On Crashworthiness Characteristics Of MetAL/CFRP Hybrid Thin-walled Structures

Lightweight design by appling lightweight materials is one of the key technologies in increasing energy efficiency,reducing air pollution,extending range capability and improving vehicle crashworthiness.Carbon fibers reinforced plastics(CFRP)have been introduced in vehicular engineering,and a remarkable lightweight efficiency has been obtained thanks to their higher specific strength and specific energy absorption capacity to the weight.Notwithstanding proven lightweight feature,CFRP structures are still of some shortcomings to be served as a crashworthy structure.First,the cost of carbon fiber is rather high.Second,CFRP are generally brittle in nature and as a result,CFRP structures may yield unstable failure when subjected to impact loading,which is not ideally conducive to energy absorption.Therefore,for cost-performance consideration,metAL/CFRP hybrid structures comprised of metals and composites are recently introduced as an effective alternative,which combines the low density and high strength of CFRP materials with low cost and high plasticity of metallic materials for crash protection structures.Nevertheless,there has been barely reported specifically addressing the crushing behaviors of hybrid structures,and there are many difficult problems needing to be deeply discussed.This paper lucubrates the aluminum/CFRP hybrid structures(AL/CFRP)and their applications into car body,and the following research works are performed in this paper: Firstly,a constitutive model and modeling approaches of CFRP are developed and then verified by the experiment results.Furthermore,the tensile response and bending behaviours of AL/CFRP hybrid laminates and crashworthiness characteristics of AL/CFRP hybrid tubes are investigated experimentally and numerically.Finally,a lightweight design of AL/CFRP hybrid front longitudinal beam is further studied.The main research works are summarized as follows:(1)The constitutive model of CFRP and modeling approaches.Based on mechanics characteristics and failure modes of CFRP and the continuum damage mechanics theory,a stacked shell model is developed to simulate the damage behaviours of CFRP.The damage model is consisted of elastic stress-stain ralation,damage criterions,plastic deformation under shear loading and evolution laws for different failure modes.Additionally,the obtaining method of the model parameters is also presented.Finally,a comparison between the single layer shell model and the stacked shell model is conducted,which is expected to provide some insights into numerical investigation of AL/CFRP hybrid tubes.(2)Experimental and numerical investigation into tensile response and bending behaviours of aluminum,CFRP,AL/CFRP hybrid plates.Firstly,according to tensile and bending tests,mechanics properties of AL/CFRP hybrid laminates are explored by comparing with aluminum and CFRP counterparts,and the effects of CFRP thickness and relative positions are also investigated.Additionally,based on abovementioned numerical models,a parametric study is further performed to investigate the effects of relative positions,thickness of aluminum layer,stacking sequence and thickness of CFRP layers on tensile response and bending behaviours of AL/CFRP hybrid laminates.It is worth noting that the study in tensile response and bending behaviours of AL/CFRP hybrid laminates is able to provide the basis for investigation of crashworthiness of AL/CFRP hybrid tubes.(3)Experimental and numerical investigation into crashworthiness characteristics of aluminum,CFRP,AL/CFRP hybrid tubes under different loading rates.Firstly,according to axial quasi-static and dynamic compression tests,crushing characteristics of AL/CFRP hybrid tubes are explored by comparing with aluminum and CFRP counterparts,and the effects of loading rates,thickness of CFRP layers and relative positions are also investigated.Furthermore,a parametric study is further performed numerically to investigate the effects of thickness of aluminum tube,stacking sequence of CFRP layers and the interfacial strength on crashworthiness of AL/CFRP hybrid tubes.(4)Lightweight design of AL/CFRP hybrid front longitudinal beam.This thesis investigates crashworthiness of aluminum,CFRP,AL/CFRP hybrid front longitudinal beam,and the advantages of hybrid front longitudinal beam are explored from the perspectives of structural crashworthiness,lightweight efficiency and material costs.In addition,an optimization algorithm using orthogonal arrays in discrete design space is implemented to obtain optimal design of AL/CFRP hybrid front longitudinal beam.