Design and application of a quasistatic crush test fixture for investigating scale effects in energy absorbing composite plates

Abstract

A crush test fixture for measuring energy absorption of flat plate specimens from an earlier study was redesigned to eliminate the problem of binding of the load transfer platen with the guide posts. Further modifications were to increase the stroke, and combine the two scaled test fixtures into one. This new crush test fixture was shown to produce load displacement histories exhibiting well developed sustained crushing loads over long strokes.

An experimental study was conducted on two material systems: AS4/3502 graphite/epoxy, and a hybrid AS4-Kevlar/3502 composite. The effect of geometric scaling of specimen size, the effect of ply-level and sublaminate-Ievel scaling of the stacking sequence of the full scale specimens, and the effect of trigger mechanism on the energy absorption capability were Investigated.

The new crush test fixture and flat plate specimens produced peak and sustained crushing loads that were lower than obtained with the old crush test fixture. The trigger mechanism used influenced the specific sustained crushing stress (SSCS). The results of this study indicated that to avoid any reduction in the SSCS when scaling from the 1/2 scale to full scale specimen size, the sublaminate-level scaling approach should be used, in agreement with experiments on tubes. The use of Kevlar in place of the graphite 45° plies was not as effective a means for supporting and containing the 0° graphite plies for crushing of flat plates and resulted in a drop in the SSCS. This result did not correlate with that obtained for tubes.