混凝土坝裂纹扩展算法(英文)

混凝土建筑物中的裂纹扩展追踪计算是确定结构安全度的重要手段。本文提出用虚拟裂纹单元及断裂力学准则(应变强度因子)追踪和模拟裂缝初始断裂、扩展并最终导致破坏的过程,给出一条逐段扩展的裂纹线,本方法计算结果与某些混凝土坝实测资料及模型试验结果吻合较好。     

内蒙古地区沥青混凝土路面裂缝的分析与防治

内蒙古地处我国北方寒冷地带,特殊的气候特点决定了对沥青混凝土路面的裂缝有着重要的影响,本文主要是结合内蒙古地区的气候特点,对沥青混凝土路面裂缝的产生原因进行了分析,并提出了相应的防治措施.     

浅析沥青混凝土路面的裂缝控制

系统地阐述了沥青混凝土路面裂缝的4种常见类型、表现形式和产生原因,并就如何减少沥青路面裂缝提出了相应的防治措施,可为如何控制沥青混凝土路面的裂缝提供参考。     

沥青混凝土路面裂缝的形成及防治

本文就沥青混凝土路面各种各样裂缝的形成及防治做了简单的阐示.     

二次老化条件下温拌再生沥青胶结料的抗车辙和低温性能评价（英文）

分别采用动态剪切流变试验和弯曲梁流变试验对二次老化条件下温拌再生沥青胶结料的抗车辙和低温性能进行测试,评价温拌技术和改性剂类型对其影响,通过傅立叶变换红外光谱试验揭示其老化和改性机理.研究表明:温拌再生沥青胶结料二次老化后高温稳定性提高,低温抗裂性降低.2种温拌技术表现出不同的作用.由于在不同温度下其物理形态会发生变化,使用Sasobit温拌剂可以显著改善再生沥青胶结料的高温性能,其车辙因子提高了4.6～5.6倍,但是对其低温性能会带来不利的影响.使用Evotherm温拌剂则会在再生沥青胶结料结构中起到润滑作用,从而造成其抗车辙性能下降,其车辙因子降低了52%～62%.推荐在温拌再生沥青胶结料中掺加丁苯橡胶乳液或者胶粉以同时改善其抗车辙和低温性能.     

沥青混凝土应用聚丙烯腈纤维的分析

聚丙烯腈纤维作为一种良好的沥青混合料添加材料,能够大大改善沥青路面的粘结力、高温稳定性、疲劳耐久性,具有防止反射裂缝和低温防裂的性能。能够较好地改善沥青混合料的路用性能,该材料在沥青混凝土中作用巨大,已经被工程界所认识和应用。     

扩展准则对混凝土裂缝黏聚区特性的影响

以无限大平板中心拉伸裂缝模型为例,分别基于强度准则和韧度准则,利用级数展开法获得了断裂过程区特性。结果表明,不同裂缝扩展准则对黏聚区长度、裂缝张开位移及黏聚力分布均具有一定的影响。相比强度准则,采用韧度准则的临界黏聚区长度有所减小。临界黏聚区长度及裂缝张开位移均随韧度增大而逐渐减小,黏聚力随韧度增大而逐渐增大。     

水泥砼路加铺沥青混凝土面层的探析

在旧水泥混凝土路面加铺沥青面层是目前比较普遍的城市道路改造方法,但由于其基层的特殊性,出现反射性裂缝在所难免。文章对基层的修复处理、加铺沥青面层施工的要点以及抑制和延缓反射性裂缝产生的若干方案进行了比较分析,以期对提高加铺工程质量、减少道路病害提供参考。     

水泥混凝土路面延长使用寿命的设计探讨

本文通过河南省许尉高速公路AC/ CC复合路面的设计,探讨了影响水泥混凝土路面及其AC复合路面设计使用寿命的诸多因素,及该路设计中采取的措施,对提高混凝土路面设计使用寿命提供了有价值的思路和借鉴.     

评价高强油井管抗应力腐蚀开裂性能的MTS试验技术

系统介绍了MTS材料试验机在评价油井管抗应力腐蚀开裂性能领域中的应用。通过实测双悬臂梁试样(DCB)加载-卸载柔度闭环曲线可以建立卸载柔度系数与裂纹长度的对应关系,实现了在疲劳预裂时对DCB试样裂纹扩展的有效测控。此外,对硫化物应力腐蚀试验(SSC)后的DCB试样进行加载-楔劈移除-卸载控制与二次疲劳裂纹扩展,可获得楔劈加载的平衡载荷与SSC诱导裂纹扩展量,从而准确测定材料的K1SSC指标。     

Simulation of top-down crack propagation in asphalt pavements

Top-down crack in asphalt pavements has been reported as a widespread mode of failure.A solid understanding of the mechanisms of crack growth is essential to predict pavement performance in the context of thickness design,as well as in the design and optimization of mixtures.Using the coupled element free Galerkin (EFG) and finite element (FE) method,top-down crack propagation in asphalt pavements is numerically simulated on the basis of fracture mechanics.A parametric study is conducted to isolate the effects of overlay thickness and stiffness,base thickness and stiffness on top-down crack propagation in asphalt pavements.The results show that longitudinal wheel loads are disadvantageous to top-down crack because it increases the compound stress intensity factor (SIF) at the tip of top-down crack and shortens the crack path,and thus the fatigue life descends.The SIF experiences a process "sharply ascending—slowly descending—slowly ascending—sharply ascending again" with the crack propagating.The thicker the overlay or the base,the lower the SIF; the greater the overlay stiffness,the higher the SIF.The crack path is hardly affected by stiffness of the overlay and base.     

An adaptive finite element procedure for crack propagation analysis

INTRODUCTION The finite element method (FEM) has proved to be very well suited for the study of fracture mechanics. Nevertheless, modelling the propagation of a crack through a finite element mesh turns out to be difficult because of the modification of the mesh topology. Use of crack propagation laws based on stress inten-sity factor range is the most successful engineering application of fracture mechanics. The stress intensity factors are a very important parameter in fracture analys…     

断裂力学的工程应用

脆性破坏是零件失效的主要形式之一,传统的防脆断方法要么很保守要么照样产生脆性破坏.从断裂力学的角度讨论带裂纹体在实际工程中的应用.     

携表面割痕的压电陶瓷柱体裂纹前缘奇异行为

研究了同时处于机械与电学载荷之下的压电陶瓷柱体表面裂纹前缘的应力场和电位移场。求得了应力及电位移的奇异性阶数和相应的两个强度因子。     

Finite element model for linear-elastic mixed mode loading using adaptive mesh strategy

An adaptive mesh finite element model has been developed to predict the crack propagation direction as well as to calculate the stress intensity factors （SIFs）, under linear-elastic assumption for mixed mode loading application. The finite element mesh is generated using the advancing front method. In order to suit the requirements of the fracture analysis, the generation of the background mesh and the construction of singular elements have been added to the developed program. The adaptive remeshing process is carried out based on the posteriori stress error norm scheme to obtain an optimal mesh. Previous works of the authors have proposed techniques for adaptive mesh generation of 2D cracked models. Facilitated by the singular elements, the displacement extrapolation technique is employed to calculate the SIK The fracture is modeled by the splitting node approach and the trajectory follows the successive linear extensions of each crack increment. The SlFs values for two different case studies were estimated and validated by direct comparisons with other researchers work.     

Stress and Fracture Strength Analysis for Three-Way Pipes

l lgtroductionIt is well known that the safety of pipeline systemsfor transpofting oil or gas is very important in the oil orgas industry, and it will be a catastTophe if an accidentoccurs. Howevef, there are a lot of methods for ensuringthe safety of such pipeline systems, for instance,TopRAM program['] (TransCanada Pipeline RiskAssessment Model), IAP program['] (The integrityAssessment Program), In-line inspection tools for crackdetection in gas and liquid pipeline['l etc. The safety …     

Finite element simulation of stress intensity factors in elastic-plastic crack growth

INTRODUCTION The finite element method (FEM) has been widely employed for solving linear elastic and elas-tic-plastic fracture problems. The evaluation of stress intensity factors in 2D geometries by FEM is a tech-nique widely used for non-standard crack configura-tions. Basically, there are two groups of estimation methods, those based on field extrapolation near the crack tip (Chan et al., 1970; Shih et al., 1976) and those using the energy release when the crack propagates. However…     

Towards fully automatic modelling of the fracture process in quasi-brittle and ductile materials: a unified crack growth criterion

Fully automatic finite element （FE） modelling of the fracture process in quasi-brittle materials such as concrete and rocks and ductile materials such as metals and alloys, is of great significance in assessing structural integrity and presents tremendous challenges to the engineering community. One challenge lies in the adoption of an objective and effective crack propagation criterion. This paper proposes a crack propagation criterion based on the principle of energy conservation and the cohesive zone model （CZM）. The virtual crack extension technique is used to calculate the differential terms in the criterion. A fully-automatic discrete crack modelling methodology, integrating the developed criterion, the CZM to model the crack, a simple remeshing procedure to accommodate crack propagation, the J2 flow theory implemented within the incremental plasticity framework to model the ductile materials, and a local arc-length solver to the nonlinear equation system, is developed and implemented in an in-house program. Three examples, i.e., a plain concrete beam with a single shear crack, a reinforced concrete （RC） beam with multiple cracks and a compact-tension steel specimen, are simulated. Good agreement between numerical predictions and experimental data is found, which demonstrates the applicability of the criterion to both quasi-brittle and ductile materials.     

反复张力下V形切口圆条的表面裂纹的疲劳扩展

研究目的：在相同的反复张力下,研究V形切口圆条表面裂纹的疲劳扩展规律。研究方法：1.构建V形切口圆条模型（图1）,基于线性二次元将模型表面离散成一个个网格点（图2）;2.以AZ-6A-T5镁合金为例,利用J积分计算应力强度因数,利用NASGRO裂纹增长率模拟裂纹的疲劳扩展;3.通过研究不同的裂纹纵横比和对应的应力强度因数之间的相关性来研究裂纹的扩展。重要结论：1.在裂纹扩展时裂纹纵横比的初始值对断裂形状的发展有重要影响;2.裂纹纵横比对疲劳负荷寿命的作用比缺口半径更加明显;3.当裂纹前缘演变成一条直线形时可观察到不稳定的裂纹扩展;4.裂纹深度一定时,断裂纵横比越小,疲劳负荷寿命越短;5.当裂纹纵横比为0.6-0.7时,出现了不稳定的裂纹扩展。     

Solution of stress intensity factors of multiple cracks in plane elasticity with eigen COD formulation of boundary integral equation

The concept of eigen crack opening displacement (COD) can be defined as the COD of a crack in infinite plate under the tractions acting on the crack surface. By introducing this concept, the eigen COD formulation of boundary integral equation is proposed in this paper, together with the solution procedures for multiple crack problems in plane elasticity. With the proposed approach, the multiple crack problems can be solved with the conventional displacement discontinuity boundary integral equations in an it...