Uploaded bySEVUGARAJAN KARUPPAIAH, BE,MS.
Failure analysis
The document provides an in-depth overview of failure analysis covering principles, types of failures, failure modes, methods for conducting analyses, and prevention strategies. It emphasizes the importance of proper observation and data collection, identifies various failure mechanisms, and outlines the role of material analysis techniques. Additionally, it discusses the qualifications of an analyst and includes practical examples of failures in engineering contexts.
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Failure analysis
- 1. Failure Analysis By -K.Sevugarajan Contact details Metz Lab Pvt.Ltd. First floor, Thangavel Nagar Walajabad Main Road, Mannivakkam-600048 Cell: +91-8190810222 Mail: sevuarajan@metzlab.org www.metzlab.org
- 2. www.metzlab.org Outline • Principles • Typesof failures • Failure modes • How to conduct failure analysis • Analyze data • Failure mechanism • Prevention of Failures • Failures examples
- 3. www.metzlab.org Introduction • The objectiveof this course is to provide a basic overview of failure analysis. It will include discussion of failure mechanisms, analytical techniques and case histories • To provide you with a clear understanding of terms used so that you can ask the right questions and interpret common observations with ease
- 4. www.metzlab.org 1. Principles Examinations ♦Detection andcharacterization of damage Materials ♦Identification of damage mechanisms, allowing application of appropriate damage initiation/ propagation modelisation Engineering Analysis ♦Identifications of damage development with respect to specific manufacturing process ♦Basis for determining safe operating periods and expected remaining life.
- 5. www.metzlab.org Qualities Desired inan Analyst • Ability to remain unbiased and reject conventional wisdom. • Ability to facilitate a group of people (if using a team) towards a common objective. • Trained in logic tree approaches to failure analysis. • Affinity for listening and questioning for understanding. • Patience and perseverance. 1. Principles
- 6. www.metzlab.org 1. Principles Failure AnalysisTasks • Prioritize - Determine what is most important to work on. • Analyze - Analyze the failure event to determine root causes. • Recommend - Develop recommendations as solutions to the causes are discovered.
- 7. www.metzlab.org 1. Principles First Principleof Failure Analysis Do Not Touch!!!!!! Observe !! Remember the phrase “See but do not touch” Visual Examination is everything Macroscopic/Microscopic Gut feel is very important Understand the Operating conditions of the part
- 8. www.metzlab.org 2. Types offailures • Ductile • Brittle • Fatigue • High Temperature Excess deformation,elastic or plastic, tearing or shear failure Cleavage, sudden Cycling load, strain, thermal, corrosion, rolling contact, fretting Creep, oxidation, local melting, warping • Static Delayed Embrittlement - Hydrogen, caustic, • Stress Raisers liquid metal, temper, environmental Sharp fracture initiation points
- 9. www.metzlab.org 3. Failure modes Failurescan be classed in three broad categories: failures caused by the deformation of parts, failures due to rupture and failures due to surface damage. PERMANENT DISTORTION : The part can no longer be used because it is deformed. FRACTURES : Various types of rupture may be distinguished, depending on the appearance of the fracture surface and the forces applied. Static sudden fracture under or static constant load, resulting from an impact or from exceedence of the maximum allowable load. Ductile and brittle fracture Delayed breakage Fracture due to hydrogen embrittlement Stress corrosion fracture Fatigue fracture Creep fracture Stress corrosion fracture
- 10. www.metzlab.org 3. Failure modes SURFACEDAMAGE : This category covers many different types of damage affecting a wide variety of mechanisms. The common characteristic of all these is that they cause deterioration of the surface of the metal, which eventually leads to the destruction of the part. Surface fatigue (or “contact fatigue”) Frosting or hairline cracks Uniform spalling Wear Abrasive wear Adhesive wear or scuffing Fretting-corrosion wear Cavitation-Erosion Thermal fatigue CORROSION
- 11. www.metzlab.org 3. Failure modes •Misuse or Abuse • Assembly errors • Manufacturing defects • Improper maintenance • Fastener failure • Design errors • Improper materials • Improper heat treatments • Unforeseen operating conditions • Inadequate quality assurance • Inadequate environmental protection/control • Casting discontinuities Causes of Failure
- 12. www.metzlab.org 3. Failure modes Frequencyof Causes of Failure in Some Engineering Industry Investigations
- 13. www.metzlab.org 3. Failure modes Frequencyof Causes of Failure in Some Engineering Industry Investigations
- 14. www.metzlab.org 4. How toconduct failure analysis Practical Issues in Failure Analysis • Visual Inspection - surface cleanliness • Electrical tests for continuity. • “Drop and suck” test - solvent placed in local area, sucked and analyzed for contaminants. • Cross sectioning to see thickness variations during processing • Scanning/Auger Spectroscopy or Rutherford Back Scattering • Delamination
- 15. www.metzlab.org 4. Steps inFailure Analysis • Description of Failure Situation • Visual Examination • Design/Stress Analysis • Chemical Analysis • Fractography • Metallographic Examination • Properties- hardness or other mechanical properties • Failure Simulation
- 16. www.metzlab.org 4. Stages Ina Failure Analysis • Collect data • Visually examine failure • Non Destructive Testing • Select samples • Examine and analyze • Determine failure mechanism • Write report
- 17. www.metzlab.org 4. Sample Preparation •Fracture surface is dirty and contaminated - Rinse in alcohol or acetone using ultrasonic cleaner - Dry - Replicate using cellulose acetate tape - Gold or carbon coat (200A) the surface - Examine in microscope
- 18. www.metzlab.org 4. Collection ofData • Collect information • Review sequence of events leading to failure • Get drawings and records, repair history • Photograph the failure in several angles before destruction for examination • Get information on good samples for comparison
- 19. www.metzlab.org 4. Visual Examination •Examine before cleaning • DO NOT TRY TO FIT THE BROKEN PIECES BACK TOGETHER! YOU MAY DESTROY THE REAL EVIDENCE- AVOID THE TEMPTATION
- 20. www.metzlab.org Acronym es Technique Information provided ECEddy current Detection of anomalies by differential electrical current response MRI Magnetic resonance imaging Identification of features and structure via introduction of alternating magnetic fields MT Magnetic particle examination Detection of surface and near surface flaws in ferromagnetic materials by flux leakage PT Penetrant testing Identification of flaws and cracks open to the surface in many materials via liquid retention RT Radiographic examination Identification of material flaws and features via density differences measured by penetrating radiation UT Ultrasonic examination Detection of anomalies by differential reflection of ultrasonic pulses 4. Typical Non destructive testing
- 21. www.metzlab.org 4.Materials analysis Chemical analysis:Chemical analysis is an integral part of an investigation, because it indicates whether a component is made of the specified material Metallography : Examination of cross sections of materials involved in a failure can provide important insights into the probable cause of the incident. Metallography can reveal such as : • macrostructure, • depth of surface hardening • microstructure, such as grain size and the phases present • non-metallic inclusions • porosities…
- 22. www.metzlab.org 4.Materials analysis Fractography andSEM examination : Fractography generally involves a scanning electron microscope SEM observations can reveal such as : • fine microstructure, such as phases and precipitations • cracks initiation and fatigue striations • fracture modes (dimples, cleavage, intergranular fracture) Microanalysis : Corrosion products, inclusions, metallurgical phases can be also chemically identified via electron microscopy and energy dispersive spectrometry. Mechanical testing :In addition to the examination methods, hardness measurements can be realized.
- 23. www.metzlab.org 4.Materials analysis Surface aspectevaluation : Surface roughness can also be evaluated. Special testing This group of tests includes all those that do not easily fit into the previous categories. The following are a few of the more important techniques. • Finite element analysis: Finite element analysis, or FEA, is an advanced modeling technique that can help to predict the magnitude of stresses on individual components within complex assemblies. • Simulation: In some instances, sophisticated test apparatus can be developed for approximating the service conditions involved in a materials failure.
- 24. www.metzlab.org 5. Analyze data Theassembled results from the different analysis and tests must be considered collectively, because the final hypothesis needs to be in substantial agreement with all physical evidence and test results.
- 25. www.metzlab.org Determine failure mechanism Apart or assembly is considered failed if one of the following conditions occur: • It becomes completely inoperable • It’s operable but no longer functions satisfactorily • It’sdeteriorated to the point it is unsafe or unreliable.
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- 27. www.metzlab.org Failure Mechanisms Characteristics ofDuctile fracture Ductile fracture has dimpled, cup and cone fracture appearance. The dimples can become elongated by a lateral shearing force, or if the crack is in the opening (tearing) mode. Steel 22MnB5 GS52 cast iron Steel 20MnCr5 with elongated manganese sulphide The size and shape of the dimples depends on the inclusions
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- 29. www.metzlab.org Failure Mechanisms Brittle fracturedisplays either cleavage (transgranular) or intergranular fracture. This depends upon whether the grain boundaries are stronger or weaker than the grains.
- 30. www.metzlab.org Prevention of Failures •Many failures can be avoided by: • Correct design • Selection of appropriate materials • Correct processing • Consideration of service environment • Required: system engineering approach
- 31. www.metzlab.org Prevention of Failures:Design • Design for maximum stress • Include safety margin • Avoid and do not create stress raisers • Do not break fiber reinforcements
- 32. www.metzlab.org Prevention of Failures:Materials • Temperature range of operation • Do not cross polymorphic transformations • Understand fatigue conditions • Stress-rupture lifetime • Quenched and tempered materials loose strength at higher temperature • Age-hardened materials lose strength at high temperature
- 33. www.metzlab.org Prevention of Failures:Processing • Cast to required grain size • Casting may create gas porosity and segregation • Cold working and forging create cracks, flaws, inclusions • Welding creates gas porosity, cracks, recrystallization affecting strength • Heat treatment may create surface cracks upon quenching, decarburize surface layers, create agglomerations at grain boundaries
- 34. www.metzlab.org Prevention of Failures:Service • Thermal and chemical environment must be understood • Avoid overload • Use tools for applications it was designed for • Control wear • Check parts by non-destructive testing methods • Have rigorous maintenance program and quality control • Avoid bogus parts
- 35. www.metzlab.org Failure Analysis Report •Description of the failed component • Service condition at the time of failure • Prior service history • Manufacturing and processing history of component • Mechanical and metallurgical study of failure • Metallurgical evaluation of quality • Event Summary of failure causing mechanism • Recommendations for prevention of similar failures
- 36. UH-1N Turbine: helicalShaft Failure F-18 Engine Shaft Torsional Buckling Torsion Failures www.metzlab.org Examples
- 37. Gross Plastic Deformation UH-1NEngine Shaft/Bearing UH-1N Turbine www.metzlab.org
- 38. Ductile & BrittleFailure in Tension Brittle www.metzlab.org
- 39. Brittle Failures fromRotor Systems www.metzlab.org
- 40. www.metzlab.org Rivermarks & Chevrons Arrowsshows origin of failure
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- 42. www.metzlab.org Bending Deformation &Failure In-flight failure
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- 44. www.metzlab.org Damaged Rotor ofGas Turbine
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- 46. www.metzlab.org Feature of StressCorrosion Cracking - Crack Branching
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- 48. www.metzlab.org Cracks due toThermal Stresses in the Weld Zone
- 49. www.metzlab.org Failure in Superheater Outlet Header
- 50. www.metzlab.org Chevron Notches inFasteners
- 51. www.metzlab.org Bolt Failure Dueto Ductile Overload
- 52. www.metzlab.org Ductile and BrittleFracture • Ductile fracture - Fracture accompanied by plastic deformation and, therefore, by energy absorption - cup and cone • Brittle Fracture - No Energy absorption Left Bolt Rc 57 Brittle Right Bolt Rc 15 Ductile
- 53. www.metzlab.org Failure of Bolts Bendingfatigue of the bolt
- 54. www.metzlab.org Failure of Gears Progressivepit of a pinion gear tooth due to surface contact fatigue
- 55. www.metzlab.org Distortion Failures failures occurDistortion whena structure or component is deformed. It fails because it can no longer support the load it was intended to carry.
- 56. www.metzlab.org Wear Failures Wear -undesired removal of material from rubbing surfaces. • Abrasive • Adhesive
- 57. www.metzlab.org Spring Failure Spring failureby combination of bending, torsion and fatigue.
- 58. www.metzlab.org Cracking in Cup Stresscorrosion cracking of deep-drawn brass cup
- 59. www.metzlab.org Cracking in Tube Stresscorrosion cracking of brass tube
- 60. www.metzlab.org Horse Bit Failure Fracturein horse bit
- 61. www.metzlab.org Stirrup Failure Horse racingstirrup failure
- 62. www.metzlab.org Bicycle Hub Failure Bicyclehub failure in rear wheel
- 63. www.metzlab.org Bicycle Pedal CrankFailure Fatigue crack in a crank
- 64. www.metzlab.org Steel Bolt Failure Hightensile steel bolt fatigue failure
- 65. www.metzlab.org Road Vehicle StubAxle Failure Bending fatigue of a steel stub axle
- 66. www.metzlab.org Car Engine Failure Combustionchamber Engine Failure
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