Advanced analysis of crack tip plastic zone under cyclic loading

The different types of plastic zones found at a crack tip under cyclic loading of a commercially available aluminium alloy are studied based on 3-dimensional finite element simulations and mechanical testing. During the experiments, the local strain field at the crack tip is computed based on digital image correlation analysis of the specimen's surface under different load levels. The simulations with an elastic-plastic material model (bilinear isotropic hardening) predict the experimental surface strain field at the crack tip pretty well. The combination of experimental results and finite element analysis allows for the accurate distinction into monotonic and cyclic plastic zone, and moreover, into backward cyclic plastic zone and forward cyclic plastic zone. Furthermore, it is possible to calculate the energy accumulation ahead of the crack tip which represents a very useful quantitative measure for the analysis of local fatigue damage accumulation inside the plastic zone ahead of a crack tip.