Effects of pre-fatigue damage on mechanical properties of Q690 high-strength steel

This paper investigates the residual strength of Q690 high-strength steel previously damaged by fatigue. Pre-fatigue damage was induced by subjecting the specimens to nine different loading cycles without causing fracturing under three initial cyclic loadings, and then subsequent tensile tests were performed on these pre-fatigued specimens to obtain their stress-strain curves and associated mechanical properties (yield strength, ultimate strength, elastic modulus and ultimate elongation). Systematic comparative analyses for the evolution of residual mechanical properties of Q690 high-strength steel with different pre-fatigue damages were carried out. Significant differences are observed in the fracture position and the morphological features of fractures of Q690 high-strength steel with different pre-fatigue damages. Meanwhile, pre-fatigue damage also exerts distinct influences on yield strength, ultimate strength and ultimate elongation of Q690 high-strength steel. Specifically, the dramatic reduction is especially noted in ultimate elongation of Q690 high-strength steel due to pre-fatigue damage. In contrast, the influence of pre-fatigue damage on the elastic modulus of Q690 high-strength steel is negligible. When pre-fatigue damage is ranging from 0 to 0.6, the maximum decrease of ultimate elongation reaches up to 49.3% and the maximum reduction of yield strength is 11.1%, however the decline of elastic modulus is less than 4.0%. According to the experimental results, a new set of predictive equations were proposed to determine the mechanical properties of Q690 high-strength steel with pre-fatigue damage and to provide the fundamentals for appropriate pre-fatigue damage evaluation of Q690 high-strength steel structures. (C) 2020 Elsevier Ltd. All rights reserved.