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    Load Relaxation Testing and Material Constitutive Relations

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    The phenomenon of load relaxation for a specimen in a tension test configuration is not in itself a material property. The resultant record of load P as a function of elapsed time t is dependent on the conditions of loading in the test as well as on the material elastic and inelastic properties. For this reason, the term “load” relaxation seems preferable to “stress” relaxation as a nomenclature for the test, and we shall employ this term in the paper.

    In order to deduce the intrinsic material flow properties from the testing results it is desirable to convert the load-time record P(t) to a specimen record of stress versus strain rate σ(ϵ). In some cases the explicit time dependence is significant, and so each stress-strain rate point can also be associated with the current time t if desired. This data conversion can be always accomplished.

    In the following we shall describe the method of data analysis that is desirable for determining the inelastic constitutive relations of a material. We shall discuss some refinements of the experimental technique that have proven very important in such analysis. We shall then illustrate the expected results for several types of ideal material behavior and finally show the type of results and conclusions for some real materials and test conditions.


    load relaxation, stress relaxation, constitutive relations, inelastic deformation

    Author Information:

    Hart, EW
    Professor of Mechanics and Materials Science, Cornell UniversityGeneral Electric Co., IthacaSchenectady, N. Y.N. Y.

    Committee/Subcommittee: E28.11

    DOI: 10.1520/STP37412S