Evolution of in-plane stresses induced fracture behaviors of Tailor Welded Blanks subjected to non-uniformly distributed load

[Display omitted] •Non-uniformly distributed forming load could improve deformation uniformity of TWBs without sacrificing the limit bulge height.•Strain components captured by DIC system were introduced into Levy-Mises law to quantitatively evaluate stress states of TWBs.•In-plane stresses of TWBs when subjected to non-uniformly distributed forming load was responsible to the improved formability.•Correlation between stress states and fracture behavior of TWBs was presented to clarify the failure mechanism of TWBs. Due to remarkable difference in material properties of Tailor Welded Blanks (TWBs), when subjected to uniform forming load, severe non-uniform metal flow and strain localization occur on TWBs’ “weaker” side, which accelerates the forming failure. In this work, non-uniformly distributed normal pressure generated by heterogeneous elastomer was used to balance the deformation on SS304/SS316 stainless steel TWBs’ two sides. Effects of load patterns (i.e., uniformly and non-uniformly distributed load) on strain distribution, stress states, and fracture morphology of TWBs were studied to clarify the change of failure mechanism based on bulge tests and analytical analysis. The results showed that, when subjected to non-uniformly distributed load, with the ratio of Young’s modulus (φ) of heterogeneous elastomers increasing from 1 to 5.33, normal pressure on the “weaker” side of TWBs (i.e., SS304 side) decreased from 8.68 MPa to 4.34 MPa while that on the “stronger” side (i.e., SS316 side) remained constant. The corresponding radial and circumferential stresses on the “weaker” side decreased by 34.76 MPa and 21.08 MPa, respectively. Excessive plastic deformation on the “weaker” side was decreased and deformation uniformity on both sides was improved. Meanwhile, in the microscopic scale, fracture morphology of materials on the “weaker” and “stronger” sides changed from fracture mode I (i.e., dimples combined with tearing edges) to fracture mode Ⅱ (i.e., two sizes of dimples). Dimples in fracture mode Ⅱ showed similar sizes with these on fractured SS304 and SS316 tensile specimens after uniaxial loading, which implied sufficient plastic deformation on both sides of TWBs.