Search

Improving the rigidity of machine tools for identifying the weak links of structural stiffness is one of the important issues in mechanical engineering. In this paper, a new weak index is proposed on a cantilever structure of the machine tool to identify the weak stiffness link. The weak index is a frequency parameter obtained via the vibration test method. In this method, the FRF coefficient of variation technique is proposed based on the FRF curvature method. The change of weak index is used to identify the weak link in the structural stiffness. The element stiffness weakening method that employs numerical examples of a cantilever beam and an elastic support beam is used to simulate the weak links of the stiffness. Compared with the FRF curvature ratio (FRF_CR) method, the FRF mutation coefficient is improved in the same frequency range. Moreover, the FRF_MCR indicator has more frequency points than the FRF_CR indicator in the same frequency range.

In practice, it is difficult to avoid the axis angle deviation when some regular surfaces are in micro-sliding, such as gears and machined surfaces. In order to better investigate the micro-motion contact characteristics, a crossed paraboloidal contact model under frictional condition is proposed to simulate both tangential displacement-controlled fretting and the evolution of the energy dissipation in a load cycle. By deriving the theoretical of the normal and tangential contact course of the model, the load–displacement curves during initial loading, unloading, and reloading stage are presented. On this basis, the hysteresis curve is then obtained by integrating the closed area surrounded by load–displacement during unloading and reloading, which also means that the empirical formulation for microslip in a load cycle is constructed. This study also reveals the plastic yield phenomenon under pure normal loading and plastic shakedown behavior caused by cyclic reciprocating displacement loads. In addition, the research on the junction growth, the evolution of tangential load, and hysteresis curve with different COFs under multiple-cycle load is also carried out. The implications of involved parameters, such as friction coefficient, axis intersection angle, normal load, and so on, are discussed with respect to hysteresis curve shape and energy dissipation. The difference in hysteresis and energy dissipation curves between the paraboloidal contact model and other classic contact models is then presented. It is discovered by comparison with other models that the paraboloidal contact model presents a relatively high energy dissipation in a load cycle.