Fatigue fracture quantification in brittle cementitious materials using acoustic emission testing and digital image correlation

Fatigue loading in brittle materials introduces damage at the micro-scale. These micro-fractures can accumulate and cause a significant reduction in material stiffness or even lead to structural failure. Deformation-based monitoring techniques can be inadequate when detecting damage at the micro-level. Hence, here is where advanced non-destructive testing (NDT) methods such as acoustic emission testing (AET) and digital image correlation (DIC) can provide a significant improvement in quantifying fatigue damage. The paper aims to combine AET and DIC for advanced fatigue damage analysis on brittle cementitious mortars. Cylindrical samples with three different sizes are subjected to fatigue loading in a Brazilian splitting test. The damage advancement quantified from cumulative AE event count and energy analysis showed a good correlation with the tensile deformation measurement of the DIC. It was observed that for low cycle loading, the slowly progressing damage evolution may not always occur, instead abrupt failure similar to monotonic loading can occur even after passing several load cycles. The size of the fracture process zone (FPZ) was measured using several AE-based and DIC-based methods. The comparison of the approaches indicated that the AE energy-based method is the most suitable to quantify the FPZ size during fatigue damage progress. From AE-based FPZ analysis of the experimental results, it was concluded that for low-cycle loadings, the lack of a well-developed FPZ can be a cause of the sudden brittle failure.