The effect of work-hardening and pile-up on nanoindentation measurements

Nanoindentation-Induced Pile-Up in the Residual Impression of Crystalline Cu with Different Grain Size

“…For 34 example, there is an apparent upward extrusion at the edge of the contact with the indenter in some 35 metals, known as pile-up, which means the actual contact area is larger than the value calculated by 36 the Oliver-Pharr method [1]. Some studies has reported that the true contact area is 60% larger than 37 the measured value as serious pile-up occurs, leading to the overestimation of the E and H [2][3][4][5][6][7].…”

“…than 0.7 [2,3]. Interestingly, most of the theoretical development reports were based on numerical 48 modelling [5,[8][9][10][11][12], with very limited experimental data being used to explain this phenomena.…”

“…Although some reports have studied the effect of work-hardening, grain orientation on the pile-up 50 formation in the metals [3,13], other factors such as grain size and deformation mechanisms 51 transformation have not been mentioned.…”

Nanoindentation-Induced Pile-Up in the Residual Impression of Crystalline Cu with Different Grain Size

“…However, in some cases there exists an apparent upward extrusion at the edge of the contact with the indenter in some metals, known as pile-up, which means that the actual contact area is larger than the value calculated by the Oliver-Pharr method [1]. Some studies have reported that the true contact area is 60% larger than the measured value as serious pile-up occurs, leading to the overestimation of the E and H [2][3][4][5][6][7]. Therefore, an understanding of the formation of the indentation pile-up in various materials and loading conditions under nanoindentation testing is invaluable.…”

“…Therefore, the easily measured h f /h max from the load-displacement curve can be used to determine the prevalence of the pile-up. It has been suggested that for materials with low work hardening ability, the amount of pile-up would become obvious as the ratio of h f /h max becomes larger than 0.7 [2,3]. Interestingly, most of the theoretical development reports were based on numerical modeling [5,[8][9][10][11][12], with very limited experimental data being used to explain this phenomenon.…”