Response surface characterization of the mechanical behavior of impact-damaged sandwich composites

In this research, Response Surface Methodology (RSM) is employed to characterize the influence of material configuration on the damage tolerance and residual strength characteristics of sandwich composites. Test specimens used were comprised of carbon-epoxy woven fabric facesheets, and Nomex honeycomb cores. The ranges of the material configuration used are typical of those employed in aircraft applications. A series of carefully selected tests were used to isolate the coupled influence of various combinations of the number of facesheet plies, core density, and core thickness on the damage formation and residual strength degradation due to normal impact. Response surface estimates suggest that impact damage development and residual strength degradation are highly material and lay-up configuration dependent. Increasing the core thickness for a specific number of facesheet plies resulted in decreasing the impact damage, whereas increasing the number of facesheet plies for a given core thickness resulted in enhancing the residual strength. The derived damage tolerance and residual strength models can lead to a better understanding of the mechanical behavior of the impact-damaged sandwich composites, and hence improve their design and expand their applications.