Abstract
KEYWORDS – dynamic stiffness, NVH, visco-elastic, modulus, non-linear
ABSTRACT
In this study two measurement methods, the ETEK and SHAKE are used to measure the dynamic modulus of brake pads over preloads from 10 bar to 30 bar. When direct out-of-plane modulus measurements are made by both testing methods on the same samples, the results are highly correlated (R2 =0.98). Additional tests are carried out comparing ETEK modulus measurements made non-destructively on as-manufactured pads with destructive SHAKE modulus measurements on small cylinders cut from pads. When this work, which involved ten pads and five different formulations, is combined with the previous results, the correlation between ETEK and SHAKE measurements is R2 =0.92. The reduced correlation is attributed to spatial non-uniformity of the pads. Although highly correlated, the ETEK modulus values are systematically higher than the SHAKE values. This difference is attributed to the friction materials viscoelastic nature and the strain rate dependence of the dynamic modulus. A “scaling model” has been developed which can be used to relate ETEK and SHAKE data. This scale factor is consistent with observations of the dynamic modulus frequency dependence observed in the kHz frequency range. The non-destructive methods based on ETEK have been automated. The ETEK test methods can be applied to intact, as-manufactured brake pads. The non-destructive test results include out-of-plane dynamic modulus, preload sensitivity, hysteresis, and pad uniformity. These techniques are useful for selecting pads based on out-of-plane modulus values prior to noise performance testing as well as quantifying the variation of out-of-plane modulus as the result of performance testing. Noise performance tests using the pad formulations measured by SHAKE and ETEK are currently in process.