Yewei Fu

Carbon-Fiber Reinforced Paper-Based Friction Material: Study on Friction Stability as a Function of Operating Variables

Carbon-fiber-reinforced paper-based friction material (CFRPF), as a new type of wet friction material for automatic transmission, was prepared by a paper-making process. The frictional response of CFRPF is highly complex under a set of dynamically variable operating conditions. To better understand the effect of operating factors (braking pressure, rotating speed, oil temperature, and oil flow rate) on friction stability of the material, tests were carried out using a single ingredient experiment and the Taguchi method. Experimental results show that the braking stability and the dynamic friction coefficient (μ d ) decrease as braking pressure, rotating speed, oil temperature, and oil flow rate increase. The influence of braking pressure on μ d is largest among the four operating factors. μ d declines gradually during the first 3000 repeated braking cycles and changes very little subsequently due to the surface topography change in friction material.

Influence of compound mineral fiber on the properties of paper-based composite friction material

Paper-based composite friction material is a kind of key functional material for automatic transmission. In this study, five types of paper-based composite friction materials with different compound mineral fiber contents were prepared using the paper-making process. The effect of compound mineral fiber content on the properties such as shear strength, thermal property, friction torque curves, dynamic friction coefficient and wear resistance was studied. Meanwhile, the sensitivity of the friction coefficients was also investigated. Worn surfaces of samples were analyzed using scanning electron microscope. Experimental results revealed that the thermal properties of the samples were improved as the compound mineral fiber content increased and the shear strength increased initially and then decreased. The friction torque curve of the sample with 20% compound mineral fiber contents was the highest among all the samples and the sample with higher compound mineral fiber contents possessed the more flat friction torque curve during the mixed asperity contact phase of the engagement process. The dynamic friction coefficient increased with the increase of compound mineral fiber content and decreased as contact pressure and rotating speed increased. The wear resistance of the sample was highest when the compound mineral fiber content was about 15%.

Investigation of the thermal property and tribological behavior of CaSO4 whisker-modified paper-based composite friction materials

In this study, CaSO4 whisker was applied to the paper-based composite friction material as the friction layer (secondary layer) by the paper-making process. The tribological and thermal properties were analyzed. Three-dimensional surface profiles were observed to discuss the wear mechanism. The results showed that the samples with higher CaSO4 whisker contents owned better thermal resistance. The sample with 4% CaSO4 whisker content had the highest dynamic friction coefficient. As the CaSO4 whisker content increased from 0% to 16%, the wear rate decreased first and then increased, and the sample with 8% CaSO4 whisker content had the highest wear resistance.

Effect of MoS2 on the tribological properties of carbon fabric composites under wet conditions

Carbon fabric reinforced phenolic composites are very attractive for use as friction materials under wet conditions due to their excellent self-lubricity, wear resistance, and high mechanical strength. However, brittle fracture of carbon fabric bundles during friction is one of the major problems that limit their application. In this work, MoS2 particles were used as additives and friction modifiers to improve the wear and friction behaviors. The composites containing different amounts of MoS2 particulates (0–20 wt%) were fabricated by impregnation technique. The influence of MoS2 on the tribological properties under oil-lubricated conditions has been studied systematically. The experimental results revealed that tribological characteristics such as coefficient of friction and wear resistance were changed significantly with the relative amount of MoS2. Addition of MoS2 within 15 wt% was found to decrease the wear rates of the composites, while 20 wt% MoS2-filled composites exhibited highest wear rate compared to other test samples. Increasing MoS2 content resulted in a rise in the wear rate of the counterparts. Wear mechanisms had been investigated by scanning electron microscope, which could support the observed wear performance.