基于细观力学的颗粒类路面材料堆积行为与骨架结构研究

发布时间：2018-09-13 14:06

【摘要】：沥青混合料由离散刚性集料和连续黏性介质组成,从体积组成来看,沥青混合料中集料占绝大部分,约占总体积的90%,属于典型的颗粒体系。合理的集料体积组成不仅可以改善沥青混合料的力学性能,也可以协调沥青混合料多相复合材料的复杂行为。从细观角度上看,集料颗粒随机地分散在沥青砂浆介质中,颗粒自身的物理力学性质、颗粒间嵌挤、摩擦作用等都对沥青混合料的力学性质产生显著影响。而现有的沥青混合料设计方法多基于连续介质理论以及宏观现象学试验分析方法,忽略了对集料及其细观结构进行系统的研究与分析。本文借助颗粒物质理论,主要利用数值模拟方法并结合室内试验,对颗粒路面材料细观结构和力学特性开展研究。首先,基于颗粒物质理论,分析集料间的摩擦、接触、嵌挤等细观相互作用机制建立了离散集料贯入试验细观模拟的PFC3D模型,讨论了模型细观参数与宏观贯入力之间的关系,结果表明贯入力对颗粒摩擦系数和孔隙率的敏感性要远大于颗粒接触刚度比,模拟试验结果与已有的室内试验结果吻合性良好。其次,基于逐级填充理论,建立多级填充的颗粒数值模型,分析连续级配和间断级配集料混合物的力学响应和细观演化规律,结合CBR和VCA的指标评价集料骨架嵌挤密实状态,并提出较优的级配组成。最后,统计分析随机堆积模型得到的初始颗粒体结构,在重力荷载作用下的离散动态计算以后,单一粒径散粒体的平均配位数随空隙率的减小而增加,混合粒径球形散粒体的平均配位数变化范围很小,基本保持常数,与文献实测结果吻合,表明文章所提出的数值计算方法能够较好的模拟颗粒体在重力场内的堆积行为。并在此基础上,分析贯入试验过程中集料混合物的细观力学响应,观察力链结构网络图和平均配位数的变化过程,通过颗粒位移矢量场的变化得到集料颗粒内部的迁移演化规律。研究表明,文章借助PFC3D平台的研究方法能够方便有效的观察颗粒类路面材料堆积行为和骨架稳定过程,为进一步研究复杂形状的颗粒迁移与力链稳定等行为奠定基础。
[Abstract]:Asphalt mixture is composed of discrete rigid aggregate and continuous viscous medium. In volume composition, aggregate accounts for most of the asphalt mixture, accounting for about 90% of the total volume, which is a typical particle system. Reasonable aggregate volume composition can not only improve the mechanical properties of asphalt mixture, but also coordinate the complex behavior of multiphase composite material of asphalt mixture. From a meso point of view, aggregate particles are randomly dispersed in the medium of asphalt mortar, the physical and mechanical properties of the particles themselves, intergranular squeezing, friction and so on have a significant impact on the mechanical properties of asphalt mixture. However, most of the existing design methods of asphalt mixture are based on continuum theory and macro phenomenological experimental analysis method, and neglect the systematic research and analysis of aggregate and its mesoscopic structure. In this paper, with the help of particle material theory, numerical simulation method and laboratory test are used to study the microstructure and mechanical properties of granular pavement materials. Firstly, based on the theory of granular matter, the PFC3D model for mesoscopic simulation of discrete aggregate penetration test is established by analyzing the mechanism of mesoscopic interaction such as friction, contact and extrusion between aggregates, and the relationship between the mesoscopic parameters of the model and the macroscopic penetration force is discussed. The results show that the sensitivity of penetration force to particle friction coefficient and porosity is much greater than that of particle contact stiffness ratio. Secondly, based on the theory of step by step filling, the numerical model of multi-stage filling particles is established, and the mechanical response and meso-evolution law of continuous and discontinuous gradation aggregate mixtures are analyzed. Combined with the indexes of CBR and VCA, the compaction state of aggregate skeleton is evaluated. The optimal gradation composition is also proposed. Finally, after statistical analysis of the initial particle structure obtained by the random packing model, after the discrete dynamic calculation under the action of gravity load, the average coordination number of the single particle size particle increases with the decrease of the porosity. The variation range of average coordination number of spherical granular particles with mixed particle size is very small, which is consistent with the measured results in literature. It shows that the numerical calculation method proposed in this paper can well simulate the stacking behavior of particles in the gravity field. On this basis, the mechanical response of aggregate mixture during penetration test is analyzed, and the variation process of the structure network diagram and the average coordination number of the observed force chain is analyzed. The internal migration and evolution of aggregate particles are obtained by the change of particle displacement vector field. The research results show that the method of PFC3D platform can be used to observe the stacking behavior and skeleton stability process of granular pavement materials conveniently and effectively, which lays a foundation for further study on the behavior of particle migration and force chain stability of complex shapes.
【学位授予单位】：长安大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：U414

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