A semi-empirical method is presented to assess battle damage due to small arms fire to composite rotor blades. The assessment method includes the development of a specialized coupon that captures typical battle damage failure modes at subscale. Damage tolerance coupon testing yields damage initiation and damage growth rate fatigue curves that are the backbone of a methodology to predict the performance of battle damaged blade spars. The coupon test based method is compared to traditional analytical methods, thereby underscoring conservatisms associated with the purely analytical approach. In addition to a damage tolerance assessment in fatigue, a static assessment is also provided. Tension and compression analysis, including rotor blade spar buckling, is used to define a potential lower structural limit for a single application of limit load that may occur under extended operations after sustaining battle damage. The method developed is subsequently compared to full scale blade static and fatigue component test data. As a result of this effort, key analysis and test data are available for the first time to support continued use of composite battle damaged rotor blades, enabling critical resources to remain available to the armed services.
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