本文關(guān)鍵詞：擴(kuò)展有限元及其在混凝土結(jié)構(gòu)中的應(yīng)用研究　出處：《昆明理工大學(xué)》2015年博士論文　論文類型：學(xué)位論文

  更多相關(guān)文章： 擴(kuò)展有限元 斷裂 應(yīng)力強(qiáng)度因子 混凝土 黏聚裂縫模型 斷裂能

【摘要】：混凝土是由骨料、水泥漿體等按一定配比制備而成的多相復(fù)合材料,受其相間特有的結(jié)構(gòu)特性影響,混凝土材料受力后易于通過相間的損傷演化而導(dǎo)致開裂。因此混凝土開裂機(jī)制與斷裂問題一直是土木水利學(xué)科領(lǐng)域的一個重要研究課題。然而,由于問題的復(fù)雜性,迄今為止該學(xué)科領(lǐng)域未能完善地建立起描述混凝土服役期損傷演化的力學(xué)模型,既能預(yù)測裂縫模式、裂縫寬度以及裂縫發(fā)展?fàn)顩r,又能模擬混凝土結(jié)構(gòu)受力開裂破壞的響應(yīng)形式。為此,研究建立相應(yīng)的計算模型來描述和解釋混凝土開裂和破壞力學(xué)行為便成了本學(xué)科領(lǐng)域研究的熱點。本文在擴(kuò)展有限元(X-FEM)框架體系內(nèi),系統(tǒng)研究了混凝土材料開裂及裂縫擴(kuò)展導(dǎo)致的斷裂問題,其內(nèi)容可分為兩個主要部分。首先基于X-FEM的基礎(chǔ)理論,研究了二維、三維斷裂問題的應(yīng)力強(qiáng)度因子求解方法。其次,建立起混凝土材料及結(jié)構(gòu)開裂的理論方法,實現(xiàn)了混凝土結(jié)構(gòu)起裂和裂縫開展的數(shù)值模擬。具體工作內(nèi)容如下：(1)基于單位分解法原理,系統(tǒng)地建立了X-FEM位移計算模式,將虛擬裂縫擴(kuò)展法與X-FEM相結(jié)合,利用X-FEM中裂紋獨立于有限元網(wǎng)格的重要特性,提出了通過求解應(yīng)變能釋放率來獲取應(yīng)力強(qiáng)度因子的直接剛度計算法。與傳統(tǒng)方法相比,這種方法省去了大量的后處理工作,提高了計算效率,且編程和數(shù)值實現(xiàn)過程都較為簡單容易。(2)推演了使用X-FEM通過回路積分方法進(jìn)行三維斷裂問題應(yīng)力強(qiáng)度因子計算的完整理論和方法。針對三維彎曲裂前問題用水平集方法計算存在的問題,分析了有限元計算網(wǎng)格對計算精度敏感性的影響,提出了使用裂前正交網(wǎng)格來改善計算精度的有效方法。(3)研究了黏聚裂縫模型使用的材料軟化曲線對混凝土結(jié)構(gòu)的力學(xué)性能影響,揭示了初始斷裂能和拉伸強(qiáng)度與常規(guī)尺寸試件(或大多數(shù)實際結(jié)構(gòu))峰值荷載之間的內(nèi)在關(guān)系,為在缺乏足夠材料軟化信息條件下分析計算混凝土結(jié)構(gòu)實際工程斷裂問題提供了計算依據(jù)。(4)通過引入局部平均方法計算裂前應(yīng)力應(yīng)變場,構(gòu)建了用X-FEM進(jìn)行混凝土結(jié)構(gòu)斷裂分析的數(shù)值計算模型。該模型不僅可以有效模擬傳統(tǒng)斷裂分析中的預(yù)設(shè)裂縫問題,而且可以較好地處理無裂縫預(yù)置的開裂問題,并能同時計算多條裂縫的開展,實現(xiàn)復(fù)合型斷裂問題裂縫連續(xù)任意開展的數(shù)值模擬。(5)利用建立的X-FEM模型與其它結(jié)構(gòu)模型單元耦合分析計算了某混凝土帶裂大壩,預(yù)測了大壩裂縫潛在的開展軌跡,評估了加固方案的可行性和大壩的安全現(xiàn)狀,得出了具有實際工程意義的重要結(jié)論。
[Abstract]:Concrete is a kind of multiphase composite material, which is made of aggregate, cement paste and so on. It is influenced by its unique structure characteristics. Concrete materials are prone to crack through interphase damage evolution after loading. Therefore, the cracking mechanism and fracture of concrete has been an important research topic in the field of civil water conservancy. Due to the complexity of the problem, the mechanical model describing the damage evolution of concrete service period has not been established in this field, which can predict the crack mode, crack width and crack development. It can also simulate the response form of concrete structure under stress cracking and failure. It has become a hot topic in this field to study and establish the corresponding calculation model to describe and explain the cracking and failure mechanical behavior of concrete. This paper is in the framework of extended finite element method (FEM). The fracture problem caused by cracking and crack propagation of concrete material is studied systematically, which can be divided into two main parts. Firstly, based on the basic theory of X-FEM, two-dimensional analysis is carried out. The method of solving the stress intensity factor of three-dimensional fracture problem. Secondly, the theoretical method of crack of concrete material and structure is established. Numerical simulation of crack initiation and crack development of concrete structure is realized. The detailed work is as follows: 1) based on the principle of unit decomposition, the X-FEM displacement calculation model is established systematically. The virtual crack propagation method is combined with X-FEM, and the important characteristic of crack independence from finite element mesh in X-FEM is used. A direct stiffness calculation method is proposed to calculate the stress intensity factor by solving the strain energy release rate. Compared with the traditional method, this method saves a lot of post-processing work and improves the calculation efficiency. And both programming and numerical implementation are simple and easy. The complete theory and method of calculating stress intensity factor of three dimensional fracture problem by using X-FEM through loop integral method are deduced. The problems existing in calculating the stress intensity factor of three dimensional bending crack problem by level set method are deduced. The effect of finite element mesh on accuracy sensitivity is analyzed. An effective method to improve the calculation accuracy by using pre-crack orthogonal grid is proposed. The influence of the material softening curve used in the cohesive crack model on the mechanical properties of concrete structures is studied. The relationship between the initial fracture energy and tensile strength and the peak loads of conventional size specimens (or most of the actual structures) is revealed. It provides a basis for analyzing and calculating the fracture problem of concrete structure under the condition of lack of material softening information.) the local average method is introduced to calculate the pre-crack stress and strain field. A numerical model for fracture analysis of concrete structures using X-FEM is constructed, which can not only simulate the preset crack problem in traditional fracture analysis effectively. And it can deal with the crack problem without crack preset, and can calculate the development of multiple cracks at the same time. Numerical simulation of continuous and arbitrary crack development in complex mode fracture problem. 5) A concrete dam with crack is calculated by using the element coupling analysis of X-FEM model and other structural models. The potential track of dam crack is predicted, the feasibility of reinforcement scheme and the present situation of dam safety are evaluated, and an important conclusion of practical engineering significance is obtained.
【學(xué)位授予單位】：昆明理工大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2015
【分類號】：TU37

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本文編號：1409737