Mechanisms and Modeling of Bake-Hardening Steels: Part II. Complex Loading Paths

The strain-path dependence of yield strength and mechanical behavior of bake hardening (BH) steels have been investigated. In addition to standard BH tensile tests, samples have been prestrained in plane tension, equibiaxial tension, and shear. After aging at 170 °C for 20 minutes, tensile and shear tests have been carried out to examine the strain-path dependence of the mechanical behavior. A polycrystalline self-consistent model was introduced to model the strain-path dependence of the BH effect. The aging treatment was simulated by an additional hardening term in the model. Simulations were performed for various strain paths, and the influence of aging on yield strength was examined. Results showed that yield strength increase follows a master curve in agreement with experiments and literature. Strain-path dependence of BH was then modeled by a macroscopic hardening term in order to carry out computations with a finite element (FE) method code. Simulations of the dent test were performed and compared with experiments for aged or unaged BH steels.