His co-author, Paris, is senior professor of mechanics at Washington University in St. Louis, MO. Known for his contributions to fracture mechanics, Paris has received awards from the American Institute of Aeronautics and Astronautics and the American Society for Testing and Materials.
Besides examples, the authors also provide excellent guidance on the intricate details of ultrasonic fatigue testing. In addition, their many useful facts on fatigue phenomena include:
• For a large number of alloys, fatigue crack initiation may occur beyond 107 cycles, and the fatigue strength may decrease by 50-200 MPa between 106 and 109 cycles.
• When fatigue occurs beyond 107 cycles in steels, the origin of the fracture is usually not at the surface but in the interior of the specimen.
• Low cycle fatigue cracks are the result of local plastic flow around surface discontinuities, whereas gigacycle fatigue cracks initiate from the interior at inclusions or microstructural defects.
• When fatigue failure occurs at 104 cycles, there are multiple crack origins at the surface; at 106 cycles, there is a single origin at the surface; and at 109 cycles, cracks initiate in the interior of the specimen.
• Equations are given that quantify the effect of nonmetallic inclusions on fatigue strength.
• Corrections are given to account for the different stress states in rotating-bending and tension-compression fatigue tests. After the correction, fatigue data give the same S-N curves regardless of the different loading methods.
• Low temperature causes a shift of the fatigue crack growth curves to higher stress intensity. This is explained by increased tensile properties.
• Gigacycle fatigue tests show the fatigue crack growth threshold ΔKth determined by conventional fatigue testing is reliable for engineering design.
