| Automobile lightweight technology is still in the development stage,lightweight materials such as aluminum alloy and CFRP(carbon fiber reinforced plastic)can not only meet the use requirements,but also achieve the lightweight effect,which is gradually favored by automobile enterprises.Compared with other connection technologies,the significant advantage of bonding is reflected in the connection between metal and non-metallic materials.Adhesives and composites are sensitive to temperature changes,and their mechanical properties will change under the short-term and long-term action of temperature.At the same time,in the hygrothermal environment for a long time,the bonding material and interface will be affected by environmental aging,resulting in performance degradation,early failure of bonding joints and potential safety hazards.To reduce the influence of hygrothermal aging on the bonding joint,sealing treatment can be used to reduce the diffusion of environmental moisture in the bonding material and interface.Therefore,this paper takes CFRP-aluminum alloy single-double lap joint as the research object.In addition to analyzing the effect of temperature and humidity factors on the mechanical properties of the lap joint,it also analyzes whether the sealing treatment can effectively reduce the influence of environmental aging on the joint properties.The research content is divided into the following three parts:(1)The effect of ambient temperature on the mechanical properties of CFRPaluminum alloy lap joints after high temperature aging is analyzed.The adhesive dumbbell sample and single-double lap joint are made with special fixture.The mechanical properties of dumbbell sample and single-double lap joint after hightemperature aging are tested by mechanical testing machine at different service temperatures,and the variation law of failure strength with aging time at different service temperatures is obtained.Combined with the failure surface morphology of the joint,the temperature action mechanism is summarized.The relationship between the average failure strength of the lap joint and ambient temperature and aging time is obtained by establishing three-dimensional response surface.(2)The effects of different hygrothermal environments on the mechanical properties of CFRP-aluminum alloy lap joints were studied.Four hygrothermal environments such as high temperature and high humidity(80?/95%RH)were selected,and the aging tests of adhesive dumbbell samples and lap joints were carried out in corresponding cycles.The variation laws of average failure strength and failure section of joints with aging time were obtained.In addition,FTIR(Fourier Transform Infrared Spectroscopy)measurements were conducted on CFRP and adhesive before and after aging to reveal the action mechanism of hygrothermal aging on lap joints.Finally,the effects of various hygrothermal environments on mechanical properties of lap joints were obtained through variance analysis.(3)The effect of sealing treatment on the mechanical properties of CFRPaluminum alloy lap joints were studied.The selected sealant is Sikaflex-265.The way of sealing treatment is to evenly apply a layer of sealant on the bonding part of the joint,and form a control test with the lap joint without sealing treatment,and carry out the hygrothermal aging test together.The corresponding dumbbell sample of sealant will be made,and the stress-strain curve of the sample will be obtained through mechanical test.The influence of hygrothermal aging on the mechanical properties of sealant will be analyzed.The failure strength of the seal aging and exposure aging lap joint was compared and analyzed,and the sealing mechanism was analyzed based on the failure surface.The failure strength of lap joint was predicted by regression analysis. |
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