Perfect elastic-viscoplastic field at mode Ⅰ dynamic propagating crack-tip

The viscosity of material is considered at propagating crack-tip. Under the assumption that the artificial viscosity coefficient is in inverse proportion to power law of the plastic strain rate, an elastic-viscoplastic asymptotic analysis is carried out for moving crack-tip fields in power-hardening materials under plane-strain condition. A continuous solution is obtained containing no discontinuities. The variations of numerical solution are discussed for mode Ⅰ crack according to each parameter. It is shown that stress and strain both possess exponential singularity. The elasticity, plasticity and viscosity of material at crack-tip only can be matched reasonably under linear-hardening condition. And the tip field contains no elastic unloading zone for mode Ⅰ crack. It approaches the limiting case, crack-tip is under ultra-viscose situation and energy accumulates, crack-tip begins to propagate under different compression situations.     

Q聚类分析在分类指导型教学中的应用

阐述了聚类分析的原理和方法，通过关于学生能力倾向分析的一个具体实例，在教学过程的“学习者分析”中引入Q型聚类分析，并对聚类分析方法使用过程中需要注意的一些问题进行了讨论。     

在梯形四能级原子系统量子调控下的左手效应

采用了一个梯形四能级原子系统,在多模光场的作用下利用量子相干技术使其实现介质的左手效应,使介质具备左手材料特性。在相互作用表象下,利用密度矩阵方程并结合相关条件下的有关公式进行理论计算,数值模拟结果显示,在合适的参量条件下,介质的相对介电常量和相对磁导率可以同时出现负值,产生了左手效应,相应的介质转化为左手材料。通过讨论在左手效应成立的条件下介质对光场的吸收和增益问题,结果表明,在弱探测场条件下,利用电磁诱导的方法也可以实现介质的左手效应。     

不同铺层厚度复合材料的低速冲击特性与损伤模式研究

复合材料凭借其轻质、高强的特性逐渐在工程材料界占据重要地位,对于复合材料的冲击损伤的研究也一直吸引着诸多研究学者的关注.为表征不同铺层厚度复合材料层合板的抗冲击性能,利用自由落体冲击设备,进行了复合材料层合板的冲击实验研究.给出了不同冲击能量下的损伤模式,并利用位移、速度、接触力以及能量的时间变化曲线,深入分析了侵入和穿透两种损伤模式的特点.研究发现,随着铺层厚度的增加,复合材料在冲击过程中吸收的能量也随之增加.引入能量平衡法,基于体系的能量守恒定律,利用Newton-Raphson数值方法求解了侵入损伤模式下的接触力大小,通过实验结果给定挠度求解了对应的速率变化情况,并将理论结果与实验结果进行比较.     

DNA碱基激光拉曼光谱检测方法的研究

以激光拉曼光谱仪采集腺嘌呤(A)、鸟嘌呤(G)、胞嘧啶(C)、胸腺嘧啶(T)的拉曼光谱图,分析了各碱基谱峰归属,并依据归属结果检测混合碱基组成。结果显示:4种碱基的特征峰集中在175～1 800cm~(-1)。相同积分时间和激光功率条件下,该波段内嘌呤碱基的激光拉曼光谱峰高于嘧啶碱基的谱峰。腺嘌呤、鸟嘌呤、胞嘧啶、胸腺嘧啶分别在723、648、791、1 368 cm~(-1)处的谱峰最强,利用这些特征峰能在2min内鉴别出混合碱基中的各碱基。     

Steady-state growing crack-tip field characteristics of mode Ⅲ elastic-viscoplastic/rigid interface cracks

The existence of viscosity effect at the interface of double dissimilar materials has an important impact on the distribution of the interface crack-tip field and the properties variety of the interface itself. The singularity and viscosity are considered in the crack-tip. The elastic-viscoplastic governing equations of double dissimilar materials at the interface crack-tip field are established. The displacement potential function and boundary condition of interface crack-tip are introduced. The numerical analysis of elastic-viscoplastic/rigid interface for mode Ⅲ is worked out. The stress-strain fields are obtained at the crack-tip and the variation rules of solutions are discussed according to each parameter. The numerical results show that the viscosity effect is a main factor of the interface propagating in the crack-tip field, and the interface crack-tip is a viscoplastic field governed by the viscosity coefficient, Mach number (Ma), and singularity exponent.     

Ⅲ型弹粘塑性/刚性界面裂纹的定常扩展裂尖场

考虑裂纹尖端的奇异性和粘性效应,建立了双材料界面扩展裂纹尖端的弹粘塑性控制方程．引入界面裂纹尖端的位移势函数和边界条件,对刚性-弹粘塑性界面Ⅲ型界面裂纹进行了数值分析,求得了界面裂纹尖端应力应变场,并讨论了界面裂纹尖端场随各影响参数的变化规律．计算结果表明,粘性效应是研究界面扩展裂纹尖端场时的一个主要因素,界面裂纹尖端为弹粘性场,其场受材料的粘性系数、Mach数和奇异性指数控制．     

基于Web Service移动机械手遥操作控制系统的实现

Web Service是建立可互操作的分布式应用程序的新平台.它定义了应用程序如何在Web上实现互操作性,主要技术有XML,SOAP,WSDL和UDDI.本文首先介绍了Web Service的工作原理,然后充分利用Web Service平台的特点对移动机械手网络遥操作控制系统进行设计,使系统具有易于开发、扩展、维护和跨平台能力强等特点.     

Field structure at mode III dynamically propagating crack tip in elastic-viscoplastic materials

An elastic-viscoplastic mechanics model is used to investigate asymptotically the mode Ⅲ dynamically propagating crack tip field in elastic-viscoplastic materials. The stress and strain fields at the crack tip possess the same power-law singularity under a linear-hardening condition. The singularity exponent is uniquely determined by the viscosity coefficient of the material. Numerical results indicate that the motion parameter of the crack propagating speed has little effect on the zone structure at the crack tip. The hardening coefficient dominates the structure of the crack-tip field. However, the secondary plastic zone has little influence on the field. The viscosity of the material dominates the strength of stress and strain fields at the crack tip while it does have certain influence on the crack-tip field structure. The dynamic crack-tip field degenerates into the relevant quasi-static solution when the crack moving speed is zero. The corresponding perfectly-plastic solution is recovered from the linear-hardening solution when the hardening coefficient becomes zero.     

动态裂纹尖端弹粘塑性场的研究

本文利用弹一粘一塑性材料力学模型,对动态扩展裂纹尖端的指数奇异性和对数奇异性进行了渐近分析。文中假定,弹性阶段的粘性效应可以略去,仅在塑性应变中粘性才起作用,对于这种模型,推导出了其率敏感型的本构关系。以Ⅱ型裂纹为例,进一步推导了两种奇异性下裂纹尖端场的渐近微分控制方程,并进行了数值仿真分析。同时讨论了粘性系数α、马赫数M^2对裂纹尖端应力应变场的影响,即,弹粘塑性材料扩展裂纹的奇异性取决于其粘性系数和马赫数,粘性系数较大时,裂纹尖端场具有对数奇异性;粘性系数较小时,裂纹尖端场具有指数奇异性。修正了文献中对数奇异性区域的大小;解释了文献中过渡区的成因;给出了过渡区尖端应力场解的形式,从而建立了裂纹尖端场的统一解。