Scaling of size/time/temperature — Part 2: Progressive damage in uniaxial compressive specimen

Abstract

Having analyzed the thermal/mechanical behavior of a uniaxial tensile bar, Part 2 of this investigation is concerned with the same geometric configuration and loading rate but the load is reversed such that material elements are in compression. The cylindrical bar would tend to bulge in compression rather than necking. Time response of the stress and strain differed for the two loading cases. Compression gives rise to a much more stable change in deformation states in contrast to tension where the deformation tends to increase more rapidly with loads that are increased monotonically at the same rate. More time is available in compression to accumulate damage prior to global failure. Thermal changes also differed qualitatively and quantitatively. Macroheating is observed during the early stage of compression instead of cooling as in the case of tension. Distortion on the surface of the compressed specimen is the more dominant mode of deformation whereas dilatation in the center of tensile specimen is more critical. These differences attribute to the contrasting features of tensile and compressive failure. Cooling/heating associated with dilatation/distortion are assessed for different size elements. Although the behavior is highly oscillatory, it is unique and deterministic provided that the size, time and temperature for each element are synchronized. This is accomplished by application of the isoenergy density theory which assumes the interdependence of surface and volume energy and applies to nonequilibrium and irreversible physical processes. The same event referred to the atomic, microscopic and macroscopic scale can thus be interconnected though their behavior may appear different at each level. Precise characterization of material behavior is different because the response is sensitive to changes in load type and history. Even in the cases of uniaxial tensile and compressive specimen, the difference is dramatic when the results are compared with those reported in Part 1 [1].