Compression-after-impact strength estimates for finite width sandwich panels
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Physically-motivated finite element estimates of compression-after-impact residual strength are developed for impact-damaged sandwich composites comprised of woven-fabric graphite-epoxy facesheets and Nomex honeycomb cores. Results from non-destructive inspection of damaged sandwich panels are used to establish initial conditions for damage in the numerical analysis. Material and geometric non-linear finite element analyses are performed that account for progressive failure of both facesheet and core. The effect of finite specimen size on residual strength is investigated using both an equivalent inclusion idealization of the damaged facesheet region as well as a "seeded damage" technique. In the latter approach, the stiffness properties of a number of randomly selected facesheet elements within the damaged region are eliminated in order to obtain a desired average stiffness reduction. In this fashion, progressive failure of facesheets containing varying degrees impact damage may potentially be simulated using a variety of standard first ply failure criteria. Numerical estimates of the impacted facesheet surface strains correlate very well with experimentally measured values obtained using the ARAMIS® three-dimensional optical imaging system. Furthermore, residual strength predictions correlate relatively well with experimental observations.
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