Papers by Keyword: Brittle Materials

Abstract: A mechanistic model capable of predicting end milling cutting forces in brittle porous media is described. A coefficient which is capable of reproducing the random shape and variation in cutting forces due to porosity is proposed. In addition, a method of experimental determination of cutting force coefficients is outlined. The proposed model is based on the hypothesis that the random shape and variation in cutting forces of brittle porous media coincide with the shape and variation of pore size and distribution in the media. The developed coefficient and model is compared to end milling tests conducted in CB1100, a porous machinable alumina based ceramic manufactured by UMECO. High correlation between predicted and measured cutting forces is shown. Experiments show that the model is capable of accurate prediction of variation in individual cutting tooth force profile shape and overall magnitude over the entire range of machining conditions tested. The benefit of the model lies in its ability to greatly reduce the number of cutting tests required when investigating cutting forces in novel brittle porous materials.

Abstract: Grinding technology is used in this study to overcome the hard machining of ceramic with hard and brittle characteristics. The grinding machine with diamond grain size 25 and 5 , spindles speed 1720 rpm and 3450 rpm are applied. Combining the unintentional roll clamp and the grinding machine, ceramic rods can be ground to the desired size.In the research, surface profilometer is applied to measure the rod surface roughness of processing results under different conditions. The results show that the grinding wheel with finer particle, the roughness of the ground ceramic rod will be better. While the rotation speed of grinding wheel is increased, the surface roughness will have the same trend.

Abstract: The inclined surface cracks are under the mixed mode I,II,III loading conditions. Direct tension experiments of brittle materials with surface crack have been carried out. The crack growth process, fracture pattern and the initiation angle of the surface crack were attained. In order to analyze the mixed-mode fracture criterion of the surface crack in brittle materials stress intensity factor of the crack front of the surface crack was calculated based on the FRANC3d firstly. And then the minimum strain energy density criterion, the maximum circumferential stress criterion and the revised maximum circumferential stress criterion were used to calculate the initiation angle. The revised maximum circumferential stress criterion proved to be fit for the attained experimental results.

Abstract: In this study, two different arrangement lapping disks fixed with brazed diamond pellets were used to lap silicon wafer and alumina ceramic. The effects of the surface morphology, roughness, and removal rate of workpiece caused by lapping pressure, lapping time, workpiece velocity, and disc arrangement were operated with serials experiments. The results of the researches provided guidance for fixed abrasive lapping of hard and brittle materials with the brazed micro powder diamond disk.

Abstract: Diamond wires are widely used in cutting hard and brittle materials such as silicon, sapphire, etc. However, present low production efficiency of diamond wires causes their high cost. To solve the problem, a drum-type manufacturing method for electroplated diamond wire tools was developed. Multi diamond wire tools could be manufactured simultaneously at high speed with a single machine. Electroplating characteristics of developed method were evaluated. Additionally, composite electroplating experiments were carried out to find optimal conditions for manufacturing diamond wire tools.

Abstract: Micro-structured surfaces on brittle materials, e.g. ceramic and glass, are gaining increasing application in a range of areas. In this paper, fast tool servo (FTS) diamond turning has been applied to machine micro-structured surfaces on brittle materials and the machined surfaces has been observed to study its machining mechanism. A machining model is presented to enable ductile-regime machining of the brittle material. Based on the model, machining characteristics can be predicted for given cutting conditions. Experimental investigation on machining of a micro-structured surface verified that ductile-regime machining can be ensured on the entire surface through path planning simulation based on the machining model.

Abstract: The new simple and effective grid remeshing method on crack propagation in brittle materials is successfully introduced which is under uniaxial compression. Numerical analysis is applied to brittle materials of a single pre-existing crack considering various dip angles, lengths and friction coefficient. According to linear elastic fracture mechanics theory, we introduce node moving method to guarantee the good shape of the grid in the process of crack growth, and set contact element between the friction surfaces, and then get the crack tip stress intensity factor by using quarter singular element. The influence of length, angle and friction coefficient on crack propagation is quantitatively described. The method is consistent with the experimental results and is effective in 2D problems.

Abstract: Engineering ceramic machining would bring out several kinds of surface damage owing to its hard and brittle nature. In this paper, a simulation model of single-grit grinding for silicon carbide (Sic) was established to explore the high-speed grinding mechanism. The material behavior was described with the Johnson-Holmquist Ⅱ (JH-2) model. According to the simulation experiment results, the optimal grinding parameters to achieve ductile grinding for Sic has been analyzed, which would provide theoretical basis and take surface damage under control.

Abstract: In this paper, a ring shaped numerical specimen is used to studying the failure process in brittle materials. The ring specimen is subjected to a compressive diametral load and contains two angled central cracks. Numerical modeling in this study is performed. It is shown that the obtained numerical results are in a very good agreement with the experiments. Effect of the crack orientation angle on the failure modes and loading-displace responses is discussed. In the range of 0°~40°, the fracture paths are curvilinear forms starting from the tip of pre-existing cracks and grow towards the loading points. For the crack orientation angle 90°, vertical fractures will split the specimen and the horizontal cracks do not influence the fracture process.

Abstract: Several experiments undertaken on cement and mortar samples with internal cracks of different shapes and sizes demonstrated that 3-D cracks growth in compression was qualitatively different from the 2-D cases. This paper employs pre-existing cracks in frozen PMMA（polymethylmethacrylate plastic） which are produced by the mechanical method to analyze the evolution of the boundary effect of PMMA and to study the mechanisms of cracks growth and coalescence. In the experiments, 3-D cracks are tested under uniaxial compression and finally draw two conclusions about failure mechanisms of PMMA and brittle materials.