1)Failure Mode & Effects Analysis (FMEA)
Defined: FMEA is a systematic tool for
identifying:
-effects or consequences of a potential
product or process failure.
- methods to eliminate or reduce the chance
of a failure occurring.
FMEA generates a living document that can be
used to anticipate and prevent failures from
occurring.
FMEA is a Tool - When to Use
- effective when it occurs before a design is
released rather than “after the fact”.
*focus should be on failure prevention not
detection.
objective of FMEA
-Uncover problems with the product that will
result in safety hazards, product malfunctions,
or shortened product life,etc
Potential Applications
-Component Proving Process
-Outsourcing / Resourcing of product
-Develop Suppliers to achieve Quality
-Renaissance / Scorecard Targets
-Major Process / Equipment / Technology
Changes
-Cost Reductions
-New Product / Design Analysis
-Assist in analysis of a flat pareto chart
FMEA Variables
Conducting FMEA
-Prior to conducting an FMEA, it is often useful
to:
*perform a functional analysis, and
*generate FMEA cause-and-effect diagrams.
-Basic and Secondary Functions - verb~noun
descriptions of what product (process) does.
*Basic Function: ingress to and egress from
vehicle
*Secondary functions - protect occupant from
noise
-Failure Mode - physical description of a
failure.
*noise enters at door-to-roof interface
-Failure Effects - impact of failure on people,
equip.
*driver dissatisfaction.
-Failure Cause - refers to cause of the failure.
*insufficient door seal.
Continuous Improvement:
-Last Columns of FMEA worksheet are used to
identify improvement plan.
*Recommend action
*Identify responsibility to complete action.
*Identify target dates to complete action.
*List action taken and reassess RPN.
Severity
-Definition: assessment of the seriousness of
the effect(s) of the potential failure mode on
the next component, subsystem, or customer
if it occurs
-Severity applies to effects
-For failure modes with multiple effects, rate
each effect and select the highest rating as
severity for failure mode
Occurrence
-Definition: likelihood that a specific
cause/mechanism will occur
-Be consistent when assigning occurrence
-Removing
or
controlling
the
cause/mechanism though a design change is
only way to reduce the occurrence rating
Detection
-Detection values should correspond with
AIAG, SAE
-If detection values are based upon internally
defined criteria, a reference
must
be
included in FMEA to rating table with
explanation for use
-Detection is the value assigned to each of the
detective controls
-Detection values of 1 must eliminate the
potential for failures due to design deficiency
Risk Priority Number(RPN)
-Severity x Occurrence x Detection
-RPN is used to prioritize concerns/actions
-The greater the value of the RPN the greater
the concern
-RPN ranges from 1-1000
-The team must make efforts to reduce higher
RPNs through corrective action
-General guideline is over 100 = recommended
action
-Risk Priority Number is a multiplication of the
severity, occurrence and detection ratings
-Lowest detection rating is used to determine
RPN
-RPN threshold should not be used as the
primary trigger for definition of recommended
actions
Benefits of FMEA
-Contributes to improved designs for products
and processes.
*Higher reliability
*Better quality
*Increased safety
*Enhanced customer satisfaction
-Contributes to cost savings.
*Decreases development time and re-design
costs
*Decreases warranty costs
*Decreases
waste,
non-value
added
operations
-Contributes to continuous improvement
Reasons FMEA’s fail
-One person is assigned to complete the FMEA
-Members of the FMEA team are not trained in
the use of FMEA
-Rushing through identifying the failure modes
to move onto the next step of the FMEA
-Listing the same potential effect for every
failure i.e. customer dissatisfied.
-Stopping the FMEA process when the RPN’s
are calculated and not continuing with the
recommended actions
2) MAGNETIC PARTICLE
-A ferromagnetic test specimen is magnetized
with a strong magnetic field created by a
magnet or special equipment. If the specimen
has a discontinuity, the discontinuity will
interrupt the magnetic field flowing through
the specimen and a leakage field will occur.
-Finely milled iron particles coated with a dye
pigment are applied to the test specimen.
These particles are attracted to leakage fields
and will cluster to form an indication directly
over the discontinuity. This indication can be
visually detected under proper lighting
conditions.
Factors Affecting Flux Leakage
-Depth of defect
-Orientation of defect shape of defect
-Size of defect
-Permeability of material
-Amount of flux available
Basic Procedure
Basic steps involved:
1.Componentpre-cleaning-contaminant
prevent particles from being attracted to
leakage fields, they may also interfere with
interpretation of indications
2.Introduction of magnetic field-The required
magnetic field can be introduced into a
component in a number of different ways.
*Using a permanent magnet or an
electromagnet that contacts the test piece
*Flowing an electrical current through the
specimen
*Flowing an electrical current through a coil of
wire around the part or through a central
conductor running near the part.
3.Application of magnetic media
4.Interpretation
of
magnetic
particle
indications
3)ULTRASONIC (ATTENUATION)
-Attenuation is the loss intensity of the
ultrasonic beam as it passes through a
material and is dependent on the physical
properties of the material.
-Two factors affect the sound attenuation:
i)Absorption
-Cause by the interaction of the particles as
they vibrate during the passage of sound
waves
-The movement of particles cause friction, and
dissipated as heat
-As the frequency increases, the absorption
greater due to raid movement
ii)Scatter
-Cause by grain boundaries, porosity, non
metallic inclusions, etc
-Larger grain size greater scattering
-Coarse grain will be more attenuative than
fine grain material
-Rough surface also cause attenuation.
Attenuation can be represented as a decaying
exponential. The amplitude change of a
decaying plane wave can be expressed as
-A0 is the unattenuated amplitude of the
propagating wave at some location.
-The amplitude A is the reduced amplitude
after the wave has traveled a distance z from
that initial location.
-The quantity  is the attenuation coefficient
of the wave traveling in the z-direction. The
dimensions of are nepers/length, where a
neper is a dimensionless quantity.
-Attenuation can also measured in terms of
decibels (dB)
dB = 20 log (I0/I)
4)FAILURE ANALYSIS refer to slides
9(failure)
i) Fracture:
in 3 general ways:
-sudden brittle fracture
- fatigue / progressive fracture
-delayed fractured
Macroscopic fracture
–Brittle: fracture on a plane normal to
principal stress
–Ductile : involves flow on planes of maximum
shear (planes at 45 to the load).
Theory of brittle fracturechapter 9
Griffith theory
-By using the concept of energy balance in
order to explain discrepancy between the
theoretical cohesive strength& observed the
fracture strength of ideally brittle material
. existing crack will propagate when the
released elastic strain energy is at least equal
to the energy required to create new crack
surface.
• Decrease in strain energy results from the
formation of of a crack
• Elastic strain energy/plate thickness UE= πa2s2/E (crack releases strain energy)
• Surface energy presence of the crack US=
4aƔs
• Total change in potential energy U= UE+ US
d U/da =0=d(4as - πa2s2/E)/da
Fracture Modes
•Simple fracture is the separation of a body
into 2 or more pieces in response to an applied
stress that is static (constant) and at
temperatures that are low relative to the Tmof
the material.
•Classification is based on the ability of a
material to experience plastic deformation.
•Ductile fracture
–Accompanied by significant plastic
deformation
•Brittle fracture
–Little or no plastic deformation
–Sudden, catastrophic
Fracture Mechanism
Imposed stress-> Crack Initiation ->Crack
Propagation
•Ductile failure has extensive plastic
deformation in the vicinity of the advancing
crack. The process proceeds relatively slow
(stable). The crack resists any further
extension unless there is an increase in the
applied stress.
•In brittle failure, cracks may spread very
rapidly, with little deformation. These cracks
are more unstable and crack propagation will
continue without an increase in the applied
stress.
FA: Thermal
Corrosion
Oxidation
Fatigue
Induce Cracking
Please refer to the
slide:9,10,11 n12