The Anvil Effect in the Spherical Indentation Testing on Sheet Metals

Spherical indentation hardness tests are widely used in manufacturing industry to obtain material property of the workpiece. For the indentation test on sheet metals, significant error can occur in measuring the penetration depth due to the anvil effect. This anvil effect is manifested with decreasing specimen thickness and increasing indentation depth. This paper critically reviews the experimental observations of the anvil effect, and studies the mechanism behind it. The experimental results and numerical simulations suggest that, when the thickness of the specimen is reduced, a change in deformation mode is experienced during the indentation process. A correction method for the anvil effect is proposed and an empirical equation is derived to determine the effective indentation depth. The experimental and numerical investigations have important implications for the interpretation of the indentation anvil effect; and the correction method for anvil effects can be used in hardness measurement to obtain accurate material property.