• Reduce magnitude of fluctuating stresses and of stress concentrations
• Beware ‘unexpected’ bending stresses
• Realistic testing (measure service load history)
• Standard cumulative damage predictions (Miner’s Law) inaccurate
• In general hardening the material raises the threshold (see above)
• Surface hardening techniques
o Carburising
o Nitriding
o Shot peening
• Introduce residual compressive stresses
• Changing the material
• Solutions difficult because of the lack of predictability
• ‘Scatter’ in lab tests great
• In service, load histories may vary dramatically:
1. Motor vehicles
2. Cranes
3. Pressure vessels
• Even greater ‘scatter’
• Non-destructive testing:
1. Oil and chalk (dye penetrants)
2. Magnetic particle
3. Ultrasonics
4. Radiography
• Interpretation?
1. Note distinction: is there a crack? How deep is it?
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