Technical PaperThe anvil effect in the spherical indentation testing of 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. As micro/nano indentations are not suitable alternatives for measuring bulk material property, the present work critically reviews the experimental observations and studies the mechanism of anvil effect with numerical simulations. The results 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 anvil effect in indentation tests; and the developed method can be used to obtain accurate material property from a common hardness test without resorting to the use of instrumented indentation method.