【作者】 田威；

【导师】 党发宁； 丁卫华；

【作者基本信息】 西安理工大学 ， 岩土工程， 2009， 博士

【摘要】 混凝土类岩土材料的破裂过程,是一个复杂的非线性材料损伤演化过程,一直是力学、材料和工程等各学科的研究热点和难点之一。破裂过程主要表现在材料内部初始缺陷能量积聚,微裂纹不断萌生,扩展、贯通直至整体失稳的过程,其宏观表现为材料力学性能的不断劣化。本文将细观力学、损伤力学、统计理论和数值计算理论相结合,运用可以有效观测材料细观损伤演化的CT技术对混凝土材料裂纹的扩展、贯通以及最后破坏的过程进行研究,以此来分析混凝土的裂纹扩展及破坏形态,揭示出混凝土材料的损伤破裂机理,本文的研究工作可以总结为以下几个方面：(1)详细介绍了最新研制的便携式CT实时动态加载设备的组成,技术指标及其特点,该仪器是国内最新为CT试验配套的动态实时加载设备,可以实现动态加载,尤其是能进行动力拉伸试验。并利用最新研制的便携式CT实时动态加载设备开展混凝土静、动力实时CT试验。(2)以混凝土材料的静力压缩、动力压缩、静力拉伸、动力拉伸的CT图像为研究对象,充分利用CT扫描信息,提出了多种CT图像、CT数分析方法,并对混凝土材料的细观损伤破裂过程进行研究,得到混凝土材料在静力压缩、动力压缩、静力拉伸、动力拉伸时的破坏特点。(3)依据CT裂纹演化规律,对混凝土破坏阶段进行分类。并利用同一断面不同应力阶段的两幅CT图像进行差值运算,通过差值图像中的低密度带表现为环状或线状影像来判断裂纹是否开裂。(4)根据混凝土破坏过程所处的阶段,对混凝土材料进行了分区描述,定义了混凝土材料的安全区、损伤区、破损区,对分区的CT阈值标准进行了探讨和经验选定。在此标准下,对CONC-10试样的扫描断面进行分区,并对各个分区上混凝土CT数随加载过程的变化规律以及破损区产生的条件进行研究。(5)利用分形理论方法,以混凝土静力压缩、动力压缩CT图像为研究对象,估算出不同扫描断面不同应力阶段的CT图像分形维数,并且在VB和MATLAB语言的基础上进行了程序可视化的开发。通过分维数的变化分析混凝土材料在静力压缩、动力压缩条件下的细观损伤演化过程。(6)本文通过总结前人依据混凝土CT试验建立的损伤本构模型,结合本文的分析结果,对混凝土的损伤变量和损伤本构模型做了进一步研究。基于混凝土损伤演化特性的细观CT试验,运用不同的方法定义了混凝土材料不同的损伤变量,并建立了相应的损伤演化方程。并以CT数变化建立的分段损伤演化方程为代表建立了损伤本构关系。将密度损伤(CT数变化)变量为基础建立的混凝土损伤演化方程和损伤本构关系与宏观力学性能的劣化相联系。(7)采用以CT数变化建立的损伤本构关系进行静载作用下混凝土试件单轴受压试验的细观数值试验。并将混凝土数值试验结果与CT试验结果进行详细的比较和分析,实现了采用细观上的简单本构关系模拟宏观上复杂的破裂现象,为改进试验设计提供力学依据,并使在可靠和有效的前提下用数值方法取代部分试验成为可能。(8)本文直接从CT扫描的数据入手,进行图像的三维重建研究。运用Matlab环境下CT切片图像的三维体重建和MIMICS环境下CT切片图像的三维重建两种不同的方法对混凝土三维细观结构进行重建,以期待可以得到混凝土真实的细观结构。利用CT试验三维重建模型进行了混凝土破裂过程的细观数值模拟,以便与CT试验结果相比较,从而校正数值分析模型。更多还原

【Abstract】 The fracture process of Concrete category in the geotechnical materials, a complex non-linear evolution of the material damage, has been one of hot issues and diffcult reasearch in the field of the mechanical, materials and engineering. In the breakdown process of material, it was the manifestations that internal energy accumulation of the initial defects, and micro-crack continually initiating and expanding till the overall instability, which were performed as constant deterioration of mechanical properties in the macroscopic. In this paper, combined with meso-mechanics, the damage mechanics, statistical theory and numerical theory, the process was researched which included the expanding cracks, finally through and the destruction of concrete material by CT technology which is a effective means of observing meso-damage evolution, so that the concrete cracks expanding and damage patterns were analyzed, and the breakdown mechanism of concrete materials was revealed. In this paper research work was summarized as follows:(1)The composition of the portable latest developed CT load equipment the, the technical indicators and their characteristics were introduced detailed. The instrument is the lastest domestic equipment which supports real-time dynamic load for CT test, using which dynamic loadingand particularly dynamic tension test especially could be achieved. And the static and dynamic real-time CT test were carried out using newly developed portable concrete testing machine(2)Studying CT images of concrete materials including static compression, dynamic compression, static tension and dynamic tension and making full use of the CT scans information, various analysis methods of CT image and CT number were put forward for the meso-damage process investigation of concrete materials, and the fracture characteristics of the concrete material in static compression, dynamic compression, static tension and dynamic tension were obtained.(3)Based on CT crack evolution laws, the damage stageof concrete was classified. At the same time,the D-value of the two CT images on the same cross-section in different stress phase were operated, and the low-density of D-value image would determine the crack whose shape was ring or linear.(4)According to the concrete failure stage, the concrete materials were distinctly described to define the safe zone, damage zone and fracture zone of concrete materials, and the CT threshold criteria on the partition was discussed and selected empirically. In this standard, the scanned cross-section of CONC-10 sample was zoned to study the change regulation and the conditions resulting in fractured zones of concrete CT number with loading process on each partition.(5)Using fractal theory, and concrete CT images of static compression and dynamic compression were acted as the research objects to estimate the fractal dimension of different scanning sections CT images in different stress stages, and based on the VB and MATLAB language, the Program of was visually developed. Through changes of fractal dimension, the meso-damage evolution process of concrete materials was analyzed in the static compression and dynamic compression.(6)In This paper, concrete damage constitutive model assembled by previous based on CT tests were summarized, combining the analysis results in this paper, the damage variables and damage constitutive model were further researched. Based on the meso-CT test characterized by Concrete damage evolution, different ways were applied to define different damage variables of concrete material and to establish the corresponding damage evolution equation. Based on the damage evolution equation created as CT change, a constitutive relation was created to assosiate the damage evolution equation based on to the density damage (CT number changes) and the constitutive relation with the degradation of macro mechanical properties.(7)The damage constitutive relation due to CT changes was used to numerical simulation of concrete in static uniaxial compression. Numerical test results of concrete were analyzed detailedly and compared with CT test results. A simple meso constitutive relation was applied to simulate the complex failure phenomena of macro and to provide mechanical basis for improving test design.At the same time, that maked it possible that the numerical method replaces of some tests in a reliable and effective premise.(8)In this paper, the CT scan data was directly acted as start point to carry out the research on three-dimensional reconstruction of images. Three-dimensional concrete meso-structure was reconstructed by using the method of three-dimensional reconstruction of CT image slice applied Matlab and MIMICS to get the real concrete meso-structure.更多还原