Computational analysis and two-dimensional tensile tests on single motor grain fins suggest that cracks in fin tips are most likely to originate at the coalescence of a fin end tip radius, with a small radius from the side of the fin. Some manufacturers have also noticed defects formed during casting at the fin tip on the fin axis. The following is an experimental investigation utilizing frozen stress photoelastic models of an existing motor grain geometry in order to clarify stress intensity factor (SIF) values and crack growth paths for cracks emanating from the two above-noted potential critical loci. Comparisons between results from cracks grown from the two loci will be made, suggesting interesting conclusions.

This paper discusses the effects of non-uniform, random particle distribution on damage initiation and growth, leading to short cracks and breakage of particle reinforced composite specimens. A multi-scale technique was employed to model and simulate damage. Damage was described at the constituent material level (i.e. micro-level) and the results were compared qualitatively and quantitatively with experimental observation. Both results agreed well. Non-uniform, random particle distribution yielded sporadic crack initiation and growth within a uniform tensile specimen. No local crack propagated beyond a certain size. Breakage of the specimens was not caused by the continuous growth of a single critical crack. Instead, coalescence of neighbouring sporadic short cracks resulted in breakage of the specimens. Computer simulation indicated that random particle distribution affected the strength of the composite significantly, but as expected, not its effective stiffness. However, if there was a pre-existing crack in the specimen before loading, the effect of the random particle distribution on the initial crack and the strength of the composite was almost negligible.

This paper studied crack initiation in a hard particle reinforced composite with a soft rubber-like matrix material using a numerical technique. The numerical specimen considered had a semi-circular notch with a linearly varying length. The initial crack size occurring at the notch tip was modeled and predicted using a micro/macro-approach along with a damage model. A criterion to predict the initial crack size was proposed based on the size of a localized unstable material zone. Different notch sizes were compared to their initial crack sizes.

Nondestructive acoustic imaging experiments and three dimensional finite element analyses were performed to study the crack-damage interaction phenomenon of a particle reinforced polymeric composite. Effects of damage size and degree of damage on the mode I stress intensity factor and the local stress fields near the crack tip were evaluated and the damage and crack growth behavior were discussed.

Hydrostatic pressure affects the damage growth in a particulate composite. As a result, an analytical model was presented to represent the damage growth in a particulate composite under various hydrostatic pressures. The model was based on a multi-level approach with damage description at the micro-level. A damage theory was presented to describe the material behavior under hydrostatic pressure. The effect of hydrostatic pressure was introduced to the damage theory through the damage function that was assumed to be a function of both deviatoric and volumetric strain energy densities. The predicted stress-strain curves with hydrostatic pressure compared well with the experimental data. Furthermore, the initial crack size at a notch tip was studied with and without hydrostatic pressure. The initial crack size determined from the computer modeling and simulation agreed well with the measured data with or without hydrostatic pressure.