Research On Mechanical Properties And Failure Mechanism Of Basalt Fiber Reforced Composite Adhesive Joint

The lightweight technology of automobiles has great significance to solve the problems of energy saving and environmental protection.Recently,the use of natural fibers as reinforcement materials to realize lightweight structures has attracted widespread attention.Basalt fiber reinforced composite material(BFRP)has gained more and more attention as an alternative material with low price and excellent performance.However,the problem of connecting composite materials with other materials has become a huge challenge hindering its large-scale application.Adhesive technology was extensively used in the bonding of FRP due to its advantages of strong mechanical properties and well adaptability.Recently,some scholars have studied the adhesive joints of carbon fiber reinforced composites(CFRP),but there is a lack of comprehensive and systematic research on the adhesive joints of BFRP.Therefore,it is necessary to research systematically in order to guide and promote the application of BFRP in automobile.In this study,experiments and analyses have been executed on the mechanical properties,failure behaviors and service performance of BFRP adhesive joints by means of experiments,simulations and microscopic characterization.The main research contents and conclusions are as follows:(1)The effects of adhesive properties and adherend materials on the mechanical behaviors were analyzed by experiments.A prediction model was established to predict the effects of three process parameters(thickness of aluminum alloy plate,length of overlap zone,and the angle between loading direction and basalt fiber)on mechanical properties of the joint based on response surface analysis.The results showed that the strength and stiffness of the joint depend on the yield strength of the adhe rend.The BFRP-BFRP adhesive joint had higher peak load,while the BFRP-Al adhesive joint had higher stiffness.The brittle adhesive could improve the strength and fracture absorption energy of the adhesive joint.A prediction model of shear strength τ was established based on response surface analysis(RSM),and the interval of the optimum parameter was predicted.The coupling effect of process parameters was analyzed according to the model.The fiber direction was negatively correlated with the joint strength,while the length of the overlap zone was positively correlated with the thickness of the aluminum alloy substrate.(2)Based on the bilinear cohesive constitutive and the traction separation hybrid model,a two-dimensional finite element model of the adhesive joint was established and compared with the failure process recorded by the digital image correlation(DIC)technology.The accuracy of the model was verified by the test results.The evolution law of damage variable,stress and strain field was analyzed.The effects of different materials,adhesive properties and different parameters on failure behaviors of adhesive joints were revealed.The results showed that the two-dimensional finite element model could accurately simulate the mechanical properties,stress and strain distribution of BFRP adhesive joints.(3)The service performance and failure mechanism of BFRP joint s under high speed shear and neutral salt spray corrosion conditions were studied by DIC,SEM,EDS and other technical methods.The results showed that a positive correlation existed between the loading rates and strength.At high loading rates,stress waves were generated and multiple peak appeared.The different loading rates affected the failure behavior of the joints.The failure modes changed from the aluminum alloy failure to the hybrid failure mode.The ratio of the thin-layer cohesive failure increased with the increase of loading rates and the failure displacement also decreased.The maximum peeling strain increased,and the position of initial cracks shifted to the edge of the aluminum alloy plates.On the other hand,the adhesive had a well blocking effect on the salt spray solution.With the time of corrosion increasing,the joint corrosion process accelerated.After 20 days of corrosion,the peak load of BFRP-Al joints decreased by16.2%,and the peak load of BFRP-BFRP joint decreased by 9.5%.The salt spray droplets infiltrated into the center of the adhesive layer from the side edge and both ends of the over-lap zone.The pitting holes formed on the surface of the aluminum alloy,destroying the interface bonding effect and increased the ratio of the adhesive failure.