Influence Of Temperature,Humidity And Load Coupling On The Mechanical Properties And Failure Mechanism Of Polyurethane Adhesive For High-Speed Railway Vehicle

The adhesion technology provides an effective way to connect the structural parts of a high-speed train body with mixed materials.However,with the increase of train service time and the accumulation of running mileage,the bonding structure of the train body suffers from the coupling effect of multiple factors such as ambient temperature,humidity and load,which brings great challenges to the safe operation of high-speed trains.It is of great practical significance to clarify the action mechanism of ambient temperature,humidity and load factors on the bonding structure of the train body,explore the damage evolution law under the coupling effect of multiple effects,and reasonably predict the service life of bonding structure,so as to ensure the sustainable development of China’s high-speed railway and provide critical technical support for the implementation of"going out"strategy of high-speed railway.Based on the project“Research on the Prediction Method for Aging Life of Adhesive Structures Oriented to Advanced Material Automotive Body（NO.51775230）”supported by the NSFC（Natural Science Foundation of China）.In this article,according to the actual service condition of high-speed train bonding structure,the failure mechanism and residual strength trend of adhesive joints in hygrothermal environment were studied,the influence of service temperature on mechanical properties of aging joints was analyzed,the influence mechanism of service temperature on fatigue properties of adhesive joints was revealed,and the influence of aging and load coupling on damage evolution and failure mechanism of mechanical properties of joints were analyzed.In order to provide a reference for the design,strength check and life prediction of high-speed train bonding structure,the failure criterion of adhesive joints was established,and the reasonable and effective life prediction method of bonding structure was proposed.（1）In order to study the aging effect of adhesive joints in temperature humidity coupling environment,two kinds of hygrothermal aging environment,high temperature（80℃）and high temperature and high humidity（80℃/95%RH）,were selected.Static tests of adhesive joints with different aging coefficients under multiple stress states were carried out using an improved Arcan device,and the variation of residual strength with aging cycle and stress state was analyzed.FTIR（Fourier transform infrared spectroscopy）was used to test the adhesive before and after aging,and the aging failure mechanism was analyzed.The failure mode of the joint sections was observed by macroscopic and SEM（scanning electron microscope）,and the failure mechanism was investigated.Finally,the secondary stress failure criterion suitable for the bonding structure was established.（2）The influence of service temperature on the adhesive structure after hygrothermal aging was studied.The mechanical properties and failure modes of the adhesive joints with different aging coefficients in the service temperature range were studied by static tests at different temperatures.The influence mechanism of temperature and hygrothermal aging on the mechanical properties of the adhesive was revealed.The failure criteria related to service temperature and aging period are established to accurately characterize the failure models of adhesive structures with different aging coefficients at different service temperatures.（3）The fatigue properties of the adhesive joints at different temperatures were tested by fatigue test,and the effect of temperature on the fatigue properties of the joints was studied.Based on the response surface method,the fatigue failure prediction method and prediction model were established.The fatigue parameters were fitted to the function of temperature,and the fatigue life relationship function with interval characteristics was constructed.The functional relationship N_f=f(T_emp,S)between the fatigue life N_fand temperature T_emp,nominal stress amplitude S in the corresponding temperature interval was obtained,and the temperature-nominal stress-fatigue life surface was obtained.Through macroscopic observation and SEM analysis,the fatigue failure sections under different temperatures were studied,and the influence law of temperature on the fatigue characteristics and fatigue failure mechanism of the joint was revealed.（4）The creep and aging behavior of adhesive joints under the coupling action of temperature,humidity environment and static load were studied.The joints were tested under different static load levels in temperature and humidity environments,and the creep deformation was analyzed,and the appropriate creep model was established.The aging test under the coupling condition of temperature,humidity and the static load was carried out to obtain the change rule of joint failure load with static load level and loading time.The influence of static load on the aging process of the bonding structure was analyzed.The fracture morphology was analyzed by SEM to discuss the failure mechanism.（5）The coupling effect of temperature,humidity environment and alternating load on joint performance was studied.The adhesive joints were tested under alternating load in high temperature（80℃）and high temperature and humidity（80℃/95%RH）environments respectively.The residual strength of the joints after different loading cycles was tested,and the variation of residual strength with load level and loading time was obtained.The effect of environment and alternating load coupling on failure mechanism was analyzed by SEM.The influence of temperature,humidity and load on the joint strength and the interaction among them were studied by variance analysis.（6）By studying the influence of environment and load factors on the strength of the bonding structure during high-speed train running,a method of life prediction based on residual strength was proposed.The appropriate accelerated aging test spectrum was established to test the adhesive joints,and the variation of residual strength and failure mode was analyzed.Combined with the strength attenuation curves of artificial accelerated aging and the natural aging of real vehicle,the corresponding functional relationship between the number of load cycles and the driving mileage of real vehicle was established,and then the life prediction of the bonding structure strength of real vehicle was carried out,and the failure behavior of the bonding structure was evaluated.