Influence of pre‐strain and bake hardening on the static and fatigue strength of a DP600 steel sheet

• Published in: Fatigue & fracture of engineering materials & structures 2023-10, Vol.46 (10), p.3622-3639
• Main Authors: Kusch, Andrea, Crivelli, Daniele, Diviani, Luca, Dotta, Matteo, Salamina, Simone, Berto, Filippo
• Format: Article
• Language: English
• Subjects: Accuracy; Baking; Dual phase steels; Fatigue strength; High cycle fatigue; Low cycle fatigue; Metal fatigue; Metal sheets; Residual stress; Strain; Stress relaxation; Tensile strength; Yield strength
• ISSN: 8756-758X; 1460-2695
• DOI: 10.1111/ffe.14095

The influence of pre‐strain on the tensile and fatigue properties of a dual phase DP600 steel was studied. The material was pre‐strained by uni‐axial tension in rolling and transverse direction. Thereafter, specimens were cut from the deformed plates in parallel or orthogonal to pre‐strain direction. It was found that pre‐strain increases yield and tensile strength. Results suggested that strain path change primarily affects the elastic‐plastic transition during early stage of reloading. Pre‐strained specimens showed an increase in high cycle regimes as a consequence of yield strength increment, irrespective of imposed pre‐straining direction. A modified stress life equation that accounts for pre‐strain was proposed and showed good agreement with experimental data. Bake hardening enhanced both tensile and high cycle fatigue resistance. Walker equation was successfully fitted to account for tensile mean stress. In low cycle fatigue, negligible influence of pre‐strain was observed due to cyclic softening and residual stress relaxation. A DP600 steel sheet is characterized under different pre‐strain conditions and after baking. Experiments indicate that pre‐strain and bake hardening are beneficial in HCF. Modified Basquin equations to account for the effect of pre‐strain and bake hardening are proposed. Walker mean stress correction shows good agreement with experimental data.