【作者】 周长红；

【导师】 王哲人； 陈静云；

【作者基本信息】 大连理工大学 ， 结构工程， 2008， 博士

【摘要】 近年来,车辙、水损坏和开裂为代表的早期损坏现象由于严重影响到沥青路面的使用性能而备受关注。研究表明,这些早期损坏总是在局部区域首先发生,然后扩展到其他区域的。为了减少和避免早期损害的发生,获得局部区域的应力状态是非常必要的。虽然试验方法可以准确的得出结果,但由于测量手段的局限性和影响因素的多样性,很难得到各种组合情况下的应力分布;而连续力学方法由于不考虑沥青混合料的不连续状态,也很难得到细观下沥青胶浆的应力分柿。非连续计算方法正是为了弥补这些方法的不足而提出的。非连续计算方法主要有离散单元法、DDA法以及数值流形法。文中分析了每种方法的基本原理和优缺点,同时考虑到沥青混合料空隙发达、多种材料耦合、颗粒松散、以及大变形等特点,通过比较认为:数值流形法能够满足这种计算的需要。不过基于规则网格的数值流形法由于受到网格的限制,在处理材料交界面处的位移协调以及特大变形时还面临很多困难。为了改进这种方法,文中采用Galerkin型无网格法与数值流形法相结合来求解沥青混合料的力学问题,得到了很好的效果。文中首先详细讨论了非连续计算面临的三个关键性技术:计算模型的生成、接触的判断与施加,以及数据的存储格式和求解方案。鉴于无网格和流形法的计算特点,文中提出了“级配-基球-预压”的沥青混合料非连续模型生成方法。并讨论了颗粒级配的控制、颗粒的嵌挤压密、多面体模型的投放、以及沥青胶浆的生成等问题。对于接触点的搜索,计算证明:采用分格检索和公共平面结合的方法可以大大提高搜索的效率。另外,为了将无网法融合到数值流形法中,重新推导了数值流形法中接触子阵的形式,并实现了不同计算节点采用不同影响节点的计算格式。通过分析非连续计算的刚度矩阵特点,认为采用动态的数据压缩格式有利于提高刚度子阵的装配效率和减少数据的存储量。同时,经过计算表明,当方程的阶数不是特别高时,采用直接求解方法可以保证计算的精度和速度,当阶数很高时,建议采用带预处理的迭代方法。其次,文中重点探讨了无网格流形法的建立和实现方法,其中包括近似方案的构造、离散格式的形成、本质边界的处理和各种子阵的计算格式等问题。针对上述形成的沥青混合料非连续模型,给出了材料交界面位移协调、沥青胶浆的连接、影响节点的搜索以及接触块体的构造等内容的处理方法。同时,通过与有限元的对比,还讨论了无网格流形方法的精度问题。文章最后对无网格流形法在沥青混合料细观应力分布和空隙水压力影响等方面的应用做了探讨。为了和连续力学方法方法对比,还介绍了采用有限元方法进行相应计算的方法。虽然文中的算例较为简单,但还是能得出很多有意义的结论:(1)沥青混合料的应力分布是与骨料和沥青胶浆的模量的比率密切相关的。比值越大,骨料的应力越集中,而比值越小,骨料和沥青的应力分布越均匀。因此可以通过调整模量比值促使骨料和沥青胶浆共同协调受力,以最大程度地发挥它们各自的极限强度。模量比值的减小虽然可以使颗粒内受力均匀,但往往会导致颗粒与颗粒间的应力的不均匀分布。(2)欧拉方程耦合计算方法中,水是作为固体的附加质量参与到受力体系中来的,它的存在导致了沥青混合料颗粒内部应力的降低,但它几乎不影响骨料与沥青的应力分配比例。更多还原

【Abstract】 Some early damage phenomenons such as rutting, moisture damage and cracking, which are seriously corrupting pavement service performance, have been drawn significant attentions in recent year. Researches show that these early damages tend to occur in local region, and then spread to other regions. In order to reduce or avoid this kind of damage, the stress condition of local region should be made clear first of all. Although the stress can be measured by experiment accurately, its distribution under multi-component load is difficult to obtain with the limited measurement instruments. Since the continuous mechanics method ignores the discontinuation status of asphalt mixture, the meso-level stress distribution is hardly gotten. The discontinuous computation method is considered advanced to cover the shortage above.Discrete Element Method, Discontinuous Deformation Analysis and Numerical Manifold Method can all be used in discontinuum mechanics numeration. The fundamental principles, advantages and disadvantages are studied in this paper. Through taking into account the characteristic of asphalt mixture (high porosity, loosening particles, coupled of multi materials with large deformation and so on), Numerical Manifold Method provids a good way to satisfy the purpose of computation after detailed comparisons. However, the Numerical Manifold Method is still limited in processing the coordination of displacement and large deformation because of the dependence of mesh. A combination with Mesh-free Galerkin Method is advanced to solve the mechanics problems of asphalt mixture. And remarkable improvement has been gained through this method.Firstly, three key technologies of discontinuous computation method: the generation of computation model, the identification and application of contact, storing and processing format of data are detailed discussed.The generation method of asphalt mixture discontinuum mechanics model named Gradation-Sphere-Precompaction is developed based on the calculation features of Mesh-free Method and Numerical Manifold Method. The controlling of particle graduation, the break-in and pressure of particles, the location of polyhedral model and the generation of asphalt mastic and other issues are outlined.The adoption of Lattice Search and Common Plane method is proved to greatly improve the efficiency in searching contact points. In addition, the sub-contact-matrix in Numerical Manifold Method is reconstituted to merge the Mesh-free method. The scheme is realized for different node with different support nodes.By analysis of discontinuous stiffness matrix, it is concluded that dynamic data compression format is benefit in improving assemble efficiency of the stiffness matrix and reducing the data storage. At the same time, the calculation proves that direct solution procedure guarantees both the precision and speed of computation when the rank of stiffness matrix is not particularly high, and pretreatment iteration method is recommended when the rank is relatively high.Secondly, the realization of Mesh-free Manifold method is focused in this paper. The problems of construction of approximate program, formation of discrete format, transaction of essence boundary and computation format of sub-matrix are indicated. According to the asphalt mixture discontinuous model, the deposit method of material boundary displacement coordinate, the link of asphalt mastic, the search of affection point and the formation of contact blocks and so on are also established. Meanwhile, the precision of this method is also discussed by comparison with finite element method.Finally, the application of Mesh-free Manifold method subjecting the deformation and infuluce of water pressure on asphalt mixture is presented. In order to comparison with the continuous mechanics method result, the corresponding calculation with finite element method is also introduced. Though simple cased is used here, some meaningful conclusions are found as follows:a) The stress distribution of asphalt mixture is closely related to the modulus ratio of stone and asphalt mastic. The stress concentration on stone is found in high ratio, while the stress profile has evenly distribution in low ratio. As a result, to maximize their ultimate strength respectively, the coordinate mechanical status of stone and asphalt mastic could be obtained by adjustment of modulus ratio. The decrease of modules leads to stress distribution balanced inside the particles, but unbalanced between the particles.b) In analysis of Solid-liquid interaction by Euler Equation, the presence of water results in stress decreasing of asphalt mixture internal particles as an additional mass of solid in the mechanic system. But it hardly affects the stress distribution ratio of stone and asphalt.更多还原