混凝土、纤维混凝土的Ⅰ型断裂

本文论述求混凝土、纤维混凝土试件在小于断裂荷载的外力作用下,裂纹的非线性扩展及如何用它来确定材料的断裂韧度。另介绍了作者提出的纤维混凝土的一般拉伸软化曲线及分析裂纹构件最大断裂荷载的有关方法。     

混凝土,纤维混凝土的I型断裂

本文论述求混凝土，纤维混凝土试件在小于断裂荷载的外力作用下，裂纹的非线性扩展及如何用它来确定材料的断裂韧度，另介绍了作者提出了纤维混凝土的一般拉伸软化曲线及分析裂纹构件最大断裂荷载有关方法。     

岩石与混凝土I—Ⅱ复合型界面裂缝临界断裂曲线的研究

用杂交元计算了双材料试件界面裂缝的应力强度因子，采用梁型试件及坝型试件，通过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，试验表明，坝型试件的Ｋｉｃ值较梁型试件的ＫＩＣ大。     

全级配混凝土I型裂缝扩展全过程数值模拟

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K_R阻力曲线。     

混凝土受拉断裂的破坏机理

本文从试验现象出发,建立了以数理统计为基础的混凝土受拉全过程曲线方程。研究表明,混凝土受拉应力应变全曲线是混凝土试件内部的粘结界面与水泥胶合物在外拉力作用下逐步断裂造成的。文章所建立的方法不仅可以解释许多试验现象,模拟混凝土受拉全曲线,而且还可以得出试验中难以测出的结果。     

基于裂缝扩展准则的K_R阻力曲线研究

根据混凝土I型裂缝扩展准则,将起裂断裂韧度作为材料参数,提出了一种新的计算混凝土结构裂缝扩展过程KR阻力曲线模型。该模型认为,裂缝扩展阻力由混凝土材料固有的抗裂能力和粘聚力提供的阻力组成并等于裂缝扩展的驱动力;应用该模型并借助有限元法计算了混凝土三点弯曲梁、楔入劈拉试件的裂缝扩展量、断裂过程区（FPZ）长度,在此基础上...     

混凝土I型裂缝扩展准则比较研究

针对混凝土I型裂缝扩展问题,分别采用以起裂韧度为参数的裂缝扩展准则、最大拉应力准则以及裂尖处应力强度因子为零的裂缝扩展准则,数值模拟了强度等级C20、C40、C60、C80和C100的混凝土三点弯曲梁裂缝扩展全过程,获取了试件的荷载-裂缝口张开位移(P-CMOD)曲线并与试验结果进行了比较。结果表明,三种准则中以起裂韧度为参数的裂缝扩展准则计算得到的峰值荷载及P-CMOD全曲线与试验结果差别最小。随着混凝土强度等级的提高,最大拉应力准则以及裂尖处应力强度因子为零的裂缝扩展准则计算出的P-CMOD曲线与试验结果相比均有较为明显的偏离,但以起裂韧度为参数的裂缝扩展准则计算结果与试验曲线更为吻合。试验与计算结果表明,以起裂韧度为参数的裂缝扩展准则更适用于不同强度混凝土材料的断裂分析。     

确定混凝土开裂与拉伸强度及双K断裂参数

该文考虑混凝土材料的非均质特性,发展了确定无尺寸效应的混凝土开裂强度与起裂韧度、拉伸强度与断裂韧度等材料参数的断裂理论与相应方法。基于三点弯曲、楔入劈拉、四点弯曲等不同类型混凝土试件的断裂试验,确定出对应的开裂强度与起裂韧度、拉伸强度与断裂韧度等材料参数,并与试验强度值及由双K断裂模型确定的双K断裂参数进行了比较,从而验证了所提模型与方法的合理性与适用性。基于确定的材料参数,分别建立了混凝土起裂与断裂破坏的全曲线,给出了确定无尺寸效应起裂韧度的混凝土试件最小理论尺寸。建立了起裂荷载与起裂韧度之间的解析公式,对三点弯曲、楔入劈拉、四点弯曲等不同类型混凝土试件的起裂荷载,以及不同混凝土的起裂韧度进行了成功预测。     

混凝土单轴拉伸的应变软化行为及描述

本文将试件和试验机置于一个系统中，对混凝土单轴拉伸试验的稳定性条件进行了分析并得到了单轴拉伸应变软件条件下部分的稳定平衡路径，结果表明，软化曲线的形状不仅与材料性质有关，还与试验机刚度和试件尺寸有关，此时不应将混凝土的软化性质单纯视为材料特性，在不同的软化阶段，应采用不同的模型表达，本文还将理论曲线与试验结果进行了比较，在软化段初上降部分模型结果与实验曲线符合较好。     

国外材料与测试文摘——碳钢储罐的约束修正J-R曲线的测定

为了研究基于断裂力学约束理论的材料断裂特性．对储罐材料A285碳钢进行了力学性能试验，设计了一组裂纹尖端约束水平不同的单边缺口弯曲(SENB)试样用于试验。裂纹尖端约束的大小变化是通过改变初始裂纹长度和试样宽度的比例达到的。试验数据表明J-R曲线取决于试样的设计情况，即受到通常所熟知的约束效应影响。约束修正J-R曲线的建立是采用了两参数断裂方法，即当J作为加载参数时，A2是约束参量的个函数。这个     

Cohesive crack modelling of a simple concrete: Experimental and numerical results

Fracture tests were performed on six types of simple concrete made with two types of mortar matrix w/c = 0.32 and w/c = 0.42, two types of spherical aggregates (strong aggregates that debonded during concrete fracture, and weak aggregates, able to break), and two kinds of matrix-aggregate interface (weak and strong).The tensile strength, fracture energy and elasticity modulus of the six types of concrete were measured. These results are intended to serve as an experimental benchmark for checking numerical models of concrete fracture and for providing certain hints to better understand the mechanical behaviour of concrete.A bilinear softening function was used to model the fracture of concrete. The influence of the type of matrix, aggregate, and interface strength on the parameters of the softening curve are discussed: particularly, the fracture energy, the cohesive strength and the critical crack opening.     

混凝土断裂过程区长度计算方法研究

该文基于粘聚裂缝概念,以起裂韧度作为裂缝起裂和扩展的准则,提出了混凝土断裂过程区长度的计算方法。以Ⅰ型裂缝为例,计算了不同初始缝长和起裂韧度情况下的断裂过程区长度值,结合以往大体积混凝土的试验数据对其进行了验证。进而分析了断裂过程区长度的影响因素,结果表明：断裂过程区长度随初始缝长的增大而逐渐增大,随起裂韧度的增大而逐渐减小。     

Large-scale testing on specific fracture energy determination of dam concrete

The specific fracture energy of dam concrete is a basic material characteristic needed for the prediction of concrete dam behavior. Data on fracture properties of dam concrete are quite limited to date. A series of tests was carried out based on the size effect due to a number of geometrically similar notched specimens of various sizes. Experimental tests include three-point bending tests. The specimens were of square cross section with a span to depth ratio of 2/5. Three different specimens with depth of 200, 400 and 800 mm were considered for the purpose of testing. Concrete mixtures are provided from the Caroon 3 dam project site using river gravel or commonly crushed stones from quarries. To compare the fracture properties of dam concrete with normal concrete five types of concrete mixes of 65, 50, 40, 30 and 20 mm maximum aggregate size were considered. For all mixes, value of relative notch depth of 0.2 is used. Experimental results show that aggregate size has an important effect on specific fracture energy values of dam concrete. According to specific fracture energy definition based on size effect, the specific fracture energy of concrete mixes of 65, 50, 40, 30 and 20 mm M.S.A. are 178, 129, 88, 79 and 72 N/m, respectively. This indicates that the high specific fracture energy of dam concrete is the result of the nature, size and properties of its aggregate. The difference between specific fracture energy of normal and dam concrete should be noticed in nonlinear analysis of concrete dams.     

Micromechanical fracture modeling of asphalt concrete using a single-edge notched beam test

Cracks in asphalt pavements create irreversible structural and functional deficiencies that increase maintenance costs and decrease lifespan. Therefore, it is important to understand the fracture behavior of asphalt mixtures, which consist of irregularly shaped and randomly oriented aggregate particles and mastic. A two-dimensional clustered discrete element modeling (DEM) approach is implemented to simulate the complex crack behavior observed during asphalt concrete fracture tests. A cohesive softening model (CSM) is adapted as an intrinsic constitutive law governing material separation in asphalt concrete. A homogenous model is employed to investigate the mode I fracture behavior of asphalt concrete using a single-edge notched beam (SE(B)) test. Heterogeneous morphological features are added to numerical SE(B) specimens to investigate complex fracture mechanisms in the process zone. Energy decomposition analyses are performed to gain insight towards the forms of energy dissipation present in fracture testing of asphalt concrete. Finally, a heterogeneous model is used to simulate mixed-mode crack propagation.     

The Fragmentation of Standard Concrete Cylinders During the Compressive Testing

The paper alternatively discusses the concrete cylinder compressive test. Basically, the fracture is treated as a single comminution process. After compressive testing, the main concrete debris as well as the samples of fine-grained particles, including grain-size distribution and grain shape, are analyzed. The fine-grained samples are distributed according to a R(osin)-R(ammler)-S(perling)-distribution. The distribution parameters depend on the mechanical properties of the concrete. The shpae factor increases as the compressive strength increases. Generally, with an increase in the strength properties, the fracture becomes non-regular due to a ‘homogenization’ of the fracture process. This revised version was published online in August 2006 with corrections to the Cover Date.     

Nondestructive Techniques for Studying Fracture Processes in Concrete

Some laboratory nondestructive evaluation techniques have been invaluable in studying fracture processes in concrete. Several nondestructive evaluation methods including acoustic emission (AE), computer vision, digital speckle pattern interferometry (DSPI), and X-ray microtomography (XMT) were used to examine the fracture behavior of concrete in tension and compression. Acoustic emission testing was used in an attempt to characterize the fracture properties of individual microcracks. As the specimens were loaded, AE waveform data was recorded, and analyzed for source location and source characterization. While DSPI analysis is limited to the specimen surface, the resolution is detailed such that microcracks on the order of 0.25 μm can be detected. Computer vision is a very useful method to measure crack openings for multiple crack development. It also can be used in conjunction with a hydraulic testing machine, which often generates vibration problem for some sensitive techniques. Crack patterns in cement-based materials under various material compositions and testing conditions are examined. This revised version was published online in July 2006 with corrections to the Cover Date.     

基于虚拟裂缝模型的混凝土断裂过程区研究

利用虚拟裂缝模型对混凝土断裂过程区进行了研究.以无限大板中心拉伸裂缝模型为例,将过程区裂缝张开位移采用多项式级数形式表示,求得了断裂过程区上的位移分布和粘聚力分布.进而分析了材料参数对断裂过程区上的位移、粘聚力、断裂过程区长度以及峰值外荷载的影响.结果表明：断裂过程区上的位移和粘聚力均为非线性分布.断裂过程区长度随骨料最大粒径增大而逐渐增大,随抗压强度增大而逐渐减小.峰值外荷载随骨料最大粒径和抗压强度增大均逐渐增大.     

Strength of a half space weakened by a plane circular crack

The methods of the mechanics of brittle fracture and the theory of generalized cleavage fracture are used for the approximate solution of the problem of strength of a half space weakened by a plane circular crack. A simplified computational scheme is proposed for the evaluation of the fracture load in the case of free (tensile) fracture. The results of theoretical investigations are experimentally confirmed by testing concrete specimens. __________ Translated from Problemy Prochnosti, No. 6, pp. 122–132, November–December, 2006.