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.

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