A three-dimensional damage percolation model
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A combined experimental and analytical approach is used to study damage initiation and evolution in three-dimensional second phase particle fields. A three-dimensional formulation of a damage percolation model is developed to predict damage nucleation and propagation through random-clustered second phase particle fields. The proposed approach is capable of capturing the three-dimensional character of damage phenomena and the three stages of ductile fracture, namely void nucleation, growth, and coalescence, at the level of discrete particles. The experimental work focuses on the acquisition of second phase particle field data and measurement of damage development during plastic deformation. Two methods of acquisition of three-dimensional second phase particle fields are considered. The first method utilizes three-dimensional X-ray tomography for the acquisition of real microstructural data. The second method involves statistical stereological reconstruction of second phase particle fields from two orthogonal metallographic sections of the as-received material. The reconstruction method is also used to introduce parametric variation of key microstructural parameters to support a study of the effect of particle clustering and second phase constituent content on formability. An in situ tensile test with X-ray tomography is utilized to quantify material damage during deformation in terms of the number of nucleated voids and porosity. The results of this experiment are used for both the development of a clustering-sensitive nucleation criterion and the validation of the damage percolation predictions. The three-dimensional damage percolation model is developed based on the acquired second phase particle fields and the damage evolution characterization using the results of the in situ tensile test. Void nucleation, growth, and coalescence are modelled within the considered second phase particle field. The damage percolation model is coupled with a commercial finite element code, LS-DYNA. The damage percolation model is applied to simulate the in situ tensile test as well as to study bendability. In particular, the effect of second phase particle field parameters on formability is examined. The volume fraction of Fe-rich and Mg2Si particles is shown to be of critical importance in controlling the formability of aluminum alloy AA5182. This study of microstructural heterogeneity using the damage percolation model has resulted in a more fundamental understanding of the processes of material degradation during deformation in the presence of second phase particles. The results of the study indicate a significant effect of second phase content on formability and provide practical recommendations to improve material formability in future alloy designs.