A thermo-elastic contact problem of functionally graded materials (FGMs) rotating brake disk with different pure brake pad areas under temperature dependent material properties is solved by Finite Element Method (FEM). The properties of brake disk change gradually from metal to ceramic by power-law distribution along the radial direction from the inner to the outer surface. Areas of the pure pad are changing while the vertical force is constant. The ratio of brake pad thickness to FGMs brake disk thickness is assumed 0.66. Two sources of thermal loads are considered: (1) Heat generation between the pad and brake disk due to contact friction, and (2) External thermal load due to a constant temperature at inner and outer surfaces. Mechanical responses of FGMs disk are compared with several pad contact areas. The results for temperature-dependent and temperature-independent material properties are investigated and presented. The results show that the absolute value of the shear stress in temperature-dependent material can be greater than that for temperature-independent material. The radial stress for some specific grading index (n = 1.5) is compressive near the inner surface for double contact while it is tensile for a single contact. It is concluded that the radial strain for some specific value of grading index (n = 1) is lower than other FGMs and pure double side contact brake disks.

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Thermo-mechanical contact problems and elastic behaviour of single and double sides functionally graded brake disks with temperature-dependent material properties.

This paper develops a three-dimensional (3D) thermal-structure coupling model, implements transient stress analysis of thermoelastic contact of disk brakes with a frictional heat variation and identifies the source of the thermal fatigue. This thermostructure model allows the analysis of the effects of the moving heat source (the pad) with a variable speed and integrates the heat flux coupling between the sliding surfaces. To obtain the transient stress/temperature fields of the brake under an emergency braking, the thermoelastic problem under this 3D model is solved by the finite element method. The numerical results from the analysis and simulation show the temperature/stress of the disk presenting periodic sharp fluctuation due to the continuous cyclic loading; its varying frequency corresponds to the rotated cycle times of the braking disk. The results demonstrate that the maximum surface equivalent stress may exceed the material yield strength during an emergency braking, which may cause a plastic damage accumulation in a brake disk, while a residual tensile hoop stress is incurred on cooling. These results are validated by experimental observation results available in the literature. Based on these numerical results, some suggestions for avoiding fatigue fracture propagation are further presented.

P. Dufrénoy

Papers

An experimental investigation of hot spots in railway disc brakes