Elsevier

Tribology International

Volume 161, September 2021, 107097
Tribology International

Contact heat transfer analysis between mechanical surfaces based on reverse engineering and FEM

https://doi.org/10.1016/j.triboint.2021.107097Get rights and content

Highlights

  • NURBS global interpolation method is used to smooth the fractal surface.

  • The micro morphology of the mechanical surface is restored by reverse engineering.

  • The mechanical joint surface has a serious impact on the thermal equilibrium time of the transient temperature field.

  • The actual contact rate between ordinary mechanical contact surfaces in this research is about 7.09%.

Abstract

In engineering application, analyzing the temperature field of structures is often necessary. The contact surface is constituted by the superposition of different scales of rough surfaces because it is not completely smooth. When heat is transferred between these two contact surfaces, the surfaces are in incomplete contact, and a temperature difference is formed on the contact surface. The non -smooth contact surface also delays the thermal equilibrium time in numerical simulation. In this paper, the W-M fractal function is used to reconstruct the rough surface of the experimental plate according to its profile parameters, then the nonuniform B-spline global surface interpolation method is used to aid the construction of a 3D surface that could keep the true shape of the plate to the greatest extent, and the 3D rough surface with the same size as the experimental plate is reconstructed by reverse engineering. Finally, the heat transfer characteristics of non-smooth contact are simulated and analyzed by using the finite element method, and verified by experiments. Experimental and simulation results show that the actual contact area of the plate is about 7.09% of the nominal contact area. The research method in this paper can be utilized to study not only the heat conduction characteristics of the contact surface but also engineering problems such as friction and wear of the contact surfaces.

Introduction

Contact heat transfer between metal surfaces is a common phenomenon in engineering, which is of great importance to the development of aerospace, automobile manufacturing, and electronic packaging. The contact state of the contact surface should be clarified to study the contact heat conduction phenomenon. However, owing to the influence of contact surface pressure, surface morphology, material hardness, and other factors, the current research can only provide several qualitative explanations, and cannot effectively characterize the contact state between contact surfaces [1], [2], [3], [4], [5], [6], [7]. Fig. 1 shows the measurement process and results of the surface topography of an ultra precision machined part,which comes from another project of our research group [8]. From the measurement results, even the surface of mechanical parts processed by ultra precision machining machine is not smooth, let alone the ordinary machined surface. Therefore, understanding the actual contact condition between general contact planes is very important in engineering analysis.

In the past, research on the characteristics of heat transfer between contact surfaces mainly focused on the determination of contact thermal resistance between contact surfaces. However, the contact surface is rough, the temperature of the contact surface is the same only at a small number of contact points, and there will be temperature settlement for the part without contact. Because contact thermal resistance is an important parameter to characterize the effect of the contact surface on the heat flow obstruction when two surfaces are in contact, which can effectively reflect the resistance of the contact surface to temperature transfer, it has attracted the attention of researchers, after nearly 80 years of development, various methods to study contact thermal resistance have been developed. The research methods can be divided into two types: theoretical method and experimental method. At present, the contact thermal resistance models established by the theoretical method include the interface layer model, the acoustic mismatch model, the diffuse mismatch model, and the partially special and partially diffuse model [9], but no theoretical model can accurately describe the thermal resistance of contact surfaces under different boundary conditions. In the past few decades, with the continuous enrichment of experimental equipment and means, various experimental methods were used to measure the thermal resistance of the contact surface. According to whether the experimental temperature changes with time, the experimental methods can be divided into steady-state method and transient method. The steady-state measurement of contact thermal resistance is carried out according to ASTM standard, and the measurement time usually lasts for more than several hours. The thermal conductivity of the measured object may be affected due to the contact measurement. By contrast, the transient method has the advantages of fast response and noninvasive measurement. The commonly used transient measurement methods include laser flash measurements [10], photoacoustic techniques [11], and transient thermo reflection [12]. However, the measurement accuracy is relatively poor due to the complexity of its theoretical derivation and many factors affected by the inherent thermal properties of materials.

Although the theoretical and experimental methods have achieved certain results,they cannot describe the temperature distribution between the contact surfaces. If the surface morphology of the contact surface can be reconstructed and the reasonable thermal boundary conditions are set, the finite element method (FEM) can be used to study the temperature distribution characteristics between the contact surfaces. At present, mechanical processing methods cannot produce a completely smooth plane, so the actual contact surface is a surface with certain roughness. The surface roughness of parts has a great influence on its performance, mainly in the following aspects. The first is wear resistance. Generally, the rougher the surface is, the greater the friction resistance is, and the faster the wear of parts is. The second is the stability of fit. For clearance fit, the rougher the surface is, the faster the wear of contour peak is, which makes the fit gap increase and destroys the fit property. In addition, the surface roughness also affects the contact stiffness. The rougher the surface of the part is, the smaller the actual contact area is, the larger the local deformation is, and the lower the contact stiffness is, which affects the vibration resistance and working accuracy of the part. Finally, the surface roughness also affects the corrosion resistance and sealing performance of mechanical parts. For rough surfaces, the surface profilometer is general usually used to characteristic the specific surface, and the surface roughness is obtained according to the arithmetic mean deviation of the surface profile. Surface roughness can be measured by the following methods: comparison method, light cutting method, interference method, needle tracing method and impression method. For the rough surface which is measured by these methods, for different precision instruments, the same surface has different profiles [13], [14], [15]. The method of characterizing the roughness depends heavily on the accuracy of the measuring instrument, neglecting the multiple -scales of the rough surface, and cannot obtain the unique characterization parameters of the rough surface. When Majumdar and Bhushan [16], [17] observed a magnetic thin film disk with using the optical interference method and scanning tunneling microscope, it was found that the surface of the magnetic thin film disc has fractal characteristics, and the fractal scale parameter can be used to uniquely determine the plane in a specific range uniquely. Inspired by Majumdar, this paper mainly introduces the application of fractal function in the studying of plane heat conduction. The problem of plane contact has been paid much attention by researchers for a long time. In the early research, it was considered that the actual contact area of two materials with similar hardness was determined by the plastic deformation of the highest convex point in the plane, which was directly proportional to the load applied on the contact surface, and had nothing to do with the actual contact area. Later, Archard [18] found that the actual contact area of the contact surface is directly proportional to the load on the contact surface even if it is purely elastic deformation. In order to find out whether the contact surface is elastic or plastic, Greenwood [19] established a standard to distinguish elastic deformation from plastic deformation. A lot of research shows that the contact between surfaces in engineering is usually plastic, but elastic contact is also very common. Majumdar and Bhushan believed that plastic contact and elastic contact exist simultaneously when the contact occurs between rough surfaces. When the load between the contact surfaces increases gradually, the point with an initial plastic contact will becomes an elastic contact. For the point of elastic contact, there is such a relationship exists between the contact load and the actual contact area. Above all, the actual contact area of the contact surface is the key content of the contact problem research, because it is closely related to the thermal conductivity and friction coefficient of the contact surface.

Based on the fractal theory, this paper studied the temperature field distribution characteristics and the delay effect of heat flow through the contact surface. Different from the previous method of directly connecting the measured data between two points for finite element analysis, this paper introduces the non-uniform rational B-spline global interpolation method, which can restore the real contact situation to the greatest extent in the heat transfer analysis of the contact surface. The structure of this paper is arranged as follows: In the second section, the method of constructing contact fractal surface entity with W-M fractal function, non-uniform rational B spline function, and reverse engineering method is mainly introduced. In the third section, the finite element method (FEM) is used to analyze the temperature distribution characteristics of the contact surface under thermal load. In the fourth section, the heat transfer process between plates under heat load is recorded by a plate heat transfer experiment, and the results are compared with the simulation results. The results show that compared with the smooth contact surface, the contact heat transfer model between rough contact surfaces constructed by the fractal function can better match the experimental results, which verifies the hypothesis that the actual contact surface is not completely contacted, and shows that the fractal contact surface model can better reflect the heat transfer between solid contact surfaces. The method introduced in this paper can well reveal the temperature blocking effect caused by the unevenness of the contact surface in the heat transfer process of the contact surface. In addition, the delay of thermal resistance on the thermal equilibrium time of the contact surface is also explained. This method can help researchers better understand the temperature field related to contact problems, such as the temperature field of machine tools, machine tool spindle, and thermal problems in microelectronic packaging, so as to solve the problem of machining accuracy loss caused by uneven temperature distribution, improve the machining accuracy of machine tools, and increase the heat dissipation performance of electronic equipment.

Section snippets

Contact surface parameters and surface reconstruction

In general, plane-to-plane contact has four main forms. As shown in Fig. 2, the contact surfaces are separated by lubricating medium. The convex part of the contact surfaces is in contact with the lubricating medium at the same time. No lubricating medium is between the contact surfaces, and the surfaces are in partial contact. The contact surfaces are in complete contact. To study the characteristics of temperature distribution and heat transfer between the actual contact surfaces, the sliding

Simulation and experiment

As mentioned above, the profile data of the contact surface of the experimental slider are obtained. To simulate the contact heat transfer of the fractal surface, the fractal surface after global interpolation is studied in millimeter scale, which is determined by the self similarity of the fractal surface. Although it will increase the thickness of the rough contact layer, it is much less than the actual thickness of the slider; thus, it has no effect on the heat transfer The influence of

Experiment

Fig. 12 shows the temperature increase of the heating table, the temperature rise of the upper surface of slider 2, and the ambient temperature change in the experiment. The transient temperature field simulates the temperature change of plane D and d in the FEM experiment. The results show that only a slight change in the ambient temperature during the whole experiment, which is stable at 27.5 °C. Thermocouple temperature sensors T3, T4, and T5 are connected, and the average temperature of

Conclusion

Based on the heat transfer theory, FEM, NURBS global interpolation method and reverse engineering technology, this paper investigates the temperature field distribution characteristics and the delay effect of heat flow through the contact surface. The results show that compared with the smooth contact surface, the contact heat transfer model between rough contact surfaces constructed by the fractal function can better match the experimental results, which verifies the hypothesis that the actual

CRediT authorship contribution statement

Leilei Zhang: Conceptualization, Methodology, Software, Investigation, Data curation, Writing - original draft, Project administration. Jianping Xuan: Conceptualization, Resources, Software, Writing - review & editing, Supervision, Funding acquisition. Jingli Yuan: Investigation, Formal analysis, Writing - review & editing. Shuai He & Shuai Huang & Shoucong Xiong: Conceptualization, Validation, Investigation. Tielin Shi: Writing - review & editing.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This research is supported by the National Key R&D Program of China (Grant No. 2020YFB2007700), the Science Challenge Project (Grant No. JDZZ2018006-0202-01), and the National Natural Science Foundation of China (Grant No. 51575202).

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