Evaluation of rate-dependent hardening behaviors of AHSS sheets with novel tension and compression test devices

Abstract

This paper is concerned with evaluation of rate-dependent hardening behaviors of AHSS sheets making use of novel tension and compression test devices. Hardening behaviors in tension and compression are indispensable for accurate numerical simulation of sheet metal forming and spring-back. In addition, it is important to consider the strain rate effect on hardening behaviors in tension and compression because sheet metal deformation prevails at intermediate strain rates up to several hundreds per second in automotive industry. This paper proposes novel tension and compression test devices which avoid the fluctuation of the measured force at intermediate strain rates up to 100 s(-1). The main concept of a new device is to install a load cell close to a specimen inside the novel devices to measure the actual force during specimen deformation regardless of vibration mode of a jig system. Hardening behaviors are evaluated with experimental results in tension-compression for TRIP980 and TWIP980 steel sheets at various strain rates ranging from 0.001 s(-1) to 100 s(-1) considering the Bauschinger effect and the permanent softening. It is confirmed from the experiments that the Bauschinger effect decreases as the strain rate increases. It is also noted that the permanent softening is observed in hardening behavior of TWIP980, but not in that of TRIP980.