自紧身管疲劳寿命的可靠性分析

基于概率断裂力学理论和Monte Carlo模拟方法，给出了自紧身管疲劳寿命的可靠性分析方法．自紧残余应力采用了符合身管材料具有强化和包辛格效应性能推导的公式计算，身管工作的应力强度因子通过权函数方法得到．实例分析结果表明，对数正态分布为身管疲劳寿命的最佳分布，同时给出了各种置信度和可靠度下的身管疲劳寿命．另外，还分析了初始裂纹尺寸和材料的断裂韧性对身管疲劳寿命的影响．该研究对保证身管的安全，避免灾难性事故的发生具有重要意义．     

Local fracture resistance based on microstructural efficiency concept and simulation of injection molding

Local fracture resistance (FR) of short (SGF) and discontinuous long glass fibre (LGF) reinforced polypropylene (PP) was predicted using the ‘microstructural efficiency concept’ together with a simulation program for fibre orientation in injection molding. The ‘microstructural efficiency concept’ describes the relation between microstructural parameters such as the fibre content, the fibre aspect ratio and the processing (injection molding) induced layer structure taking also into account the local fibre orientation. The local fibre orientation in injection molding was predicted with the MOLDFLOW^®-software. The predicted local FR was compared with the measured one, which was determined by using compact tension samples and linear elastic fracture mechanics (LEFM). The comparison showed, that for SGF-PP good consistence between the predicted and measured FR existed, for LGF-PP the discrepancy was higher. Yet for both materials, the ‘microstructural efficiency concept’ together with the results obtained from the simulation of the fibre orientation can be used for FR prediction of an injection molded workpiece.     

On Cavitation, Configurational Forces and Implications for Fracture in a Nonlinearly Elastic Material

Experiments on polymers indicate that large tensile stress can induce cavitation, that is, the appearance of voids that were not previously evident in the material. This phenomenon can be viewed as either the growth of pre-existing infinitesimal holes in the material or, alternatively, as the spontaneous creation of new holes in an initially perfect body. In this paper our approach is to adopt both views concurrently within the framework of the variational theory of nonlinear elasticity. We model an elastomer on a macroscale as a void-free material and, on a microscale, as a material containing certain defects that are the only points at which hole formation can occur. Mathematically, this is accomplished by the use of deformations whose point singularities are constrained. One consequence of this viewpoint is that cavitation may then take place at a point that is not energetically optimal. We show that this disparity will generate configurational forces, a type of force identified previously in dislocations in crystals, in phase transitions in solids, in solidification, and in fracture mechanics. As an application of this approach we study the energetically optimal point for a solitary hole to form in a homogeneous and isotropic elastic ball subject to radial boundary displacements. We show, in particular, that the center of the ball is the unique optimal point. Finally, we speculate that the configurational force generated by cavitation at a non-optimal material point may be sufficient to result in the onset of fracture. The analysis utilizes the energy-momentum tensor, the asymptotics of an equilibrium solution with an isolated singularity, and the linear theory of elasticity at the stressed configuration that the body occupies immediately prior to cavitation. This revised version was published online in June 2006 with corrections to the Cover Date.     

Nonlinear phase field theory for fracture and twinning with analysis of simple shear

A phase field theory for coupled twinning and fracture in single crystal domains is developed. Distinct order parameters denote twinned and fractured domains, finite strains are addressed and elastic nonlinearity is included via a neo-Hookean strain energy potential. The governing equations and boundary conditions are derived; an incremental energy minimization approach is advocated for prediction of equilibrium microstructural morphologies under quasi-static loading protocols. Aspects of the theory are analysed in detail for a material element undergoing simple shear deformation. Exact analytical and/or one-dimensional numerical solutions are obtained in dimensionless form for stress states, stability criteria and order parameter profiles at localized fractures or twinning zones. For sufficient applied strain, the relative likelihood of localized twinning vs. localized fracture is found to depend only on the ratio of twin boundary surface energy to fracture surface energy. Predicted criteria for shear stress-driven fracture or twinning are often found to be in closer agreement with test data for several types of real crystals than those based on the concept of theoretical strength.     

高速通道压裂裂缝的高导流能力分析及其影响因素研究

高速通道压裂是近年在非常规致密油气资源开采中出现的新工艺, 已在世界范围内推广实施, 并取得了良好的增产效果. 该技术可使支撑剂在人工压裂缝中形成簇团式分布, 从而形成油气高速流动通道, 提高裂缝的导流能力. 但目前对于高速通道压裂裂缝高导流能力的形成机理及其影响因素尚不清楚. 对此, 本文从流体力学理论出发, 首先将高速通道压裂裂缝内形成的支撑剂簇团视为渗流区域, 簇团间的大通道视为自由流动区域; 然后基于Darcy-Brinkman方程建立了裂缝内的流动数学模型, 采用均匀化理论对该流动数学模型进行了尺度升级, 推导得到了高速通道压裂裂缝的渗透率, 揭示了其高导流能力的形成机理; 并以此为基础, 分析了不同支撑剂簇团形状、大小以及分布方式等因素对其导流能力的影响, 可为高速通道压裂工艺参数设计与优化提供基础.     

各向异性复合材料尖劈和接头的奇性应力指数研究

提出了一个新的、基于位移的、求解三维尖劈端部奇性应力指数问题的非协调元特征分析法。该方法假定尖劈端部邻域内的位移场没有采用奇异变换技术，导出虚功方程的出发点不同于过去原有求解裂纹尖端近似场的有限元特征分析法，在有限元离散时采用的单元形式为非协调元。文中运用该方法给出了若干求解各向异性复合材料尖劈／接头端部奇性应力指数的算例。所有的计算结果表明，本文方法能够求解复杂尖劈／接头的全部奇性应力指数，使用的单元少而且精度高。     

一维快速拉伸下无氧铜的动态断裂与破碎

利用电磁膨胀环技术对无氧铜环进行了不同加载电压下的动态拉伸实验。对无氧铜在破碎前出现塑性失稳多重颈缩进行了初步分析,利用能量平衡的破碎理论给出了无氧铜环的破碎分布。三维数值模拟结果表明,颈缩区温升比非颈缩区高,且多重颈缩在环周上的分布服从泊松分布。     

氧化锆陶瓷的摩擦磨损行为与机理

氧化锆陶瓷的工程应用前景广阔，在许多场合都必须与水或水溶液接触，但有关这种陶恣在水中的摩擦磨损行为和机理的研究报道不多见，而且已有的工作也不够深入。因此，对氧化锆陶瓷分别在水润滑和干摩擦下的摩擦学特性及其磨损机理进行了考察。     

拱形试件动态断裂的动光弹分析

本文采用动光弹方法,分析了对带边裂纹的拱形三点弯曲试件在抢击加载条件下的瞬态反应。从多火花动光弹仪记录下来的16幅断裂过程的照片和微机输出的电火花光信号图上,得到了各时刻的等差线图形和裂纹长度。使用运动裂纹尖端附近的应力场解,去计算动应力强度因子。对环氧树脂材料,测定了动态应力强度因子与裂纹扩展速度之间的关系,并给出了当裂纹扩展速度达到410m/s时,为裂纹产生分叉的条件。     

表面裂纹准静态扩展的有限元模拟计算

由于现有断裂准则未能考虑表面裂纹前沿各点实际断裂阻力的变化，所作的表面裂纹准静态扩展模拟计算不能很好地预测几何形貌的真实变化规律。本文提出了一个考虑应力状态不同对实际断裂阻力影响的变阻力断裂准则；并以该准则作为表面裂纹前沿局部断裂扩展的判据，通过三维有限元法进行了表面裂纹准静态扩展的模拟计算；还将模拟预测值与用多试件法测得的实验值进行比较，验证了变阻力断裂准则作为裂纹稳态扩展判据的有效性