Three Stages of Fatigue Failure Identifying （三个阶段的疲劳故障识别）.pdf

Over the Next Several Days Some History What is Fatigue? Rail car axles Types of Fatigue Loading The all-important microcrack Empirical Data Role of stress concentrations Estimating Endurance/Fatigue Strength Strategies for Analysis Comet airplanes Uniaxial Fully Reversed Uniaxial Fluctuating Multiaxial Crack Growth Three Stages of Fatigue Failure Identifying Fatigue Fractures Crack Initiation Crack Propagation beachmarks oscillating stress… crack grows, stops growing, grows, stops growing… with crack growth due to tensile stresses Fracture sudden, brittle-like failure Three Approaches Low vs. High Cycle 103 cycles, high cycle fatigue stress-based, for high-cycle fatigue, aims to Stress-Life prevent crack initiation car crank shaft – ~2.5 E8 Rev/105 miles manufacturing equipment @ 100 rpm – 1.25 E8 Rev/year Strain-Life useful when yielding begins (i.e., during 3 crack initiation), for low-cycle fatigue 10 cycles, low cycle fatigue LEFM (Fracture best model of crack propagation, for low- Mechanics)