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应用ANSYS软件对低活化马氏体/铁素体钢(RAFMs)中厚板多道焊接过程进行三维有限元模拟,将得到的温度场和应力场分别与实验对比,对焊缝区和热影响区宽度进行预测,并通过焊接实验进行验证,同时对焊后的试件进行了金相分析和硬度测试。结果表明：温度场和应力场模拟结果和实测结果基本一致,焊缝区以及热影响区宽度的模拟结果和实测结果基本吻合;采用316L焊丝填充的焊缝,焊缝与母材熔合较好,焊缝没有明显缺陷;硬度检测呈现：焊缝的硬度大大高于热影响区和母材。     

考虑磁通流动效应的超导薄膜基底结构界面断裂行为研究北大核心CSCD

超导薄膜是一种采用化学涂层制备而成的多层薄膜结构,作为性能优越的导电功能结构材料,其载流能力与结构完整性直接相关.在超导薄膜制备过程中,超导层与金属基底之间的界面裂纹很难避免.因此,在载流运行过程中,由于外磁场的存在,这类界面裂纹的强度问题成为关键.为此,该文针对超导薄膜结构,以磁通量子穿透薄膜理论和线弹性断裂理论为基础,建立了研究超导层与基底界面裂纹强度问题的解析模型.深入分析了外加磁场作用下界面裂纹强度问题,得到了超导磁通流动对裂纹尖端应力场和能量释放率的影响.结果表明:磁通流动速度越大,界面裂纹尖端处应力越大且能量释放率越大,这将导致界面更容易发生裂纹破坏.该文所得结果有助于分析相关的界面裂纹问题.     

正交异性双材料反平面界面端应力场分析

研究了正交异性双材料反平面平板搭接界面端问题,采用复合材料断裂复变方法,构造了特殊应力函数,通过求解一类广义重调和方程组的边值问题,推导出平板搭接界面端的应力场、位移场及应力强度因子的表达式,结果显示:反平面搭接界面端只有一个奇异性,上下材料常数比Γ＞0时,应力场具有幂次奇异性,且随着Γ增长,奇异指数趋于-1/2,并利用有限元算例分析验证了理论结果的正确性.     

Elastic-viscoplastic fields near the tip of a propagating crack under anti-plane shear

The elastic-viscoplastic model proposed by Bingham was used to analyse the stress and strain surrounding the tip of a propagating crack under antiplane shear. The proper displacement pattern was given ; the asymptotic equations were derived and solved numerically. The analysis and calculation show that for smaller viscosity the crack-tip possesses logarthmic singularity, and for larger viscosity it possesses power-law singularity.In critical case, the two kinds of singularity are consistent with each other. The result revealed the important role of viscosity for crack-tip field.     

三维弹塑性结构下限分析的边界元方法

基于极限分析的下限定理,建立了用常规边界元方法进行三维理想弹塑性结构极限分析的求解算法.下限分析所需的弹性应力场可直接由边界元方法求得.所需的自平衡应力场由一组带有待定系数的自平衡应力场基矢量的线性组合进行模拟,这些自平衡应力场基矢量由边界元弹塑性迭代计算得到.下限分析问题最终被归结为一系列未知变量较少的非线性数学规划子问题并通过复合形法进行求解.给出的计算结果表明该算法有较高的精度和计算效率.     

Stress field at a tip of a prefabricated spiral V-notch

Based on the tranditional V-notched blasting, a technique of spirally V-notched blasting to loosen earth and rock was presented. Fracture mechanics and Westergaard stress function were adopted to build a complex stress function to derive the plane stress and strain fields at one tip of the crack under a quasi-static pressure. An expression was formulated to define the stress intensity factor of spiral V-notch loosen blasting. Factors that have effects on the stress intensity factor were studied. It is demonstrated that spiral V-notch loosen blasting is an extension of vertical V-notch blasting, straight cracking, and alike theories.     

功能梯度材料裂纹尖端动态应力场

研究受反平面剪切作用的功能梯度材料动态裂纹问题,通过积分变换-对偶积分方程方法推出了裂纹尖端动态应力场,时间域内的动态应力强度因子由Laplace数值反演获得,研究结果表明功能梯度材料的梯度越大,相应的裂纹问题的动态应力强度因子值越低。     

力学边界对透射型光学元件激光破坏阈值的影响

 建立了激光与透射型光学元件相互作用的热弹性力学模型,解析求解了自由、固定以及一种人为边界条件下光学元件热-力学响应的定解问题。研究发现,不同的边界条件对破坏阈值有很大的影响。针对光学元件中热应力的演变情形,设计了一种“最佳”边界,消除了激光作用过程中产生的拉应力,从而使破坏阈值在理论上达到最大值。     

正交各向异性功能梯度材料反平面裂纹尖端应力场

采用积分变换-对偶积分方程方法,研究了正交各向异性功能梯度材料反平面裂纹问题,文中假定材料沿两个主轴方向的剪切模量成比例按双参数梯度模型变化,通过求解对偶积分程并考虑变形Bessel函数的渐特性,推导出了裂纹尖端应力场,最后考察了材料非均匀性及正交性对应力强度因子的影响。     

Review of mass-flow hopper design with respect to stress fields and surcharge loads

Current procedures for mass-flow hopper design are based on the radial stress theory developed byJenike and involve the determination of the critical outlet dimensions for flow to be initiated. These procedures ignore the surcharge loads on the hopper and involve a study of the passive or arched stress field that exists under flow conditions. An alternative approach as applied to hopper wall load analysis is to employ the horizontal slice method. The arched stress field and horizontal slice methods of analysis are compared. The influence of surcharge loads in the determination of hopper geometry is investigated.