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.

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.

scholarly journals A New Combined Model for considering the Plasticity Effects in Contacting Asperities

2020 ◽  
Vol 2020 ◽  
pp. 1-12
Author(s):  
Mohammad Amini Sarabi ◽  
Parisa Hosseini Tehrani
Keyword(s):  
Surface Roughness ◽  
Contact Area ◽  
Contact Stiffness ◽  
Contact Angles ◽  
Combined Model ◽  
Stick Slip ◽  
Railway Engineering ◽  
Asperity Distribution ◽  
Contact Parameters ◽  
High Contact Pressure

Wheel-rail contact in railway engineering is an important topic. Due to different materials and surface roughness of wheel and rail, the contact characteristics can alter significantly. This article aims to investigate the effects of surface roughness and asperities on the contact parameters such as contact area, contact force, and contact stiffness. The lateral contacts between asperities are assumed to be the general contact condition. Azimuthal and contact angles distributions are assumed to be spherical harmonic distribution. This assumption is compatible with the asperity distribution on the wheel and the rail surfaces. Besides, a new combined model is developed to cover the stick-slip and the plasticity effects in contacting asperities. The results of the presented model offer very good estimations for the asperities contact characteristics, especially at the small-contact area and separation where high-contact pressure and plastic deformation usually exist.

Perfectly Elastic Axisymmetric Sinusoidal Surface Asperity Contact

2016 ◽  
Vol 138 (3) ◽  
Author(s):  
S. Saha ◽  
Y. Xu ◽  
R. L. Jackson
Keyword(s):  
Contact Area ◽  
Material Properties ◽  
Point Contact ◽  
Asperity Contact ◽  
Hertz Contact ◽  
Practical Applications ◽  
Wide Range ◽  
Complex Models ◽  
Complete Contact ◽  
Sinusoidal Surface

This work presents a finite element (FE) study of a perfectly elastic axisymmetric sinusoidal-shaped asperity in contact with a rigid flat for different amplitude to wavelength ratios and a wide range of material properties. This includes characterizing the pressure required to cause complete contact between the surfaces. Complete contact is defined as when there is no gap remaining between two contacting surfaces. The model is designed in such a way that its axisymmetric and interaction with the adjacent asperities are considered by the effect of geometry at the base of the asperity. The numerical results are compared to the model of curved point contact for the perfectly elastic case (known as Hertz contact) and Westergaard's solution. Once properly normalized, the nondimensional contact area does not vary with nondimensional load. The critical pressure required to cause complete contact is found. The results are also curve fitted to provide an expression for the contact area as a function of load over a wide range of cases for use in practical applications, such as to predict contact resistance. This could be a stepping stone to more complex models.

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.

Synchronous Observation With Friction Measurement Prior to and During Occurrence of Scuffing

2010 ◽  
Author(s):  
Kazuyuki Yagi ◽  
Joichi Sugimura ◽  
Seiji Kajita ◽  
Toshihide Ohmori ◽  
Atsushi Suzuki
Keyword(s):  
Friction Coefficient ◽  
Contact Area ◽  
Wear Debris ◽  
Point Contact ◽  
The Other ◽  
Test Rig ◽  
Friction Measurement ◽  
Inlet Zone ◽  
Sapphire Disc ◽  
Ball On Disc

In the current work, scuffing phenomenon was investigated by a direct observation of a contact area. A ball-on-disc test rig was used, which produced a point contact area between a rotating sapphire disc and a stationary steel ball. Sequence of the friction and photograph in the contact area was synchronously obtained prior to and during occurrences of scuffing. Experiments were conducted in a dry condition and a lubricated condition with hexadecane. In the lubricated condition, wear debris accumulated in the inlet zone entered suddenly into the contact area to sharply increase the friction coefficient. On the other hand, macro plastic flow occurred in the whole contact area in the dry condition during a rapid increase in friction coefficient.

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.

Damping Performance of Axial Turbine Stages With Loosely Assembled Friction Bolts: The Non-Linear Dynamic Assessment — Part II

2007 ◽  
Author(s):  
J. Szwedowicz ◽  
Th. Secall-Wimmel ◽  
P. Du¨nck-Kerst
Keyword(s):  
Contact Stiffness ◽  
Contact Condition ◽  
Operating Conditions ◽  
Friction Forces ◽  
Linear Dynamic ◽  
Resonance Frequencies ◽  
Contact Behaviour ◽  
Wide Range ◽  
Dynamic Analyses ◽  
Non Linear

An entire family of twisted and tapered low pressure steam turbine SK-blades with pinned radial root and loosely assembled conical bolts is designed by scaling of the aerodynamic and mechanical properties of the smallest airfoil. For SK-blades operating with variable speed, the friction bolts, mounted in the upper airfoil part, provide either damping or coupling capabilities for the blades with respect to resonance conditions. The damping and coupling performance have been proved experimentally in the test rig of the real turbine. The measurements of the smallest SK-disc assembly under different operating conditions have allowed understanding the dynamic and damping behaviour of the bolts that are either friction dampers or coupling devices for the vibrating blades depending on the excitation level. In this paper, non-linear dynamic analyses of the smallest and large SK-turbine stage are performed and compared with the experimental data. The modal blade dynamics is defined by 30 complex FE mode shapes of the freestanding blades coupled by the disc whereby the bolt’s motion is described by 6 rigid body modes. The sticking contact condition between the blades and bolts is represented by the normal and tangential contact stiffness. These values are firstly estimated analytically with the Hertz’s formulas for the FE reaction forces and contact areas. More realistic contact stiffness values are obtained from the iterative process, in which the resonance frequencies are calculated with the steady-state simulations and compared to the FE nodal diameter curves for sticking contact conditions that meet the experimental frequencies very well (GT2007-27502). In non-linear simulations, in case of exceeding the sticking contact condition, the induced friction forces are linearized by the Harmonic Balance Method. In this manner, the micro-slipping and sticking contact behaviour at all contact points are calculated iteratively for the specified excitation amplitudes, friction coefficient, contact roughness and aerodamping values that are known from the experiment. The computed results of the tuned smallest SK-blades agree with the experimental resonance stresses of 12 measured blades. Differences between the computed and measured stresses are caused by mistuning, which was not quantified in the experiment. The non-linear dynamic analyses provide evidence of good damping performance for the smallest and large SK-blades with respect to wide range of excitation forces, different friction coefficients and various aerodynamic damping values. For the analyzed resonances of the 8th engine order, the scalability of damping performance is found for the SK-blades of different sizes.

Structure and properties of compact articles from high-alloyed iron powder with adding of boron nitride

2020 ◽  
pp. 39-48
Author(s):  
B. O. Bolshakov ◽  
◽  
R. F. Galiakbarov ◽  
A. M. Smyslov ◽  
◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Boron Nitride ◽  
Grain Boundary ◽  
Bending Strength ◽  
Physical And Mechanical Properties ◽  
Operating Conditions ◽  
Structure And Properties ◽  
Steam Turbines ◽  
Friction Forces ◽  
Wide Range

The results of the research of structure and properties of a composite compact from 13 Cr – 2 Мо and BN powders depending on the concentration of boron nitride are provided. It is shown that adding boron nitride in an amount of more than 2% by weight of the charge mixture leads to the formation of extended grain boundary porosity and finely dispersed BN layers in the structure, which provides a high level of wearing properties of the material. The effect of boron nitride concentration on physical and mechanical properties is determined. It was found that the introduction of a small amount of BN (up to 2 % by weight) into the compacts leads to an increase in plasticity, bending strength, and toughness by reducing the friction forces between the metal powder particles during pressing and a more complete grain boundary diffusion process during sintering. The formation of a regulated structure-phase composition of powder compacts of 13 Cr – 2 Mо – BN when the content of boron nitride changes in them allows us to provide the specified physical and mechanical properties in a wide range. The obtained results of studies of the physical and mechanical characteristics of the developed material allow us to reasonably choose the necessary composition of the powder compact for sealing structures of the flow part of steam turbines, depending on their operating conditions.

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.

Experimental and numerical study on cavitation under elastohydrodynamic lubrication point contact

2021 ◽  
pp. 135065012110527
Author(s):  
Mingfei Ma ◽  
Wen Wang ◽  
Wenxun Jiang
Keyword(s):  
Contact Area ◽  
Numerical Study ◽  
Ambient Pressure ◽  
Point Contact ◽  
Elastohydrodynamic Lubrication ◽  
Hertzian Contact ◽  
Pressure Area ◽  
Cavitation Pressure ◽  
Experimental Researches ◽  
State 1

As a common phenomenon in elastohydrodynamic lubrication, cavitation has an effect on the completeness of the oil film in the contact area. Many studies have therefore been conducted on cavitation. Experimental researches on cavitation usually rely on optical interference observation, which offers a limited resolution and observation range. In this paper, an infrared thermal camera is used to observe the cavity bubbles on a ball-on-disc setup under sliding/rolling conditions. The results show that the cavity length increases with an increases of the entrainment speed and the viscosity of the lubricants. These observations are explained by a numerical model based on Elrod's algorithm. Effects of entrainment speed and lubricant viscosity on the breakup of cavitation bubbles and the cavitation states are investigated. Both the simulation and experimental results show that a negative pressure area is present behind the Hertzian contact area. The ambient pressure plays a role in maintaining cavitation state 1. The cavitation pressure is close to the vacuum pressure when the entrainment speed is low and to the ambient pressure instead when the entrainment speed is high.

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