Author(s): BIAN Hong-xia, ZHU Liang, TU Peng, ZHOU Hui
Pages: 111-115,144
Year: 2014 Issue:  5
Journal: Journal of Plasticity Engineering
Keyword:  load instability; geometrical instability; work hardening exponent; strain rate sensitivity coefficient;
Abstract: The characteristics of high temperature geometrical instability of plastic materials have been investigated through the tensile test and tensile unload test of two low nickel austenite stainless steels at the temperatures of 950℃ ~1200℃ .The results show that the geometrical instability occurs after a period of uniform deformation ,rather than immediately upon load instability during high temperature tensile .The specimen deformation is uniform before load instability ,and is non-uniform in the local posi-tion of specimen from the load instability stage to the geometric instability ,while the local non-uniform deformation does not di-rectly lead to the instability .With the increasing of the deformation temperature ,there is little obvious variation for both load in-stability strain and strain hardening exponent n ,and the load instability true strain is close to the value of n .The results indicate that the load instability true strain depends on the value of n .Both the geometric instability strain and strain rate sensitivity coeffi-cient m increase with the increasing of the temperature ,and the value of m determines the strain from load instability to geometric instability ,which is the major factor for the geometric instability strain .