Determination of defects on the passenger car brake disc using vibration parameters

Brake systems in vehicles have an important role for safely slowing down and stopping the vehicle. Brake disc is one of the most significant parts of this system, and it is important to be faultless. Brake discs are generally manufactured by casting of grey cast iron followed by machining operations. There should not occur any defects such as cracks, dimensional inconsistencies in the disc structure during manufacturing process. One of the common methods for defect detection in a brake disc is to monitor its natural frequencies. This method is based on the principle that natural frequencies of the disc change because of defects. In other words, there occurs a certain amount of decrease on the damaged disc's natural frequencies compared to the healthy disc. By this way, existence of a crack like defect can be identified. In this thesis, it is aimed to determine the distance from the disc center, length, orientation angle and depth parameters of a crack like damage on the functional surfaces of a brake disc. For this purpose, first, experimental modal analysis of a brake disc is performed to determine the natural frequencies and the mode shapes for updating the finite element model of the disc. By this way, a realistic model is obtained which is compatible with the experimental data. Then, design of experiment using the central composite design method is carried out for the damage parameters so that a suitable design space is obtained. Later, response surface method is applied to obtain mathematical models including crack parameters and the natural frequencies. It is observed that, with the developed mathematical models, crack lengths and depths could be determined with admissible amount of errors for certain damage cases. As a second way, crack parameters of the disc are obtained through an optimization procedure based on adaptive multiple objective optimization method. However, compared to the response surface based approach proposed in this thesis, it is observed that the optimization based method needs more computational time and effort. Besides, it is valid only for a certain damage case, i.e. if the same disc with different damage state is considered, the optimization should be repeated, which requires more computational time and effort. However, the introduced approach is more general than the optimization based method considering that the developed mathematical models may be used for the same disc with different damage scenarios.