Papers by Keyword: Real Contact Area

Abstract: Experimental determination of the real contact area is essential for the development and validation of advanced friction models in sheet metal forming. However, existing experimental approaches are limited by the need for transparent counterfaces or third agents in the interface, high sensitivity to relocation errors, or unreliable assumptions about the contact shape. This study proposes a novel ex-situ method to determine the real contact area using topographical information from the original and deformed sheet surfaces. The approach identifies a minimum contact area with high confidence and reconstructs from it the full contact area. It provides the real contact area ratio, the contact topography and height distribution. The method is evaluated using results from normal load simulations based on the Pullen and Williamson model as the reference and is compared with other ex-situ methods from literature. Results demonstrate that the proposed method is robust against realistic relocation errors and yields more accurate contact area values than existing approaches. The method offers a reliable experimental tool for tribological analysis and friction modelling in sheet metal forming.

Abstract: In the post CMP cleaning, the contact condition between PVA brush and surface is very important. In this study, we observed the real contact area between a brush and surface using a collimating LED light and prism. As a result, we found that the real contact area increases with increasing the brush compression. In addition, we also found that the real contact area decreases when the brush starts to move, and the brush was locally compressed due to its deformation.

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: Vibration-assisted micro-forging was proposed for metal foil surface finishing. The mechanism was investigated by analysis of strain, surface roughness, microhardness, real / nominal contact area ratio and forming work at different vibration time and frequencies. Results show that vibration time and frequency influence the surface deformation by means of real contact area and forming work accordingly.

Abstract: No surface in engineering is absolutely smooth. It is important to analyze and calculate the real contact area for a better understanding of friction, wear, lubrication and thermal conductance. To obtain the accurate real contact area between rough surface and smooth surface, a rough-non-rigid-smooth surface contact finite element model is proposed in which the rough surface is characterized by fracture theory. In finite element modeling and analyzing process, MATLABEXCEL and AutoCAD are used to process data, and the smooth surface is considered to be non-rigid body. Compared with the traditional modeling, this method can obtain data quickly and is closer to the actual situation.

Abstract: The contact stiffness is measured at interfaces of several materials that are often used for the machine tool support. Models of machine tool supports and contact stiffness are described. Then, a measurement method of the contact stiffness is proposed according to the model and demonstrated. The unit normal contact stiffness is 1-2×10⁶ N/mm/mm² for general steel and cast iron. The unit normal contact stiffness is p^{Superscript text}ositively correlated with the longitudinal elastic modulus. The unit tangential contact stiffness is 1/10-1/5 of the unit normal contact stiffness and not correlated with the elastic shear modulus. The surface roughness of the specimen should be small to reduce the dispersion of the measured unit contact stiffness.

Abstract: The Coulomb friction model is frequently used for sheet metal forming simulations. This model incorporates a constant coefficient of friction and does not take the influence of important parameters such as contact pressure or deformation of the sheet material into account. This article presents a more advanced friction model for large-scale forming simulations based on the surface changes on the micro-scale. When two surfaces are in contact, the surface texture of a material changes due to the combination of normal loading and stretching. Consequently, shear stresses between contacting surfaces, caused by the adhesion and ploughing effect between contacting asperities, will change when the surface texture changes. A friction model has been developed which accounts for these microscopic dependencies and its influence on the friction behavior on the macro-scale. The friction model has been validated by means of finite element simulations on the micro-scale and has been implemented in a finite element code to run large scale sheet metal forming simulations. Results showed a realistic distribution of the coefficient of friction depending on the local process conditions.

Abstract: In this study, a three-body microcontact model for rough surfaces is proposed in order to understand the effects of particles between surfaces on contact characteristics and its application on polishing of wafer. Both transitional surface-to-surface and particle-to-surface two-body microcontact simulations can be obtained according to the simplification of this model. In the three-body contact situation, the curves of contact area ratio versus dimensionless load are located in the range between two straight lines. The surface-to-surface two-body contact situation is the upper bound and the particle-to-surface two-body contact situation is the lower bound. As the value of D/σ increases, the contact situation will approach the pure particle-to- surface 2-body contact situation. The model also is used to study the wear mechanisms of the silicon wafer.