基于拉伸振动精确化理论求解含孔厚板弹性波散射问题

针对采用弹性力学平面问题求解波动/振动时常产生较大误差的问题,基于厚板拉伸振动精确化方程,采用复变函数方法对含孔平板中弹性波散射与动应力集中问题进行了研究。利用正交函数展开的方法将待解的问题归结为对一组无穷代数方程组的求解。给出了含椭圆孔厚板拉压弹性波散射与动应力集中的数值结果。研究结果表明:动应力集中系数与分布取决于入射波数、平板厚度、椭圆偏心率等无量纲化参数。     

数控转塔冲上下料机器人本体研究及仿真分析

在数控转塔冲生产过程中,仅借助人力进行上、下料操作会使生产效率低下.针对这一问题,在选择合理的机构自由度及分析机构运动学特性的基础上,设计了一种专门应用于数控转塔冲上、下料过程的机器人机构模型,并且借助于UG7.0对该模型进行了仿真分析.分析结果显示此机构完全能满足生产要求.     

注塑模数字化设计与加工仿真一体化技术研究

阐述一种注塑模数字化设计及加工过程仿真一体化技术.运用Pro/Engineer软件的通用功能模块及其模架设计专家(EMX)模块,进行塑件及其注塑模设计,并将模具中的成形零部件模型数据转换到MasterCAM中进行数控编程和加工仿真.以相机面壳注塑模设计与加工仿真为例,验证了该方法的可行性.该方法可以提高塑料注射模具的开发效率.     

Pulse energy-storage performance and temperature stability of Bi2O3-added BaTiO3 based ceramics

The temperature stability and temperature stability range of barium titanate-based pulse energy-storage ceramics were modified by Bi₂O₃ tailoring in (Ba_0.98-xLi_0.02Bi_x) (Mg_0·04Ti_0.96)O₃ (x = 0, 0.025, 0.05, 0.075, 0.1) and (Ba_1.03-1.5xLi_0.02Bi_x) (Mg_0·04Ti_0.96)O₃ (x = 0.125, 0.15, 0.2, 0.25) ceramics. Excellent pulse energy-storage performances of ceramic films are achieved via the new dual priority strategy of establishing cationic vacancies and forming a liquid phase. The dielectric constant plateau appears due to the cubic phase and space charges. Outstanding temperature stability, frequency stability and antifatigue performance are obtained in the ceramics, and their variations are all less than 15%. The comprehensive energy-storage properties with dual priority parameters of energy-storage density and efficiency of 3.13 J/cm³ and 91.71%, accompanied by an excellent pulse discharge energy density of 2.48 J/cm³, current density of 1313.23 A/cm² and power density of 195.26 MW/cm³ are gained at x = 0.1. The perfect pulse energy-storage performances as well as ultrahigh stability are correlated with synergistic effects of multiphase coexistence, cubic phase, liquid-phase sintering, grain size, ceramic resistance, space charges and polar nanoregions. The comprehensive parameters indicate that the (Ba_0·88Li_0·02Bi_0.1) (Mg_0·04Ti_0.96)O₃ ceramics have potential application in high precision fields.     

基于铝质薄壁筒件切削加工的自动装夹技术研究

铝罐零件的刚性差,在切削过程中,容易受到切削力和夹紧力的作用而发生变形,从而影响产品的质量。合理的装夹方法可以有效地减小加工变形。因此设计了一种新的装夹方法,提高了加工精度,保证了加工质量,同时实现一次装夹完成切口与翻边的一体化加工。     

Temperature-independent physical properties of electrophoretic Ti5NbO14 films for high-temperature capacitors

Ti₅NbO₁₄ (T5NO) films were developed on Pt/Ti/SiO₂/Si substrates by electrophoretic method by using T5NO³⁻ nanosheets. The film deposited at room temperature (RT) contained organic defects, which were almost eliminated in the film annealed at 700 °C. The film deposited at RT revealed (100) planes with an inter-planar distance of 1.1 nm because of the existence of TBA⁺ defects. However, for the films annealed at higher temperatures (≥400 °C), two types of structures formed: (100) planes with 0.55 nm inter-planar distance (group-1 structure), and (100) planes with 1.42 nm inter-planar distance (group-2 structure). The dielectric constant (ε_r) of the film annealed at 700 °C was 61 with a low dielectric loss of 1.0%. Variations in the ε_r according to the film thickness, electric field, and temperature were small. This film displayed a high insulating property up to 300 °C with a small temperature coefficient of capacitance (−56.7 ppm/K) up to 400 °C.     

Study on UV laser machining quality of carbon fibre reinforced composites

The large differences in material properties of the carbon fibre and the epoxy resin in carbon fibre reinforced plastic (CFRP) composite make laser processing very challenging. The heat affected zone (HAZ) has been the major obstacle for wide industry applications of laser machining of CFRP composites. This paper investigates the quality of CFRP machined by a diode pumped solid state (DPSS) UV laser. The results show that minimum HAZ (about 50 μm) is achievable in machining of CFRP composite by using short pulsed UV laser. The study found that heat is easily accumulated in the material during laser processing, especially when the carbon fibres are sliced into small pieces. The paper discusses how to make use of the heat accumulation and how to avoid potential damage by the heat accumulation. Bearing strengths test and fracturing mechanisms study were conducted. Method of characterization of thermal damage in polymer matrix is developed.     

Thermal performance of a trapezoidal-shaped solar collector/energy store

A simple, low-cost solar water heater has been developed for operation in Mediterranean Europe or regions of similar latitude (40–45° north). It takes the form of a trapezoidal-shaped water store in direct contact with an inclined flat-plate solar collector assembly. This cross-section induces thermal stratification in the water store, and provides sufficient energy storage to meet typical daily hot-water demand. Its thermal performance is critically dependent on the waterside convective heat-transfer coefficient on the backward-reclining collector plate; previously evaluated by Cruz et al. (Cruz JMS, Hammond GP, Reis AJPS. Buoyancy-driven convective heat exchange in a trapezoidal-shaped solar collector/thermal store. In: Proc. of the 5th ASME/JSME Joint Thermal Engineering Conf., San Diego, CA (ASME, New York), 1999, 9 pp). In the current design, the absorber plate inclination to the horizontal was fixed at 45° (close to the local latitude) in order to yield maximum solar gain over a typical year. The energy saving provided by the solar collector/thermal store demonstrator largely depends on the amount of thermal stratification within the trapezoidal storage cavity. This was evaluated via both computation and measurements of the temperature field. A thermal network analysis model was then used to assess the energy-saving potential of the composite system. It indicated that a 30–70% reduction in daily load could be obtained in contrast to direct, electrical or gas, heating: the smaller saving occurred at times of greatest use or hot-water take-off.