Simulation of Thermal Stresses in a Brake Disc
Abstract: In this thesis thermal stresses in a brake disc during a braking operation are simulated. The simulations are performed by using a sequential approach where the temperature history generated during a frictional heat analysis is used as an input for the stress analysis. The frictional heat analysis is based on the Eulerian method, which requires signicantly lower computational time as compared to the Lagrangian approach. The stress analysis is performed using a temperature dependent material model both with isotropic and kinematic hardening behaviors. The results predict the presence of residual tensile stresses in circumferential direction for both hardening behaviors. These residual stresses may cause initiation of radial cracks on the disc surface after a few braking cycles. For repeated braking an approximately stable stress-strain loop is obtained already after the rst cycle for the linear kinematic hardening model. So, if the fatigue life data for the disc material is known, its fatigue life can be assessed. These results are in agreement with experimental observations available in the literature.The simulation results predict one hot band in the middle of the disc for a pad with no wear history. It is also shown that convex bending of the pad is the major cause of the contact pressure concentration in middle of the pad which results in the appearance of a hot band on the disc surface. The results also show that due to wear of the pad, dierent distributions of temperature on the disc surface are obtained for each new brake cycle and after a few braking cycles, two hot bands appear on the disc surface.This sequential approach has proved tremendously cheap in terms of computational time so it gives the freedom to perform multi-objective optimization studies. Preliminary results of such a study are also presented where the mass of the back plate, the brake energy and the maximum temperature generated on the disc surface during hard braking are optimized. The results indicate that a brake pad with lowest possible stiness will result in an optimized solution with regards to all three objectives. Another interesting result is the trend of decrease in maximum temperature with an increase in back plate thickness.Finally an overview of disc brakes and related phenomena is presented as a literature review.
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