Constraint Effects on Energy Absorption in Unidirectional PMC Tubes

Abstract

An investigation was carried out to understand the effect of an external constraint on the failure modes and energy absorption capability of unidirectional polymeric composite (PMG) tubes. The constraint was a steel ring that was tightened on the outside of the tube. This ring could slide during tube crushing. The tightness of the ring was determined using a strain gage positioned on the ring. The effect of the constraint was shown to depend on the initial position of the ring along the tube. The study was performed on fiberglass/polyester tubes and the results showed that the external constraint not only can improve the specific energy absorption of the tubes, but also can reduce significantly the undesired high initial peak loads. A nonlinear finite element approach was used to model the fundamental failure modes that dominate the energy absorption of the tubes with an external constraint. These modes including delamination and longitudinal crack propagation (splitting), were modeled using the finite element code ABAQUS. A user friendly FOR-TRAN subroutine was implemented to the code to incorporate the material failure model for predicting the fiber/matrix failures that occur as crushing is experienced by the tube. The predicted model results compared well with the experimental data for the various crushing stages of the polyester tubes.