Research On The Effect Of Ambient Temperature On The Failure Of Adhesively Bonded Single Lap Joints For Automotive

With the continuous development of automobile lightweight technology,many new lightweight materials will be more widely used in body structure.Bonding technology also plays an important role in the process of body lightweight due to its unique advantages in the connection of different materials.However,the adhesive used for the bonding connection is sensitive to ambient temperature.Moreover,the adhesive will age under the long-term effect of temperature and the coupling effect of temperature with other factors,which may lead to premature failure of the connection structure and bring hidden dangers to the safety of the body structure.Focusing on the effect of temperature on the failure of adhesively bonded joints,this paper takes the single lap joints composed of sikaflex-265 polyurethane adhesive and 6000 series aluminum alloy as the research object.With the reference to the actual service environment of the automobile,investigate the effect of temperature on quasi-static failure of adhesively bonded joints,the effect of temperature on fatigue performance of adhesively bonded joints,the effect of temperature aging environment and the coupling of temperature and other factors aging environment on the performance of adhesively bonded joints.The main research contents are as follows:(1)For the effect of temperature on the quasi-static failure of adhesively bonded joints,polyurethane adhesive and aluminum alloy substrate were selected to complete the production of single-lap joints under a reasonable and standardized manufacturing process.The quasi-static tensile tests were carried out at the temperature of 80°C,50 °C,20?,-10 °C and-40 °C,referring to the service temperature environment of automobile(-40~80°C).The failure loads and failure section morphology of the adhesively bonded joints with the change of temperature were obtained.The polyurethane adhesive specimen was tested by DSC equipment,and the reasons of joint failure load and failure mode changing with temperature were analyzed with the glass transition temperature of the adhesive.The curve fitting of the failure strength data of the adhesively bonded joints at five temperature was performed.The fitting function can be used to estimate the failure strength of these polyurethane adhesive single lap joints in the service temperature range.(2)For the effect of temperature on the fatigue performance of adhesively bonded joints,under five temperatures of 80°C,50°C,20°C,-10°C and-40°C,different load levels were selected to perform tensile-tensile cycle loads on the adhesively bonded joints.Then,the nominal stressfracture cycle number curves of adhesively bonded specimens at different temperatures were fitted,and that temperature has a significant effect on the fatigue performance of the adhesively bonded joints was founded.With the same number of fatigue cycles,when the temperature rises,the fatigue strength of adhesively bonded joints will show a declining trend,and the fatigue failure sections of adhesively bonded joints at different temperatures show different Characteristics.With the introduction of temperature variable,a fitting function of the nominal stress-fracture cycle number was established and verified.It was found that the number of fracture cycles calculated by this function is very close to the experimental value,which has certain reference significance for the fatigue performance prediction of these polyurethane adhesive single lap joints under the tensile-tensile cycle load at different temperatures.(3)For the effect of temperature aging environment and the coupling of temperature and other factors aging environment on the performance of adhesively bonded joints,an accelerated aging test was performed on the adhesively bonded joints at 80°C to study the effect of high temperature aging on the failure strength and failure modes of the adhesively bonded joints.Then,under the condition of high temperature and high humidity(80°C/95%RH),an aging test was performed on the adhesively bonded joints to analyze the change law of the joint failure strength and failure section morphology with the aging time.Furthermore,on this basis,the static load was introduced into the aging environment.High temperature and high humidity and static load coupling aging test was performed to study the effect of coupling environment aging on joint failure.After the aging test,the function of the failure strength of the adhesively bonded joints with the aging time in each aging environment is fitted.This function can provide a reference for the mechanical property prediction of these polyurethane adhesive joints after aging.