本文選題：濕熱力耦合 + 失配本征應(yīng)變　； 參考：《北京交通大學(xué)》2017年博士論文

【摘要】：混凝土是由砂漿、骨料以及界面過渡區(qū)構(gòu)成的復(fù)合材料,其濕熱力狀態(tài)之間互相影響,本文基于細(xì)觀力學(xué)研究了其相關(guān)力學(xué)問題,具體內(nèi)容如下:首先研究了混凝土的濕熱力耦合計(jì)算方法。將混凝土視作砂漿骨料組成的二相復(fù)合材料,分析了二者的失配本征應(yīng)變。作者把砂漿視作彈性損傷材料,將失配本征應(yīng)變導(dǎo)致的應(yīng)力引入砂漿的損傷分析中,建立了混凝土濕熱力耦合計(jì)算方法。損傷通過傳導(dǎo)系數(shù)的變化影響濕熱傳輸,濕熱狀態(tài)對應(yīng)力狀態(tài)的影響體現(xiàn)在濕熱應(yīng)力和失配本征應(yīng)變產(chǎn)生的損傷。混凝土骨料與砂漿的應(yīng)力應(yīng)變關(guān)系使用Mori-Tanaka方法計(jì)算。對路面板的計(jì)算表明,失配本征應(yīng)變對混凝土濕熱力狀態(tài)的影響不可忽視。將該濕熱力耦合計(jì)算方法應(yīng)用到濕熱擴(kuò)散對混凝土強(qiáng)度影響的分析中,計(jì)算了干燥和降溫情況下圓柱構(gòu)件的應(yīng)力分布和強(qiáng)度變化。研究表明,濕熱擴(kuò)散使得圓柱構(gòu)件的應(yīng)力分布不均勻,較長的擴(kuò)散時(shí)間和較小的構(gòu)件尺寸顯著降低了構(gòu)件的壓縮強(qiáng)度。本文在考慮水灰比和礦物組成的基礎(chǔ)上,提出了一個(gè)簡單的水泥水化動力學(xué)模型。該模型使用Avrami方程描述初始階段的水化進(jìn)程,采用Bents模型刻畫隨后階段的水化過程。使用該方法可以確定不同礦物的水化速度和各種水化產(chǎn)物的體積分?jǐn)?shù)。該方法只需要一個(gè)待定參數(shù),簡單易用,可以預(yù)測較長時(shí)間的水化狀態(tài)。本文進(jìn)一步提出了考慮固體體積分?jǐn)?shù)和初始水灰比的水泥初凝閾值計(jì)算方法,并以連通固體相體積為基礎(chǔ),結(jié)合細(xì)觀力學(xué)均勻化方法,研究了水化水泥早期彈性模量的演化,模型預(yù)測結(jié)果與實(shí)驗(yàn)數(shù)據(jù)基本一致。隨后,基于Powers水化模型,推導(dǎo)了適用于普通硅酸鹽水泥的簡化模型。界面過渡區(qū)是混凝土中最弱的一相,本文基于細(xì)觀力學(xué)研究了其力學(xué)性能及其對混凝土力學(xué)行為的影響。將混凝土界面過渡區(qū)視作由兩相復(fù)合材料組成的球殼,并假設(shè)其組分的體積分?jǐn)?shù)沿半徑方向變化。根據(jù)不同的細(xì)觀力學(xué)均勻化方法,推導(dǎo)了不同的解析方法和數(shù)值方法,分析了界面過渡區(qū)的力學(xué)性能。在解析方法中,分別采用了并聯(lián)材料和串聯(lián)材料的細(xì)觀力學(xué)均勻化方法,求得了梯度球殼的彈性解、塑性解和穩(wěn)態(tài)熱應(yīng)力解。在數(shù)值方法中,將梯度球殼分成若干層球殼,每一層球殼的組分體積分?jǐn)?shù)為常數(shù),其力學(xué)性質(zhì)分別采用并聯(lián)材料、串聯(lián)材料和M-T方法來確定。利用層間位移和應(yīng)力連續(xù)條件得到了梯度球殼的解。該數(shù)值方法計(jì)算量小,精度高,與對應(yīng)的解析解一致性良好。研究結(jié)果表明,界面過渡區(qū)對混凝土力學(xué)性能的影響與骨料體積分?jǐn)?shù)和粒徑有關(guān),降低了混凝土剛度,但對初始損傷載荷影響不大。
[Abstract]:Concrete is a composite composed of mortar, aggregate and interfacial transition zone. The main contents are as follows: firstly, the wet-thermal coupling calculation method of concrete is studied. The concrete is regarded as a two-phase composite composed of mortar aggregate, and their mismatched intrinsic strain is analyzed. The mortar is regarded as an elastic damage material, and the stress caused by mismatched intrinsic strain is introduced into the damage analysis of mortar, and the coupled calculation method of moisture, heat and force of concrete is established. The damp-heat transfer is affected by the change of conduction coefficient, and the effect of damp-heat state on the stress state is reflected in the damage caused by the hygrothermal stress and mismatched intrinsic strain. The stress-strain relationship between concrete aggregate and mortar is calculated by Mori-Tanaka method. The calculation of the pavement panel shows that the effect of mismatched intrinsic strain on the wet and thermal state of concrete can not be ignored. The coupled method is applied to the analysis of the effect of hygrothermal diffusion on the strength of concrete, and the stress distribution and strength change of cylindrical members under the condition of drying and cooling are calculated. The results show that the stress distribution of cylindrical members is not uniform due to the hygrothermal diffusion. The compression strength of the members is significantly reduced by the longer diffusion time and the smaller member size. In this paper, a simple hydration kinetic model of cement is proposed on the basis of considering the ratio of water to cement and mineral composition. The Avrami equation is used to describe the hydration process in the initial stage and the Bents model is used to describe the hydration process in the subsequent stage. This method can be used to determine the hydration rate of different minerals and the volume fraction of various hydration products. The method requires only one parameter to be determined and is easy to use and can be used to predict the hydration state for a long time. In this paper, the calculation method of initial setting threshold of cement considering solid volume fraction and initial water-cement ratio is put forward, and the evolution of early elastic modulus of hydrated cement is studied based on the volume of connected solid phase and the mesomechanical homogenization method. The predicted results of the model are in good agreement with the experimental data. Then, based on the Powers hydration model, a simplified model for ordinary Portland cement is derived. The interfacial transition zone is the weakest phase in concrete. In this paper, the mechanical properties of the interfacial transition zone and its influence on the mechanical behavior of concrete are studied on the basis of meso-mechanics. The transition zone of concrete interface is regarded as a spherical shell composed of two phase composite materials, and the volume fraction of its components is assumed to vary along the radius. According to different meso-mechanical homogenization methods, different analytical methods and numerical methods are derived, and the mechanical properties of the interfacial transition region are analyzed. In the analytical method, the elastic solution, plastic solution and steady state thermal stress solution of gradient spherical shell are obtained by using the meso-mechanical homogenization method of parallel material and series material, respectively. In the numerical method, the gradient spherical shell is divided into several layers of spherical shells. The volume fraction of the components of each layer is constant. The mechanical properties of each layer are determined by parallel material, series material and M-T method respectively. The solution of gradient spherical shell is obtained by using the continuous condition of interlayer displacement and stress. The numerical method has the advantages of low computational complexity, high accuracy and good consistency with the corresponding analytical solution. The results show that the influence of interfacial transition zone on the mechanical properties of concrete is related to the volume fraction and particle size of aggregate, which reduces the stiffness of concrete, but has little effect on the initial damage load.
【學(xué)位授予單位】：北京交通大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2017
【分類號】：TU528

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