Contact area

About: Contact area is a research topic. Over the lifetime, 12358 publications have been published within this topic receiving 256401 citations. The topic is also known as: contact patch & contact region.

Contact mechanics: contact area and interfacial separation from small contact to full contact

Abstract: We present a molecular dynamics study of the contact between a rigid solid with a randomly rough surface and an elastic block with a flat surface. The numerical calculations mainly focus on the contact area and the interfacial separation from small contact (low load) to full contact (high load). For a small load the contact area varies linearly with the load and the interfacial separation depends logarithmically on the load. For a high load the contact area approaches the nominal contact area (i.e. complete contact), and the interfacial separation approaches zero. The numerical results have been compared with analytical theory and experimental results. They are in good agreement with each other. The present findings may be very important for soft solids, e.g. rubber, or for very smooth surfaces, where complete contact can be reached at moderately high loads without plastic deformation of the solids.

Design and understanding of anisotropic conductive films (ACF's) for LCD packaging

Abstract: Anisotropic conductive film (ACF) composed of an adhesive resin and fine conductive fillers such as metallic particles or metal-coated polymer balls are key materials for fine pitch chip-on-film (COF) and chip-on-glass (COG) LCD packaging technologies. To understand and design better quality ACF materials, the theoretical electrical conduction model with physical contact mechanism was simulated and experimentally proven. To understand the contact area changes, two pressure dependent models (1) elastic/plastic deformation; (2) finite element method (FEM) model were developed, and experimentally proven by various ACF's fabricated in our laboratory. Experimental variables were applied bonding pressure, number, size, mechanical and electrical properties of nickel powders and Au-coated polymer conductive particles. It was found that the models were in good agreement with experimental results except at higher bonding pressures. In general, as bonding pressure increases, a sharp decrease of contact resistance followed by a constant value is observed after reaching the critical bonding pressure. However, an excessive bonding pressure rather increased the connection resistance of ACF interconnection. If more conductive particles-were added, the connection resistance rapidly decreased and then became constant. This is because the counter-effect of two opposing factors, the resistance increase caused by a decrease of contact area per one particle and the resistance decrease caused by increasing number of conduction path. In addition, environmental effects on contact resistance such as thermal aging, high temperature/humidity aging, and temperature cycling were also investigated. As a whole, better design of ACF materials can be achieved by understanding the ACF conduction mechanism.

Measurement and Modeling of Normal Contact Stiffness and Contact Damping at the Meso Scale

Abstract: Modeling of contact inteffaces that inherently include roughness such as joints, clamping devices, and robotic contacts, is very important in many engineering applications. Accurate modeling of such devices requires knowledge of contact parameters such as contact stiffness and contact damping, which are not readily available. In this paper, an experimental method based on contact resonance is developed to extract the contact parameters of realistic rough surfaces under lightly loaded conditions. Both Hertzian spherical contacts and flat rough surfaces in contact under normal loads of up to 1000 mN were studied. Due to roughness, measured contact stiffness values are significantly lower than theoretical values predicted from smooth surfaces in contact. Also, the measured values favorably compare with theoretical values based on both Hertzian and rough contact surfaces. Contact damping ratio values were found to decrease with increasing contact load for both Hertzian and flat surfaces. Furthermore, Hertzian contacts have larger damping compared to rough flat surfaces, which also agrees with the literature. The presence of minute amount of lubricant and wear debris at the interface was also investigated. It was found that both lubricant and wear debris decrease the contact stiffness significantly though only the lubricant significantly increases the damping.

Deformation and fracture of mica-containing glass-ceramics in Hertzian contacts

Abstract: The Hertzian indentation response of a machinable mica-containing glass-ceramic is studied. Relative to the highly brittle base glass from which it is formed, the glass-ceramic shows evidence of considerable “ductility” in its indentation stress-strain response. Section views through the indentation sites reveal a transition from classical cone fracture outside the contact area in the base glass to accumulated subsurface deformation-microfracture in the glass-ceramic. The deformation is attributed to shear-driven sliding at the weak interfaces between the mica flakes and glass matrix. Extensile microcracks initiate at the shear-fault interfaces and propagate into the matrix, ultimately coalescing with neighbors at adjacent mica flakes to effect easy material removal. The faults are subject to strong compressive stresses in the Hertzian field, suggesting that frictional tractions are an important element in the micromechanics. Bend-test measurements on indented specimens show that the glass-ceramic, although weaker than its base glass counterpart, has superior resistance to strength degradation at high contact loads. Implications of the results in relation to microstructural design of glass-ceramics for optimal toughness, strength, and wear and fatigue properties are discussed.