Determination Of Percentage Reduction Of Area By Continuous Ball Indentation Test

As a convenient and non-destructive test technique, continuous ball indentation test is adopted to evaluate the metal mechanical property of equipment in service, which can be meaningful in engineering practice. However, nobody mentions how to use it to evaluate the plasticity of material. According to the continuous damage accumulation theory, a failure criterion is proposed in this paper. On that basis we can calculate the area reduction rate to evaluate the plasticity of steels. Continuous ball indentation test is performed on two steels which are widely used in pipeline and vessel. The area reduction of the materials is calculated through the method proposed in this paper. The main contributions of this work are as follow:(1) Propose a failure criterion in continuous ball indentation test. A new failure criterion is proposed in this paper. The result of the new criterion is consistent with the old one.(2) Propose a method to evaluate plasticity of steels through continuous ball indentation test. The failure indentation depth can be obtained with the criterion mentioned above. On that basis, the representative strain can be calculated. Eventually, the area reduction rate can be calculated.(3) Analyze the errors. The area reduction rate obtained from ball indentation test is obviously higher than that in the tensile test. The influence related to the "pile-up" and "sink-in" phenomenon, grain size effect and ASME local strain limit criterion is considered in this paper.(4) The relations which introduced by Mathews and Hill to fix the effect of pile up height cannot be applied to continuous ball indentation test. In order to constrain the effect of "pile-up" and "sink-in" phenomenon, we should try bigger indenter.