A microslip friction model with normal load variation induced by normal motion

Abstract

A two-dimensional microslip friction model with normal load variation induced by normal motion is presented in this paper. The model is a distributed parameter model, which characterizes the stick-slipseparation of the contact interface and determines the resulting friction force, including its time variance and spatial distribution, between two elastic structures. When the relative motion is simple harmonic motion, the stick-slip-separation transition angles associated with any point in the contact area can be analytically determined within a cycle of motion. In addition, if the relative motion is given, stick-slip-separation transition boundaries inside the contact area and their time variances can be determined. Along with an iterative multi-mode solution approach utilizing harmonic balance method (HBM), the developed model can be employed to determine the forced response of frictionally constrained structures. In the approach, the forced response is constructed in terms of the free mode shapes of the structure; consequently, it can be determined at any excitation frequency and for any type of normal load distribution. Two examples, a one-dimensional beam like damper and a more realistic blade to ground damper, are employed to illustrate the predictive abilities of the developed model. It is shown that while employing a single mode model, transition boundaries for the beam like damper agrees with the results given in the literature, the developed method identifies the phase difference along the slip to stick transition boundary when a multi-mode model is employed. Moreover, while partial slip is illustrated in the two examples, typical softening and hardening effects, due to separation of the contact surface, are also predicted for the blade to ground damper.

Forced Response of Shrouded Blades With Variable Operating Points

“…1, a widely used model in dynamical systems with frictional contacts [6,7,11]. For the calculation of a three-dimensional spatial contact, it is assumed that the tangential components are independent of each other, a common assumption in forced response calculations with frictional contacts [7].…”

Modelling Friction Contacts in Structural Dynamics and its Application to Turbine Bladed Disks

“…Then as the tangential contact load grows larger, the slipping area extends progressively to the whole contact area and gross slip occurs. The transition state between the sticking and the gross slipping conditions is called microslip (Filippi et al, 2004;Cigeroglu et al, 2007;Allara, 2009). It is an important contact state, since most of the friction contacts in industrial application works in microslip conditions.…”

Dynamic Response of a Simplified Turbine Blade Model with Under-Platform Dry Friction Dampers Considering Normal Load Variation

“…Cigeroglu et al [8] adopted a one-dimensional dynamic microslip friction model, including the damper inertia. This microslip friction model was further developed for a two-dimensional distributed parameter model with normal load variation induced by normal motion [9], in which they explored the use of this new model with harmonic balance method in frictionally constrained structures with a varying normal load. Further on, Cigeroglu et al [10] implemented this model on wedge-shaped under-platform dampers in a bladed disc assembly.…”

“…In [9,12] the dampers could partially detach from the blade platforms during vibration. In [13,14] the dampers were modeled with the finite elements.…”