The Role of Friction in Mechanical Joints

2001 ◽  
Vol 54 (2) ◽  
pp. 93-106 ◽  
Author(s):  
L. Gaul ◽  
R. Nitsche
Keyword(s):  
Contact Forces ◽  
Hertzian Contact ◽  
Experimental Investigations ◽  
Mechanical Joints ◽  
Research Activities ◽  
Nonlinear Transfer ◽  
Practical Engineering ◽  
Engineering Models ◽  
Transfer Behavior ◽  
Damped Systems

Vibration properties of most assembled mechanical systems depend on frictional damping in joints. The nonlinear transfer behavior of the frictional interfaces often provides the dominant damping mechanism in a built-up structure and plays an important role in the vibratory response of the structure. For improving the performance of systems, many studies have been carried out to predict, measure, and/or enhance the energy dissipation of friction. This article reviews approaches for describing the nonlinear transfer behavior of bolted joint connections. It gives an overview of modeling issues. The models include classical and practical engineering models. Constitutive and phenomenological friction models describing the nonlinear transfer behavior of joints are discussed. The models deal with the inherent nonlinearity of contact forces (eg, Hertzian contact), and the nonlinear relationship between friction and relative velocity in the friction interface. The research activities in this area are a combination of theoretical, numerical, and experimental investigations. Various solution techniques commonly applied to friction-damped systems are presented and discussed. Recent applications are outlined with regard to the use of joints as semi-active damping devices for vibration control. Several application areas for friction damped systems due to mechanical joints and connections like shells and beams with friction boundaries are presented. This review article includes 134 references.

Friction-Induced Vibration, Chatter, Squeal, and Chaos—Part II: Dynamics and Modeling

1994 ◽  
Vol 47 (7) ◽  
pp. 227-253 ◽  
Author(s):  
R. A. Ibrahim
Keyword(s):  
Nonlinear Modeling ◽  
Turbine Blades ◽  
Cutting Tools ◽  
Rotating Disk ◽  
Contact Forces ◽  
Hertzian Contact ◽  
Experimental Investigations ◽  
Stick Slip ◽  
Nonlinear Dynamical ◽  
Research Activities

This part provides a comprehensive account of the main theorems and mechanisms developed in the literature concerning friction-induced noise and vibration. Some of these mechanisms are based on experimental investigations for classical models. Bilinear and nonlinear dynamical models have been considered to explain such friction phenomena as stick-slip, chatter, squeal, and chaos. Nonlinear modeling includes two types of nonlinearities which differ from those encountered in structural dynamics. These nonlinearities, in addition to the observed uncertainty of friction between sliding surfaces, form a formidable difficulty in developing accurate and reliable modeling. They include the inherent nonlinearity of contact forces (eg, Hertzian contact), and the nonlinear relationship between friction and sliding relative velocity. Research activities in this area are a mixture of theoretical, numerical, and experimental investigations. Theoretical investigations are prevailed by deterministic analysis with few attempts of stochastic treatment. The models include classical and practical engineering models such as the mass-spring model sliding on a running belt or on a surface with Hertzian contact, a pin sliding on a rotating disk, beams with friction boundaries, turbine blades, water-lubricated bearings, wheel-rail systems, disc brake systems and machine cutting tools. There is a strong need for further research to promote our understanding of the various friction mechanisms and to provide designers of sliding components with better guidelines to minimize the deteriorating effects of friction.

Assessment of Unsteady Flows in Turbines

1992 ◽  
Vol 114 (1) ◽  
pp. 79-90 ◽  
Author(s):  
O. P. Sharma ◽  
G. F. Pickett ◽  
R. H. Ni
Keyword(s):  
Unsteady Flow ◽  
Three Dimensional ◽  
Flow Simulation ◽  
Experimental Investigations ◽  
Flow Parameters ◽  
Research Activities ◽  
Flow Features ◽  
Computational Fluid Dynamics Cfd ◽  
Turbine Design ◽  
The Impact

The impacts of unsteady flow research activities on flow simulation methods used in the turbine design process are assessed. Results from experimental investigations that identify the impact of periodic unsteadiness on the time-averaged flows in turbines and results from numerical simulations obtained by using three-dimensional unsteady Computational Fluid Dynamics (CFD) codes indicate that some of the unsteady flow features can be fairly accurately predicted. Flow parameters that can be modeled with existing steady CFD codes are distinguished from those that require unsteady codes.

Experimental Investigation on the Rubbing Process of Labyrinth Seals Considering the Material Combination

2020 ◽  
Author(s):  
Lisa Hühn ◽  
Oliver Munz ◽  
Corina Schwitzke ◽  
Hans-Jörg Bauer
Keyword(s):  
Turbine Blades ◽  
Design Guidelines ◽  
Operating Conditions ◽  
Contact Forces ◽  
Experimental Investigations ◽  
Process Data ◽  
Labyrinth Seals ◽  
Material Combination ◽  
Higher Temperature ◽  
And Control

Abstract Labyrinth seals are used to prevent and control the mass flow rate between rotating components. Due to thermally and mechanically induced expansions during operation and transient flight maneuvers, a contact, the so-called rubbing process, between rotor and stator cannot be excluded. A large amount of rubbing process data concerning numerical and experimental investigations is available in public literature as well as at the Institute of Thermal Turbomachinery (ITS). The investigations were carried out for different operating conditions, material combinations, and component geometries. In combination with the experiments presented in this paper, the effects of the different variables on load due to rubbing are compared, and discussed with the focus lying on the material combination. The influence of the material on the loads can be identified as detailed as never before. For example, the contact forces in the current experiments are higher due to a higher temperature resistance of Young’s modulus. The analysis will also be based on the rubbing of turbine blades. Design guidelines are derived for labyrinth seals with improved properties regarding tolerance of rub events. Based on the knowledge obtained, guidelines for designing reliable labyrinth seals for future engines are discussed.

Experimental Study on Compressive Strength of Recycled Aggregate Concrete

2008 ◽  
Vol 385-387 ◽  
pp. 381-384 ◽  
Author(s):  
Wei Wang ◽  
Hua Ling ◽  
Xiao Ni Wang ◽  
Tian Xia ◽  
Da Zhi Wang ◽  
...  
Keyword(s):  
Experimental Study ◽  
Compressive Strength ◽  
Coarse Aggregate ◽  
Recycled Aggregate Concrete ◽  
Time Dependent ◽  
Recycled Aggregate ◽  
Experimental Investigations ◽  
Aggregate Concrete ◽  
Cement Ratio ◽  
Practical Engineering

With the increase in the use of recycled aggregate concrete (RAC), it is necessary to clearly understand its behavior and characteristics. In this paper, experimental study on compressive strength of RAC with same water/cement ratio is conducted. Firstly, influence of recycled coarse aggregate contents on cube compressive strength of RAC is studied. Secondly, experiment on time-dependent strength developing process of RAC is conducted with different solidification ages. Finally, based on above experimental investigations, empirical formula for compress strengths of RAC with different ages is presented. The result of this paper is helpful to theoretical analysis and practical engineering design of RAC structures.

scholarly journals Modeling and Dynamic Analysis of Spherical Roller Bearing with Localized Defects: Analytical Formulation to Calculate Defect Depth and Stiffness

2016 ◽  
Vol 2016 ◽  
pp. 1-11 ◽  
Author(s):  
Behnam Ghalamchi ◽  
Jussi Sopanen ◽  
Aki Mikkola
Keyword(s):  
Dynamic Model ◽  
Contact Stiffness ◽  
Roller Bearing ◽  
Measurement Data ◽  
Contact Forces ◽  
Hertzian Contact ◽  
Radial Clearance ◽  
Outer Race ◽  
Rolling Elements ◽  
Localized Defects

Since spherical roller bearings can carry high load in both axial and radial direction, they are increasingly used in industrial machineries and it is becoming important to understand the dynamic behavior of SRBs, especially when they are affected by internal imperfections. This paper introduces a dynamic model for an SRB that includes an inner and outer race surface defect. The proposed model shows the behavior of the bearing as a function of defect location and size. The new dynamic model describes the contact forces between bearing rolling elements and race surfaces as nonlinear Hertzian contact deformations, taking radial clearance into account. Two defect cases were simulated: an elliptical surface on the inner and outer races. In elliptical surface concavity, it is assumed that roller-to-race-surface contact is continuous as each roller passes over the defect. Contact stiffness in the defect area varies as a function of the defect contact geometry. Compared to measurement data, the results obtained using the simulation are highly accurate.

scholarly journals Automated Virtual Testing Rig Incorporating Multi-level Models of Gas Turbine Engines

2018 ◽  
Vol 220 ◽  
pp. 03001
Author(s):  
Andrey Tkachenko ◽  
Ilia Krupenich ◽  
Evgeny Filinov ◽  
Yaroslav Ostapyuk
Keyword(s):  
Gas Turbine ◽  
Power Plants ◽  
Educational Process ◽  
Turbine Engines ◽  
Experimental Investigations ◽  
Gas Turbine Engines ◽  
Engine Operation ◽  
Virtual Testing ◽  
Research Activities ◽  
Multi Level

This article describes the multi-level approach to developing the virtual testing rig of gas turbine engines and power plants. The described virtual rig is developed on the basis of computer-aided system of thermogasdynamic calculations and analysis ASTRA, developed at Samara National Research University. Existing testing rig is widely used in educational process to supply the students’ research activities with the information on engine operation in a variety of ambient and flight conditions during transients. An approach to upgrading the virtual testing rig is proposed. The described modifications would provide the capabilities to solve more complex research tasks, including investigation of influence of geometry of engine elements on the engine characteristics, multidisciplinary investigations, identification of engine models using the results of experimental investigations and identification of sources of engine deficiencies during the development phase of engine designing.

scholarly journals Studies on Static Frictional Contact Problems of Double Cantilever Beam Based on SBFEM

2017 ◽  
Vol 11 (1) ◽  
pp. 896-905
Author(s):  
Zhu Chaolei ◽  
Gao Qian ◽  
Hu Zhiqiang ◽  
Lin Gao ◽  
Lu Jingzhou
Keyword(s):  
Mathematical Programming ◽  
Differential Equations ◽  
Cantilever Beam ◽  
Frictional Contact ◽  
Double Cantilever Beam ◽  
Contact Problems ◽  
Contact Forces ◽  
Contact Conditions ◽  
Good Convergence ◽  
Practical Engineering

Introduction: The frictional contact problem is one of the most important and challenging topics in solids mechanics, and often encountered in the practical engineering. Method: The nonlinearity and non-smooth properties result in that the convergent solutions can't be obtained by the widely used trial-error iteration method. Mathematical Programming which has good convergence properties and rigorous mathematical foundation is an effective alternative solution method, in which, the frictional contact conditions can be expressed as Non-smooth Equations, B-differential equations, Nonlinear Complementary Problem, etc. Result: In this paper, static frictional contact problems of double cantilever beam are analyzed by Mathematical Programming in the framework of Scaled Boundary Finite Element Method (SBFEM), in which the contact conditions can be expressed as the B-differential Equations. Conclusion The contact forces and the deformation with different friction factors are solved and compared with those obtained by ANSYS, by which the accuracy of solving contact problems by SBFEM and B-differential Equations is validated.

A Review of Laminar Single-Phase Flow in Microchannels

2001 ◽  
Author(s):  
Ian Papautsky ◽  
Tim Ameel ◽  
A. Bruno Frazier
Keyword(s):  
Fluid Flow ◽  
Single Phase ◽  
Experimental Investigations ◽  
Phase Flow ◽  
Single Phase Flow ◽  
Research Activities ◽  
Internal Fluid ◽  
Internal Fluid Flow ◽  
Microscale Flows ◽  
New Applications

Abstract Microfluidics plays a major role in the development of many innovative research activities aimed at the development of miniaturized devices and systems, and new applications related to microscale handling of fluids. As the field of microfluidics continues to grow, it is becoming increasingly important to understand the mechanisms and fundamental differences involved in microscale fluid flow. This paper presents a summary of the experimental research efforts in the area of microscale single-phase internal fluid flow and discusses issues associated with investigating microscale flows. While the currently available experimental data indicate the presence of microscale phenomena, they do not unequivocally identify the effects. There is a clear need for additional experimental investigations.

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