Fatigue crack initiation and propagation in re-entrant auxetic cellular structures

The investigation of the fatigue behaviour of an auxetic cellular structure made of Al-alloy 7075-T651 is presented in this study. The complete fatigue process of the analysed cellular structure is divided into the crack initiation (N-i) and crack propagation (N-p) period, where the total fatigue life (N-t) is defined as the sum of N-i and N-p. The crack initiation period, N-i, is determined using the strain life approach in the framework of the Fe-Safe computational code, where elastic-plastic numerical analysis is performed to obtain the total strain amplitude in the critical cross-section of the analysed cellular structure. The number of stress cycles, N-p, required for the fatigue crack propagation from the initial to the critical crack length is also determined numerically using a finite element model in the framework of the Abaqus computation FEM code. The Maximum Tensile Stress (MTS) criterion is considered when analysing the crack path inside the cellular structure. Finally, experimental fatigue testing has also been performed to validate the computational results.