Experimental research on variable-amplitude fatigue behavior of cracked mortar after epoxy grouting

Abstract This paper presents the experimental results of the fatigue behavior of cracked mortar specimens after epoxy grouting reinforcement under high-frequency variable-amplitude fatigue loading. Grouting can effectively suppress the stress concentration at the crack tip and enhance the fatigue resistance of the sample. The final failure mode of the specimen depends on the loading sequence order. We consider the equivalent coefficient and loading sequence, and the multi-step stress level can be equal to a constant value. A log-linear relationship can be obtained between the equivalent stress level and the total fatigue life for both grouted and cracked specimens. In the process of multi-stage fatigue loading, using strain as the damage parameter, it is found that the damage in each loading stage accumulates non-linearly, and the prediction using Palmgren-Miner's rule may be conservative. We propose a nonlinear damage accumulation prediction model that fully considers the loading sequence, equivalent stress level, stress ratio, and other parameters. The test results show that the model can better meet damage accumulation rules and make better prediction effects for multi-stage variable-amplitude fatigue loading.