Vibration and acoustic analysis of brake pads for quality control

Two procedures have been used for the damage detection of brake pads presenting two kind of defects, i.e. cracks and braking material detachments. Both the procedures are based on the monitoring of the pad structural resonances that changes in presence of defects. The first procedures employs a Laser Doppler Vibrometer (LDV) for the measurement of the vibration velocity of the pad forced into vibration by means of an impact hammer. The second one, instead, uses a system based on four microphone probe developed by SenSound and called SenQC system since is made for quality control. Both the techniques allowed to recognized damaged pads from the good ones from a sample of 37 elements. The sensitivity of the procedure to environment temperature has also been studied, since the structural resonance can be influenced by this parameter. The sensitivity analysis to temperature has been performed by using the LDV technique and by repeating the measurement on four different pads (two good and two damaged). The temperature has been varied from 15 to 30°C with a resolution of 2°C in order to monitor the complete range of the environmental temperature that can be reached in working conditions in the production line.