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  本文關鍵詞： 孔隙材料 滲透性 裂紋網(wǎng)絡 連通度 逾滲　出處：《清華大學》2015年博士論文　論文類型：學位論文

【摘要】：孔隙材料在力學荷載和環(huán)境因素作用下會產(chǎn)生裂紋。裂紋產(chǎn)生、擴展和連通對材料的滲透性影響顯著,進而影響材料的使用性能。本文通過理論分析、數(shù)值模擬和試驗研究對含隨機裂紋網(wǎng)絡孔隙材料的滲透性進行了系統(tǒng)研究。本文首先基于連續(xù)區(qū)逾滲理論并考慮裂紋網(wǎng)絡的分形特征提出了有限區(qū)域內裂紋網(wǎng)絡的連通度定義。然后在含裂紋夾雜的相互作用直推(IDD)理論模型基礎上,引入裂紋網(wǎng)絡的連通度和裂紋的開度信息,定義與連通度相關的水平裂紋密度,按照增量法將表征連通特征的水平裂紋嵌入有效基體中,以此方式來考慮裂紋夾雜間的相互作用,提出了考慮裂紋連通特征的擴展IDD模型。隨后開展了含裂紋網(wǎng)絡孔隙材料滲透率逾滲模型的研究,采用裂紋面密度作為逾滲基本變量,計算了不同裂紋網(wǎng)絡的逾滲閾值以及閾值附近的標度指數(shù);考慮裂紋網(wǎng)絡的連通度和主裂紋團的曲折度給出了滲透率標度律的解析解,分別考慮了裂紋網(wǎng)絡的幾何逾滲特征、孔隙材料滲透率以及裂紋開度比。以水泥基孔隙材料為研究對象,研究了裂紋網(wǎng)絡對材料滲透率和電導率等傳輸性質的影響。為了沿試件厚度方向得到上下表面一致的二維裂紋網(wǎng)絡,本文采用人工制造裂紋再拼接的方法得到不同開裂程度的薄片試件。對開裂試件表面的二維裂紋形貌特征進行了定量分析,包括裂紋的密度、取向、裂紋開度、連通度等。測試了普通混凝土和砂漿材料的等溫吸附與脫附曲線,得到兩種材料的水分特征曲線。然后嘗試使用水分遷移的多相流模型來模擬試件的干燥過程,同時對比干燥實驗中不同開裂程度試件的質量變化過程來回歸其對應的本征滲透率。最后給出裂紋網(wǎng)絡不同的形貌參數(shù)對滲透率和電導率的影響。研究表明:(1)通過裂紋網(wǎng)絡幾何分析可知,隨機裂紋局部團簇效應會降低裂紋網(wǎng)絡的整體連通性,數(shù)值結果驗證了連通度定義方法的合理性;(2)從數(shù)值的角度分別驗證了不連通和部分連通裂紋網(wǎng)絡擴展IDD模型的適用性;(3)當裂紋的局部滲透率與基體滲透率比值高于106后,裂紋開度對滲透率不再有影響;(4)當裂紋密度大于臨界閾值0.3時,滲透率和電導率增加迅速。滲透率與裂紋開度成指數(shù)關系,指數(shù)接近2.0,而電導率與裂紋開度大致呈線性關系。由于試驗研究在二維裂紋網(wǎng)絡上進行,利用試驗結果可以檢驗之前建立數(shù)值和理論模型的準確性。
[Abstract]:Cracks will occur in porous materials under mechanical loads and environmental factors. Crack generation, propagation and connectivity have a significant effect on the permeability of the material, and then affect the performance of the material. The permeability of porous materials with random crack networks is studied by numerical simulation and experimental research. Firstly, based on the continuous percolation theory and considering the fractal characteristics of crack networks, a finite area crack network is proposed. Then based on the IDD model of interaction with crack inclusions, By introducing the connectivity and crack opening information of the crack network, the horizontal crack density related to the connectivity is defined, and the horizontal crack representing the connectivity characteristic is embedded in the effective matrix according to the incremental method. In this way, the interaction between crack inclusions is considered, and a propagating IDD model considering crack connectivity is proposed. Then, the permeability percolation model of porous materials with cracks is studied, and the crack surface density is used as the basic percolation variable. The percolation threshold and scale exponent near the threshold value of different crack networks are calculated, the analytical solution of permeability scaling law is given considering the connectivity of crack networks and the twists of main crack clusters, and the geometric percolation characteristics of crack networks are considered, respectively. Permeability and crack opening ratio of porous materials. The effect of crack network on the permeability and conductivity of materials is studied. In order to obtain a two-dimensional crack network with consistent upper and lower surfaces along the thickness of the specimen, In this paper, a method of artificial crack reassembly is used to obtain thin specimens with different cracking degrees. The two-dimensional crack morphology of the cracked specimen surface is quantitatively analyzed, including crack density, orientation, crack opening, etc. The isothermal adsorption and desorption curves of ordinary concrete and mortar materials were measured, and the water characteristic curves of the two materials were obtained. Then the multi-phase flow model of water migration was used to simulate the drying process of the specimens. At the same time, the corresponding intrinsic permeability was regressed by comparing the mass variation process of specimens with different cracking degree in drying experiment. Finally, the effects of different morphology parameters of crack network on permeability and conductivity were given. Geometric analysis of cracked network shows that, The global connectivity of crack networks can be reduced by the local cluster effect of random cracks. The numerical results verify the rationality of the connectivity definition method. (2) from a numerical point of view, the applicability of the IDD model for the propagation of disconnected and partially connected crack networks is verified respectively.) when the ratio of local permeability to matrix permeability of the crack is higher than 10 6, the applicability of the IDD model is verified respectively. When the crack density is greater than the critical threshold 0.3, the permeability and conductivity increase rapidly, and the permeability is exponentially related to the crack opening. The exponent is close to 2.0, and the conductivity is approximately linear with the crack opening. Since the experimental study is carried out on a two-dimensional crack network, the accuracy of the numerical and theoretical models established before the experiment can be verified by using the experimental results.
【學位授予單位】：清華大學
【學位級別】：博士
【學位授予年份】：2015
【分類號】：TU52

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本文編號：1495656