负泊松比蜂窝结构覆盖层的动态压缩行为研究

为提高舰船的生命力及安全性,在舰船湿表面敷设某种材料的防护覆盖层,能起到一定的抗冲击作用。提出了一种负泊松比蜂窝结构,建立了该结构的力学分析模型,利用有限元软件建模及仿真,研究周期分布空腔结构覆盖层的动态压缩行为,分析其在动态压缩过程中,单元节点位移、加速度以及能量等物理参数随时间的变化特性。研究结果表明,在相同的载荷,不同的初速度作用下覆盖层结构响应不同;随着初速度的增加,覆盖层结构的动态压缩行为表现愈加明显。该研究结果对此类覆盖层结构的动力学特性具有一定的指导作用,同时可对潜艇湿表面抗冲覆盖层结构的进一步优化设计提供参考。     

黏弹性材料动态时温模型及其宽频域动态力学特性研究

受真实作业工况中高频冲击载荷的影响,黏弹性材料的动态力学特性产生了较大的变化。为了准确预测宽频域内材料动态力学特性的变化情况,依据时温等效原理,结合Vogel-Fulcher-Tammann黏度方程,建立黏弹性材料动态时温等效（DTT）模型,并与分数阶温频等效模型进行对比。结果表明：DTT模型构造的主曲线具有更好的连续性和一致性,能更加精准地预测宽频域内黏弹性材料的动态力学特性。基于DTT模型,提出了构造宽频域内材料动态力学特性主曲线和诺模图的方法,同时,为了降低计算成本,缩短产品研制周期,研发了一款黏弹性材料动态力学性能计算与分析专用软件。     

基于双模式超声换能器的选择性激光熔化316L制件弹性常数无损表征研究

选择性激光熔化技术(SLM)可以快速成型任意结构的金属零件,但其制件的内部组织和材料性能与传统制件有着显著区别。基于双模式超声换能器对SLM 316L不锈钢制件的不同方向弹性常数及其分布进行表征研究。首先通过设计并制备高性能双模式超声换能器,搭建超声弹性常数分布测量系统。对SLM制备的316L不锈钢试样依次进行纵波和两个正交横波声速测量,获得同位置处不同方向弹性模量和泊松比。通过不同成型方向的声速测量,发现SLM制件在堆积z方向熔化层内呈现显著区别,表现出明显的各向异性。而y-z平面内弹性常数分布表征表明,杨氏模量E_(13)大于E_(12),泊松比σ_(13)小于σ_(12),且制件各熔化层弹性常数分布规律相似。此外,还讨论了加工过程中扫描速度和扫描间距等工艺参数对弹性参数的影响。选择性激光熔化制件弹性常数的有效无损表征将为增材制件内部质量控制和工艺改善提供技术基础。     

含共线裂纹功能梯度材料断裂问题分析

应用分层原理分析了具有不同弹性模量含共线双裂纹的功能梯度材料断裂问题。通过积分变换得到嵌入功能梯度材料裂纹的应力场和位移场,结合边界条件、连续条件及单个裂纹的应力场和位移场,将求解该裂纹问题转化为求解奇异积分方程组。通过求解奇异积分方程组得到裂纹的应力强度因子。最后针对材料弹性模量和裂纹几何参数对应力强度因子的影响进行了探讨。结果表明材料弹性模量分布形式对裂纹的应力强度因子影响显著,该结果可为功能梯度材料制备及材料设计等提供理论依据。     

正态分布非均匀各向同性弹性材料的有效力学性质分析

结合有限单元法和数理统计技术,采用随机格形模型研究正态分布非均匀各向同性弹性材料微结构非均匀性对有效力学性质的影响.首先,建立随机格形模型,结合舍选法得到若干组材料参数序列,作为随机格形模型的输入数据,以模拟材料正态分布的微结构力学性质,对模型试样施加单向位移拉伸载荷,开展数值模拟实验,获得非均匀材料有效力学性质子样,最后运用数理统计技术处理数据,得到材料有效力学性质的统计特征.结果表明,组分弹性模量呈正态分布的非均匀材料,其有效力学性质参数也呈正态分布,而且有效泊松比还表现出很弱的方向性;有效弹性模量期望值则小于组分弹性模量的期望值.     

基于扫频响应反推黏弹性材料分数阶导数模型

提出了基于测试获得的扫频响应反推黏弹性材料分数阶导数模型参数的方法。在同时考虑黏弹性材料阻尼和剩余等效黏性阻尼的基础上,建立了基础激励作用下黏弹性复合板动力学方程,给出了求解振动响应的方法。提出利用基于灵敏度的匹配计算实现分数阶导数模型参数辨识的方法。以贴敷ZN-1型黏弹性材料的悬臂钛板为例,辨识得到了该黏弹性材料的分数阶导数模型。将结果代入到黏弹性阻尼板振动响应分析模型中,通过理论与实验的对比,证明了辨识参数的合理性。     

研究纯金属弹性常数的一种新的力学模型

弹性常数是用于表征物体抵抗弹性变形能力的物理量,是材料力学行为的主要指标.以弹性力学、连续介质力学、固体物理学、势函数理论等为基础,以一个由同种的、可用球模型近似的粒子组成的、单层粒子的平面固体薄板为研究对象,建立基于粒子间作用力的连续介质二维模型.基于该模型,推导出模型中任意一个三角形区域的弹性常数的计算公式;提出理想微结构的概念,推导出模型为理想微结构时的整体弹性常数、弹性模量、泊松比的计算公式,其中泊松比是一个等于1/3的常数.求解纯铜的弹性常数和弹性模量,并验证该模型的合理性和正确性.     

剪切载荷作用下胶接材料界面动应力强度因子的研究

主要研究剪切载荷作用下,胶接材料中弹性和粘弹性界面间Griffith裂纹尖端动态应力强度因子的时间响应.采用积分变换方法,得到Laplace域内弹性和粘弹性材料的应力和位移的含未知系数的表达式;引入位错密度函数,并通过边界条件和界面连接条件,导出反映裂纹尖端奇异性的奇异积分方程组,采用Gauss积分,并运用Gauss-Jacobi求积公式化奇异积分方程组为代数方程组,利用配点法进行求解;最后经过Laplace逆变换,求得动态应力强度因子的时间响应.得到Ⅱ型动应力强度因子随着粘弹性材料的剪切松弛参量的增加而增大,膨胀松弛参量的增加而减小;随着弹性材料的剪切模量和泊松比的增加而增大.     

双材料平面斜裂纹问题超奇异积分方程方法

由双材料平面问题的弹性力学基本解，应用互等功定律和坐标变换，得到双材料平面任意斜裂纹问题位移场及应力分量表达式，经代入裂纹岸应力边界条件，获得以裂纹岸位移间断作为基本未知量的超奇异积分方程组；通过适当的积分变换，用有限部积分原理处理超奇异积分，建立该问题的相应数值算法。文中对任意位置的裂纹问题进行计算，并较为系统地分析界面对裂纹应力强度因子的影响，当裂纹垂直或平行于双材料界面时，计算结果与已有结果一致。     

钛合金杨氏模量与泊松比测试分析

测量1Cr18Ni9Ti合金钢(高温时效处理)的杨氏模量与泊松比,为热处理新工艺提供材料的弹性系数指标,为工程实际提供力学参数;采用应变电测原理和技术(应变片测量法),在试样纵向和横向粘贴电阻应变片,通过静态电阻应变仪测量试样纵向和横向应变,得出了1Cr18Ni9Ti合金钢的弹性模量和泊松比.1Cr18Ni9Ti合金钢为低模量材料.     

Minimal Realization of Linear Graph Models for Multi-physics Systems

An engineering system may consist of several different types of components,belonging to such physical"domains"as mechanical,electrical,fluid,and thermal.It is t...     

Quantum Cooperative Robotics and Autonomy

The intersection of Quantum Technologies and Robotics Autonomy is explored in the present paper.The two areas are brought together in establishing an interdisci...     

考虑进油孔有限长滑动轴承油膜力的近似解析解

针对具有进油孔的有限长滑动轴承油膜力求解问题,采用变分原理和分离变量法,求得了有限长滑动轴承油膜压力分布的近似解析表达式。将油膜压力分布的近似解析表达式在油膜存在区域上进行积分,即得到了油膜力。将提出的计算有限长滑动轴承油膜力方法与无限长轴承模型、有限元方法的计算结果进行了比较,发现了提出的方法与有限元方法的计算结果很接近。最后,研究了进油孔位置和进油压力对油膜存在区域、油膜力等的影响,研究结果表明进油孔位置和进油压力对油膜存在区域和油膜力有较大的影响。     

三绕组变压器的双绕组等效建模及在Matpower中的应用

针对实际电网存在着大量的三绕组变压器,但国际上一些著名商业软件,如BPA仿真软件、Matpower这一权威潮流计算开源软件,均只提供双绕组变压器模型,限制了其在具有三绕组变压器的电力系统中的应用的问题,潮流计算是自主开发的电力系统各种应用软件的核心模块,因此依托国际权威开源程序进行二次开发,是一种较好的选择。对Matpower要求的数据格式进行了归纳,对变压器的一般的等值电路及带理想变压器的等值电路和带标幺值的等值电路进行了分析研究,提出了三绕组变压器转换为双绕组等效模型的建模方法,使得原先只适应双绕组变压器的潮流计算软件可以适用于三绕组变压器电网的潮流计算;最后以Matpower软件为例进行了案例计算,并用PSASP仿真软件进行对比验证。研究结果证明,所提出的建模方法是有效的。     

On the Relation of Load to Average Gap in the Contact Between Surfaces with Longitudinal Roughness

A computer simulation model for the contact between longitudinally-oriented rough surfaces has been formulated. This model closely duplicates the actual surf ace contact deformation behavior by taking into account the elastic interactions between the asperities. There were no assumptions made about the shapes, or any deformation behavior of the asperities, except for their obeying the laws of elasticity. The plastic deformations on the high asperity peaks were taken into account by setting a ceiling on their contact pressures at the material hardness value. The simulations used real surface profiles which were digitized from unworn circumferentially ground steel surfaces. Each pair of these profiles was mathematically combined to form an equivalent rough profile pressing against an infinitely rigid flat and having the appropriately adjusted elastic modulus. A total of 28 different pairs of profiles were used in the simulations. Each contacting pair was subjected to 30 different load levels and the local contact pressures and deformations were calculated. The contact simulations yielded some important mathematical relationships between parameters, such as the real area of contact, average gap, and average asperity load through statistical curve fitting. Two analytical functions were generated to relate the average load to average gap and the real area of contact to load.     

INTEGRAL EQUATION METHOD＇S APPLICATION IN HOLE-EDGE STRESS OF COMPOSITE MATERIAL PLATE WITH DIFFERENT SHAPED HOLES

The strength of composite plate with different hole-shapes is always one of the most important but complicated issues in the application of the composite material. The holes will lead to mutations and discontinuity to the structure. So the hole-edge stress concentration is always a serious phenomenon. And the phenomenon makes the structure strength decrease very quickly to form dangerous weak points. Most partial damage begins from these weak points. According to the complex variable functions theory, the accurate boundary condition of composite plate with different hole-shapes is founded by conformal mapping method to settle the boundary condition problem of complex hole-shapes. Composite plate with commonly hole-shapes in engineering is studied by several complex variable stress fimction. The boundary integral equations are founded based on exact boundary conditions. Then the exact hole-edge stress analytic solution of composite plate with rectangle holes and wing manholes is resolved. Both of offset axis loadings and its influences on the stress concentration coefficient of the hole-edge are discussed. And comparisons of different loads along various offset axis on the hole-edge stress distribution of orthotropic plate with rectangle hole or wing manhole are made. It can be concluded that hole-edge with continuous variable curvatures might help to decrease the stress concentration coefficient; and smaller angle of outer load and fiber can decrease the stress peak value.     

Fifth International Summer School on Screw-Theory Based Methods in Robotics

正3-11 September,2014University of Bologna,Bologna,Italy www.summerscrews.org summerscrews2014.ing.unibo.it SUMMER 20SCREWS 14In 2014,our screw-theory school comes to the world's oldest university.In early September,Summer Screws'14 will gather six experts in the application of screw theory in robotics and up to 40 participants at the University of Bologna,Bologna,Italy.The school will teach attendees how to apply existing methods and empower them to develop new ones in their own research.The basic theoretical notions will be introduced in a rigorous manner,emphasizing examples,applications,and exercises.Scholarships are available.     

电站锅炉模糊风险评价方法研究与应用

针对电站锅炉风险等级评价问题,将模糊综合评价技术应用到电站锅炉风险等级评价中。开展了电站锅炉失效影响因素及模糊评价因素的重要程度分析,建立了一套科学合理适于在线评价的电站锅炉风险评价体系,提出了模糊综合评价技术与改进的模糊层次分析法相结合的模糊风险评价方法,利用改进的模糊层次分析法计算了指标体系中各层指标权重。对某一台电站锅炉的实际运行工况影响子因素进行了模糊风险评价,采用模糊合成算子进行模糊综合运算得到电了站锅炉运行工况影响子因素的评价向量。研究结果表明:电站锅炉的运行工况影响子因素的风险评价等级为第6级,失效可能性等级为小,该电站锅炉运行工况良好。     

INDUSTRIAL ENGINEERING AND VISUALISATION-A PRODUCT DEVELOPMENT PERSPECTIVE

Taking the actual project of teaching and researching process for example, the relationship between the industrial engineering and product development is discussed. And use the novel visualization technology to support the industrial engineering and product development. How to use the new computer modeling and simulating technologies to support the product development and industrial engineering, is introduced especially. The support includes both domestic products and industrial systems. The visualization and computer technologies take a very important role in some system or multi-direction modeling, those technologies mentioned above can help the industrial engineers study the effect of design on the whole life circle, including the producing steps. So the engineers can avoid making the wrong decision which may cause bad effects on the whole industrial engineering.     

Non-monotonic material contrast in scanning ion and scanning electron images

30 keV Ga⁺ focused ion beam induced secondary electron (iSE) imaging was used to determine the relative contrast between several materials. The iSE signal compared from C, Si, Al, Ti, Cr, Ni, Cu, Mo, Ag, and W metal layers does not decrease with an increase in target atomic number Z₂, and shows a non-monotonic relationship between contrast and Z₂. The non-monotonic relationship is attributed to periodic fluctuations of the stopping power and sputter yield inherent to the ion–solid interactions. In addition, material contrast from electron-induced secondary electron (eSE) and backscattered electron (BSE) images using scanning electron microscopy (SEM) also shows non-monotonic contrast as a function of Z₂, following the periodic behavior of the stopping power for electron–solid interactions. A comparison of the iSE and eSE results shows similar relative contrast between the metal layers, and not complementary contrast as conventionally understood. These similarities in the contrast behavior can be attributed to similarities in the periodic and non-monotonic function defined by incident particle–solid interaction theory.