Insights into the plastic deformation during Berkovich nanoindentation

This study presents a systematic investigation of lateral interaction effects in sequential nanoindentation across three material classes: glassy (fused silica), polymeric (polycarbonate and polymethyl methacrylate) and metallic (copper and aluminium), using a Berkovich indenter. By varying the normalised indent spacing (dI/hm) from 1 to 30, where dI is the lateral distance between indents and hm is the maximum indentation depth, the critical lateral extent of plastic deformation was quantified. The influence of adjacent residual indents on load-depth of penetration (P-h) response, maximum applied load (Pm), stiffness (S) and residual imprint morphology was analysed. Results demonstrate that interaction effects are highly material-dependent: in fused silica, plastic deformation interactions extend up to ∼5.26hm due to densification; in polymers, interactions stabilise at dI/hm ≥ 6, regardless of strain rate (P˙/P), with notable effects on load relaxation and pile-up; and in metals, interaction effects persist up to dI/hm ≥ 10 due to dislocation mechanisms and work hardening. These findings establish material-specific critical interaction distances essential for accurate interpretation of nanoindentation data in high-resolution mechanical property mapping, particularly in small-scale or heterogeneous systems.