Determination of friction coefficients for cutting brush — road surface interaction through FEM

A novel Finite Element Model (FEM) is used to determine the coefficients of friction between the bristles of a cutting brush of street sweepers and a concrete road surface. The model deals with brush dynamics and entails a 3-D transient non-linear structural analysis involving contact. Each row of clusters is modeled by a single beam. The beams are subjected to inertia forces, and the surface is rotated and raised until the required penetration is achieved. Values of the friction coefficients are calculated for three rotational speeds: 60, 100, and 140 r/min. Transient effects are rapidly damped out and the coefficients of friction can be determined with accuracy. In order to obtain these, experimental results in [1] are compared to those of this work. It is concluded that the FEM is valid, and it is corroborated that, contrary to a flicking brush, the brush vertical force is not affected significantly by the coefficient of friction. Finally, it is found that the coefficients of friction, which are obtained from torque results, depend on the sliding velocity. The results were fitted to an exponential curve that corresponds to μs = 0.70, μk = 0.27, and cv = 0.40 s/m.