Predicting a contact's sensitivity to initial conditions using metrics of frictional coupling

Flicek, Robert C.; Brake, Matthew Robert; Hills, D.A.

doi:10.1016/j.triboint.2016.09.038

Cited by 12 publications

(2 citation statements)

References 19 publications

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“…(2), p i w (t), q i w (t) are the nodal forces that would be produced by the external loads if the nodes were all welded in contact at v = w = 0. The matrix B is a measure of the coupling between the normal and tangential contact problems [14] and plays a crucial role in the historydependence of the frictional evolution problem.…”

Section: Problem Descriptionmentioning

confidence: 99%

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Wedging of Frictional Elastic Systems

2019

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We consider discrete two-dimensional elastic systems with Coulomb friction contacts, and investigate the conditions that must be satisfied if these are to be capable of becoming ‘wedged’ --- i.e. of remaining with non-zero elastic deformations when all external loads have been removed. The condition for wedging is reduced to the requirement that a prescribed set of constraint vectors should fail to positively span the N-dimensional vector space of nodal displacements. We also show that the range of admissible wedged states increases monotonically with the coefficient of friction f and that there exists a unique critical coefficient fw such that wedging is impossible for f < fw and possible for f > fw.

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Section: Problem Descriptionmentioning

confidence: 99%

“…The pair of constraints (10) (11) is satisfied for all nodes i  (1, N), in which case B=0 and the system is 'uncoupled' [14].…”

Section: Positive Spanmentioning

confidence: 99%

Wedging of Frictional Elastic Systems

2019

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Parametric study for model calibration of a friction-damped turbine blade with multiple test data

Ferhatoglu,

Botto,

Zucca

2024

Nonlinear Dyn

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Model updating using multiple test data is usually a challenging task for frictional structures. The difficulty arises from the limitations of nonlinear models which often overlook the uncertainties inherent in contact interfaces and in actual test conditions. In this paper, we present a parametric study for the model calibration process of a friction-damped turbine blade, addressing the experimentally measured response variability in computational simulations. On the experimental side, a recently developed test setup imitating a turbomachinery application with mid-span dampers is used. This setup allows measuring multiple responses and contact forces under nominally identical macroscale conditions. On the computational side, the same system is modeled in a commercial finite element software, and nonlinear vibration analyses are performed with a specifically developed in-house code. In numerical simulations, the multivalued nature of Coulomb’s law, which stems from the inherent variability range of static friction forces in permanently sticking contacts, is considered to be the main uncertainty. As the system undergoes vibration, this uncertainty propagates into the dynamic behavior, particularly under conditions of partial slip in contacts, thus resulting in response variability. A deterministic approach based on an optimization algorithm is pursued to predict the limits of the variability range. The model is iteratively calibrated to investigate the sensitivity of response limits to contact parameters and assembly misalignment. Through several iterations, we demonstrate how uncertain initial contact conditions can be numerically incorporated into dynamic analyses of friction-damped turbine blades. The results show a satisfactory level of accuracy between experiments and computational simulations. This work offers valuable insights for understanding what influences test rig response and provides practical solutions for numerical simulations to improve agreement with experimental results.

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