Global formability and bendability of ultra-high strength steels: Effect of mechanical properties on the strain distribution and behaviour in air-bending

Bendability is a key property for ultra-high strength steels, that affects their usability in many industrial applications. Previous research and efforts on improving the bendability of high-strength steels have focused mostly on the minimum bend radius. However, as the minimum bend radius has been deemed insufficient as a measure of bendability, a new approach may be necessary for further advancements in bendability research. In this paper, bendability of nine materials is investigated from a global formability perspective, through bending tests and tensile tests. Digital image correlation is used for strain measurement in both the bending and tensile tests. Linear regression is used for determining the relationships between the obtained tensile test results and bending strain distributions. The findings of this paper show that applying a “local/global formability” approach to bendability could be beneficial for future research, as better description of the bending behaviour can be obtained and the factors affecting certain bending behaviours can be thoroughly investigated. [Display omitted] •The strain distribution at a given bend angle can be quantified by the peak strain.•Larger strain-hardening exponent in tensile decreases peak strain in bending.•Larger uniform elongation in tensile decreases peak strain in bending.•Sensitivity to punch radius change is higher for low strain-hardening materials.