A “Toolbox” for Forensic Engineers

3 Establishing the Load Transfer Path 61
3.1 Loads, Forces and Design 61
3.2 Abnormal Externally Applied Force — Stepladder 62
3.3 Establishing the Load Transfer Path 66
3.4 Effect of Faults and Weaknesses 73
3.5 Cause of Failure of Axle Bracket in Racing
Motorcycle Sidecar 76
4 A “Toolbox” for Forensic Engineers 85
4.1 Introduction 85
4.2 An Initial Approach to a Failure 86
4.2.1 Significance of Initial Observations 87
4.3 Assessing the Situation 89
4.4 Inside the Toolbox 90
4.4.1 Photography and Sample Handling 91
4.4.2 Product and Material Standards 92
4.4.3 Macroscopic Examination
4.4.4 Examination under Magnification: Optical
93
Microscopic Inspection 94
4.4.5 Metallographic Sectioning 94
4.4.6 Scanning Electron Microscopy (SEM) 100
4.5 Mechanical Testing 105
4.5.1 Tensile Testing 105
4.5.2 Hardness Testing 107
4.5.3 Moh’s Hardness Test 107
4.5.4 Vickers Hardness Test 107
4.5.5 Brinell Hardness Test 108
4.5.6 Rockwell Hardness Test 109
4.5.7 Tensile Strength and Hv 109
4.5.8 Bend Tests 111
4.5.9 Torsion Testing 113
4.6 Indirect Strain Measurement 115
4.6.1 Brittle Lacquer 115
4.6.2 Crack Detection Methods 117
4.6.3 Other Crack Detection Techniques 118
4.7 Chemical and Thermal Analysis 121
4.7.1 Differential Scanning Calorimetry (DSC) 121
4.7.2 Infrared Spectroscopy 124
4.7.3 Chromatography 126
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