黏弹性体界面裂纹的冲击响应

研究两半无限大黏弹性体界面Griffith裂纹在反平面剪切突出载荷下,裂纹尖端动应力强度因子的时间响应,首先,运用积分变换方法将黏弹性混合黑社会问题化成变换域上的对偶积分方程,通过引入裂纹位错密度函数进一步化成Cauchy型奇异积分方程,运用分片连续函数法数值求解奇异积分方程,得到变换域内的动应力强度因子,再用Laplace积分变换数值反演方法,将变换域的解反演到时间域内,最终求得动应力强度因子的时间响应,并对黏弹性参数的影响进行分析。     

孔边裂纹对SH波的散射及其 动应力强度因子1)

采用Green函数法研究任意有限长度的孔边裂纹对SH波的散射和裂纹尖端场动应力强度因子的求解.取含有半圆形缺口的弹性半空间水平表面上任意一点承受时间谐和的出平面线源荷载作用时位移函数的基本解作为Green函数,采用裂纹``切割'方法并根据连接条件建立起问题的定解积分方程,得到动应力强度因子的封闭解答.最后给出了孔边裂纹动应力强度因子的算例和结果,并讨论了圆孔的存在对动应力强度因子的影响.     

孔边裂纹对SH波的散射及其动应力强度因子

采用Ｇｒｅｅｎ函数法研究任意有限长度的孔边裂纹对ＳＨ波的散射和裂纹尖端场动应力强度因子的求解．取含有半圆形缺口的弹性半空间水平表面上任意一点承受时间谐和的出平面线源荷载作用时位移函数的基本解作为Ｇｒｅｅｎ函数,采用裂纹“切割”方法并根据连接条件建立起问题的定解积分方程,得到动应力强度因子的封闭解答．最后给出了孔边裂纹动应力强度因子的算例和结果,并讨论了圆孔的存在对动应力强度因子的影响     

功能梯度压电带中裂纹对SH波的散射

研究功能梯度压电带中裂纹对SH波的散射问题,为了便于分析,材料性质假定为指数模型,并假设裂纹面上的边界条件为电渗透型的.根据压电理论得到压电体的状态方程,利用Fourier积分变换,问题转化为对偶积分方程的求解.用Copson方法求解积分方程.求得了裂纹尖端动应力强度因子、电位移强度因子的解析表达式,最后数值结果显示了标准动应力强度因子与入射波数、材料参数、带宽、波数以及入射角之间的关系.     

SH波对一维六方准晶中直裂纹的散射

分析了SH波对一维六方准晶中直裂纹的散射问题。利用积分变换技术,结合Copson方法,通过求解对偶积分方程,得到声子场和相位子场应力、位移及裂纹尖端动应力强度因子的解析表达式。通过数值算例讨论了裂纹长度、入射角和入射波频率对标准动应力强度因子的影响,此研究在工程材料应用中有一定的参考价值。     

薄膜涂层材料中币形界面裂纹的弹性波散射

研究了薄膜涂层材料中币形界面裂纹的弹性波散射问题,建立了含有币形界面裂纹的覆层半空间模型,采用Hankel积分变换,将裂纹对弹性波散射的问题转化为求解矩阵形式的奇异积分方程。结合渐近分析和围道积分技术得到积分方程的解,进一步推导了散射波的应力场和位移场,以及动应力强度因子的理论计算公式。在数值算例中,分析了不同材料组合和裂纹尺寸情况下动应力强度因子与入射波频率的关系,并给出了裂纹张开位移的结果。为薄膜涂层材料的动态破坏分析提供了一定的理论基础。     

反平面扩展裂纹的J积分与COD

给出一个以任意速率扩展的反平面裂纹与路径无关的Ｊ积分，证明Ｊ积分扩展裂纹尖端的张开位移（动态ＣＯＤ）之间有的简单的关系，Ｊ积分与能量释放率，动应力强度因子之间也有简单关系，利用这些关系，给出了动态ＣＯＤ与动应力强度因子之间的关系式。     

粘弹性介质中扩展裂纹与J积分

本文提出了在线弹性及粘弹性介质中扩展裂纹与路径无关的J~*积分,并给出了严密的证明。文中证明了J~*积分与扩展裂纹尖端的张开位移(动态COD)之间有简单的关系,同时利用J~*积分求得了粘弹性介质中变速扩展裂纹尖端的奇异性。当裂纹以常速扩展时,J~*积分与能量释放率、动应力强度因子之间也有简单的关系。利用这些关系,我们给出了动态COD与动应力强度因子之间的关系式。     

功能梯度压电压磁材料中裂纹对SH波的散射

研究无限大功能梯度压电/压磁复合材料中裂纹对SH波的散射问题.为了便于分析,假设材料性质沿着裂纹的法线方向是指数变化.利用Fourier余弦变化,将问题转化为对偶积分方程的求解,此对偶积分方程采用Copson方法求解.然后求得应力强度因子、电位移强度因子、磁通量强度因子的解析表达式,最后数值算例给出了材料参数、入射角及波数对标准动应力强度因子的影响.     

压电体中孔边Ⅲ型界面裂纹的动应力强度因子

采用Green函数法研究界面上含圆孔边界径向有限长度裂纹的两半无限压电材料对SH波的散射和裂纹尖端动应力强度因子问题.首先构造出具有半圆型凹陷半空间的位移Green函数和电场Green函数,然后采用裂纹"切割"方法构造孔边裂纹,并根据契合思想和界面上的连接条件建立起求解问题的定解积分方程.最后作为算例,给出了孔边界面裂纹尖端动应力强度因子的计算结果图并进行了讨论.     

Material behavior of steel – Modeling of complex phenomena and thermodynamic consistency

Steel has a complex material behavior. Stress- and strain-dependent phase transformations, transformation-induced plasticity (TRIP), and its interactions with plasticity are important phenomena of both theoretical and practical interest, as they may cause distortion of work-pieces. These phenomena continue to be intensively studied both experimentally and theoretically. In order to simulate real processes like heat treatment of work-pieces, one has to include the relevant phenomena in a suitable bulk model. It is the aim of the current paper to contribute to the formulation of such a model in the context of macroscopic continuum mechanics and to discuss the capabilities. Due to the possible interaction (coupling) of TRIP and plasticity, the usual approach in plasticity without phase transformations has to be modified substantially. We apply a general approach for non-linear hardening, allowing to model observable effects of interaction of plasticity and TRIP. Besides this, we prove the thermodynamic consistency under sufficient conditions.     

Three dimensional asperity analysis of worn surfaces

An algorithm has been developed for the analysis of asperities of various types of machined surfaces, in order to characterize wear processes in the course of dry friction. Wear experiments and surface roughness measurements were performed to study the microtopographies of worn surfaces. Investigations extended to wear in the case of the non-lubricated ceramic-steel clutch and lubricated camshaft and bushing. A statistical analysis of asperities and scratches was completed with distribution curves to display the results. The peak angle, the rate of the major and minor axis and orientation were analyzed to characterize the shape of asperities and the overall characteristics of the surface.     

生物力学与基因-献给周培源教授诞辰100周年

生物界包罗万象,其中有力的作用,所以有生物力学.自Galileo,Harvey, Boreli, Hooke, Euler,Young等创始以来,生物力学阐明了鸟飞鱼游,人体运动,血液循环,人工脏器等,对人世社会,有所贡献.生物力学的基础是质点力学,传统地用连续体力学的概念来简化.但近年做生物组织在应力的作用下改造的问题,引起了必须更改传统连续体力学的几个公理的问题.我们将仔细讨论这些公理,然后指出新公理存在的理由,是由于基因在细胞里的日常工作.基因不单主宰遗传,变异;并且忙着控制日常生活.不过,现在仅见其端倪.详细的情形,要等将来来阐发了.      

层流射流流动的简化Navier-Stokes方程(SNSE)解

本文利用十一种简化 Navier-Stokes 方程(SNSE) 求解已知Navier-Stokes(NS)方程准确解的层射流流动,表明:多数SNSE~([1-6])的解与NS方程的准确解不一致;少数SNSE~([7,8])的解与NS方程的准确解一致,文中在射流的喉部和拐点位置,给出几种SNSE解与准确解的相对偏差,并把粘性及惯性诸项加以定量比较,强调指出:按照边界层理论量级分析为Re~(1/2)和Re~1量级的惯性项以及Re~(-1/2)量级的粘性项具有重要影响;据此从力学角度论证了简化 NS 方程时,保留全部惯性项和合理取舍粘性项的必要性。     

A Theoretical Model for the Simulation of Microdamage Accumulation and Repair in Compact Bone*

This paper describes a new theoretical approach to bone microdamage, in which a population of cracks is explicitly modelled. A given sample of bone is assumed to contain a certain number of cracks, whose growth characteristics are described with an equation containing stochastic variables to create statistical differences from one crack to another. This type of model allows us to predict a wide variety of data. The present paper illustrates the different types of prediction which can be made, including: (i) standard damage parameters such as the number and length of cracks and the reduction in stiffness; (ii) fatigue test data such as the number of cycles to failure as a function of stress level, including scatter; (iii) effects due to the living system, including repair, remodelling and adaptation. A useful feature of the model is our ability to examine the statistics of the crack population in detail to find, for example, the number of cracks which are potentially dangerous as opposed to those which are dormant, and to investigate the reasons for increased crack numbers in the bones of older people. The potential also exists to use the model to investigate different theories of bone remodelling and adaptation.     

挠性转子系统碰摩故障传播特性的实验研究

研究了柔性联接的双跨度挠性转子发生碰摩时系统的响应征兆;将振动信号的快速付立叶变换(FFT)幅值谱阵列和轴心轨迹设置为特征参量,对不同截面和2个相互垂直方位的碰摩特征进行了对比.结果表明:碰摩故障在转子间具有传播能力,靠近碰摩部位的响应强度最大;碰摩的典型特征表现为FFT谱中1X分量幅值增大,并出现2X、3X、4X谐波分量;轴心轨迹形状显示出碰摩作用点的截面方位信息;最典型征兆表现为碰摩响应的1X分量所对应的频率坐标降低,其降低幅度与碰摩的程度相关.     

Elastodynamic analysis of anisotropic liquid-saturated porous medium due to mechanical sources

Elastodynamic analysis of an anisotropic liquid-saturated porous medium is made to study a deformation problem of a transversely isotropic liquid-saturated porous medium due to mechanical sources.Certain physical problems are of the nature,in which the deformation takes place only in one direction,e.g.,the problem relating to deformed structures and columns.In soil mechanics,an assumption of only vertical subsidence is often invoked and this leads to the one dimensional model of poroelasticity.By consid- ering a model of one-dimensional deformation of the anisotropic liquid-saturated porous medium,variations in disturbances are observed with reference to time and distance. The distributions of displacements and stresses are affected due to the anisotropy of the medium,and also due to the type of sources causing the disturbances.     

双向张弦梁找形的有限元法

根据双向张弦梁上弦压力和下弦拉力在节点产生的竖向分力与撑杆高度之间的关系推导了单元刚度矩阵,根据外荷载与上弦和下弦在节点产生的竖向分力相等的原则建立了以撑杆高度为未知数的双向张弦梁找形的线性有限元列式并编制了有限元程序,给出了张弦梁计算时下弦拉索初应变确定方法和张拉控制方法;通过对平屋顶和曲面屋顶双向张弦梁2个算例找形计算和受力分析验证了找形方法的正确性以及撑杆高度与屋面形状的无关性,本文给出的计算方法将撑杆高度作为未知量,考虑了上弦为曲面时拱的作用,计算方便、结果准确.     

一种薄壳厚壳通用的轴对称曲壳单元

有限元法分析轴对称壳体时，常需区分薄壳和厚壳并选用不同的单元，给计算带来不便．为此，通过对现有的轴对称壳体单元的研究，基于加权残值法，将广义协调条件引入剪应变场，构造了一种挠度和转角各自独立的新型轴对称曲壳单元．算例结果表明，新单元具有很高的精度，既可用于厚壳，也可用于薄壳．该单元可用于轴对称壳体结构的计算分析．     

Bimodal model of slurry viscosity with application to coal-slurries. Part 1. Theory and experiment

The rheological behavior of stable slurries is shown to be characterized by a bimodal model that represents a slurry as made up of a coarse fraction and a colloidal size fine fraction. According to the model, the two fractions behave independently of each other, and the non-Newtonian behavior of the viscosity is solely caused by the colloidal fraction, while the coarse fraction increases the viscosity level through hydrodynamic interactions. Data from experiments run with colloidal coal particles of about 2–3 µm average size dispersed in water show the viscosity of these colloidal suspensions to exhibit a highly shearrate-dependent behavior and, in the high shear limit, to match very closely the viscosity of suspensions of uniform size rigid spheres although the coal volume fraction must be determined semi-empirically. Different amounts of coarse coal particles are added to the colloidal suspension and the viscosity of the truly bimodal slurries measured as a function of shear rate. In agreement with the bimodal model, the measured shear viscosities show the coarse fraction to behave independently of the colloidal fraction and its contribution to the viscosity rise to be independent of the shear rate. It is shown that the shear rate exerted on the colloidal fraction is higher than that applied by the viscometer as a result of hydrodynamic interactions between the coarse particles, and that it is this effective higher shear rate which is necessary to apply in the correlations. For determining the coal volume fraction a relatively simple and quite accurate measurement technique is developed for determining the density and void fraction of coarse porous particles; the technique directly relates volume fraction to mass fraction.