基于细观非均质模型的水稳碎石基层材料疲劳开裂研究

Fatigue cracking of cement−treated composites with mesoscale heterogeneous model

为了研究细观非均质性对水稳碎石基层(CTB)材料疲劳开裂行为的影响,首先,采用离散元法(DEM)和随机算法建立细观非均质随机骨料数值模型;其次,利用数字图像处理技术(DIP)实现模型重构,并结合纳米压痕试验确定材料力学参数分布;第三,基于建立的DIP重构模型进行参数反演获取模型参数,并基于平行黏结衰变表征循环荷载下的疲劳衰变行为;最后,基于建立的细观模型开展虚拟半圆弯曲(SCB)强度和疲劳试验,模拟细观疲劳开裂过程,并探索细观非均质性对结构疲劳开裂行为的影响。研究结果表明:CTB材料疲劳裂纹的形成经历了平稳扩展和快速贯通的过程,张力是疲劳开裂演化的驱动力,砂浆−骨料界面是疲劳开裂的薄弱区域;疲劳损伤在循环加载过程中呈非线性累积,应力与疲劳寿命之间呈指数函数关系;提升材料的抗拉强度是改善结构疲劳抗裂能力的关键措施。砂浆材料的性能随机场显著影响水稳碎石的疲劳断裂行为。随着材料属性离散程度增加,同等应力比水平下CTB材料损伤增长速度降低,裂纹扩展路径延长,试件断裂时的微裂纹总量提高,疲劳寿命增大,然而,过于离散的材料性能又显著降低材料的抗拉强度,削弱结构的承载能力,降低疲劳寿命。在施工过程中,合理控制砂浆的均匀性有益于提高CTB材料的抗疲劳开裂能力。

To investigate the influence of microscopic heterogeneity on fatigue cracking behavior of cement-treated base(CTB)materials,firstly,mesoscale heterogeneous numerical model was established by discrete element method(DEM)and randomization algorithm.Secondly,digital image processing(DIP)technology was employed to reconstruct real specimen.Nano-indentation test was adopted to determine the material mechanical parameter distribution.Thirdly,based on DIP reconstruction model,the material parameters were obtained by inverse analysis.The parallel bond evolution method was also developed to characterize the time-dependent fatigue damage behavior under cyclic loading.Finally,based on the established mesoscale heterogeneous model,virtual semicircular bending strength and fatigue tests were carried out.The process of mesoscopic fatigue cracking was simulated and the influence of microscopic heterogeneity on fatigue cracking behavior was further studied.The results show that fatigue crack has experienced a process of smooth propagation and rapid penetration.Tension is the driving force of fatigue crack evolution.The interface of mortar-aggregate is the weak area of fatigue cracking.The fatigue damage presents nonlinear accumulation during cyclic loading and the relationship between stress and fatigue life is exponential function.The increase of tensile strength of mortar materials is the key measure to improve the fatigue crack resistance of structures.The material random field has significant influence on the fatigue fracture behavior of CTB.With the increase of the dispersion degree of material properties,the growth rate of fatigue damage decreases,the crack propagation path extends,and the total number of microcracks at fracture increases.As a result,CTB with significant heterogeneity will have a higher fatigue life at the same stress ratio level.However,excessively discrete material properties significantly reduce tensile strength,weaken bearing capacity of the structure,and reduce fatigue life.The reasonable control of the uniformity of mortar during construction is beneficial to improve the fatigue resistance of CTB materials.