Analysis And Optimization On The Crushing Performance Of Adhesively Bonded CFRP HAT-shaped Thin-walled Beam

Based on the requirement of weight reduction in automobile body,more and more car companies are paying attention to CFRP(Carbon Fibre Reinforced Plastics)vehicle body structure due to the high specific modulus and specific energy absorption,low density and ease of manufacture,etc.Thus the crashworthiness of CFRP vehicle body is becoming the research focus in recent years.Research on the optimization of cross-section dimensions and ply thickness for HAT-shaped thin-walled beam was carried out in this thesis through a combined experiment-simulation-optimization design method.The related work is described as follows:(1)CFRP HAT-shaped thin-walled beam and samples were manufactured with prepreg USN15000 through hot press forming in a specially-designed mould;CFRP samples were tested to obtain the basic mechanical properties for the subsequent modelling procedure according to ASTM testing standards;The adhesively bonded CFRP beam was then tested under quasi-static axial crushing load to obtain load-displacement curves as well as failure morphology.(2)The axial crushing process of CFRP thin-walled beam was numerically modelled in LS-DYNA.Chang-Chang failure criterion was adopted to determine the failure in MAT54 material model;Tiebreak contact was inserted between the outer layer and inner layer of CFRP(i.e.interlaminar resin)as well as the structural adhesive,considering a two-layer shell.(3)Based on the effective FE modelling results,the parameters of the cross-sectional dimensions including L1 and L2 and the ply thickness of 0o,45o,-45o,90o were used as the optimum variables,with the lowest manufacturing cost and the highest energy absorption as the optimization target;For the purpose of establishing a Radial Basis Functions(RBF)model,the Optimal Latin Hypercube Design(Opt LHD)was used to selected sample points in the constrained design space.Finally,Non-Dominated Sorting Genetic Algorithm-II(NSGA-Ⅱ)combined with RBF model was used to optimize the model.The results showed that no crack was observed in the adhesive layer due to the fact that the failure strength of the structural adhesive is higher than that of the resin,which signifies that adhesive bonding is an effective way for CFRP vehicle body connection.The kinematic energy was well absorbed by interlaminar failure,fibre fracture and bending during the crush of CFRP HAT beam.The two-layer finite element model using MAT54 material model is an effective way to predict the fracture behaviour of CFRP HAT beam.The numerical simulation showed good agreement with the experiment in the aspect of initial peak load and energy absorption property,which means that the finite element model has high accuracy.Finally,the optimization model combined RBF and NSGA-Ⅱ successfully reduced the mass and Cost and increased EA and SEA of CFRP HAT beam,thus the goal of optimization was achieved.This study can provide an effective evaluation method for the design and application of CFRP HAT-shaped beam in vehicle body structure.