Balanced Biaxial Testing of Advanced High Strength Steels in Warm Conditions

The main purpose of the present work is to measure the stress-strain behavior under warm conditions (about 100 A degrees C) of advanced high strength steel (AHSS) sheets up to large strains compared to uniaxial tension. The test equipment consists of two main parts, i.e., a hydraulic bulge tester and a heating device. A mechanical system is attached to the test equipment for measuring the membrane stress and thickness strain at the bulge pole. The stress-strain curves were measured for three kinds of AHSS sheets with the proposed test method for various initial temperatures (10, 50 and 100 A degrees C). The proposed method does not provide isothermal stress-strain curves because the specimen temperature increases during the test due to the effect of deformation-induced heating. A numerical scheme using thermo-mechanical finite element (FE) simulations is suggested to deconvolute the isothermal stress-strain curves.