Characteristics extraction and numerical analysis of the rough surface macro-morphology

2019 ◽  
Vol 36 (3) ◽  
pp. 765-780
Author(s):  
Qingchao Sun ◽  
Xiaokai Mu ◽  
Bo Yuan ◽  
Jiawen Xu ◽  
Wei Sun
Keyword(s):  
Surface Morphology ◽  
Contact Pressure ◽  
Contact Area ◽  
Contact Stiffness ◽  
Contact Model ◽  
Normal Contact ◽  
Content Type ◽  
Macro Scale ◽  
Machined Parts ◽  
Morphology Characteristics

PurposeThis paper aims to distinguish the relationship between the morphology characteristics of different scales and the contact performance of the mating surfaces. Also, an integrated method of the spectrum analysis and the wavelet transform is used to separate the morphology characteristics of the actual machined parts.Design/methodology/approachFirst, a three-dimensional (3D) surface profilometer is used to obtain the surface morphology data of the actual machined parts. Second, the morphology characteristics of different scales are realized by the wavelet analysis and the power spectral density. Third, the reverse modeling engineering is used to construct the 3D contact models for the macroscopic characteristics. Finally, the finite element method is used to analyze the contact stiffness and the contact area of the 3D contact model.FindingsThe contact area and the nominal contact pressure Pn have a nonlinear relationship in the whole compression process for the 3D contact model. The percentage of the total contact area of the macro-scale mating surface is about 70 per cent when the contact pressure Pn is in the range of 0-100 MPa, and the elastic contact area accounts for the vast majority. Meanwhile, when the contact pressure Pn is less than 10MPa, the influence factor (the relative error of contact stiffness) is larger than 50 per cent, so the surface macro-scale morphology has a weakening effect on the normal contact stiffness of the mating surfaces.Originality/valueThis paper provides an effective method for the multi-scale separation of the surface morphology and then lays a certain theoretical foundation for improving the surface quality of parts and the morphology design.

A Contact Mechanics Model for Rough Surfaces Based on a New Fractal Characterization Method

2018 ◽  
Vol 10 (06) ◽  
pp. 1850069 ◽  
Author(s):  
Jianjun Sun ◽  
Zhengbo Ji ◽  
Yuyan Zhang ◽  
Qiuping Yu ◽  
Chenbo Ma
Keyword(s):  
Contact Mechanics ◽  
Rough Surface ◽  
Contact Pressure ◽  
Contact Area ◽  
Rough Surfaces ◽  
Contact Stiffness ◽  
Measurement Scale ◽  
Real Contact Area ◽  
Sample Length ◽  
Normal Contact

There are mainly two kinds of contact mechanics models for rough surfaces. One is based on the statistical characteristic parameters and depends on the measurement scale of rough surface topography. The other is based on the fractal parameters, which is independent of the measurement scale. However, most of the contact models for rough surfaces based on fractal theory use the size that is corresponding to the contact area of an asperity or the sample length as the base diameter of an asperity to describe the initial profile of asperities. As a result, the obtained deformation mechanism of asperities is not correct. To solve this problem, a new fractal characterization method for rough surfaces based on the fractal dimension [Formula: see text], fractal roughness [Formula: see text] and the highest asperity height is proposed, and then a fractal contact model independent of the measurement scale is established. The contact mechanism of asperities and variation trends of the real contact area and contact stiffness are discussed. When the contact pressure of the rough surface is less than its yield strength, its normal contact stiffness can be expressed as the first derivative of the contact pressure versus the normal compression, regardless of the deformation forms of asperities.

Dynamic Analysis and Optimization on Assembly Parameters of Rod Fastening Rotor System With Manufacturing Tolerances

2019 ◽  
Author(s):  
Bingxi Zhao ◽  
Qi Yuan ◽  
Pu Li
Keyword(s):  
Contact Pressure ◽  
Timoshenko Beam ◽  
Contact Stiffness ◽  
Beam Element ◽  
Normal Contact ◽  
Tightening Force ◽  
Mass Imbalance ◽  
Rod Fastening Rotor ◽  
Bearing System ◽  
Timoshenko Beam Element

Abstract Rod fastening rotor (RFR), as a typical rotor structure of gas turbine which is different from the integral rotor, is comprised of a set of discs clamped together by a central tie rod or several tie rods on the pitch circle diameters. In process of machining, tolerances of the disc are inevitable, of which the parallelism error and mass imbalance are focused on in this paper. Firstly, the complex bending of RFR by accumulation of parallelism errors of discs is derived through the coordinate transmission. Then the static analysis of RFR is performed to obtain the additional pressure by the effect of unbalanced forces, which is related to the assembly angles and rotating speed, on contact surfaces using a linear hypothesis, based on which the distribution of contact pressure considering the original pre-tightening force is obtained. Then the Bifractal-Regular theory is adopted to acquire the micro-topography of the contact interface and derive the contact stiffness related to normal contact pressure, fractal upper length limit and regular shape of the contact interfaces. After that, the zero thickness element is introduced to obtain the equivalent stiffness matrices of the contact surface. In addition, the circumferential uniformly distributed rods are modeled as a spring element which provides additional bending stiffness for the RFR. Based on the analysis above, the dynamic model of the RFR-bearing system containing 10 discs is established using the Timoshenko beam element where the continuous part of the shaft is modeled by Timoshenko beam element considering shear effect. Finally, the multi-optimization is carried out on the vibration response by the coupled effects of both initial bending and mass imbalance of the RFR-bearing system through which the optimal assembly angles are obtained. The results show a good performance in decreasing vibration as well as bending of the RFR system.

A Contact Model for Nonlinear Forced Response Prediction of Turbine Blades: Calculation Techniques and Experimental Comparison

2008 ◽  
Author(s):  
Christian M. Firrone ◽  
Marco Allara ◽  
Muzio M. Gola
Keyword(s):  
Normal Load ◽  
Contact Stiffness ◽  
Turbine Blades ◽  
Harmonic Balance Method ◽  
Forced Response ◽  
Contact Forces ◽  
Contact Model ◽  
Experimental Comparison ◽  
Normal Contact ◽  
Contact Models

Dry friction damping produced by sliding surfaces is commonly used to reduce vibration amplitude of blade arrays in turbo-machinery. The dynamic behavior of turbine components is significantly affected by the forces acting at their contact interfaces. In order to perform accurate dynamic analysis of these components, contact models must be included in the numerical solvers. This paper presents a novel approach to compute the contact stiffness of cylindrical contacts, analytical and based on the continuous contact mechanics. This is done in order to overcome the known difficulties in simultaneously adjusting the values of both tangential and normal contact stiffness experimentally. Monotonic loading curves and hysteresis cycles of contact forces vs. relative displacement are evaluated as a function of the main contact parameters (i.e. the contact geometry, the material properties and the contact normal load). The new contact model is compared with other contact models already presented in literature in order to show advantages and limitations. The contact model is integrated in a numerical solver, based on the Harmonic Balance Method (HBM), for the calculation of the forced response of turbine components with friction contacts, in particular underplatform dampers. Results from the nonlinear numerical simulations are compared with those from validation experiments.

Investigation of normal and tangential contact stiffness considering surface asperity interaction

2019 ◽  
Vol 72 (3) ◽  
pp. 379-388
Author(s):  
Hongping Yang ◽  
Xiaowei Che ◽  
Cheng Yang
Keyword(s):  
Contact Mechanics ◽  
Fractal Geometry ◽  
Contact Stiffness ◽  
Contact Theory ◽  
Normal Contact ◽  
Tangential Contact ◽  
Content Type ◽  
Elastic Plastic ◽  
Stiffness Model ◽  
The Relationship

Purpose This paper aims to propose a normal and tangential contact stiffness model to investigate the contact characteristics between rough surfaces of machined joints based on fractal geometry and contact mechanics theory considering surface asperities interaction. Design/methodology/approach The fractal geometry theory describes surface topography and Hertz contact theory derives the asperities elastic, elastic-plastic and plastic contact deformation. The joint normal and tangential contact stiffness are obtained. The experiment method for normal and tangential contact stiffness are introduced. Findings The relationship between dimensionless normal contact load and dimensionless normal and tangential contact stiffness are analyzed in different plasticity index. The results show that they are nonlinear relationships. The normal and tangential contact stiffness are obtained based on theoretical and experimental methods for milling and grinding machined specimens. The results indicate that the present model for the normal and tangential contact stiffness are consistent with experimental data, respectively. Originality/value The normal and tangential contact stiffness models are constructed by using the fractal geometry and the contact mechanics theory considering surface asperities interaction, which includes fully elastic, elastic-plastic and fully plastic contacts deformation. The present method can generate a more reliable calculation result as compared with the contact model no-considering asperities interaction.

Repair of Lateral Meniscus Posterior Horn Detachment Lesions

2012 ◽  
Vol 40 (11) ◽  
pp. 2604-2609 ◽  
Author(s):  
Carl K. Schillhammer ◽  
Frederick W. Werner ◽  
Matthew G. Scuderi ◽  
John P. Cannizzaro
Keyword(s):  
Acl Reconstruction ◽  
Contact Pressure ◽  
Contact Area ◽  
Lateral Meniscus ◽  
Posterior Horn ◽  
Normal Contact ◽  
Intact State ◽  
Peak Contact Pressure ◽  
Maximum Contact ◽  
Contact Pressures

Background: Posterior horn detachment (PHD) lesions of the lateral meniscus are commonly associated with acute anterior cruciate ligament (ACL) tears. Multiple surgeons have advocated for repair of this lesion at the time of ACL reconstruction. However, the biomechanical consequences of this lesion and its subsequent repair have not been evaluated. Hypothesis: The PHD lesion of the lateral meniscus will lead to increased tibiofemoral contact pressures, and repair of this lesion to bone via a tibial tunnel can restore normal contact pressures during simulated gait. Study Design: Controlled laboratory study. Methods: Lateral compartment contact pressures were measured via a sensor on the tibial plateau in 8 cadaver knees with the knee intact, after sectioning the posterior horn of the lateral meniscus to simulate PHD, and after repairing the injury. The repair was performed using an ACL tunnel guide to drill a tunnel from the anteromedial tibia to the posterior horn attachment site. Dynamic pressure data were continuously collected using a conductive ink pressure sensing system while each knee was moved through a physiological gait flexion cycle. Results: Posterior horn detachment caused a significant increase in tibiofemoral peak contact pressure from 2.8 MPa to 4.2 MPa ( P = .03). After repair of the lesion to bone was performed through a transtibial tunnel, the peak contact pressure was 2.9 MPa. Posterior horn detachment also significantly decreased the maximum contact area over which tibiofemoral pressure is distributed from 451 mm2 in the intact state to 304 mm2 in the detached state. Repair of the PHD lesion increased the maximum contact area to 386 mm2, however, this area was also significantly less than in the intact state ( P = .05). Conclusion: Posterior horn detachment of the lateral meniscus causes increased peak tibiofemoral contact pressure. The peak pressure can be reduced to a normal level with repair of the lesion to bone via a transtibial tunnel. Clinical Relevance: Posterior horn detachment of the lateral meniscus is a lesion often associated with an acute ACL tear. Debate exists concerning the importance of repairing PHD lesions at the time of ACL reconstruction. The data provided in this study may influence surgeons’ management of the lesion.

An Elliptical Microcontact Model Considering Elastic, Elastoplastic, and Plastic Deformation

2003 ◽  
Vol 125 (2) ◽  
pp. 232-240 ◽  
Author(s):  
Yeau-Ren Jeng ◽  
Pei-Ying Wang
Keyword(s):  
Plastic Deformation ◽  
Contact Pressure ◽  
Contact Area ◽  
Contact Model ◽  
Real Area Of Contact ◽  
Elliptical Contact ◽  
The Mean ◽  
Elliptic Contact ◽  
Circular Contact ◽  
Real Area

This study developed an elastic-plastic microcontact model that considers the elliptical contact of surface asperities. In the elastoplastic regime, the relations of the mean contact pressure and contact area of asperity to its contact interference are modeled considering the continuity and smoothness of variables across different modes of deformation. Results obtained from this model are compared with other existing models such as that calculated by the GW, CEB, Zhao and Horng models. The elliptic contact model and circular contact model can deviate considerably in regard to the separation and real area of contact.

Experimental Verification of Friction Behaviors Under Periodically-Varied Normal Force by Developing a Two-Directional Friction Test System

2015 ◽  
Author(s):  
Kunio Asai ◽  
Muzio M. Gola
Keyword(s):  
Contact Pressure ◽  
Contact Area ◽  
Normal Force ◽  
Contact Stiffness ◽  
Tangential Force ◽  
Test System ◽  
Dissipated Energy ◽  
Friction Test ◽  
Force Coefficient ◽  
Tangential Contact

In order to achieve more accurate friction damping of turbine blades equipped with shroud covers and under-platform dampers, it is necessary to clarify such friction behaviors as tangential contact stiffness, micro-slips, and dissipated energy, under periodically varied normal force instead of constant normal force. Although some analytical studies were reported on the contact mechanics under alternating normal force, only minimal research has been conducted on the experimental verification of such behaviors, as friction tests were commonly done under constant normal force. In this study, we developed an original two-directional friction test system that can apply any combination of alternating normal and tangential forces by changing the displacement-controlled loading direction. In this system, relative displacement and contact force were measured simultaneously by using a laser Doppler displacement sensor and force transducers of the strain gage type. By using our original test system, we examined the dissipated energy under constant normal force and periodically-varied normal force whose amplitude is the same as that of tangential force with no phase difference. We then obtained a new finding that dissipated energy depends on alternating normal force under the same mean normal force and alternating tangential force. More specifically, when the tangential force coefficient, defined as the ratio of the amplitude of alternating tangential force to mean normal force, is large enough to cause a macro-slip, dissipated energy under variable normal force is smaller than that under constant normal force. Conversely, when tangential force coefficient is small in the micro-slip region, dissipated energy under variable normal force is larger than that under constant normal force. This behavior was successfully reproduced by FE analysis based on a macro-slip model, where an array of macro-slip elements was used to describe micro-slip behavior. It was found that alternating normal force makes it easier to cause a micro-slip in a certain area of the contact surface under variable normal force, resulting in higher dissipated energy than at constant normal force when tangential force coefficient is small. In this study, basic friction data were also obtained regarding the tangential contact stiffness with variations in contact pressure, as well as the relation between a micro-slip and the tangential force coefficient. Tangential contact stiffness increases as contact pressure increases. In addition, tangential contact stiffness increases with the nominal contact area, but is not proportional to the area. The non-dimensional slip range (corresponding to the ratio of slip range to stick displacement) was confirmed as being described in a unified form against different contact area (6 and 18 mm2) and contact pressure ranging from 3 to 40 MPa.

Analysis of the contact interactions between fingertips and objects with different surface curvatures

2005 ◽  
Vol 219 (2) ◽  
pp. 89-103 ◽  
Author(s):  
J Z Wu ◽  
R G Dong
Keyword(s):  
Contact Pressure ◽  
Contact Area ◽  
Contact Surface ◽  
Soft Tissues ◽  
Contact Stiffness ◽  
Element Model ◽  
Point Of View ◽  
Contact Interactions ◽  
Grasp Stability ◽  
Simulation Results

Previous experimental observations indicated that the contact interactions between finger and tool handle interfere with the grasp stability, affecting the comfort and manipulations of handheld tools. From a biomechanical point of view, the curvature of the contact surface should affect the contact pressure and contact area, and thereby the comfort and manipulations of hand tools. The current authors analysed, via a finite element model, the contact interactions between fingertips and objects with different curvatures. The effects of the curvature on the contact stiffness, fingertip deformations, contact pressure distributions, and stress/strain distributions within the soft tissues were analysed. The simulation results indicated that the curvature of the contact interface influences the contact characteristics significantly. For a given contact force, the contact area and the contact stiffness increase but the contact pressure and the fingertip deformation decrease with the decrease of the contact surface curvature. The present simulation results will be useful for ergonomic designers in their aim to improve the design of tool handles.

Contact Analysis for Joint Interfaces of Machine Tools Based on a 3-D Anisotropic Asperity Model

2011 ◽  
Vol 189-193 ◽  
pp. 114-120 ◽  
Author(s):  
Hai Tao Liu ◽  
Wan Hua Zhao ◽  
Jun Zhang
Keyword(s):  
Finite Element ◽  
Contact Pressure ◽  
Contact Stiffness ◽  
Contact Analysis ◽  
Joint Interface ◽  
Average Height ◽  
Exponential Relationship ◽  
Normal Contact ◽  
Normal Deformation ◽  
Normal Contact Pressure

In this paper, a 3-D contact model for anisotropic rough surfaces based on 3-D statistically measurements is established and finite element contact analysis is conducted. The average height of the asperity (h), the average summit distances between two neighboring peaks of asperities (Sx and Sy) are selected as the characterized parameters of the rough surface. Finite element simulation results show that the normal contact pressure has an exponential relation with the normal deformation and an exact linear relationship between the normal deformation and the real contact pressure of the surfaces is obtained. At last, the normal contact stiffness of the joint interface is obtained empirically with the exponential relationship assumption.

A MODIFIED COMPLETE NORMAL CONTACT STIFFNESS MODEL OF A FRACTAL SURFACE CONSIDERING CONTACT FRICTION

Fractals ◽  
2020 ◽  
Vol 28 (05) ◽  
pp. 2050081
Author(s):  
CHUNLING WEI ◽  
HUA ZHU ◽  
SHIHUI LANG
Keyword(s):  
Contact Stiffness ◽  
Fractal Dimensions ◽  
Frictional Resistance ◽  
Contact Model ◽  
Contact Friction ◽  
Fractal Surface ◽  
Normal Contact ◽  
Stiffness Model ◽  
Fractal Roughness ◽  
Normal Contact Stiffness

This paper presents a modified complete normal contact stiffness model of a fractal surface considering contact friction. We use this model to study the influence of fractal dimensions and fractal roughness on normal contact stiffness. The fractal micro-contact model of an asperity and the complete length scale contact model of fractal surface (both contrasting classical mechanics) are revised. The influence of frictional resistance at micro-contact interfaces on normal contact stiffness is also considered. Predictions of the new model are found to be in greater agreement with the results of the experiments than the predictions of the original model. The study analyzes the influence of fractal dimensions and fractal roughness on the normal contact stiffness. With the increase of these two fractal parameters, their influences on the normal contact stiffness are opposite and are different under high pressure and low pressure.

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