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Subsurface fatigue cracks are a significant issue in large-size case hardened bevel gears. Observation and confirmation of the failure mode is difficult due to the subsurface nature. An onset subsurface crack can grow in fast and sudden increments during operation in applications, such as marine industry. Conducting any repair is difficult and expensive. The purpose of this study is to evaluate the criticality of subsurface cracks when considering long-life applications and service intervals. The study is conducted through numerical analysis based on finite element methods, namely Virtual Crack Closure Technique is used for crack tip modeling. A significant relationship was found between residual stresses and critical cracks. It was also shown that the alignment of an early, onset crack with respect to the gear flank is important when analyzing the criticality of the crack to grow. The study provides understanding to subsurface crack initiated failures in gears, especially, why some cracks propagate to ultimate failure and other do not.
Virtanen et al. (Wed,) studied this question.