Separation work analysis of cohesive law and consistently coupled cohesive law

An appropriate coupled cohesive law for predicting the mixed mode failure is established by combining normal separation and tangential separation of surfaces in the cohesive zone model （CZM） and the cohesive element method. The Xu-Needleman exponential cohesive law with the fully shear failure mechanism is one of the most popular models. Based on the proposed consistently coupled rule/principle, the Xu-Needleman law with the fully shear failure mechanism is proved to be a non-consistently coupled cohesive law by analyzing the surface separation work. It is shown that the Xu-Needleman law is only valid in the mixed mode fracture when the normal separation work equals the tangential separation work. Based on the consistently coupled principle and the modification of the Xu-Needleman law, a consistently coupled cohesive （CCC） law is given. It is shown that the proposed CCC law has already overcome the non-consistency defect of the Xu-Needleman law with great promise in mixed mode analyses.

基于Voronoi建模和Cohesive单元的PBX细观力学模型

针对PBX的细观力学模型存在模型结构与真实PBX细观形貌不符、破坏行为描述不全面(仅考虑界面脱粘)、研究对象单一(大多针对PBX-9501)等问题,建立了基于Voronoi建模和Cohesive单元的PBX细观力学模型。首先,基于光学显微镜下的细观结构图,采用Voronoi方法构建了更贴近实际形貌的PBX炸药细观模型;然后,采用内聚力有限元方法在炸药晶体内部、黏结剂内部及炸药颗粒/黏结剂界面处都引入了Cohesive单元,以在二维尺度上实现任意路径破坏行为的模拟;最后,针对某HMX基-F2311黏结剂炸药和某HMX基-F2313黏结剂炸药标定了模型参数,模拟了这两种炸药的准静态拉伸行为。结果表明,两种炸药数值模拟的拉伸变形曲线、破坏应力、破坏应变都与试验数据吻合良好,表明该模型不仅适用于不同PBX炸药材料(线弹性PBX、非线性PBX)的变形行为描述,还可以分析PBX炸药在拉伸破坏过程中的细观机理,刻画不同PBX炸药的裂纹萌生、扩展和贯穿的过程。

Finite Element Simulations of the Localized Failure and Fracture Propagation in Cohesive Materials with Friction

Strain localization frequently occurs in cohesive materials with friction(e.g.,composites,soils,rocks)and is widely recognized as a fundamental cause of progressive structural failure.Nonetheless,achieving high-fidelity simulation for this issue,particularly concerning strong discontinuities and tension-compression-shear behaviors within localized zones,remains significantly constrained.In response,this study introduces an integrated algorithmwithin the finite element framework,merging a coupled cohesive zone model(CZM)with the nonlinear augmented finite elementmethod(N-AFEM).The coupledCZMcomprehensively describes tension-compression and compressionshear failure behaviors in cohesive,frictional materials,while the N-AFEM allows nonlinear coupled intraelement discontinuities without necessitating extra nodes or nodal DoFs.Following CZM validation using existing experimental data,this integrated algorithm was utilized to analyze soil slope failure mechanisms involving a specific tensile strength and to assess the impact of mechanical parameters(e.g.,tensile strength,weighting factor,modulus)in soils.

Extended finite element-based cohesive zone method for modeling simultaneous hydraulic fracture height growth in layered reservoirs

In this study,a fully coupled hydromechanical model within the extended finite element method(XFEM)-based cohesive zone method(CZM)is employed to investigate the simultaneous height growth behavior of multi-cluster hydraulic fractures in layered porous reservoirs with modulus contrast.The coupled hydromechanical model is first verified against an analytical solution and a laboratory experiment.Then,the fracture geometry(e.g.height,aperture,and area)and fluid pressure evolutions of multiple hydraulic fractures placed in a porous reservoir interbedded with alternating stiff and soft layers are investigated using the model.The stress and pore pressure distributions within the layered reservoir during fluid injection are also presented.The simulation results reveal that stress umbrellas are easily to form among multiple hydraulic fractures’tips when propagating in soft layers,which impedes the simultaneous height growth.It is also observed that the impediment effect of soft layer is much more significant in the fractures suppressed by the preferential growth of adjoining fractures.After that,the combined effect of in situ stress ratio and fracturing spacing on the multi-fracture height growth is presented,and the results elucidate the influence of in situ stress ratio on the height growth behavior depending on the fracture spacing.Finally,it is found that the inclusion of soft layers changes the aperture distribution of outmost and interior hydraulic fractures.The results obtained from this study may provide some insights on the understanding of hydraulic fracture height containment observed in filed.

Investigation of FRP and SFRC Technologies for Efficient Tunnel Reinforcement Using the Cohesive Zone Model

Amid urbanization and the continuous expansion of transportation networks,the necessity for tunnel construction and maintenance has become paramount.Addressing this need requires the investigation of efficient,economical,and robust tunnel reinforcement techniques.This paper explores fiber reinforced polymer(FRP)and steel fiber reinforced concrete(SFRC)technologies,which have emerged as viable solutions for enhancing tunnel structures.FRP is celebrated for its lightweight and high-strength attributes,effectively augmenting load-bearing capacity and seismic resistance,while SFRC’s notable crack resistance and longevity potentially enhance the performance of tunnel segments.Nonetheless,current research predominantly focuses on experimental analysis,lacking comprehensive theoretical models.To bridge this gap,the cohesive zone model(CZM),which utilizes cohesive elements to characterize the potential fracture surfaces of concrete/SFRC,the rebar-concrete interface,and the FRP-concrete interface,was employed.A modeling approach was subsequently proposed to construct a tunnel segment model reinforced with either SFRC or FRP.Moreover,the corresponding mixed-mode constitutive models,considering interfacial friction,were integrated into the proposed model.Experimental validation and numerical simulations corroborated the accuracy of the proposed model.Additionally,this study examined the reinforcement design of tunnel segments.Through a numerical evaluation,the effectiveness of innovative reinforcement schemes,such as substituting concrete with SFRC and externally bonding FRP sheets,was assessed utilizing a case study from the Fuzhou Metro Shield Tunnel Construction Project.

Survey Research into Cohesive Device Misuses in Business English Writing

Cohesive devices in students’business English writing are regarded as the object of the research.Based on Haliday and Hasan’s cohesion theory,this paper introduces commonly-used cohesive devices in English writing.With the method of quantitative data,use and misuse frequency of cohesive devices in students’writings can be known.The paper will also analyze why misuses happen through qualitative data analysis and explore right ways of using cohesive devices.

Cohesion in Writing of EFL Learners

Cohesion tends to be denser and more noticeable in written discourse than in spoken discourse. A text will become problematic or is not easy to make sense to readers if any cohesion is troubled. The present paper is going to investigate cohesion in Chinese advanced learners' expository writing by comparing and analyzing the cohesive ties in two student writers' essays.

基于XFEM与Cohesive模型分析PBX裂纹产生与扩展

利用扩展有限元法(XFEM)分析PBX-9502带孔板状试件在整体压缩下由局部裂纹萌生到裂纹扩展全过程的开裂破坏机理。采用应力状态相关的强度面、非关联流动法则及Cohesive模型,描述了材料在复杂应力状态下的非线性本构行为以及材料的破坏行为。进行了数值模拟结果与美国洛斯阿拉莫斯国家实验室(LANL)试验结果的对比。结果表明,含孔洞的平板在整体压应力环境下孔洞周围产生局部拉伸应力,这种拉伸条件导致局部裂纹萌生。数值模拟的裂纹发展趋势与试验结果相吻合,包括裂纹时程的整体走势和拐点、启裂时刻、裂纹初期扩展速度等。基于扩展有限元方法和内聚模型法,可模拟高聚物粘结炸药(PBX)含能材料的裂纹萌生、扩展。

An In-depth Discourse Analysis of One Radio Interview From the Perspective of Cohesion

As a major criterion for textuality and a prominent term in discourse analysis, discourse cohesion is used on the one hand, to identify the linguistic features that cause the sentences to ＂cohere＂, and on the other hand, is to make the sentences in the discourse display some kind of mutual dependence. The paper has intensively analyzed the radio interview between Edward Heath and an interviewer from the perspective of discourse cohesion. After an in-depth analysis, the paper concludes that the interview is quite structurally cohesive by adopting several grammatical cohesive devices or ties, such as the verbal form, the time relator, the conjunction, the reference, the substitution, and the ellipsis, especially the reference and conjunction

基于Cohesive单元法的弃置井水泥塞-套管界面胶结失效数值模拟

水泥塞-套管界面胶结失效对弃置井井筒完整性提出了严峻挑战。考虑地下流体与水泥塞的流固耦合作用,基于cohesive单元方法,建立水泥塞-套管-水泥环-地层系统三维有限元模型,模拟垂直井水泥塞-套管界面裂缝剥离过程,研究地应力对界面裂缝损伤演化的影响,并分析水平地应力、水泥塞力学参数及界面性质对裂缝剥离高度的影响。结果显示:水平地应力均匀时剥离裂缝沿着整个界面圆周延伸且高度相等,水平地应力非均匀时剥离裂缝倾向于沿着界面某一圆周角扩展且在最大水平地应力方向具有较大的高度;水泥塞弹性模量从30 GPa减小到1 GPa,裂缝剥离高度降低9.3 m,临界法向强度从0.25 MPa增大到2.0 MPa,裂缝剥离高度降低6.5 m,表明较低的弹性模量及较大的临界法向强度有利于减小水泥塞-套管界面胶结失效的风险;水泥塞泊松比从0.35减小到0.10,裂缝剥离高度仅降低2.0 m,临界剪切强度从0.5 MPa增加到4.0 MPa,裂缝剥离高度仅降低3.3 m,表明泊松比和临界剪切强度对界面胶结失效影响较小。建立的模型能够为水泥浆配方优选和井筒弃置工艺优化提供指导。

Numerical study of fatigue damage of asphalt concrete using cohesive zone model

In order to investigate the fatigue behavior of asphalt concrete, a new numerical approach based on a bi-linear cohesive zone model （CZM） is developed. Integrated with the CZM, a fatigue damage evolution model is established to indicate the gradual degradation of cohesive properties of asphalt concrete under cyclic loading. Then the model is implemented in the finite element software ABAQUS through a user-defined subroutine. Based on the proposed model, an indirect tensile fatigue test is finally simulated. The fatigue lives obtained through numerical analysis show good agreement with laboratory results. Fatigue damage accumulates in a nonlinear manner during the cyclic loading process and damage initiation phase is the major part of fatigue failure. As the stress ratio increases, the time of the steady damage growth stage decreases significantly. It is found that the proposed fatigue damage evolution model can serve as an accurate and efficient tool for the prediction of fatigue damage of asphalt concrete.

Effect of slice scope on data slice-based class cohesion metrics

This paper suggests that a single class rather than methods should be used as the slice scope to compute class cohesion. First, for a given attribute, the statements in all methods that last define the attribute are computed. Then, the forward and backward data slices for this attribute are generated by using the class as the slice scope and are combined to compute the corresponding class data slice. Finally, the class cohesion is computed based on all class data slices for the attributes. Compared to traditional cohesion metrics that use methods as the slice scope, the proposed metrics that use a single class as slice scope take into account the possible interactions between the methods. The experimental results show that class cohesion can be more accurately measured when using the class as the slice scope.

基于Cohesive单元的石拱桥主拱圈二相数值模拟方法

为解决石砌体材料非均质的描述问题,提出一种基于Cohesive单元的石拱桥主拱圈两相数值模拟方法。视石砌体为两相材料(砌块和砌缝),采用实体单元模拟砌块并引入非线性本构描述其破坏行为,在相邻砌块间插入Cohesive单元考虑砌缝砂浆的剪切和拉伸破坏。通过室内试验与数值模拟对比验证方法的有效性及适用性,分析了砌缝抗剪摩擦系数μ、加载位置等敏感参数对拱桥承载力的影响。结果表明:基于Cohesive单元的石砌体两相数值模型,可以有效描述石砌体材料的非均匀性及石拱桥的破坏过程(尤其是砌缝剪切滑移破坏行为),可为石拱桥极限承载力评估提供重要信息,如荷载-位移曲线、破坏模式等。此外,研究结果还发现主拱圈破坏机制由拱的受弯、受剪特性决定,并与砌缝抗剪摩擦系数μ强相关。

Study on the Development of Urban Cohesion

Urban cohesion is a new development phenomenon of urbanization, requires further study in both practices and theories. In this study, the connotation, development premise and existing problems of urbanization have been primarily explored, to obtain useful ideas.

Delamination analysis of woven fabrication laminates using cohesive zone model

A new test method was proposed to evaluate the cohesive strength of composite laminates. Cohesive strength and the critical strain energy for Mode-II interlamiar fracture of E-glass/epoxy woven fabrication were determined from the single lap joint(SLJ) and end notch flexure(ENF) test, respectively. In order to verify their adequacy, a cohesive zone model simulation based on interface finite elements was performed. A closed form solution for determination of the penalty stiffness parameter was proposed. Modified form of Park-Paulino-Roesler traction-separation law was provided and conducted altogether with trapezoidal and bilinear mixed-mode damage models to simulate damage using Abaqus cohesive elements. It was observed that accurate damage prediction and numerical convergence were obtained using the proposed penalty stiffness. Comparison between three damage models reveals that good simulation of fracture process zone and delamination prediction were obtained using the modified PPR model as damage model. Cohesive zone length as a material property was determined. To ensure the sufficient dissipation of energy, it was recommended that at least 4 elements should span cohesive zone length.

基于JKR-Cohesion模型的湿颗粒松散堆积体滑坡模拟分析

为深入研究湿颗粒松散堆积体滑坡的运动特征,提出采用JKR-Cohesion模型模拟湿颗粒堆积体的运动行为。基于离散单元法(DEM)建立了三维松散堆积体滑坡水槽模型,模拟堆积体整个运移过程,并将计算结果与干燥颗粒堆积体运动结果进行对比。计算结果表明:湿颗粒松散堆积体的运动受水的粘附力影响很大,相对于干燥颗粒,运动速度最大值更小,运动时间更短,且大部分颗粒堆积在坡面上;湿颗粒堆积体在运动过程中解体为小团体单独运动,而干燥颗粒运动连续性好,运动距离更远。提出的方法对于含水堆土的滑坡模拟有一定借鉴作用。

Lexis Cohesion and English Reading

This article discusses one of the important cohesion means—lexis cohesion, and applies it to English reading. This cohesion contributes to the improvement of reading ability for its immediateness and accessibility. It aims at specifying the potentials of the theory in English reading learning by analysis and exemplification.

An Analysis of the Means of Cohesion in “of Studies” by Francis Bacon

This thesis aims to analyze the means of cohesion in"of Studies"by Francis Bacon.According to the systemic-functional linguistics,the paper is intended to explore cohesion means applied in Of Studies by Francis Bacon.It gives an account of the functions in grammatical cohesion in the several fields,they are reference,substitution,ellipsis,and conjunction respectively.Finally,it is expected that these analyses can help readers gain a better and deeper comprehension of the structure and content of the text.

The System of Reference and Lexical Cohesion in Newspaper-An Example of Analyzing "Beijing and Shanghai in Race to Attract Top Foreign Talents"

Discourse analysis is gaining its prominence in teaching reading. The paper presents an example of analyzing the system of reference and lexical cohesion of a news report. It demonstrates how to involve discourse analysis into the teaching of newspaper reading in order to make students get a clear framework of reference and lexical cohesion in a functional-grammar-conscious manner.

On Reference and Cohesion

In the study of textlinguistics,cohesion is one important subject. According Halliday and Hasan,cohesion can be achieved through two ways. One is lexical cohesion and the other is grammatical cohesion. Reference is one of the most important devices in grammatical cohesion. It can be divided into personal reference,demonstrative reference,and comparative reference. Some of these references can be used as cataphora,some can be used as anaphora and some can be used as both. Analysis and explanation as well as examples are provided in this paper to facilitate the reader's understanding and use of reference.