Finite element method simulation of crack propagation in a brittle microcracking solid

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A finite element method simulation of crack propagation was used to study the effects of microcracking at facets as a damage process in brittle composites and the consequence for material toughness. A continuum model for microcracking at grain boundary facets was used in conjunction with the elasticity law. The model accounts for modulus reduction only and neglects residual strain effects. The nonlinear finite element equations were solved incrementally. The solution for each load increment was obtained using a Newton iteration method. Crack propagation was achieved by successive tip node relaxation upon satisfaction of a critical energy release rate criterion. The crack was allowed to propagate by approximately ten times the height of the initial microcrack zone. A substantial increase of the height of the damage zone prior to steady state propagation was observed. The applied stress intensity factor was increased to sustain crack growth, and crack tip shielding occurs as a result of the wake. The amount of toughening was up to 40% in terms of stress intensity factor and was influenced by the parameters of the constitutive law. Stress, strain, and microcrack density distributions near the tip of the steadily growing crack are discussed.