Deformation and failure analysis of laser-welded joints in bending I-core sandwich panels by finite element and digital image correlation

The T-joint is a weak point in laser-welded metal sandwich panels (MSPs), exhibiting complex stress-strain responses and failure evolution during bending. This study employs a finite element analysis coupled with digital image correlation (FEA-DIC) to investigate the deformation mechanism of MSPs and the strain-failure evolution of T-joints under three-point bending. The results reveal that MSPs generally undergo a four-stage bending response: elastic, initial plastic, asymmetric deformation and failure. However, in short-span specimens, the reduction in load-bearing capacity is primarily caused by weld cracking, whereas in long-span specimens, plastic bending of the face plate precedes weld cracking. Short-span specimens exhibit maximum shear strain transfer between cores. In long-span specimens, the ratio of γ_xy to ε_yy within each joint increases with deflection. Both ε_yy and γ_xy are crucial to structural failure. The face-core interface opens on one side and compresses on the other, with the cracking mechanism shifting from tension-dominated to shear-dominated, as confirmed by fractography. The coupled FEA-DIC method provides an efficient approach to analyzing the strain evolution in sandwich structures.