Papers by Keyword: Contact Stiffness

Abstract: Contact modeling could be widely used for different machine elements normal contact pressure calculations and wear simulations. However, classical contact models as for example Hertz contact models have many assumptions (contact bodies are elastic, the contact between bodies is ellipse-shaped, contact is frictionless and non-conforming). In conditions, when analytical calculations cannot be performed and experimental research is economically inexpedient, numerical methods have been applied for solving such engineering tasks. Contact stiffness parameters appear to be one of the most influential factors during finite element modeling of contact. Contact stiffness factors are usually selected according to finite element analysis software recommendations. More precise analysis of contact stiffness parameters is often required for finite element modeling of contact.

Abstract: A numerical model was proposed to investigate the contact behaviour of a solid with a rough surface squeezed against a rigid flat plane. We considered simulated hierarchical surface structures as well as scanned surface data obtained by the profilometry of isotropically roughened specimens. The simulated and treated surfaces were characterised using statistical and fractal parameters. The evolution of contact stiffness under increasing normal compression was analysed through the total truncated area at varying heights, in order to relate contact mechanics to different surface parameters employed for surface characterisation. For a relatively small surface interference, the predicted stress-dependent normal contact stiffness of both scanned and simulated surfaces is in good agreement with experimental observation from nanoindentation tests, revealing a power-law function of the normal load, with the exponent of this relationship closely depending on the fractal dimension of rough surfaces. The numerical results show that the amplitude of a fractal rough surface mainly contributes to the magnitude of the contact stiffness at a given normal load.

Abstract: Profiled steel sheeting dry board (PSSDB) system is made of profiled steel sheeting that is connected to the dry board using a self-drilling, self-tapping screw. This study aims to predicts the load-deflection behavior of PSSDB panel system under the influence of geopolymer concrete infill with finite element modeling. To achieve the target objective, the laboratory testing approach and a theoretical system behavior prediction are considered. Through a bending test, the stiffness of PSSDB full board with geopolymer concrete infill (FBGPC) panel is 27.42 kNm² and the ultimate load is 13.13 kN/m². The developed finite-element modeling (FEM) successfully predicts the behavior of PSSDB with geopolymer concrete infill panel with >85% accuracy.

Abstract: Joints used to fasten different parts are the source of local non-linearity with predominance of contact damping in comparison to inherent material damping. The conventional numerical models can predict the dynamic behaviour to a good accuracy, but their implementation for the large system under real time dynamic excitations - like random vibration are encountered with problems of numerical convergence and high computational cost. This paper proposes an approach to model the contact interfaces using discrete elements, with a non-homogeneous definition for the equivalent contact stiffness and damping over the contact interface. The non-homogeneous definition captures the non-linear effects and the local linearisation provides the capability to perform the frequency domain analysis for non-deterministic excitations. The proposed model is validated with experimental results for a test structure excited with random white noise base excitation.

Abstract: This paper discusses the occurrence and non occurrence of low-frequency stick-slip motion on a simple caliper-slider experimental model. The analysis focused on the relationship between stiffness, i.e. contact stiffness and structure’s stiffness, and the generation of stick-slip motion. The occurrence of stick-slip motion is determined by analyzing the frequency characteristic of resulted vibration acceleration at the beginning of sliding which is resulted from a simultaneous application of force in tangential direction and slow release of force in normal direction. The results show that the occurrence and non occurrence of stick-slip motion can be classified into three regions according to the parameter of stiffness ratio, i.e. non occurrence region, mixed region, and occurrence region. The stiffness ratio S_r, the ratio of contact stiffness K_c to structure’s stiffness K_s, of 40 is found to be critical for the low-frequency stick-slip generation in this experimental model.

Abstract: In previous study, the quantitative measurement method of contact stiffness of the joint considering real contact area is developed by experimental approach. However, the measurement of contact stiffness needs special device and skillful measuring technique. Therefore, in this paper, simplified calculation method with material properties and profile data of surface roughness obtained by profilometer is considered. As a result, real contact area, contact stiffness and contact spring stiffness calculated from specific wavelength of rough surface are near agreement with experimental value. Hence, it is revealed that there is dominant configuration in surface roughness.

Abstract: This study was aimed to investigate the dynamic characteristics of a multi-axis feeding stage of a milling machine. In order to clarify the influence of the guide system on the structure performance, we have proposed finite element approach to modeling the X-Y working tables with sliding and rolling guide, respectively. The results show that the machine models with sliding and rolling guides show similar vibration behavior. But the sliding guides give more constraints to the motion of working table, showing higher vibration frequency when compared to the rolling guides. This obviously indicates that the guide system significantly influences the resonant frequency and the response amplitudes of a feeding stage.

Abstract: In the grinding operation, grinding wheels are deformed by grinding forces, so that residual stock removal of the workpiece takes place. Since this residual stock removal of the workpiece causes low machining efficiency and deterioration of machining accuracy, high hardness grinding wheels may be selected in order to obtain high machining efficiency and/or high quality machining accuracy. On the other hand, when grinding operations used by low hardness grinding wheels are carried out, it is well known that ground surface roughness is smaller than in case of higher hardness grinding wheels. From such a viewpoint, this study aims to investigate experimentally the effect of the contact stiffness of grinding wheel on the ground surface roughness and the residual stock removal of the workpiece. Grinding operations were carried out using three grinding wheels which are different hardness type, and ground surface roughness and residual stock removal of the workpiece were measured. The contact stiffness of grinding wheel was calculated by a support stiffness of single abrasive grain and a contact area between grinding wheel and workpiece. Comparing the contact stiffness of grinding wheel with the ground surface roughness and the residual stock removal of the workpiece, it was known that ground surface roughness increases and residual stock removal of workpiece decreases with increaseing the contact stiffness of grinding wheel. From these results, since elastic deformation of the grinding wheel changed depending on the suppot stiffness of single abrasive grain, it was clarified that the ground surface roughness and the residual stock removal of the workpiece were changed by the contact stiffness of grinding wheel.

Abstract: In this article, according to WenShuHua and Zhangxueniang fractal model, we point out the deficiency. Based on the fractal theory and Zhang, Wens contact stiffness fractal model, this paper puts forward Gamma distribution of rough joint surface normal contact stiffness. This paper considers micro convex body for ellipsoid, contact area for elliptic. This is slightly convex body for sphere hypothesis is more close to the actual situation. At the same time by using statistics theory, considering the contact ellipse long, short axis a and b are greater than zero, the assumption of a and b to two-dimensional Gamma distribution, it is more suitable for engineering practice.

Abstract: Atomic force acoustic microscopy (AFAM) is a technique combining the atomic force microscope (AFM) and ultrasonic technique, where the cantilever or the sample surface is vibrated at ultrasonic frequencies while a sample surface is scanned with the sensor tip contacting the sample. At a consequence, the amplitude of the cantilever vibration as well as the shift of the cantilever resonance frequencies contain information about local tip-sample contact stiffness and can be used as imaging quantities. It has been demonstrated to be a powerful tool for the investigation of the local elastic prosperities of sample surface. The sample is tested in the contact mode, the resonant frequency of the cantilever is measured, by which the contact stiffness is calculated based on the model of vibration of the cantilever, and then the elastic property of sample is evaluated according to the contact theory. Therefore, the contact model has an important impact on the calculation of elastic modulus. This paper analyzes the contact model between the AFM probe and the sample, and it is investigated based on finite element method (FEM) that the results of the test are affected by parameters.