【作者】 常明丰；

【导师】 陈拴发； 裴建中；

【作者基本信息】 长安大学 ， 道路与铁道工程， 2013， 博士

【摘要】 目前，对沥青混合料的研究主要集中于借助基于现象学的经验方法和室内试验，常用的连续介质模型适用于密集颗粒系统的准静态条件下分析和研究系统内部的力学特性，该模型并未考虑系统内各组成介质的尺寸效应。因此，基于连续介质方法和模型在分析由复合材料组成的沥青混合料时无法揭示细观结构与宏观性能之间的关系。然而，细观力学方法采用多尺度力学理论研究非均匀介质，并且沥青混合料在材料组成上属于颗粒物质材料，大量的试验测试和数值模拟发现颗粒物质体系具有对外界荷载的敏感性、非线性响应、自组织行为等精细力学特性，与连续介质理论和宏观表象结果存在本质区别。鉴于上述结果，使得借助细观力学方法和颗粒物质力学，构建沥青混合料的细观模型，并用于研究沥青混合料的细观响应有据可循。本文以沥青混合料的细观特性为主线，分析了荷载作用下集料、混合料结构的力链分布特征分析，构建沥青混合料数字试件进行间接拉伸试验的数值模拟，分析了沥青混合料细观力学特性的影响因素和试件内部的力链分布；挖掘沥青混合料试件内部结构，测定沥青混合料和砂浆的动态指标，为构建沥青混合料的细观模型提供细观粘弹性参数；监测试件内部的应力、应变随时间的变化，追踪加载过程中各相组分内部颗粒间接触力力链、位移场、速度场的分布随时间的演化，阐释集料与砂浆界面处的相互作用，以及内部组成与外部荷载、变形的关系。本文主要研究内容如下：(1)借助针对颗粒物质的光弹性应力试验和压痕试验分别检测集料颗粒间的力链，获取力链的分布规律；(2)基于离散元方法构建集料、混合料的细观模型，通过数值模拟得到相应的力链场和位移场，并构建沥青混合料数字试件，分析伺服加载条件下沥青混合料细观力学特性的影响因素和试件内部的力链演化；(3)以SGC(Superpave旋转压实)成型沥青混合料试件、以静压成型沥青砂浆试件，分别进行简单性能试验(Simple Performance Test，SPT)，测定不同温度、频率沥青混合料和沥青砂浆的动态模量和相位角；(4)切割SGC成型的沥青混合料试件，对获取的截面图像进行图像处理，把二维图像导入离散元软件中生成沥青混合料的数字试件，对试件施加半正弦荷载进行SPT试验的数值模拟，对比分析模拟结果和试验结果动态模量和相位角的差异，追踪试件内部的力链演化，以及各相组分的位移场和速度场随时间的变化。通过对上述内容的研究，可得到如下的结论：(1)光弹性应力试验中，颗粒接触处越亮，接触应力越大。对于竖向加载的规则排列的结构，仅形成力的竖向传递路径，错落排列结构的内部颗粒间存在四个传力点，而在水平方向，两种结构基本不存在接触力的传递；(2)压痕试验中，接触力力链的概率分布先增大后减小，并出现明显的概率峰值，峰值后的力链分布以负指数形式衰减；(3)对于有侧向约束的集料细观结构，力链网络呈左右对称分布，颗粒间仅形成法向接触力，与光弹性应力试验结果一致，上层颗粒Y向位移较大，随着深度的增大位移减小；(4)对于无侧向约束的混合料细观结构，规则排列的结构仅产生压力力链，错落排列的结构中产生的接触力主要为压力，拉力区域比较分散，主要位于结构的中下部，呈不对称分布，上层颗粒位移较大，随着深度的增大位移减小；(5)沥青性质对沥青混合料细观响应的影响方面，粘结刚度比增大，应力峰值和劈裂强度均增大，配位数变化较小，随着粘结强度比的增大，应力峰值、劈裂强度减小，配位数变化较小，粘结强度比对劈裂强度、配位数和微裂缝的影响大于粘结刚度比；(6)集料性质对沥青混合料细观响应的影响方面，摩擦系数越大，峰值应力、劈裂强度越大，配位数减小，产生的微裂缝数增加；(7)加载条件对沥青混合料细观响应的影响方面，加载速率增大，应力峰值、劈裂强度增大，配位数减小，颗粒间的接触力变大，接触力力链网络中的强力链传递较大的应力，延伸方向平行于与最大主应力方向，位移主要沿加载方向向两侧移动；(8)随着油石比的增加，沥青混合料、沥青砂浆的动态模量减小，相位角增大，随着温度的升高，动态模量减小，相位角增大；(9)动态模量和相位角的实测值和模拟值相差不大；(10)集料内部的力链表现为压力力链，砂浆和集料/砂浆界面处的力链包含压力和拉力力链，且以压力为主，其中强力链均为压力力链，方向沿竖直方向，弱力链为较小的压力力链和拉力力链，方向分散性较大；(11)随着加载时间的增加，集料和砂浆的最大位移逐渐增大，但两者差异较小，砂浆的位移稍大于集料，位移由上至下逐渐减小，加载初始阶段，集料和砂浆的速度均较大，随着时间的延长，速度逐渐增大，但砂浆的速度变化小于集料。更多还原

【Abstract】 At present, the research of asphalt mixture has focused on the experience methods basedon phenomenology and laboratory tests, and the commonly used continuum model isapplicable to analyze the dense granular systems under quasi-static conditions and researchthe mechanical properties within these systems. But the size effect of component medium inthe systems is not considered by this model. Therefore, the relationship betweenmeso-structure and macroscopic performances cannot be revealed in analyzing asphaltmixture consisting of composite material based on continuum methods and models. However,the mesomechanics method studies an inhomogeneous media with multiscale mechanicaltheory, and asphalt mixture belongs to particulate matter material in material composition, andit is found that particulate matter systems have the loading sensitivity, nonlinear responses andself-organization behaviors from a large number of tests and numerical simulations, there areessential differences between the mesomechanics and continuum theory, macroscopicappearance results. In view of the above results, it provides the evidence in constructing themesomechanical models and studying meso-responses of asphalt mixture by mesomechanicsand particulate matter mechanics.Mesoscopic characteristics of asphalt mixture were taken as a mainline in thisdissertation. The distribution characteristics of force chains were analyzed for aggregate andasphalt mixture structures. Digital specimens of asphalt mixture were constructed to simulatethe indirect tensile test numerically and the influence factors of mesomechanics characteristicsof asphalt mixture and distributions of force chains within specimens were analyzed. Internalstructure of asphalt mixture specimen was excavated and dynamic indicators of asphaltmixture and sand mastic were measured to provide the mesoscopic viscoelastic parameters formesomechanical model of asphalt mixture. Stress and strain changes with time weremonitored, and the distribution changes of contact force chains, displacement field andvelocity field with time were traced inside the component particles during loading process,and the interaction at the interfaces between aggregate and sand mastic, and the relationshipbetween internal component and external loading, deformation were interpreted.The main research contents are as follows: (1) Photoelastic stress test and indentation test for particulate matter were used to detectthe force chains among aggregate particles and obtain the distribution law of force chains;(2) Mesoscopoic models of aggregates and asphalt mixture were constructed based ondiscrete element method, and the force chain field and displacement field were obtained bynumerical simulation, and digital specimen of asphalt mixture was constructed to analyze theinfluence factors of mesomechanical properties of asphalt mixture and force chain evolutionwithin specimen under servo-loading conditions;(3) Asphalt mixture specimens were prepared by SGC (Superpave Gyratory Compactor)and sand mastic specimens were prepared by static compaction, the dynamic moduli andphase angles of asphalt mixtures and sand mastic were determinated by Simple PerformanceTest (SPT) at different temperatures, frequencies;(4) Asphalt mixture specimens prepared by SGC were cut, the cross-sectional imageswere processed by digital picture processing technique, and the two-dimensional image wasimported discrete element software to generate the digital specimen of asphalt mixture.Simple Performance Test was simulated with semi-sinusoidal loading numerically,comparative analysis was taken to achieve the difference of dynamic modulus and phaseangle between simulated results and tested results. Finally, the force chain evolution withinspecimens and the changes of displacement field and velocity field with time were traced.The conclusions of this dissertation are follows:(1) In photoelastic stress test, the brighter the contacts among particles were, the greaterthe contact force was. Regular array structures under vertical loading only formed the verticaltransmission path of contact force, irregular array structures existed four transmission pointsof contact force among internal particles while the two structures had no transmission ofcontact force in horizontal direction basically;(2) In indentation test, the probability distribution of contact force chains increasedfirstly and then decreased, and there existed a significant probability peak value, and thedistribution of force chains decreased in negative exponential over the peak value;(3) For the aggregates meso-structures with lateral restraint, the force chain networkshowed a symmetrical distribution and only normal contact force formed among particleswhich was consistent with the results of photoelastic stress test, and the displacements of upper particles along Y direction were greater and decreased with the increase of depth;(4) For the aggregates meso-structures without lateral restraint, the regular arraystructures only formed compression force chains, the contact forces in irregular arraystructures were mainly compression forces and tension force area was scattered which mainlylocated in the middle and lower parts and was asymmetrical distribution, and thedisplacements of upper particles were greater and decreased with the increase of depth;(5) In the influence of asphalt nature on the meso-responses of asphalt mixture, stresspeak values and splitting strengths increased with the increase of bond stiffness ratio, andcoordination numbers had small changes. Stress peak values and splitting strengths decreasedwith the increase of bond strength ratio, and coordination numbers had small changes, too.The influences of bond strength ratio on splitting strengths, coordination numbers andmicro-cracks were greater than those of bond stiffness ratio;(6) In the influence of aggregates on the meso-responses of asphalt mixture, the greaterthe friction coefficients were, the greater the peak stress values and splitting strengths werewhile the smaller the coordination numbers were, and the number of micro-cracks increased;(7) In the influence of loading conditions on the meso-responses of asphalt mixture,stress peak values and splitting strengths increased with the increase of loading rate, and thecoordination numbers decreased. Contact forces among particles become larger and the strongforce chains in contact force chains networks transfered greater stress, their extensiondirections were parallel to the maximum principal stress direction, and the displacements weremainly along loading directions and moved to both sides;(8) Dynamic moduli of asphalt mixture and sand mastic reduced, phase angles increasedwith the increase of asphalt-aggregate ratio. Dynamic modului reduced while phase anglesincreased with the increase of temperature;(9) There was less difference between the measured values and simulated values ofdynamic moduli and phase angles;(10) Force chains within aggregates were all compression force chains, force chains ofsand mastic and aggregate/sand mastic interface included compression and tension forcechains, compression force chains dominated and strong force chains were all compressionforce chains which were along the vertical direction, but the weak force chains were smaller compression and tension force chains with larger dispersibility;(11) The maximum displacements of aggregates and sand mastic gradually increasedwith the increase of loading time, but the difference was smaller, and the displacements ofsand mastic were slightly larger than those of aggregates. Their displacements decreased fromtop to bottom gradually. The velocities of aggregates and sand mastic were both greater at theinitial stage. In addition, the velocities increased with the increase of time gradually, but thevelocity changes of sand mastic were less than those of aggregates.更多还原