共查询到18条相似文献,搜索用时 687 毫秒
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混凝土断裂及亚临界扩展的细观机制 总被引:15,自引:1,他引:14
通过模型和三点弯曲断裂SEM试验,详细研究了混凝土断裂全过程及亚临界扩展的细观机理。结果表明:混凝土断裂是一个复杂的不规则过程,存在明显的亚临界扩展现象。混凝土亚临界扩展路径是曲折的,并非经典断裂力学假定的平直路径,混凝土亚临界扩展和临界失稳扩展呈现分形特征。用起裂断裂韧性iICK和分形等效断裂韧性feICK,来描述混凝土抵抗初裂和临界失稳扩展的能力。给出了考虑亚临界扩展弯折效应的混凝土亚临界扩展长度、混凝土起裂断裂韧性iICK和分形等效断裂韧性feICK,的计算表达式。计算表明:混凝土失稳断裂时的分形等效断裂韧性feICK ,与混凝土亚临界扩展的分维数D成正比。 相似文献
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《工程力学》2010,(9)
该文采用光弹贴片方法对最大尺寸为2500mm×600mm×200mm的混凝土四点剪切梁,Ⅰ-Ⅱ复合型裂缝起裂、稳定扩展直至失稳破坏全过程进行了系统的研究,通过照相机拍摄光弹贴片所显示的裂缝扩展全过程,得到了混凝土裂缝稳定扩展阶段完整而直观的观测结果。根据光弹贴片所显示的彩色条纹序列,测得了四点剪切荷载作用下裂缝尖端附近主应变场分布,得到了荷载-裂缝扩展量曲线。根据光弹贴片所观察的裂缝扩展长度?a,借助有限元计算了裂缝扩展过程中尖端应力强度因子的变化,并模拟断裂过程。结果表明,对于混凝土Ⅰ-Ⅱ复合型断裂,裂缝在失稳扩展前存在着明显的亚临界扩展,采用光弹贴片方法可有效地记录这一过程,而以往不考虑裂缝扩展量得到的断裂准则是偏于保守的。试验结果还表明,在裂缝起裂后,虽然加载方式仍为Ⅰ-Ⅱ复合型,但断裂类型已由Ⅰ-Ⅱ复合型退化为纯Ⅰ型断裂。 相似文献
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混凝土系列K判据及其临界曲面 总被引:2,自引:0,他引:2
K判据是断裂力学的常用判据,由于裂缝扩展形态可能是单一的,也可能是复合型的,故其相应判据式中的临界值Kc可能是一个临界值,一条临界曲线或一个临界面曲,对一种材料而言,临界曲面及其相应的三维断裂判据式是最全面的,二维断裂临界曲线及一维断裂临界点为其特殊的退化情况。本文用一种单边裂缝方形混凝土试件进行了各种单一型和复合型断裂破坏试验,由大量试验数据得出了一个全面的混凝土系列K判据及其相应的临界曲面,曲 相似文献
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用能量方法研究混凝土断裂过程区的力学性能 总被引:1,自引:1,他引:0
准脆性混凝土自由裂缝前缘断裂过程区的发展与其非线性断裂特征及尺寸效应现象密切相关。它的物理力学行为的量化分析对理解混凝土断裂破坏机理和建立适用于混凝土结构裂缝稳定分析和安全评估断裂准则尤为重要,一直是混凝土断裂力学研究的核心问题。该文依据Hillerborg给出的断裂能定义,给出了计算单位长度断裂过程区发展能量耗散的通用表达式。以三点弯曲梁为例,采用非线性软化本构关系,进一步给出了计算此平均能量耗散的具体步骤及对应的公式。在根据实测的三点弯曲梁的断裂能回归拟合了特征裂缝张开位移w0后,计算了每个试件整个断裂全过程中不同荷载时刻断裂过程区耗能的平均值。结果表明:随着裂缝扩展,断裂过程区能量耗散的变化和试件尺寸无关,可描述断裂过程区混凝土材料的力学性能。 相似文献
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主裂缝亚临界扩展所形成的虚拟裂缝区的粘聚力是影响混凝土断裂韧度尺寸相关性的重要因素。根据混凝土准脆性材料的断裂特性,建立了一种基于虚拟裂缝模型的求解混凝土等效断裂韧度的实用解析方法。首先根据复合材料力学和线弹性断裂力学的基本原理,将虚拟裂缝的粘聚力作为相应的边界条件,运用修正的剪滞理论,分区引入变异层,建立了分层剪滞模型;然后根据能量法则,推导出求解混凝土等效断裂韧度的解析计算模式;最后针对相关试验的数值解,得到了混凝土等效断裂韧度的解析解。结果表明,对于不同的子层数,体积系列试件的混凝土等效断裂韧度均方差和变异系数分别低于0.0398和0.0384,高度系列试件的混凝土等效断裂韧度均方差和变异系数分别低于0.0394和0.0363,从而证明了混凝土等效断裂韧度是与试件尺寸无关的断裂参数;且与数值解相比,解析解的均方差和变异系数更小,证明了本文解析方法具有更好的鲁棒性。由此得出结论,基于虚拟裂缝模型所建立的解析模式为求解混凝土等效断裂韧度提供了一种可靠的、实用的解析方法。 相似文献
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该文将起裂断裂韧度作为裂缝扩展的判定依据,应用ANSYS软件,对全级配混凝土I型裂缝扩展过程进行数值模拟,分别计算了混凝土楔入劈拉试件的荷载-裂缝口张开位移曲线、临界裂缝长度和双K 断裂韧度,并与溪洛渡大坝的断裂试验结果进行比较,吻合良好。同时,结合试验数据,将该文计算结果与《水工混凝土断裂试验规程》规定的标准尺寸试件断裂参数计算结果进行对比。结果表明:规程规定的方法也适用于大尺寸非标准试件双K 断裂参数的计算,其误差率在5%以内。此外,对于全级配混凝土,只要通过试验测得其弹性模量、抗拉强度、抗压强度和起裂荷载,即可用该文提出的方法计算混凝土的双K 断裂韧度和裂缝扩展全过程。应用该方法还可以得到全级配混凝土的KR阻力曲线。 相似文献
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An experimental investigation on the FPZ properties in concrete using digital image correlation technique 总被引:2,自引:0,他引:2
ZhiMin Wu Hua Rong JianJun Zheng Feng Xu Wei Dong 《Engineering Fracture Mechanics》2011,78(17):2978-2990
This paper presents an experimental investigation on the properties of the fracture process zone (FPZ) in concrete using the digital image correlation (DIC) technique. Based on the experimental results, it is found that the FPZ length increases during crack propagation but decreases after the FPZ is fully developed. The FPZ length at the peak load and the maximum FPZ length increase with an increase in specimen height, but decrease by increasing the notch depth to specimen height ratio. It is also found that the crack extension length at the peak load is about 0.25 times the ligament length. 相似文献
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Experimental and numerical investigations on fracture process zone of rock–concrete interface 下载免费PDF全文
W Dong D Yang X Zhou G Kastiukas B Zhang 《Fatigue & Fracture of Engineering Materials & Structures》2017,40(5):820-835
A crack propagation criterion for a rock–concrete interface is employed to investigate the evolution of the fracture process zone (FPZ) in rock–concrete composite beams under three‐point bending (TPB). According to the criterion, cracking initiates along the interface when the difference between the mode I stress intensity factor at the crack tip caused by external loading and the one caused by the cohesive stress acting on the fictitious crack surfaces reaches the initial fracture toughness of a rock–concrete interface. From the experimental results of the composite beams with various initial crack lengths but equal depths under TPB, the interface fracture parameters are determined. In addition, the FPZ evolution in a TPB specimen is investigated by using a digital image correlation technique. Thus, the fracture processes of the rock–concrete composite beams can be simulated by introducing the initial fracture criterion to determine the crack propagation. By comparing the load versus crack mouth opening displacement curves and FPZ evolution, the numerical and experimental results show a reasonable agreement, which verifies the numerical method developed in this study for analysing the crack propagation along the rock–concrete interface. Finally, based on the numerical results, the effect of ligament length on the FPZ evolution and the variations of the fracture model during crack propagation are discussed for the rock–concrete interface fracture under TPB. The results indicate that ligament length significantly affects the FPZ evolution at the rock–concrete interface under TPB and the stress intensity factor ratio of modes II to I is influenced by the specimen size during the propagation of the interfacial crack. 相似文献
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The effect of acid corrosion on crack propagation of concrete beams was theoretically studied by the method of crack extension resistance curve. Based on this method, a calculation approach was proposed to determine fracture stress intensity factors in crack propagation of concrete beams. Loop iteration analysis was carried out to calculate maximum bearing capacity load, unstable crack toughness, resistance toughness curve, cohesive toughness curve and load–crack mouth opening displacement. Both bilinear and nonlinear softening traction–separation curves were adopted for each of these calculation parameters. The analysis results of each showed the effect of acid corrosion degrees. The influence of acid corrosion on fracture properties was discussed through the calculated results of cohesive toughness curves. These five kinds of simulated results were basically consistent, before the load attained the maximum value. However, with further crack propagation, cohesive toughness of nonlinear softening model was significantly larger than that of bilinear softening model, and the descending branch of P–CMOD curve by nonlinear law is higher than that by bilinear law. To validate the approach, tests of specimens under six different corrosion periods were experimentally studied, using three-point bending notched concrete beams soaked in sulphuric acid solution. The Double-K fracture parameters were investigated based on the test results, and load–crack mouth opening displacement curves for different acid conditions were obtained using synchronous sampling of a load sensor and clip-gauge. Numerical results by bilinear softening model showed a good correlation with the experimental ones. 相似文献
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In conventional analysis and design procedures of reinforced concrete structures, the ability of concrete to resist tension
is neglected. Under cyclic loading, the tension-softening behavior of concrete influences its residual strength and subsequent
crack propagation. The stability and the residual strength of a cracked reinforced concrete member under fatigue loading,
depends on a number of factors such as, reinforcement ratio, specimen size, grade of concrete, fracture properties, and on
the tension-softening behavior of concrete. In this work, a method is proposed to assess the residual strength of reinforced
concrete beams subjected to cyclic loading. The crack extension resistance based approach is used for determining the condition
for unstable crack propagation. The effect of reinforcement is modeled as a closing force counteracting the effect of crack
opening produced by the external moment. The effect of percentage reinforcement and specimen size on the failure of reinforced
beams is studied. Finally, the residual strength of the beams are computed by including the softening behavior of concrete. 相似文献
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This paper presents an extension of the recently-developed finite element–scaled boundary finite element (FEM–SBFEM) coupled method to model multiple crack propagation in concrete. The concrete bulk and fracture process zones are modelled using SBFEM and nonlinear cohesive interface finite elements (CIEs), respectively. The CIEs are automatically inserted into the SBFEM mesh as the cracks propagate. The algorithm previously devised for single crack propagation is augmented to model problems with multiple cracks and to allow cracks to initiate in an un-cracked SBFEM mesh. It also addresses crack propagation from one subdomain into another, as a result of partitioning a coarse SBFEM mesh, required for some mixed–mode problems. Each crack in the SBFEM mesh propagates when the sign of the Mode-I stress intensity factor at the crack tip turns positive from negative. Its propagation angle is determined using linear elastic fracture mechanics criteria. Three concrete beams involving multiple crack propagation are modelled. The predicted crack propagation patterns and load–displacement curves are in good agreement with data reported in literature. 相似文献