Principles of Failure Analysis General Procedures for Failure Analysis
Definition of Failure When a part or device can no longer perform its intended function, the part has failed.
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Definition of Failure When a part or device can no longer perform its intended function, the part has failed.
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Definition of Failure Analysis A systematic, science-based method employed for investigation of failures occurring during tests or in service.
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Fundamental Sources of Failure * Deficiencies in design. * Deficiencies in selection of materials. * Imperfections in materials. * Deficiencies in processing. * Errors in assembly. * Improper service conditions. 4 of 37
Impact of Failure Analysis on Society * Cost of failure. * Cost of failure analysis. * Improvement of products.
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Spring 2014 • • • • • • •
MSE 624 – Failure Analysis Time: Tues 7:00 – 9:45 pm, room JD 3504 Instructor: Dr. Behzad Bavarian Office: JD 3513, Tel: 818-667-3917, Office Hour: T 6:00 – 7:00 pm Email:
[email protected] Website: http://www.csun.edu/~bavarian/mse_624.htm
• Course Description: An introductory course in failure analysis using basic materials properties and engineering principles for understanding the causes of failures and methods of preventing future failures by applying the lessons learned in the process of studying failures. A number of real-life case studies will be used to reinforce topics discussed in the lectures.
Grading Policy: • Mid-term
35%
• Term Paper/ Oral Presentation,
15%
• (Pert, paper Due by May 6, 2014) • Homework (6 assignments)
10%
• Final Exam
40%
Grading System: A through F with Plus/Minus Grading Homework format: Short report (~3-4 pages on the subject including the list of references)
• Failure means nonperformance of something required or expected • Failure means cessation of normal operation and breakdown.
Failure ? • How do cracks that lead to failure form? • How is fracture resistance quantified? How do the fracture resistances of the different material classes compare? • How do we estimate the stress to fracture? • How do loading rate, loading history, and temperature affect the failure behavior of materials?
Ship-cyclic loading from waves. Adapted from chapter-opening photograph, Chapter 9, Callister & Rethwisch 4e. (by Neil Boenzi, The New York Times.)
Computer chip-cyclic thermal loading.
Hip implant-cyclic loading from walking.
Adapted from Fig. 22.30(b), Callister 7e. (Fig. 22.30(b) is courtesy of National Semiconductor Corporation.)
Adapted from Fig. 22.26(b), Callister 7e.
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Fracture mechanisms • Ductile fracture – Accompanied by significant plastic deformation
• Brittle fracture – Little or no plastic deformation – Catastrophic
Ductile vs Brittle Failure Very Moderately Fracture
• Classification:
behavior:
Ductile
Ductile
Large
Moderate
Brittle
Adapted from Fig. 9.1, Callister & Rethwisch 4e.
% AR or %EL • Ductile fracture is usually more desirable than brittle fracture!
Ductile: Warning before fracture
Small Brittle: No warning
Pipe Failures
• Ductile failure:
-- one piece -- large deformation
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• Brittle failure: -- many pieces -- small deformations Figures from V.J. Colangelo and F.A. Heiser, Analysis of Metallurgical Failures (2nd ed.), Fig. 4.1(a) and (b), p. 66 John Wiley and Sons, Inc., 1987. Used with permission.
bedispl ayed.
Moderately Ductileshearing Failure void growth void
• Failure Stages: necking
σ
• Resulting fracture surfaces
nucleation
and coalescence
at surface
fracture
50 50mm mm
(steel) 100 mm particles serve as void nucleation sites.
From V.J. Colangelo and F.A. Heiser, Analysis of Metallurgical Failures (2nd ed.), Fig. 11.28, p. 294, John Wiley and Sons, Inc., 1987. (Orig. source: P. Thornton, J. Mater. Sci., Vol. 6, 1971, pp.
Fracture surface of tire cord wire loaded in tension. Courtesy of F. Roehrig, CC Technologies, Dublin, OH. Used with permission.
Moderately Ductile vs. Brittle Failure
cup-and-cone fracture
brittle fracture
Adapted from Fig. 9.3, Callister & Rethwisch 4e.
Brittle Failure Arrows indicate point at which failure originated
Adapted from Fig. 9.5(a), Callister & Rethwisch 4e.
• Transgranular Brittle 304 Fracture Surfaces (through grains) S. Steel
• Inter granular
(between grains)
(metal)
4 mm
316 S. Steel (metal)
Reprinted w/permission from "Metals Handbook", Reprinted w/ permission 9th ed, Fig. 633, p. 650. from "Metals Handbook", Copyright 1985, ASM 9th ed, Fig. 650, p. 357. International, Materials Copyright 1985, ASM Park, OH. (Micrograph by International, Materials J.R. Keiser and A.R. Park, OH. (Micrograph by Olsen, Oak Ridge D.R. Diercks, Argonne National Lab.) National Lab.)
Polypropylene (polymer)
Al Oxide (ceramic)
Reprinted w/ permission from R.W. Hertzberg, "Defor-mation and Fracture Mechanics of Engineering Materials", (4th ed.) Fig. 7.35(d), p. 303, John Wiley and Sons, Inc., 1996.
Reprinted w/ permission from "Failure Analysis of Brittle Materials", p. 78. Copyright 1990, The American Ceramic Society, Westerville, OH. (Micrograph by R.M. Gruver and H. Kirchner.)
1 mm (Orig. source: K. Friedrick, Fracture 1977, Vol.
160 mm
3 mm
•
Brittle Fracture of Ceramics Characteristic Fracture behavior in ceramics – Origin point – Initial region (mirror ) is flat and smooth – After reaches critical velocity crack branches • mist • hackle
Adapted from Figs. 9.14 & 9.15, Callister & Rethwisch 4e.
Crazing During Fracture of Thermoplastic Polymers Craze formation prior to cracking – during crazing, plastic deformation of spherulites – and formation of microvoids and fibrillar bridges aligned chains
fibrillar bridges
microvoids
crack
Adapted from Fig. 9.16, Callister & Rethwisch 4e.
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Design Strategy: Stay Above The DBTT! • Pre-WWII: The Titanic
Reprinted w/ permission from R.W. Hertzberg, "Deformation and Fracture Mechanics of Engineering Materials", (4th ed.) Fig. 7.1(a), p. 262, John Wiley and Sons, Inc., 1996. (Orig. source: Dr. Robert D. Ballard, The Discovery of the Titanic.)
• WWII: Liberty ships
Reprinted w/ permission from R.W. Hertzberg, "Deformation and Fracture Mechanics of Engineering Materials", (4th ed.) Fig. 7.1(b), p. 262, John Wiley and Sons, Inc., 1996. (Orig. source: Earl R. Parker, "Behavior of Engineering Structures", Nat. Acad. Sci., Nat. Res. Council, John Wiley and Sons, Inc., NY, 1957.)
• Problem: Steels were used having DBTT’s just below room temperature.
Fatigue failure crack origin
Adapted from Fig. 9.28, Callister & Rethwisch 4e. (Fig. 9.28 is from D.J. Wulpi, Understanding How Components Fail, American Society for Metals, Materials Park, OH, 1985.)
•
Creep Failure Failure: along grain boundaries. g.b. cavities applied stress
From V.J. Colangelo and F.A. Heiser, Analysis of Metallurgical Failures (2nd ed.), Fig. 4.32, p. 87, John Wiley and Sons, Inc., 1987. (Orig. source: Pergamon Press, Inc.) 44
14 Stages of Failure Analysis 1. Background data.
8. Metallography
2. Preliminary exam.
9. Failure mode.
3. Nondestructive tests.
10. Chemical analysis.
4. Mechanical tests.
11. Fracture mechanics
5. Sample selection.
12. Simulated tests.
6. Macroscopic exam.
13. Analysis & report.
7. Microscopic exam.
14. Recommendations.
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1. Collection of background data and samples. * Manufacturing history.
* Inventory of parts.
* Service history.
* Abnormal conditions.
* Photographic records.
* Sequence of fractures.
* Wreckage analysis.
* Sample selection.
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Fracture A preceded fracture B. 49 of 37
Fracture A preceded fractures B and C.
2. Preliminary Examinations. * Most important part of failure analysis. * Visual inspection of all parts. * Detailed photography of all parts. * Study of the fractures.
3. Nondestructive Inspections. * Magnetic particle inspection. * Liquid penetrant inspection. * Electromagnetic inspection. * Ultrasonic inspection. * Radiography. * Residual stress analysis.
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4. Mechanical Testing. * Hardness testing. * Tensile testing. * Shear testing. * Impact testing. * Fatigue testing. * Fracture mechanics testing.
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5. Selection and Preservation of Fracture Surfaces. * How? Very Carefully!!! * Prevent chemical damage to samples. * Prevent mechanical damage to samples. * Prevent thermal damage to samples. * Careful cleaning: Least destructive technique first.
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6. Macroscopic Examinations * Use low power stereo-microscopes. * Determine Origin of failure. * Determine direction of crack growth: Chevron patterns, beach marks etc... * Determine ductile or brittle fracture. * Locate other cracks.
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7. Microscopic Examinations * Light microscopes: shallow depth of field. * Transmission Electron Microscopes (TEM): sample preparation problems. * Scanning Electron Microscopes ( SEM): conductivity problems. coating and replication techniques.
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Dimples typical of a ductile overload fracture by micro-void coalescence mechanism 60 of 37
Striations typical of fatigue failures 61 of 37
Cleavage fracture typical of brittle overload fracture 62 of 37
Rock candy structure typical of intergranular fracture
8. Metallographic Examination * Class of Material: Cast or Wrought * General Microstructure. * Crack Path: Transgranular and/or Intergranular * Heat Treatment Problems: Decarburization, Alpha-Case, etc….
Lap defect in forging 65 of 37
Intergranular crack in copper tube 66 of 37
Crack branching in martensitic steel 67 of 37
9. Failure Modes * Ductile: Plastic Deformation Equiaxed or Shear Dimples Dull, Gray and usually Transgranular. * Brittle: No Macroscopic Plastic Deformation Cleavage, Intergranular or Striations Difficult to diagnose.
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Modes of Fracture * Monotonic Overload Brittle Ductile * Sub-Critical Crack Growth Static Loads Dynamic Loads
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Mechanisms of Fracture * Overload - Fracture with application of load. Ductile or Brittle * Crack Growth - Under Load Over Time. Fatigue Stress Corrosion Cracking Hydrogen Embrittlement Creep
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Sub-Critical Crack Growth under Dynamic Loads * Fatigue * Corrosion Fatigue * Thermal Fatigue
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Sub-Critical Crack Growth under Static Loads * Stress Corrosion Cracking * Hydrogen Embrittlement * Liquid Metal Embrittlement * Creep Rupture
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Some Common Fractographic Features Brittle Overload
Cleavage
Ductile Overload
Dimples
Stress Corrosion Cracking
Intergranular
Hydrogen Embrittlement
Intergranular
Creep Rupture
Intergranular
Fatigue
Striations
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10. Chemical Analysis * Optical Emission Spectroscopy * Wet Chemical Analysis * X-ray, Electron & Neutron Diffraction * X-ray Fluorescence * Infrared & Ultraviolet Spectroscopy * Energy and Wavelength Dispersive X-ray Analysis. * Surface Analysis Techniques 74 of 37
11. Fracture Mechanics * Fracture Toughness Testing. * Strain Rate Sensitivity. * Notch Sensitivity. * Triaxiality
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12. Simulated-Service Testing * Of Limited Value. * Simulated Corrosion Tests. * Deciding between several possible mechanisms. * Errors by Changing Severity of Conditions.
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13. Conclusions and Report * Be Clear & Concise. * Do not Express Opinions Without Facts. * Consider the Client. * Site the Sources of External Data. * Check list is a good idea.
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14. Recommendations * Should lead to prevention of future failures. * Should lead to product improvements. * Do not rush to change material or process specifications without complete analysis of possible interaction with other parts of the system.
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General principles of root cause analysis •
The primary aim of RCA is to identify the factors that resulted in the nature, the magnitude, the location, and the timing of the harmful outcomes (consequences) of one or more past events in order to identify what behaviors, actions, inactions, or conditions need to be changed to prevent recurrence of similar harmful outcomes and to identify the lessons to be learned to promote the achievement of better consequences. ("Success" is defined as the near-certain prevention of recurrence.)
•
To be effective, RCA must be performed systematically, usually as part of an investigation, with conclusions and root causes identified backed up by documented evidence. Usually a team effort is required.
•
There may be more than one root cause for an event or a problem, the difficult part is demonstrating the persistence and sustaining the effort required to develop them.
•
The purpose of identifying all solutions to a problem is to prevent recurrence at lowest cost in the simplest way. If there are alternatives that are equally effective, then the simplest or lowest cost approach is preferred.
•
Root causes identified depend on the way in which the problem or event is defined. Effective problem statements and event descriptions (as failures, for example) are helpful, or even required.
•
To be effective, the analysis should establish a sequence of events or timeline to understand the relationships between contributory (causal) factors, root cause(s) and the defined problem or event to prevent in the future.
•
Root cause analysis can help to transform a reactive culture (that reacts to problems) into a forward-looking culture that solves problems before they occur or escalate. More importantly, it reduces the frequency of problems occurring over time within the environment where the RCA process is used.
•
RCA is a threat to many cultures and environments. Threats to cultures often meet with resistance. There may be other forms of management support required to achieve RCA effectiveness and success. For example, a "non-punitory" policy towards problem identifiers may be required.
• The 6 Ms (used in manufacturing) • Machine (technology) • Method (process) • Material (Includes Raw Material, Consumables and Information.) • Man Power (physical work)/Mind Power (brain work): Kaizens, Suggestions • Measurement (Inspection) • Milieu/Mother Nature (Environment)
• • • • • • • • •
The 8 Ps (used in service industry) Product=Service Price Place Promotion/Entertainment People(key person) Process Physical Evidence Productivity & Quality
• Evaluating root cause analysis •
Root Cause Analysis Reports, like other 'deliverables' can vary in quality. Each stakeholder can have their own qualitative and quantitative acceptance criteria. There are some general possibilities for evaluating root cause analysis outputs.
•
First: Is it readable? If it is readable it will be grammatically correct, the sentences will make sense, it will be free on internal inconsistencies, terms will be defined, it will contain appropriate graphics, and the like.
•
Second: Does it contain a complete set of all of the causal relationships? If it did contain a "complete set of all of the causal relationships" one could (at least):
•
1. Trace the causal relationships from the harmful outcomes to the deepest conditions, behaviors, actions, and inactions.
•
2. Show that the important attributes of the harmful outcomes were completely explained by the deepest conditions, behaviors, actions, and inactions.
• The 5 Ss (used in service industry) • Surroundings • Suppliers • Systems • Skills • Safety
Common cause analysis (CCA) Common modes analysis (CMA) •
Common caus Common causee analy analysis sis (CCA (CCA)) common common mode modess analy analysis sis (CM (CMA) A) are are evolv evolving ing engineering techniques for complex technical systems to determine if common root causes in hardware, software or highly integrated systems interaction may contribute to human error or improper operation of a system. Systems are analyzed for root causes and causal factors to determine probability of failure modes, fault modes, or common mode software faults due to escaped requirements. Also ensuring complete testing and verification are methods used for ensuring complex systems are designed with no common causes that cause severe hazards. Common cause analysis are sometimes required as part of the safety engineering tasks for theme parks, commercial/military aircraft, spacecraft, complex control systems, large electrical utility grids, nuclear power plants, automated industrial controls, controls, medical devices devices or other safety safety safetycritical systems with complex functionality.
•
A major major issu issuee with with comm common on caus causee analy analysis sis is that that it ofte often n depen depends ds on on previously completed completed weak, ineffective, ineffective, and erroneous root root cause analyses on individual events.
• What is causal mapping? • A caus causal al map map is is a type type of of conc concep eptt map map in in whic which h the the link linkss between nodes represent causality or influence. Causal mapping is the process of creating a causal map. When done by an individual to clarify their own thinking, it is referred to as "cognitive mapping". It may be b e called "oval mapping" when done by a group, named after the small oval pieces of paper containing each idea.
Fundamentals of Nondestructive Testing
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Benefits of Nondestructive Testing • Improvement in Product Quality • Improvement of Product Reliability • Increase in Manufacturing Efficiency • Reduction in Scrap Rate • Reduction in Manufacturing Cost
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A bit of Philosophy • A part is a collection of defects • An acceptable part is one with irrelevant defects • A scrap has defects that are critical to the application
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Basic Principle of NDT • A technique to measure the critical properties of a part without affecting its performance. • Every basic principle of physics can be used as probe for NDT
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Energies used for NDT • Electromagnetic Energies • Dynamic or Sonic Energies
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Electromagnetic Energies • Electrical Energies • Magnetic Energies • Optical Energies • Infra-Red Energies • Ultra-Violet Energies • X-Ray Energies • Gamma Ray Energies 96 of 20
Dynamic or Sonic Energies • Audible Sound Energies • Ultrasonic Energies • Thermal Energies
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Basic Property of Waves
• Velocity = Frequency * Wavelength
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Typical NDT System • Input Transducer • Sample • Output Transducer • Processor and Display System • Decision
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Properties Tested in NDT • Geometric Properties • Mechanical Properties • Thermal Properties • Electrical and Magnetic Properties • Physical Properties
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Geometric Properties • Dimensions • Porosity • Discontinuities • Cracks
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Mechanical Properties • Stress • Strain • Hardness • Modulus of Elasticity
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Thermal Properties • Thermal Conductivity • Thermal Expansion • Thermal Stress • Thermoelectric Properties (Thermocouples)
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Electrical and Magnetic Properties • Electrical Resistivity • Magnetic Permeability • Eddy Current
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Physical Properties • Density • Composition • Grain Size • Grain Orientation • Index of Refraction • Coefficient of Friction 105 of 20
Transducers (Heart of the System) • Luminous Energy Transducers (eyes + help)
• Photographic Films • Photoelectric Transducers • Penetrating Radiation Transducers (α, β, γ, x, neutron…….Geiger)
• Magneto-electric Transducers Lens’ Law
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Transducers (Heart of the System) continued
• Thermoelectric Transducers thermocouples
• Liquid Crystals change in color with temperature, cholesteric
• Potentiometers displacement, velocity, acceleration, liquid level
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Transducers (Heart of the System) continued
• Photoconductive Cells semiconductors
• Resistance Wire Strain Gauge Ohm’s Law and Hooke’s Law
• Capacitance Transducers C = 0.225 K*A/d
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Transducers (Heart of the System) continued
• Variable inductance transducers • Variable reluctance transducers • Magneto striction transducers • Variable transformer transducers • Differential transformer transducers
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Display Systems • Galvanometers • Electronic Voltmeters • Oscilloscopes • Digital Indicators • Chart Recorders
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