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Mr. John Smith

Job title



The load-deflection relationship of automotive brake friction materials (also known as “compressibility”) is a characteristic which may both influence and advise as to brake performance, including driver experience, noise and vibration behaviour, and manufacturer quality control. It has been reported that changes in environmental humidity may significantly alter friction material compressibility in a formulation-dependent fashion – effects which are important considerations for testing protocols and real-world applicability. Greening’s presentation includes a rigorous investigation of humidity-dependent properties across differing friction materials and manufacturers, taking advantage of the high resolution and excellent repeatability of the Greening Model 1140 Compressibility Test Machine. Sets of brake pads from (at least) two different manufacturers and of varied material type (non-asbestos organic, semi-metallic, low-metallic, etc.) will be weighed to assess changes to moisture content after climate-controlled storage for at least 24 hours at Ambient, Low, and High relative humidity levels. Pad compressibility at ambient temperature and 130 bar simulated brake line pressure will be measured a total of 8 times (24-hoursoak before each test) at [2 x] Ambient, [2 x] Low, [2 x High], and [2 x Ambient] humidity levels. This testing protocol will allow for confirmation of repeatability at comparable moisture levels. Humidity-dependent differences relative to material types, manufacturers, and individual pad variation will be presented, as will the measurement of rebound/recovery after repeated rounds of testing. Results will provide a valuable resource in the awareness and understanding of how humidity effects may play a role in the design, testing, and manufacture of automotive brake friction materials

Greening Testing Labs: Mr. Charles Greening, Mr. Edward Sendler, Mr. Brent Greening

Effect of humidity levels on the compressibility of automotive brake friction materials

EB2022-TSD-010 • Full • EuroBrake 2022 • Testing requirements and friction couples


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