Some Critical Experimental Tests of the MATMOD Constitutive Equations with Respect to Directional Hardening and Cyclic Deformation

    Published: Jan 1982

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    Cyclic torsion data on pure aluminum and Type 304 stainless steel have been generated recently that test several assumptions and predictions of the MATMOD equations (a unified, broad, phenomenological model for nonelastic deformation). Generally the new data support the model, but in at least one area they suggest a needed improvement. Firstly, the data show that when back stresses are measured by a Bauschinger effect technique (as opposed to the usual stress-drop method) the ratio of the steady-state back stress to flow stress is essentially a constant, independent of the flow stress level; this helps confirm a key assumption in the equations, but also suggests the need for an additional directionally-hardenable contribution to the strain rate. Secondly, strain softening is observed within some of the hysteresis loops, especially at large strain ranges after cyclic hardening; this is in agreement with predictions of the model. Finally, the peak back stresses observed at a given strain range are observed to increase along with the isotropic strength level; this behavior differs from that predicted by the constitutive equations.


    constitutive equations, mechanical properties, cyclic deformation, aluminum, austenitic stainless steel, creep, back stresses, strain softening

    Author Information:

    Miller, AK
    Associate Professor and Research Assistant, Stanford University, Stanford, Calif.

    Ziaai-Moayyed, AA
    Associate Professor and Research Assistant, Stanford University, Stanford, Calif.

    Committee/Subcommittee: E28.03

    DOI: 10.1520/STP28888S

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