Abstract:
In order to obtain the relationship between the acoustic emission process and fracture evolution of concrete material, the concept of relevant fractal function of acoustic emission process is given .The existence of fractal characteristics of acoustic emission process is proved through experiments firstly. Then. The variation tendency of relevant fractal dimensions in the fracture process of material is analyzed by three-point bending test of concrete specimen. The identification pattern of fractal characteristics for critical fracture is determined. The results show that the acoustic' emission process of concrete material is of obvious fractal characteristics, and the different fractal characteristic parameters of acoustic emission in the critical state show some "identification pattern" which can be used to identify the characteristics of critical fracture.

Abstract:
细观结构特性是混凝土材料最重要的特性之一，细观结构参数的改变直接影响混凝土弹性模量、抗拉抗压强度等宏观力学性能变化．首先采用混凝土随机骨料模型进行混凝土细观数值试验，将混凝土看成由骨料、水泥砂浆以及两者之间的界面过渡区(ITZ)组成的三相复合材料，并在水泥砂浆中引入不同孔径、孔隙率的孔隙，使用有限元分析软件MSC.Marc，通过数值试验研究了孔径、孔隙率对混凝土抗拉抗压强度和弹性模量的影响规律．试验结果表明 混凝土弹性模量在同一孔径下随着孔隙率的增长呈线性下降，在同一孔隙率下随着孔径增大呈对数下降；混凝土抗拉抗压强度随着孔隙率和孔径增大呈对数下降．其次，将数值试验结果与经验公式进行了对比，验证数值试验结果的正确性．最后，根据数值试验结果，建立了混凝土初始损伤与孔隙率和孔径之间的关系，描绘了细观尺寸下混凝土的初始损伤面，为建立混凝土细观结构参数和宏观力学特性之间的联系，改善混凝土的力学性质打下了基础． Microscopic structure characteristic is one of the most important behaviors of concrete. The change of microscopic structure parameters affects the macroscopic mechanical behaviors of concrete, such as the elastic modulus, the tensile and compressive strengths. Firstly, the numerical experiment of concrete is carried out with the random aggregate model. The concrete material is discretized as the three-phase composite material with aggregate, cement mortar and the interfacial transition zone (ITZ) and the void element with different porosity ratio and pore diameter is introduced to simulate the porosity of concrete. Using the finite element analysis software MSC. Marc, the specimens are simulated numerically to study the effects of porosity ratio and pore diameter on the elastic modulus, the tensile and compressive strengths of concrete. Experimental results show that the concrete elastic modulus decreases linearly with the increasing porosity ratio at the same pore diameter and decrease logarithmically with the increasing pore diameter at the same porosity ratio. The tensile and compressive strengths of concrete decrease logarithmically with the increasing porosity ratio and pore diameter. Secondly, the numerical results and the empirical formula are compared to verify the correctness of the numerical experiment results. Finally, according to the numerical experiment results, the relationship between the initial damage and the porosity ratio and the pore diameter of concrete is established and the initial damage surface of concrete is depicted on the micro-scale, which lays a foundation for establishing the relationship between the microstructure parameters and the macroscopic mechanical properties of concrete, and improving the mechanical properties of concrete in the future.

Abstract:
the experimental results of testing structures or structural parts are limited and, sometimes, difficult to interpret. thus, the development of mathematical-numerical models is needed to complement the experimental analysis and allow the generalization of results for different structures and types of loading. this article makes two computational studies of reinforced concrete structures problems found in the literature, using the finite element method. in these analyses, the concrete is simulated with the damage classical model proposed by mazars and the steel by a bilinear elastoplastic constitutive model. numerical results show the validity of the application of constitutive models which consider the coupling of theories with the technique of finite element discretization in the simulation of linear and two-dimensional reinforced concrete structures.

Abstract:
【目的】在线弹性断裂力学的基础上，对高地下水位弧底梯形混凝土衬砌渠道冻胀断裂破坏力学模型进行研究，为弧底梯形衬砌渠道的设计提供依据。【方法】将高地下水位弧底梯形渠道混凝土衬砌简化为简支梁结构并建立其冻胀力学模型，在考虑材料本身缺陷的基础上结合断裂力学理论，提出了高地下水位弧底梯形渠道冻胀断裂破坏力学模型。运用断裂力学及结构力学等相关理论，考虑法向冻结力的作用，通过适当的简化计算弧底梯形渠道衬砌的相关内力，并提出适用于弧底梯形渠道衬砌的断裂力学破坏准则，利用计算实例对所建立的渠道冻胀断裂破坏力学模型进行验证。【结果】渠道衬砌板的冻胀断裂符合Ⅰ-Ⅱ复合型裂纹的特点，通过建立的弧底梯形渠道混凝土冻胀断裂力学模型，可以计算出渠道阴坡、阳坡、渠底的衬砌板厚度。计算实例证明，所建立的高地下水位弧底梯形渠道冻胀断裂破坏力学模型正确可行、简单实用。【结论】弧底梯形混凝土衬砌渠道优于梯形渠道，是一种冻胀力及冻胀变形较小的结构形式。 【Objective】Based on the liner elastic fracture mechanics,this study explored the frost heave fracture damage mechanical model of arc bottom trapezoidal concrete lining channel at the high underground water level,aimed provide to improve the design of arc bottom trapezoidal channel lining.【Method】The concrete lining of high groundwater level arc bottom trapezoidal channel was simplified for the simply supported beam structure and established the frost-heaving mechanical model.Considering the defect of material and combining with the fracture mechanics theory presenting the high groundwater level arc bottom trapezoidal channel frost-heaving fracture damage mechanical model.Using the theory of the fracture mechanics and structural mechanics and considering the normal freezing force,relevant internal forces of arc bottom trapezoidal channel lining were calculated through appropriate simplification and the failure criterion suitable for fracture mechanics of arc bottom trapezoidal channel lining was proposed.The frost heaving fracture mechanical model was also evaluated using numerical example.【Result】Channel lining plate frost heave fracture fit the Ⅰ-Ⅱ complex style fracture,and the lining plate thickness of channel shady slope,sunny slope and channel bottom could be calculated using the established arc bottom trapezoidal channel concrete frost heaving fracture mechanical model.Calculation examples proved the frost-heaving fracture damage mechanical model for arc bottom trapezoidal channel at high groundwater level was correct practicable simple and useful.【Conclusion】Arc bottom trapezoidal concrete lining channel was structure with small frost heaving force and frost heave deformation was superior to the trapezoidal channel

Abstract:
We show that a length scale xi can be extracted from the spatial correlations of the "steep cliffs" that appear on fracture surface. Above xi, the slope amplitudes are uncorrelated and the fracture surface is mono-affine. Below xi, long-range spatial correlation lead to a multi-fractal behavior of the surface, reminiscent of turbulent flows. Our results support a unifying conjecture for the geometry of fracture surfaces: for scales > \xi the surface is the trace left by an elastic line propagating in a random medium, while for scales < \xi the highly correlated patterns on the surface result from the merging of interacting damage cavities.

Abstract:
Using a fractat model, we give a new interpretation of the reversed sigmoidal curves of fracture surface profile length obtained in some experiments. It is pointed out that a single parameter (fractal dimension D) is not sufficient to characterize a fractal curve completely. It is shown that the initiator length L0 is also important to characterize a fractal curve. We have derived a formula which correlate the fracture energy with the fractal parameters of the fracture surfaces and analyzed some experimental data.

Abstract:
对静力、动力拉伸荷载条件下混凝土的细观破损过程进行了CT试验研究，获得了试样内部裂纹萌生、扩展、贯通的全过程CT图像。通过对CT图像及图像兴趣区中整体统计区域、局部统计区域CT 数均值的分析，研究了混凝土拉伸荷载条件下细观破损过程。结果表明：静力拉伸荷载条件下，裂纹在界面的薄弱区域形成后逐渐往相邻的薄弱部位扩展,两个统计区域CT 数均值呈降低趋势，试样破坏时伴有少量骨料被拉断的现象；动力拉伸荷载条件下，裂纹从界面薄弱区域形成后追随最快的路径扩展，局部统计区域CT 数均值呈下降趋势,而整体统计区域CT数均值变化幅度较小，破坏后骨料沿界面脱离砂浆粘结，且试样破裂面更为平整；由于加载速率的提高，骨料被拉断的现象非常显著。 The real time scanning observation on meso damage process in concrete was carried out using CT technology. CT images of crack propagation，coalescence and failure were obtained under static and dynamic tension. Meso-damage mechanism of concrete under tension was analyzed the mean CT numbers in large statistical region small statistic region of scanning layers ROI.The results showed that the cracks developed in the interface of weak region and expanded to adjacent weak partsthe mean CT numbers of the two statistical regions showed decreasing trend. Parts of aggregates were ruptured when the concrete was damaged under static tension. While in small statistic region，the cracks developed in the interface of weak region and expanded along the fastest path，and the mean CT numbers showed a decreasing trend The mean CT numbers in large statistical region changed slightly. The aggregate divorced from mortar along interface，and the failure plane was smoother when the concrete was damaged under dynamic tension. So，the aggregate was ruptured obviously because the loading rate was higher.

Abstract:
By means of fractal analysis,the fractal dimension with relation to the impact toughness,im- pact fracture characteristics and mierostructures of steel under low temperature impact have been investigated.Experimental results show that the logarithms of impact toughness in- creases monotonically with the increase of fractal dimension.The microstruetures have a great influence on fraetal dimension.There is an appropriate correlation between fraetal dimension and fracture mechanism.

Abstract:
The study of human dynamics has attracted much interest from many fields recently. In this paper, the fractal characteristic of human behaviors is investigated from the perspective of time series constructed with the amount of library loans. The Hurst exponents and length of non-periodic cycles calculated through Rescaled Range Analysis indicate that the time series of human behaviors is fractal with long-range correlation. Then the time series are converted to complex networks by visibility graph algorithm. The topological properties of the networks, such as scale-free property, small-world effect and hierarchical structure imply that close relationships exist between the amounts of repetitious actions performed by people during certain periods of time, especially for some important days. Finally, the networks obtained are verified to be not fractal and self-similar using box-counting method. Our work implies the intrinsic regularity shown in human collective repetitious behaviors.

Abstract:
A damage-plasticity constitutive model for the description of fracture in plain concrete is presented. Two approaches, the local model comprising the adjustment of the softening modulus and the nonlocal model based on spatial averaging of history variables, are applied to the analysis of a concrete bar subjected to uniaxial tension and to a three-point bending test. The influence of mesh size and the decomposition into damage and plasticity components are discussed. It is shown that for the two examples studied, both approaches result in mesh-independent results. However, the nonlocal model, which relies on spatial averaging of history variables, exhibits sensitivity with respect to boundary conditions, which requires further studies.