Validation of Test Rig Measurements and Prediction Tools for Friction Interface Modelling

2010 ◽  
Author(s):  
C. W. Schwingshackl ◽  
E. P. Petrov ◽  
D. J. Ewins
Keyword(s):  
Good Accuracy ◽  
Contact Stiffness ◽  
Contact Interface ◽  
Friction Contact ◽  
Test Rig ◽  
Normal Stress Distribution ◽  
Nonlinear Interface ◽  
Two Parameters ◽  
Contact Parameters ◽  
Interface Behaviour

The modelling of friction contact interfaces in structural dynamics attracts much interest in the gas turbine industry. In order to obtain reliable predictions of typical friction interfaces, such as encountered in under platform dampers or blade roots, accurate characteristics of friction interfaces must be provided to the analysis. It must be ensured that a sufficient number of parameters are provided, characterising all aspects of the friction contact, that the values are measured accurately, and that the contact parameters are interpreted and used correctly in the numerical modelling of the contact interfaces. This investigation demonstrates that measured friction coefficient and tangential contact stiffness are sufficient to reproduce the experimental friction interface behaviour and that these two parameters can be measured reliably in the available test rig. In combination with fine nonlinear interface meshes and accurate contact pressure representations, the measured interface behaviour of stick, micro- and macroslip is reproduced with good accuracy. The capability of modelling the microslip behaviour for the contact interface by a multitude of friction contact elements is explored and the effect of the normal stress distribution over the contact area on the microslip is studied.

Method for Direct Parametric Analysis of Nonlinear Forced Response of Bladed Discs With Friction Contact Interfaces

2004 ◽  
Author(s):  
E. P. Petrov
Keyword(s):  
Parametric Analysis ◽  
Large Scale ◽  
Normal Load ◽  
Forced Response ◽  
Finite Element Models ◽  
Contact Interface ◽  
Friction Contact ◽  
Interface Parameters ◽  
First Time ◽  
Contact Parameters

An effective method for direct parametric analysis of periodic nonlinear forced response of bladed discs with friction contact interfaces has been developed. The method allows, for the first time, forced response levels to be calculated directly as a function of contact interface parameters such as the friction coefficient, contact surface stiffness (normal and tangential coefficients), clearances, interferences, and the normal stresses at the contact interfaces. The method is based on exact expressions for sensitivities of the multiharmonic interaction forces with respect to variation of all parameters of the friction contact interfaces. These novel expressions are derived in the paper for a friction contact model, accounting for the normal load variation and the possibility of separation-contact transitions. Numerical analysis of effects of the contact parameters on forced response levels has been performed using large-scale finite element models of a practical bladed turbine disc with underplatform dampers and with shroud contacts.

Method for Direct Parametric Analysis of Nonlinear Forced Response of Bladed Disks With Friction Contact Interfaces

2004 ◽  
Vol 126 (4) ◽  
pp. 654-662 ◽  
Author(s):  
E. P. Petrov
Keyword(s):  
Parametric Analysis ◽  
Large Scale ◽  
Normal Load ◽  
Forced Response ◽  
Finite Element Models ◽  
Contact Interface ◽  
Friction Contact ◽  
Bladed Disks ◽  
Interface Parameters ◽  
Contact Parameters

An effective method for direct parametric analysis of periodic nonlinear forced response of bladed disks with friction contact interfaces has been developed. The method allows, forced response levels to be calculated directly as a function of contact interface parameters such as the friction coefficient, contact surface stiffness (normal and tangential coefficients), clearances, interferences, and the normal stresses at the contact interfaces. The method is based on exact expressions for sensitivities of the multiharmonic interaction forces with respect to variation of all parameters of the friction contact interfaces. These novel expressions are derived in the paper for a friction contact model, accounting for the normal load variation and the possibility of separation-contact transitions. Numerical analysis of effects of the contact parameters on forced response levels has been performed using large-scale finite element models of a practical bladed turbine disk with underplatform dampers and with shroud contacts.

Test Rig for Extraction of the Contact Parameters for Plane on Plane Contact

2012 ◽  
Author(s):  
D. Botto ◽  
M. Lavella ◽  
M. M. Gola
Keyword(s):  
Contact Area ◽  
Contact Stiffness ◽  
Point Contact ◽  
Real Plane ◽  
Operational Environment ◽  
Test Rig ◽  
Friction Forces ◽  
Plane Contact ◽  
Wide Range ◽  
Contact Parameters

The modelling of the friction interfaces has received much attention in recent years from the aerospace industry. In order to obtain reliable prediction of the nonlinear dynamic behaviour of the disc and blades in the aerospace engine the friction forces at interfaces, such as in under-platform dampers, blade and fir tree roots or shrouds, must be modelled accurately. Two contact parameters, namely the contact stiffness and the coefficient of friction, are sufficient to model, with good accuracy, the friction contact. The contact parameters are obtained experimentally, and are of interest for the designer only if representative of the operational environment of the engine. To pursue this aim a test rig has been designed to perform experiments in a wide range of temperatures, with different combinations of normal and tangential load, frequencies and mating materials, representative of the real operating condition of the engine. Most of the rigs found in literature perform most likely point contact even if the two bodies have plane mating surfaces. The design of a real plane-on-plane contact test rig is not an easy task but despite the difficulty a solution was found in the design shown in this work. The core of the rig is a tilting mechanism enabling one surface to lies down on the other so that the plane-on-plane contact is achieved, at least within the flatness geometrical tolerance of the surfaces. The results of the experiments are the hysteresis loops, namely the tangential contact force against the relative displacement, from which the contact parameters can be calculated. Measurements of displacements are taken very close to the actual contact area and are performed by means of two laser interferometers. Localized heating is achieved by means of an induction heating machine while a thermocouple measures the temperature at points close to the contact area.

Test Rig for Wear and Contact Parameters Extraction for Flat-on-Flat Contact Surfaces

2011 ◽  
Author(s):  
M. Lavella ◽  
D. Botto ◽  
M. M. Gola
Keyword(s):  
Friction Coefficient ◽  
Contact Stiffness ◽  
Inertial Mass ◽  
Aircraft Engine ◽  
Wear Behaviour ◽  
Test Rig ◽  
Contact Surfaces ◽  
Blade Failure ◽  
Contact Parameters ◽  
Flat Contact

In aircraft engine the blade resonant vibration amplitude is reduced by increasing the structural damping by using, for example, tip shrouds. These devices dissipate the energy generated at the contact surfaces between the relative motion and the friction force. Contact parameters as friction coefficient and contact stiffness are required to characterize the dynamics of the shrouded blade systems. Moreover if at the contact surfaces severe wear occurs a loss of interference takes place, the shroud is not longer able to dissipate energy and a catastrophic blade failure could take place. A test rig for contact parameters measurement and micro wear characterization of flat-on-flat contact surfaces has been developed. One of the specimens is attached to the rig frame, basically an inertial mass and four springs, excited by an electromagnetic shaker. The second specimen is allowed to approach the first specimen and to rotate in such a way the geometric contact between the two surfaces occurs on three points. In this way a real “flat-to-flat” contact has been obtained. The tangential contact force and the relative displacements between specimens are measured and the friction coefficient and contact stiffness, are determined. The expected results are the contact parameters and the wear behaviour of real flat-on-flat contact surfaces. The aim of this work is to describe the design principle of the test rig and show the first measurements.

Measurement of Contact Parameters of Flat on Flat Contact Surfaces at High Temperature

2012 ◽  
Author(s):  
D. Botto ◽  
M. Lavella ◽  
M. M. Gola
Keyword(s):  
Friction Coefficient ◽  
Vibration Amplitude ◽  
Contact Stiffness ◽  
Relative Displacement ◽  
Wear Behaviour ◽  
Test Rig ◽  
Contact Parameter ◽  
Contact Surfaces ◽  
Contact Parameters ◽  
Flat Contact

In aircraft engines the blade resonant vibration amplitude is normally reduced by increasing the structural damping by using, for example, tip shrouds. These devices dissipate the energy generated at the contact surfaces between the relative motion and the friction force. Contact parameters, principally the friction coefficient and contact stiffness, are required to characterize the dynamics of shrouded blade system. Moreover, if at these contact surfaces severe wear occurs, a loss of interference takes place and the energy dissipated by the shroud decreases. Consequently the blade vibration amplitude increases and a catastrophic blade failure could take place. In this work a test rig for the contact parameter measurements and micro wear characterization of flat-on-flat contact surfaces has been developed. The test rig works at high temperatures of up to 1000 °C, by means of induction heating. One of the specimens was attached to the rig frame, basically an inertial mass and four springs, and subsequently excited by an electromagnetic shaker. The second specimen was allowed to approach the first specimen and to rotate in such a way than the geometric contact between the two surfaces occurred at three points. In this way a real “flat to flat” contact was obtained. The two surfaces were kept in contact by means of a constant normal load. The tangential contact force was measured by a force sensor while the relative displacements between the contact surfaces were measured by two laser vibrometers. The relative displacement was kept under control by acting on the shaker force. Tangential force and relative displacement were used to describe the hysteresis loop and, consequently, to obtain the friction coefficient and contact stiffness during the wear process. The temperature is feedback controlled by using two thermocouples placed within the specimens near the contact surfaces. The expected results are the contact parameters and the wear behaviour of real flat-on-flat contact surfaces. The aim of this work is to describe the design principle of the test rig and present the initial measurements.

The elastic contact influences on passive walking gaits

Robotica ◽  
2010 ◽  
Vol 29 (5) ◽  
pp. 787-796 ◽  
Author(s):  
Feng Qi ◽  
Tianshu Wang ◽  
Junfeng Li
Keyword(s):  
Coulomb Friction ◽  
Dynamic Models ◽  
Contact Stiffness ◽  
Contact Forces ◽  
Hertz Contact ◽  
Walking Gait ◽  
Routes To Chaos ◽  
Coulomb Friction Law ◽  
Contact Parameters ◽  
Passive Model

SUMMARYThis paper presents a new planar passive dynamic model with contact between the feet and the ground. The Hertz contact law and the approximate Coulomb friction law were introduced into this human-like model. In contrast to McGeer's passive dynamic models, contact stiffness, contact damping, and coefficients of friction were added to characterize the walking model. Through numerical simulation, stable period-one gait and period-two gait cycles were found, and the contact forces were derived from the results. After investigating the effects of the contact parameters on walking gaits, we found that changes in contact stiffness led to changes in the global characteristics of the walking gait, but not in contact damping. The coefficients of friction related to whether the model could walk or not. For the simulation of the routes to chaos, we found that a small contact stiffness value will lead to a delayed point of bifurcation, meaning that a less rigid surface is easier for a passive model to walk on. The effects of contact damping and friction coefficients on routes to chaos were quite small.

scholarly journals Modeling and prediction for gas production during coalbed methane drainage based on two indirect reservoir parameters

2018 ◽  
Vol 36 (6) ◽  
pp. 1424-1437 ◽  
Author(s):  
Mingjun Zou ◽  
Xiaochun Lv ◽  
Zhiquan Huang ◽  
Simin Wei ◽  
Miao Zhang ◽  
...  
Keyword(s):  
Coalbed Methane ◽  
Good Accuracy ◽  
Simulated Data ◽  
Gas Production ◽  
Methane Drainage ◽  
Modeling And Prediction ◽  
Cubic Polynomial ◽  
Southern Qinshui Basin ◽  
Two Parameters ◽  
Gas Production Prediction

Two indirect parameters influencing coalbed methane (CBM) drainage performances are proposed in this paper, which are effective desorption radius and difference between reservoir pressure and critical desorption pressure (DRPCDP). Variations of the two parameters during CBM drainage are investigated, which shows that they have a linear relationship. By using formula derivations, a theoretical model for gas production prediction is built. It suggests that the cumulative gas production is a product of square of effective desorption radius with DRPCDP, and there is also a cubic polynomial relationship between cumulative gas production and linear average DRPCDP. Furthermore, well PM01 located at southern Qinshui basin of China is selected as a case, and a commercial software is adopted to predict the gas production. Compared with the simulated and modeled cumulative gas productions, the simulated data match well with the modeled data, which indicates that the model has a good accuracy.

Fretting Wear of CMSX4 at Blade Tip Interface With and Without Coating

2009 ◽  
Author(s):  
M. Lavella ◽  
D. Botto ◽  
M. M. Gola
Keyword(s):  
Flat Surface ◽  
Contact Stiffness ◽  
Three Dimensional ◽  
Large Change ◽  
Fretting Wear ◽  
Wear Behaviour ◽  
Wear Process ◽  
Blade Tip ◽  
Coated Surfaces ◽  
Contact Parameters

Fretting wear is a complex phenomenon that occurs at component interfaces that are subjected to low amplitude oscillation under high contact pressure. In turbomachinery fretting occurs also at the blade tip interfaces where shrouds, that have the aim to reduce the blade resonant vibration amplitude, are machined. To diminish the fretting damage coatings are applied to the blade tips. The aim of this study is to compare the fretting wear behaviour of single crystal CMSX-4 superalloy interfaces with and without plasma sprayed T-800 coating. Experiments have been conducted with hemispherical surface in contact with a flat surface of the same materials at temperature of 800 °C. The hysteresis cycles have been measured through the experiment. The comparison of the hysteresis cycles shown that the tangential contact stiffness of the coated surfaces is greater then that of the surfaces without coating. At the end of wear process, the mating surfaces have been characterized by three-dimensional optical interferometry and SEM analysis. After 10×106 wear cycles, the uncoated surfaces show a large change in the contact parameters and fretting cracks on the flat surface. On the other hand, the coated surfaces do not shows a measurable change in the contact parameters while the coating damage on the flat surface leads to predict an incipient catastrophic wear.

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