Estimation of biaxial surface stress by instrumented indentation with sharp indenters Original Research Article

The influence of non-equi-biaxial surface stress on the shape of indentation load versus depth curve was studied experimentally by instrumented sharp indentation tests on artificially strained samples of API X65 steel. The shifts in the indentation loads for several stressed states from that of the unstressed state had a linear relationship with average equi-biaxial stresses separated from the biaxially applied stresses. Micromechanical contact analyses for the stress-induced load shifts yielded stress values comparable to the applied in-plane stresses except for the pure shear stress state, where the effect of the applied stress on indentation plasticity is negligible. This study supports the proposition that the surface stress in an arbitrary biaxial state can be evaluated through a theoretical model combined with the ratio of two principal stress components.