Since advanced high strength steels (AHSS) were introduced in the 1980's, they have become the backbone of the automotive industry, contributing greatly to reducing the weight of cars as well as improving the passenger safety. The third generation AHSS consists of ultra fine microstructure constituents such as martensite and bainite in combination with retained austenite (RA), which offers an excellent strength-ductility combination and high crash performance at a reasonable cost.
In order to transfer novel high performance steel solutions from laboratory to actual vehicle designs, computer simulations predicting the crash behaviour is of key importance. Crash resistance in AHSS is determined by crack initiation and crack propagation, where the latter can be a considerable part of the entire fracture energy. It is thus crucial for the computer simulations to take this propagation energy into account in order to take full advantage of the new steel grades. Crash&Tough will work on increasing the accuracy of crash simulations for 3rd generation AHSS and further boost their applicability in car safety parts.
Experiments are needed to characterise the new steel grades and to calibrate the new simulation models. Crash situations are highly complex mechanical phenomena involving a wide range of strain rates. Investigating the dynamic behaviour of the materials and their strain rate sensitivity is thus crucial in order for a complete picture of the materials, and Digital Image Correlation (DIC) using a high speed camera is used to extract dynamic experimental results. Earlier research has also shown that fracture toughness can be used as an intrinsic material property to rationalise crash resistance. Fracture mechanical tests at different strain rates are thus also conducted to further investigate the effect of microstructure on fracture toughness and crash resistance of AHSS.