Multi-scale design of DP steels for automotive applications

DP steels are often used to form variety of automobile parts due to their impressive mechanical properties such as high strength and good ductility. Since most of these structural members are prone to failure under different loading conditions, failure initiation and damage mechanisms are considered as important areas to investigate and have been the subject of extensive research work. The current research work aims to study the effect of microstructural features such as martensite phase fraction and morphology, ferrite grain size and additional phases such as bainite on the mechanical and failure behaviour of DP steels. For this purpose, a microstructure based approach by means of representative volume elements (RVE) is utilized to incorporate the microstructure deformation distribution and the failure mechanisms on this scale. Micro sections of DP microstructures with various amounts of martensite are converted to 2D RVEs, while 3D RVEs are constructed statistically with randomly distributed phases. A dislocation-based model is used to describe the flow curve of each ferrite and martensite phase separately as a function of carbon partitioning and microstructural features. Evolotuin of GNDs during ferrite to martensite phase transformation was quantified. Numerical tensile tests of RVE are carried out using the ABAQUS/Standard code to predict the mechanical properties and failure behavior of DP steels taking in to account GNs. For validation, a comparison between predicted and experimental flow curves is carried out.