Experimental and Numerical Investigation of Contact Parameters in a Dovetail Type of Blade Root Joints

this paper focuses on the contact characteristics of the blade root joints subjected to the dry friction damping under periodic excitation. The numerical method and experimental procedure are combined to trace the contact behavior in the nonlinear vibration conditions. In experimental procedure, a novel excitation method alongside the accurate measurements is used to determine the frequencies of the blade under different axial loads. In numerical simulations, local behavior of contact areas is investigated using the reduction method as a reliable and fast solver. Subsequently, by using both experimental measurements and numerical outcomes in a developed code, the global stiffness matrix is calculated. This leads to find the normal and tangential stiffness in the contact areas of a dovetail blade root joints. The results indicate that the proposed method can provide an accurate quantitative assessment for investigation the dynamic response of the joints with focusing the contact areas.

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A Comparison of Two Microslip Contact Models for Studying the Mechanics of Underplatform Dampers

Volume 7C: Structures and Dynamics ◽

10.1115/gt2018-76007 ◽

2018 ◽

Cited By ~ 1

Author(s):

Chao Xu ◽

Dongwu Li ◽

Muzio M. Gola ◽

Chiara Gastaldi

Keyword(s):

Friction Coefficient ◽

Friction Model ◽

Tangential Displacement ◽

Tangential Stiffness ◽

Contact Loads ◽

Contact Kinematics ◽

Contact Models ◽

Friction Models ◽

Microslip Friction ◽

Contact Parameters

In turbine blade systems, under-platform dampers are widely used to attenuate excessive resonant vibrations. Subjected to vibration excitation, the components with frictionally constrained interfaces can involve very complex contact kinematics induced by tangential and normal relative motions. To effectively calculate the dynamics of a blade-damper system, contact models which can accurately reproduce the interface normal and tangential motions are required. The large majority of works have been developed using macroslip friction models to model the friction damping at the contact interface. However, for those cases with small tangential displacement where high normal loads are applied, macroslip models are not enough to give accurate results. In this paper two recently published microslip models are compared, between them and against the simple macroslip spring-slider model. The aim is to find to which extent these models can accurately predict damper mechanics. One model is the so called GG array, where an array of macroslip elements is used. Each macroslip element of the GG array is assigned its own contact parameters and for each of them four parameters are needed: normal stiffness, tangential stiffness, normal gap and friction coefficient. The other one is a novel continuous microslip friction model. The model is based on a modification of the original classic IWAN model to couple normal and tangential contact loads. Like the GG array the model needs normal and tangential stiffness, and friction coefficient. Unlike the GG array the model is continuous and, instead of the normal gap required by the GG array, the Modified IWAN model needs a preload value. The two models are here applied to the study of the mechanics of a laboratory under-platform damper test rig. The results from the two models are compared and allow their difference, both for damper mechanics and for the complex-spring coefficients, to be assessed.

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Validation of a Finite Element Humeroradial Joint Model of Contact Pressure Using Fuji Pressure Sensitive Film

Journal of Biomechanical Engineering ◽

10.1115/1.4031976 ◽

2015 ◽

Vol 138 (1) ◽

Cited By ~ 5

Author(s):

Sunghwan Kim ◽

Mark Carl Miller

Keyword(s):

Finite Element ◽

Contact Stress ◽

Contact Area ◽

Axial Loads ◽

Contact Areas ◽

Pressure Sensitive ◽

Maximum Contact Stress ◽

Sensitive Film ◽

Pressure Sensitive Film ◽

Maximum Contact

A finite element (FE) elbow model was developed to predict the contact stress and contact area of the native humeroradial joint. The model was validated using Fuji pressure sensitive film with cadaveric elbows for which axial loads of 50, 100, and 200 N were applied through the radial head. Maximum contact stresses ranged from 1.7 to 4.32 MPa by FE predictions and from 1.34 to 3.84 MPa by pressure sensitive film measurement while contact areas extended from 39.33 to 77.86 mm2 and 29.73 to 83.34 mm2 by FE prediction and experimental measurement, respectively. Measurements from cadaveric testing and FE predictions showed the same patterns in both the maximum contact stress and contact area, as another demonstration of agreement. While measured contact pressures and contact areas validated the FE predictions, computed maximum stresses and contact area tended to overestimate the maximum contact stress and contact area.

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Experimental Investigation of a Platform Damper With Curved Contact Areas

Volume 6A: 18th Biennial Conference on Mechanical Vibration and Noise ◽

10.1115/detc2001/vib-21391 ◽

2001 ◽

Author(s):

Martin H. Jareland

Keyword(s):

Simulation Model ◽

Coefficient Of Friction ◽

Normal Force ◽

Contact Interface ◽

Friction Damper ◽

Contact Areas ◽

Tangential Stiffness ◽

Series Of Experiments ◽

Contact Surfaces ◽

The Difference

Abstract This paper presents a set of experiments which have been performed with a new friction damper for a high pressure turbine. The main objective of these experiments was to tune a simulation model for the current damper. The simulation model used is valid for both microslip and macroslip. A number of other topics were also investigated, such as influence of glued platforms, repeatability of an experiment, comparison of new and used dampers, and the change in surface structure of the contact areas. A similar set of experiments has been performed earlier with the current damper. On that occasion, it was found that the experiments and simulations did not agree as desired and therefore a new set of experiments was suggested. This paper presents the new experiments and the new simulations with a more precisely tuned model. The simulation model is tuned by selecting a suitable coefficient of friction and tangential stiffness for the contact interface model. It is found that the simulations agree well with the experimental results when the normal force is held constant and the excitation force is varied. The properties of the contact, contact area and pressure, are unchanged when the normal force is constant. If a new damper is compared with a damper that has been used in a series of experiments, it is found that the resonance shifts to a lower frequency and that the amplitude increases. This is probably caused by a decrease in coefficient of friction due to wear of the contact surfaces. The repeatability of an experiment has been investigated by running the same experiment five times in succession. It was found that the repeatability was very good if the position of the damper was not changed. The differences that were found were mainly due to wear on the contact surfaces. A comparison of sweeping forward or backward in frequency was also performed. It showed that the difference was small both for experiments with small motions in the contacts and for experiments with a high amount of macroslip.

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