MKT 3821
Design of Machine Elements
By Haydar Livatyalı
Engineering Materials and Material Selection
Fall 2023-24
1
The expansion of the materials world
•
In his day: a few hundred materials
No polymers – now over 45,000
No light alloys – now several thousand
No composites – now hundreds ……
•
Today: > 160,000 engineering materials
•
Creates two needs:
1 Education – how best teach materials?
2 Industry – how manage materials
information ?
•
Solutions:
1 The CES EduPack – Education
James Stuart, Professor of
Engineering at Cambridge
1875 - 1890
2
Today
2 Granta mi – Industry
1
The world of materials
Polymers,
elastomers
Metals,
alloys
Hybrids,
composites
Ceramics,
glasses
3
The world of materials
Metals,
alloys
Polymers,
elastomers
Hybrids,
composites
4
2
PROPERTIES SUBJECT TO SELECTION
IN MECHANICAL DESIGN
1.
Density
Weight, loading
2.
Yield Strength
Plastic Deformation
3.
Tensile Strength (ultimate)
Rupture
4.
Hardness
Surface damage
5.
Elastic modulus
Flexibility, stiffness
6.
Fatigue Strength
Fracture under cyclic load
7.
Maximum elongation
Ductile vs. brittle
5
How to Characterize Material Behavior?
6
1.
Tensile test
Most common for static strength
2.
Compression test
Preferred for brittle materials
3.
Hardness
Good, if tensile test is not available
4.
Fatigue test(s)
To determine endurance limit
5.
Impact test
To determine transition temperature
6.
Creep test
For high temperature applications
7.
Bending test
Composite and brittle materials
8.
Cupping test
For sheet metal formability
3
TENSILE TEST
7
DUCTILE VS. BRITTLE METALS
8
4
9
10
5
11
IMPACT TEST
12
6
13
EFFECT OF TEMPERATURE
14
7
CREEP
15
The most commonly used engineering material?
16
1.
Cast Iron(s)
Gray cast iron, Spherodized cast iron
2.
Cast Steel
Many alloys
3.
Wrought Steels
Hot/cold rolled; Forged; Extruded, Drawn
8
17
CODING: CAST ALLOYS
18
9
19
STANDARD SECTIONS
20
10
HEAT TREATMENT
21
22
11
23
24
12
25
COMPOSITES
26
13
MATERIAL SELECTION
27
28
14
29
30
15
31
32
16
Organising information: the MATERIALS TREE
Kingdom
Family
Class
• Ceramics
& glasses
Steels
Cu-alloys
• Metals
& alloys
Materials
data-table
Al-alloys
Ti-alloys
• Polymers
& elastomers
Ni-alloys
Zn-alloys
• Hybrids
Member
1000
2000
3000
4000
5000
6000
7000
8000
Attributes
Al 6463
Al 6060
Density Al 6061
Density
Mechanical
Densityprops.
Mechanical props.
Thermal
props. props.
Mechanical
Thermal props.
Electrical
props.
Thermal
props.
Electrical props.
Optical
props.
Electrical props.
Optical props.
Corrosion
Opticalprops.
props.
Corrosion props.
Documentation
Corrosion props.
Documentation
-- specific
Documentation
-- specific
-- general
-- specific
-- general
-- general
Structured
information
Unstructured
information
Material records
33
Structured information for ABS*
Acrylonitrile-butadiene-styrene (ABS) - (CH2-CH-C6H4)n
General Properties
Density
Price
1.05 2.1 -
Mechanical Properties
Young's Modulus
Elastic Limit
Tensile Strength
Elongation
Hardness - Vickers
Endurance Limit
Fracture Toughness
Thermal Properties
Max Service Temp
Thermal Expansion
Specific Heat
Thermal Conductivity
1.1
18
27
6
6
11
1.2
-
350 70
1500 0.17 -
1.07 Mg/m^3
2.3 US $/kg
2.9
50
55
8
15
22
4.2
GPa
MPa
MPa
%
HV
MPa
MPa.m1/2
370 K
75 10-6/K
1510
J/kg.K
0.24 W/m.K
Electrical Properties
Conductor or insulator?
Good insulator
Optical Properties
Transparent or opaque?
Opaque
Corrosion and Wear Resistance
Flammability
Average
Fresh Water
Good
Organic Solvents
Average
Oxidation at 500C
Very Poor
Sea Water
Good
Strong Acid
Good
Strong Alkalis
Good
UV
Good
Wear
Poor
*Using the CES Level 2 DB
34
17
Unstructured information for ABS*
What is it? ABS (Acrylonitrile-butadiene-styrene ) is tough, resilient, and easily molded. It
is usually opaque, although some grades can now be transparent, and it can be given vivid
colors. ABS-PVC alloys are tougher than standard ABS and, in self-extinguishing grades, are
used for the casings of power tools.
Design guidelines. ABS has the highest impact resistance of all polymers. It takes color
well. Integral metallics are possible (as in GE Plastics' Magix.) ABS is UV resistant for
outdoor application if stabilizers are added. It is hygroscopic (may need to be oven dried
before thermoforming) and can be damaged by petroleum-based machining oils.
ABS can be extruded, compression moulded or formed to sheet that is then vacuum thermoformed. It can be joined by ultrasonic or hot-plate welding, or bonded with polyester, epoxy,
isocyanate or nitrile-phenolic adhesives.
Technical notes. ABS is a terpolymer - one made by copolymerising 3 monomers: acrylonitrile, butadiene and syrene. The
acrylonitrile gives thermal and chemical resistance, rubber-like butadiene gives ductility and strength, the styrene gives a glossy surface,
ease of machining and a lower cost. In ASA, the butadiene component (which gives poor UV resistance) is replaced by an acrylic ester.
Without the addition of butyl, ABS becomes, SAN - a similar material with lower impact resistance or toughness. It is the stiffest of the
thermoplastics and has excellent resistance to acids, alkalis, salts and many solvents.
Typical Uses. Safety helmets; camper tops; automotive instrument panels and other interior components; pipe fittings; home-security
devices and housings for small appliances; communications equipment; business machines; plumbing hardware; automobile grilles;
wheel covers; mirror housings; refrigerator liners; luggage shells; tote trays; mower shrouds; boat hulls; large components for recreational
vehicles; weather seals; glass beading; refrigerator breaker strips; conduit; pipe for drain-waste-vent (DWV) systems.
The environment. The acrylonitrile monomer is nasty stuff, almost as poisonous as cyanide. Once polymerized with styrene it
becomes harmless. ABS is FDA compliant, can be recycled, and can be incinerated to recover the energy it contains.
*Using the CES Level 2 DB
35
18
10/9/2023
MKT 3821
Design of Machine
Elements
by
Haydar Livatyalı
Yıldız Technical University
FALL 2023-2024
1
What is engineering design?
• Design is the formulation of a plan to satisfy a
particular need, real or imaginary
• Design represents the process of problem solving
• Engineering design is the process of applying
science and engineering methods to prescribe a
component or a system in sufficient detail to permit
its realization
• A system constitutes several different elements
arranged to work together as a whole
2
1
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MÜDEK defines
• Engineering design as the process of devising a system,
component, or process to meet desired needs
• It is a decision-making process (often iterative), in which
the basic science and mathematics and engineering
sciences are applied to convert resources optimally to
meet a stated objective
• Fundamental elements of the design process are the ;
establishment of objectives and criteria,
synthesis,
analysis,
construction,
testing and
Evaluation.
3
A design MUST be:
4
2
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Design considerations
5
6
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Design
process
7
Solving a Design Problem
1 Given: Define the problem and known quantities
2 Find: State consistently what is to be determined
3 Assumptions: List simplifying idealizations to be
made
4 Solution: Apply the appropriate equations to
determine the unknowns
5 Comments: Discuss the results briefly
8
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Time Management
9
Significant Digits
10
5
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Preferred Numbers
The ISO has defined four basic series of preferred
numbers:
R5: 10, 16, 25, 40, 63, 100.
R10: 10, 12.5, 16, 20, 25, 31.5, 40, 50, 63, 80, 100.
R20: 10, 11.2 12.5, 14, 16, 18, 20, 22.4, 25, 28, 31.5, 35.5,
40, 45, 50, 56, 63, 71, 80, 90, 100.
R40: 10, 10.6, 11.2, 11.8, 12.5, 13.2, 14, 15, 16, 17, 18,
19, 20, 21.2, 22.4, 23.6, 25, 26.5, 28, 30, 31.5, 33.5, 35.5,
37.5, 40, 42.5, 45, 47.5, 50, 53, 56, 60, 63, 67, 71, 75, 80,
85, 90, 95, 100.
11
Factor of Safety
Factor of safety (>1) is employed in design to ensure
against uncertainities involving loading and material
strength.
Allowable load: Service load of working load
Allowable stress: Applied stress, working stress or design
stress
Material Strength: Yield or Ultimate Tensile Strength
12
6
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FoS in terms of Materials and Loading
Conditions
Reference for ductile materials: Yield Strength or Endurance Limit
for brittle materials: Ultimate Tensile Strength
13
Design and Safety Codes
• ASME (American Society of Mechanical Engineers)
• ISO (International Standards Organiization)
• TSE (Turkish Standards Institute)…
g = 9,81 m/s2
14
7
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Units
15
Reliability
The statistical measure of the probability that a
mechanical element will not fail in use is called
the reliability of that element.
0<R<1
Ex:
95% reliable means 95 out of 100 products will
function without failure within the design envelope
and time (probabilistically).
It is NOT a deterministic measure.
16
8
10/9/2023
A Machine: Centrifugal Pump
outlet
Liquid
Inlet
Electric motor
Another design
17
18
9
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bolt
casing
nut
rotor
bearing
seal
shaft
cap
bracket
screw
washer
19
20
10
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21
22
11
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Types of Mechanical Design Problems
• Select the most economical material that will NOT
fail (= calculation of stresses, size known)
• Select the minimum size (cross section diameter,
height, width, thickness) of the mechanical element
(material known or pre-selected)
• Find the minimum number of elements (bolts,
rivets, welds, threads etc.) that are needed
(material and size known or pre-selected)
23
Case: Design of a Tie-rod
= Two Force Member
Given: Length, circular cross-section, Tensile Force, SAE 1040 Annealed
Find: Diameter
Assumptions: Two-force member, static tensile load only
Factor of Safety=2,0
Solution:
from s = F/A … Sy = 4nF/pd2
gives
d=(4nF/Sy)1/2
Comments: A tie-rod subject to only tensile load is a gross assumption
Length is a redundant parameter for tensile loading
24
12
9.10.2023
MKT 3821
Design of Machine
Elements
STRENGTH OF MATERIALS REVIEW
by
Haydar Livatyalı
Yıldız Technical University
FALL 2023-2024
1
What is A MACHINE?
MACHINES are technical systems that;
• Generate
• Transmit
• Convert
energy, perform work.
Machines consist of components that are
called MACHINE ELEMENTS.
2
1
9.10.2023
Machine Elements
3
Race Bike; ~890-900 components
4
2
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5
Calculation Methodology
6
3
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7
The Order of Calculations
1.
8
4
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The Order of Calculations
Forces:
9
Stresses
10
5
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11
Tension-Compression
12
6
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Components under tensile load
13
Shear
14
7
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15
Components under shear
16
8
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Bending
17
Bending
18
9
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19
Standard Sections
20
10
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Components under bending
21
Torsion
22
11
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23
24
12
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Polar Moment
of Inertia
25
Components under torsion
26
13
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Stress Concentration
27
28
14
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Stress Concentration
29
Strain
30
15
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Tensile Test
31
32
16
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33
Shear Deformation
34
17
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Shear Deformation under Shear Stress
35
Poisson’s Ratio
36
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State of Stress
37
3D State of Stress
38
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A 2D Simplification: Plane Stress
39
40
20
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Plane Stress
41
42
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43
44
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Principal Stresses
45
Stress-Strain
Simple Tension
(s2=s3= 0)
46
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47
48
24
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49
50
25
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51
Failure Theories
52
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Why do we need a Failure Criterion?
Failure theory gives an Equivailent Stress that can be compared to material strength.
53
Maximum Normal Stress Theory
54
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55
Maximum Shear Stress Theory
56
28
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… also called as Tresca Criterion
𝜎
=
𝜎 −𝜎
𝜎
=
2
−𝜎
2
• Maximum Shear Stress (Tresca) Theory is
mathematically practical.
• Applies well to ductile metals.
• It is a conservative ciriterion.
57
Maximum Distortion Energy Theory
58
29
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also called the Von Mises Criterion.
59
Tresca vs. Von Mises
60
30
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61
Coulomb-Mohr Theory
62
31
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63
32
17.10.2023
MKT 3821
Design of Machine Elements
STIFFNESS & FATIGUE FAILURE
by
Haydar Livatyalı
Yıldız Technical University
Fall 2023-2024
1
Most machines fail due to weak STIFFNESS
STIFFNESS (k): is the extent to which an object resists
deformation in response to an applied force. The
complementary concept is flexibility or pliability: the
more flexible an object is, the less stiff it is. It is a
function of material elasticity and part geometry.
ELASTICITY (E): is the ability of an object or material
to resume its normal shape after being stretched or
compressed; stretchiness. E = Stress/Strain
RIGIDITY: Inability to be to bent or be forced out of
shape. So, usually, it means bending stiffness.
2
1
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3
4
2
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Long-Slender (Euler) Columns
5
Effective Lengths
6
3
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7
8
4
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9
CYCLIC LOADING & FATIGUE FAILURE
10
5
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11
Fatigue Test
Moore’s
Rotational
Bending
Tester,
Test Specimen
& Loading
regime
12
6
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STRESS vs. LIFE
Life = Number of Load Cycles
13
S-N (Woehler) Curve
14
7
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ENDURANCE LIMIT
15
FATIGUE & SURFACE
16
8
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FATIGUE & SIZE
17
FATIGUE & LOADING
18
9
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FATIGUE & TEMPERATURE
19
FATIGUE & RELIABILITY
20
10
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MISCALLENEOUS FACTORS
21
22
11
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FATIGUE & STRESS CONCENTRATION
Fatigue Stress Concentration Factor:
Where
Kt Theoretical Stress Concentration Factor
q notch sensitivity factor
Se=kakbkckdkekf(1/Kf)Se’
23
q-Charts
24
12
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25
26
13
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27
When the loading is NOT Fully Cyclic
28
14
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29
30
15
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• For the fatigue factors some boks use «C» and some
books use «K».
• Size, temperature, reliability, surface and stress
concentration factors are take into account in this case.
• All other factors are assumed to be 1,0.
31
32
16
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33
34
17
10/17/2023
MKT 3821
Machine Elements
Solved Examples on Strength and Stiffness
From:
Ugural A, Mechanical Design of Machine Components, 2nd Ed. CRC Pr.
&
Mott RL, Machine Elements in Mechanical Design, 5th Ed. Pearson
H. Livatyalı Fall 2023
1
Philosophy of Safe Design:
Ensure that the stress level is below yield in ductile
materials, so that the part will not break under static
load.
For brittle materials, ensure the stress levels are well
below the ultimate tensile strength.
Also, analyze deflection where it is critical to the
safety or performance of a part.
Make your selection or decision on the safe side.
2
1
10/17/2023
Calculation Methodology
3
Problem Solving Order
List the Given
List the Unknown
List the Assumptions (including Safety Factor)
Select the Mathematical Model
Make the Calculations, solve the Problem
Make your Design Decision based on the calculated
result
List the Output: Material or
Dimensions or
Size or code according to a standard
machine element
4
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5
6
3
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7
8
4
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9
10
5
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11
Torsional Shear
12
6
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13
14
7
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15
16
8
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17
18
9
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19
20
10
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21
22
11
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23
24
12
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25
26
13
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27
28
14
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29
30
15
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31
32
16
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Stress Concentration
33
34
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35
36
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37
38
19
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39
40
20
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42
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46
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47
48
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49
50
25
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51
52
26
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53
54
27
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55
56
28
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57
58
29
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59
Fatigue; Endurance Limit
60
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62
31
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63
64
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65
66
33
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68
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70
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72
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74
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24.10.2023
MKT 3821
Design of Machine Elements
POWER SCREWS
by
Haydar Livatyalı
Yıldız Technical University
Fall 2023-2024
1
A power screw is a motion-displacement transmission
mechanism.
2
1
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3
4
2
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5
6
3
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Power Screw Thread Forms
7
8
4
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9
10
5
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11
12
6
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where fc and dc are the friction coefficient and diameter of the collar
13
14
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Self-Locking
15
Screw Efficiency
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18
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20
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22
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26
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32
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33
Ref: Thomson Linear Catalogue, 2022
34
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24.10.2023
MKT 3821
Design of Machine Elements
THREADED FASTENERS:
Bolts-Nuts, Screws and Studs
by
Haydar Livatyalı
Yıldız Technical University
Fall 2023-2024
1
2
1
24.10.2023
Threaded Fasteners
3
What is a Bolt-Nut?
4
2
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5
STANDARDIZATION
6
3
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7
8
4
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9
10
5
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11
12
6
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13
14
7
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15
Not used for bolts, nuts and screws.
Used in power screws.
16
8
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17
Proof Strength
Proof strength is a value less then yield strength.
Used as a safe static design parameter.
18
9
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• Axial Stress
• Torsional Shear
19
• Bearing Stress
• Direct Shear
20
10
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Bolt Tightening Pre-Load
Torque Needed
21
22
11
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23
24
12
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25
26
13
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27
28
14
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29
30
15
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31
32
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33
Empirical Method for Member Stiffness
34
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35
36
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37
38
19
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39
40
20
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41
42
21
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43
44
22
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45
23
11/3/2023
MKT 3821
Rivets, Adhesive Joints & Welds
YTU Mechatronics Engineering Department
Fall 2023-2024
1
2
11/3/2023
3
Rivets
Advantages – Disadvantages
4
11/3/2023
Rivet Types
5
Rivet Materials and Manufacturing
6
11/3/2023
Riveted Joints
7
8
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9
Rivets Sharing Moment (as shear force)
10
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11
12
11/3/2023
Adhesive Joints
Advantages
13
Adhesive Joints: Disadvantages
14
11/3/2023
Adhesive Joints: Applications
15
16
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Adhesive Types
17
Failure
18
11/3/2023
Design Rules
19
20
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Stress Analysis
21
22
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Welded Joints
23
24
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25
Lap Joint
26
11/3/2023
Butt Joint
27
28
11/3/2023
29
30
11/3/2023
31
32
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33
Butt Joints
34
11/3/2023
35
36
3.11.2023
MKT 3821
Shafts & Axles
YTU Mechatronics Engineering Department
Fall 2023-2024
1
What is a shaft?
2
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3
4
2
3.11.2023
5
6
3
3.11.2023
7
8
4
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Axles
9
Rotating and Non-rotating Axles
10
5
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11
Shaft Design Principles
12
6
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13
Example Problem: Simple Static Stress and Deflection Analysis
… Remember: c = d/2
14
7
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15
Combined Loading
16
8
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Just Bending+Shear
17
18
9
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19
20
10
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Torque Capacity When Shaft is Hollow
where
D is outer diameter
d is the inner diameter
tall is the allowable shear stress.
21
Combined Loading of Hollow Shaft
22
11
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23
24
12
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25
26
13
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27
FLYWHEELS
Rotational energy storage component
Analogous to a capacitor
28
14
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29
30
15
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31
32
16
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33
Punch Press
34
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36
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38
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40
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42
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44
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11/3/2023
MKT 3821
Couplings & Keys
Haydar Livatyalı
Fall 2023-2024
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2
1
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Coupling Types
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4
2
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5
6
3
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8
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No torsional flexibility
with
No bending flexibility
9
No torsional flexibility
with
No bending flexibility
10
5
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11
Cardan (Universal) Joint
No torsional flexibility
with
Good angular misalignment
Good axial tolerance
with
Some oscillation
12
6
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Inevitable Oscillations in a Cardan Joint
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14
7
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15
16
8
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17
CV (Continuous Velovity) Coupling
No torsional flexibility
with
Large angular misalignment
Good axial tolerance
with
No oscillation; therefore good for high rotational velocity
18
9
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Oldham Coupling
No torsional flexibility
with
Good tolerance for parallelism problems
19
Jaw Coupling
20
10
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Ratched (Dişli) Coupling
Good for very heavy duty applications;
High torsional stiffness
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22
11
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Chain (Zincir) Coupling
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24
12
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Elastic Disk Coupling
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26
13
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27
Some torsional flexibility
with
No bending flexibility
28
14
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Periflex Coupling
Some torsional flexibility
with
Some bending flexibility
29
High torsional flexibility
with
Some bending flexibility
good for
Low temperature applications
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15
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Bibby Coupling
31
Bibby Coupling
Some torsional flexibility
with
Some bending flexibility
32
16
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High torsional flexibility
with
Little bending flexibility
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34
17
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35
36
18
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Steel Disc Coupling
High torsional rigidity
with
Some bending flexibility
and
Some axial filexibility
37
Bellow Coupling
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19
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High torsional rigidity
with
High bending flexibility
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40
20
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42
21
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44
22
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Keys
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23
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Pins
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Retaining (snap)
Rings
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24
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Splines
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50
25
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51
52
26
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53
54
27
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55
56
28
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57
58
29