Contact Stiffness Of Joint Surface Research Articles

Introduction study on the influence of residual stress on contact stiffness of joint surface

The effects of residual stress on material properties can be divided into two main categories: its influence on material strength, such as fatigue, and its influence on harmful deformation, such as dimension deviation during or after processing. To investigate the effects of residual stress on the mechanical properties of material components, we select a simple structure that underwent loading and unloading cycles. In our finite element numerical simulation, we establish both a macroscopic solid model and an asperity model. Three different models are chosen, and load-displacement curves are obtained. The effects of residual stress on the stiffness of the contact surface are analyzed. Our results show that residual stress has a significant impact on the stiffness of the joint surface, from macroscopic to microscopic perspectives. Specifically, stiffness increases with residual stress when it is tensile stress.

Statistical Model of Normal Contact Stiffness of Fixed Joint Surface during Unloading after First Loading

Based on Kogut and Etsion’s model (KE model), a statistical method is used to establish a model of normal contact stiffness of fixed joint surface during unloading after first loading. Simulation results show that, for the elastoplastic contact, normal contact stiffness of joint surface is the nonlinear function of mean surface separation during loading and unloading and decreases as the separation increases. For different plasticity indexes, the normal contact stiffness of joint surface varies differently following the change of mean surface separation during loading and unloading.

Estimation for normal contact stiffness of joint surfaces by considering the variation of critical deformation

PurposeThis paper aims to study the relationship between normal contact stiffness and contact load. It purpose a new calculation model of the normal contact stiffness of joint surfaces by considering the elastic–plastic critical deformation change of asperities contact.Design/methodology/approachThe paper described the surface topography of joint surfaces based on fractal geometry, and fractal parameters and of fractal function derived from measurement data. According to the plastic–elastic contact theory, the contact deformation characteristic of asperities was analyzed; the critical deformation estimation model was presented, which expressed critical deformation as the function of fractal parameters and contact deformation; the contact stiffness calculation model of single asperity was brought forward by considering critical deformation change.FindingsThe paper combined the surface topography description function, analyzed the asperity contact states by considering the critical deformation change, and calculated normal contact stiffness based on fractal theory and contact deformation analysis. The comparison between theoretical contact stiffness and experimental data indicated that the theoretical normal contact stiffness agreed with the experimental data, and the estimation model for normal contact stiffness was appropriate.Research limitations/implicationsOwing to the possibility of plastic deformation during the loading process, the experimental curve between the contact stiffness and the contact load is nonlinear, resulting in an error between the experimental results and the theoretical calculation results.Originality/valueThe paper established the relationship between critical deformation and fractal surface topography by constructing asperity distribution function. The paper proposed a new normal contact stiffness calculation model of joint surfaces by considering the variation of critical deformation in contact process.

Influence of contact stiffness of joint surfaces on oscillation system based on the fractal theory

In this paper, in view of microscopic surface topography characteristic, the relationship of microscopic surface topography characteristic and the dynamic characteristic of macroscopic system is established, and the influence of fractal contact stiffness on the stability and nonlinearity of modal coupling system is studied based on microscopic surface topography. According to the fractal characteristic of metal surface machined, the normal and tangential contact stiffness fractal models of joint surfaces are established and verified. In this paper, a critical two-degree-of-freedom modal coupling model is listed, the fractal contact stiffness obtained is embedded into oscillatory differential equation to study the influence of the coupling between friction coefficient and stiffness ratio of joint surfaces and the coupling between natural frequency and stiffness ratio of joint surfaces on the system stability, and the influence of fractal contact stiffness on the limit cycle of system is further analyzed. The above theoretical analysis can provide a reference for the design of suitable surface topography in the engineering.

Fractal Model of Normal Contact Stiffness between Two Spheres of Joint Interfaces with Simulation

The contact stiffness of joint surface plays a significant role in the overall static and dynamic characteristics of mechanical systems. When considering joint interfaces with two rough surfaces, the traditional model based on Hertz contact theory between a sphere and a plane is difficult to use, especially for increasingly complex engineering surfaces. In order to overcome the weakness, here we propose a new contact stiffness model in view of the influence of domain extension factor between two rough surfaces. We study the deformation mechanism and the critical contact parameters. Subsequently, we analyze evolution of the elastic-plastic contact involving three distinct stages ranged from complete elastic through elastic-plastic to fully plastic deformation. Our fractal model is more universal than the traditional model based on some strict assumptions which simplify the contact of two rough surfaces to a rough surface and a rigid plane. In fact, the traditional model could be regarded as a special case in our new model. Simulations show that non-dimensional normal contact stiffness increases with dimensionless contact total load under the mechanism of elastic-plastic transition when the fractal dimension is between 1.1 to 1.5. The results indicate that contact stiffness of our fractal model is appropriate and the theoretical contact stiffness is consistent with the experiment data. DOI: http://dx.doi.org/10.5755/j01.mech.23.5.19356

Statistical analysis of tangential contact stiffness of joint surfaces

To investigate the tangential contact stiffness of joint surfaces, the asperity contact of the joint surfaces is considered as an elliptically shaped contact, with the major and minor semi-axes of the contact areas assumed to follow a two-dimensional Gamma distribution. Hertz theory for the pressure distribution on an elliptical contact area is applied to solve for the tangential contact stiffness in a single asperity. Numerical results reveal a change in the tangential contact stiffness, with the influential factors being normal load, tangential load, eccentricity of elliptical asperities, correlation coefficient of asperity distribution, measured asperity height, and standard deviation of asperity distribution on joint surfaces. All of the results should provide theoretical guidance for evaluating or refining the tangential contact stiffness of joint surfaces.

A modified normal contact stiffness model considering effect of surface topography

The contact stiffness of joint surfaces is an important factor influencing the static and dynamic characteristics of the mechanical equipment. In the present research, a modified normal contact stiffness model of two rough surfaces is proposed. First, the stiffness model of a single asperity contact pair is obtained based on shoulder-shoulder contact in conjunction with the elastic-plastic contact model proposed by Jackson and Green. Second, the topographies of contact surfaces are analyzed, and the locations of asperities and the statistical distributions of asperity heights and radii are acquired experimentally. The asperities are then generated using Monte Carlo method with the information to simulate the real contact. Finally, the asperities contact state is determined and if the contact occurs, the stiffness of the single asperity pair is calculated and summed as the total normal stiffness of two contact surfaces. The proposed stiffness model is validated by experiments with the errors less than 10%.

Fractal prediction model and simulation of contact stiffness considering friction factors between joint surfaces

In order to accurately consider the influence of friction on the joint surfaces, the fractal prediction model of the contact stiffness of joint surfaces is established based on tribology theory and fractal contact theory. Then the kinetic model of joint surfaces is improved to a certain extent. The influence of actual contact area, contact force and friction coefficient on the contact stiffness is revealed with the research of numerical simulation. Simulation results indicate that normal contact stiffness of joint surfaces increased with the increase of actual contact area, increased with the increase of contact force. And when the friction coefficient is less than 0.3, the normal contact stiffness appears linear attenuation with the increase of the friction coefficient. And when the friction coefficient is larger than 0.3, normal contact stiffness appears exponential attenuation with the increase of the friction coefficient. Tangential stiffness appears to be the similar rules with different parameters.