Project Report On Simulation Of Thermal Stresses In A Disc Break

1.Introduction .
            During braking, the kinetic energy of the moving vehicle is converted into heat energy due to friction between disc and pad. As a result the temperature of the disc in contact with the pad is suddenly increased. Upon cooling the heat is dissipated by convection and radiation leaving some residual thermal stresses. During very hard braking the temperature of the disc can reach to very high value. The sudden change in temperature causes thermal shock and thermal stress inside disc. Plastic deformation occurs due to large thermal expansion/contraction. After repeated number of braking cycles, cracks might be initiated on the disc surface which leads to failure.

1.1 Background
In the previous work, Niclas Strömberg [1] used an Eulerian approach for the disc-pad system. Contact interface between disc and pad was defined by node-to-node contact. Frictional heating is considered between the pad and thermo-elastic rotating disc. The temperature profiles in the disc are compared with the experimental results of thermography tests and found to be very similar to each other. To continue the work, stress analysis is to be done.

1.2 Objective
The thermo-mechanical contact problem is divided into two parts for analysis, heat problem and stress problem. The finite element method is used to obtain the temperature, thermal stresses and strains for the disc-pad system. To investigate the elastic-plastic thermal stress analysis for a brake disc under cyclic temperature gradients, the plasticity theory and flow rules are discussed. Proper consideration is also given to the material hardening models. In this thesis, the disc-pad system is studied only for few repeated braking cycles so that to establish the background for predicting the low cycle fatigue life (based on plastic strain amplitude) of the disc brake, which is the ultimate objective of this whole project.

1.3 Limitations
Due to sliding of disc and pad with each other wear is developed, which is not included in the analysis. The temperature field is obtained considering constant angular velocity. The material properties are assumed to be temperature independent. Viscoplasticity is also not taken into account to analyse stresses.


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