The finite element analysis of a strain hardening layered medium under normal loading by (a) a rigid and (b) a deformable indenter

The finite element method (FEM) is used to investigate the normal indentati on problem of a deformable indenter in contact with a strain hardening subs trate coated with an elastic-perfectly plastic layer. In order to assess th e influence of the deformable indenter, the solution is compared with resul ts of a rigid sphere indenting the same system. The comparison shows that, when the indenter is assumed to be rigid, the contact pressures are signifi cantly higher than those for the deformable indenter during elastic deforma tion. When plasticity is more pronounced, the peak pressures at just inside the contact edge are also higher for the rigid indenter. Similarly, the re sults assuming a rigid indenter give a lower value of maximum radial tensil e stress along the coating surface when compared with those using a deforma ble indenter, which is responsible for the cracking of the film. In order t o examine the effects of strain hardening, the above solutions are compared with a system having an elastic-perfectly plastic substrate. Comparison be tween the two sets of results shows that the strain hardening medium develo ps a smaller contact area and higher central and peak contact pressures ins ide the contact edge during plastic deformation. It also shows that the use of a strain hardening substrate alleviates the maximum radial tensile stre ss just outside the contact edge.