Abstract
Advanced high-strength steels (AHSSs) are widely adopted in car body structures to achieve weight reduction for energy efficiency and crash safety. This study investigates the effects of material strength and notch shapes on crack initiation and propagation behaviors in AHSS sheets used in car body structures. Tensile tests were conducted for three types of Japanese grade AHSS (JSC590, JSC980, and JSC1180) specimens and two notch root radii (R0.5 and R5). The crack initiation and propagation behaviors were found to strongly depend on the material strength and notch root radius. The crack generated from the notch root for the R0.5 specimens, whereas it generated from 1 to 2 mm inside the notch root for the R5 specimens. Unstable crack propagation occurred beyond the maximum load for the R5 and JSC1180 specimens, whereas only stable crack propagation occurred for the R0.5 specimens. From the digital image correlation analyses, we found that the specimen notch radius affects the stress triaxiality and equivalent plastic strain around the notch root. The JSC980 material had the highest crack initiation energy, which correlates with the plastic dissipation energy utilized for thickness reduction. The JSC590 material exhibited the highest crack propagation energy, which correlates with the true fracture strain.
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