基于PFC3D的沥青混合料虚拟试验研究

发布时间：2018-01-10 07:34

本文关键词：基于PFC3D的沥青混合料虚拟试验研究　出处：《东南大学》2015年硕士论文　论文类型：学位论文

【摘要】：沥青混合料是一种各向异性多相复合材料,具有与温度相关的复杂物理力学特性,在宏观尺度上分析沥青混合料内部结构的受力、变形等特点与机理较为困难。离散元凭借其处理非连续介质、材料大变形问题等方面的优势,可以模拟沥青混合料室内试验的细观结构。因此,本文基于离散单元法对沥青混合料进行从低温到高温的室内试验性能研究,从细观力学角度分析沥青混合料高低温及疲劳性能,主要步骤如下：首先,由集料级配、油石比以及空隙率推导出每档粗集料(2.36mm以上集料)占虚拟试件的体积分数和沥青砂浆(2.36mm以下集料、矿粉与沥青组成)的密度计算公式,集料预先以等粒径的球单元投放到虚拟试件中,再以矿料间隙率校核集料的体积分数,提取校准后的几何信息作为生成多面体集料的初始参数,在不规则多面体集料生成算法基础上,结合室内试件空隙的实际分布,进行沥青混合料三维结构的数字重构,生成与室内试验尺寸相同的沥青混合料三维离散元虚拟试件。其次,根据试验温度和破坏模式选取合适的细观接触模型,设计沥青砂浆试验获取细观参数。由沥青砂浆劈裂试验以及单轴蠕变试验获取不同温度下的宏观弹性与粘弹性参数,并验证Burgers粘弹性模型的温度和荷载适用区间,由宏观与细观参数的转化关系获得沥青砂浆内部单元、沥青砂浆与集料单元之间、集料单元之间的细观参数。最后,模拟沥青混合料低温断裂试验,观察试件的开裂与裂缝扩展特征,分析三点弯曲小梁试件的内在断裂机理和影响因素；模拟四点弯曲疲劳试验,观察试件内部应力应变实时变化状态,分析疲劳开裂机理,分析不同级配对虚拟疲劳寿命的影响；模拟缩减时间下的单轴蠕变试验,其中蠕变试验的一二阶段采用无损伤的Burgers粘弹性模型模拟,针对第三阶段的蠕变损伤是通过引入损伤因子实现材料参数的衰减,从而引起材料的劣化,最后实现蠕变损伤。结果表明：集料体积分数、砂浆的粘结强度、温度、细观接触模型、加载应力、加载方式等对沥青混合料的高低温以及疲劳性能均有显著影响。
[Abstract]:Asphalt mixture is an anisotropic multiphase composite with complex physical and mechanical properties related to temperature. The internal structure of asphalt mixture is analyzed on macroscopic scale. The characteristics and mechanism of deformation are difficult. Discrete element can simulate the mesoscopic structure of asphalt mixture in laboratory test by virtue of its advantages in dealing with discontinuous medium and large deformation of materials. In this paper, based on discrete element method, the indoor performance of asphalt mixture from low temperature to high temperature is studied, and the high and low temperature and fatigue properties of asphalt mixture are analyzed from the point of view of meso-mechanics. The main steps are as follows: first. The volume fraction of coarse aggregate above 2.36 mm per grade and the aggregate below 2.36 mm of asphalt mortar are derived from aggregate gradation, oil stone ratio and void ratio. The density calculation formula of mineral powder and asphalt), the aggregate is put into the virtual specimen with the equal diameter ball unit in advance, and then the volume fraction of aggregate is checked with the mineral aggregate clearance rate. The geometric information after calibration is extracted as the initial parameter to generate polyhedron aggregate. Based on the algorithm of generating irregular polyhedron aggregate, the actual distribution of the void in indoor specimen is combined. Digital reconstruction of 3D structure of asphalt mixture is carried out to generate 3D discrete element virtual specimen of asphalt mixture with the same size as indoor test. Secondly, appropriate mesoscopic contact model is selected according to test temperature and failure mode. The macro elastic and viscoelastic parameters at different temperatures were obtained from asphalt mortar splitting test and uniaxial creep test. The temperature and load applicable range of Burgers viscoelastic model were verified. The internal units of asphalt mortar and the units of asphalt mortar and aggregate were obtained from the transformation relationship between macro and meso parameters. Finally, simulate the low-temperature fracture test of asphalt mixture, observe the crack and crack propagation characteristics of the specimen, analyze the internal fracture mechanism and influencing factors of three-point bending trabeculae. The four point bending fatigue test was simulated to observe the real time variation of stress and strain, to analyze the mechanism of fatigue cracking, and to analyze the effect of different grades on virtual fatigue life. Uniaxial creep tests were simulated under reduced time, in which one and two stages of creep tests were simulated by Burgers viscoelastic model without damage. In view of the creep damage in the third stage, the material parameter is attenuated by introducing the damage factor, which leads to the deterioration of the material and finally the creep damage. The results show that the volume fraction of aggregate and the bond strength of mortar are obtained. Temperature, meso contact model, loading stress and loading mode have significant effects on the high and low temperature and fatigue properties of asphalt mixture.
【学位授予单位】：东南大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：U414

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