Dynamic Axial Crush of Automotive Rail-Sized Composite Tubes: Part 2 — Tubes With Braided Reinforcements (Carbon, Kevlar®, and Glass) and Non-Plug Crush Initiators

Abstract

This paper documents the braided reinforcement portion of a successful fundamental study of the dynamic axial crush of automotive rail-sized composite tubes. Braided reinforcements were comprised principally of carbon fiber but also of Kevlar® and E-glass and combinations of the three. Fourteen different braids were used, six of which were tri-axial and the remainder bi-axial. Tubes were manufactured using Resin Transfer Molding (RTM) with processing and molding techniques that are suitable for the low cost high volume needs of the automotive industry. Braids were obtained as continuous rolls of tubular sock-like material and pulled over metal mandrels one ply at a time. Carbon fiber tow sizes ranged from 6k to 48k. Dow Derakane 470 vinylester resin was used for all tubes. Tube geometry, a 88.9×88.9 mm square cross section with 2.54 mm thick walls, approximated that of the first 500 mm of the lower rail of a typical mid-size vehicle. Note in particular that tube wall thickness was fixed at a single value in this study. A 45° bevel on the outside edge of the lead end of each tube served as the crush initiator. In total 71 dynamic axial crush tests were conducted. In terms of important findings, consistent with the woven fabric portion of this program [1], desirable dynamic axial crush response was demonstrated for RTM’d automotive rail-sized carbon fiber reinforced tubes. For almost all parameter configurations, the tubes exhibited stable and progressive crush with a reasonably flat plateau force level and an acceptable crush initiation force, i.e. one that can be withstood by the backup structure. Additionally, crush debris from such tubes was found to neither contain objectionable sharp brittle splinters nor pose a health risk. Displacement average values of dynamic axial crush force ranged from 11.88 to 26.51 kN and values of SEA (specific energy absorption) ranged between 10.42 and 22.44 kJ/kg. In terms of parameter effects, the fiber type and reinforcement architecture were found to be capable of more than doubling/halving the dynamic axial crush force and SEA.