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

D Frómeta,C Suppan,A Lara,L Grifé,J Rehrl,D Casellas,T Dieudonné,J Calvo,P Dietsch

doi:10.1007/s11661-020-06119-y

Abstract

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 (wei), the specific essential work of fracture (we), and the hole expansion ratio (HER), are assessed. The specific essential work of fracture (we) 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.

Highlights

ADVANCED high-strength steels (AHSS) play a fundamental role in the development of modern lightweight automobiles
Even though we has shown to be independent of the specimen geometry and can be obtained from different geometries,[40,42] for thin sheets, the essential work of fracture (EWF) testing protocol[53] developed by the European Structural Integrity Society (ESIS) recommends the use of double edge notched tension (DENT) specimens because of its
The greater content of retained austenite (RA) in TRIP780 leads to higher uniform and total elongation compared to DP780 (Figure 7), thanks to the contribution of the transformation-induced plasticity (TRIP) effect

Summary

Introduction

ADVANCED high-strength steels (AHSS) play a fundamental role in the development of modern lightweight automobiles. The use of these steels for structural and safety related automotive components is undergoing a continuous increase in the last years. The body structure of current passenger cars can have up to 51 pct of AHSS[1] and this percentage might grow up to 65 pct in upcoming vehicles.[1,2] The main advantage of AHSS is their excellent combination of high strength and good ductility, which has significantly contributed to reduce the total vehicle mass, while improving crash performance. Manuscript submitted August 4, 2020; accepted November 12, 2020.

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