The effects of off-axis loading on the compression after impact strength of quasi-isotropic face sheet honeycomb core sandwich structure

This study presents experimental results of compression after impact (CAI) testing of aluminum honeycomb core sandwich structure with face sheets made of co-cured T1100/3960 quasi-isotropic carbon/epoxy when tested at +22.5 degrees and -22.5 degrees with respect to the 0 degrees fibers. In a previous study examining the CAI strengths of honeycomb sandwich structure, it was found that specimens had different CAI strengths, based on a [-45/90/+45/0]S layup, depending on whether they were tested in the 0 degrees direction (face sheet layup of [-45/90/+45/0](S)) or 90 degrees direction (face sheet layup of [+45/0/-45/90](S)). The CAI strength results showed that the specimens tested in the 90 degrees direction had a 19% drop in CAI strength compared to specimens tested in the 0 degrees direction. This was attributed to the 0 degrees load bearing plies in the 0 degrees direction specimens being tucked in at the center of the specimen thus providing more stability against microbuckling. This raised the question as to what CAI strength would specimens tested at +22.5 degrees (face sheet layup of [-22.5/-67.5/+67.6/+22.5](S)) and -22.5 degrees (face sheet layup of [-67.5/+67.5/+22.5/22.5](S)) have compared to specimens tested in the 0 degrees and 90 degrees direction. Results presented in this study show that the specimens loaded at +22.5 degrees and -22.5 degrees have a similar average CAI strength compared to the specimens loaded in the 0 degrees direction. The specimens loaded in the 90 degrees direction exhibit 16% lower average CAI strength. Additional specimens were tested in the +45 degrees direction to put the 0 degrees load bearing fibers on the outside of the specimen to see if this would decrease the strength as has been documented for undamaged strength. These specimens have average CAI strength values between the 0 degrees direction average CAI strength values and the 90 degrees direction average CAI strength values.

Automated summary

This study presents experimental results of compression after impact (CAI) testing of aluminum honeycomb core sandwich structure with face sheets made of co-cured T1100/3960 quasi-isotropic carbon/epoxy at different loading angles. The study found that the specimens loaded at +22.5 degrees and -22.5 degrees had similar CAI strength compared to the specimens loaded in the 0 degrees direction, while the specimens loaded in the 90 degrees direction had 16% lower CAI strength. Additional specimens loaded at +45 degrees showed intermediate CAI strength values between the 0 degrees and 90 degrees direction.