Practical aspects in automatic crack growth analysis of a drive system gear

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Practical aspects in automatic crack growth analysis of a drive system gear

Sane, Ashok D. / Larchuk, Terry J. / Curtin, Thomas C.

The safe life approach is conventionally used in the rotorcraft industry to determine the fatigue life of drive system or other fatigue critical components. However, the current trend is to place an increasing emphasis on the fatigue life by damage tolerance/crack growth analysis. While the fatigue crack growth analysis of many components can be performed with simplified programs with built-in geometries/sections, a full 3D crack fatigue growth analysis is needed in case of components (especially the rotorcraft drive system components) with complex geometries and complex loading. The life or the remaining life (for in-service cracked components) can be established with 3D crack growth analysis. Inspection intervals can also be established for cracked in-service components for safe operation. Such analyses require not only the crack length vs. flight hours but also the crack path to establish critical crack lengths. Software capable of performing the automatic fatigue crack growth analysis is required for efficiency and expeditiousness of the analytical process. The BEASY boundary element analysis program developed by CMI (Computational Mechanics Inc.) is used by Boeing Rotorcraft for performing 3D crack growth analysis. This paper presents and discusses practical aspects of the automatic fatigue crack growth analysis of a drive system gear. The issues involved in automatically predicting the crack growth path and growing the crack incrementally are discussed including new features and additions implemented in BEASY software.