STICK-SLIP-SEPARATION ANALYSIS AND NONLINEAR STIFFNESS AND DAMPING CHARACTERIZATION OF FRICTION CONTACTS HAVING VARIABLE NORMAL LOAD

Mechanical systems in which moving components are mutually constrained through contacts often lead to complex contact kinematics involving t angential and normal relative motions. A friction contact model is pro posed to characterize this type of contact kinematics that imposes bot h friction non-linearity and intermittent separation non-linearity on the system. The stick-slip friction phenomenon is analyzed by establis hing analytical criteria that predict the transition between stick, sl ip, and separation of the interface. The established analytical transi tion criteria are particularly important to the proposed friction cont act model for the transition conditions of the contact kinematics are complicated by the effect of normal load variation and possible interf ace separation. With these transition criteria, the induced friction f orce on the contact plane and the variable normal load perpendicular t o the contact plane can be predicted for any given cyclic relative mot ions at the contact interface and hysteresis loops can be produced so as to characterize the equivalent damping and stiffness of the frictio n contact. These non-linear damping and stiffness methods along with t he harmonic balance method are then used to predict the resonant respo nse of a frictionally constrained two-degree-of-freedom oscillator. Th e predicted results are compared with those of the time integration me thod and the damping effects, the resonant frequency shift, and the ju mp phenomenon are examined. (C) 1998 Academic Press Limited.