Study On The Mechanism Of Wet Skid Resistance For Tire Tread

In the last decades, with the demand of energy conservation and emission reduction in our country and the increased requirements of security, energy-saving, and comfort for cares, good wet-skid resistance (WSR), abrasion resistance and low rolling resistance becomes the essential desire for high-performance tires, which are often called "magic triangle" in the tire industry. The new European label, accroding to three basic properties of tire tread, including the rolling resistance, WSR and voice, will be carried out in 2012. Therefore, the study on the mechanism of WSR is one of the research focuses and of significant importance. In the rencent twenty yeaars, the study on WSR gardually increased but without producing a systematial theory. Since the'green'tire was commercialized, it was found that besides the low rolling resistance, this tire featured better WSR. The viscoelasticity could no longer explain the better WSR of silica filled composites, which is disadvantages to the design of tire tread with high WSR. It becomes a changlling topic. Therefore, it is essential to study the contribution of viscoelasticity to WSR for filled rubber composites and the influence of other factors to WSR, which is the main research direction of this thesis.In the first part, we mainly studied the WSR of carbon black (CB)- and silica-filled SSBR (Solution styrene-butadiene rubber) composites measured with LAT-100 abrader and analyzed the influening factors. A dynamic mechanical thermal analyzer was used to obtain the visoelasticity of the composites. The results showed that the silica-filled composites exhibited better WSR than CB-filled composites under the measuring conditions. It was not sufficient to represent WSR just using viscoelasticity. The temperature, velocity and the hardness of the composites also have effect on WSR. The WSR increases with the decreasing temperature and the increasing velocity, which was caused by the water lubrication effect and viscoelasticity. The conclusions of this part are in favor of choosing the influencing factors of WSR and have significance on the subsequent parts.In the second part, we mainly revisited the role of viscoelasticity in WSR of rubber composites by comparing the effects of CB and silica on WSR. The WSR on wet ground glass was obtained with a portable British Pendulum Skid Tester (BPST). Under shear and tensile modes, tanδof the composites was measured at 0℃in a wide range of strains (0.7%-10%) via a dynamic mechanical analyzer. For different sizes of CB-filled composites, a high correlation coefficient (R2=0.98) between WSR and tan 8 under both shear (0.7%-10%) and tensile (4%-7%) modes was obtained. Tanδat tensile strain 4% was thus adopted as a parameter to characterize viscoelasticity. Good correlations at tensile strain of 4% was also found for CB- and silica-filled SBR composites with rough surface, while a good correlation was also observed for rubber composites with smooth surface regardless the type of filler. The higher WSRs of silica-filled composites over those filled with CB were mainly due to the higher nanohardness of silica. All these results demonstrate that WSR can be predicted from viscoelasticity for composites with similar surface roughness and micro-hardness. Basing on this conclusion, it is helpful to analyze the contribution of viscoelasticity to WSR. Besides, it guides us to explore the mechanism of WSR for different fillers-filled system. Therefore, the conclusions of this part are in favor of choosing the influencing factors of WSR and have significance on the subsequent parts.In the third part, we mainly studied the wet skid resistance (WSR) of SSBR/BR (Butadiene rubber) composites filled with carbon black, silica, and nano-diamond partly replacing carbon black or silica, respectively, with BPST. A 3D scanning white-light interfering profilometer was used and the scratch test performed to characterize surface roughness and micro-roughness, respectively, of the composites. WSR of the silica filled composite was better than that of the carbon black filled one, and further enhancement of WSR was obtained by replacing silica with nano-diamond. Tanδof the composites at 0℃,10 Hz, and tensile strain of 5% did not show good correlation with WSR. The surface roughness of the composites had effects on WSR. The scratch test was designed to compare the micro-hardness of the composites surface, which indicated that the higher the hardness of the filler in the composite, the higher the micro-hardness and the better the WSR. Therefore, the surface micro-hardness of the composites is an important factor affecting WSR, besides viscoelasticity and surface roughness. Besides, we studied the influence of water film thickness for WSR for the composites filled with carbon black, silica, and nano-diamond. It further indicated that the effect of stiff particles is of significant importance for improving WSR when the water film is thick (50μm-1mm).