Identification of Coulomb Friction Existing at Supporting Points of Hinged-hinged Beam

Systems with slight Coulomb friction at the supporting point have very small dead zone in which the system stops after free oscillation. Small stiffness makes the dead zone very wide even under slight Coulomb friction, because it is determined by the ratio between Coulomb friction and stiffness. In the previous study, it is theoretically and experimentally clarified in the neighborhood of buckling point that slight Coulomb friction produces large dead zone around the stable and unstable steady states of the pitchfork bifurcation in the case without Coulomb friction. Therefore, it is very important in the analyses on behavior of the low stiffness system such as flexible structures in space agency, to estimate the value of Coulomb friction. In this paper, we propose an experimental identification method for bending moment due to Coulomb friction at the supporting points of hinged-hinged beam. The moment due to dynamic friction is identified from experimental free oscillation by separating the effects of viscous damping and dynamic friction. For static friction, we use the dead zone in bifurcation diagram due to static friction. In the vicinity of the buckling point, the zone is very wide and its boundary is easily obtained from experiment. We show an identification method of the moment due to dynamic friction from the experimentally obtiained boundary.