On The Axial Energy Absorption Behaviour Of Composite Tubes With Crush Triggers

With the development of composite manufacturing techniques, carbon fiber reinforced polymer (CFRP) have been widely applied in the aerospace and automotive industries to meet the crashworthy and lightweight design requirements; therefore, their energy absorption characteristics have received great attention in recent years. In this dissertation, the energy absorption capability of CFRP circular tubes is investigated systematically by utilyzing the methodology of experiments combined with numerical simulations. Special attention has been paid to the crush trigger, an important issue affecting the energy absorption of composite structures. The main contents of this dissertation are as follows:(1) Three new crush triggers, called internal-bevel trigger, crown trigger and slot trigger are designed and fabricated at one end of composite tubes. Quasi-static axial compressive tests are conducted to investigate the effect of these triggers on the energy absorption characteristics. Experimental results are compared with energy absorption behaviour of tubes with an external-bevel trigger and without any crush trigger for evaluating the triggering effects.(2) Based on the shape memory effects of Ni-Ti shape memory alloy (SMA) wire, two novel SMA triggers, called snap-ring SMA trigger and cross-winding SMA trigger, are proposed and fabricated for composite tubes. Quasi-static axial compressive tests are conducted to investigate the effects of the SMA triggers on the crashworthiness of composite tubes. It is found that these two SMA triggers can efficiently initiate a stable progressive crushing process and significantly improve the energy absorption capability of composite tubes.(3) Composite tubes with different cross-sectional shapes, including quarter circle, half circle and three-quarter circle, are axially crushed to study the boundary effects on the energy absorption of cylindrical shells. Based on the experimental data of the quarter-circle composite tubes, a semi-empirical analysis method is proposed for predicting the energy absorption of half circle or full circle composite tubes.(4) Taking composite tubes with an external-bevel trigger as an example, an analysis method for the design of crashworthy structures based on elastic-perfectly plastic model is proposed, and the tactics for the determination of equivalent parameters is provided. This numerical modelling strategy requires less computation burden to predict the crashworthiness of composite tubes, and makes it possible to perform the crashworthiness design analysis of full-scale composite aircraft structures with an ordinary personal computer.(5) To model the mid-surface delamination of composite tubes, a two-layer finite element model with the Chang-Chang failure criteria is established. Commericial finite element software LS-DYNA is used in the simulations. The numerical modelling stratregies of external-bevel trigger and slot trigger, as well as the determination tactics of failure parameters for the MAT₀54 composite damage model are also addressed. It is found that the proposed modelling stratregies are effective in simulating the energy absorption characteristics and crushing failure mode of composite tubes.Based on the results reported in the dissertation, some conclusions are drawn. Some issues to be investigated futher are also given.The dissertation was supported by the National Natural Science Foundation of China (50675100).