Abstract
Indentation is widely used to evaluate mechanical properties of structural materials. It has been known that a measured hardness value increases with increase of the indentation strain rate. By using this inconvenient phenomenon, a new method for determining of constants for Cowper-Symonds constitutive equation by using a sharp indentation is proposed in this research. The first report evaluates the influence of strain rate on strain field, and the later report will propose the determining method based on the principle which is shown in the first report. The first report shows that a finite element model with Cowper-Symonds constitutive equation can simulate the strain rate effect such as a load increase with strain rate increase and a penetration increase during a holding time, and then the authors investigate on several parameters which may affect indentation results for a material, which shows dependence of strain rate. The investigated parameters are a critical strain, an indenter velocity, an indenter angle and a roundness of indenter tip. The obtained results are the following; the maximum strain rate appears near indentation crater rim and the strain value at this area is close to the value of the critical strain which describes important strain region for indentation load. A sharper indenter angle produces higher strain rate and makes indentation load higher due to strain rate effect. The roundness of indenter tip decreases the strain rate under the indenter, but an error caused by the roundness of indenter tip can be easily corrected with the conventional technique.
