Equivalent Crack, Fracture Size Effect, and Cohesive Stress Zone of Plain Concrete under Quasi-Static and Variable High-Cycle Fatigue Loading

Abstract

Compliance-derived equivalent cracks are often used in high-cycle fatigue cracking predictions for computational expediency. Its dependence on the cohesive stress zone, however, may limit general applicability under high-cycle variable amplitude fatigue loading and limit the objectivity of the Paris constants and fatigue fracture toughness. In this paper, notched three-point bend concrete specimens of different sizes are subjected to (1) different loading modes: quasi-static and high-cycle fatigue; and (2) different fatigue loading sequences: constant, variable, and random. The results indicate that the fracture toughness does not depend significantly on loading sequence or loading mode. The Paris constants are not size dependent when a crack resistance curve is inserted into a modified Paris law within the range of experimental conditions considered here. The observations and statistical comparisons were consistent for both beam sizes, although they exhibited some significantly different cohesive and fracture properties. More research is required, however, to further generalize these results by expanding the current experimental conditions to include different specimen sizes, geometries, and concrete mix designs.