On The Thermally Induced Interfacial Delamination Of A Segmented Coating

The thermally induced interfacial delamination problem of a segmented coating is investigated using finite element method (FEM). The coating-substrate system, modeled as a coated semi-infinite medium with periodic segmentation cracks within coating, is assumed to be exposed to convective cooling from surface. The failure criterion based on the interfacial fracture toughness is adopted, in which the energy release rate for an interface crack is considered to be the driving force for interfacial delamination extension. The results confirm that a segmented coating has higher delamination resistance than an intact one under the same thermal transients, as the segmentation crack spacing is smaller than a critical value. Based on dimensional analysis, sensitivity analyses of the crack driving force are also obtained as a function of various dimensionless parameters such as time, convection severity and material constants. These results may provide some helpful references for the integrity of coating-substrate systems under thermal loading. (C) 2007 Elsevier B.V. All rights reserved.

On The Thermally Induced Cracking Of A Segmented Coating Deposited On The Outer Surface Of A Hollow Cylinder

In this work, the thermally induced cracking behavior of a segmented coating has been investigated. The geometry under consideration is a hollow cylinder with a segmented coating deposited onto its outer surface. The segmentation cracks are modeled as a periodic array of axial edge cracks. The finite element method is utilized to obtain the solution of the multiple crack problem and the Thermal Stress Intensity Factors (TSIFs) are calculated. Based on dimensional analysis, the main parameters affecting TSIFs are identified. It has been found that the TSIF is a monotonically increasing function of segmentation crack spacing. This result confirms that a segmented coating exhibits much higher thermal shock resistance than an intact counterpart, if only the segmentation crack spacing is narrow enough. The dependence of TSIF on some other parameters, such as normalized time, segmentation crack depth, convection severity as well as material constants, has also been discussed. (C) 2008 Elsevier B.V. All rights reserved.

Thermal stress-induced birefringence in borate glass irradiated by femtosecond laser pulses

Thermal stress-induced birefringence in borate glass which has been irradiated by 800-nm femtosecond laser pulses is observed under cross-polarized light. Due to the high temperature and pressure formed in the focal volume, the material at the edge of the micro-modified region is compressed between the expanding region and the unheated one, then stress emerges. Raman spectroscopy is used to investigate the stress distribution in the micro-modified region and indicates the redistributions of density and refractive index by Raman peak shift. We suggest that this technique can develop waveguide polarizers and Fresnel zone plates in integrated optics.

Thermally induced Fe atom transition from substitutional to interstitial sites in InP and its influence on material property

As-grown Fe-doped semi-insulating InP single crystal has been converted into n-type low-resistance material after high temperature annealing. Defects in the InP materials have been studied by conventional Hall effect measurement, thermally stimulated current spectroscopy, deep level transient spectroscopy and X-ray diffraction respectively. The results indicate that Fe atoms in the InP material change from the substitutional to the interstitial sites under thermal activation. Consequently, the InP material loses its deep compensation centers which results in the change in types of conduction. The mechanism and cause of the phenomena have been analyzed through comparison of the sites of Fe atom occupation and activation in doping, diffusion and ion implantation processes of InP.

Thermally induced evolution of phase transformations in gas hydrate sediment

Thermally induced evolution of phase transformations is a basic physical-chemical process in the dissociation of gas hydrate in sediment (GHS). Heat transfer leads to the weakening of the bed soil and the simultaneous establishment of a time varying stress field accompanied by seepage of fluids and deformation of the soil. As a consequence, ground failure could occur causing engineering damage or/and environmental disaster. This paper presents a simplified analysis of the thermal process by assuming that thermal conduction can be decoupled from the flow and deformation process. It is further assumed that phase transformations take place instantaneously. Analytical and numerical results are given for several examples of simplified geometry. Experiments using Tetra-hydro-furan hydrate sediments were carried out in our laboratory to check the theory. By comparison, the theoretical, numerical and experimental results on the evolution of dissociation fronts and temperature in the sediment are found to be in good agreement.

高重复率半导体激光抽运Nd：YAG放大器激光特性的实验研究

实验研究了高重复率、大功率半导体激光二极管阵列（LDA）侧面环绕抽运的Nd：YAG激光放大器的放大特性、热焦距变化和热致双折射效应引起的退偏特性。偏振光绎千赫兹高功率单通激光放大器，获得约3倍的光脉冲能量放大，脉冲宽度基本保持不变，其输出的P分量与S分量的能量比趋于常数3：1，实验测得的能量放大倍率及放大光束的椭圆偏振度与理论预期吻合很好。

热退偏损耗完全补偿的千赫兹电光调QNd:YAG激光器

为了同时补偿固体增益介质的热致双折射及热透镜效应,进一步提高重复频率1 kHz激光二极管(LD)侧向抽运高平均功率电光调Q Nd:YAG激光器的输出功率,设计了一种完全消除热退偏损耗的双调Q开关谐振腔结构,此结构在传统调Q谐振腔的基础上沿着偏振片的退偏方向增加了一个调Q谐振支路,并使得激光从增益介质方向输出。实验结果表明,此激光器的单脉冲能量比单Q开关结构的非补偿腔输出能量高出74.7%。当侧面抽运的激光二极管输出脉冲能量达到307 mJ时,激光输出能量达到26.2 mJ,光-光转换效率为8.5%,光束发

Depolarization loss compensated resonator for electro-optic Q-switched solid-state laser

A novel laser resonator for compensating depolarization loss that is due to thermally induced birefringence in active rod is reported. As this new structure being applied to an electro-optic Q-switched LIDA side-pumped Nd:YAG laser operating at a repetition rate of 1000 Hz, substantial reduction in depolarization loss has been observed, the output pulse energy is improved about 56% from that of a traditional resonator without compensation structure. With incident pump energy of 450 mJ per pulse, linearly polarized output energy of 30 mJ per pulse is achieved, the pulse duration is less than 15 ns, and the peak power of pulse is about 2 MW. The extinction ratio of laser beam is better than 10:1, and the beam divergence is 1.3 mrad with beam diameter of around 2.5 mm. (c) 2006 Published by Elsevier B.V.

热容型板条激光器的感应折射率计算

高平均功率固体激光器的增益介质由于受热而容易发生畸变,如常用材料YAG,波前畸变和去偏振现象会同时发生,高热负载固体激光介质的热效应已成为制约激光器输出功率进一步提高的严重障碍。给出一种计算热容型板条激光器热感生折射率的方法。把YAG晶体的四阶压光张量从晶胞坐标系转换到实验室坐标系,采用经过坐标转换后的新的张量,可以分析在YAG激光器中任意应力分布引起的热感应双折射。进一步的计算表明,在zigzag板条激光器中,应力双折射率与板条从晶体毛胚上切割成材的角度有关。同时也对热容板条激光器的热效应和应力特性进行了二维的理论性概述。

Electron irradiation induced defects in high temperature annealed InP single crystal

Electron irradiation induced defects in InP material which has been formed by high temperature annealing undoped InP in different atmosphere have been studied in this paper. In addition to Fe acceptor, there is no obvious defect peak in the sample before irradiation, whereas five defect peaks with activation energies of 0.23 eV, 0.26 eV, 0.31 eV, 0.37 eV and 0.46 eV have been detected after irradiation. InP annealed in P ambient has more thermally induced defects, and the defects induced by electron irradiation have characteristics of complex defect. After irradiation, carrier concentration and mobility of the samples have suffered obvious changes. Under the same condition, electron irradiation induced defects have fast recovery behavior in the FeP2 ambient annealed InP. The nature of defects, as well as their recovery mechanism and influence on material property have been discussed from the results.

Measurement of Microscopic Deformation in a Cualni Single Crystal Alloy by Nanoindentation with a Heating Stage

Thermally induced recovery of nanoindents in a CUAINi single crystal shape memory alloy was studied by nanoindentation in conjunction with a heating stage. Nanoindents formed by a Berkovich indenter at room temperature were heated to 40, 70 and 100 degrees C. Partial recovery was observed for the nanoindents. The recovery ratio depended on the heating temperature. Indentation of CuAlNi can induce inelastic deformation via dislocation motion and a stress-induced matensitic transformation. The percentages of dislocation-induced plastic strain would affect the thermal deformation of CuAlNi, because the induced dislocations could stabilize stress-induced martensite plates even when the temperature above austenite finish temperature, A(f). When the applied indentation load is low (less than 10,000 mu N), the shape recovery strain is predominant, compared with the dislocation-induced plastic strain. Therefore, the degree of indent recovery in the depth direction, delta(D), is high (about 0.7-0.8 at 100 degrees C).

双调Q开关热退偏补偿全固态激光器

为了有效地补偿激光二极管(LD)侧向抽运1000 Hz重复率电光调Q Nd:YAG激光器棒状增益介质内存在的热致双折射损耗，设计了一种新颖的双调Q晶体开关复合谐振腔结构。实验结果表明，设计的双调Q晶体开关结构Nd:YAG激光器输出激光脉冲能量比单调Q晶体开关结构的非补偿腔输出能量提高了56%，当侧面抽运半导体激光器输出功率达到450 W时，激光输出达到30 mJ/pulse，输出光束偏振度优于10:1，激光脉冲宽度约14 ns。并获得6.7%的光-光转换效率。通过对双调Q开光激光谐振腔进行建模，并用求解速

Annihilation of deep level defects in InP through high temperature annealing

Deep level transient spectroscopy (DLTS) and thermally stimulated current spectroscopy (TSC) have been used to investigate defects in semi-conducting and semi-insulating (SI) InP after high temperature annealing, respectively. The results indicate that the annealing in iron phosphide ambient has an obvious suppression effect of deep defects, when compared with the annealing in phosphorus ambient. A defect annihilation phenomenon has also been observed in Fe-doped SI-InP materials after annealing. Mechanism of defect formation and annihilation related to in-diffusion of iron and phosphorus is discussed. Nature of the thermally induced defects has been discussed based on the results. (c) 2007 Elsevier Ltd. All rights reserved.

Photoluminescence characteristics of InP annealed in phosphorus and iron phosphide ambiences

Photo luminescence (PL) spectroscopy has been used to study InP annealed in phosphorus and iron phosphide ambiences. Noticeable PL emissions related with thermally induced defects have been detected in undoped InP annealed in iron phosphide ambience. Origins of the PL emissions have been discussed. (c) 2004 Elsevier Ltd. All rights reserved.

Characterization of defects and whole wafer uniformity of annealed undoped semi-insulating InP wafers

Semi-insulating (SI) InP wafers of 2 and 3 in. diameters have been prepared by annealing undoped LEC InP at 930 degreesC for 80 h under pure phosphorus ambient (PP) and iron phosphide ambient (IP). The electrical uniformity of annealed undoped SI wafers, along with a Fe-doped as-grown SI LEC InP wafer, has been characterized by whole wafer PL mapping and radial Hall measurements. Defects in these wafers have been detected by photo-induced current transient spectroscopy (PICTS). The results indicated that the uniformity of IP wafer is much better than that of PP wafer and as-grown Fe-doped Si InP wafer. There are fewer traps in undoped SI InP IP wafer than in as grown Fe-doped and undoped SI InP PP wafer, as evidenced by PICTS. The good uniformity of the IP wafer is related to the nonexistence of high concentration of thermally induced defects. The mechanism for this phenomenon is discussed based on the results. (C) 2002 Elsevier Science B.V. All rights reserved.