钢衬钢筋钢纤维混凝土压力管道非线性有限元分析

针对钢衬钢筋混凝土压力管道在运行期因裂缝过宽导致的结构耐久性问题,在混凝土中掺入体积率分别为0.5%、1.0%、1.5%、2.0%的钢纤维形成钢纤维混凝土,基于模型试验获得的钢纤维混凝土的拉伸软化曲线,采用大型数值分析平台ABAQUS仿真分析了钢衬钢筋钢纤维混凝土压力管道受力开裂的全过程,并与原钢衬钢筋混凝土压力管道的模型试验结果进行了对比分析。结果表明,在相同内水压力荷载下,钢衬钢筋钢纤维混凝土压力管道的承载能力与普通钢衬钢筋混凝土压力管道相比,不仅其初裂荷载有所提高,管道的最大裂缝宽度明显降低,钢材的应力值也随钢纤维体积率的增加而减少。     

基于二维多向固定裂缝模型的钢筋混凝土梁开裂过程模拟

作为一种准脆性材料,钢筋混凝土开裂是一个复杂的非线性问题。基于二维多向固定裂缝模型,运用DIANA软件对钢筋混凝土三点弯曲梁进行数值模拟。结果表明,在梁内无钢筋、有钢筋、钢筋加密三种条件下的混凝土变形和裂缝扩展过程均可被有效模拟;钢筋的横截面积越大,裂缝的宽度越小,变形结果符合相关理论,且裂缝扩展和分布情况符合实践经验。说明二维多向固定裂缝模型适用于钢筋混凝土结构的开裂模拟。     

基于混凝土三维CT重构氯离子扩散过程数值模拟

近年来,氯盐导致钢筋混凝土结构耐久性失效问题,氯离子破坏钢筋表面的钝化膜,加速了钢筋的锈蚀,同时裂缝的存在促进了氯离子的扩散,从而形成了恶性循环。基于混凝土三维CT重构技术,建立了湿-热-氯盐-裂缝多场耦合的氯离子扩散数值模型,研究了裂缝宽度、深度、等效裂缝形式对混凝土内氯离子分布的影响。结果表明,裂缝宽度促进了氯离子的扩散,但裂缝中氯离子浓度不与裂缝宽度成正比,裂缝宽度对氯离子浓度分布影响随着裂缝宽度的增加在减弱。裂缝深度对钢筋表面氯离子浓度具有显著影响,在诸多因素中起控制作用,采用楔形裂缝形态模拟氯离子在混凝土中分布与实际情况较吻合。     

水电站蜗壳结构设计参数H与D值影响敏感性分析

在HD值相同的条件下，改变H值和D值，应用三雏有限元程序对蜗壳结构进行线性和非线性分析，以研究H值和D值对蜗壳结构受力特性影响的敏感性。得出参数敏感性的影响规律是，随D值减小（H值增大），钢衬和混凝土的应力呈增大趋势，钢衬承载比逐渐增大，裂缝宽度和范围减小；当D值较大时，腰线处混凝土应力和钢筋应力分布规律与传统相反，即外侧应力大于内侧。故当HD值相同、H值较小、D值较大时，应增加钢筋量，且在腰线处外侧配筋大于内侧。     

钢-PVA纤维混凝土早龄期力学性能及弹性模量研究

为研究钢-PVA纤维混凝土早龄期力学性能，将钢纤维和PVA纤维掺入混凝土中，测试早龄期力学性能和弹性模量发展变化规律。结果表明，钢-PVA纤维可以提高混凝土早龄期力学强度，其中轴拉强度增幅最大，受拉弹性模量次之，轴压强度增幅最小；此外，钢-PVA纤维还可以提高早龄期轴拉峰值应变，改善混凝土脆性。根据试验结果提出了钢-PVA混凝土早龄期力学强度计算模型，并与试验值比较，验证了所建模型的有效性。     

钢衬壁厚对抽蓄电站围岩内水压力分担率的影响

根据实际工程需要,采用FLAC3D数值模拟软件通过改变钢衬壁厚,分析了不同设计内水压力组合条件下,钢衬、混凝土垫层和围岩的位移和变形特征及钢衬环向拉应力,研究了引水钢衬壁厚对围岩内水压力分担率的影响。结果表明,随着壁厚增大,虽可相应减少钢衬径向位移和环向拉应力,但减幅小,效果不显著;随着壁厚变小,钢衬径向位移变大,根据变形协调,有助于荷载传递,提高了围岩分担率,有利于"钢衬-垫层-围岩"联合承载;在满足抗外压稳定验算、焊接工艺和施工安装前提下,壁厚可较大幅减小。研究成果不仅有利于减少不必要的投资,还有利于降低硐室钢衬运输安装等施工难度,可供类似工程设计参考。     

应变率效应对混凝土力学性能影响的细观仿真分析

针对混凝土结构在使用过程中经常会遭遇动荷载作用且作为一种率敏感性材料的动态力学性能将直接影响结构的承载力问题,从细观层次出发,结合试验实测的混凝土各组分静动态应力—应变曲线,拟合了混凝土各组分不同应变率下的本构模型,采用自主开发的混凝土非线性有限元软件,对混凝土试件轴拉试验细观数值进行了仿真,探讨了混凝土抗拉强度、弹性模量随应变率的变化规律。结果表明,混凝土抗拉强度和弹性模量均随应变率的增加而增加,但弹性模量的率敏感性低于抗拉强度的率敏感性,且计算结果与试验结果相吻合。     

高混凝土重力坝抗震配筋效果的模型试验研究

提出了高碾压混凝土重力坝抗震配筋试验的基本思路,选择了合适的模型试验材料,给出了模型试验设计比尺、观测点位置及振动台地震波输入范围,做了有无配筋情况下的混凝土构件试验及钢筋混凝土的动、静弹性模量试验.利用加固后坝体不同的仿真混凝土弹模比做了挡水坝段模型的起裂加速度对比试验.结果表明,满库情况下挡水坝段的起裂位置有所不同,不同配筋率的抗震钢筋对坝体起裂加速度的影响较小,抗震钢筋的存在对抑制初始裂缝的产生并无显著作用.     

压力隧洞钢筋混凝土衬砌开裂数值模拟研究

立足于直接求解压力隧洞设计所关注的衬砌裂缝条数和裂缝宽度,同时考虑混凝土衬砌的开裂、钢筋的作用、钢筋与混凝土间的粘结滑移以及围岩的作用,建立了压力隧洞钢筋混凝土衬砌开裂的数值模型,并编制了相应的计算程序。采用该计算程序对压力隧洞钢筋混凝土衬砌开裂问题进行数值模拟研究,分析了钢筋量、围岩条件对裂缝条数和裂缝宽度的影响,并着重与现行规范进行对比分析。结果表明,所建模型能反映压力隧洞钢筋混凝土衬砌作为地下结构的受力特性;围岩条件对裂缝条数和宽度均有明显影响;压力隧洞钢筋混凝土衬砌限裂的关键在于改善围岩条件,不宜盲目加大钢筋量。该研究结果对压力隧洞工程实践具有一定的指导价值。     

韦水倒虹钢筋混凝土管钢筋锈蚀成因分析

混凝土中的钢筋锈蚀主要与其所处环竟有关,经过对韦水倒虹钢筋混凝土管钢筋锈蚀原因分析,认为韦水倒虹钢筋混凝土管钢筋锈蚀主要原因为:钢筋保护层厚度、钢筋混凝土管周围温度及湿度、运用条件、混凝土裂缝宽度等。针对造成钢筋锈蚀的原因,提出了工程处理措施。     

大坝背管混凝土裂缝前馈网络的预测研究

基于人工神经网络的BP网络方法和全局优化方法的基本理论,对坝后背管外包混凝土结构裂缝预测进行了研究,提出了基于神经网络的管道混凝土裂缝预测模型,并重点研究了水头的变化对压力管道混凝土最大裂缝宽度的影响,最后对三峡电站压力管道混凝土结构裂缝进行了预测。     

Thermal Stresses Around Two Collinear Interface Cracks between a Nonhomogeneous Bonding Layer and One of the Two Dissimilar Elastic Half-Planes Under Uniform Heat Flux

In composite materials, in which two dissimilar elastic half-planes are bonded by a nonhomogeneous elastic layer, two collinear cracks are situated at the interface between the nonhomogeneous elastic layer and one of the two dissimilar half-planes. The stress intensity factors are solved under uniform heat flux normal to the cracks. The material properties of the bonding layer vary continuously from the lower half-plane to the upper half-plane. The boundary conditions are reduced to dual integral equations using the Fourier transform technique. In order to satisfy the boundary conditions outside the cracks, the differences in temperature and displacements at the crack surfaces are expanded in a series of functions that vanish outside the cracks. The unknown coefficients in each series are evaluated using the Schmidt method. The stress intensity factors were calculated numerically for selected crack configurations.     

用Ansys有限元程序分析水工钢筋混凝土隧洞结构

采用Ansys有限元分析水工钢筋混凝土隧洞结构，通过建立有限元模型来模拟水工隧洞衬砌钢筋混凝土结构的实际工作状态，了解结构的应力分布、裂缝宽度和钢筋混凝土衬砌中钢筋的工作状态，从而可以有针对性地提高水工隧洞钢筋混凝土结构设计的安全性与可靠性。     

Parametric study on interfacial crack propagation in solid oxide fuel cell based on electrode material

Interfacial delamination is one of the typical failure modes of solid oxide fuel cell, which is caused by interfacial crack propagation. In order to improve the stability, durability and mechanical integrity of the cell, the influence of electrode material properties on the interfacial crack propagation is studied. Based on a large number of experimental data, the material model of anode and cathode adopts approximate linear model and the different material optimization schemes are set by changing the material parameters, i.e., the ratio of elastic modulus and thermal expansion coefficient between electrode and electrolyte. The crack energy release rate and crack propagation length are taken as important objective functions to compare the extent of interfacial crack propagation under different material optimization schemes. The internal relationship between electrode material parameters and interfacial crack propagation behavior is analyzed, and the optimization scheme of electrode material is obtained to reduce the possibility of delamination in the cell. This research provides guidance for the improvement of stability and integrity of solid oxide fuel cell.     

CRACK PROBLEMS FOR FUNCTIONALLY GRADED MATERIALS UNDER TRANSIENT THERMAL LOADING

The problem considered in this article is the response of a graded composite material plate containing some noncollinear cracks subjected to dynamic thermal loading. It is assumed that all the material properties depend only on the coordinates y (along the thickness direction) . In the analysis, graded regions are treated as a series of perfectly bonded composite layers, each layer being assigned slightly different material properties. Utilizing the Laplace transform and Fourier transform techniques, the general solution for each layer is derived. The complete solution of the entire medium is then obtained by introducing the mechanical boundary and layer interface conditions. The main features of the proposed method are: (1) the material may be orthotropic, (2) multiple crack problem, (3) the material properties may vary arbitrarily along the thickness direction, and (4) with the inertial terms taken into account, the present algorithm can be applied to a fracture problem under dynamic mechanical loading. Numerical examples are provided for a FGM and a substrate FGM coating structure under a nonuniform heating condition. Transient and steady-state thermal stress intensity factors are calculated and their variation due to a change of the material gradient and the location of the crack are studied.     

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.     

Thermal Stresses Around Two Parallel Interface Cracks Between a Nonhomogeneous Bonding Layer and Two Dissimilar Elastic Half-Planes Under Uniform Heat Flux

Composite materials consisting of two dissimilar elastic half-planes bonded by a nonhomogeneous elastic layer contain two interface cracks; one is situated at the lower interface between the layer and the lower half-plane, while the other is situated at the upper interface between the layer and the upper dissimilar half-plane. The stress intensity factors are solved under uniform heat flux normal to the cracks. The material properties of the bonding layer vary continuously from the lower half-plane to the upper half-plane. The boundary conditions are reduced to dual integral equations using the Fourier transform technique, and they are satisfied outside the cracks by expanding the differences in temperature and displacements at the crack surfaces using a series of functions that vanish outside the cracks. The unknown coefficients in each series are evaluated using the Schmidt method. The stress intensity factors were calculated numerically for selected crack configurations.     

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.