Accelerated wear testing of carbon brake materials

Brake-dynamometer is an expensive and time consuming technique for quality control or selection of brake materials. Brake-dynamometer is a technique used for performance evaluation of the braking device under the realistic vehicle speed, mass and inertia. The price of a brake-dynamometer is estimated to be greater than € 250.000. However, such an expensive technique is only limited for testing the braking device. Moreover, the brake materials has to be shaped into a component to make the braking device that fit into the brake-dynamometer.

The best solution is to use the pin-on-disk or rotary tribometer for friction and wear testing of the brake materials. Although this test method will not reproduce the vehicle mass and inertia but it can reproduce the vehicle driving speed pattern- acceleration, cruise, deceleration and the high temperature (up to 600°C) in the braking device. Ducom Multi Capability Tribometer (see Figure 1) is cheaper than brake-dynamometer moreover it offers the ease of testing and high throughput research focused on selection of brake-material.

Figure 1. Ducom Multi Capability Tribometer POD 4.0

In this study, the test speed is varied according to the vehicle driving pattern or European urban driving cycle - UDC (see Figure 2). 

Figure 2. Speed profile (UDC). Each cycle is comprised of acceleration, cruise, deceleration.

Figure 3 shows the UDC speed profile reproduced using Ducom Multi Capability Tribometer POD 4.0.

Figure 3. Speed profile in Ducom POD 4.0

Table 1 summarizes the test parameters and materials used in this study. Labview based WinDucom software was used to control the pin temperature, acquire the friction force and linear wear during the test.

Table1. Test parameters and materials.

Test Results | Ambient Temperature

Test Results | 600 °C

Test Results | During Deceleration

Test Results | Carbon Peak Analysis (XPS)

• In a quick test set-up (800 s per sample) we conclude that the ultralow friction and wear behavior of carbon – carbon brake materials is influenced by temperature.
• At 600 °C of pre-heat temperature and during deceleration phase of driving cycle the friction coefficient and wear increases to 5 and 30 times, respectively.
• Despite severe wear there is no change in the carbon – carbon binding as determined by X-ray photoelectron spectroscopy (XPS).
• High speed control and open air heating of the pin and disk is very useful in testing brake pad materials.