Characterization of the Effect of Material Configuration and Impact Parameters on Damage Tolerance of Sandwich Composites 2006-01-2443

A series of carefully selected tests were used to isolate the coupled influence of various combinations of the number of facesheet plies, impact energies, and impactor diameters on the damage formation and residual strength degradation of sandwich composites due to normal impact. The diameter of the planar damage area associated with Through Transmission Ultrasonic C-scan and the compression after impact measurements were used to describe the extent of the internal damage and residual strength degradation of test panels, respectively. Standard analysis of variance techniques were used to assess the significance of the regression models, individual terms, and the model lack-of-fit. In addition, the inherent variability associated with given types of experimental measurements was evaluated. Response surface estimates of the size of the planar damage region and compressive residual strength as a continuous function of the face sheet thickness and impact parameters correlated reasonably well with experimentally determined values. The regression results suggest that impact damage development and residual strength degradation is highly face sheet configurations and impact parameters dependent. In general, for the mid to high number of face sheet plies, the estimated planar damage diameter increases with increasing impact energy, or increasing impactor diameter. An increase in the impact energy generally resulted in a decrease in the compression after residual strength for those cases where face sheet penetration was likely not a concern. 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 relationships between material configuration and impact parameters that lead to improved damage tolerance/resistance.