PII] S99114985"87#999079 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 [ 0887 Elsevier Science Ltd [ All rights reserved[ Keywords] A [ indentation and hardness \ B [ elasticplastic material \ C [ _nite elements[