Non-ideal Joints Research Articles

Influence of weld rigidity on the non-linear structural response of beams with a curved distortion

This study investigates an analytical beam model to improve the analyses of welded thin plates with welding-induced curved distortions. The model addresses the rigidity of a butt-welded joint and its effect on plate bending and structural stress by including a rotational spring at the welded end. The spring rotational stiffness, ka, is replaced by the fixity factor, ρa. The validity of the model is based on the assumption of small displacement and moderate rotation of the mid-plane of the welded plate. Using the Finite Element Analysis of a two-dimensional model, a semi-analytical method for the fixity factor computation is developed. Compared with the numerical analysis, the beam model showed a maximum error of 3% in deflection and hot-spot structural stress. Results suggest that the fixity factor is mainly dependent on the width of the weld bead and the far-end constraint. The introduction of ρa can improve the analytical solution by 9% in the evaluation of the hot-spot structural stress. Neglecting the non-ideal joint rigidity may lead up to 54% underestimation in terms of fatigue life, when the S–N curve slope, m, equals 5. However, the relevance of ρa decreases for increasing geometric slenderness of the welded plates.

Enhancing pantograph-catenary dynamic performance using an inertance-integrated damping system

ABSTRACT For modern electrical rail systems, the pantograph-catenary dynamic performance is one of the most critical challenges. Too much fluctuation in contact forces leads to either accelerated wear of the contacting components or losses of contact and, consequently, arcing. In this work, inertance-integrated pantograph damping systems are investigated with the objective of reducing the contact force standard deviation. Firstly, a multibody pantograph model is developed with its accuracy compared with experimental data. The model is improved through the calibration of the pantograph head suspension parameters and the introduction of both non-ideal joint and flexibility effects. Using the calibrated model, beneficial inertance-integrated damping systems are identified for the pantograph suspension. The results show that the configuration with one inerter provides the best performance among other candidate layouts and contends a 40% reduction of the maximum standard deviation of the contact force over the whole operating speed range in the numerical modelling scenario analysed. Considering the identified configuration, time-domain analysis and modal analysis are investigated. It has been shown that the achieved improvement is due to the fact that with the beneficial inertance-integrated damping system, the first resonance frequency of the pantograph system coincides with the natural frequency of the catenary system.

РАСЧЕТ ИЗГИБАЕМЫХ ПРЕДВАРИТЕЛЬНО НАПРЯЖЕННЫХ СБОРНО-МОНОЛИТНЫХ ЭЛЕМЕНТОВ НА ОСНОВЕ ВАРИАЦИОННОГО МЕТОДА ВЛАСОВА-МИЛЕЙКОВСКОГО С УЧЕТОМ ПОДАТЛИВОСТИ КОНТАКТНОГО ШВА

The paper presents a methodology for the selection of a solid finite element models for load-bearing systems of machine tools. The technique is based on the analysis of the results of computer simulation of different models of load-bearing systems of three machines with different layouts. The variability of the models is determined taking into account the traction devices and joints in the conjunctions. The traditional approach for modeling the non-ideal joint in the form of elastic elements set is used, despite the fact that modern CAE systems for modeling non-ideal contact in mates offer special contact finite elements. The conducted computational experiments demonstrate that the most accurate model is obtained by using models of traction devices and joints. In this case, the computational model requires significant computational resources. It is found that the exception of the design model of the bearing system of the machine traction devices can lead to an increased modeling error in static problems up to 25 %. The results of modal and dynamic calculations are more resistant to changes in the design model of the machine, as the error of the design parameters does not exceed 10 %. In addition, the computational models of tightened joint, with a stiffness of more than N/m, are not much different from models with ideal contact. It is shown that with an acceptable 25% modeling error, it is preferable to use a computational model of the load-bearing system without taking into account the non-ideal contact and traction devices

МЕТОДИКА ВЫБОРА ТВЕРДОТЕЛЬНЫХ КОНЕЧНО-ЭЛЕМЕНТНЫХ МОДЕЛЕЙ НЕСУЩИХ СИСТЕМ СТАНКОВ ПРИ ПРОВЕДЕНИИ ИХ ИНЖЕНЕРНОГО АНАЛИЗА

The paper presents a methodology for the selection of a solid finite element models for load-bearing systems of machine tools. The technique is based on the analysis of the results of computer simulation of different models of load-bearing systems of three machines with different layouts. The variability of the models is determined taking into account the traction devices and joints in the conjunctions. The traditional approach for modeling the non-ideal joint in the form of elastic elements set is used, despite the fact that modern CAE systems for modeling non-ideal contact in mates offer special contact finite elements. The conducted computational experiments demonstrate that the most accurate model is obtained by using models of traction devices and joints. In this case, the computational model requires significant computational resources. It is found that the exception of the design model of the bearing system of the machine traction devices can lead to an increased modeling error in static problems up to 25 %. The results of modal and dynamic calculations are more resistant to changes in the design model of the machine, as the error of the design parameters does not exceed 10 %. In addition, the computational models of tightened joint, with a stiffness of more than N/m, are not much different from models with ideal contact. It is shown that with an acceptable 25% modeling error, it is preferable to use a computational model of the load-bearing system without taking into account the non-ideal contact and traction devices

Modal Analysis of the Setar: A Numerical–Experimental Comparison

The setar, a Persian long-necked lute, is analyzed by means of experimental modal analysis and finite element (FE) method. The experimental analysis is performed using a combination of impulse hammer and laser Doppler vibrometer (LDV), which has led to the extraction of structural mode shapes, natural frequencies, and modal dampings. The FE model is developed taking into account structural details, such as orthotropic properties of the wood, direction of the grains, nonideal joints, and the effect of strings preload. Numerical results are shown to be in a very good agreement with the experimental data over a wide range of frequencies.

Dynamic analysis of a slider-crank mechanism with two types of non-ideal revolute joints

Rolling element bearings and journal bearings are typical components comprising a revolute joint in a mechanical system. In the traditional dynamic analysis of multi-body systems, these two types of bearings are generally treated as ideal revolute joints and are modelled by kinematic constraints. The non-linearity of such bearings including internal radial clearance, local contact deformation, friction, lubrication and other phenomena associated with real joints are routinely ignored. In this work, an approach to the dynamic modelling of a multi-body system with these two types of non-ideal revolute joints is outlined. These non-ideal joints were modelled by their force interaction. In rolling element bearings, the frictionless multi-point contacts and bearing kinematics are considered. In the case of a journal bearing, the normal contact force and tangential dry friction force are considered. A planar slider-crank mechanism with multiple non-ideal revolute joints including a rolling ball bearing and two journal bearings is presented as a numerical example to demonstrate application of this approach. The variations of slider kinetic characteristics and the bearing reaction force are used to expound the dynamic characteristics of the mechanism when multiple non-ideal revolute joints are considered.

On the Samarskii-Andreev transmission conditions in the theory of elastic beams

It is proved that the transmission conditions for elastic beams in the case of a nonideal joint are limiting in the construction of asymptotics for the transmission problem for two thin elastic bodies if the boundary between the bodies is filled by slightly extendible material.

Dynamic Analysis of Satellite Antenna System with Joint Clearance and Reflector Flexibility

AbstractA methodology for modeling and analysis of satellite antenna systems is presented considering the effects of the joint clearance and reflector flexibility in the system. The joint clearance model is established based on a thorough geometric description of the eccentricity vector. The contact-impact forces are evaluated based on a Hertz contact theory and a modified Coulomb’s friction law. The fixed-interface component-mode synthesis method and Lagrange’s equations are used to achieve a lower-order dynamic model by modal truncation. Furthermore, in the process of dynamic modeling, the changes of topology were expressed as constraint variations; namely, adding or deleting the variable structure constraint in the dynamic model. Finally, the multibody dynamics of satellite antenna are analyzed by considering a flexible reflector with ideal and nonideal joints. Thus, the simulation results can predict the dynamic characteristics of satellite attitude and antenna pointing with the effects of clearance a...

A discrete model of a rope with bending stiffness or viscous damping

A discrete model of a rope is developed and used to simulate the plane motion of the rope fixed at one end. Actually, two systems are presented, whose members are rigid but non-ideal joints involve elasticity or dissipation. The dissipation is reflected simply by viscous damping model, whereas the bending stiffness conception is based on the classical curvature-bending moment relationship for beams and simple geometrical formulas. Equations of motion are derived and their complexity is discussed from the computational point of view. Since modified extended backward differentiation formulas (MEBDF) of Cash are implemented to solve the resulting initial value problems, the technique scheme is outlined. Numerical experiments are performed and influences of the elasticity and damping on behaviour of the model are analyzed. Basic energy principles are used to verify the obtained results.

Comparison Between Elastic Foundation and Contact Force Models in Wear Analysis of Planar Multibody System

In this paper, two procedures to analyze planar multibody systems experiencing wear at a revolute joint are compared. In both procedures, the revolute joint of interest includes a clearance whose shape and size are dictated by wear. The procedures consist of coupled iterative analyses between a dynamic system analysis with nonideal joints and a wear prediction to determine the evolution of the joint clearance. In the first procedure, joint forces and contact pressures are estimated using the elastic foundation model with hysteresis damping via the dynamic analysis. In the second procedure, a contact force model with hysteresis damping is used to estimate the joint forces. In the latter case, however, the contact pressure is estimated using a finite element method (FEM). A comparison in performance of the two models is facilitated through the use of an experimental slider-crank mechanism in which wear is permitted to occur at one of the joints. It is observed that the two procedures provide similar estimates for the dynamic response and wear volumes but substantially different predictions on the wear profiles. Additionally, experimental results show that while predictions on the wear volume from both models are reasonably accurate, the FEM-based model produced more accurate predictions on the wear profile.

Experimental Determination of Thermal Contact in a Diode-Heat Sink Assembly

This study examines experimentally the quality of contact of mechanical joints in a diode heat sink assembly. Steady-state contact conductance, h, is used as a quantitative measure of the quality of contact of a joint. The emphasis of the work is on determining the contact conductance, h, for a nonideal joint using a noncontact method of recording temperature distribution in a complex geometry. Thermal contact conductance for an interface is known to depend on parameters such as contact pressure, mean interface temperature and the surface roughness characteristics of the mating surfaces. The results are presented for three different conditions of the interface namely (i) the mating surfaces are bare (ii) aluminum foil is inserted between the mating surfaces, and (iii) a high thermal conductivity grease is applied to the mating surfaces. Two levels of contact pressure are used for the interface with aluminum foil. The results indicate that the contact conductance increases with the mean temperature of the interface in all the cases. At low interface temperature, the contact conductance was greatest for the bare interface conditions. At high interface temperature, the contact conductance was greatest for the aluminum foil interface condition.