Journal Published Online: 01 September 1976
Volume 4, Issue 5

Local Strain Behavior Prior to Fatigue Crack Nucleation



The local strain behavior of cold-rolled HSLA (niobium) steel was investigated in the vicinity of a circular hole for first loading, first unloading, and in the unloaded state after 50 000 and 82 000 cycles by determining εθ as a function of distance from an 0.02-in. (508-μm) circular notch by direct comparison of optical micrographs at approximately ×1000. This technique allows changes in length to be determined to ±0.15 μm which, over a 100-μm gage length, corresponds to an engineering strain resolution of ±0.15%. The resolution is sufficiently high to allow local strain distributions, as calculated from elasticity and plasticity theory, to be compared with the experimental data. A pseudo-plastic solution was developed from the plane stress solution by considering A. E. Green's three-dimensional solution and Neuber's relation between stress and strain concentrations. The monotonic deformation law obeyed by cold-rolled niobium steel was experimentally determined and combined with the pseudo-plasticity result to obtain a quantitative prediction of the local strain behavior on first loading. Experimentally obtained strain behaviors for first loading provide good agreement with the pseudo-plasticity result for each of the strain levels investigated. The strain distribution measured after the first unloading demonstrated that a compressive residual stress is generated during the first cycle. The strain distribution developed by repeated tension loading is also presented and discussed.

Author Information

Quesnel, DJ
Materials Research Center, The Technological Institute, Northwestern University, Evanston, Ill.
Meshii, M
Materials Research Center, The Technological Institute, Northwestern University, Evanston, Ill.
Pages: 8
Price: $25.00
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Stock #: JTE10519J
ISSN: 0090-3973
DOI: 10.1520/JTE10519J