Study On Coupled Heat Transfer, Stress And Wear Behavior In Brakes

Brakes are important safety components of a vehicle. Braking isaccompanied by strong temperature-stress-wear coupling phenomenon.Simulating and predicting this coupling phenomenon accurately is of greatsignificance to the design of brake assembly, the control of brake system, thechoice of braking strategy and the optimization of brake components.The rapid progress of computer performance and the development ofcomputing science make it possible to simulate the heat-stress-wear couplingbehavior during braking period with numerical method. Little literature hasbeen reported on the method of solving this coupling process, so there are boththeoretical and technological problems to be broken through.Firstly, the key of wear simulation lies in the establishment of wear model.Pin-Disc wear experiments were adopted to study the influence of temperatureand load on wear rate and friction coefficient of brake pad material. The wearexperiments were designed by full factorial method. Ambient temperatureranged from25-175oC, while load varied from50-500N (0.35-3.5MPa). Theresults illustrate the curve of wear rate versus temperature resembles a convexparabola, and that friction coefficient rises with the increment of temperature.The effect of load on wear rate is almost linear, while no explicit relationshipis occurred between friction coefficient and load. A wear model is establishedby the quadratic regression of the experiment results.Secondly, numerical methods based on FEM for simulating coupled heattransfer, stress and wear behavior was studied elaborately. Methods forsimulating stress-wear coupled problems, temperature-stress-wear fullycoupled problems and sequentially coupled problems were developedrespectively according to different tribological and wear cases. Thestress-wear coupled simulation method and temperature-stress-wearsequentially coupled simulation method were applied to the case of pin/discwear experiments, the results of which showed the evolution of temperature,stress and wear. Wear and temperature results of simulations are in accord with those from experiments, vindicating the procedure of temperature-stress-wearcoupling simulation.Finally, rig tests of drum brake were conducted to acquire temperatureand wear during braking in classical braking cases. Then the multi-fieldscoupling during run-in test, single brake test,15consecutive brake test andwear test were simulated. The temperature of drum and linings obtained bysimulation was in great consistence with that from experiment, and the relativeerror of mean wear between simulation and experiment was less than5%. Thesimulation results of rig test took on the influence of wear on contactcircumstances between drum and linings, and revealed the evolving traits ofand interaction between temperature field, stress field and wear during brakingand cooling phases.Numerical methods for simulating coupled heat transfer, stress and wearbehavior are not limited to brakes, but can be applied to any mechanicalproducts involving dry sliding contact and wear.