Proposal for ISO 14577 : Metallic materials-Instrumented Indentation test for hardness and materials parameters - 1st. Re-evaluation of unloading curve's profile at neighborhood of unloading starting point and discussion of real maximum contact depth)

摘要

Dependences of the computed Young's modulus on the indentation depth or test force arc clearly observed in the instrumented indentation tester. In the first step in order to investigate the cause of these dependences, re-evaluations between the test force and unloading displacement for the unloading curve's profile at the neighborhood of the unloading starting point are performed. On the analyzed results for both of the authors experimental data and those quoted from Oliver et al's paper, the relationships between the test force and unloading displacement are approximately straight lines. These phenomena are discussed on the indentation processes and the elastic contact theories. Also the reliability of the measured values with Fiscerscope PICODENTOR HM 500 is confirmed comparing the theoretical curves with the approximately elastic experimental curves. Agreement of both curves is good. Since the relationships between the test force and unloading displacement are approximately straight lines at the neighborhood of the unloading starting point therefore the real maximum contact depth in the indentation will be h_ε. Namely, h_ε is defined as the point of intersection of the tangent at F_(max) with the indentation depth-axis, although the depth of the contact h_ε of the in-denter with the test piece at F_(max) is defined as h_ε=h_(max)- (3/4) (h_(max)-h) and used in ISO 14577-1, where F_(max) is the maximum test force and h_(max) is the maximum displacement.