含曲线裂纹复合圆柱体的扭转断裂分析

研究含任意曲线裂纹的复合圆柱体的Saint-Venant扭转,将内外材料的交界面视为一边界,将问题划归为内、外边界和裂纹上的积分方程的求解.提出了新的边界元数值方法,分别对含有直线裂纹和曲折裂纹的典型问题进行了数值计算,并与文献中数据结果进行了比较,证明了该文方法的正确性和有效性.     

含内聚裂纹弹性体的能量释放率与断裂能

根据内聚裂纹模型,含裂纹的弹性体在裂纹尖端附近存在一内聚区,内聚区断裂参数表达是其核心研究内容.该文假定弹性平板直线裂纹尖端存在一带状内聚区,并由一条虚拟线裂纹代替,其张开位移与内聚力存在确定的非线性函数关系.以Ⅰ型边裂纹为例,导出了满足虚拟裂纹条件的解析解;在此基础上给出了物理裂纹尖端扩展的能量释放率G_a、内聚裂纹尖端扩展的能量释放率G_b的计算公式;讨论了G_b,J积分和断裂能G_F之间的关系;从理论上证明了临界能量释放率G_bc就是断裂能G_F,G_bc可以作为含内聚区材料裂纹失稳扩展的断裂参数.提出的方法适用于所有含Ⅰ、Ⅱ、Ⅲ型内聚裂纹的弹性体.     

复合材料桥纤维拔出问题的动态裂纹模型

在一无限的正交各向异性体的弹性平面上,对具有桥纤维平行自由表面的一个内部中央裂纹,进行了弹性分析．提出了复合材料桥纤维拔出的一个动态模型．由于纤维破坏是由最大拉应力支配,纤维断裂并且裂纹扩展将以自相似的方式出现．通过复变函数的方法将所讨论的问题转化为Reimann-Hilbert混合边界值问题的动态模型,呈现一简单的和容易的解．求得了正交异性体中扩展裂纹受运动的阶梯载荷、瞬时脉冲载荷作用下问题的解析解,并利用这一解,通过迭加最终求得该模型的解．     

关于复合材料单层板裂纹尖端的J积分

该文采用复变函数方法,通过将裂纹尖端的应力和位移代入J积分的一般公式,推出了线弹性正交异性复合材料单层板受对称载荷作用的非弹性主方向的裂纹尖端犑积分的复形式－ 复变函数积分的实部,证明了该J积分的路径无关性,得到了它的具体计算公式     

骨单位密质骨含单条曲线微裂纹模型

研究了骨单位附近密质骨间质骨含单条曲线微裂纹平面问题.该问题的求解可看成间质骨不含微裂纹和间质骨含微裂纹这两个基本问题的叠加.利用Kolosov-Muskhelishvili复势,得到了间质骨不含微裂纹问题的应力场;利用位错方法,得到了间质骨含微裂纹问题所满足的积分方程组.     

粘弹体中裂纹演化的细观力学分析

根据Eshelby等效夹杂理论研究含残币形裂纹的粘弹体中裂纹张开位移随时间的缓慢增大以及含裂纹粘弹性体的等效模量随时间的变化。对于Maxwell粘弹性材料给出了模量随时间变化的显式表达式,结果表明裂纹的缓慢张开使材料模量减小更快。     

含裂纹的圆柱体的弯曲

含裂纹的圆柱体弯曲的研究有十分重要的意义。文献[1]～[4]研究过含径向裂纹或裂纹系的情形,[5]研究过有同心圆弧裂纹的圆柱体的弯曲。本文继续[6]对内部出现在任意位置的直线裂纹的圆柱体在力与裂纹垂直时的弯曲问题,用弹性理论复变函数方法进行了讨论;得到了位移、应力和应力强度因子用级数表示的表达式;对Ah小的这种弯曲问题的应力强度因子给出了好的近似式,分析了它们随裂纹中心的变化规律。最后对裂纹的一个尖端在原点的径向裂纹圆柱体的扭转率和弯曲中心进行了计算,其结果与[1]几乎完全相同。     

关于一个含参量的Hilbert型积分不等式

通过估算权函数及引入Beta函数,建立一个含参量的、具有最佳常数因子的Hilbert型积分不等式.同时建立它的两种最佳推广式及相应的等价形式.     

关于分组化验模型的一个猜想

运用概率和微分学基本理论推导出分组化验法的适用范围,给出最佳分组的存在性证明,并提出最佳分组人数的一个猜想.     

On Micromechanical Damage Modelling Of Fibre Reinforced Composites

The numerical analysis of engineering structures is usually based upon the assumption of a homogeneous as well as a continuous medium. Macroscopic homogeneity is maintained also for heterogeneous, fibre reinforced composite structures by replacing the inhomogeneous medium through a model of a mathematically homogenized material. The constitutive behaviour is then described in terms of volume averaged quantities that smear the heterogeneities of the microscale. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

A Deformation Model for Dispersely Failing Elastoplastic Unidirectionally Reinforced Composites

A calculation model is proposed for unidirectionally reinforced elastoplastic composites capable of gradually accumulating disperse microdamages under loading. The composite is assumed to be a homogeneous transversely isotropic solid. To describe its elastoplastic behavior, an incremental plasticity theory with a nonlinear combined hardening mechanism is invoked. At each point of the solid, its damage is characterized by a centrally symmetric scalar function on a unit sphere. This function is approximated by a fourth-rank tensor, which is used for describing the degradation of the elastic properties of the solid due to the accumulation of disperse microdamages. It is shown how to determine, using the known experimental data, all material constants appearing in the theoretical relations suggested.     

Micromechanical Modeling of Woven Fiber Composites for the Construction of Effective Anisotropic Polyconvex Energies

In computer simulations where constitutive equations are considered polyconvex energies can preferably be used because the existence of minimizers is then automatically guaranteed. In this work we investigate the capability to simulate woven fiber composites using polyconvex energies. A virtual experiment of the microstructure of the considered composite is performed and the results are used for the specification of an effective macroscopic anisotropic polyconvex model. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

三轴压缩下岩石/混凝土的三维细观损伤模型

考虑三轴压应力作用下的无限大体深埋椭圆形裂纹的变形场,给出了闭合椭圆形微裂纹的能量释放率.采用能量平衡方法分析了闭合椭圆形微裂纹的扩展条件,得到了代表性体积单元中具有任意空间取向的单个闭合椭圆形微裂纹及其扩展引起的附加柔度张量.分析了闭合椭圆形微裂纹的偏折扩展,得到了微裂纹偏折扩展引起的附加柔度张量.采用Taylor方法考虑微裂纹系统对代表性体积单元变形的影响,引入概率密度函数,得到了三轴压缩下岩石/混凝土的三维细观损伤模型.分析了混凝土的单轴压缩特性,结果表明该模型能够很好地描述实验现象.     

FEM Simulation of a Micromechanical Model for Textured Polycrystalline Shape Memory Alloys with n-Variants

This paper is about the numerical implementation of a known, but advanced model with a projected Newton algorithm and a residual including only two vectors of unknowns. In a complex stress driven example the superelastic behavior is investigated. (© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Efficient Simulation of Short Fibre Reinforced Composites

In this paper we present a way how short fibre reinforced composites, produced by injection moulding, can be simulated in a linear thermoelastic setting, with an stationary heat equation. The main problem is the unknown stochastic fibre orientation. The only information known about this orientation field are the first moments of its distribution. (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Time-Dependent Behavior of Randomly Reinforced Polymeric Composites

This article summarizes the recent experimental results and constitutive formulations concerning the behavior of two types of randomly reinforced polymeric composites. It is shown that the mechanical behavior of these composites can be modeled by means of coupled viscoelasticity and continuum damage theories.     

Efficient Simulation of Short Fibre Reinforced Composites

In this paper we present a way how short fibre reinforced composites, produced by injection moulding, can be simulated in a linear thermoelastic setting, with an instationary heat equation. The main problem is the unknown stochastic fibre orientation. The only information known about this orientation field are the first moments of its distribution. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Efficient Simulation of Short Fibre Reinforced Composites

Lightweight structures become more and more important and one great class within these structures are parts produced by injection moulding. To improve the mechanical properties of these parts short fibers are injected within the molten plastics. Now a way to describe these properties without knowing the fibre orientation exactly is needed. We show an intuitive way, how mechanical properties of short fibre reinforced composites for linear thermoelasticity can be described and show the relation to other approaches. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)