| A thin layer of frictional bi-products commonly forms on the rubbing surfaces during braking events. The effect of this friction layer on brake performance as well as noise and vibration is an active area of research, and requires knowledge of the friction layer thickness, mechanical properties and surface topography. Most methods to determine these parameters are destructive in nature. Hence there is a critical need for nondestructive methods to find these parameters that would allow for extensive studies of the friction layer, its evolution as well as its affect on brake performance. The overall objective of this study is the development of nondestructive techniques that will eventually provide whole-field mappings of friction layer thickness, mechanical properties and surface topography. Ultrasonics is selected as the method of evaluation because it provides a simple, economical and robust means for detecting the before mentioned parameters. Four techniques have been developed that include a frequency domain deconvolution, a time domain adaptive FIR "spiker" filter, a selective echo dual parallel transducer, and a dual angled transducer. The frequency domain deconvolution technique was verified on four separate applications: a known polyethylene film (50.8 mum) on a Plexiglas substrate, a sol-gel (19--30 mum) layer on an aluminum substrate, a cast iron automotive brake rotor with a friction layer (6--30 mum) and a c/c debris compacted layer (400--660 mum) on an epoxy substrate. The deconvolution technique proved to lend itself well to braking applications as it is automated so full field thickness information is readily available. The time domain adaptive FIR "spiking" filter technique was also verified on the same four applications.; The selective echo dual parallel transducer technique theory was presented which allows for selective echo capture by "holding" a receiving transducer using an electrical current. Holding the transducer it is possible to let undesirable echoes pass by the element then by releasing the transducer allows the desirable echoes to excite the element and be detected. It was also shown that the dual angled transducer technique did not work well for the detection of the friction layer thickness. In conclusion, the frequency domain deconvolution and the FIR filter techniques were shown to successfully measure the friction layer thickness. This is expected to pave the way for the measurement of whole-field mappings of the friction layer thickness, material properties and surface topography. |
