Fracture Resistance of Advanced High-Strength Steel Sheets for Automotive Applications

The fracture resistance of different advanced high-strength steel (AHSS) sheets for automotive applications is investigated through conventional tensile tests, fracture toughness measurements, and hole expansion tests. Different fracture-related parameters, such as the true fracture strain (TFS), the true thickness strain (TTS), the fracture toughness at crack initiation (we), the specific essential work of fracture (w), and the hole expansion ratio (HER), are assessed. The specific essential work of fracture is shown to be a suitable parameter to evaluate the local formability and fracture resistance of AHSS. The results reveal that fracture toughness cannot be estimated from any of the parameters derived from tensile tests and show the importance of microstructural features on crack propagation resistance. Based on the relation fracture toughness-local formability, a new AHSS classification mapping accounting for global formability and cracking resistance is proposed. Furthermore, a physically motivated fracture criterion for edge-cracking prediction, based on thickness strain measurements in fatigue pre-cracked DENT specimens, is proposed.

Automated summary

By investigating the fracture resistance of different AHSS sheets, it was found that the specific essential work of fracture is an important parameter for evaluating local formability and fracture resistance. Results show that fracture toughness cannot be estimated from parameters derived from tensile tests, and the importance of microstructural features on crack propagation resistance. A new AHSS classification mapping and a physically motivated fracture criterion for edge-cracking prediction based on thickness strain measurements were proposed.