Design And Thermal-structural Coupling Analysis Of The Reduced-scale Railway Friction Pairs

The reduced-scale test based on the similarity theory is one of important ways to evaluate thermal performance of discs,and the data have good comparability with 1:1 bench data.Combining with numerical simulation,it can significantly reduce test cost,simplify test procedure,and shorten product development cycle in early design stage.Temperature and stress are important evaluation indicators in design and test phase of disc,and they are also the direct factors that affect service life.Therefore,the reserach on temperature field and stress field of disc is of great significance to the development of disc and even high-speed railway industry.In this paper,the CRH 5 EMU friction pair was used as prototype to determine key parameters and reduction ratio according to similarity principle.The methods of same ratio of circumferential contact arc length and the ratio of radial contact length were introduced in design stage of the reduced-scale friction pair.The 1:1 finite element model and the scaled finite element model were established by ADINA.The distribution of temperature field and stress field of discs in 1:1 model and the small-scaled model under different working conditions by simulation,and the equivalence was discussed and verified by test.Related conclusions as follow:(1)The key parameters in braking test and corresponding reduction ratio are determined based on similarity theory.During the design process of reduced brake pairs,the methods of equal ratio of circumferential contact arc length and radial contact length are introduced to ensure two models had equivalent pads distribution.The shrinkage ratio of friction area is 1/4,the reduction ratio of friction radius is 1/2,the hrinkage ratio of disc effective heated volume is 1/4,and the reduction ratio of inertia is 1/16.(2)3S model has best agreement with 1:1 model in terms of disk surface temperature distribution,node temperature history curve of friction radius,and stress field distribution,other scaled models have large deviations.The high-temperature zone width of 2S model is significantly wider than other models,and location is closest to outer edge.The peak temperature of 6S model is the lowest,and the rest models are much better.The radial temperature curves and radial stress curves of 3S model are the same as 1:1 model,both are"M"shape,but other scaled models are all unimodal.(3)The peak temperature divation between 3S model and 1:1 model decreased with the increase of pressure and increased with the increase of speed.When the speed is 100 km/h,the peak temperature difference between 1:1 model and scaled model decreased from 12.7%at 0.50 MPa to 9.9%at 1.10 MPa.The contact state of two friction pairs at low speed conditions is so similar that temperature distribution of discs are in good agreement,and the peak temperature difference is 3.8 ? and 19.1 ?.The high temperature under high speed causes pads generate thermal deformation in diffierent degree,resulting in a divation of 10%in actual contact area of two models.In addition,the brake time difference of 5.0s leads to a different speed of heat transfer,which ultimately leads to both disk surfaces.The peak temperature difference is as high as 70.8?.(4)The test results of 3S model are basically consistent with simulation of 1:1 model.Both types of discs have undergone a temperature change process of rising first and then decreasing.The temperature field is non-axisymmetric and the radial temperature gradient is large.Due to different contact position and contact state of friction pairs,the position of high-temperature zone is different,and improved with increasing of speed and pressure.The divation in peak temperature and radial peak temperature between two moedls are negatively correlated with pressure and positively correlated with speed.(5)The influence of braking conditions on distribution of disc temperature during braking is the change of friction pairs contact state ultimately,the essence is the different conversion rate of the third body between plate state and granular state,then show different surface morphology and unsteady fluctuation of friction coefficient.