基于MCFT理论的钢纤维混凝土梁的截面分析

根据钢纤维混凝土的特性,对MCFT理论的裂后混凝土平均主应力-平均主应变关系进行了修正。在Vecchio和Collins对钢筋混凝土板在纯剪作用下截面分析的基础上,叠加了弯矩的作用,建立了钢纤维混凝土梁在弯剪复合作用下的截面分析模型。利用作者以及其他研究者的试验对该模型进行了验证,结果表明计算得到的钢纤维混凝土梁的剪力-箍筋应变曲线和极限荷载与实测结果吻合良好。该文还利用该模型对钢纤维和箍筋对梁抗剪性能的影响效率进行了比较。     

GEOMETRICALLY NON-LINEAR AND ELASTOPLASTIC THREE-DIMENSIONAL SHEAR FLEXIBLE BEAM ELEMENT OF VON-MISES-TYPE HARDENING MATERIAL

A three-dimensional elastoplastic beam element being capable of incorporating large displacement and large rotation is developed and examined. Elastoplastic constitutive equations are applied to the beam element based upon the assumption of small deformational strain leading to a material formulation which is completely objective for the application of stress update procedures. The continuum-type equations of plastic model of J₂ mixed hardening are transformed into the beam equations by satisfying beam hypotheses. An effective stress update algorithm is proposed to integrate elastoplastic rate equations by means of the so-called multistep method which is a method of successive control of residuals on yield surfaces. It avoids severe divergence when the displacement increments become large which is usual for the continuation methods. Material tangent stiffness matrix is derived by using consistent elastoplastic modulus resulting from the integration algorithm and is combined with geometric tangent stiffness matrix. Different from other elements, the present element is shear flexible and can satisfy the plasticity condition in a pointwise fashion. A great number of numerical examples are analysed and compared with the literature. The proposed beam element is verified to be not only quite accurate but also very effective for the analyses of pre-buckling and large deflection collapse of spatial framed structures.     

无背索斜拉桥稳定分析的能量法

无背索斜拉桥在理想的成桥状态下,面内失稳模态为主梁屈曲。将主梁简化成弹性地基梁计算模型,选用正弦级数作位移函数,运用能量方法,提出了主梁屈曲临界荷载的计算公式。结合该类桥梁的结构布置特点,用简洁的连续函数描述主梁轴压力和拉索弹性支承刚度的变化,同时用简单的线形折减系数反映斜塔变形对拉索弹性支承刚度的影响。最后以长沙市洪山大桥为例,用该方法计算了其成桥状态屈曲临界荷载,其结果与有限元解对比具有很好的精度。     

An interactive computer program for elliptical beam optimization

Elliptical antenna beams are used for planning of direct broadcast satellite systems. In this paper concepts of the beam optimization process are described briefly. A method of plotting the optimized beam on a suitable map projection is discussed. An interactive computer program, which can be used for the optimization and plotting of beams on a given territory, is described with the help of examples.     

衍射光学束匀滑器件性能的空间频谱分析

采用空间频谱方法分析了衍射光学束匀滑器件的焦面光强分布 ,重新定义了光能利用率及顶部不均匀性两个参数 ,由于其定义的溯源性 ,能够真实准确地评价束匀滑器件的设计性能。最后 ,采用这两个参数对精细化设计前后的衍射光学束匀滑器件性能进行了对比 ,结果证明了精细化设计的有效性     

冷发射电子束掺杂磷

一种新的冷发射电子束掺杂方法已研究成功。这种方法可实现高浓度(C_(max)=2.8×10~(20)/cm~3),超浅结[(x_j)_(min)≤0.1μm],而且损伤比离子注入的小得多。用这种方法制备的太阳能电池控制器件性能很好。     

Vibration Characteristics of Fatigue Damage of Beam-Type Structural Components

We consider free vibration of an elastic cantilever beam with a closing edge crack. The crack is simulated by an elastic pivot whose compliance is taken to be finite and is determined from the energy equivalence criterion. An algorithm has been constructed for sequential calculation of the beam vibration modes for each beam vibration cycle, whereas the number of cycles is limited. It is demonstrated that the beam vibration modes other than the initially preset one are induced during the crack opening and closing. The distinct features of such modes have been studied. We have analyzed the sensitivity of the vibration-damage characteristics which are determined from the assessment of nonlinear distortions of the displacement, acceleration, and strain waveform of the cross sections of the beam with a closing crack.     

离子源偏压对PIA-EB-Hf法制备的HfO2激光薄膜性能的影响

探究HfO₂薄膜的激光损伤特性以进一步提高激光损伤阈值(Laser Induced Damage Threshold, 简称LIDT), 对其在高功率激光系统中的广泛应用具有重要的意义。在不同的离子源偏压下, 采用等离子体辅助电子束蒸发金属铪(Hf)并充氧(O₂)进行反应沉积法制备了中心波长为1064 nm, 光学厚度为4H的HfO₂薄膜样品。测试了薄膜组分和残余应力; 根据透射谱拟合了薄膜的折射率; 通过XRD谱图和SEM表面形貌图分析了薄膜的微观结构; 对激光损伤阈值、损伤特性和机理进行了论述。结果表明: 偏压100 V时制备的薄膜具有最佳O/Hf配比; 薄膜压应力和折射率均随偏压降低而减小。薄膜内存在结晶, 激光能量在晶界缺陷处被强烈聚集和吸收, 加速了膜层的破坏, 形成由几百纳米的烧灼坑聚集而成的海绵状损伤结构。随着偏压降低, 膜结晶取向由(\stackrel{\text{?}}{1}11)晶面向(002)晶面转变, 界面能降低; 晶粒减小, 结构更均匀, 缓解了激光能量在晶界处的局部聚集与吸收, 表现出较大的激光损伤阈值。