| In the long-term service process of automobiles,on the one hand,the applied bonded structure will often be in different harsh working conditions.As a kind of polymer material,the mechanical properties of adhesive and composite epoxy resin are significantly affected by the service environment(water,temperature,etc.).On the other hand,when the bonded structure of composite materials is subjected to frontal impact or lateral impact,the strain rate of the material will affect the bearing capacity of the structure.Therefore,it is of great significance to carry out laboratory aging tests to evaluate the effects of aging time and loading rate on mechanical properties of bonded structures.The effects of joint form,hygrothermal aging and loading rate on mechanical properties of CFRP/aluminum alloy joints were studied.By analyzing the failure load,failure mode and microstructure of the joint,the influence mechanism of single factor on CFRP/aluminum alloy bonded joint and bonded-riveted joints was revealed.On this basis,the influence rule and mechanism of hygrothermal aging time and quasi-static loading rate on CFRP/aluminum alloy bonded joints and CFRP/aluminum alloy bonded-riveted joints were studied by comparing the aluminum alloy/aluminum alloy bonded joints and aluminum alloy/aluminum alloy bonded-riveted joints.Finally,through the impact test of CFRP/aluminum alloy joints,the influence rule and mechanism of hygrothermal aging on the impact performance of CFRP/aluminum alloy joints were studied.The details are as follows:Firstly,the lap-shear tests of CFRP/aluminum alloy bonded joints and bonded-riveted joints with three adhesives(Araldite~?2015,Araldite~?AV138M,Devcon 14270)at two loading rates were designed.The failure mechanism was explained by combining the macroscopic failure mode and microscopic morphology of the joints.A typical adhesive,Araldite~?2015,was selected for further tests to obtain the mechanical properties of the CFRP/aluminum alloy bonded joints and bonded-riveted joints with6 loading rates.Secondly,the hygroscopic properties of CFRP/aluminum alloy joints and the bonded-riveted joints under typical hygrothermal environment were tested.The hygroscopic rate of the joints was obtained.By means of lap-shear test and SEM test of the joints after equilibrium hygroscopicity,the influence mechanism and rule of hygrothermal aging on the mechanical properties of CFRP/aluminum alloy bonded joints and bonded-riveted joints were analyzed.Thirdly,on the basis of above research,this paper select five hygrothermal aging cycles to conduct hygrothermal aging treatment for CFRP/aluminum bonded joint,CFRP/aluminum bonded-riveted joint,aluminum alloy/aluminum alloy bonded joint and aluminum alloy/aluminum alloy bonded-riveted joint.Three loading rates were selected to conduct lap-shear test on the joints.The influence of hygrothermal aging cycles and loading rates on CFRP/aluminum alloy bonded joint,CFRP/aluminum alloy bonded-riveted joint,aluminum alloy/aluminum alloy bonded joint and aluminum alloy/aluminum alloy bonded-riveted joint were studied.By analyzing the failure load and failure mode of the joints,the influence mechanism of the hygrothermal aging cycles and loading rates on the joints were studied.Fourthly,a special impact fixture was designed and processed.Five hygrothermal aging cycles were selected to conduct hygrothermal aging tests on CFRP/aluminum alloy bonded joints and CFRP/aluminum alloy bonded-riveted joints.By analyzing the failure load and failure mode of the mentioned joints,the influence of the hygrothermal aging cycles on the impact performance of CFRP/aluminum alloy joints was analyzed.In this paper,the mechanical properties of CFRP/aluminum alloy joints with different hygrothermal aging cycles and loading rates were studied by means of the designed fixture and test method.The research results of this paper can be used as a basic technical reference and support for the design and application of adhesive structure in body connection technology. |
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