Forensic Engineering

Colin R. Gagg, M.Sc., holds an honours degree in engineering technology and a master’s degree in management and technology of manufacturing. He is a chartered engineer and professional member of the Institute of Mechanical Engineering. His practical experience includes 2 years at the Structures Laboratories of Imperial College of Science, Technology and Medicine and 4 years at the Engineering Department of the University of Toronto. He currently holds the post of research projects officer at The Open University and, for the past 10 years, he has been a member of the Forensic Engineering and Materials Group. Mr. Gagg’s prior research interest focused on advanced processing techniques such as Ospray processing, thixo-casting and melt spinning, from which a long-standing avenue of interest developed, engineering in medicine. His current research interests lie in two distinct areas: solder studies and forensic engineering. Solder assessment focuses on creep, creep rupture and monotonic characteristics of lead and lead-free solder systems. A principal aim of the work is to ensure that stress analysis and modeling for life prediction employ appropriate and reliable data. In addition to research publications, results generated have been fed directly into mainstream course production and into a specifically tailored course for the Taiwanese market. The second channel of research pursuit is forensic engineering, an area of research that is fed directly into the teaching stream as case study input. Mr. Gagg’s academic interests center on forensic engineering, where he is a contributing author for a postgraduate forensic engineering course. He maintains his enthusiasm for teaching the subject by tutoring 20 to 30 postgraduate students per year and serving as a member of the examination board for the course. He is also an examiner for M.Sc. dissertations in the manufacturing program at The Open University. Mr. Gagg has written 24 papers for journals and international conferences and has produced more than 100 technical reports dealing with failure of metallic products. His consulting activities include resolving production difficulties and component failure issues. He acts as a single joint expert in product failure, personal injury disputes and failure during surgical procedures. He has appeared as an expert witness in court proceedings related to personal and fatal injury.

I Preface

II Contents

III Acknowledgements

Chapter 1

Failure analysis or forensic engineering?

1.0 Synopsis

1.1 Historic failure analysis

1.2 Conventional failure analysis

1.3 Product defects

1.4 Causal Analysis

1.4.1 Computer aided causal analysis

1.4.2 Case Study: wear markings as ‘fingerprints’

1.5 Design calculations and modelling

1.5.1 Miner’s Law for life time cumulative damage prediction

1.6 Summation of conventional failure analysis

1.7 Forensic engineering

1.7.1 Case Study: Collapse of the Rana Plaza factory

1.8 Range of competence

1.8.1 A generic failure analysis or a forensic investigation?

1.9 Forensic approach to failure

1.9.1 Reverse engineering

1.9.2 Associated costs of forensic investigation

1.10 Historic failures

1.10.1 Computer-aided technology limitations

1.11 Analytical techniques

1.12 Dissemination of knowledge and experience

1.12.1 Popular books

1.12.2 Event reporting

1.12.3 Text books

1.12.4 Forensic engineering teaching

1.13 Case study themes

1.13.1 The Sayano-Shushenskaya power station accident of 2009

1.14 Research enriched teaching

1.15 Concluding remarks

1.16 References

Chapter 2

Initial aspects of forensic failure investigation








Introduction



2.1 Three essential ‘abstract’ assets for the investigator

2.1.1 Assessing the situation

2.1.2 Initial visual observation as a fact-finding exercise

2.1.3 The failure scenario

2.1.4 Summary of understated investigative skills

2.2 Visual observation

2.2.1 Case study: visual comparison

2.2.2 Case study: common (engineering) sense

2.3 Forensic photography

2.4 Record keeping

2.5 Witness evidence

2.6 Documentary evidence

2.6.1 Case study: Fatal aircraft crash

2.7 Product and material standards

2.7.1 Case study: Step ladder accident

2.8 Patents

2.9 Surviving remains (detritus)

2.9.1 Gathering of evidence and the ‘Chain of Evidence’

2.10 Product liability

2.10.1 Case study: Premature failure of a presentation cake knife

2.11 The ‘Corporate’ environment

2.11.1 Case study: Bird-strike testing of aircraft engines

2.12 Abuse or misuse

2.12.1 Case study: abuse

2.12.2 Case study: miss-use

2.13 References

Chapter 3

A framework or methodology for forensic investigation








Introduction



3.1 Background to failure analysis methodology

3.2 An investigative path followed by the writer

3.2.1 Intuition (reasoning) and a ‘structured’ investigation framework

3.2.2 Individual stages of investigation

3.2.3 The field investigation kit

3.2.4 Initial approach to failure investigation

3.2.5 Background data collection

3.2.6 Sifting the evidence

3.2.6.1 Case study: Failure of a new design of horse bit

3.2.7 Records

3.2.8 Single items of evidence

3.3 The failure detective

3.3.1 Transformation stresses

3.3.2 Establishing a load transfer path to determine the ‘weakest link’

3.3.3 Case study: The weakest link principle

3.3.4 Case study: Failure of a backhoe dipper arm

3.4 Computer-aided technologies

3.4.1 Case study: failure of an open-ended spanner

3.5 The forensic engineering Report

3.6 Concluding remarks

3.7 References

Chapter 4

Analytical methods

4.0 Introduction to a typical forensic engineering ‘toolbox’

4.1 Non-destructive testing (NDT)

4.1.1 Case study: Failure of a power transmission shaft

4.2 Crack detection and the human eye

4.2.2 Surface appearance of common cracks

4.2.3 Other crack detection techniques

4.3 Hardness testing

4.3.1 Case study: Pin-punch splintering

4.3.2 Relationship between hardness and tensile strength

4.4 Indirect stress/strain analysis

4.4.1 Brittle lacquer technique

4.4.2 Case study: Cycle accident

4.4.3 Photo-elastic stress measurement

4.5 Conventional (contact) radiography

4.5.1 Case study: Failure of a vehicle motherboard

4.5.2 Case study: Heavy goods vehicle fire

4.6 Summary of NDT inspection

4.7 Forensic optical microscopy

4.7.1 Macroscopic examination

4.7.2 Examination under magnification: optical microscopy

4.7.3 Reflected light microscopy

4.7.4 Stereo microscopy

4.8 Metallography

4.9 Scanning electron microscopy

4.9.1 The environmental scanning electron microscope (ESEM)

4.9.2 Case study: Hit and run accident

4.10 Optical versus scanning microscopy

4.10.1 Case study: Printed circuit board (PCB) failure

4.10.2 Case study: Prototype PCB failure

4.11 Energy dispersive X-Ray analysis (EDAX)

4.12 Destructive testing methods

4.12.1 Tensile testing

4.12.2 Flexure or bending

4.12.3 Case study: Cracking of aluminium pressings

4.12.4 Torsion testing

4.12.5 Shear testing

4.12.6 Izod or Charpy impact test

4.12.7 Differential scanning calorimetry (DSC)

4.12.8 Case study: Electronic component registration difficulties

4.13 Novel tools and techniques

4.13.1 The contour method

4.13.2 Neutron diffraction

4.13.3 Nano test systems

4.13.4 Flash thermography

4.13.5 Thermographic Signal Reconstruction (TSR)

4.13.6 Electromagnetically induced acoustic emission (EMIAE)

4.13.7 Pulsed eddy current (PEC)

4.13.8 Microwave technology

4.14 References

Chapter 5

Sources of stress and service failure mechanisms

5.0 Introduction

5.1 Fundamental mechanical background

5.1.1 Stresses and strains

5.1.2 Ductile and brittle transition

5.1.3 Fracture toughness and linear elastic fracture mechanics (LEFM)

5.1.4 Limitations of a fracture mechanics approach

5.1.5 Stress Concentration (Kt)

5.1.6 Case study: stress concentration – cement mill power input shaft

5.1.7 Residual stresses

5.1.8 Summary of fundamental mechanical background

5.2 Service failure mechanism

5.2.1 Case study: Hubble space telescope mirror and the Team Philips catamaran

5.3 Mechanical Failure

5.4 Hydrogen Embrittlement

5.4.1 Sources of hydrogen

5.4.2 Hydrogen induced brittle failure

5.5 Impact

5.6 Bending

5.7 Torsion

5.8 Creep

5.9 Fatigue

5.9.1 Minimizing susceptibility to onset of fatigue failure

5.9.2 Case study: Failure of a power transmission gear wheel

5.9.3 Fatigue related failure modes

5.9.4 Approximating the history of a fatigue failure

5.9.5 Summation of fatigue as a service failure mechanism

5.10 Wear

5.11 Corrosion

5.11.1 Case study: The Statue of Liberty

5.11.2 Stress Corrosion Cracking (SCC)

5.11.3 Case study: SCC of brass impeller blades

5.12 Manufacturing fabrication as a source of stress

5.12.1 Casting

5.12.2 Casting Failure Analysis

5.12.3 Case study: Extrusion press

5.12.4 Welding

5.12.5 Quench cracking

5.12.6 Tempering and toughening

5.13 References

Chapter 6

Fracture morphology and topography

6.0 Introduction

6.1 What is meant by the term ‘failure’?

6.2 Fracture and fracture path morphology

6.3 Ductile or brittle failure

6.4 Brittle overload (fast) fracture features

6.5 Ductile-brittle transition

6.6 Fracture surface features

6.7 Fatigue fracture

6.7.1 Low and high Cycle Fatigue

6.7.2 Chevron and striation combination

6.7.3 Case study: Internal combustion engine crank-shaft failure

6.7.4 Splined shafting

6.7.5 Ratchet marks

6.7.6 Thermal Fatigue

6.8 Additional modes of progressive failure

6.8.1 Corrosion

6.8.2 Stress Corrosion Cracking (SCC)

6.8.3 Crevice corrosion

6.8.4 Environmentally assisted cracking (EAC)

6.8.5 Wear

6.8.6 Wear of rolling contact elements

6.8.7 Case study: an agricultural bearing failure

6.9 Summary

6.10 References

Chapter 7

The engineer in the courtroom








Introduction
7.1 The role of the ‘expert’

7.2 The expert report

7.3 Pre-trial meeting of experts

7.4 Alternative dispute resolution (ADR)

7.5 The single joint expert (SJE)

7.6 The role of Case Law

7.7 The engineer in the Court room

7.8 In summary

7.9 References

Chapter 8

The Art of case study analysis as a teaching tool




Introduction



8.1 Historic use of case study analysis

8.2 Air accidents, mortality statistics and failure case studies

8.3 What constitutes a ‘case study’?

8.3.1 Case study: North-sea ferry engine bolts

8.3.2 Case study: Hot-spot boiling erosion

8.4 Writing a relevant case study

8.4.1 Case study: Crankpin axle from a bicycle

8.5 Examples of case study themes.

8.5.1 Case study: Collapse of terminal 2E Charles de Gaulle International Airport.

8.5.2 Marine disaster case study examples

8.5.3 Case study: loss of the first British off-shore oil drilling platform

8.5.4 Case study: loss of the Alexander Kielland semi-submersible oil drilling platform

8.5.5 Colliery disaster case study examples








Engineering in medicine
8.6.1 Case study: the DePuy Ultamet Metal-on-Metal (MOM) Articulation hip replacement




Concluding remarks



References



Chapter 9

Failure due to manufacturing faults - case studies

9.0 Introduction

9.1 Traumatic failure

9.2 Femoral stem failure of a total hip prosthesis

9.3 Failure of Freight Containers

9.4 Splintering Failure of a Pin punch

9.5 Failure of a vehicle fuel delivery rail

9.6 Failure of a Presentation Cake Knife

9.7 Failure of an Aerobic Mini-Stepper

9.8 Failure of oil pump gearing

9.9 Replacement Gears for HGV (heavy truck) Gearbox

9.10 Vehicle engine radiator cooling fan

Chapter 10

Automotive component failure: road traffic incidents and accidents – case studies

10.0 Introduction

10.1 Motor Vehicle Accidents as a Result of Steering Shaft Failure

10.1.1 Fatal Crash of a Small Family Saloon Car

10.1.2 Heavy Goods Vehicle (HGV) Accident

10.1.3 Steering Shaft Failure on a Vintage Car

10.1.4 The ‘Boy Racer’

10.2 Wheel Detachments

10.2.1 Wheel Nut Loosening and Stud Fatigue

10.2.2 Wheel Dish Cracking

10.2.3 Stub Axle Failure

10.3 Brake Pipe Failures

10.3.1 Brake Failure by Fatigue

10.3.2 Failure of a Polymeric Air-Brake Hose

10.4 Gearbox Synchronizer Ring failure

10.5 Fatal Tow Hitch accident

Chapter 11

Fraudulent insurance claims - Case studies

11.0 Introduction

11.1 Perforated central heating radiator

11.2 Perforated Oil Filter

11.3 Major Engine Damage, Allegedly Due to Loss of Oil

11.3.1 A probable motive for inflicting the damage observed

11.4 Engine hairline cracking as a result of an alleged impact

11.5 Agricultural tractor engine damage

11.6 Con-Rod failure

11.7 Piston Failure on a Racing Car

Chapter 12

Criminal Case studies

12.0 Introduction

12.1 Counterfeit Coins

12.1.1 The Use of Currency as a Feedstock Material for counterfeiting

12.1.2 The Base Metal One Pound Coin

12.1.3 The ‘Struck’ One Pound Coin

12.1.4 Footnote to Counterfeiting

12.2 Staged or Fraudulent Road Traffic Accidents Within the UK

12.2.1 Deliberate ‘damage’

12.2.2 Car hire insurance fraud

12.2.3 Staged ‘accidents’

11.3 Shotgun Pellets

12.4 Metal Theft

12.4.1 An Additional Metal Theft Case

12.5 Chain from Murder

12.6 Coin Box Busters

12.7 Re-melting Beer Barrels