Compliance Ratio Method for Calculating Energy Release Rates in Structural Steels

This paper introduces a compliance ratio (CR) method for the estimation of energy release rates in structural steels. In the method, the elastic and plastic components of energy release are calculated from the area under the load versus load-line displacement assuming no crack extension that can be constructed directly from the standard unloading compliance curve. The method is used to investigate the energy release rates in the compact tension, C(T), fracture specimens fabricated with both conventional and high performance steels used in bridge structures. The conventional steels consist of the ASTM designations A572, A588, and A913. The high performance steels are the ASTM designation A709 grades HPS 345W, HPS 485W, and HPS 690W. The results indicate that (1) the total energy release rate is large at an early stage of crack growth and approaches a constant value in specimens with long crack extension; (2) the elastic energy release rate is significantly smaller than the plastic energy dissipation rate during crack extension for all steels; and (3) the elastic energy release rates in most HPS are higher than those in conventional steels. The paper also shows that the elastic energy release rates obtained from the method are in agreement with those calculated by the stress intensity factor equation in ASTM E399-90.