Abstract
In this study, through severe reduced-scale braking tests, we investigate the wear and integrity of organic matrix brake pads against gray cast iron (GCI) discs. Two prototype pad materials are designed with the aim of representing a typical non-metal NAO and a low-steel (LS) formulation. The worn surfaces are observed with SEM. The toughness of the pad materials is tested at the raw state and after a heat treatment. During braking, the LS-GCI disc configuration produces heavy wear. The friction parts both keep their macroscopic integrity and wear appears to be homogeneous. The LS pad is mostly covered by a layer of solid oxidized steel. The NAO-GCI disc configuration wears dramatically and cannot reach the end of the test program. The NAO pad suffers many deep cracks. Compacted third body plateaus are scarce and the corresponding disc surface appears to be very heterogeneous. The pad materials both show similar strength at the raw state and similar weakening after heat treatment. However, the NAO material is much more brittle than the LS material in both states, which seems to favor the growth of cracks. The observations of crack faces suggest that long steel fibers in the LS material palliate the brittleness of the matrix, even after heat damage.
Highlights
Academic Editor: Andrzej DzierwaReceived: 2 August 2021Accepted: 21 September 2021Published: 24 September 2021Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.Licensee MDPI, Basel, Switzerland.Friction materials used for commercial automotive brake pads mostly belong to the family of non-asbestos organic (NAO) materials
The severe braking tests conducted in this study were able to discriminate a lowsteel and a NAO-pad formulation sliding against cast iron discs
The two configurations generated different coefficient of friction (CoF) values, but more importantly, they showed major differences regarding the wear and integrity of the brake pads
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Friction materials used for commercial automotive brake pads mostly belong to the family of non-asbestos organic (NAO) materials. These materials usually consist of a resin matrix, various types of fibers, filler components, as well as friction and wear modifiers. These formulations can include metallic constituents such as iron or copper. NAO formulations containing a small amount of steel fibers are called low-steel (LS) materials
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