Papers by Keyword: Dimple

Abstract: The 7000 series aluminum alloys suffer from intergranular fracture (IGF) that limits the use of the alloys, although they have highest strength among aluminum alloys. The types of IGF can be classified into two categories: (i) with smooth fracture surface showing practically no plastic deformation that takes place in hydrogen embrittlement and stress corrosion cracking, and (ii) with shallow and fine dimples on the fracture surface showing localized plastic deformation inside precipitate free zones. In this study, attempts have been made to suppress the IGF of both types by (a) controlling precipitate microstructure on grain boundaries by quench control and (b) controlling grain boundary morphology by strain induced boundary migration. The IGF of type (i) (hydrogen embrittlement) was successfully suppressed both by the two controlling processes.

Abstract: Insufficient endothelialization of stent grafts tends to cause a problem of thrombosis formation. Because the structure of nanofibers, generally defined as fibers with a diameter below 1 μm, resembles the structure of an extracellular matrix, nanofibers are applied to scaffolds for regenerative medicine. Using nanofibers as the covering material of the stent graft can be expected to solve the problem of the stent graft. Previous studies have shown that a porous scaffold offers better surfaces to anchor and culture endothelial cells than a nonporous scaffold. Therefore, fibers with nanoorder dimples are expected to promote endothelialization. As a method of forming the dimple shape on the surface of the PET fiber, there is a method utilizing a difference in the volatilization rate of the solvent in the high humidity environment in the electrospinning method. For practical application of the stent graft to artificial blood vessels, the mechanical properties of the dimpled PET fiber should be clarified. In this study, the mechanical properties of single nanofibers and nonwoven fabrics of PET fibers with dimples on their surface were evaluated by tensile test. By forming the dimple shape on the fiber surface, the tensile strength of single PET fibers with dimples was 90 % lower than that of single PET fibers with a smooth surface. In the fabrication process of nonwoven fabric, the addition of EG delayed the volatilization of the PET solution, and the fibers adhered to each other. The bonding between the fibers contributed to the tensile strength of the nonwoven fabric.

Abstract: An ultrasonic motor using thrust ball bearing with dimple structure on the friction surface has been proposed. The bearing balls are rotated by the friction force caused by the ultrasonic vibration of the stator, and transfer torque to the rotor. The dimple structure on the sliding surface can hold the ball position and rotate the balls and the rotor without a retainer. The newly proposed motor can avoid the friction loss between balls and the retainer. The balls of 2.4 mm in radius are used and the radii of the curvature of the dimples of 2.0 mm and 3.0 mm are used in this research. The radius difference changes the contact condition between the balls and the dimple structure. Fundamental motor characteristics are measured and discussed.

Abstract: Dimple is a slight indentation in a surface. Dimples create turbulence by creating vortices which delays the boundary layer separation resulting in decrease of drag, increasing aerodynamic efficiency, manoeuvrability and also the angle of stall. The present work focused on the understanding of the effect of dimples on boundary layer separation, lift, drag, critical angle of attack, aerodynamic efficiency of wings. The airfoils without any dimples and with circular dimples as inward and outward on are studied. Types of dimples considered in 3D studies are circular and octagon dimple then computational analysis is done using ANSYS FLUENT CFD software, applying subsonic flow, in three dimensional co-ordinate system. The results are compared with a straight wing without dimples. Then suggestions and conclusions are made.

Abstract: Aim at finding the relation between flow structure and heat enhancement, this paper change the dimple depth to print diameter from 0.06 to 0.3, with an interval of 0.02, and keep the print diameter constant. Through vortex structure analysis and Nu number integration, find out that: Vortex structure varies with dimple depth. Shallow depth dimple induces horseshoe vortex; middle depth dimple induces symmetric tornado-like vortex; deep depth dimple induces tornado-like vortex. Heat enhancement is closely related to vortex structure. Where spiral separation focus point exists, there the lowest Nu/Nu0 exists. Flow impingement at the windward side of dimple and new viscous layer generation at immediate plane after the dimple enhance heat transfer. The highest Nu/Nu0 exists in the sharp rearward dimple edge. From Fig 6, the deeper the dimple is, the higher the average Nu/Nu0 is, so does the pressure drop. But from 0.06 to 0.2 dimple, heat enhancement increased because of vortex structure changed. From 0.2 to 0.3 heat enhancement increased because of the increased area.

Abstract: Indirect laser peening applied to the substrate of austenitic stainless steel with the sheet of similar material. Effects of indirect laser peening condition on the formation of the dimple and the residual stress were investigated in this paper. Shape of the dimple and distribution of the residual stress were measured by laser microscope and X-ray diffraction, respectively. It was observed by the microscope that clean substrate surface of as-received state kept after indirect laser peening because of protection by the sheet. However, fracture of sheet occurred slightly in high pulse energy condition. The diameter and the depth of the dimple by indirect laser peening increased with the increase of laser power. Efficiency of dimple formation decreased with the increase of pulse energy. Affective condition region of indirect laser peening with a combination between the substrate and the sheet of austenitic stainless steel may be limited below the laser power density of 10GW/cm². It was confirmed that indirect laser peening induced compressive residual stress in the substrate. One of peak of compressive residual stress in residual stress distribution existed near the bottom of the dimple. Residual stress distribution which was produced by indirect laser peening may affect change of quasi bending modulus which was obtained by three-point bending test.

Abstract: It is possible to successfully propose the physical-metallurgical and structural conditions for the equilibrium between steel strength and toughness by designing structural parameters which have a positive effect on the relation between local and macroscopic fracture processes. In carbon steels and microalloyed steels for a wide range of technical uses, whose structure after heat treatment consists of a basic matrix of tempered lower bainite with precipitated carbides and sometimes other types of inclusions, toughness is dependent primarily on the size distribution of second phase particles, their volume ratio, and also the strength of the matrix/particle phase boundary and the mechanical properties of structural phases. By modelling and simulating the process of main crack formation during high-energy ductile fracture, it is possible to propose optimum physical-metallurgical and geometric parameters of steel structure in order to achieve the required relation between strength characteristics and toughness. This paper presents an analysis of results achieved in several tasks carried out to predict mechanical properties in ductile fracture, and it outlines potential future developments. The aims are to determine the limit characteristics of mechanical behaviour of structural steels which can be achieved with a view to the current structural situation and technological possibilities, and furthermore to propose future methods for determining relations between microstructure and toughness.

Abstract: The influence of dimples on the inner surface of big end bearing in internal combustion engine (ICE) on tribological performances of the bearing was investigated based on Navier-Strokes equation and other associated equations. In doing so, the CFD modulus in the software ANSYS12 version is used to analyze the dimple effect on the tribological performances of the bearing using two-way fluid-solid coupling algorithm. Some mechanisms are revealed about the dimple effect on the load-carrying capacity and friction coefficient of oil film, and the deformation and stress for the textured big end bearing.

Abstract: The influence of cavitation in a lubricant between textured surfaces on tribological performances of the surfaces was investigated based on an extended Reynolds equation and other associated equations. The tribological performances of the surfaces holding dimples with divergent-convergent shape were analyzed with the cavitation effect consideration at different dimple numbers. In doing so, the elastic deformation of the surface is evaluated using continuous convolution fast Fourier transform (CC-FFT). Some mechanisms are revealed about the cavitation effect on the friction coefficient, friction force, load-carrying capacity and cavitated area of the textured surfaces.

Abstract: Observation of fratcure morphology and energy spectrum analysis of fracture toughness specimens of high strength aluminum alloy was carried out on scanning electron microscope (SEM), and the fracture behaviour of this alloy has also been studied. It is revealed that the fracture surface can be divided into 3 regions: precrack region, propagation region and rapid fracture region, the appearance of which is similar to that of cleavage fracture, mixed mode fracture and static fracture, respectively. The fracture of high strength aluminum alloy is primarily influenced by coarsed Fe-rich particles which is relatively brittle, and the major fracture mode of this kind of alloy is toughness fracture casued by coarsed second phase particles.