The current compressibility measurement method generates compression stress-strain curves. The strain during the 3rd compression is called “compressibility”. In physics, compressibility is defined as a reciprocal of compression modulus. Using this definition, the tangent and secant compression moduli are obtained from the compression stress-strain curves and corresponding compressibility numbers are obtained. The tangent modulus increases while the secant modulus decreases with increasing moisture content of brake pads. When disc pads are exposed to humidity, the pads gain weight following a linear relationship between the weight and the square root of exposure time in the initial stage of moisture sorption. As disc pads contain 2 – 5 v.% of elastomers and 12-22 v.% porosity, the possibility of viscoelastoplastic and poroelastoplastic behaviour of pads during compression is discussed. A possible relationship between compressibility and hardness is reviewed.

ASK Automotive: Mr. Shiv Raj Singh; SKR Consulting LLC: Mr. Seong Kwan Rhee