Investigation of the influence of loading direction after pre-forming on the formability and mechanical properties of DP600

The material behaviour after non-proportional strain paths is subject of numerous current investigations. These investigations show that in addition to the stress state, a change in the direction of loading also has a significant influence on the material behaviour. In this work, the influence of non-proportional strain paths on the mechanical properties such as tensile strength, uniform strain, elongation at fracture and yield strength as well as the influence on formability is determined. For this purpose, a dual-phase steel CR330Y590-DP, with a thickness of 0.8 mm, is investigated in more detail. The material is pre-strained to different strain values and then further examined with Nakajima and tensile tests. The influence of the loading direction is determined by five different post-strain directions (0°, 22,5°, 45°, 67.5°and 90°) to the initial pre-strain direction. In addition to the method according to the standard, the yield strength is determined by a temperature-dependent determination method, which is based on the thermoelastic effect. This method has already been qualified for simple uniaxial tensile tests and a relation to the microstructural behaviour was proven. Thus, it provides valuable conclusions on the microstructural behavior for the tests performed within this study with a change in the loading direction.