Friction Material Elastic Property Round Robin Study

A method for ultrasonic measurement of friction material elastic constants was evaluated through a round-robin process. The purpose of the study was two-fold: 1) to formulate and evaluate a standard test method (SAE J2725) for measuring elastic constants using ultrasound and 2) to quantify the measurement variability when the testing method is applied by multiple operators and instrumentation. The study involved measurement of 6 different friction materials by multiple operators at 5 different laboratories. All participants measured the same 6 samples. The friction material sample set ranged in density from 2.3 gm/cc to 3.2 gm/cc, the in-plane modulus varied from 11 GPa to 25 GPa, and the through-the-thickness modulus varied from 3 GPa to 7 GPa. All measurements were carried out at ambient temperature in accordance with procedures outlined in the draft SAE test specification (J2725).