A novel ductile-brittle damage law for the numerical simulation of low cycle fatigue of a Al2024-T351 Aluminium alloy in its related S-direction is proposed. To illustrate the predictive capabilities of the brittle damage model, a benchmark example is presented. Some material parameters have been calibrated to Al2024 considering fatigue crack growth.

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The current paper deals with the assessment and the numerical simulation of low cycle fatigue of an aluminum 2024 alloy. According to experimental observations, the material response of Al2024 is highly direction-dependent showing a material behavior between ductile and brittle. In particular, in its corresponding (small transversal) S-direction, the material behavior can be characterized as quasi-brittle. For the modeling of such a mechanical response, a novel, fully coupled isotropic ductile-brittle continuum damage mechanics model is proposed. Since the resulting model shows a large number of material parameters, an efficient, hybrid parameter identification strategy is discussed. Within this strategy, as many parameters as possible have been determined a priori by exploiting analogies to established theories (like P' law), while the remaining free unknowns are computed by solving an optimization problem. Comparisons between the experimentally observed and the numerically simulated lifetimes reveal the prediction capability of the proposed model.

One of the important considerations in the design of components is the estimation of cyclic lifetime and analysis of the critical regions of a construction. The local approach of lifetime estimation using continuum damage mechanics (CDM) has shown a great potential in predicting material failure not only for monotonic, but also for fully reversed loadings. In this paper, the CDM model of Desmorat-Lemaitre [1] was investigated regarding the prediction of cyclic lifetime. A series of experiments on tension specimens with different geometries were performed. The latter were used for the determination of model parameters as well as for the validation of the predictive capability of the model.

Detection of cracks in Al2024 T351 specimens subjected to low cycle fatigue loading by a certain non-destructive inspection technique is demonstrated. In the experimental phase of the study, notched round specimens were fatigue loaded. The tests were performed at different constant strain amplitudes at room temperature. For identifying the crack initiation loci, the specimens were removed from the testing machine after a certain number of cycles and were non-destructively inspected via X-ray technique. Pictures were taken successively while incrementally turning the sample. The reconstructed data were visualized via software (VGStudio MAX 2.1) to obtain a 3D image of the specimen, showing all the details of its inner structure. By taking "virtual" slices from the data, quantification of microstructural properties was done using classical methods. This allowed verifying some frequently mentioned statements concerning the low cycle fatigue behavior of high-strength aluminum alloys. Furthermore, new findings related to the tri-axiality dependence on the resulting fracture process and those related to damage initiation caused by decohesion were also discovered.