ME 371 Study Guide - Final Guide: Fracture, Stress Concentration, Free Surface

• School: University of Illinois
• Department: Mechanical Engineering
• Course: ME 371
• Professor: A Dunn

Document Summary

Fatigue failure is a type of component failure that is distinct from static yielding. The overall mechanism of a fatigue failure is the initiation and propagation of a small crack over time due to cyclic loading. Once the crack is deep enough, the stress concentrations that occur are too high, and a brittle fracture results in catastrophic failure of the component. The unique feature of fatigue that made it elusive to early engineers is that it occurs at stresses below which the static loading predicts yielding. High cycle fatigue is especially problematic in rotating components and connected components due to the inherent cyclic loading they experience. Consider a ductile metal under a repeated tensile load (figure 1) that cycles between zero and a positive value, t. Even though there is no bulk yielding, the strain is relieved at the microscale by slip dislocations within grains of a ductile metal.