From Damage to Fracture in Dual-Phase Steels: a Focused Experimental–Numerical Approach

In the automotive industry the trend is to use ever more and stronger High-Strength Steel (HSS), such as dual phase steel which consist a soft matrix of ferrite and hard martensite islands (Figure 1). The motives is to improve crash safety without making the car heavier or while even decreasing the weight of cars since this also deceases the energy consumption and C02 emission. For the car crash safety, one needs to understand the fracture behavior of materials. The aim of the project is experimental characterization of damage evolution in dual phase steel.

PhD candidate:Chaowei Du
Supervisors: Johan Hoefnagels, Marc Geers
Institutions: Materials innovation institute (M2i) and Tata Steel

Although a lot of research has been done on the fracture of dual phase steel, there is still debate on the fracture mechanisms which are mainly grouped as the decohension between ferrite and martensite and the martensite cracking. The project is aimed to characterize the fracture behavior on both micro-scale and macro-scale. For the former case, a single fracture event will be characterized in detail for each mechanism. In the second case a statistical research on the fracture events will be carried out to figure out the dominant mechanism and the competition between different mechanisms.

EBSD will be used to identify the grains of ferrite and martensite in the specimen and to find the origin of fracture. In-situ tensile experiments will be carried out in SEM until the fracture of the specimens. Digital image correlation will be used to analyze the local strain.