Papers by Keyword: Brittle Materials

Abstract: Brittle materials such as ceramics, glass or single-crystal silicon are extensively used for industrial applications and recently become an object of actual research due to the development of new products and technologies. In cases, where special attention is paid to the surface layer, mechanical processing with a diamond tool is of interest as one of the most efficient technology to manufacture products from brittle materials. In this paper, simulation method is presented, which allows to estimate an effect of cutting force on the size of defects zone formed in a hard brittle plate during machining. In the proposed model, there is a distinguished surface layer, which can have its own unique properties that differ from the properties of the brittle plate. In this work, the ANSYS finite element program is used to simulate the technological processes and solve the problem of stress distribution in a quasi-static formulation.

Abstract: With the development of advanced manufacturing technology, ceramic matrix composite materials, a typically hard and brittle material, have been widely used in high-tech fields such as aerospace manufacturing. Due to the anisotropy of materials, the quality of conventional processing workpieces is poor, and the processing accuracy is difficult to guarantee. In this experiment, ceramic matrix composite materials are machined by ultrasonic vibration grinding with the CBN grinding rods. The influence of amplitude on the grinding force and the surface quality of the workpiece in the grinding process are analyzed by a series of experiments on ceramic matrix composites. The results show that, compared with the conventional grinding process, in the ultrasonic vibration-assisted grinding process, the grinding force is reduced by about 60%, and the surface quality is also improved significantly,the surface roughness Sa is reduced by about 25%.

Abstract: Geothermal systems have a big draw as a provider for free thermal energy for electrical generation. The resource based on fracture networks that permit fluid circulation, and allow geothermal heat to be extracted. Most geothermal resources occur in rocks that posses lack fracture permeability and fluid circulation. Hence, the fluid will be heated due to the Hot Dry Rock (HDR). The flow is circulated through the cracks, and extracts the heat to the ground. The emphasis of the simulators is on the HDR and on the development of methods that produce the hydraulic fractures. Linear elastic fracture mechanics approach (LEFM) was used to predict the crack propagation for initial crack. Finite element method (FEM) is used to predict the maximum stress areas, hence, determining the crack initiation.

Abstract: A wire tool having electrodeposited diamond grains is frequently used for machining hard and brittle materials such as silicon ingots, magnetic materials, ceramics, and sapphires. This study aims to examine the wear characteristics of the tool during the microgrooving of ceramics. We conducted microgrooving experiments for alumina ceramics. The results indicate that the grooving time and the machining distance influence the groove depth. However, as the damage in a wire tool progresses, the groove depth does not depend on the machining distance. A fast relative velocity leads to serious damage in the wire tool even when the machining time is short. In the case of wet grooving, the damage to the wire tool was smaller than that in the case of dry grooving.

Abstract: An electroplated diamond wire tool is frequently used for the machining of hard and brittle materials such as silicon ingots, magnetic materials, ceramics, and sapphires. This study aims to examine the influence of brittle behavior of work materials on machinability (including tool wear); therefore, we conduct dynamic ultramicro hardness measurements and microgrooving experiments for three types of ceramics. The results indicate that the groove depth of a work material tends to increase with the processing time. Moreover, material properties of a work material, such as hardness and toughness, have a significant impact on the fluctuations in its groove depth. However, kerf width of a work material does not depend on the processing conditions and material properties. In addition, a faster relative velocity improves processing efficiency but also increases tool wear.

Abstract: Building structures use brittle materials extensively. Under impact or blast loads these structures perform poorly due to tensile strains caused by Poisson’s effect normal to the direction of such loadings. Auxetic materials exhibit negative Poisson’s ratio – a property which can be exploited to eliminate those tensile strains. In this study, Auxetic layers embedded masonry is modelled using a representative volume element (RVE) with periodic boundary conditions and an explicit finite element (EFE) modelling method for a boundary value problem of a masonry wall with an Auxetic foam rendered face is subject to out-of-plane load. The RVE is limited to in-plane loads only and hence subjected to in-plane shear and compression and the EFE was used to assess the performance under out-of-plane loading. The results show significant post-yield strain hardening under axial compression and in-plane shear and high increase in capacity for walls under out of plane flexure.

Abstract: The high hardness of brittle materials always make it hard to machine with traditional grinding wheels. Conventionally a diamond grinding wheels was used to improve the poor processing capability. Usually the specific grinding energy had been used as an indicator of machinability. According to its definition, the specific grinding energy increases with the active contact area of the grinding wheel decreases. In other words, reducing the surface contact area of the grinding wheel can enhance the specific grinding energy effectively. Conditioning grooves on grinding wheels not only enhance the specific grinding energy, but also achieve the effect of reducing the heat dissipated during the grinding processes. With the proper selection parameters, the high cost of diamond grinding wheel may be replaced by less expensive conventional green carbon and aluminum oxide wheel. In this studies, the relationship between the surface topography of grinding wheels and the grinding capability of brittle materials was investigated. The results show that, the traditional grinding wheel dressing properly while the depth of cut less than 20μm with the rhombic pattern and the depth of cut more than 20μm with the groove-like pattern can grind the brittle materials as good as using diamond wheel.

Abstract: Ultra-precision grinding is an effective method to machine the optical micro v-groove, which is one of microstructures applied to the fiber-optics connectors, displays and other photonics devices. The ultra-precision grinding technology directly obtains high surface quality for brittle materials when the grinding process is under the ductile mode. This paper introduces general aspects of ultra-precision grinding technology in the fabrication of the micro v-grooves structures and introduces the essential features of ultra-precision grinding. The process of the manufacturing of the optical micro v-grooves components is presented in this paper. It contains the prediction models of surface roughness and form accuracy in the ultra-precision grinding and the optimization model under the consideration of the influences of grinding parameters,grinder factors and the material properties on the surface quality and machining efficiency. This study therefore contributes to providing a further understanding on the mechanisms of material removal and surface generation in ultra-precision girnding.

Abstract: The dynamic process of cracks initiation in brittle materials during high speed cutting is primary for the analysis of material fracture mode and finished surface. Cast iron was considered in this paper and discrete element method (DEM) was employed to create a density packed bonded-particle model for studying its machining cracks. The numerical tests of split Hopkinson pressure bar (SHPB) and oblique plane impact were conducted to calibrate the dynamic behaviour of the model. The cutting simulations were carried out for a range of rake angles and cutting speeds. The results showed that both the processes of cracks initiation and the cracks distribution were different greatly under different cutting conditions and the cracks number increased with the cutting speed. In addition, within the detection zone in the model, the duration of crack initiation decreased dramatically with the increase of cutting speed in the lower range. But for the high speed cutting, the duration tended to be stable and was not affected by cutting speed and it was very close to the time of stress wave produced by cutting arriving at the zone. Furthermore, the stress state of particles’ connectors under the action of stress wave was analysed, which suggests that the stress wave is the key factor causing cracks initiation of brittle materials during high speed cutting.

Abstract: In laser induced thermal crack propagation (LITP) cutting brittle materials, according to the laser absorption ability, materials are divided into the body absorption and surface absorption. This paper indicates the fracture mechanism of LITP cutting surface absorption brittle materials. The crack extension appears in the lower surface firstly in this stress distribution state, then the crack extends to the upper surface and the laser scanning direction with the LITP cutting. The stress field of cutting ZrO₂ ceramic is studied by finite element software ANSYS. The crack propagation process of cutting silicon wafer is studied by finite element software ABAQUS. According to the fracture mechanism, the curve cutting the ZrO₂ ceramic experiments and the cooling lower surface cutting the silicon wafer experiments are carried out in this paper. Optical microscope and laser scan confocal microscope (LSCM) photographs of the curve path the ZrO₂ ceramic and separation surface cutting the silicon wafer are obtained to examine the cutting quality. The quality of the curve path is very good. The quality of the separation surface in cutting the silicon wafer with the cooling lower surface is better than conventional environment.