Study on cracked plates, shells and 3 dimensional bodies

This paper presents a summary of the authors' recent work in following areas: (1) The stress-strain fields at crack tip in Reissner's plate. (2) The calculations of the stress intensity factors in finite size plates. (3) The stress-strain fields at crack tip in Reissner's shell. (4) The calculations of the stress intensity factors and bulging coefficients in finite size spherical shells. (5) The stress-strain fields along crack tip in three dimensional body with surface crack. (6) The calculation of stress intensity factors in a plate with surface crack.

On the non-linear stability theory of spinning solid bodies with liquid-filled cavities and its application to the columbus problem

In this paper, we first present a system of differential-integral equations for the largedisturbance to the general case that any arbitrarily shaped solid body with a cavity contain-ing viscous liquid rotates uniformly around the principal axis of inertia, and then develop aweakly non-linear stability theory by the Lyapunov direct approach. Applying this theoryto the Columbus problem, we have proved the consistency between the theory and Kelvin'sexperiments.

Characteristics of Wake Flow in Long Bluff Bodies

Vortex shedding is the main characteristics of bluff bodies, which will cause the bluff bodies to vibrate and sometimes result in the structures failure. In this paper the wake flow characteristics of 21 bluff bodies with rectangular, rounded and angular profiles and the length-to-width ratio in the range of 4~12 were deeply studied by Micro ADV. Two parameters, namely the relative intensity of the load due to Karman vortices and the large scale vortex intensity, were introduced to measure the wake flow intensity. Generally, the values of these parameters for different bluff bodies are consistent with each other. The experiment results showed that the key factor affecting the wake flow characteristics is the bluff edge, especially the leading edge geometry. The wake flow in bluff bodies with rounded edge profiles has more regular vortices and becomes more periodic than that in bluff bodies with rectangular ones. A bluff body with angular edged profile was witnessed to have not only small wake loading but small hydraulic resistance also.

Investigations of cohesive zone properties of the interface between metal film and ceramic substrate at nano- and micro-scales

Cohesive zone characterizations of the interface between metal film and ceramic substrate at micro- and nano-scales are performed in the present research. At the nano-scale, a special potential for special material interface (Ag/MgO) is adopted to investigate the interface separation mechanism by using MD simulation, and stress-separation relationship will be obtained. At the micro-scale, peeling experiment is performed for the Al film/Al2O3 substrate system with an adhesive layer at the interface. Adhesive is a mixture of epoxy and polyimide with mass ratio 1:1, by which a brittle cohesive property is obtained. The relationships between energy release rate, the film thickness and the adhesive layer thickness are measured during the steady-state peeling. The experimental result has a similar trend as modeling result for a weak adhesion interface case.

Determination Of Interfacial Properties Between Metal Film And Ceramic Substrate With An Adhesive Layer

Peel test measurements and inverse analysis to determine the interfacial mechanical parameters for the metal film/ceramic system are performed, considering that there exist an epoxy interface layer between film and ceramic. In the present investigation, Al films with a series of thicknesses between 20 and 250 mu m and three peel angles of 90, 135 and 180 degrees are considered. A finite element model with the cohesive zone elements is used to simulate the peel test process. The finite element results are taken as the training data of a neural network in the inverse analysis. The interfacial cohesive energy and the separation strength can be determined based on the inverse analysis and peel experimental result. (C) 2008 Elsevier Ltd. All rights reserved.

Mechanisms of thermal shock failure for ultra-high temperature ceramic

The materials considered in our analysis were ZrB2 ceramic matrix composites. Effect of two different additives (graphite and AlN) on thermal shock stability for the materials was measured by water quench test. It showed that it may provide more stable thermal shock properties with additives of graphite. It was explained by different thermal properties and crack resistance of the two materials in detail. Surface oxidation was one of main reasons for strength degradation of ceramic with additives of graphite after quenched in water, and surface crack was one of main reasons for strength degradation of ceramic with additives of AlN after quenched in water. It was presented that it was a potential method for improving thermal shock stability of ZrB2 ceramic matrix composites by introducing proper quantities of graphite.

Experimental Study Of Multi-Hole Cooling For Integrally-Woven, Ceramic Matrix Composite Walls For Gas Turbine Applications

In this paper, multi-hole cooling is studied for an oxide/oxide ceramic specimen with normal injection holes and for a SiC/SiC ceramic specimen with oblique injection holes. A special purpose heat transfer tunnel was designed and built, which can provide a wide range of Reynolds numbers (10(5)similar to 10(7)) and a large temperature ratio of the primary flow to the coolant (up to 2.5). Cooling effectiveness determined by the measured surface temperature for the two types of ceramic specimens is investigated. It is found that the multi-hole cooling system for both specimens has a high cooling efficiency and it is higher for the SiC/SiC specimen than for the oxide/oxide specimen. Effects on the cooling effectiveness of parameters including blowing ratio, Reynolds number and temperature ratio, are studied. In addition, profiles of the mean velocity and temperature above the cooling surface are measured to provide further understanding of the cooling process. Duplication of the key parameters for multi-hole cooling, for a representative combustor flow condition (without radiation effects), is achieved with parameter scaling and the results show the high efficiency of multi-hole cooling for the oblique hole, SiC/SiC specimen. (C) 2008 Elsevier Ltd. All rights reserved.

Experimental investigation of optical beam deflection based on PLZT electro-optic ceramic

Based on the optical characteristics of PLZT electro-optic ceramic, two kinds of electro-optic deflectors, triangular electrode structure and optical phased array technology, are studied in detail by using transverse electro-optic effect. Theoretically, the electro-optic deflection characteristics and mechanisms of the deflectors are analyzed. Experimentally, the optical characteristics of ceramic wafer, such as the phase modulation, the hysteresis and the electro-induced loss characteristics, are measured firstly, and then the beam deflection experiments are designed to verify the theoretical results. Moreover, the effect of temperature on the performance of triangular electrode deflector is investigated. The characteristics of both deflectors are also compared and illuminated. (c) 2007 Optical Society of America.

Experimental study of Ti : sapphire laser end-pumped Nd : YAG ceramic laser Q-switched by Cr4+: YAG saturable absorber

By employing a continuous-wave (CW) Ti:sapphire tunable laser as a pumping source and a Cr4+:YAG single crystal as the saturable absorber (SA), a passively Q-switched Nd:YAG ceramic laser has been demonstrated at room temperature. With an absorbed pumping power of 541 mW at 808 nm, an average output power of 61 mW at 1064 nm has been obtained with 3.5 mu J pulse energy, 15 ns pulse width and 18.18 kHz repetition rate, and the corresponding slope-efficiency is 15%. The relationships between the pulse width, repetition rate, average output power, pulse energy, and peak power on the absorbed pumping power for different initial transmission of the Cr4+:YAG SA are discussed separately. The Nd:YAG ceramic is one of the most promising laser materials for compact, efficient, all-solid-state pulsed lasers.

High optical-optical efficiency of 52.5% obtained in high power Nd : YAG ceramic laser

Using a quite uniformly side-around arranged compact pumping system, a high power Nd:YAG ceramic quasi-CW laser has been demonstrated with high optical-to-optical conversion efficiency over 50% for the first time. With 450 W quasi-CW stacked laser diode bars pumping at 808 run. 236 W Output at 1064 run was obtained and no saturation phenomena were observed.

Nd : YAG ceramic laser obtained high slope-efficiency of 62% in high power applications

By using quite uniformly nine-stacks side-around arranged compact pumping system, a high power Nd:YAG ceramic quasi-CW laser with high slope efficiency of 62% has been demonstrated. With 450 W quasi-CW stacked laser diode bars pumping at 808 nm, performance of the Nd: YAG ceramic laser with different output coupling mirrors has been investigated. Optimum output power of 236 W at 1064 nm was obtained and corresponding optical-to-optical conversion efficiency was as high as 52.5%. The laser system operated quite stably and no saturation phenomena have been observed, which means higher output laser power could be obtained if injecting higher pumping power. The still-evolving Nd: YAG ceramics are potential super excellent media for high power practical laser applications. (c) 2005 Optical Society of America.

Kilohertz electro-optic Q-switched Nd : YAG ceramic laser

We investigate the lasing characteristics of a laser-diode-array side-pumped electro-optic Q-switched Nd:Y3Al5O12 ceramic laser operating at 1000 Hz pulse repetition rate. Using a YAG poltcrystalline rod with Nd3+ concentration at 1 at.% as the gain medium, pumping with 808 nm laser-diode-arrays, the Q-switched laser output at 1064 nm wavelength with 23 mJ pulse energy and less than 12 ns FWHM pulse width are obtained at a pumping power of about 400 W, the slope efficiency is around 15%, the output beam divergence angle is about 1.2 mrad.

5.5W CWYb3+ : Y2O3 ceramic laser pumped with 970 nm laser diode

CW laser output has been demonstrated for polycrystalline transparent 10 at.% Yb3+-doped Y2O3 ceramics. End-pumped with 970 nm laser diode, a maximum output power of 5.5 W has been obtained with absorbed pump power of 31.1 W. The slope efficiency is 25% while the threshold pump power is 5.6 W. Saturation is not observed in our experiments, indicating higher laser output can be expected with higher pump power. (C) 2004 Elsevier B.V. All rights reserved.