本文選題：混凝土　切入點(diǎn)：開裂過程　出處：《哈爾濱工業(yè)大學(xué)》2014年碩士論文

【摘要】：混凝土是一種多相復(fù)合的非勻質(zhì)材料，其開裂過程與內(nèi)部結(jié)構(gòu)密不可分。許多年來，國內(nèi)外大量的研究者致力于水泥基材料開裂過程的研究，提出過大量的裂縫模型，但基本停留于宏觀層次研究，沒有深入到材料微觀結(jié)構(gòu)，也很難給出裂縫動態(tài)開裂過程。針對上述問題，本文將多尺度方法與格構(gòu)斷裂模型相結(jié)合，首先開發(fā)了一種實(shí)時(shí)跟蹤裂縫寬度動態(tài)變化過程的Python程序算法完成了微觀尺度下水泥漿體格構(gòu)斷裂分析，然后針對細(xì)觀尺度隨機(jī)骨料投放，，提出了采用HYMOSTRUC3D模型快速生成三維隨機(jī)球形骨料模型研究了細(xì)觀尺度砂漿與混凝土的開裂過程。本文主要研究內(nèi)容如下： 采用隨機(jī)度的概念定量描述了水泥基材料不規(guī)則、非勻質(zhì)性質(zhì)，并分析了隨機(jī)度對格構(gòu)斷裂模擬的影響。結(jié)果表明：隨機(jī)度能夠反映了材料內(nèi)部物相不均勻程度。隨著隨機(jī)度增大，格構(gòu)模型整體彈性模量，抗拉強(qiáng)度以及峰值應(yīng)變均減小。 基于格構(gòu)斷裂模型的計(jì)算理論，推導(dǎo)了格構(gòu)模型裂縫寬度理論計(jì)算公式，編寫了MATLAB以及Python程序，將其植入商用有限元計(jì)算軟件ABAQUS中，能夠跟蹤格構(gòu)模型不同應(yīng)力水平下裂縫寬度數(shù)值變化。該程序算法的基本思想為：每次格構(gòu)斷裂計(jì)算中，不從格構(gòu)系統(tǒng)中直接剔除σ/ft比值最大單元，而是設(shè)置為裂縫單元，裂縫單元是指單元的彈性模量數(shù)值設(shè)置為相對于其他格構(gòu)單元可以忽略不計(jì)，即二者彈性模量的比值趨于0。通過計(jì)算裂縫單元節(jié)點(diǎn)位移增量得到變形量的精確值，如果每次重新計(jì)算數(shù)據(jù)庫中所有裂縫單元的變形量，那么，就實(shí)現(xiàn)了對不同應(yīng)力水平下裂縫寬度變化跟蹤計(jì)算。本文數(shù)值結(jié)果表明，本算法能夠有效追蹤裂縫寬度動態(tài)變化過程。 在隨機(jī)骨料模型方面，本文利用MATLAB編程進(jìn)行數(shù)字圖像處理，借鑒F. Bernard采用NIST's CEMHYD3D程序代碼生成了砂漿結(jié)構(gòu)模型的方法，提出采用HYMOSTRUC模型快速生成三維隨機(jī)球形骨料模型。這解決了當(dāng)前混凝土數(shù)值模擬中隨機(jī)骨料投放效率低下的問題。 基于遞階的多尺度建模方法，采用HYMOSTRUC3D模型生成了水泥漿體微觀結(jié)構(gòu)晶格圖像，并離散化為二維晶格圖像建立格構(gòu)網(wǎng)絡(luò)模型。對微觀尺度下水泥漿體進(jìn)行格構(gòu)系統(tǒng)線彈性有限元計(jì)算。將微觀尺度下得到的水泥漿體本構(gòu)關(guān)系作為細(xì)觀尺度下砂漿格構(gòu)分析的輸入?yún)?shù)，對細(xì)觀尺度砂漿進(jìn)行非線性有限元計(jì)算，這種非線性是通過多步迭代降低單元的彈性模量與抗拉強(qiáng)度的方法實(shí)現(xiàn)的。按照這樣的多尺度格構(gòu)斷裂分析方法得到了混凝土的應(yīng)力應(yīng)變曲線、裂縫位置分布圖、不同應(yīng)力水平下的裂縫寬度分布等。特別地，從裂縫位置分布圖來看，裂縫最先在初始孔隙周圍產(chǎn)生，然后逐漸向內(nèi)部擴(kuò)展形成主裂縫，裂縫寬度分布總是表現(xiàn)出兩個(gè)正態(tài)分布的疊加，第一個(gè)正態(tài)分布均值代表微裂縫寬度，且微裂縫數(shù)目大多占50%左右；第二個(gè)正態(tài)分布均值代表大裂縫寬度，且裂縫數(shù)目與應(yīng)力水平相關(guān)。裂縫分布圖表明：砂漿與混凝土中裂縫首先在界面過渡區(qū)產(chǎn)生然后逐漸向水泥漿或砂漿基體中發(fā)展。
[Abstract]:Concrete is a multiphase inhomogeneous material, the cracking process and internal structure are inseparable. For many years, a lot of researchers at home and abroad dedicated to the process of cracking of cement based materials, put forward a lot of crack model, but the basic stay at the macro level, not deep into the microstructure of the material, but also it is difficult to give a dynamic crack cracking process. Aiming at the above problems, the multiscale method of lattice fracture model combining Python program algorithm firstly developed a real-time tracking of the dynamic process of the crack width of the micro scale cement physical structure fracture analysis, then the meso scale random aggregate supply, put forward the rapid generation of HYMOSTRUC3D models of three-dimensional random aggregate model of spherical cracking process of meso scale mortar and concrete. The main research contents of this paper are as follows:
By using the concept of quantitative description of the randomness of cement-based materials is irregular, heterogeneous nature, and analyzes the randomness of lattice fracture simulation. The results show that the random degree can reflect the material internal phase inhomogeneity. With random degree increases, the lattice model overall elastic modulus, tensile strength and the peak strain decrease.
Theoretical calculation of lattice fracture model based on lattice model, deduced the theoretical calculation formula of crack width, write MATLAB and Python procedures, into the commercial finite element software ABAQUS, can track the change of lattice model of crack width values under different stress levels. The basic idea of the program is: each lattice algorithm fault calculation, do not constitute the system directly removed o /ft the ratio of the maximum unit from the grid, but is set to crack element, crack element is to set the elastic modulus value unit as compared to other lattice elements can be ignored, i.e. the ratio of the two elastic modulus tends to 0. through the exact value calculation of crack element node displacement increment deformation if the amount of deformation, each re calculate all crack element in the database so as to achieve the different change of crack width under the stress of the tracking calculation. The numerical results show that the algorithm can effectively track the dynamic change process of crack width.
In the random aggregate model, this paper uses the MATLAB programming of the digital image processing, using F. Bernard using NIST's CEMHYD3D code generation method of mortar structure model, the rapid generation of three-dimensional random aggregate model of spherical HYMOSTRUC model. It solves the problem that when the numerical concrete random aggregate on the problem of low efficiency.
Multiscale modeling method based on hierarchical, using HYMOSTRUC3D model to produce cement paste microstructure and lattice image, discrete two-dimensional lattice image establish lattice network model. On the micro scale cement paste for lattice system of linear elastic finite element calculation. The cement paste microstructure scale under the constitutive relation as the input parameters of the meso scale lattice analysis of mortar, mortar of meso scale nonlinear finite element calculation, the nonlinear is implementation method to reduce the elastic modulus and tensile strength of the unit through the iteration. According to multiple scales the fracture analysis of the concrete stress-strain curve, crack distribution map, under different stress level of the crack width distribution. Especially, judging from the position of the crack distribution, the crack was first produced in the initial void around, and then gradually inward Part of the formation of the main crack propagation, crack width distribution always showed two normal distribution overlay, micro crack width first normal distribution mean, and the number of micro cracks are mostly accounted for about 50%; second normal distribution mean crack width, and the number of cracks and the stress level. The crack distribution map shows that: cement mortar and concrete cracks in the first generation of interface transition zone and then gradually to the development of cement paste or mortar matrix.

【學(xué)位授予單位】：哈爾濱工業(yè)大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2014
【分類號】：TU528

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