Modeling of cyclic crack growth

The phenomenon of fatigue of materials is characterized by cyclic loading, where the external thermo-mechanical loads are cycled between low and high values, resulting in a slow degradation with time of the material and structure.

Significant research efforts have been aimed towards experimental investigations, for example to determine the incremental crack growth per cycle.  We are currently interested in developing simulation techniques for investigating the failure evolution of cyclically loaded structures, in particular of multilayered structures. A frequent degradation mechanism associated with failure of multilayered structures consists of growth and coalescence of the interfacial cracks (i.e. cracks between adjacent layers). When a crack reaches a critical length, a part of the layers spalls, challenging the usefulness of the structures. Realistic simulations play a key role in designing a multilayered system, since many aspects of the structure’s behavior in real life conditions can be predicted.

Based on the finite element method, we have developed a modeling frame for simulating the interfacial separation of material structures composed of various constituents (e.g., materials containing inclusions). This modeling frame assumes that the structure analyzed is described as a set of continua and interfaces in a fully parametric manner. Further, the finite element (FE) model is generated automatically and a user prescribed number of loading cycles is simulated. After each computed cycle, the interfaces between different constituents are analyzed and updated. The user can implement various interfacial degradation criteria (considered relevant) based on any quantity available in the FE model (e.g., stress, strain, energy dissipation etc.)

The two figures show the stress fields after a structure has been subjected for cyclic loading: a coating delaminating from a substrate and the interfacial crack growth of a random participle reinforced matrix.