The effect of stiffness of the loading system on determination of tensile characteristics from the results of small punch tests

Abstract

The assessment of the residual lifetime of critical components of industrial plants requires the knowledge of mechanical properties prior to operation, respecting all technological operations realized throughout the   manufacture of the component, and the knowledge of mechanical properties after actual time of operation (actual mechanical properties). The conventional mechanical tests require relatively large volume of testing material and extracting it from an operating component can impair its integrity. The need for evaluating the actual mechanical properties by direct testing method has led to development of innovative techniques based on miniaturized specimens. Among these, a technique called the Small Punch (SP) test has emerged as a promising candidate. It enables measurement of the realistic material properties at the critical locations in the component both prior and after long-term operation. Yield stress and tensile strength at ambient temperature are determined from empirical correlations between SP and standardized test results. In the present paper the empirical correlations obtained in two laboratories for determination of yield stress and tensile strength of low alloy steel of type 14MoV6-3 in as received state from the results of SP tests are compared and the differences obtained are discussed. The results obtained demonstrate the significance of loading system stiffness on the results of SP tests at laboratory temperature.