Lamb波在复合材料板中传播的谱有限元建模和仿真

基于谱有限元对Lamb波在复合材料层合板中的传播进行了模拟。结合Gabor小波分析对谱有限元及传统有限元模拟结果与理论结果进行了对比, 并对相控阵法结构探伤的扫描过程进行了模拟和分析, 给出了Lamb波的传播和扫描图像。结果表明, 在得到更精确模拟结果的同时, 谱有限元较传统有限元法能大大缩短计算时间, 证实了该方法在模拟Lamb波在复合材料板中的传播方面的优越性。同时, 谱有限元法能很好地模拟相控阵法探伤的扫描过程, 模拟结果与实际结果吻合, 证实了本文建模方法的可行性和精确性。      

分子动力学方法的模拟参数对结果的影响

主要研究了利用分子动力学方法(MD)模拟等离子体与材料表面相互作用过程时分子动力学方法的参数对模拟结果的影响.详细分析了Berendsen热浴的应用时间、耦合强度和模拟时间量(单个轨迹的作用时间、弛豫时间)对模拟结果的影响,结果表明,热浴的应用时间对模拟结果的影响很大,而其它参数对模拟结果没有太大的影响.     

靶雷目标尺度和亮点模拟效果分析

新型靶雷具有目标尺度和亮点模拟功能.本文首先简要介绍了靶雷的声学模拟特征,阐述了目标尺度和亮点模拟效果检测方法.采用多波束测量模拟目标的覆盖扇面角,通过计算获得目标的模拟尺度和回波亮点强度.提供了湖上部分测试结果,并对结果进行了分析.结果表明该型靶雷目标模拟效果逼真,模拟方法可行,检测手段合理.     

靶雷目标尺度和亮点模拟效果分析

新型靶雷具有目标尺度和亮点模拟功能.本文首先简要介绍了靶雷的声学模拟特征,阐述了目标尺度和亮点模拟效果检测方法.采用多波束测量模拟目标的覆盖扇面角,通过计算获得目标的模拟尺度和回波亮点强度.提供了湖上部分测试结果,并对结果进行了分析.结果表明该型靶雷目标模拟效果逼真,模拟方法可行,检测手段合理.     

金属板材成形的静力隐式有限元分析与程序设计

阐述了用于板材成形过程静力隐式数值模拟的弹塑性大变形有限元方法,基于给出的方法编制了板材成形过程数值模拟软件,并对矩形板的液压胀形进行了有限元分析,计算结果与典型的实验结果吻合很好.对球形模具拉伸成形过程进行了数值模拟,给出了计算结果.     

单粒子效应激光模拟试验技术研究

介绍了一种新的单粒子效应模拟试验技术——脉冲激光模拟试验方法。对脉冲激光束进行单粒子效应试验研究的基本机理进行了分析讨论。总结分析了电子器件及集成电路单粒子效应激光模拟试验研究结果,给出了单粒子效应脉冲激光模拟试验的一般评估方法,并对采用脉冲激光模拟单粒子翻转试验获得的试验数据与重离子试验数据的等效性进行了比对分析。结果表明,激光模拟试验得出的LET阈值大小与重离子试验结果基本一致。     

某种钛合金精密成形铸件铸造变形的数值模拟

目的 基于ProCAST,建立钛合金铸件铸造变形的模拟预测方法。方法 以某板状钛合金铸件为例,模拟了充型凝固、型壳内冷却和脱壳后冷却3个过程,并分别对各过程进行了相应假设和参数设置。为验证模拟结果,根据模拟模型设计了浇注验证实验。结果 铸件中间部位向外侧凸起,加强筋部位向内侧凹陷,和实验结果基本一致,变形量预测吻合度在60%~72%之间。结论 通过合理设置模拟流程和材料参数模型,数值模拟可以预测钛合金铸件的变形规律,并为变形量预测提供重要参考。     

基于 COMSOL 的包装食品微波炉加热模拟

目的研究使用COMSOL Multiphysics模拟微波炉加热包装食品的可行性。方法应用有限元分析软件COMSOL Multiphysics建立了食品介电性能随时间变化的电磁-热传导双向耦合模型,考虑加热过程中的表面热对流,模拟微波炉加热包装食品的过程,并与实验结果进行比较。结果食品内外温度分布的实验结果和模拟结果总体上接近,7个特征点的模拟结果和实验结果接近,特征点最终温度的实验结果与模拟结果均方根误差为1.75℃。结论使用COMSOL Multiphysics来进行微波炉加热包装食品的模拟是可行的。     

动态环境下工作分析定性模拟方法研究

传统工作分析方法的工作环境静态假设与企业实际面临的动态环境现实相违背,使得其工作分析结果缺乏动态适应性,可以采用定性模拟的方法对原有的分析结果进行修正.首先设计了工作分析的定性因果关系模型、变量知识的定性表述方法、状态变量转换规则及模拟步骤;为防止模拟组合爆炸,设计了基于管理常识的过滤器;最后给出了企业管理岗位职能变化过程的模拟应用实例,模拟结果符合企业管理相关理论.     

两种正交多项式模拟湍流波前的比较

针对Zemike多项式仅在连续单位圆上正交,用于在离散点上构造光学波前必然会引起误差的问题,本文提出用能够在离散点上正交的多项式来模拟经过大气湍流的光学波前.该方法根据湍流的统计理论,采用Gram-Schmidt正交化方法,构造了Malacara多项式表示的湍流波前,并进行了数值模拟.将模拟结果与直接用Zemike多项式模拟的结果进行了比较分析,结果表明:在相同的条件下,该方法的模拟结果更接近统计理论值.     

Synthesis-microstructure-mechanical properties-wear and corrosion behavior of an Al-Si (12%)—Flyash metal matrix composite

In the present investigation, Aluminium based metal matrix composite containing up to 15% weight percentage of flyash particulates were successfully synthesized using vortex method. The properties like density, hardness, microhardness, ductility and ultimate tensile strength were investigated. The MMC produced was also subjected to corrosion, dry sliding wear and slurry erosive wear test to investigate its behavior under different material wearing conditions. The results of microhardness revealed higher hardness of the matrix material in the immediate vicinity of flyash particle. The addition of flyash particles reduces the density of composite while increasing some of their mechanical properties. The results of wear studies have shown that the resistance to wear increases with increase in percentage of flyash. Corrosion resistance decreases with increase in flyash content. The macrostructural and microstructural characteristics of the MMC were investigated with particular emphasis on the distribution of flyash particles in the matrix. Macrostructural studies have shown near uniform distribution of flyash particles in matrix. Analysis of fractured surface of tensile test specimen is also made which revealed brittle fracture behavior of MMCs.     

浮空器用柔性复合材料的力学性能

通过试验研究了某浮空器蒙皮用柔性复合材料的基本力学性能和断裂力学性能。通过单轴拉伸试验研究了该材料经向和纬向试样的力学特性,结果发现两者的弹性模量均在10GPa左右,复合材料的柔软度很高;而经向拉伸试样的抗拉强度比纬向拉伸试样的高出约32％;通过改变切口相对宽度的撕裂试验发现撕裂试验的载荷一位移曲线和裂纹扩展特性基本表现为脆性断裂特性,试验结果和根据弹塑性断裂理论计算得到的结果相一致,即随着切口相对宽度的增加,柔性复合材料的极限载荷降低。     

Effect of local volume fraction of microporosity on tensile properties in Al–Si–Mg cast alloy

Abstract

Porosity in Al–Si–Mg cast alloys utilised in automotive parts affects directly products quality, i.e. mechanical properties. In this study, the effect of micropores on mechanical properties has been investigated by X-ray tomography from the viewpoint of clustering micropores. The local volume fraction (LVF) of porosity was introduced to analyse the effect of clustering micropores. The statistical Weibull method was also used in order to explain strength of the alloy tested. The fracture strain decreased drastically from 17 to 3% on an inverse parabolic relationship with increasing porosity. In the case of the specimens that contain the largest pore higher than 100 m m, the ultimate tensile strength decreases monotonically. It is found that the fracture surface passes through high LVF regions. The fracture strain obviously depends on the ratio of LVF higher than 10%. It is confirmed that the LVF, which represents unevenly distribution of micropores cluster, is one of important dominant factor for managing the mechanical properties in the Al–Si–Mg cast alloy.     

Investigation on the mechanical properties and fracture toughness of graphite

In the present study, mechanical properties and fracture toughness of graphite as a brittle material were investigated. At first, some specimens were examined in two perpendicular directions to derive Young's modulus and ultimate tensile strength. Then, graphite fracture toughness tests were conducted using some three‐point bending specimens with a sharp machined V‐notch by two different methods. The first method is based on the applied force at the moment of fracture, and the second one uses energy released during the test. Moreover, a technique was adopted to reduce differences between the two methods. It was observed that considering the effect of dehydration of the specimens, the fracture toughness was reduced by about 8%. Finally, crack growth simulation of the experiment was performed and indicated that finite element analysis predicts about 25% lower crack length values when critical energy release rate is utilized as a crack growth criterion instead of fracture toughness. In other words, the required input displacement for crack growth would be overestimated by using the critical energy release rate criterion.     

The structure and tensile properties of Al-Si alloy hybrid reinforced with alumina-aluminosilicate short fibre

Alumina-aluminosilicate fibre hybrid reinforced aluminium-silicon alloy was fabricated by pressure infiltration route. Tensile test results at room temperature and at 300°C are reported. It is shown that the alumina-aluminosilicate fibre ratio does have a strong influence on the ultimate tensile strength (UTS) of these hybrid composites. At an alumina-aluminosilicate ratio of 32, the optimum UTS of hybrid metal matrix composites (MMC) was obtained. The UTS of only alumina fibre reinforced MMC was improved with increasing fibre volume fraction at 300°C. No fibre put-out was observed on the fracture surface and longitudinal section.     

A computational and experimental method for estimating degradation of mechanical characteristics of steels under the conditions of high-temperature pyrolysis

The possibility of using computational and experimental methods of strain and fracture mechanics for describing degradation of mechanical properties of steels under conditions of pyrolysis is demonstrated. Experimental and theoretical temperature dependences of the ultimate strength of 10Kh23N18 steel which are characterized by a high degree of correlation are obtained. It is revealed that it is necessary to use correlation coefficients in the equations for calculating the ultimate strength depending on the service time to increase the accuracy of forecasting variations in the mechanical characteristics of steel under operating conditions.     

某稠油井Ф88．9mm×6．45mm110EU油管挤毁原因分析

对某井在稠油开采、反注稀油过程中发生的油管挤毁和断裂事故进行了调查研究。对挤毁油管和同批新油管取样进行材质分析、尺寸测量和挤毁试验,认为油管材质和尺寸均符合标准要求。对挤毁油管外表面形状检查结果表明,油管挤毁之前没有机械损伤,油管挤毁与机械损伤无关。通过推理分析,认为油管首先发生挤毁,然后才发生断裂。通过力学分析和计算,认为油管挤毁和断裂的原因是其所受的外力超过了油管的屈服强度。     

预测低合金钢试样破坏的弹塑性断裂模型

该文建立了预测低合金钢结构断裂破坏的弹塑性断裂理论与模型。将两个独立判据——强度及韧度准则联系起来,搭起结构特性与材料参数间的纽带桥梁:可由处于弹塑性断裂控制的小尺寸低合金钢试样的结构特性确定其材料参数;基于确定的材料参数,可建立起预测低合金钢结构破坏的全过程曲线。该文进行了多组相同尺寸而不同裂缝长度的Q345B钢的单边拉伸试验,基于所提模型及试验结果,确定出无尺寸效应的断裂韧度、屈服与极限强度等材料参数;进而构建了可涵盖所有试验点的Q345B钢的安全设计曲线（±10%界限）。研究成果可为确定金属材料参数及预测金属结构破坏提供新思路。     

均匀化处理对Mg-13Gd-3.5Y-2Zn-0.5Zr镁合金组织和力学性能的影响

对Mg-13Gd-3.5Y-2Zn-0.5Zr镁合金铸锭进行均匀化处理,温度为505～525℃,时间为4～24h,并采用光学显微镜(OM)、扫描电子显微镜(SEM)、X射线衍射仪(XRD)和万能材料试验机等检测手段分析均匀化处理前后合金微观组织和力学性能的变化。结果表明:均匀化处理后,原始组织中网状分布共晶化合物转化成晶界处不连续分布的块状LPSO相,离散分布的方块状富稀土相溶解。力学性能测试显示,铸态镁合金的抗拉强度为172.9MPa,伸长率为1.8%,经过均匀化处理后合金的力学性能得到提高,在515℃/16h均匀化制度下,合金室温抗拉强度为212.3MPa,伸长率为3.1%;在200℃下抗拉强度为237.2MPa,伸长率为9.7%,性能达到最佳。断口扫描显示,铸态合金是以撕裂棱与解理台阶为主的解理脆性断裂,均匀化处理后的合金中出现小而浅的韧窝,但仍然是以解理台阶为主的准解理断裂,塑性提高有限,长程有序相可成为裂纹的萌生源。     

某壳体断裂原因分析

目的分析某产品壳体在靶场试验中出现断裂疵病的原因,并提出预防和改进措施。方法通过对断口进行宏微观观察、金相组织检查和化学成分分析检测、力学性能试验、验证试验及强度计算等,初步确定了壳体断裂性质和原因。结果对改进结构的壳体进行了结构强度的验证试验,经对射击试验后回收的壳体进行拆分检测,原发生断裂现象的位置无破坏、裂纹现象,变形量满足产品图定要求,改进结构的壳体结构强度满足要求。结论通过验证试验再次确定了断裂原因:壳体密封圈槽处壁厚差超差;壳体材质C元素含量偏高,材料的脆性较大;断口处材料偏析严重;结构设计强度裕度不足。根据壳体断裂原因,提出了相应的预防措施。