AN INTERPRETATION OF LOWER YIELD POINT PLASTIC FLOW IN THE DYNAMIC TESTING OF MILD STEEL

Evaluation of the role of rapid plastic flow in the fracture process necessitates some measure of elastic and plastic strength which will be suitable for high strain rates. For a limit to the static elastic strength of mild steel, the lower yield stress is a generally accepted criterion. Its use for the dynamic test, although common in the literature, is more difficult to justify because here neither the lower yield strain along the specimen, nor the lower yield stress, are even approximately constant. The variability of both is a consequence of the fact that in the high strain rate test, a "steady state" form of the Luders strain front is not obtained, nor is it then contained within the length of the specimen. For this paper, strain distribution is measured after stopping a dynamic machine during the lower yield. From head displacement and load records obtained during the test and also from plastic flow rate sensitivity measured in other high-speed tests on the same material, the strain distribution is predicted. The predicted strain distribution behind the Luders band front is found in good agreement with that measured. When the velocity of the band front is corrected for its diminution owing to continued flow behind the front it is related to driving stress with a sensitivity corresponding to that for the upper yield point--or the delayed yield.

  • Corporate Authors:

    Naval Research Laboratory

    4555 Overlook Avenue, SW
    Washington, DC  United States  20375-5320

    Ship Structure Committee

    National Academy of Science, 2101 Constitution Avenue, NW
    Washington, DC  United States  20418
  • Authors:
    • Krafft, J M
  • Publication Date: 1961-6-26

Media Info

  • Features: References;
  • Pagination: 19 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00331911
  • Record Type: Publication
  • Source Agency: Ship Structure Committee
  • Report/Paper Numbers: SSC-123 Prog Rpt.
  • Contract Numbers: NObs-72046
  • Files: TRIS
  • Created Date: May 21 1981 12:00AM