The work describes a numerical method to study compression failure of porous ceramics in relation to its volume fraction. The microstructure of an alumina-based foam material manufactured by mechanical stirring of a s...
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The work describes a numerical method to study compression failure of porous ceramics in relation to its volume fraction. The microstructure of an alumina-based foam material manufactured by mechanical stirring of a slurry is studied here. A finite element-based compression failure simulation of a real microstructure obtained from micro computed tomography (mu CT) scans is conducted. A recently developed microstructure reconstruction al-gorithm is utilized to generate 3D artificial microstructures statistically equivalent to the real one obtained from mu CT. The accuracy of the reconstruction procedure is established by comparing the simulated effective compression stress-strain behaviour of the reconstructed microstructure with that of the real one along with the experimentally measured results. The effect of sample size on the mean and variability of compression strength is studied by computing effective stress-strain curves for varying sizes of the reconstructed microstructures. Further, artificial microstructures of porous ceramics with different volume fractions are reconstructed along with computing effective stress-strain behaviour to establish relationship between ceramic content (volume fraction) and compression strength of this material. The failure modes of the microstructures with different volume fractions are studied by analysing failure site locations and their evolution with loading. The results are compared with the analytical models and the experimental observations available in the literature.
The fast tool servo (FTS) technology has unique advantages in the machining of complex surfaces such as special-shaped targets and free-form surfaces. In view of the shortcomings in the performance of the existing FTS...
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The fast tool servo (FTS) technology has unique advantages in the machining of complex surfaces such as special-shaped targets and free-form surfaces. In view of the shortcomings in the performance of the existing FTS device, this paper puts forward a novel FTS which uses two piezoelectric ceramics instead of flexure hinges to provide restoring force. Firstly, the feasibility of the double-drive principle is verified theoretically, and the corresponding mechanism is optimized accordingly. Then, the system control hysteresis model is established and identified, and the appropriate control strategy is designed. Finally, the performances of the proposed FTS device are tested, and a typical microstructure is machined based on the device and ultra-precision lathe. The results indicate that the proposed device effectively improves the performance of the FTS system, which is useful for the processing of microstructures and free-form surfaces.
Micro structures in silicon are applied in different fields of industry, medicine and research. Examples are micro mechanical sensors for car security systems, nozzle plates for printer, and optical elements for X-ray...
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ISBN:
(纸本)081944376X
Micro structures in silicon are applied in different fields of industry, medicine and research. Examples are micro mechanical sensors for car security systems, nozzle plates for printer, and optical elements for X-ray beam splitting. Wherever the accuracy of etched silicon structures is not required, laser processes with short pulses and small wave length can be an option with the advantage of shorter process time High quality cutting and drilling of silicon can be achieved by application of diode pumped q-switched Nd:YAG-lasers and harmonics generation. The short pulses (15 ns) and the UV wave length (355 nm) of the Gator UV from Lambda Physik AG, for example, allow a reduction of thermal effects like deposition of molten material and heat effected zones at the edges. Especially in the case of deep structures the ablation plasma causes powerful heating of the walls. An reduction of the plasma temperatures and so the heat influence on the walls can be realized by a small laser wave length with low plasma absorption. Short laser pulse durations are necessary to reduce the heat effected depth or melting due to heat flow from the ablation area into the bulk material. Also the duration and intensity of plasma heating is reduced by short laser pulses. In this contribution the possibilities and limits of laser machining of Si by diode pumped Nd:YAG-lasers with harmonics generation will be presented by means of structures processed by application of a scanner with f-theta-optic. The results will be discussed concerning the experimental setup and the laser parameters.
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