A THEORETICAL-ANALYSIS OF BREAKAWAY FRICTION MEASUREMENT

The transient response of an I-beam friction measurement system to a constant disk acceleration is theoretically analyzed. The friction measurement system is modeled as a single-degree-of-freedom system. It is found that the true breakaway friction is different from the measured breakaway friction, and that the true breakaway time is also different from the measured breakaway time. The system measurement error is evaluated as a function of the acceleration, the effective mass, the spring stiffness, as well as the static and kinetic coefficients of friction. A closed-form dimensionless solution is derived for the system measurement error. If the dynamic effect of the measurement system can be neglected by selecting an appropriate effective mass and acceleration, the maximum possible discretization error can be estimated as a dimensionless function of the discretization frequency, the breakaway friction, the spring stiffness, and the acceleration.