SEDL / STP / STP811-EB / STP30552S

Characterization of Microplasticity Developed During Fatigue

Field, JL
Graduate Research Assistant, Graduate Research Assistant, and Assistant Professor of Engineering Mechanics, The Pennsylvania State University, University Park, PA

Behnaz, F
Graduate Research Assistant, Graduate Research Assistant, and Assistant Professor of Engineering Mechanics, The Pennsylvania State University, University Park, PA

Pangborn, RN
Graduate Research Assistant, Graduate Research Assistant, and Assistant Professor of Engineering Mechanics, The Pennsylvania State University, University Park, PA

Pages: 24    Published: Jan 1983

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Abstract

X-ray line-broadening studies and stress analyses were employed to characterize quantitatively the fatigue-induced lattice deformation and change in the residual stress prior to crack initiation. Measurements were made after surface layer removals to evaluate surface and subsurface microplasticity, and X-rays with different penetration capability were used in order to facilitate a similar comparison nondestructively. At high maximum stress amplitudes imposed by bending fatigue, rapid distortion of the surface layer followed by an extended period of recovery contrasted with a more steady accumulation of lattice imperfection in the subsurface region. Concomitant modification of residual stresses during the cycling included the development of a maximum compressive stress early in the life and a transition to tension during the intermediate life fractions, reaching a peak tensile stress when the line breadths for the near-surface and subsurface converged. The differentiation in surface and subsurface line broadening during cycling at high and low maximum stress levels was accredited to the operation of different crack initiation mechanisms, and the potential for postponing crack initiation through surface layer removal was investigated.