【作者】 毛成；

【导师】 邱延峻；

【作者基本信息】 西南交通大学 ， 道路与铁道工程， 2004， 博士

【摘要】 疲劳开裂是沥青路面主要的早期破损形式之一，由于交通荷载和低温应力的反复作用，沥青路面中的微裂纹不断扩展、增密并贯穿连通形成宏观裂纹，导致路面结构破坏。开展沥青路面裂纹形成机理及裂纹扩展行为的研究可以更加全面地评价路面的力学行为，明确裂纹扩展时的应力状态和扩展路径，进一步理解路面损伤与早期破损的机理，并为路面工程师提供沥青路面设计与养护指导。认识和理解沥青路面结构裂纹形成机理及扩展过程，对提高沥青路面结构抗裂性能，优选沥青混合料，改进现有的路面设计方法都是非常重要的。 本文首先搜集回顾了大量国内外相关文献和研究成果，对沥青路面裂缝类早期破损的现象和机理识别进行了详细的研究和总结。鉴于影响沥青路面早期裂缝的因素多而复杂，给出了影响沥青路面裂缝的因素及其相互作用关系图帮助识别裂纹形成机理。基于线弹性断裂力学有限元方法和窗口移动技术，编写了能同时处理四边形8结点等参单元和三角形6结点奇异等参单元的二维沥青路面裂纹扩展路径模拟程序——APCPPS^2D（2-D Asphalt Pavement Crack Propagation Path Simulator）, APCPPS^2D程序能同时考虑交通荷载和温度荷载的作用，能同时模拟多条裂纹的扩展行为。通过对3个有解析解和实验结果的算例的模拟分析，表明了APCPPS^2D程序能够较为准确地计算出裂纹尖端的Ⅰ型和Ⅱ型应力强度因子，能够较好地模拟Ⅰ型、Ⅱ型和Ⅰ-Ⅱ复合型裂纹的扩展行为。 设计了模拟沥青混凝土复合型裂纹扩展行为的偏直裂纹三点弯曲梁试验，并对一系列三点弯曲梁中复合型裂纹的扩展路径进行了实验和数值模拟。结果表明，随着预制裂纹偏离梁中线距离的增加，裂纹的起裂角和峰值荷载都增大。裂纹扩展路径总体上遵循一定的规律，试验结果表明，由于沥青混凝土材料颗粒的不均匀性，裂纹扩展路径通常沿着集料颗粒边界扩展而很少切断颗粒。 在国内首次通过网格显式地模拟了沥青路面结构中裂纹的扩展路径。应用APCPPS^2D程序分别模拟了两种路面开裂形式：一种是沥青路面表面存在一条表面裂纹的开裂路面；另一种是沥青路面表面有一条表面裂纹且基层底面有一条反射裂纹。在开裂路面的综合参数研究中详细评价了不同的交通荷载兰止乙一一‘一亘些巡支墅胜鲤丝与低温荷载组合、不同的路面结构组合、非均匀分布轮胎压力及超载和荷载谱（大小和相对裂纹的位置）的影响。荷载的位置连同沥青面层和基层刚度对裂纹的扩展有很大的影响，计算出了裂纹增长的方向且表明随着裂纹长度的增加其扩展方向会发生改变。正常路面结构表面裂纹的形成及进一步的扩展主要是由低温应力及低温疲劳应力引起的，其开裂方式主要是I型开裂。低温下交通载荷的重复作用也会加速路面裂纹的疲劳扩展。路面结构（厚度和刚度）的不同组合对沥青路面表面裂纹的扩展行为有较大的影响。基层底面裂纹的应力强度因子随着基层模量的增加而增加，随着面层模量的增加而减小;而表面裂纹的应力强度因子随着基层模量的增加而减小，随面层模量的增加而增加。水平荷载对表面裂纹复合型应力强度因子有较大的影响，而对基层底面裂纹复合型应力强度因子的影响较小。非均布轮胎压力对路面表面裂纹和基层底面裂纹应力强度因子的影响也较大。裂纹随着交通荷载作用位置的不同而表现出明显不同的裂纹扩展路径，表面裂纹呈现向下偏离荷载的曲线扩展路径，而基层底面裂纹表现为向上偏向荷载的曲线扩展路径。沥青面层和基层的弹性模量对表面裂纹和基层底面裂纹的扩展路径有较大的影响。 通过沥青路面裂纹扩展行为的分析表明，裂纹扩展的机理主要是拉应力，无论荷载的位置如何，剪应力对控制裂纹的生长并不重要。虽然裂纹尖端处于I一11复合型应力状态下，但拉应力仍然是裂纹扩展的主要驱动力。更多还原

【Abstract】 Fatigue cracking is one of the major modes of premature distresses in asphalt pavements. Cracks of asphalt pavements start as microcracks and later propagate, densify, and coalesce due to repeated traffic loading or low temperature thermal stresses or combinations of both to form macrocracks, and result in structural distresses of asphalt pavements. Research on initiation mechanism and propagation behavior of cracks in asphalt pavements is necessary for a sound evaluation of mechanistic behavior of pavements. It is a great help to us to knowledge the state of the stress field and crack propagation path, to improve understanding of the mechanism of pavement damage and premature failure, and to provide guidance for pavement engineers in designing and maintaining asphalt pavements. The knowledge and understanding of the mechanism of crack initiation and propagation processes are very important to enhance the resistance cracking performance of asphalt pavement structure, to select optimum asphalt mixtures and to improve the present design methods.Firstly, based on literature review of a large number of relevant domestic and international research findings, the mechanism of premature distresses and identification of cracks in asphalt pavements were investigated and summarized in detail. As there are many complicated factors that have influence on premature cracking of asphalt pavements, a schematic of influencing factors having interaction relationship is given to help identify crack initiation mechanism. Using linear elastic fracture mechanics and finite element method and window moving technique, a two-dimensional asphalt pavement crack propagation path simulator (APCPPS2D) program has been developed with a combination of 8-node quadrilateral isoparametric element and 6-node triangular collapsed singular isoparametric element. APCPPS2D program can consider traffic loading and temperature variance simultaneously, and can simulate the propagation paths of multiple cracks at the same time. Verification and validation studies were conducted and results were compared to three examples published in literature that have analytical solutions and experimental results. The results indicate that theprogram is capable of accurately calculating the stress intensity factor and modeling the propagation paths of mode I crack, mode II crack and mixed mode I-II crack.In order to model the mixed mode crack propagation behavior of asphalt concrete, a three point bending beam with mixed mode notched has been designed. A series of mixed mode three point bending beam tests and numerical simulations have been performed to simulate mixed mode crack initiation and growth. The results showed that the crack initiation angle and the peak load increased as the distance of the preexisting crack from the midpoint of the beam increased. The crack propagation path follows some regularity in general. The experimental results showed that the crack propagation path followed, mainly, the boundaries of the grains and rarely cut through the grains with differences attributed to the grain size effect in asphalt concrete.It is the fist time that crack propagation path in asphalt pavements is modeled explicitly by the mesh in domestic. Two kinds of cracked pavement structures have been simulated using APCPPS2D program. One is a cracked pavement with a near surface crack; another is a cracked pavement with a near surface crack and a reflective crack at the bottom of the base. A comprehensive parametric study of the cracked pavement has been performed to evaluate effects of various combinations of traffic load and low temperature load, effects of various combinations of pavement structure, effects of non-uniform distributed tire pressures and overload and load spectra (magnitude and positioning with respect to crack). Load positioning was shown to have the most influence on crack propagation, along with asphalt and base layer stiffness. The direction of crack growth was computed and was shown to change with increasing crack length. The near surface cra更多还原