断裂动力学有限元程序的开发及在天然气管道裂纹扩展问题上的应用

许多工程问题是由于流（气）体压力导致了结构开裂,裂纹迅速扩展或者止裂,这被认为是断裂动力学最前沿的研究领域。本文描述了应用于分析流体／结构／断裂耦合作用问题的计算程序ＰＦＲＡＣ（ＰｉｐｅｌｉｎｅＦＲａｃｔｕｒｅＡｎａｌｙｓｉｓＣｏｄｅ）,和它在天然气管道裂纹迅速扩展问题上的应用。基于断裂动力学的模式,提出了裂纹扩展和止裂的判据。对于裂纹驱动力的计算,给出了节点力释放技术和能量平衡方法的具体应用。根据实际管道开裂试验的数据,提出了便于非耦合作用计算的裂纹后面气体压力衰减模式。针对钢制和塑料制天然气工程管道,给出了部分计算和试验的结果。     

高压天然气管线的断裂性能评估

本文在断裂动力学生成模式的理论基础上，运用有限元单节点力释放技术。通过流体／结构／断裂软件ＰＦＲＡＣ对高压长距离钢制天然气管线作出了断裂性能评价，进而分析了动态裂纹扩展中的尺寸效应。     

T型焊接接头损伤判据的修正CEGB法

本文提出了一个控制焊接结构宏观裂纹形成的损伤判据，用ＡＢＡＱＵＳ对Ｔ型焊接接头作了非线性有限元分析，数值结果表明损伤判据能很好预测Ｔ型焊接接头的宏观裂纹的形成，通过有限元计算分析了含裂纹的Ｔ型接头双评定参数的裂纺驱动力和破坏荷载，进行了含裂纹的Ｔ型接头在拉伸和弯曲组合载荷作用下的试验，将评定曲线和数值及试验结果作了比较，结果表明，修正的ＣＥＧＢ方法适用于含缺陷的焊接了Ｔ型接头的安全评定。     

用裂纹驱动力分析管道的承压能力

本文以弹塑性断裂力学的Ｊ积分理论为基础，综合考虑裂纹的Ｊ积分弹性解和全塑性解，导出了促使管道的轴向内表面裂纹扩展的裂纹驱动力Ｊ。通过裂纹驱动力图与管材的ＪＲ阻力曲线的叠加，实现了对含有一定初始裂纹管道的承压能力的分析评定，本文的分析结果与相关文献的完整性评定结论基本吻合。     

管道的断裂与落锤撕裂试验

介绍了避免油、气集输管道低应力断裂扩展的上裂原理与速度判据。管道裂纹的扩展速度主要取决于管道钢的转变温度ＦＡＴＴ。ＦＡＴＴ可由落锤撕裂试验测定。论述了落锤撕裂试验的特点、方法和标准，以及该试验在管道钢材、压力容器钢和船体结构钢薄板上的应用情况。     

用裂纹扩展片测量SFRC的静,动态裂纹扩展

本文用箔式裂纹扩展片测试，研究了钢纤维增强砼三点弯曲切口梁试件在蠕变断裂和动态断裂时的裂纹扩展，分别得到了裂纹扩展量与时间，裂纹扩展量与加载点位移及动态裂纹扩展速度与应变率的关系，根据实验结果分析了ＳＦＲＣ的静，动态裂纹展规律。     

高速柴油机曲轴动态特性研究

本文利用ＳＵＰＥＲ ＳＡＰ９１微机版工程分析软件，对某高速柴油机曲轴进行了有限元计算模态分析，获得了其前五阶模态参数；利用随机信号与振动分析系统ＣＲＡＳ４．１版对该曲轴进行了试验模态分析，其固有频率与计算结果的相对误差在５．７％之内，验证了计算结果的正确性，为结构的动态特性分析提供了可靠的数据。     

研究高聚物结构的广角X射线衍射系列方法

全面论证了广角Ｘ射线（ＷＡＸＤ）系列方法：分峰ＭＰＳ、径向分布函数（ＲＤＦ）（Ｒ）、圆柱分布函数ＣＤＦ（Ｒ，α）、取向分布函数ＯＤＦ（α）、对称透射径向ＷＡＸＳ方位角扫描、对称反射径向ＷＡＸＳ扫描等分析法的基础理论、实验方法、计算程序及其可获得的结构参数，阐明了笔者建立ＷＡＸＤ测试分析高聚物聚集态结构专家系统的有关工作，这一研究架构的具体实现，将使得ＷＡＸＤ系列方法研究高聚物物理中的核心领域，即高     

两类有限元方法对于复杂体型高层建筑的地震反应分析

本文通过用有限元程序ＡＬＧＯＲ ＦＥＡＳ和通用结构计算程序ＴＢＳＡ两个软件对于同一个高层建筑的地震反应分析，对比两种分析方法的差别，说明这两种方法对于较复杂体型高层结构分析的适用性。同时级出模型振动台试验结果的对比。     

屈服强度对40CrMnSiMoVA超高强度钢腐蚀疲劳裂纹扩展的影响

研究了屈服强度对４０ＣｒＭｎＳｉＭｏＶＡ（ＧＣ－４）超高强度钢腐蚀疲劳（ＣＦ）裂纹扩展行为的影响，结果表明，不同屈服强度时，ＧＣ—４钢在３．５％ＮａＣｌ溶液中的ＣＦ裂纹扩展曲线上，都出现了类似于应力腐蚀的平台区，而且随屈服强度提高，平台区裂纹扩展速度显著增大。研究表明，氢脆在ＧＣ—４钢的腐蚀疲劳中起重要作用，进一步的理论分析与计算表明，屈服强度会影响高强钢氢致开裂的过程和速度．     

Numerical analysis of dynamic T stress of moving interfacial crack

A method to extract dynamic T stress term of moving interfacial crack is proposed. Anisotropic bimaterial which has subsonic crack propagation is considered, and interaction energy method is applied. Stress fields by the constant T stress and stress fields by the point force moving with the crack are obtained by using the series expansion method and Stroh formalism. J based interaction energy (J^I) between the constant T stress and the point force is calculated by Yeh formulation and the relation between interaction energy and T stress is obtained. Energy release rate and T stress of a moving interfacial crack are calculated numerically. Elastodynamic finite element code is developed to investigate fracture parameters for the propagating crack. Four nodes linear elastodynamic element is used and Newmark formulae are applied to integrate displacement and velocity. Node release method is adapted to simulate crack propagation along the interface. The energy release rate is calculated in the area moving with crack. T stress term is calculated from the interaction energy with a stress field formed by the moving point force. Five examples are solved to show the validity and time history of energy release rate and T stress. The energy release rate calculated from numerical analysis agrees well with an analytic solution and experimental results. The T stress of homogeneous specimen under the steady state condition shows a slightly different value compared with the stationary result. It is observed that the T stress of polymethyl methacrylate–steel specimen shows continuous change and the T stress of aluminum-polymethyl methacrylate specimen shows discontinuous jump when the initial crack initiates. From the result of the variation of T stress, the effect of T stress on the stability of crack propagation is observed.     

R-Kurven von energiedissipativen Werkstoffen mit Schädigungszone. Teil 1: Energieumsatz am Riß

R-Curves of Energy Dissipative Materials Part 1: Energy Consumption at the Crack The paper deals with the way in which the energy balance should be formulated when nonlocal damage processes associated with energy dissipation accompany crack growth. The local energy balance is used to rearrange the relationships between the different energies consumed both in the process of material separation and due to nonlocal damaging around the crack tip. The first law of thermodynamics allows the identification or definition of appropriate crack driving forces. The results are compared with recent ideas of Turner on defining tearing resistance for uncontained yield through energy dissipation rate.     

The recent development of analysis methodology for rapid crack propagation and arrest in gas pipelines

Several dynamic analysis issues relating to rapid crack propagation (RCP) and arrest in gas piplines were developed recently, and are presented in this paper. This is based on a fluid/structure/fracture interaction package, PFRAC. Some developments have been implemented into this finite element code to simulate the behavior of the fractured pipes. The criteria for crack initiation, propagation and arrest have been discussed. As the crack propagates along the pipeline, the gas pressure decompression ahead of the crack tip and an efficiency of a linear decay behind the crack have been used in the computation. For the calculation of crack driving force G, the numerical approaches using the nodal force release and energy balance methods are described. This paper also presents a novel analysis methodology that has been developed to investigate the suitability of crack arrestors. Several numerical results for the cracked steel pipes with arrestors are presented along with comparisons with pipes that do not have arrestors.     

Some results on crack propagation in media with spatially varying elastic moduli

Energy release rates are calculated for cracks propagating in media with spatially varying elastic moduli, this variation being in a direction perpendicular to the crack growth direction. Results are given for transient problems of semi-infinite cracks in infinite media for certain special forms of the variation in shear modulus. Steady state crack propagation in a displacement loaded strip is also considered and it is shown by the use of a certain path independent integral that a simple formula for the energy release rate can be obtained for quite general variations in clastic moduli provided these variations are in a direction perpendicular to the crack. Other path independent integrals are derived which may be of use for transient crack tip stress analysis in strips in a similar way to that used in [4] for the homogeneous elastic problem.     

基于谱元法的裂Lamb纹梁波传播特性研究

首次提出用一种无质量弹簧元来模拟含横向裂纹梁的轴弯耦合效应,并结合谱元法分析含裂纹梁内Lamb波的传播特性.由卡氏定理和断裂力学方法推导弹簧元的刚度,以此构建裂纹处的平衡条件和位移协调条件,建立损伤谱元模型.通过和传统的有限元模型进行比较,表明在显著提高计算效率的同时,所提出模型在分析结构固有特性和Lamb波传播特性上都具有较高的精度.在所提出模型的基础上又推导出基于谱元法的能量计算公式,通过裂纹处的能量守恒再次验证损伤模型的正确性和有效性,同时研究结果表明裂纹处转化生成的Lamb 波各模态能量随裂纹深度的变化具有单调性,该结论可以为结构健康监测中定量识别裂纹提供实用依据.     

Analysis of stable crack propagation in filled rubber based on a global energy balance

Stable crack propagation in filled rubber is investigated by means of experimental and finite element analyses. Based on an experimental evaluation of multiple specimens under different loading states, dissipation rates are computed by applying a global energy balance. The dissipation rates calculated analogously from results of a numerical simulation of the multiple specimen method are in good accordance with the experimental findings. A further comparison of simulation results evaluated on basis of the material force method with energy release rates computed by means of an energy balance of two crack states under fixed loading conditions shows that the measured fracture sensitivity values are mainly related to the development and increase of a dissipative zone.     

Mechanical Properties of Si and Some d-electron Metals: Force Laws, Electron Correlation and Bond-breaking

1.BackgroundandOutlineThemechanicalpropertiesofsolidsconstituteanareaofmaterialsscience0fcontinuingimportance,themotivati0nbeingbothdeeperunderstanding0fprin-ciplesandconceptsinvolvedand,ofcourse,techno-logicalapplications.Naturally,though,intheoreticalstudiessuchasthosetobereportedbelow,simplifica-tionsofthesystemstreatedhavet0bemade.Thoughdensityfunctionaltheory(DFT)l',']withapproxima-tionsmadeinthel1nknownexchange(x)-c0rrelation(c)energyfunctionalEx.[p],wherep(r)istheground-stateelectrond…     

Determination of dynamic rock Mode-I fracture parameters using cracked chevron notched semi-circular bend specimen

Rock dynamic fractures are common in many geophysical processes and engineering applications. Characterization of rock dynamic fracture properties such as the initiation fracture toughness, the fracture energy, and the fracture velocity, is thus of great importance in rock mechanics. A novel method is proposed in this work to measure dynamic Mode-I rock fracture parameters using a cracked chevron notched semi-circular bend (CCNSCB) specimen loaded by a split Hopkinson pressure bar (SHPB) apparatus. A strain gauge is mounted on the sample surface near the chevron notch to detect the fracture onset, and a laser gap gauge (LGG) is used to monitor the crack surface opening distance (CSOD) during the dynamic test. With dynamic force balance achieved in the tests, the stable–unstable transition of the crack propagation crack is observed and the initiation fracture toughness is calculated from the dynamic peak load. The average dynamic fracture energy as well as the fracture propagation toughness are calculated based on the first law of thermodynamics. The measured dynamic fracture properties of Laurentian granite using CCNSCB method are consistent with those reported in the literature using other methods.     

Life prediction by ferrite–pearlite microstructural simulation of short fatigue cracks at high temperature

This paper dealt with fatigue behavior simulation based on ferrite–pearlite microstructure modeled by correctional Voronoi-polygons. The model took grain size, grain orientation and the percentage of pearlite and ferrite into consideration. The basal energy was proposed to represent the inherent energy for slip-band and grain boundary to cracking. The driving force for crack initiation and propagation caused by load condition was considered as the energy increment of slip-band and grain boundary. The fatigue behavior including crack initiation, propagation, coalescence and interference were simulated based on Monte Carlo method. The simulation results show a satisfying agreement with the experimental ones.     

The wave propagation and vibrational energy flow characteristics of a plate with a part-through surface crack

In the view of structure-borne sound, vibrational wave and energy flow characteristics of infinite thin plate of finite width with a part-through surface crack are investigated. The case of an all-over part-through crack parallel to the finite side of the plate is considered. The crack is modeled as a line spring and the flexibility of the spring is deduced from the relationship between the strain energy and stress intensity factor in fracture mechanics. The responses of both intact plate and cracked plate under the excitation of harmonic force are reduced with wave propagation approach, then the input energy flow and transmitted energy flow of intact and cracked plates are calculated. The results show that the vibrational energy flow of cracked plate is highly related to the depth and location of the part-through crack. The location and the depth of the crack can be identified by the contour lines of normalized input energy flow with different driving frequencies. The research provides theoretical basis for the crack detection by measuring the vibrational energy flow in cracked plate structures.