In the automotive braking system, brake pads are the core component ensuring driving safety, and their performance directly depends on the selection and research of materials. As the automotive industry moves towards high-speed, lightweight, and energy-efficient development, traditional brake pad materials gradually expose performance shortcomings, while the emergence of new composite materials is promoting a comprehensive innovation in brake pad technology.

Table of contents：

Traditional Brake Pad Materials: Transition from Asbestos-based to Semi-metallic

New Composite Materials: Technological Breakthroughs in Ceramic-based and Carbon Fiber-based

Future Development Direction: Integration of Intelligent Materials and Nanotechnology

Traditional Brake Pad Materials: Transition from Asbestos-based to Semi-metallic

The development of traditional brake pad materials has gone through a key stage of "asbestos-based materials - semi-metallic materials". In the early days, asbestos-based materials became the mainstream choice for brake pads due to their low cost, stable friction coefficient, and low processing difficulty, and were widely used in various fuel vehicles. However, the fatal flaws of asbestos fibers gradually became prominent: during material production, brake pad wear, and waste disposal, fine asbestos fibers are easy to suspend in the air. When inhaled by the human body, they will adhere to the lungs, and long-term accumulation may cause serious diseases such as asbestosis and lung cancer. At the same time, they will also cause persistent pollution to soil and water sources. At present, more than 50 countries and regions around the world have explicitly prohibited the use of asbestos materials in automotive parts such as brake pads.

After asbestos-based materials withdrew from the market, semi-metallic brake pads quickly became alternative products. Its main components include metal particles such as steel fibers and copper fibers (usually accounting for 30%-50%), combined with phenolic resin adhesives, graphite, and other friction modifiers, which are formed through processes such as pressing and curing. Compared with asbestos-based materials, the high-temperature resistance of semi-metallic brake pads has been significantly improved. In the frequent braking environment of 300-500℃, it can still maintain a stable friction coefficient of 0.3-0.5, meeting the daily braking needs of mid-to-low-end models. However, the addition of metal components also brings new problems: on the one hand, the hard friction between metal particles and cast iron brake discs is prone to generate high-frequency vibrations, leading to "squealing" noise during low-speed braking. The noise decibel value can reach 65-80dB, affecting the riding experience; on the other hand, the high thermal conductivity of metals will accelerate the thermal fatigue wear of the brake disc, shortening the service life of the brake disc by 20%-30%, and the falling metal debris may also pollute the wheel hub and the environment.

New Composite Materials: Technological Breakthroughs in Ceramic-based and Carbon Fiber-based

To solve the limitations of semi-metallic materials, researchers have focused on the research and development of new composite materials. Among them, ceramic-based composite materials and carbon fiber-reinforced composite materials have become the current research hotspots and mainstream applications of brake pad materials due to their excellent performance.

(1) Ceramic-based Brake Pads: An Ideal Choice for Environmental Protection and Mute Operation

Ceramic-based brake pads take inorganic non-metallic materials such as ceramic fibers, alumina, and silicon carbide as core components, supplemented by a small amount of resin adhesives and rare earth element modifiers, and are made through high-temperature sintering processes. Their performance advantages are concentrated in three aspects: first, ultra-low noise. The flexibility of ceramic particles can buffer the impact force during braking and reduce the vibration frequency of the friction surface. Experimental data shows that the braking noise of ceramic-based brake pads can be controlled at 45-55dB, which is 15-20 decibels lower than that of semi-metallic brake pads, close to the urban environmental background noise level; second, extreme high-temperature resistance. In a high-temperature environment above 800℃, its friction coefficient can still be stably maintained at 0.35-0.45, avoiding the "thermal recession" phenomenon of traditional materials caused by high-temperature carbonization, and greatly reducing the risk of brake failure during high-speed braking; third, low wear and environmental protection. Ceramic materials have strong chemical stability, almost no metal debris is generated during the braking process, and the wear rate of the brake disc is reduced by more than 30% compared with semi-metallic brake pads. Moreover, the waste brake pads can be recycled through crushing and harmless treatment, which meets the requirements of the EU "RoHS" environmental protection directive. At present, ceramic-based brake pads have been widely used in mid-to-high-end family cars, SUVs and other models, and their market share is increasing year by year.

(2) Carbon Fiber-reinforced Composite Brake Pads: A Performance Choice for High-end Models

Carbon fiber-reinforced composite brake pads are designed for the needs of high-end models and special vehicles. It uses high-strength carbon fibers (with a tensile strength of more than 3000MPa) as the reinforcing phase, combined with high-temperature resistant resins or metal matrices, and is made through complex processes such as weaving, forming, and carbonization. The core advantage of this material lies in "high strength + lightweight": on the one hand, carbon fiber has excellent thermal conductivity, which can quickly dissipate heat to the entire friction surface during braking, avoiding performance degradation caused by local overheating. Even in the extreme scenario of continuous emergency braking of racing cars, it can maintain a stable braking effect; on the other hand, the density of carbon fiber is only 1/4 of that of steel, and the weight of the made brake pad is 40% lighter than that of traditional semi-metallic brake pads, which can effectively reduce the unsprung mass of the car, improve the chassis handling and fuel economy (the fuel consumption per 100 kilometers can be reduced by 0.3-0.5L). At present, carbon fiber brake pads have become standard equipment for racing cars, luxury cars (such as BMW M series, Mercedes-Benz AMG series) and heavy-duty trucks. With the maturity of carbon fiber mass production technology, the cost is expected to decrease by 50% in the future, and gradually popularize to mid-end models.

Future Development Direction: Integration of Intelligent Materials and Nanotechnology

From asbestos materials to new composite materials, every innovation in brake pad materials revolves around the three core goals of "safety, environmental protection, and efficiency". In the future, with the in-depth integration of intelligent materials and nanotechnology, brake pads will develop towards the direction of "self-diagnosis, self-repair, and multi-functionality".

In terms of self-diagnosis, researchers plan to embed nano-scale pressure sensors and temperature sensors in brake pad materials to monitor the wear thickness, temperature change, and pressure distribution of the friction surface in real time. The data is transmitted to the instrument panel through the on-board bus. When the brake pad wear reaches the critical value (usually 3-5mm), an alarm prompt is automatically triggered to avoid braking risks caused by the user's neglect of inspection. In terms of self-repair, shape memory alloy particles will be added to the composite material. When the brake pad has small cracks due to wear, triggered by the braking heat, the shape memory alloy will automatically restore its original shape, fill the crack gaps, and extend the service life of the brake pad (it is expected to increase by 20%-30%). In addition, some research institutions are also exploring "antibacterial brake pads". By coating the surface of the material with a nano-silver coating, bacterial growth is inhibited, and the problem of peculiar smell caused by bacterial reproduction near the car wheel hub is solved.

These technological breakthroughs will further break the performance boundary of brake pad materials, promote the upgrade of automotive braking systems from "passive safety" to "active safety", and provide more reliable safety guarantees for the development of future intelligent cars.