A study of directionality of latent hardening behavior in aluminium single crystals

By defining the yield stress in a latent hardening test as the first deviation from the elastic straight line, the yielding and hardening behavior on a latent system in the positive and negative slip direction was studied in aluminium single crystals. It is shown that the yield stresses on both the positive and negative latent systems are about equal to or a little lower than the maximum resolved shear stress in the primary test, but much higher than that of the active system. The influence of relative orientation and prestrain on latent hardening and initial work-hardening in the secondary test was also investigated, and it was found that there is a considerable effect on initial work-hardening, but none on latent hardening. With reasonable approximation, a hardening rule for single crystal could be proposed from the experimental results, that is, except for the yield stress on the system negative to the active system that is very low, hardening on the other systems is nearly the same as self-hardening.     

铝单晶体潜在硬化的指向性行为研究

应用高纯铝单晶体，采用偏离弹性线法定义其在潜在滑移系统在屈服应力，研究了潜在滑移系在正负两个滑移方向上的屈服及应变硬化行为。结果表明，潜在滑移系负行为的差异要远远小于动滑移系的Ｂａｕｓｃｈｉｎｇｅｒ效应，其正负方向的屈服应力一般均等于或略小于预应变时的最大分切应力，大大高于动滑移系的负向屈服应力，潜在滑移系和原始滑移系的相对取向及预应变的大小对单晶体潜在移系在潜在硬化的影响不大，但对其起始过渡区应     

A general theory of thermoporoelastoplasticity for saturated porous materials

A general theory of thermoporoelastoplasticity for saturated porous materials is presented. The theory is derived from the thermodynamics of open systems and irreversible processes. The thermal effects, due to the saturating fluid, are taken into account through a latent heat associated with the increase of fluid mass content. The theory does not assume incompressibility nor infinitesimal displacements for the saturating fluid. To take into account the plastic compressibility of the skeleton, the notion of plastic porosity is introduced. This plastic porosity is different from the overall plastic dilatation. The usual isothermal phenomenological theories appear to be particular cases of the proposed general theory.     

Energy consumption for creep fracture of metallic materials

The energy conservation law is applied to formulate the ductile and brittle creep fracture criterion for metallic materials. The criterion contains a summary of heat and latent energies. Assuming that the heat energy is given out so it has no effect on the fracture process, the ductile creep fracture criterion is simplified. To take into account the evaluation of the damage state of materials the compressibility condition is introduced and the brittle creep fracture law is formulated.     

结构模态分析的有限元并行模拟

以子结构模态综合分析为基础,提出一种求解大型结构特征值问题的并行解法．采用子结构模态综合算法,结构特征模态采用子空间迭代方式并行求解．这种子空间迭代法的子结构并行计算的实施是利用子结构的刚度阵和质量阵而不必完全组集系统刚度阵和质量阵求解综合系统的特征值问题．数值结果表明这种求解大型结构特征值问题的并行算法是可行有效的．     

结构动力修改的一种方法

本文提出一种修改后的结构的振动特性计算方法;此法利用测量频率响应函数矩阵,将结构的修改量作为作用在结构上的力处理,分析计算出修改后结构的频率响应函数矩阵。其优点是理论简单、计算量小、便于直接指导实际结构修改。     

有阻尼振动系统的自由界面子结构综合法

研究了阻尼振动系统的自由界面子结构综合法.为了在最终给出的系统综合方程中考虑剩余柔度矩阵的影响,本文利用质量矩阵、阻尼矩阵和结构保留模态矩阵构造了一种与保留模态矩阵加权正交的矩阵.在计算自由-自由结构的剩余柔度矩阵时,通过这种加权正交矩阵能够避免直接对子结构刚度矩阵的求逆运算.在此基础上提出了一种新的有阻尼振动系统的自由界面子结构综合法.算例分析表明,本文的方法具有很高的计算精度.     

槽型宽翼受压构件剪力滞分析的传递矩阵法

利用能量变分法,建立了槽型宽翼受压构件考虑剪力滞效应时的平衡控制微分方程,给 出了该方程在轴向均布载荷作用下的初参数解,导出了求解槽型宽翼受压构件内力、应力和 位移的场矩阵和点矩阵,提出一种研究槽型宽翼受压构件剪滞效应的传递矩阵法. 数值算例 表明,该方法计算便捷、精度好、具有较高的工程应用价值.     

基于改进残余力向量法的桁架结构损伤诊断

提出一种基于改进残余力向量法的桁架结构损伤诊断方法. 先由灵敏度分析, 求出结构刚度联系矩阵,再由刚度联系矩阵将损伤后的刚度摄动矩阵展开成对角矩阵,代入 残余力向量方程,得到由刚度联系矩阵表示的新的残余力向量方程,此方程可以直接求解, 即可诊断出桁架结构的损伤杆件及其损伤程度. 对于实测中难以获得完备振型的情况,采用 模态扩阶的方法来获得完备的测试振型. 最后以一桁架结构进行数值仿真分析,证实了该方 法的有效性.     

Partial polar decomposition inverse method applied to determination of internal stresses in an elastic complex structure

An inverse method is developed to evaluate a distribution of internal-stress tractions on an internal surface of an elastic complex structure. The traction distribution is evaluated by measuring a remote displacement field generated when the surface of interest is sectioned. This formulation employs partial polar decomposition (PPD) of a rectangular matrix within the global finite element stiffness matrix for the process of inversion. A systematic regularization process is also provided for the PPD inverse method. This method avoids cumbersome rigid body displacement control required in the formalism of compliance matrix inversion. The method is robust in measuring residual stresses in an elastic complex structure, in particular, multiply connected regions. The inversion method has been tested experimentally by using electronic speckle pattern interferometry (ESPI) with a specimen of multiply connected regions. Experimental results show that the regularized solution using partial polar decomposition converges quickly with a small number of series terms.     

二维编织陶瓷基复合材料应力-应变行为

对二维编织陶瓷基复合材料拉伸应力-应变行为进行了试验研究和理论模拟. 将二维 编织结构简化为：正交铺层结构和纤维束波动结构. 基于基体随机开裂、纤维随机断裂分布 理论,得到正交铺层结构的应力-应变关系;基于体积平均方法,将纤维束波动部分进行分割, 引入强度分析模型,得到纤维束波动部分的应力-应变关系. 结合正交铺层部分和纤维束波动 部分的应力-应变关系,得到二维编织结构的应力-应变行为,理论与试验吻合较好.     

Adaptive force density method for form-finding problem of tensegrity structures

A numerical method is presented for form-finding of tensegrity structures. Eigenvalue analysis and spectral decomposition are carried out iteratively to find the feasible set of force densities that satisfies the requirement on rank deficiency of the equilibrium matrix with respect to the nodal coordinates. The equilibrium matrix is shown to correspond to the geometrical stiffness matrix in the conventional finite element formulation. A unique and non-degenerate configuration of the structure can then be obtained by specifying an independent set of nodal coordinates. A simple explanation is given for the required rank deficiency of the equilibrium matrix that leads to a non-degenerate structure. Several numerical examples are presented to illustrate the robustness as well as the strong ability of searching new configurations of the proposed method.     

结构杆件撤除后简化分析一般方法

本文提出结构杆件撤除后简化分析的一般方法,视杆件撤除后新结构的解为原结构的解与原结构上加以关联荷载解的叠加,利用原结构的解及总体刚度矩阵的逆矩陈求解新结构,无需进行结构重分析,使计算量大大减小,文中基于有限元法导出求关联荷载的一般算式。该法适用于空间网格结构和刚架结构一根杆件撤除问题,也适用于多根杆件同时撤除问题。     

曲线桥分析的精细传递矩阵法

将精细积分与传递矩阵法相结合,提出一种新的精细传递矩阵格式,应用于曲线桥的分析中。与传统的传递矩阵法相比,无需对微分方程组进行求解,只需迭代即可得到所需要的传递矩阵。根据边界条件,得到结构的内力及变形。算例表明,该方法正确有效。     

热环境中旋转运动功能梯度圆板的强非线性固有振动

研究热环境中旋转运动功能梯度圆板的非线性固有振动问题．针对金属－陶瓷功能梯度圆板,考虑几何非线性、材料物理属性参数随温度变化以及材料组分沿厚度方向按幂律分布的情况,应用哈密顿原理推得热环境中旋转运动功能梯度圆板的非线性振动微分方程．考虑周边夹支边界条件,利用伽辽金法得到了横向非线性固有振动方程,并确定了静载荷引起的静挠度．用改进的多尺度法求解强非线性方程,得出非线性固有频率表达式．通过算例,分析了旋转运动功能梯度圆板固有频率随转速、温度等参量的变化情况．结果表明,非线性固有频率随金属含量的增加而降低;随转速和圆板厚度的增大而升高;随功能梯度圆板表面温度的升高而降低．     

2D编织陶瓷基复合材料应力-应变行为的试验研究和模拟

本文对2D编织陶瓷基复合材料拉伸应力-应变行为进行了试验研究和理论模拟。将2D编织结构简化为：正交铺层结构和纤维束波动结构。基于基体随机开裂、纤维随机断裂的统计分布理论,得到正交铺层结构的应力-应变关系;基于体积平均方法,将纤维束波动部分分割为若干子单元;由于纤维束的波动使各子单元材料方向与加载方向不一致,因此考虑了各子单元的线性行为和非线性行为对材料响应的影响,同时引入强度分析模型,得到纤维束波动部分的应力-应变关系。结合正交铺层部分和纤维束波动部分的应力-应变关系,得到2D编织结构的应力-应变行为,理论与试验吻合较好。     

一维格子结构动力分析的传递矩阵法

本文将传递矩阵法推广应用于分析一维格子结构的波传播和动力响应特性。一个格子结构的元件可分为主元件和次元件,传递矩阵沿主元件形成并考虑次元件的作用。文中通过例子说明形成一个周期单元传递矩阵的方法,指出利用传递矩阵计算无限或半无限长格子结构波传播的传播常数及有限长格子结构固有频率和频率响应函数的方法。作为数例,文中计算了一维平面格子结构的传播常数和频率响应函数。     

大规模动力系统改进的快速精细积分方法

提出一种针对大规模动力系统的改进的快速精细积分方法（FPIM）。以精细积分方法为基础,利用大规模动力系统矩阵的稀疏性和动力问题的物理特性,分析了矩阵指数的特殊结构,并基于此给出一种计算大规模动力系统矩阵指数及其动力响应的高效率方法。     

用回传波射矩阵法分析框架的地震效应

结构在地震载荷作用下的瞬态响应分析对抗震设计很重要. 大部分地震效应 研究采用时程积分等数值方法. 回传波射矩阵法是桁架和框架结构瞬态响应的一种新的频域 矩阵分析法. 基于Bernulli梁理论的回传波射矩阵法扩展到地面加速度载荷的情形, 对一榀钢制框架在地面El Centro波加速度作用下的瞬态应力计算, 结果表明该方法 能准确有效地进行结构的地震效应分析.     

Fast precise integration method for hyperbolic heat conduction problems

A fast precise integration method is developed for the time integral of the hyperbolic heat conduction problem. The wave nature of heat transfer is used to analyze the structure of the matrix exponential, leading to the fact that the matrix exponential is sparse. The presented method employs the sparsity of the matrix exponential to improve the original precise integration method. The merits are that the proposed method is suit- able for large hyperbolic heat equations and inherits the accuracy of the original version and the good computational efficiency, which are verified by two numerical examples.