Papers by Keyword: Brittle Material

Abstract: The free-form surface closed to a sphere of brittle material has been used widely, but it is difficult for machining and the efficiency of processing is insufficient. In order to get a product, several processes are needed, such as rough machining, semi-finishing and finishing. Axisymmetric curved surface can take place of the free-form surface in roughing or semi-finishing for wiping off the mass allowance efficiently. Therefore, a spherical approximation algorithm of free-form surface closed to sphere is presented in which free-form surface optical lens will be replaced by a spherical surface in semi-finishing and get the approximate sphere of the free-form surface. It can be certified in the test that this method is simple and reliable. The efficiency and precision in machining is excellent and the distribution of allowance for finishing is uniform in the whole surface, which has great practical significance in machining of optical free-form surface of brittle materials.

Abstract: Numerical investigations on failure process of rock-like materials with a single flaw were carried out under uniaxial compression based on the fracture analysis software: Fracture Analysis Code in Two Dimensions (FRANC2D/L). The change of the displacements and stress distribution were recorded around the crack. Comparative analysis is made among samples containing different angled flaw, which has great influnce on the process of crack initiation and propagetion, and with the increase of flaw angle from 30° to 75°, peak strength of the specimen increases linearly, basically. Which are in good agreement with those of experiments.

Abstract: The paper describes the creation of the arched frame structures made of brittle material. Pasta were chosen as the base material. Their basic geometrical and mechanical characteristics were evaluated. Finite element analysis of the pasta frame structure was made in SCAD and ANSYS. The internal force factors arose in the structure were compared. Its actual carrying capacity was determined in virtue of the structural solidity and material`s experimental evidence. Also the features of optimized structure design were found, the assembly process was described, the test results of the construction were presented. The comparison of the results of finite element modeling and actual laboratory tests was done.

Abstract: Engineering ceramics have received significant attention in the recent years owing to their exceptional mechanical properties, which are expected to be beneficial for engineering applications. However, it has always been a great challenge to realize ductile-mode grinding in engineering ceramics, with one of the critical obstacles being the heat generation that limits the removal rate. As a result, thermal damages are often observed on the ground surfaces. This paper presents the ductile-mode grinding. In the process the grinding wheel is excited along the radial direction by applying an ultrasonic vibration of frequency is 38.5 kHz and amplitude of 0-2 μm. The wheel comes in contact with the Al₂O₃ ceramic at constant forces 18-24 N. Experimental results indicate that the ground surface is devoid of thermal damages, when removal rate of the vibration-assisted process is approximately 1.5 times higher than without vibration.Keywords: ductile-mode grinding, radial directional vibration, hard and brittle material, engineering ceramic, thermal damage

Abstract: Graphite chip formation is important for the understanding of high speed milling of brittle graphite. This paper is aimed to reveal the influence of cutting conditions on the graphite chip formation in high speed milling. The relationship between the maximum undeformed chip thickness and cutting parameters was analyzed, and the influence of cutting parameters, tool geometry and milling patterns on the chip formation of brittle graphite was studied. It is concluded that the transitions of graphite chip formations were highly dependent on the undeformed chip thickness which is decided by the combination setting of feed per tooth and radial depth of cut. Big fractured block chip occurs more easily in up milling than down milling. Tool rake angle influences the chip formation according to the maximum undeformed chip thickness.

Abstract: The failure shaking table model test of mass concrete structures is an important basis for understanding to the actual failure of structures. This paper derived all kinds of similar scales between model and prototype in nonlinear dynamic shaking table test, and constructed the reduced scale nonlinear numerical simulation model. The numerical results show that the failure of model and prototype matches the nonlinear similarity theory. Besides, the effect of the characteristics of ground motion was studied and it cannot be ignored to ensure the accuracy of the test.

Abstract: Ultra-precision microstructures on brittle materials are critical components in optical communication industry. The requirements for Ultra-precision microstructures manufacturing are increasing recently. Traditional etching and deposition technology can not satisfy the demands of accuracy and efficiency. Ultra-precision flycutting process is presented to machining microstructures on brittle materials. The geometric model of flycutting is analyzed. A formula is established to describe the relationship between the effective cutting depth and cutting parameters. The critical depth for brittle to ductile transition is obtained by cutting experiments with varying cutting depth on quartz glass. The ductile cutting chips are achieved in fly-cutting process. A microgroove array with optical quality is obtained. It proves that ultra-precision flycutting process is an available method to manufacture microstructures with optical quality on brittle materials.

Abstract: This paper aims to investigate the mechanism of ductile machining of brittle material based on information available in the literature. It also explores the challenges associated with the ductile machining of brittle materials which stop the technology from being applied in practical fields. In addition, few factors that assist to improve productivity of ductile machining of brittle material have been discussed. It is found the higher tool wear is the main obstacle of this technology. The application ofmicro-laser heating,ultrasonic vibration and coolants improve the machining time and tool life significantly.

Abstract: An efficient numerical framework suitable for three-dimensional analyses of brittle material failure is presented. The proposed model is based on an (embedded) Strong Discontinuity Approach (SDA). Hence, the deformation mapping is elementwise additively decomposed into a conforming, continuous part and an enhanced part associated with the kinematics induced by material failure. To overcome locking effects and to provide a continuous crack path approximation, the approach is extended and combined with advantages known from classical interface elements. More precisely, several discontinuities each of them being parallel to a facet of the respective finite element are considered. By doing so, crack path continuity is automatically fulfilled and no tracking algorithm is necessary. However, though this idea is similar to that of interface elements, the novel SDA is strictly local (finite element level) and thus, it does not require any modification of the global data structure, e.g., no duplication of nodes. An additional positive feature of the advocated finite element formulation is that it leads to a symmetric tangent matrix. It is shown that several simultaneously active discontinuities in each finite element are required to capture highly localized material failure. The performance and predictive ability of the model are demonstrated by means of two benchmark examples.

Abstract: Rotary ultrasonic machining(RUM) as a precise and efficient processing method for hard and brittle materials can be used for significantly improving processing efficiency, reducing the cutting force and cutting heat, improving the surface quality. Development of high performance RUM machine tools and equipments has been caused on widespread attention from the worldwide scholars. In this paper, the development of the RUM machine tools has been reviewed about the accessory RUM head and load matching system.