A NUMERICAL STUDY OF INDENTATION WITH SMALL SPHERICAL INDENTERS

The finite element method for the conventional theory of mechanism-based strain gradient plasticity is used to study the indentation size effect. For small indenters (e.g.,radii on the order of 10 μm),the maximum allowable geometrically necessary dislocation (GND) density is introduced to cap the GND density such that the latter does not become unrealistically high. The numerical results agree well with the indentation hardness data of iridium. The GND density is much larger than the density of statistically stored dislocations (SSD) underneath the indenter,but this trend reverses away from the indenter. As the indentation depth (or equivalently,contact radius) increases,the GND density decreases but the SSD density increases.