Instability in the Tensile Test.

Local deformation and local deformation rate were investigated at site and time functions in the tensile test with constant elongation rate. The results show that small inaccuracies in the shape of the test specimen or inhomogeneities in the material cause nonuniform deformation distribution at the very beginning of the test. In materials with high rate sensitivity the nonuniformity of deformation distribution is more or less impeded, so that the reduction-of-area process is retarded and elongation increases.