Effect of Cold-Forming on the Strain Controlled Fatigue Resistance of Automotive Steels 920666

Bar stock of two steels -- a micro-alloyed grade and 1541, a C-Mn forging grade -- in both the as-rolled and several cold-drawn conditions were fatigue tested under strain-control. The present results are compared to previous results from strain-controlled fatigue tests on sheet, plate, shape, and bar stock by Bethlehem and others on a wide range of grades in various conditions -- as-rolled, cold-worked, aged, heat-treated, etc. The fatigue strength at one-million cycles is plotted versus the monotonic or engineering tensile strength for present tests as well as previous and published tests on a wide range of steel products. Generally, it is implied that the scatter in such a plot is experimental variability. A superior correlation is shown herein when the cyclic true stress-strain parameters developed from strain-controlled fatigue tests are used. Introduction of the cyclic parameters tightens the correlation between static and cyclic strength because the effects of cyclic hardening or softening are now included.
Bar stock of two steel grades - MAS (micro-alloyed) and 1541 (C-Mn forging grade) -- in both the as-rolled and several cold-drawn conditions were fatigue-tested under strain-control. Such testing was selected because: (1) it assesses the notch-fatigue resistance of a material, and (2) the results can be used as input to a widely used state-of-the-art life assessment model -- the Local Strain or Neuber Model.


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