基于XFEM超高韧性水泥基复合材料裂纹扩展的数值模拟分析

发布时间：2018-06-14 15:56

本文选题：超高韧性水泥基复合材料 + 扩展有限元　；参考：《山东科技大学》2017年硕士论文

【摘要】：混凝土是实际生产中不可或缺的建筑材料,随着生产的需要,高性能混凝土发挥越来越重要的作用。其中,超高韧性水泥基复合材料(UHTCC)的研究也引起人们的重视。超高韧性水泥基复合材料通过优化基体、纤维、纤维与基体界面的基本性能以及三者之间的相互作用,使得该材料在纤维掺量很少的情况下,具有多缝开裂和应变硬化的特点。近几十年来,国内外学者对UHTCC在静力和动载方面对裂缝开展和断裂韧度方面做了很全面和详细的试验研究,但是对UHTCC断裂方面的仿真研究尚少,目前使用主要方法是扩展有限元(XFEM)法。扩展有限元(XFEM)是在常规有限元框架上求解不连续问题的有效数值模拟方法。其网格划分、材料尺寸与表面物理状态无关,对解决裂纹尖端高应力区和变形区的网格加密复杂问题有着无可比拟的优势,在动态裂纹扩展的历程中也不需要随裂纹扩展更新网格。本文结合单轴拉伸试验研究结果并利用软件模拟优势,对UHTCC的裂纹扩展进行仿真分析并与试验结果对比,主要研究内容包括了以下几个方面。1) UHTCC单轴直接拉伸试验研究通过采用尺寸为305 mm× 76 mm× 13 mm的试件进行纤维掺量和普通水泥基的单轴直接拉伸试验,研究材料的应变硬化现象和纤维掺量对基体的增韧效果,并计算UHTCC试件的断裂能。(1)使用一定掺量的纤维混凝土比普通混凝土有较好的韧性,随着纤维掺量的不同,出现不同程度的应变硬化现象。当纤维掺量为2%,应变硬化现象最为明显,受力比较均匀。当掺加一定量纤维时,混凝土的破坏不再是脆性破坏,并在主裂缝周围出现许多微细裂缝。(2)由试验得出的应力-裂缝宽度曲线,根据曲线包围的面积,以2%纤维掺量试件(5AF-2)为例,计算出其断裂能为11190N/m。2)三点弯曲梁静载试验研究了 PVA纤维的掺入、尺寸效应、缝高比等因素对试件的断裂性能影响和裂缝扩展的现象,利用双K断裂准则,分析其起裂荷载、峰值荷载、起裂韧度和失稳断裂韧度。(1)对于纤维水泥基体试件,同一尺寸,同一配合比试件,初始缝高比越大,起裂荷载和峰值荷载越小,起裂韧度几乎不随缝高比的增大发生变化,失稳断裂韧度在一定程度上有所降低。对于无纤维掺量水泥基随着初始缝高比的增加,其起裂韧度和失稳断裂韧度增幅并不明显,呈现一定的离散性。(2)同一配合比,同一缝高的纤维混凝土基体,当试件尺寸变大时,相应的起裂韧度和失稳断裂韧度也会明显增加。3)利用XFEM方法模拟研究UHTCC三点弯曲梁的不同缝高比的裂纹扩展规律和断裂性能,并将模拟结果与试验结果对比分析,验证利用XFEM模拟UHTCC断裂问题的可行性,得到以下结论:(1)通过后处理的应力云纹图,在裂缝未起裂前,在预制缝的尖端部分有较明显的应力集中现象,当裂缝扩展时应力集中现象消失,并且随着缝高比的增加,应力集中现象更加明显。(2)在一定的缝高比范围内,同一尺寸的UHTCC试件梁,随着缝高比的增加,起裂韧度影响较小,失稳断裂韧度逐渐变小,试验测出的起裂荷载、峰值荷载与模拟计算得出相差不大,根据起裂荷载、峰值荷载计算出的起裂韧度和失稳断裂韧度离散性较小。因此,利用ABAQUS中的扩展有限元(XFEM)分析UHTCC的断裂性能具有一定的可行性。
[Abstract]:Concrete is an indispensable building material in actual production. With the need of production, high performance concrete plays a more and more important role. Among them, the research of ultra high toughness cementitious composites (UHTCC) has also aroused people's attention. The ultra high toughness cementitious composites have passed the basic interface of the matrix, fiber, fiber and matrix. The interaction between the three and the three makes the material characterized by multiple crack cracking and strain hardening in the case of little fiber content. In recent decades, domestic and foreign scholars have done a comprehensive and detailed study on the fracture development and fracture toughness of the cracks in static and dynamic loads, but for the fracture of UHTCC. The main method is the extended finite element (XFEM) method. The extended finite element (XFEM) is an effective numerical simulation method to solve the discontinuous problem on the conventional finite element framework. The grid division, the material size and the surface physical state are independent, and the complex problem of the grid encryption in the high stress zone and the deformation zone at the tip of the breaking point is solved. With unparalleled advantage, there is no need to extend the mesh with the crack propagation in the process of dynamic crack propagation. This paper combines the results of the uniaxial tensile test and uses the advantages of the software simulation to simulate the crack propagation of UHTCC and compare it with the experimental results. The main research contents include the following aspects: the single axis of the.1) UHTCC The direct tensile test of direct tensile test by using a specimen with a size of 305 mm x 76 mm x 13 mm to carry out the uniaxial direct tensile test of fiber content and ordinary cementitious test, studies the strain hardening of the material and the toughening effect of the fiber content to the matrix, and calculates the fracture energy of the UHTCC specimen. (1) the fiber concrete is mixed with a certain amount of fiber. There is a good toughness in the soil. With the different fiber content, strain hardening occurs at different degrees. When the fiber content is 2%, the strain hardening is most obvious and the stress is more uniform. When adding a certain amount of fiber, the damage of concrete is no longer brittle failure, and there are many fine cracks around the main crack. (2) the test results are obtained. The stress crack width curve, according to the area surrounded by the curve, is taken as an example of the 2% fiber content test specimen (5AF-2). The fracture energy is 11190N/m.2) and the three point bending Liang Jing load test is used to study the effect of PVA fiber incorporation, the size effect, the crack height ratio and other factors on the fracture performance and crack expansion of the specimen, and the analysis of the double K fracture criterion is used. The cracking load, the peak load, the crack toughness and the instability fracture toughness. (1) for the fiber cement matrix, the same size, the same size, the higher the initial joint height ratio, the smaller the cracking load and the peak load, the crack toughness almost does not change with the increase of the seam height ratio, and the instability fracture toughness decreases to a certain extent. With the increase of the initial crack height ratio, the increase of the crack toughness and the instability fracture toughness is not obvious, and a certain discreteness is presented. (2) the same mix ratio, the same joint height of the fiber concrete matrix, when the specimen size becomes larger, the corresponding crack toughness and the instability fracture toughness will also increase obviously.3) using the XFEM method model. It is proposed to study the crack propagation law and fracture performance of UHTCC three point bending beam with different slots and height ratios. The simulation results are compared with the test results to verify the feasibility of using XFEM to simulate the UHTCC fracture problem. The following conclusions are obtained: (1) the stress moire chart of the post treatment is more obvious in the tip of the prefabricated seam before the crack is not cracked. The stress concentration phenomenon is disappearing when the crack expands, and the stress concentration phenomenon is more obvious with the increase of the seam height ratio. (2) in the range of certain seam height ratio, the UHTCC specimen beam of the same size, with the increase of the seam height ratio, the effect of the crack toughness is smaller, the instability fracture toughness gradually becomes smaller and the test crack load is measured. The difference between the peak load and the simulated calculation is small. According to the cracking load, the fracture toughness and the instability fracture toughness calculated by the peak load are smaller. Therefore, it is feasible to use the extended finite element (XFEM) in the ABAQUS to analyze the fracture properties of UHTCC.
【学位授予单位】：山东科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU528

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