Damage and fracture behavior of a metal sheet under in-plane compression–shear deformation

Increasing demands for lightweight manufacturing accelerate the application of lightweight materials in the transportation, aviation, and power industries. High-strength steel is a popular candidate among various lightweight materials. Transformation-induced plasticity (TRIP) steel, a high-strength, lightweight steel, is promising for forming processes owing to its high strength and toughness. However, the increase in the flow strength of metals will create big challenges for material formability and fracture issues for manufacturing processes. Ductile fracture is still the main failure form during the forming process of TRIP steel. Sheet metal is subject to complex stress states when it undergoes diverse loading paths. Failure modes in metal forming can be mainly classified into the following: tensile, compression, shear, tensile–shear, and compression–shear. Because the metal sheet is prone to buckling failure when it undergoes in-plane compression–shear deformation, it is difficult to induce fracture during the corresponding negative stress triaxiality range. To solve this issue, a novel experimental setup and a specimen were designed to analyze fracture behaviors of an advanced high-strength steel TRIP800 sheet. For the same specimen, the failure behaviors of diverse stress states could be achieved by adjusting the angles between the loading direction and specimen positions. The parallel numerical simulations of in-plane compression–shear deformations under three typical loading angles of 20°, 30°, and 45° were performed on the ABAQUS/Explicit platform. The predicted stress triaxiality in the local deformation region of the three cases was less than zero, and the lowest was up to −0.485, which verifies that the fracture failure analysis of negative stress triaxiality range could be realized with the designed device. In addition, the fracture onset information and damage evolution were analyzed based on the modified Mohr–Coulomb (MMC) fracture criterion. Furthermore, the fracture strain at the fracture point decreased with the decrease in stress triaxiality when the stress triaxiality was less than −1/3.