Experimental Elucidation of volume change and local behavior of deformation of Nylon 66 and PC Materials by DIC Method and Micro-Vickers Hardness Test

It is a well-known fact that there is significant difference in magnitude of flow stresses and work hardening rates of polymeric materials between in tension and compression. There is a possibility that hydrostatic pressure is involved in this asymmetry to the loading axis, in which case volume change occurs in plastic deformation. And also, the propagation of localized deformations is often observed as a deformation behavior of polymeric materials. In such cases, it has been confirmed that the propagating portion of the crack must be hardened, but the deformed portion is softened. The aim of this study is to measure the variation of plastic Poisson’s ratio by means of Digital Image Correlation method to clarify the existence of the plastic compressibility of Naylon66 and Polycarbonate. Another aim is to elucidate the mechanism of softening at the neck. The authors conducted tensile tests of thin strip specimens and measured the axial and lateral strains by DIC method, then, plastic Poisson's ratio was derived. The result showed that plastic Poisson’s ratio of Naylon66 and Polycarbonate was smaller than the value of 0.5, that result in the existence of plastic compressibility in these materials. The Micro-Vickers hardness measurement for a gauge length was also performed to clarify the strength distribution of a specimen, and the results showed that the necking part of the materials was softened.