The Changes in The Compressive and Tensile Yield Strengths During Uniaxial Cyclic Loading

80 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1983.Many of the multiaxial unified-creep plasticity theories which have been proposed as a means to improve design at elevated temperatures have suffered from the drawback that the manner in which the state variables change is difficult to measure. A unified creep-plasticity theory for uniaxial loading which uses the yield strengths in tension, Y(,1), and compression, Y(,2), as the state variables is investigated as the means of improving the formulation of such theories. The yield strengths are easily measured and can be readily transformed to the state variables commonly used in the multiaxial theories.The yield strengths were measured during a completely reversed cyclic strain amplitude history for 304 stainless steel at 23(DEGREES)C and 600(DEGREES)C, and for Inconel 751 at 788(DEGREES)C and 927(DEGREES)C. The data from these experiments were then plotted in the (Y(,1),Y(,2)) plane and a geometric model of how the state variables change during loading was constructed.The model clearly demonstrates that on each loading reversal kinematic hardening is the predominate type of hardening. The observed limit cycle behavior of the state variables requires that there be an isotropic softening, or decrease in the elastic range, at the beginning of each reversal. This is followed by a rapid isotropic hardening at the end of the reversal. However, this behavior was obscured by the scatter in the data which was on the order of 10 percent of the elastic range.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD