Damage Resistance Characterization of Sandwich Composites Using Response Surfaces

The coupled influence of material configuration (number of facesheet plies, core density, core thickness) and impact parameters (impact velocity and energy, impactor diameter) on the impact damage resistance characteristics of sandwich composites comprised of carbon-epoxy woven fabric facesheets and Nomex honeycomb cores was investigated using empirically based quadratic response surfaces. The diameter of the planar damage area associated with TTU C-scan measurements and the peak residual facesheet indentation depth were used to describe the extent of internal and detectable surface damage, respectively. Estimates of the size of the planar damage region correlated reasonably well with experimentally determined values. For a fixed set of impact parameters, estimates of the planar damage size and residual facesheet indentation suggest that impact damage development is highly material and lay-up configuration dependent. Moreover, those combinations of material system and impact parameters leading to the maximum estimated internal damage do not correspond to those that result in the greatest facesheet indentation. Hence, blunt object impacts may result in appreciable damage that is not amenable to visual inspection. These efforts may facilitate sandwich panel design by establishing relationships between material configuration and impact parameters that lead to improved damage tolerance/ resistance.