Semi-analytical three-dimensional elasticity solutions for generally laminated composite plates

Semi-analytical solutions for bending and free vibration of composite laminated plates have been derived based on three-dimensional elasticity theory using a newly developed hybrid analysis, which perfectly combines the state space approach (SSA) and the technique of differential quadrature (DQ). The thickness direction of laminates is selected as the transfer direction in SSA, and the DQ technique is employed to discretize the in-plane domains. This actualizes the transformation of the original partial differential equations into a state equation consisting of first-order ordinary differential equations. In particular, the use of DQ technique makes ease of the treatment of various boundary conditions, which cannot be considered in the conventional exact SSA. To avoid numerical instabilities in the conventional transfer matrix method, artificial interfaces are introduced to divide each layer into several sub-layers to reduce the transfer distance and the joint coupling matrices are established according to the continuity conditions at actual and artificial interfaces to implement the global analysis. Comprehensive numerical examples are preformed to validate the present hybrid method. Effects of some parameters on mechanical properties of the laminates are discussed.     

塑性损伤本构模型的自由能势函数研究

自由能势函数是不可逆热力学量及其共轭量的标量泛函,是广义标准材料模型的重要组成.论文根据损伤状态、过程、作用和伪势的定义和定理,分析了损伤耗散势的数学和物理含义,探讨了损伤耗散势的理论基础和描述耗散势的一般理论方法.研究了耗散势、损伤作用和自由能势函数的相互关系,给出了满足上述基本原理的自由能表达式,基于增量最小原理的变分形式得到了损伤理论基本方程的数值离散方程,实验模拟验证了该文理论和数值方法的正确性和有效性.     

Graded index broadband antireflection coating prepared by glancing angle deposition for a high-power laser system

This paper reports that SiO₂ is selected to fabricate broadband antireflection (AR) coatings on fused silica substrate by using glancing angle deposition and physical vapour deposition. Through accurate control of the graded index of the SiO₂ layer, transmittance of the graded broadband AR coating can achieve an average value of 98% across a spectral range of 300--1850~nm. Moreover, a laser-induced damage threshold measurement of the fabricated AR coating is performed by using a one-on-one protocol according to ISO11254-1, resulting in an average damage threshold of 17.2~J/cm$^{2}$.     

Diode-pumped Q-switched Nd:GdVO4/KTP green laser formed with a flat–flat resonator

A diode-pumped acousto-optically Q-switched intracavity frequency-doubled Nd:GdVO₄/KTP green laser formed with a flat–flat resonator was demonstrated. 3.05 W of average green output power at pulse repetition frequency (PRF) of 40 kHz was obtained with an optical conversion efficiency of 18.4%, the effective intracavity frequency-doubling efficiency was 57%. At the incident pump power of 15 W, the shortest laser pulse occurred at PRF of 25 kHz with FWHM width of 14 ns, yielding the highest peak power of 7.44 kW; while the largest pulse energy of 0.14 mJ was achieved at PRF of 15 kHz.     

Investigation of LD end-pumped Nd:YVO4 crystals with various doping levels and lengths

The absorption properties of Nd:YVO₄ crystals with various doping levels and lengths are reported. The effective stimulated emission cross-sections of different doping levels are calculated with measured upper-level lifetimes. Our investigation gives good advice on the optimization of LD end-pumped Nd:YVO₄ laser.     

Two-photon absorption and nonlinear optical properties of a new organic dye PSPI

Trans-4-[p-(pyrrolidinyl)styryl]-N-methylpyridinium iodide (abbreviated as PSPI thereafter) is a two-photon absorption (TPA) dye newly synthesized by our research group. It possesses much larger TPA cross-section and much stronger upconversion fluorescence emission than those of common organic dye (such as rhodamine) when excited with near infrared (IR) radiation. TPA spectrum and upconversion efficiency spectrum of HEASPI solution at various wavelengths were measured. There is 34 nm blue shift for the central wavelength of the TPA induced absorption peak compared with two times of the linear absorption peak. The biggest molecular TPA cross-section σ₂^′ is 2.85×10⁻⁴⁷ cm⁴ s/photon at 930 nm. At 1064 nm, σ₂^′ is 3.12×10⁻⁴⁸ cm⁴ s/photon. The highest efficiency is 3.9% at 1010 nm, whereas 2.9% at 1064 nm. Its optical power limiting properties at 930 nm have also been illustrated.     

The optimum configuration for the third-harmonic generation of 1.064 μm in a YCOB crystal

A method of determining the spatial configuration of a YCa₄O(BO₃)₃ (YCOB) crystal is introduced. The type-I phase-matching points for the sum-frequency of 1.064 μm and 0.532 μm, as well as the conversion efficiency for YCOB samples cut in different directions, have been measured. When the input intensity is 0.76 GW/cm², the third-harmonic generation (THG) conversion efficiency for the (106°, 77.2°)-cut YCOB crystal reaches 26.2%, which is the highest that we know so far. Both the calculations and the experiments show that the optimum THG configuration for a YCOB crystal is near (106°, 77.2°), or other equivalent directions in space. Received: 11 September 2000 / Revised version: 25 January 2001 / Published online: 27 April 2001     

金刚石锯片在锯切过程中的受力与失效分析

对金刚石锯片在锯切过程中的受力及弧区内直接参与切削的金刚石数量进行了测量和估算,并分析了节块表面抛光和微破碎金刚石比例与锯片寿命和效率之间的关系,结果表明：单颗粒金刚石的受力远低于其静压强度;其低强度失效的原因是锯切过程中金刚石晶体内产生的热应力。     

张量空间中的多面体锥

本文利用文献 [1 ]中的结果给出了张量空间中多面体锥的性质 ,指出当 K1,K2 分别为 V1,V2中的多面体锥时 ,由它们所生成的 V1 V2 中的最小真正锥也是多面体锥 ,这一条件不仅是充分的也是必要的 .并利用这一结果对多面体锥的已有结论给出了新的证明     

溅射气压对X射线多层膜反射率的影响

本文在不同的溅射气压的情况下制备了具有相同结构参量的Mo/Si多层膜,测出了其对应的小角度X衍射曲线,在北京同步辐射实验室测量了多层膜的软X射线反射率.小角X射线衍射谱表明:随着溅射气压升高,多层膜的小角X射线衍射曲线的高次峰的峰高急剧变小,半峰宽变大.反射率测量结果也表明:多层膜的X射线反射率随溅射气压的升高而急剧降低.