Material fracture on the back side is clearly observed in SPG result, while FEM with element erosion simply removes all the material in the drilling area. It is important to point out that the effective plastic strain for SPG bond failure is 0.4, but the effective plastic strain in the material reaches 0.7 or more. The reason is the material continues to evolve stress and strain after bond failure (as explained earlier) until all the bonds fail.
Very promising results are obtained both qualitatively and quantitatively. The numerical results show sensitivity to material strength, coefficient of friction between tool and workpiece, which is physical. On the other hand, the results do not show too much sensitivity to the bond failure criteria, which makes the numerical scheme robust and reliable since the major criteria for bond failure do not need to be tuned.
Convergence study on force and moment response