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This paper provides a systematic approach to identify the root cause of the squeal noise of a disc brake by using advanced experimental tools. Modal analysis was used to identify the modal participation factors when the brake was squealing according to the reproduced squeal phenomenon and acquired operational displacement shape (ODS) using pulsed electronic speckle pattern interferometry. Modal coupling between the disc and pad/caliper assembly is found to be the key to produce squeal. It has been demonstrated that using mass loading/damping can de-couple the modes between the disc and pad/caliper assembly and reduce the assembly vibration from which the squeal is eliminated.

This paper benchmarks some methods of nondestructive testing for zero and high mileage spot weld quality/integrity and degradation evaluation (pin holes, voids, cracks, fatigue, corrosion, etc.). The methods include X-ray radiography, ultrasonic imaging, ultrasonic pulse/ echo, pulsed infrared or thermography, and laser/TV holographic interferometry imaging. The advantages and limitations of each method are provided with descriptive principles and real test examples. It is found that X-ray radiography combined with ultrasonic echo technique is the most favorable one considering time and cost for the current zero and high mileage spot weld evaluation.