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Thermoelastic instabilities in the contact of brake friction material cause hotbands and hotspots on the surface of brake disc. These phenomena generate thermal stresses that result in generation of cracks, which limit the lifetime of the discs. In the present work, the influence of the chemical composition of brake discs on the thermoelastic behavior of the system and on the lifetime of the discs was investigated. The experimental evaluation was carried out in an inertial dynamometer using the SAE J3080 standard procedure applied on a brake system. Two discs (namely A and B) with different chemical compositions were subjected to the tests. The brake pad composition was kept fixed. The thermoelastic effects on the inner surface of the disc were observed by contact (thermocouple) and noncontact measurement techniques (thermography), as well as through photographic images of the disc’s surfaces. Disc A showed negligible amount of Nb while disc B exhibited 0.360%.

The current study presents some testing procedures which have been designed for friction and noise measurements of brake friction materials using a laboratory-scale tribometer. The uncertainties (errors) and precision of the measurements are also described in this paper. Some case studies related to friction, wear and noise related issues in brake friction materials were chosen to show the respective testing procedures. Through the error study, it was shown that the uncertainties of the lab. test bench are mainly associated with 3 variables: torque, force and sliding radius. The combined uncertainty of the friction measurements is less than or equal to ±1%, considering the typical operating range of the machine. The possibility of using two samples from a single brake pad also contributes to the reliability of the machine test and procedures.

The present paper addresses an investigation about the definition of a parameter for quantifying the creep-groan propensity in brake pads. Creep-groan is a self-excited vibration caused by stick-slip phenomenon [1, 2, 3]. For the definition of the creep-groan propensity parameter, extensive experimental work was performed on a laboratory-scale tribometer. The experiments are divided in two main parts: (i) study of correlation between accelerometer signal with physical and operating parameters. (ii) validation of the chosen parameter, which was based on stick-slip tests performed with three different materials, one low-metallic (low-met) and two non-asbestos organic (NAO 1 and 2). From the first study, it was found that both the slip power and mean torque multiplied by torque variation showed a slightly higher correlation with the acceleration signal.

The current paper addresses the comparative analysis of the performance (friction and wear) produced by original and aftermarket brake pads. The brake pads selected in this study belongs to a large circulation vehicle in Brazil, which also has a high number of sales. An original and 4 others aftermarket brake pads were purchased at Porto Alegre, Brazil. The braking tests were performed on a braking tribometer, which is located on the University facilities. Experimental data of the coefficient of friction produced by each brake pad have been recorded. A precision scale was used to measure the mass loss of the materials subjected to the tests. Results of the performance obtained by the brake pads are evaluated and discussed in this paper. Results have shown that the original brake pad has superior properties in terms of friction performance (magnitude and variation), while aftermarket 1 and aftermaket 2 materials have the lowest vibration magnitudes.

The current paper presents some friction characterization obtained by using a multifunctional tribometer. The effect of two parameters (temperature and caliper drag) on friction were investigated by means of two different type of tests: i) high temperature tests, where braking tests are executed at different levels of temperature and ii) caliper drag tests, where the sample was intentionally kept in contact with the disc surface during the cooling period that occurs after each braking. The multifunctional tribometer proved to be a suitable tool for friction characterization at different temperature levels. Results show that is possible to evaluate fade effect by using the mentioned technology. Results from caliper drag tests showed that a low-metallic friction material is more prone to this effect than an organic friction material.

Braking system failure due to overheating is a problem that affects commercial vehicles in severe braking conditions. Repeatedly brake activations in downhills executed to maintain the vehicle in a safe velocity range can cause brakes overheating. It can hinder the brake efficiency and, consequently, provoke accidents. This paper presents a model to simulate the brake heating of a standard truck in some typical Brazilian's downhills. Different conditions of load, velocity and engine brake were carried out by simulations. The high brake temperatures obtained indicate the possibility of brake system failure in some cases. Specific vehicle trajectories are proposed for safer driving in such downhills.

This work presents the development of a braking system model to be applied in the evaluation of anti-lock braking system (ABS) control logics. The anti-lock braking system model was attached to a vehicle model to simulate possible braking conditions. The results show that the vehicle stopping distance with a standard anti-lock braking system is reduced when compared to the passive braking case and that the wheel slip is much closed to the desired wheel slip, confirming the appropriate working of the proposed anti-lock braking system control logic. The simulations were performed for snow, wet and dry asphalt. The parameters used to verify the performance advantage obtained with ABS braking in relation to passive braking were the stopping distance, the anti-lock braking system index of performance (ABSIP) and the vehicle side slip angle for the tests with steering input. In these cases, the results also show an efficiency improvement with the proposed anti-lock braking system.