【作者】 吴丹；

【导师】 乔丕忠；

【作者基本信息】 上海交通大学 ， 固体力学， 2019， 硕士

【摘要】 混凝土材料从细观尺度上主要可以分为骨料、水泥基体、界面过渡区和孔隙四相。考虑到实际工程应用中各相的力学性能和组分比例都会随时间和环境因素发生变化,且由于混凝土各相组分分布的非均匀性,仅研究其宏观力学性能难以准确对各类混凝土建筑结构的耐久性进行评估。由此,国内外学者对于混凝土材料细观-宏观跨尺度力学性能评估的研究热情日益高涨。在此背景下,本文以混凝土材料为研究对象,分析其在冻融循环作用下的性能退化机理,并重点考虑孔隙对于力学性能评估的影响,同时结合纳米压痕测试技术对混凝土各相的力学性能随冻融循环作用的衰减变化进行分析。本论文的研究成果主要包括以下内容:(1)对混凝土材料微细观结构各组分进行纳米压痕试验,骨料、基体和界面分别取不同的压痕试点。通过高斯混合模型对试验数据进行处理,得到各组分弹性模量。结果表明:随着冻融循环次数的增加,骨料弹性模量衰减不明显,而基体和界面的弹性模量衰减迅速。(2)给出含孔隙低退化骨料混凝土胞元预测模型,基于蒙特卡洛方法和双向游走法,生成并投放随机骨料和孔隙。(3)研究冻融循环作用下混凝土细观各组分的力学性能变化对其宏观力学行为的影响程度以及胞元模型中考虑孔隙的重要性。基于渐进均匀化理论,对已建立的胞元模型施加周期性边界条件进行求解,并利用Abaqus软件模拟比较。结果表明,随着冻融循环次数的增加,混凝土有效弹性模量衰减明显,胞元模型中忽略孔隙影响会对预测结果产生较大影响,均匀化求解结果和Abaqus模拟结果吻合良好。总的来说,本文总结和扩展了混凝土力学性能研究的多尺度方法,给出了含孔隙骨料混凝土单胞模型,进行了低退化骨料混凝土的细观试验和均匀化理论计算模拟。本文的研究工作为分析混凝土冻融循环作用下的老化机理提供了新的思路和方法。更多还原

【Abstract】 Concrete material is consisted of aggregate,cement matrix,interfacial transition zone and pore in mesoscale level.Considering that in practical engineering applications,the mechanical properties and component ratios of each phase will vary with time and environmental conditions.Meanwhile,because of the heterogeneity of concrete meso-structure,it is difficult to evaluate the durability of concrete structures by only studying its macroscopic mechanical properties.As a result,scholars all over the world are increasingly enthusiastic about the research on meso-and macroscale mechanical properties of concrete materials.In this context,the paper analyzes degradation mechanism of concrete material under freeze-thaw cycles,and focuses on the effect of pores on mechanical properties evaluation.At the same time,the mechanical properties of concrete with different freeze-thaw cycles are analyzed by nanoindentation technique.The main work in this thesis are as follows:1.The indentation tests are carried out on the aggregate,matrix and interface with the different indentation grids respectively.Using Gauss mixed model to process the experimental data,the modulus of elasticity of each component is obtained.The results show that the modulus of elasticity of aggregate varies little,and the modulus of elasticity of matrix and interface decreases greatly with the increase of freeze-thaw cycles.2.A prediction cell model of concrete with low-degradation aggregates and pores is proposed,and aggregates and pores are generated with the random locations using Monte Carlo method and abidirectional walk method.3.The influences of pores and the mechanical properties of each component on the macroscopic mechanical behavior of concrete are considered under the effect of freeze-thaw cycles.Based on asymptotic homogenization theory,the periodic boundary conditions are applied on the cell model,and the obtained results are compared the results of Abaqus software simulation.It turns out that the effective modulus of elasticity degrades obviously with the increase of freezing and thawing cycles.Neglecting the pores effect have a great impact on the results.The theoretical calculation results are in good agreement with these of Abaqus simulation.In conclude,this paper summarizes the multiscale method for studying the mechanical properties of concrete,proposes a cell model of concrete with pores and carries out the mesoscopic experiment and homogenization method simulation.New ideas and methods for analyzing the aging mechanism of concrete under the freeze-thaw cycles are provided in this work.更多还原