Testing

Infrared and Thermal Testing

Laser Testing

Leak Detection
Introduction to Nondestructive Testing
Definition of NDT
 The use of noninvasive
techniques to determine the
integrity of a material,
component or structure
or
 quantitatively measure some
characteristic of an object.
i.e. Inspect or measure without doing harm.
Methods of NDT
Visu
al
What are Some Uses of NDE Methods?

Flaw Detection and Evaluation

Leak Detection

Location Determination

Dimensional Measurements

Structure and Microstructure Characterization

Estimation of Mechanical and Physical Properties

Stress (Strain) and Dynamic Response Measurements

Material Sorting and Chemical Composition
Determination
When are NDE Methods Used?

To assist in product development

To screen or sort incoming materials

To monitor, improve or control manufacturing
processes

To verify proper processing such as heat
treating

To verify proper assembly

To inspect for in-service damage
Six Most Common NDT Methods
•
•
•
•
•
•
Visual
Liquid Penetrant
Magnetic
Ultrasonic
Eddy Current
X-ray
Visual Inspection
 Most basic and common
inspection method.
 Tools include
fiberscopes,
borescopes, magnifying
glasses and mirrors.
Portable video inspection
unit with zoom allows
inspection of large tanks
and vessels, railroad tank
cars, sewer lines.
Robotic crawlers permit observation
in hazardous or tight areas, such as
air ducts, reactors, pipelines.
Liquid Penetrant Inspection
 A liquid with high surface wetting characteristics
is applied to the surface of the part and allowed
time to seep into surface breaking defects.
 The excess liquid is removed from the surface
of the part.
 A developer (powder) is applied to pull the
trapped penetrant out the defect and spread
it on the surface where it can be seen.
 Visual inspection is the final step in the
process. The penetrant used is often loaded
with a fluorescent dye and the inspection is
done under UV light to increase test
sensitivity.
Magnetic Particle Inspection

The part is magnetized. Finely milled iron particles coated with a
dye pigment are then applied to the specimen. These particles are
attracted to magnetic flux leakage fields and will cluster to form an
indication directly over the discontinuity. This indication can be
visually detected under proper lighting conditions.
Magnetic Particle Crack Indications
Radiography
 The radiation used in radiography
testing is a higher energy (shorter
wavelength) version of the
electromagnetic waves that we
see as visible light. The radiation can
come from an X-ray generator or a
radioactive source.
High Electrical Potential
Electrons
+
-
X-ray Generator
or Radioactive
Source Creates
Radiation
Radiation
Penetrate
the Sample
Exposure Recording Device
Film Radiography
The part is placed between the
radiation source and a piece of film.
The part will stop some of the
radiation. Thicker and more dense
area will stop more of the radiation.
X-ray film
The film darkness (density)
will vary with the amount of
radiation reaching the film
through the test object.
= less exposure
= more exposure
Top view of developed film
Radiographic Images
Eddy Current Testing
Coil
Coil's
magnetic field
Eddy current's
magnetic field
Eddy
currents
Conductive
material
Eddy Current Testing
Eddy current testing is particularly well suited for detecting
surface cracks but can also be used to make electrical conductivity
and coating thickness measurements. Here a small surface probe is
scanned over the part surface in an attempt to detect a crack.
Ultrasonic Inspection (Pulse-Echo)
 High frequency sound waves are introduced into a
material and they are reflected back from surfaces or
flaws.
 Reflected sound energy is displayed versus time, and
f
inspector can visualize a cross section of the specimen
showing the depth of features that reflect sound.
initial
pulse
crack
echo
back surface
echo
crack
0
2
4
6
8
Oscilloscope, or flaw
detector screen
10
plate
Ultrasonic Imaging
High resolution images can be produced by plotting
signal strength or time-of-flight using a computercontrolled scanning system.
Gray scale image produced using
the sound reflected from the
front surface of the coin
Gray scale image produced using the
sound reflected from the back surface
of the coin (inspected from ―heads‖ side)
Common Application of NDT
Inspection
of Raw Products
Inspection
Following Secondary Processing
In-Services
Damage Inspection
Inspection of Raw Products
Forgings,
Castings,
Extrusions,
etc.
Inspection Following
Secondary Processing
Machining
Welding
Grinding
Heat treating
Plating
etc.
Inspection For
In-Service Damage
 Cracking
 Corrosion
 Erosion/Wear
 Heat
 etc.
Damage
Power Plant Inspection
Periodically, power plants are
shutdown for inspection.
Inspectors feed eddy current
probes into heat exchanger
tubes to check for corrosion
damage.
Pipe with damage
Probe
Signals produced
by various
amounts of
corrosion
thinning.
Wire Rope Inspection
Electromagnetic devices and
visual inspections are used to
find broken wires and other
damage to the wire rope that
is used in chairlifts, cranes
and other lifting devices.
Storage Tank Inspection
Robotic crawlers use
ultrasound to
inspect the walls of
large above ground
tanks for signs of
thinning due to
corrosion.
Cameras on long
articulating
arms are used
to inspect
underground
storage tanks
for damage.
Aircraft Inspection
 Nondestructive testing is used
extensively during the
manufacturing of aircraft.
 NDT is also used to find cracks
and corrosion damage during
operation of the aircraft.
 A fatigue crack that started at
the site of a lightning strike is
shown below.
Jet Engine Inspection
 Aircraft engines are overhauled after
being in service for a period of time.
 They are completely disassembled,
cleaned, inspected and then
reassembled.
 Fluorescent penetrant inspection is
used to check many of the parts for
cracking.
Crash of United Flight 232
Sioux City, Iowa, July 19, 1989
A defect that
went undetected
in an engine disk
was responsible
for the crash of
United Flight 232.
Pressure Vessel Inspection
The failure of a pressure vessel
can result in the rapid release of
a large amount of energy. To
protect against this dangerous
event, the tanks are inspected
using radiography and ultrasonic
testing.
Rail Inspection
Special cars are used to
inspect thousands of miles
of rail to find cracks that
could lead to a derailment.
Bridge Inspection
 The US has 578,000
highway bridges.
 Corrosion, cracking and
other damage can all
affect a bridge‘s
performance.
 The collapse of the
Silver Bridge in 1967
resulted in loss of 47
lives.
 Bridges get a visual
inspection about every 2
years.
 Some bridges are fitted
with acoustic emission
sensors that ―listen‖ for
sounds of cracks growing.
Pipeline Inspection
NDT is used to inspect pipelines to
prevent leaks that could damage
the environment. Visual inspection,
radiography and electromagnetic
testing are some of the NDT
methods used.
Remote visual inspection using a
robotic crawler.
Magnetic flux leakage inspection. This
device, known as a pig, is placed in the
pipeline and collects data on the
condition of the pipe as it is pushed
along by whatever is being transported.
Radiography of weld joints.
Special Measurements
Boeing employees in Philadelphia were given the privilege of
evaluating the Liberty Bell for damage using NDT techniques.
Eddy current methods were used to measure the electrical
conductivity of the Bell's bronze casing at various points to
evaluate its uniformity.
SEE YOU
IN THE
EXAM
233
Demo: trade off plots
Contribution
Comment
Observation
235