Abstract
Abstract : The influence of material configuration and impact parameters on the damage tolerance characteristics of sandwich composites comprised of carbon-epoxy woven fabric facesheets and Nomex honeycomb cores was investigated using empirically based response surfaces. A series of carefully selected tests were used to isolate the coupled influence of various combinations of the number of facesheet plies, core density, core thickness, impact energy, impactor diameter, and impact velocity on the residual strength degradation due to vertical impact. The ranges of selected material parameters were typical of those found in common aircraft applications. Quadratic response surface estimates of the compressive residual strength as a continuous function of sandwich configuration and impact parameters did not correlate as well as impact resistance because of bifurcations between failure modes. For a fixed set of impact parameters, regression results suggest that impact damage development and residual strength degradation is highly sandwich configuration dependent. Increasing the number of facesheet plies and the thickness of the core material resulted in the greatest improvement in the damage tolerance characteristics. An increase in the impactor diameter and impact energy results in a significant decrease in the estimated residual strength, particularly for those sandwich panels with thicker facesheets. The effects of impact velocity on damage formation and loss of strength were also addressed. The developed response surfaces for the compressive residual strength may have limited use, particularly as the measured data at low- energy impact levels, small impactor diameter, and thin facesheets exhibit significant scatter. Employing the methodology outlined here, it may be possible to tailor sandwich composite designs in order to obtain enhanced damage tolerance characteristics over a range of expected impacts. Such efforts may facilitate sandwich panel design by establishing
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