【作者】 万成；

【导师】 张肖宁；

【作者基本信息】 华南理工大学 ， 结构工程， 2010， 博士

【摘要】 沥青混合料是由集料、沥青砂胶和空隙三部分组成,这三部分的体积组成及沥青砂胶的粘弹特性,使得沥青混合料的力学性能十分复杂,在实际工程当中加载频率、加载幅度以及环境的变化更加剧了这种复杂性。利用X-ray CT(X-ray Computerized Tomography),结合数字图像和数值模拟技术针对传统沥青混合料研究方法的局限性,从微细观尺度研究混合料结构对其性能的影响,进行沥青混合料内部结构分析和沥青混合料力学性能虚拟试验即数值试验是近年来国内外研究热点。但是纵观国内外对沥青混合料的微细观研究,绝大部分的研究工作主要集中在以下两个方面:(1)沥青混合料内部结构的定量或定性分析;(2)基于试样的一个或几个二维截面,结合数字图像处理技术建立二维数值模型进行力学模拟。研究明显具有局限性,而基于实际试样真实三维微细观分布模型的力学数值试验的研究更是屈指可数,主要是因为在模型三维重构和力学数值模拟时遇到重重困难,而这两点又正好是实现沥青混合料虚拟试验模拟计算成功的关键之所在。本文尝试不仅定性地,而且定量地解决上述难题。根据沥青混合料三维重构原理,把握从三维可视化模型向三维数值模型转化的本质特点,深入分析问题的难点所在:三维数值试样重构,提出了基于CT技术对沥青混合料进行三维数值重构算法,自行开发程序建立三维数值试样。三维模型重构后,最重要的一步是选择能恰当反映沥青砂胶粘弹特性的本构模型。本论文在系统阐述沥青混合料的粘弹性本构关系理论的基础上,讨论了沥青混合料粘弹本构关系的有限元实现。采用动态剪切流变仪对沥青砂胶进行蠕变试验,通过不同应力水平下的蠕变试验,建立了模型参数与加载应力函数关系,得到Burgers模型蠕变方程一般表达式,分析模型参数对蠕变过程的影响。目前对单轴蠕变的数值模拟时建立的模型为连续均质体,很难真实地模拟实际情况。本论文基于试件的真实微细观分布建立三维数值模型,对FAC-13混合料的粗型、中等粗型和细型三种不同级配的数值试件进行单轴静载蠕变数值模拟。模拟在相同温度和荷载条件下,三种不同级配的变形响应,模拟结果真实反映了不同试样的变形响应,与实际试验结果一致。为了更进一步验证上述方法和程序的可行性,结合室内间接拉伸试验,采用X-ray CT对FAC-13试件进行扫描,进行间接拉伸数值试验。模拟在低温快速加载条件下试件的受力分布状态,定性评价应力分布的不均匀性;对试件进行间接拉伸动态模量数值试验,研究3个不同温度、6个不同荷载频率下试件动态模量的变化,并与实际试验结果相比较进行验证,验证了整个方法和程序切实可行。更多还原

【Abstract】 Asphalt mixture is composed of aggregates, sand matrix and air voids. volume compositions of three parts and viscoelastic properties of sand matrix make the mechanical properties of asphalt mixture complex. In practical engineering field, loading frequency, loading magnitude, and environment change exacerbate complexity. Because of the limitation of traditional methods, combining with digital image processing and numerical simulation technology, X-ray CT(X-ray Computerized Tomography) was used to study the microstructure of asphalt mixture for analyzing internal structure of asphalt mixture. Virtual mechanics test namely digital test was performed as hot research focus at home and abroad in recent years.However, the most research about microstructure of asphalt mixture focused on following two aspects: (1) quantitatively or qualitatively analyzing the internal structure of asphalt mixture; (2) Based on one or several two-dimensional cross-sections of specimen, combining with digital image processing technology , two-dimensional numerical model was established for mechanics simulation. It is obvious that the research is limited. Oppositely, The research about digital test based on the model for real three-dimensional micro-samples is few, mainly because it is difficult for reconstructing three-dimensional model and mechanical numerical simulation, these two points are the key to achieve a virtual test.This paper attempts to challenge the research limits, not only qualitatively but also trying to solve the problem quantitatively. According to principles of three-dimensional reconstruction of asphalt mixture, grasping the essential characteristics from three-dimensional visualization model transformation to three-dimensional numerical model, analyzing difficult problems in-depth: three-dimensional reconstruction of digital specimen. Based on CT technology, numerical reconstruction algorithm was proposed and program was developed for reconstructing digital specimen. After three dimensional model reconstruction, the most important step is choosing appropriate constitutive model that reflecting viscoelastic properties of asphalt sand matrix. On this basis the viscoelastic constitutive relationship of asphalt mixture was systematically expounded and FEM realization of viscoelastic constitutive of asphalt mixture was discussed. Using Dynamic Shear rheometer (DSR), creep test of sand matrix was conducted. Through different stress level creep test, the relationship between model parameters and loading stress function was established. Creep equation general expression of Burgers model was obtained and impact for the model parameters on creep process was analyzed.Currently, most reconstruction model for uniaxial creep of numerical simulation is continuous homogeneous, which is difficult to simulate actual situation. After model reconstruction based on real microcosmic distribution of specimen, uniaxial static load creep numerical simulation of digital specimen was conducted for three different gradations of FAC-13: fine, middle course and coarse gradation. The purpose of simulation is to reflect different deformation response of three different gradations. The simulation results truly reflected actual experimental results.To further verify the feasibility of the methods and program, combining with indoor indirect tensile test, X-ray CT was used to scan the FAC-13 specimen. Under low-temperature and rapid loading conditions, digital test of indirect tensile test was conducted for evaluating inhomogeneity of stress distribution qualitatively;Under three different temperatures and six different frequencies conditions, digital test of dynamic modulus was conducted. The simulation results were compared with actual experimental results. It was found that the whole methods and procedures were validated practical.更多还原