BMFB 4283 NDT & FAILURE ANALYSIS

1. BMFB 4283NDT & FAILURE ANALYSIS Lectures for Week 8 Prof. QumrulAhsan, PhD Department of Engineering Materials Faculty of Manufacturing Engineering

2. Failure Analysis 8. Introduction to Failure Analysis 8.0 Objective of failure analysis. 8.1 Approach to failure analysis 8.2 Tools of Failure Analysis 8.3 Failure Mode and Effect Analysis (FMEA)

3. Outline of Failure Analysis • Vast topic, many failure modes and mechanisms, overlap, disputes • Always exceptions • Focus on: • Failure analysis process • Some common failures • Highlight some interesting failures • Primarily steel, but present in most materials

4. Objectives of Failure Analysis • Objective investigation of material facts associated with a part or system failure • To understand the failure mechanism of the failed component • To determine the primary/root cause of the failure • To recommend the corrective actions • Determine: • Timeline, chain of events • Root-cause of incident / contributing factors • Post incident fitness for purpose • Repair options • Mitigating future failures

5. What is failure? • Part and/or system no longer complies with design intent for part or system • Subjective definition based on operation • Not always structural • Leaking hydraulic seals • Inappropriate stiffness in component • Rate of corrosive decay/breakdown • Part/system lifetime • Operating/maintenance costs • Aesthetics • Any design parameter

6. Facts of Failures • Manifestation of failure (elastic & plastic deformation, rupture or fracture, change of metals) • Failure inducing agent (force, time, temperature, reactive environment) • Failure locations (body type, surface type) • Failure Mode (ductile, brittle, fatigue, creep, wear, weld etc)

7. Where to Apply • Industrial / Manufacturing • Manufacturing equipment (presses, fixtures) • Consumer Products • Design improvement, validation • Civil Structures / Infrastructure • Structural stability • Utilities (inspection, testing, failure analysis) • Insurance / Legal cases • Root cause, forensics

8. Tools of the Trade • Instrumentation • Strain gage, accelerometer, data acquisition • Inspection • NDT, weld inspection, cracking, corrosion • Analysis • Failure analysis, Fitness for purpose, Stress analysis, Finite Element Analysis (FEA), Metallurgical • Testing • Load testing, cycle testing, instrumented tests, impact test, tensile test

9. Contributing Factor Areas • Original Design • Material Properties • Manufacturing and processing • Service Factors • Loading • Environment • Repair Procedures • Weld Repair

10. Frequency of Causes of Failure Analysis

11. Failure Analysis Process • Description of the failure situation (Background information) • Visual Examination (Record Keeping) • Mechanical Design Analysis (NDT and Destructive Testing) • Macroscopic examination( Appearance, Fractography) • Microscopic examination (Metallography) • Properties • Chemical Design Analysis • Failure Simulation

12. Investigator Requirements • OBJECTIVENESS • Visual Cues • Verbal Cues • Documentation • Names, dates, times, quantities, history • Questioning Attitude • Vagueness of Language • Opposing views of an incident • Broad background in failure mechanisms

13. Technological Tools • Photography and lighting • Optical Microscopy up to 600X • Scanning Electron Microscopy (SEM) over 10,000X • Chemical Analysis • SEM/EDS • Spark Emission Spectroscopy • Fourier Transform Infra Red (FTIR)

14. Optical Microscopy (7) • Use polished and etched specimens • Limited depth of field • Shows individual grain structure

15. SEM Image (7) • Individual grains • Large depth of field • Vacuum chamber • Charging

16. SEM-EDS (3) • Elements give distinct peaks, often primary and secondary

17. FTIR (4) • Measurement of frequencies that are absorbed by organic media

18. Technological Tools • Mechanical Testing • Hardness, micro-hardness, tensile, shear, physical testing • NDT (UT, MT, PT, RT ET etc) • Stress Analysis / FEA • Magnitude, principal direction, sensitivity • Instrumentation • Strain Gages, accelerometers, thermocouples, ect. • Non-Destructive Testing (NDT)

19. Finite Element Analysis • Used to answer particular questions • Stress, strain deflection, principal directions, mode shapes, thermal, impact, etc. • 3500 ton forging press frame, cracking problems

20. Strain Gages • Attach to surface to measure surface strains • Available in hundreds of configurations • Used to calibrate FEA models, measure loads, dynamic • Signal conditioning, error elimination, ground loops etc.

21. ASM Failure Analysis • American Society of Metals (ASM) outline • Experts in each area • Remain OBJECTIVE • Important to be thorough, information will be lost • Failure analysis becomes less reliable with less information

22. ASM Failure Analysis • 1. Background • Location, name, P/N, description, manufacturer, fabricator • Function of item • Maintenance / cleaning history • Operational history • Operational documentation • Normal stress orientations • Extent of incident • Precipitating events • Drawings, photographs, reports, inspections • Service deviations • Opinions of related personnel

23. ASM Failure Analysis • 2. Visual Examination • Survey the entire region • Macroscopically classify the fracture • Estimate manner of loading • Determine associated equipment • Observe colors, contaminants, corrosion products, grinding marks, weld progression, other structures in region • Base material quality, uniformity, coatings • Document and record

24. ASM Failure Analysis • 3. Fractographic Examination • Often necessary to ascertain failure mode • Identify microstructure • Note fracture progression • Note deformation • Isolate contaminants • Note colors • Anomalies • Distinguish post incident damage

25. ASM Failure Analysis • 4. Chemical Analysis • Base metal composition • Contaminant composition • Presence of coating on fracture surface • Corrosion product composition

26. ASM Failure Analysis • 5. Mechanical Properties • Bulk material properties • Anomalous material properties • Hardness • Ductility • Tensile strength • Corrosion susceptibility • SCC susceptibility

27. ASM Failure Analysis • 6. Macroscopic Examination • Overall homogeneity • Uniform cracking • Any differences

28. ASM Failure Analysis • 7. Metallographic Examination • Section polish and etch • 8. Microhardness • Traverse across crack, HAZ. Determine gradients • Inclusions, metallographic phases

29. ASM Failure Analysis • 9. SEM analysis • Identify microscopic fracture modes • Ductile dimpling, inter-granular, cleavage • Presence of contamination on fracture surface • 10. Microprobe • SEM-EDS of individual areas • Graphite, carbides, precipitates

30. ASM Failure Analysis • 11. Residual Stresses and phases • X-Ray diffraction, strain gage methods • 12. Simulation / Tests • FEA, stress analysis • Testing • Consistent with findings? • 13. Summarize findings • 14. Report and Distribute • 15. Follow-up

31. ASM Failure Analysis • 16. Preserve Evidence • Package carefully • DO NOT put fracture faces together • Use desiccant • Other experts, new information • Sometimes destructive testing is required

32. Failure Mechanisms • Parts “Fail” for many reasons (Deficiency) • Operational • Plastic deformation (permanent set, buckling) • Excessive deflection (floors, beams, shafts) • Excessive vibration (machine mounts) • Acoustics issues • Fracture • Ductile, Brittle, Fatigue, Thin Lip…

33. Failure Mechanisms • Corrosion • Thinning • Stress Concentrators (risers) • Corrosion Products • Wear • Thinning • Wear Products • Welding

34. Synergistic Effects • All failures have components of multiple failure mechanisms associated • Simultaneous presence, interacting • Task is to determine the important ones from the auxiliary modes

35. Some Techniques in FA • Cleaning Fracture Surfaces and SEM Observation • Clean the surface using acetone, alcohol, ultrasonic cleaner and then dry • Replicating surfaces by • Wetting the fracture surface • Wetting the adhesive side of the acetate tape • Rub the wet surface of tape to fracture surface to put impression on the tape and collecting debris • Tape is coated with gold/carbon and carried out SEM and EDAX

36. Some Techniques in FA • Preparation of Replicas for the TEM • Take the tape replica • Put a thin(200 A) layer of a carbon on it in a vacuum coater • Alternatively carbon can be coated on the fracture surface and then removed by the adhesive tape • Put a thin(200 A) layer of a heavy metal (Cr, Pt) to enhance contrast • Acetate tape is dissolved in a solvent (acetone) ; freeing the thin and fragile replica • Replica is removed onto a screen or grid

37. Some Techniques in FA • Steremicroscopy • Stereo imaging involves recording a given field of view twice at slightly different orientations and simultaneously viewing the stereo pair such that a three dimensional image is percieved • The four methods to record stereo pairs • The tilt method- where angle is applied between the the two micrographs • The lateral shift method - where there is a horizontal displacement between the two micrographs • The rotation methods-where the specimen is rotated between exposure • Electromagnetic deflection of the electron beam between two images

38. 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. • Ideally, FMEA’s are conducted in the product design or process development stages [conducting an FMEA on existing products or processes may also yield benefits] • FMEA generates a living document that can be used to anticipate and prevent failures from occurring. (note: documents should be updated regularly.)

39. FMEA/FMECA History • The history of FMEA/FMECA goes back to the early 1950s and 1960s. • U.S. Navy Bureau of Aeronautics, followed by the Bureau of Naval Weapons: • National Aeronautics and Space Administration (NASA): • Department of Defense developed and revised the MIL-STD-1629A guidelines during the 1970s.

40. FMEA/FMECA History (continued) • Ford Motor Company published instruction manuals in the 1980s and the automotive industry collectively developed standards in the 1990s. • Engineers in a variety of industries have adopted and adapted the tool over the years.

41. Published Guidelines • J1739from the SAE for the automotive industry. • AIAG FMEA-3 from the Automotive Industry Action Group for the automotive industry. • ARP5580 from the SAE for non-automotive applications.

42. FMEA is a Tool - When to Use • FMEA is most effective when it occurs before a design is released rather than “after the fact”. • focus should be on failure prevention not detection. FMEA is often a standard process used in the development of new products.

43. System Design Process Components Subsystems Main Systems Components Subsystems Main Systems Manpower Machine Method Material Measurement Environment Focus: Minimize failure effects on the System Focus: Minimize failure effects on the Design Focus: Minimize failure effects on the Processes Machines Objectives/Goal: Maximize System Quality, reliability, Cost and maintenance Objectives/Goal: Maximize Design Quality, reliability, Cost and maintenance Objectives/Goal: Maximize Total Process Quality, reliability, Cost and maintenance Tools, Work Stations, Production Lines, Operator Training, Processes, Gauges

44. What tools are available to meet our objective? • Benchmarking • customer warranty reports • design checklist or guidelines • field complaints • internal failure analysis • internal test standards • lessons learned • returned material reports • Expert knowledge

45. What are possible outcomes? • Actual/potential failure modes • customer and legal design requirements • duty cycle requirements • product functions • key product characteristics • Product Verification and Validation

46. FMEA Roadmap

47. FMEA Variables

48. Design FMEA Format Item Action Results Action Results C C O O D D Current Current Potential Potential Response & Response & Potential Potential Potential Potential S S l l c c e e R R Design Cause(s)/ Cause(s)/ Recommended Recommended Target Target S S O O D D R R Failure Failure Effect(s) of Effect(s) of e e a a c c t t P P Controls Controls Action Action Mechanism(s) Mechanism(s) Actions Actions Complete Complete E E C C E E P P Mode Mode Failure Failure v v s s u u e e N N Taken Taken Of Failure Of Failure Date Date V V C C T T N N s s r r c c Function Prevent Prevent Detect Detect

49. General Item Action Results Action Results • Every FMEA should have an assumptions document attached (electronically if possible) or the first line of the FMEA should detail the assumptions and ratings used for the FMEA. • Product/part names and numbers must be detailed in the FMEA header • All team members must be listed in the FMEA header • Revision date, as appropriate, must be documented in the FMEA header C C O O D D Current Current Potential Potential Response & Response & Potential Potential Potential S S l l c c e e R R Design Cause(s)/ Cause(s)/ Recommended Recommended Target S S O O D D R R Failure Effect(s) of Effect(s) of e e a a c c t t P P Controls Controls Action Action Mechanism(s) Mechanism(s) Actions Actions Complete Complete E E C C E E P P Mode Failure Failure v v s s u u e e N N Taken Taken Of Failure Of Failure Date Date V V C C T T N N s s r r c c Function Prevent Prevent Detect Detect

50. 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