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 the function of distance from an 0.02-in. (508-micro m) circular notch by direct comparison of optical micrographs at approximately x1000. The technique allows changes in length to be determined to plus or minus 0.15 micro m which, over a 100-micro m gage length, corresponds to an engineering strain resolution of plus or minus 0.15%. The resolution is sufficiently high to allow local strain distribtutions, 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.

• Corporate Authors:

  American Society for Testing and Materials (ASTM)

  100 Barr Harbor Drive, P.O. Box C700
  West Conshohocken, PA  United States  19428-2957
• Authors:
  • Quesnel, D J
  • Meshii, M
• Publication Date: 1976-9

Media Info

• Features: Figures; References; Tables;
• Pagination: p. 319-326
• Serial:
  • ASTM Journal of Testing and Evaluation
  • Volume: 4
  • Issue Number: 5
  • Publisher: Federal Highway Administration

Subject/Index Terms

• TRT Terms: Cracking; Fatigue (Mechanics); Steel; Strain measurement; Stresses
• Uncontrolled Terms: Crack propagation; Stress concentration
• Subject Areas: Geotechnology; Highways; Materials; Research;

Filing Info

• Accession Number: 00142196
• Record Type: Publication
• Report/Paper Numbers: Conf Paper
• Files: TRIS
• Created Date: Dec 15 1976 12:00AM