Effects of fracture area measurement method and tension test specimen type on fracture strain values of 980 class AHSS

Abstract

With increasing focus on "local formability" and fracture behavior of advanced high strength steels (AHSS), the effects of tension test specimen type and fracture area measurement method on fracture strain values were examined. Three 980 class AHSS and three standard tension test specimens with various widths were evaluated. Fractures types were grouped into three categories according to appearance and thickness profile "shape" - Type 1: Perpendicular to the tensile axis (across specimen width) with a V-shape thickness profile; Type 2: Irregular transition from Type 1 to Type 3 with a W-shape thickness profile; and Type 3: Angled across the specimen width with a U-shape thickness profile. All materials exhibited Type 1 fractures when tested with Subsize specimens. However, as the specimen width-to-thickness ratio increased, the fracture type changed from Type 1 to Type 2 or from Type 1 to Type 3. In contrasting the effects of specimen type and fracture area measurement method, specimen type (width) has a far greater impact on the consequent fracture strain value. For tension testing no clear universal relationship exists between the width-to-thickness ratio and the fracture strain. These observations suggest that, when reporting fracture strain values, the specimen type, the material thickness, and the fracture area measurement method must be indicated.