Rocket motor grain consists of rigid particles embedded in a soft, rubbery matrix. The ingredients are chosen to maximize the burning properties, but when cracks develop during curing or storage, burn properties are altered. The present study was directed towards a study of the loss of the inverse square root singularity in the neighborhood where a crack intersects the free surface in simulated motor grain. Experiments were conducted on both cracked simulated pure binder and cracked simulated motor grain and algorithms were developed for computing fracture parameters from the data. Severe crack tip blunting prior to crack growth initiation was observed in the simulated motor grain which required a modification of the algorithm used for single phase materials. Efforts to determine the dominant eigenvalue after crack growth have met with limited success to date due to increasing data scatter.

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