Design and analysis of test coupons for composite blade repairs
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abstract
Advancements in composite material technology have spurred an increase in the use of composites in modem rotorcraft structures. In addition to the desirable high strength, low-weight features of these material systems, the enhanced fatigue strength and damage tolerance has made composites particularly attractive for advanced structural applications. Even though these structures are often damaged during service and need repair, composites can be repaired consistently. In order to assure successful repair, it is crucial to be able to predict the strength, life and possible damage modes of a repaired component for reliability and design issues. This paper focuses on the first phase of a composite repair methodology development program where the goal is to develop appropriate test specimens to evaluate computationally and experimentally the effects of static and cyclic loads on a composite blade with a repair site. The first phase addresses the design of the test coupons representative of overlap and scarf precured-patch repairs and their analysis for static loading conditions. A global blade model is used to determine the strain distribution for a given set of loads. A local finite element model which represents the test coupon geometry, is then created with the appropriate boundary conditions. From this local model, overlap and scarf patch models are generated. These models are analyzed under uniaxial compressive and tensile loads. A user subroutine, based on the ultimate stress allowable is incorporated into the analysis to detect the initiation and progression of damage in the adhesive. 1997 Elsevier Science Ltd.
