Investigating the crashworthiness characteristics of carbon fiber/epoxy tubes

Abstract

As composite materials are integrated into the primary structures of today’s vehicles, it is important that their crashworthiness characteristics are well understood. This research focuses on the energy absorption mechanisms that occur in composite tubes during axial crushing and how those mechanisms are affected by material, geometric, and testing variables.

A literature review was completed on composite tube testing for crashworthiness applications to provide background information on the subject. Methods of measuring crashworthiness performance were introduced as well as the three broad classifications of failure modes that occur during axial crushing. Fiber and matrix type, preform type, specimen geometry, trigger type, and strain rate were all found to have a significant effect on the amount of energy composite tubes absorbed. It was observed that several of these variable effects on carbon fiber prepreg/epoxy tubes were not well agreed upon, allowing for additional investigation.

Based on observations from the literature an investigation into strain rate and triggering effects was performed on IM7/8552 prepreg tubes. Three layups were designed to represent the three broad classifications of failure modes. Circular and square cross tubes were used to test the effect of bevel and tulip triggers at both quasi-static and dynamic test speeds for all failure modes. Circular cross sections were found to be more efficient that square cross sections when comparing similar test variables. Tulip triggers were found to increase energy absorption for the brittle fracture and fiber splaying failure modes at quasi-static test speeds. Strain rate effects varied widely across layups, trigger types, and cross sectional shapes and were attributed to changes in failure mode. It was found that the brittle behavior of the 8552 matrix at high strain rates was responsible for this behavior.