无风条件下马蹄波波面演化特征的实验研究

在实验室无风条件下对马蹄波进行了实验研究. 得到了L2型的马蹄波,也发现了两种新的类似马蹄波的波型,给出了马蹄波的横向波长和波高参数的几何特征,分析了马蹄波演化的过程中波面时间历程和振幅谱特征,讨论了马蹄波产生的机理和条件.      

天然纤维增强复合材料力学性能及其应用

本文介绍了天然纤维的化学成分、结构以及力学性能;综述了天然纤维的表面处理方式,分析了其作用机理,并讨论了表面处理对其复合材料力学性能的影响;从增强体形式出发,介绍了短纤维、纤维毡、纤维织物以及单向纤维增强复合材料,并研究了成型工艺、纤维含量和表面处理等对其拉伸、弯曲、界面性能和冲击强度以及断裂韧性的影响;最后总结了天然纤维增强复合材料在汽车、建筑土木等领域的应用现状,并展望了其发展和应用前景.     

碾压混凝土坝变形安全监控模型研究

研究了碾压混凝土坝本体、施工层面及坝基等各部分的变形规律,采用不同的模型描述了上述各部分的本构关系,据此分析了影响碾压混凝土坝变形的主要影响因素,探讨了水压分量、温度分量以及时效分量的影响因子,并重点对不同荷载作用下的时效分量的组成进行了研究,提出了碾压混凝土坝变形安全监控模型。文末结合工程实例,分析了变形安全监控模型的建模过程,讨论了变化荷载作用下时效分量的模拟方法。     

金属表面改性中界面力学性能的实验研究

提出了适用于微区测量的两步数字图像相关法,采用二阶泰勒多项式子区位移模式有效地降低了截断误差;采用B-样条插值函数提高了亚像素重建的精度;采用拟牛顿迭代法提高了计算速度等,使微区内应变测量精度控制在100~150με。在残余应变测量中通过数字标记点相关技术实现了试件的精确复位,提高了其测量精度。文中利用上述方法测量了镀层改性试件跨界面的位移场和应变场,分析了裂纹对镀层的影响以及测出了基材中引起的残余应变;同时对镀层改性界面结合性能作了定量比较。     

缝合复合材料层板刚度预报

提出了缝合复合材料层板的刚度预报模型,该模型考虑了缝合针脚处的孔洞对刚度的影响,描述了缝合孔洞的几何形态,建立了孔洞形态与纤维弯曲的关系,采用平均刚度法和经典层合板理论进行了刚度预报,获得了与试验数据相吻合的预报结果,表明了该模型的有效性,详细探讨了缝合孔洞对缝合层板刚度的影响规律,得到一些有益结论。     

陀螺马达电源的研究

本文讨论了三相交流陀螺马达电源的工作原理。根据主要技术指标的要求，设计了陀螺马达电源，给出了该电源的各个组成部分的线路设计，解决了研制中出现的电源振荡问题，论述了该电源的设计特点，给出了使用结论     

基于加窗傅立叶变换的SR-CT滤波反投影重建

SR-CT(Synchrotron Radiation Computed Tomography同步辐射X射线计算机断层扫描)实验中,原始投影图像存在噪声,从而影响了滤波反投影重建图像的质量.为提高重建图像质量,提出了一种基于加窗傅立叶变换滤波改进重建图像质量的方法.通过对原始投影图像噪声和滤波反投影算法的讨论,对利用该方法提高重建图像质量的可行性进行了分析.利用加窗傅立叶滤波方法对两组SR-CT实验得到的投影图像分别进行了处理,抑制了原始投影图像的噪声,提高了重建图像的质量.实验的结果验证了该方法的有效性.     

混凝土断裂能

本文从能量的观点分析了混凝土Ⅰ型和Ⅱ型断裂能表达式,探讨了梁自重对Ⅰ型断裂能的影响;介绍了Ⅰ型断裂能的测试方法,给出了拉应变软化曲线.     

湍流基础问题研究进展:能量传递,相互作用尺度,各向同性衰减的自保持性

为了更深入地了解湍流的物理过程,本文综述了各向同性湍流的基础问题．在评述了Ｋｏｌｍｏｇｏｒｏｖ能谱及能量级串过程后,深入讨论了Ｋｏｌｍｏｇｏｒｏｖ局部各向同性假设．接着综述了涉及能量传递的以及包括三元组相互作用的各向同性湍流相互作用尺度的详细物理过程．还讨论了惯性区、自相似性以及小尺度对大尺度各向异性的响应和末期衰减过程．之后为了举例说明这些论点,详细讨论了根据各向同性湍流直接模拟及大涡模拟得到的结果（包括对亚格子模型的讨论）.最后,综述了各向同性湍流的自保持性,并展望了今后的研究方向．文末列出了１５５篇参考文献     

在普通力学课程中开展研究性学习的探索

讨论了研究性学习的内涵,给出了力学研究性学习的部分参考课题,通过教学案例归纳了研究性学习中的师生互动的6个步骤,并对教师的角色转变进行了分析.通过研究性学习的实施,学生学习力学的积极性得到了提高,创新意识和能力得到了增强.为在力学课程中开展研究性学习提供了重要的参考和借鉴.     

What to Learn,What to Learn

Experimental Techniques -     

An Introduction to the Adjoint Approach to Design

Optimal design methods involving the solution of an adjoint system of equations are an active area of research in computational fluid dynamics, particularly for aeronautical applications. This paper presents an introduction to the subject, emphasising the simplicity of the ideas when viewed in the context of linear algebra. Detailed discussions also include the extension to p.d.e.'s, the construction of the adjoint p.d.e. and its boundary conditions, and the physical significance of the adjoint solution. The paper concludes with examples of the use of adjoint methods for optimising the design of business jets. This revised version was published online in July 2006 with corrections to the Cover Date.     

An Introduction to Differential Geometry with Applications to Elasticity

Journal of Elasticity -     

Global and local approaches to fracture normal to interfaces

The problem of a crack perpendicularly approaching a bimaterial interface is examined using both global and localapproaches to fracture. The global approach is based on the J-integral with a second parameter, Q, which scales the stress triaxiality ahead of the crack. The local approach is based on either brittle fracture(Beremin model ) or ductile fracture (Rice and Tracey model ). In the first case, the Weibull stress over the plasticzone is calculated. In the second case, the void growth rate is calculated at the tip of the crack over a representativevolume (generally associated with a characteristic length of the material ). After a brief summary of each approach,the results for a crack near an elastically homogeneous, plastically mismatched interface are presented. Thebehaviour of the bimaterial is expressed in relation to the behavior of the homogeneous material. It is shown thatthere is an effect on the crack behavior which depends on the direction of crack propagation, i.e. from the hardermaterial to the softer material or vice versa. This effect is examined as a function of change in yield strength ratioand hardening exponent, n. For the case of brittle fracture, the effect of changing the Weibull modulus, m, is also examined. The models based on the local approach show that both stress- and strain-controlledfracture mechanisms must be accounted for. This implies the necessity of using the two parameters J and Q in the global approach. This is due to the fact that the stress–strain fields ahead of the crack tip areaffected by the nature of the second material.     

Relationship between paddy soil adhesion to steel and to rubber

Forty-three pairs of samples concerning adhesion of paddy soil to steel and to rubber are used to identify the relationship between these two groups of variables. Results show that there is no significant difference between them, implying that they are roughly equal to each other in engineering practice.     

Methodology to assess integrity with application to collector copper lamellas

The performance of engineering components and structures is strongly influenced by the interaction between design, manufacture and materials. A methodology to assess the integrity of a circular collector is presented by investigating the failure of copper lamellas. The investigated circular collector, having 315 copper lamellas, is one of the main parts of an electric motor. The fracture of the copper lamellas was observed in normal operation. This unexpected fracture required an investigation of the fracture origin, in order to improve the initial design. The numerical results of the finite element analysis on the stress field in the copper lamellas for the operating regimes, and the stress concentration effects are shown. Failure assessment diagram, based on notch stress intensity factor, was considered in order to estimate if crack initiation can occur. Finally a study of crack propagation will present comparatively the numerical obtained crack path against the one observed in-service.     

Extension to three dimensions of a holographic-moiré technique to separate patterns corresponding to components of displacement

The holographic-moiré technique to obtain separate patterns for the Cartesian components of the displacement vector is extended to curved surfaces. An initial pattern which is often required for the observation of the displacement fringes is analyzed for this case. Criteria are established for the localization of this initial pattern to follow close to the contour of the object surface. A PVC pipe subjected to torsion demonstrates the proposed technique and, when analytical arguments are checked experimentally, a close correlation is observed.