Recently unintentional BSR (Buzz, Squeak, Rattle) problems have been occurred in automotive interior parts, especially case in 1-2 years of used car. Polymers used widely in automotive interior parts are changed in material structures and its properties due to long-term degradation. These are may be contributed to BSR problems.
In this study, the effect of the degradation under conditions of heat, humidity and UV on polypropylene copolymers are studied to seek the possible relationship between changed mechanical properties of the materials and squeak noises. Combined accelerated degradation tests were carried out to evaluate the characterization of the degradation of PP copolymers. The specimens were exposed to xenon-arc radiation using a varying exposure time under harsh environmentals. Changes of chemical structure on PP copolymers were analyzed by Microscope, FT-IR spectroscopy and energy dispersive spectroscopy (EDX). Formation of carbonyl group of carboxylic acids was observed mainly peaks resulted from combined accelerated degradation tests. Also, quantitative analysis was conducted by calculating carbonyl index (CI).
In addition, mechanical tests were conducted by tensile test, hardness test, coefficient of friction and warping effect of the materials. During degradation in PP copolymers are generated, as well as chain scission and cross-linking. As net effects of these degradation mechanisms respective increases in crystallinity, higher values such as modulus of elasticity, tensile strength, hardness and coefficient of friction at late stages of degradation were observed. Also, surface cracking and more distorting shape of the specimens were observed. Theses changes in chemical structures and material properties can cause a variation in stick-slip motion induced by frictional impulses during the sliding of two specimens. Experiments are performed for combination of the degraded specimens with several normal load and velocity. For the effect of the surface degradation, increased the coefficient of friction can give an unstable vibration that stores energy to another surface. Furthermore, during sliding two surfaces generated stick-slip each other, frequency analysis was performed by using one-third octave method. The results indicate that degraded materials are higher sound pressure level than no combination of degradation specimens
The results of this study are intended to reflect that long-term degradation affects generated squeak noise, changing stick-slip motion related to material properties, surface profile, coefficient of friction and transformation its shape