Copper-free NAO disc pads of passenger cars were investigated for a combination of prior braking conditions and moisture adsorption influencing in-stop friction during low-speed and moderate-speed stops. Disc pads adsorb moisture continuously with time via 3 stages when exposed to humidity. Prior braking conditions and moisture adsorption strongly influence subsequent in-stop friction behavior at room temperature. The low-speed in-stop friction behavior looks totally different from that of moderate-speed stops. Moderate prior braking conditions create increased moisture sensitivity for subsequent low-speed braking at low temperatures as compared with severe prior braking conditions. The low-speed in-stop friction increases and oscillates with increasing moisture adsorption and goes down towards the end of a stop, thus generating a positive Mu-V curve. The moderate-speed stops produce a U-shape in-stop friction curve and the depth of the U becomes deeper and deeper with increasing humidity adsorption. The moisture content needs to be quantified/specified to obtain repeatable and reproducible brake test results as the moisture is an unintended and uncontrolled ingredient of a friction material.

Mr. Meechai Sriwiboon, Technical Director, King Mongkut’s University of Technology; Dr. Saiprasit Koetniyom, MAE Doctoral Curriculum Chairman, ASAE Program Coordinator, Lecturer and Researcher, The Sirindhorn International Thai-German Graduate School of Engineering; Dr. Seong Kwan Rhee, President, SKR Consulting LLC; Mr. Jittrathep Sukultanasorn, R&D Supervisor, Compact international (1994); Ms. Kritsana Kaewlob, Product and Raw materials Research Project Manager, Compact international (1994)