Characterization of fatigue crack growth of concrete mortar under cyclic indentation loading

- Computational model for contact fractures in concrete mortar under cyclic indentation is established.
- AE method can be utilized to detect crack growth during cyclic indentation test.
- FEM computation with a damage-based cohesive zone model is successfully employed.
- It is found that our computation can simulate fatigue crack growth during cyclic indentation.

This study establishes a computational model for contact fractures in concrete mortar subjected to both monotonic and cyclic contact loadings. We perform experiments using monotonic and cyclic indentation tests with a ball indenter (i.e., cyclic spherical indentation). During the tests, the acoustic emission (AE) method is utilized to detect micro-scale damage in contact fractures. For monotonic contact loading, we determine the critical contact load when the radial crack initiates. It is found that radial cracks occur outside the contact zone (outside of the impression crater). Next, cyclic contact loading is performed, and it is found that the crack propagates with the increasing number of cycles. This fatigue crack growth can be captured by the AE method. In addition, a finite element method (FEM) is used to elucidate the stress distribution of crack initiation and crack propagation during both indentation loadings. FEM computation with a damage-based cohesive zone model (CZM) is carried out to simulate crack growth during cyclic indentation tests. The cohesive model follows a linear damage-dependent traction-separation relationship coupled with a damage evolution equation. It is found that our computation successfully simulates fatigue crack growth. By using the comprehensive experimental/computational framework, the nucleation process (mechanism) of such a complicated crack system is clarified. This methodology may be useful for examining crack propagation of other brittle materials under both monotonic and cyclic contact loadings.