A 'unified' and a (ΔK+·Kmax)1/2 crack growth models for aluminum 2024-T351

The 'unified' approach presented by Vasudevan and Sadananda is used to build an empirical crack growth model for aluminum 2024-T351, based on experimental results published in the literature. This model depicts the existence of two threshold parameters, ΔKth* and Kmaxth*, and provides a method to describe crack growth without any reference to crack closure theories. The crack growth process (crack length as a function of load cycles) is solved numerically. A lower limit of initial crack length a* is found, below which cracks do not propagate. Results were compared to a model based on Walker-Kujawski (ΔK+·Kmax)0.5 parameter, and a very good agreement was found. Some contradiction was found in some of the published experimental results. The results used for curve fitting in the NASGRO program exhibit a slope (of the da/dn vs. ΔK curves) smaller than those described in Kujawski works, and therefore, the NASGRO data yields higher number of cycles to failure. The method described can be used to build empirical crack growth models for other materials, for which experimental data exists, thus providing a practical tool for structures' designers. The model described here will be used in the future to also describe the probabilistic behavior of the crack growth.