The Mechanics of Size!dependent Indentation

Indentation tests at scales on the order of one micron have shown that measured hardness increases signi_cantly with decreasing indent size\ a trend at odds with the size!independence implied by conventional plasticity theory[ In this paper\ strain gradient plasticity theory is used to model materials undergoing small!scale indentations[ Finite element implementation of the theory as it pertains to indentation modeling is brie~y reviewed[ Results are presented for frictionless conical indentations[ A strong e}ect of including strain gradients in the constitutive description is found with hardness increasing by a factor of two or more over the relevant range of behavior[ The results are used to investigate the role of the two primary constitutive length parameters in the strain gradient theory[ The study indicates that indentation may be the most e}ective test for measuring one of the length parameters[ Þ 0887 Elsevier Science Ltd[ All rights reserved[