Enhanced bendability in sheet metal produced by cladding a ductile layer

The effect of cladding on the bendability of sheet metal is investigated numerically using the finite element method by employing the Gurson-Tvergaard-Needleman (GTN) model. The bendability and fracture strain increase significantly by cladding the sheet. In clad sheet metal, the development of the stress triaxiality in the region of the fracture slows down, thereby delaying the nucleation and growth of voids. In thin clad layers, the damage is initiated in the core but the crack is blunted at the clad core interface until the cladding thins and fails with increasing bending. Failure occurs in the cladding at sufficiently large cladding thickness. The effect of mandrel span length on bendability, which reflects the degree of bending in a three-point bend test, is also investigated to understand how failure transition from core fail to clad failure occurs. Finally, the effect of work hardening in the cladding material is examined, and bendability increases if the rate of hardening in the cladding material increases. Numerical results are found to be in good agreement with experimental observations.