dsgxfg dndgfndfb

1. Introduction to Materials Science
(BTCMTPCC301)
Prof Projjal Basu
Department of Metallurgical Engineering
Dr Projjal Basu

2. Materials : factors affecting performance
Dr Projjal Basu
External factors Internal factors
• Working load (w.r.t. design load)
• Loading pattern (direction, cyclic /non-
cyclic, impact, low strain rate loading, etc.)
• Surrounding medium (reactive / non-
reactive)
• Working temperature (constant /
fluctuating)
• Use (continuous / intermittent)
• Shape of the component (aspect ratio,
surface/volume ratio, stress raisers)
• Chemical composition
• Composition homogeneity
• Presence of inclusion
• Presence of microscope defects
• Presence of inclusions
• Size / shape / distribution of
grains

3. Materials failure methods
Dr Projjal Basu
Plastic Fatigue
Twinning
Elastic
Erosion
Slip
Materials Failure Mechanisms
Fracture Creep
Oxidation
Microstructural
Changes
Chemical /
Electrochemical
Degradation
Grain Growth
Physical
Degradation
Twinning
Phase
Transformation
Wear
Plastic Coarsening
Corrosion

4. Material failure analysis
Fish Bone Diagram / Ishikawa Diagram / Cause & Effect Diagram
Dr Projjal Basu

5. Material failure : Fish Bone Analysis
Example
Dr Projjal Basu

6. Material failure : Fish Bone Analysis
Example
:
Weld
Defects
Dr Projjal Basu

7. (Failure Mode) and (Effect Analysis)
Dr Projjal Basu
Material failure : FMEA Analysis
FMECA : (Failure Mode) (Effects) and (Criticality Analysis)
Specific ways in which failures could have
occurred for the particular component /
assembly / sub-system being analyzed
Studying the impact of identified
failure modes on the entire system
Specific ways in which failures could have
occurred for the particular component /
assembly / sub-system being analyzed
Studying the impact of
identified failure modes on
the entire system
Quantifying the level of risks
associated with identified
failure modes

8. Types of FMEA
• Design failure mode and effects analysis (DFMEA)
• Aims to create long-lasting products
• Considers how the product might fail at each phase of its life cycle
• Process failure mode and effects analysis (PFMEA)
• Looks at each step of a process
• Considers sourcing, assembly processes, transportation, data processing, etc.
• Determines where the process could break down
• Functional failure mode and effects analysis (FFMEA)
• Looks at the system as a whole
• Instead of correcting the failure, it tries to bypass it entirely
Dr Projjal Basu

9. How to perform FMEA
• FMEA and FMECA aim to provide a list of potential failure modes
ranked by:
• Importance: Is it a key component?
• Effect: What else can happen if it fails?
• Probability: How likely is it to happen?
• To decide which FMEA to choose : Design FMEA / Process FMEA /
Functional FMEA?
• To gather information from : drawings, schematics, component lists,
and interface information, Computer database, Materials report, etc.
etc.
• Now computer models, e.g. Computerized Maintenance Management
System or (CMMS) are helpful
Dr Projjal Basu

10. How to perform FMEA
• How to define malfunction?
• part/system performs an unintended function
• poor performance
• reduced functionality
• failure to complete the intended function
• “Hidden” failure modes which are difficult spot:
• micro-cracking
• electrical short circuit
• torque fatigue
• excessive deformation
• unskilled labour
• Human fatigue / job inattentiveness, etc etc
Dr Projjal Basu

11. How to perform FMEA
To prepare a
worksheet
(e.g. for the
failure of a
bicycle frame)
Dr Projjal Basu

12. How to perform FMEA
• To assign Severity
Ranking Number
(SRN)
• To rank each failure
on a scale of 0 to 10 :
• 0 = This failure has no
measurable impact
• 10 = This failure
would be dangerous
and requires
immediate
intervention
Dr Projjal Basu

13. How to perform FMEA
• To assign Occurrence Ranking :
• Consider how often this failure is likely to happen
• Rank possible failures on a scale of 0 to 10 :
• 0 = This failure is unlikely to ever happen
• 10 = This failure is virtually guaranteed
• To evaluate and assign Failure Detection Rating :
• Consider how easy or difficult it will be to detect this failure with the
available resources (visual inspection to using sophisticated equipment)
• Ideally, problem should be detected before it results in a complete failure (for either
the component or the whole system before the issue cascades)
• Rank each failure on a scale of 0 to 10 :
• 0 = Almost guaranteed to detect the failure early
• 10 = Neither the failure nor its possible causes can be detected
Dr Projjal Basu

14. How to perform FMEA
Failure Detection Rating
Dr Projjal Basu

15. How to perform FMEA
• Calculate Risk Priority Number (RPN)
• For example : A moderately severe failure (5 out of 10) with a very low chance of
occurrence (2 out of 10) but also high difficulty of detection (8 out of 10) has an RPN of
80 (5 x 2 x 8)
• To calculate RPN for every failure, then order the failures from high risk to low risk
• Decide a “critical” level (in high precision industries or settings (laptop / mobile phone), it
might be <2, but in a low precision set up (cookware), it might be as high as 50)
• Some seemingly minor failures could be triggers for other catastrophic malfunctions
Dr Projjal Basu

16. How to perform FMEA
Actions to be taken
• To look for ways to lower the RPN by adjusting at least one of the
three factors that contribute to it:
• Occurrence
Make the potential failure causes more robust, so they fail less often (ff
possible, remove that component altogether)
• Detection
Add more control plans (e.g. sensors with alarms or IoT integrations, these
condition monitoring systems are an integral part of condition-based
monitoring and predictive maintenance)
• Severity
Put controls in place so that the consequences are not so significant
Dr Projjal Basu