Fatigue crack growth in cementitious materials under cyclic compressive loads

Abstract

This paper presents experimental results and a discussion of the mechanisms of fatique crack growth under uniaxial cyclic compressive loads in cementitious materials containing stress concentrations. It is demonstrated that the application of cyclic compressive loads to single edge-notched specimens of mortar induces Mode I fatigue cracks from the notch-tip in a direction normal to the far-field compression axis. The experiments of this study, in conjunction with the recent work of Suresh and coworkers on the compression fatigue behavior of a wide range of ceramics and ceramic composites, suggest that the driving force for Mode I crack advance is the generation of a zone of residual tensile stresses in the near-tip region of the stress concentration upon unloading from the far-field compressive stress. Numerical simulations of notch-tip residual stresses in brittle solids, including mortar and plain concrete, indicate that the residual tensile stresses are of sufficient magnitude to induce fracture along the plane of the notch. This Mode I fatigue crack growth mechanism in cyclic compression, observed at nominal compressive stress values far below the uniaxial compressive strength, is vastly different from the splitting mode of failure generally found in cementitious materials under monotonic compression. Practical implications of the cyclic compression fracture mechanism are highlighted.