Role of indenter angle on the plastic deformation underneath a sharp indenter and on representative strains: An experimental and numerical study

The subsurface microhardness mapping technique of Chaudhri was utilized to determine the shape, size and distribution of plastic strain underneath conical indenters of varying semi-apex angles, α (55°, 65° and 75°). Results show that the elastic–plastic boundary under the indenters is elliptical in nature, contradicting the expanding cavity model, and the ellipticity increases with α. The maximum plastic strain immediately under the indenter was found to decrease with increasing α. Complementary finite-element analysis was conducted to examine the ability of simulations to capture the experimental observations. A comparison of computational and experimental results indicates that the plastic strain distributions as well as the maximum strains immediately beneath the indenter do not match, suggesting that simulation of sharp indentation requires further detailed studies for complete comprehension. Representative strains, εr, evaluated as the volume-average strains within the elastic–plastic boundary, decrease with increasing α and are in agreement with those estimated by using the dimensional analysis.

► Plastic strain fields underneath sharp indenters were examined systematically.
► Strain fields and the elastic-plastic boundary were found to be elliptical in nature.
► The ellipticity are sensitive to parameters like yield strength and work hardening exponent.
► Volume averaged strains within the elastoplastic boundary decrease with increasing cone angle.
► More experiments are needed for a comprehensive understanding of plastic flow during indentation.