岩石与混凝土界面裂缝断裂准则及断裂能的

对梁型试件进行试验研究得到了岩石与混凝土Ⅰ-Ⅱ复合型界面裂缝的临界断裂曲线方程;并对三点弯曲梁测出荷载-位移全曲线,计算出断裂能GF.     

混凝土Ⅰ、Ⅱ复合型裂纹断裂准则及其尺寸效应的试验研究

本文用三点弯曲试件和四点加荷试件对混凝土Ⅰ、Ⅱ复合型断裂进行了试验研究,试验结果表明:混凝土的临界断裂曲线与最大拉应力准则相符,K_(IC)存在尺寸效应,但断裂时的K_Ⅰ/K_(IC),K_Ⅱ/K(IC)不存在尺寸效应.     

粘性土断裂准则的地表裂缝深度计算

基于断裂力学理论对基坑开采引起的地表裂缝发育规律进行研究;在分析已有的多种粘性土断裂准则的基础上,对土体的Griffith-Mohr联合断裂准则进行简化,并提出了开采地表裂缝最大深度的计算公式。     

弧形坡脚梯形渠道砼衬砌冻胀破坏断裂力学模型及应用

为给实际弧形渠道冻胀设计提供一种简单有效的计算方法,应用材料力学方法对渠道砼衬砌冻胀问题进行合理简化,建立了弧形坡脚梯形渠道砼衬砌冻胀力学模型,并在该模型基础上引入断裂力学,将砼衬砌板断裂视为(Ⅰ+Ⅱ)复合型(张拉型+剪切型)裂缝扩展问题,并利用已有的断裂准则,建立弧形坡脚梯形渠坡、渠底两个部位的冻胀断裂力学模型。实例应用结果表明,所建模型计算的砼衬砌板厚度满足抗冻胀要求,且与实际情况相吻合。     

滑塌式危岩体剪切断裂过程中的启动分析

为判断滑塌式危岩体主控结构面断裂扩展方向和稳定性,在分析压剪复合裂纹尖端应力场的基础上,运用断裂力学,建立压剪裂纹的最大剪应力断裂判据,将岩石断裂问题与岩石Mohr-Coulumb破坏准则相联系,在裂纹端部压应力区建立基于Mohr-Coulumb准则的断裂判据。实例计算结果表明,两种断裂判据与已有的最大拉应力断裂判据结合使用,讨论其最不利稳定性,分析结果与极限平衡理论方法相吻合,并给出了裂纹端部破裂面发展方向。     

重力坝劈头裂缝成因分析

针对重力坝劈头裂缝已构成危害重力坝结构的安全,采用三维有限单元法对Deorshak重力坝劈头裂缝的成因进行仿真计算和探讨,得出坝体内外温差、缝面水压和材料断裂韧度的下降导致了裂缝的扩展,指出采取有效的工程措施可避免重力坝出现劈头裂缝.     

基于小波变换的某重力拱坝背水坡转异裂缝序列的分析

裂缝转异诊断对分析大坝安全稳定运行有重要意义。将小波变换应用于大坝裂缝转异分析中,并结合某重力拱坝背水坡裂缝X18-1的实测数据,分别从小波系数图的过零点和极值点、多尺度下模极大值线及奇异性变化角度讨论其与裂缝转异时刻的关系,最终综合判断出裂缝的转异时刻。分析结果表明,小波系数图、模极大值线和奇异性均可反映裂缝的转异,但各自独立的诊断结果不完全相同,综合分析可准确判定裂缝的转异时刻,为裂缝转异诊断提供了新思路。     

基于扩展有限元的非对称四点梁复合型开裂分析

针对裂纹在三维实体中沿曲线或曲折路径扩展问题,应用三维扩展有限元的基本原理,结合ABAQUS有限元分析软件和粘聚裂缝模型,对混凝土梁在荷载作用下的复合型开裂过程进行了数值模拟分析。模拟结果与试验资料对比分析结果表明,基于扩展有限元法的三维模型对裂纹路径具有较高的预测精度,能有效分析实际工程中的复杂断裂失效问题。     

不同配筋率对钢筋混凝土三点弯曲梁断裂韧度的影响

为深入了解配筋率对钢筋混凝土断裂韧度的影响,制作了3组12根带预制裂缝的钢筋混凝土三点弯曲梁并做了断裂试验,根据试验导出了钢筋混凝土三点弯曲梁试件断裂参数解析计算公式,分析了不同配筋率对钢筋混凝土三点弯曲梁断裂韧度的影响程度。结果表明,钢筋混凝土三点弯曲梁试件的开裂荷载主要由混凝土主体结构所决定,最大荷载主要由混凝土内部配置的钢筋情况所决定;裂缝亚临界扩展相对值随着配筋率的增加呈线性增加;配筋率的变化对失稳断裂韧度有一定影响,但对起裂断裂韧度影响不大;配筋率的增加,可有效提高试件的韧性和抵抗失稳破坏的能力。     

混合弹流润滑条件下风电行星直齿轮内啮合动态特性分析

当大型风力发电机在低速重载条件时,齿轮在混合弹流润滑条件下的啮合动态特性难以分析.针对该问题提出齿面接触并联刚度模型,建立行星齿轮啮合动力学模型.基于粗糙峰承载平衡理论,将承载因子理论引入刚度模型中,并与混合弹流润滑理论相结合,可得出计算齿面油膜刚度的新公式,为齿轮混合弹流润滑问题研究提供参考.通过计算结果,可认为在混...     

3-D elastic-plastic finite element analysis of interface cracks under mixed mode load

A three-dimensional finite element computation was performed for a throughedge cracked bimaterial steel specimen under mixed mode loadings in which the crack was lying on an interface between an elastic-plastic material and a perfectly rigid substratum. In order to take account of the average effect of microvoid nucleation and growth in the deformation, the modified Gurson's constitutive equation suggested by Tvergaard and Needleman was used. It was found that due to the interaction between the singularity along the crack front and that along the interface on the specimen surface, the distributions of stresses, plastic deformations, J-integral and void volume fraction in a bimaterial specimen were significantly different from those in a homogeneous specimen. Based on the numerical results on the distributions of void volume fraction and J-integral, the locations of fracture initiation in bimaterial and homogeneous specimens under mixed mode loadings are discussed.     

Analysis of an interface crack of arbitrary shape in a three-dimensional transversely isotropic magnetoelectrothermoelastic bimaterial—part 1: Theoretical solution

The extended displacement discontinuity boundary integral–differential equation method is developed for the analysis of an interface crack of arbitrary shape in a three-dimensional (3D), transversely isotropic magnetoelectrothermoelastic bimaterial. The extended displacement discontinuities (EDDs) include conventional displacement discontinuities, electric potential discontinuity, magnetic potential discontinuity as well as temperature discontinuity across the interface crack faces, correspondingly, while the extended stresses represent conventional mechanical stresses, electric displacement, magnetic induction, heat flux, etc. By virtue of the potential functions and Hankel transformation technique, the fundamental solutions for unit-point EDDs on the interface in a 3D transversely isotropic magnetoelectrothermoelastic bimaterial are derived, then the extended displacements and stresses are all obtained in terms of EDDs. An analysis method is proposed based on the analogy with the solution in an isotropic thermoelastic bimaterial. The singular indices and the singular behaviors of the near crack-tip fields are studied. The combined extended stress intensity factors for three new fracture modes are derived in terms of the EDDs and are compared with those in magnetoelectroelastic bimaterials.     

Two-dimensional finite element analysis of stably growing cracks in inhomogeneous materials

The finite element method was applied to a generation phase analysis for stable crack growth in inhomogeneous materials. Experimental data on stable crack growth in bimaterial CT specimens, which were made of a weldment of the A533B Class 1 steel and HT80 steel, were numerically simulated using the node-release technique to obtain the variations of the fracture mechanics parameters such as the J-integral, T^*-integral, -integral and CTOA with crack extension. New evaluation schemes for the integral fracture mechanics parameters were proposed as being valid for integral paths passing a fusion line of dissimilar materials. It was examined whether the simple formulae of the J-integral for a monolithic CT specimen can be applied to a bimaterial CT specimen or not. The effect of inhomogeneity on the fracture mechanics parameter is discussed in terms of the Q-factor.     

A sub-interface thermal crack problem for bonded dissimilar plates with interfacial thermal resistance

The present work aims to investigate the effect of interfacial thermal resistance on thermal fracture behavior of bonded and composite materials. We consider a sub-interface crack parallel to the interface between two semi-infinite dissimilar plates subjected to remote heat flux thermal loading. A constant thermal resistance is assumed to exist along the interface. The temperature distribution along the crack, the thermal stress intensity factors (TSIFs), and the crack opening/sliding displacements (COD/CSD) are obtained using an integral transform/superposition method. The numerical results for Al₂O₃/Si₃N₄ bimaterial systems show that the magnitude of the mode I TSIF generally decreases with increasing thermal resistance of the interface but increases with increasing thermal resistance for cracks that are very close to the interface. On the other hand, the model II TSIF increases with increasing thermal resistance if the crack is in the Al₂O₃ semi-infinite plate, and decreases if the crack is in the Si₃N₄ semi-infinite plate. The COD/CSD are also significantly influenced by the thermal resistance of the interface.     

Further applications of variable singularity boundary elements in the study of neighbouring singularities

The application of two new variable singularity boundary elements (BEs) in the solution of interaction of neighbouring singularities is presented. The first element can model the variable order strain and traction singularities at one end of the element. The second element can simulate the variable strain and traction singularities at both ends of the element simultaneously. These elements are employed for the computation of stress intensity factors in crack–crack interaction problems. To improve the accuracy of such computations a modified crack closure integral (MCCI) method is adopted. To illustrate the usefulness of these elements in the study of neighbouring singularities, a number of examples are presented including, Z-shaped crack, multiple kinked surface crack, multiple edge cracks, interaction of a microcrack with a cross-shaped crack at a bimaterial strip.     

Circumferentially Cracked Bimaterial Hollow Cylinder Under Mechanical and Transient Thermal Loading

The analytical solution for the problem of a circumferential inner surface crack in an elastic, infinitely long composite hollow cylinder, made of two concentric perfectly bonded transversely isotropic cylinders is considered. Uniform axial loading and thermal loading in the form of a sudden cooling on the inner boundary are considered. Out of 10 material parameters involved, two bimaterial parameters and three material parameters for each layer upon which the stress intensity factor depends under uniform loading, are identified. The problem is reduced to a singular integral equation that is solved numerically. Stress intensity factors are presented for various values of material and geometric parameters.     

MODELING OF THERMAL CRACKING IN ELASTIC AND ELASTOPLASTIC TWO-PHASE SOLIDS

A review is given about fracture mechanical investigations concerning the thermal crack initiation and propagation in one of the segments or in the material interface of two-arid three-dimensional self-stressed two-phase compounds. The resulting boundary value problems of the stationary thermoelasticity and thermoplasticity for the cracked two- and three-dimensional bimaterial structures considered are solved using the finite element method. Furthermore, by applying an appropriate crack growth criterion based on the numerical calculation of the total energy release rate G of a quasistatic mixed-mode crack extension the further development of thermal crack paths starting at the intersection line of the material interface with the external stressfree surface of the two- and three-dimensional elastic bimaterials could be predicted. In the case of the disklike two-phase compounds, the theoretically predicted crack paths show a very good agreement with results gained by associated cooling experiments. Several specimen geometries consisting of different material combinations and subjected to uniform and nonuniform temperature distributions have been studied using the relevant methods of fracture mechanics. Thereby thermal cracks propagating in one segment of an elastic bimaterial only obey the condition G_II = 0, whereas for interface cracks a mixed-mode propagation is always existent where the G_II values play an important role. Moreover, by applying the proposed crack growth criterion the possible crack kinking direction ? of an interface crack tip out of the interface could be predicted by taking into consideration the finite thickness of an interlayer (interphase). In addition, an analysis of the stress and strain fields in the vicinity of thermal interface cracks in the discontinuity area of two- and three-dimensional elastoplastic two-phase compounds has been performed by using the FE-method. Thereby a heat source Q was assumed in one of the two materials in the neighborhood of an interface crack tip. The corresponding stress states in the bimaterial structuresand especiallyin the vicinity of the interface crack tip have been calculated by applying the incremental I₂-plasticity and using a bilinear hardening material law and based on a sequentially coupled solution of the heat transfer and the thermal stress boundary value problems. Finally, the failure assessment has been performed on the basis of the local J-integral which, for three-dimensional interface cracks, was recently generalized by two of the authors.     

Three-dimensional thermal weight function method for the interface crack problems in bimaterial structures under a transient thermal loading

Different from previous two-dimensional thermal weight function (TWF) method, a three-dimensional (3D) TWF method is proposed for solving elliptical interface crack problems in bimaterial structures under a transient thermal loading. The present 3D TWF method based on the Betti's reciprocal theorem is a powerful tool for dealing with the transient thermal loading due to the stress intensity factors (SIFs) of whole transient process obtained through the static finite element computation. Several representative examples demonstrate that the 3D TWF method can be used to predict the SIFs of elliptical interface crack subjected to transient thermal loading with high accuracy. Moreover, numerical results indicate that the computing efficiency can be enhanced when dealing with transient problems, especially for large amount of time instants.     

ON THE EVALUATION OF THE FREE-EDGE STRESS INTENSITY FACTORS FOR A JOINT SUBJECTED TO A UNIFORM CHANGE IN TEMPERATURE

A contour integral is applied to the evaluation of the stress intensity factors at interface corners of bimaterial joints subjected to a uniform change in temperature. In order for the contour integral to work for the free-edge stress intensity factors, closed-form solutions for the stress and displacement fields near interface corners of bimaterial joints subjected to a uniform temperature change are derived. The derivation is based on the hypothesis that the two dissimilar materials, which are bonded along their common interface, experience identical rigid body displacements. Accordingly, the asymptotic displacements are continuous along the interface irrespective of the rigid body displace ments near the interface corner. A case study is carried out for a problem where the combination between the material properties and the geometry at the interface corner is such that the stresses at the interface corner are comprised of several stress fields of the form Hr     

Fracture analysis of adhesive joints in wind turbine blades

Modern wind turbine rotor blades are usually made from fibre‐reinforced composite subcomponents. In the final assembly stage, these subcomponents are bonded together by several adhesive joints. One important adhesive joint is situated at the trailing edge, which refers to the downstream edge where the air‐flow rejoins and leaves the blade. Maintenance inspections of wind turbine rotor blades show that among other forms of damage, local debonding of the shells along the trailing edge is a frequent failure type. The cause of trailing edge failure in wind turbine blades is complex, and detailed information is scarce. This paper is concerned with the fracture analysis of adhesive joints in general, with a particular focus on trailing edges. For that, the energy release rates in prescribed cracks present in the bond line of a generic trailing edge joint are investigated. In connection with this examination, the paper elucidates the influence of geometrical non‐linearity in form of local buckling on both the increase of the energy release rate and the change of mode mixity. First, experimental results on adhesively bonded small‐scale subcomponents are presented. Thereafter, a practical approach is presented, which links the experimental results conducted on a small scale to the numerical failure prediction of large‐scale models. The proposed method is based on the virtual crack closure technique and defines the mode mixity at bimaterial interfaces unambiguously. The method is consequently applied to a wind turbine blade submodel in order to predict crack growth in the trailing edge. Thereby, the influence of different crack lengths on crack initiation and propagation is considered. The paper concludes with general thoughts on adhesively bonded trailing edge joints regarding the prevention of local debonding. Copyright © 2014 John Wiley & Sons, Ltd.