【作者】 白卫峰；

【导师】 陈健云；

【作者基本信息】 大连理工大学 ， 水工结构工程， 2008， 博士

【摘要】 与混凝土工程应用繁荣兴旺的背景相比较,关于混凝土科学、尤其是混凝土本构关系研究明显赶不上发展的需要。正确合理的揭示材料损伤破坏机理,已成为混凝土损伤力学能否进一步发展的关键。围绕着我国西部大开发、西电东送及南水北调等战略需求,我国西部地区正在或即将兴建一大批重力坝和拱坝等高坝水电项目。我国西部地区属于地震高发区,同时高坝混凝土结构大部分处于深水高压饱和状态,因此针对孔隙水压对混凝土材料静动态力学性能的研究具有重要的现实意义。本文结合国家自然科学基金重点项目(90510018)和国家自然科学基金面上项目(50679006),针对混凝土材料细观损伤演化机制以及湿态混凝土力学特性进行了系统深入的研究。1.通过对连续损伤力学与细观统计损伤力学的基本理论进行比较,指出现有损伤力学模型的缺陷和不足,将混凝土材料细观损伤对宏观力学性能的影响重新概括为断裂损伤和屈服损伤两种模式。基于平行杆模型PBS,并结合现代非线性科学中协同学、突变论、混沌学的有关原理以及声发射试验的有关成果,确定了细观两种损伤模式演化过程的特征参数,建立了描述混凝土等准脆性材料单轴拉伸变形破坏全过程的细观统计损伤模型。将材料整个拉伸破坏过程分为两个损伤阶段,均匀损伤阶段和局部破坏阶段;区分了峰值名义应力状态和临界状态,解释了两状态对应的物理含义,强调了临界状态在整个拉伸破坏过程中所起的关键性作用。假设了局部破坏阶段断裂过程区内的变形机制,并建议临界状态作为本构模型的最终破坏点。2.固体的破坏过程是力学家与固体物理学家为之奋斗了三个半世纪的跨层次难题,揭示材料的损伤破坏机理,是数十年来众多国内外研究者矢志不渝的目标和方向。基于所建立的细观统计损伤模型描述的混凝土单轴拉伸损伤演化过程,本文提出了新的准脆性材料破坏理论——材料内在力学性能发挥机制理论。结合协同学的观点,将混凝土等准脆性材料看作是能动的、具有自组织行为特性的复杂系统;认为材料变形破坏过程本质上是材料以“损伤”为代价,通过自身潜在的力学性能不断发展和释放以适应外界荷载环境变化的能动的自组织行为过程;而这个自组织行为赖以进行所遵循的内在动力学机制由材料内在力学性能发挥机制控制。采用类比的科学分析方法,通过将材料损伤演化、生物进化、社会发展这三类客观世界中典型的非线性运动形式进行比较,证明本文提出的材料破坏理论的正确性和合理性。3.混凝土材料的动态力学性能和静态相比有显著的不同,一般认为混凝土动态应变率效应包括惯性效应和孔隙水粘性效应两部分。传统唯象的宏观损伤本构模型无法反映材料复杂的细观损伤演化机制,因此更无法描述动态应变率效应对材料细观损伤演化机制的影响。本文针对干燥混凝土建立了考虑惯性效应的单轴拉伸动态统计损伤模型,针对饱和混凝土建立了综合考虑惯性效应和粘性效应的单轴拉伸动态统计损伤模型。材料自身的惯性效应引起材料破坏形态以及细观损伤演化过程的改变,模型中通过调整两种细观损伤模式演化过程的特征参数来模拟;水的粘性效应则调整了混凝土基体的受力状态,模型中通过并联一个阻尼元件来模拟。所建议模型物理意义直观、明确,形象的呈现出了干燥及饱和混凝土动态拉伸破坏过程的物理图景;从宏细观相结合的角度进一步揭示了混凝土等准脆性材料损伤破坏的力学机制。4.混凝土的压缩破坏过程实质上是由于泊松效应在细观产生局部拉应变从而引起微裂纹萌生、扩展、成核的连续损伤演化过程。传统唯象的宏观压缩本构模型无法反映材料的细观损伤演化机制。本文根据混凝土材料单轴压缩破坏过程的细观损伤机理,在单轴拉伸统计损伤模型的基础之上,进一步建立了混凝土单轴压缩统计损伤模型。根据柏松效应引起的横向拉损伤的演化过程,确定受压方向的损伤演化规律并建立相应的压应力-应变本构关系。通过理论预测和试验结果进行比较,初步说明采用本文建议的统计损伤模型描述混凝土材料单轴受压过程损伤破坏机理的可行性和适用性。5.大部分针对湿态或饱和混凝土力学性能的研究均是在试验的基础上给出宏观现象的描述,而很少有从理论层面上探讨影响机理。本文采用复合材料等效夹杂理论,将细观孔隙分为活性孔隙和非活性孔隙,建立了双类孔隙夹杂模型,预测不同饱和度情况下孔隙及孔隙水对混凝土材料弹性模量的影响。将两类孔隙和水泥砂浆作为等效基体,粗骨料作为硬化夹杂,建立了双重夹杂模型,并结合细观断裂力学方法,建立了综合考虑多种因素统一的混凝土单轴压缩强度公式,探讨细观各种组分不同体分比、不同孔隙率以及不同饱和度情况对湿态混凝土抗压强度的影响。将太沙基有效应力原理引入到饱和混凝土力学性质的研究中,建立了符合混凝土材料自身微结构特点的有效应力原理表达式,探讨复杂受力环境中孔隙水压力对混凝土抗压强度的影响机制。根据大量的试验结果研究了湿态混凝土强度、初始弹模与饱和度、加载应变率之间的关系。考虑含水率对混凝土强度和初始弹性模量的影响,结合现有规范建议的混凝土本构模型,建立了湿态混凝土静、动态工况单轴拉伸、压缩应力-应变全过程曲线实用经验表达式。更多还原

【Abstract】 Comparing with the booming background of the engineering application of concrete,the research on the concrete science and especially the constitutive relation of concrete couldn’t satisfy the need of the development of the concrete engineering.Correct and rational understanding of the damage and failure mechanism of material is the key point to the development of concrete damage mechanics.With the progress of Grand Western Development Program,West-East Power Transmission program and South-to-North Water Diversion,quite a few high darn hydropower projects are being or will soon be constructed in the Western.The Western of China is the frequently-occurring earthquake area,and the most concrete regions of high dam are in the deep water,high pressure and saturated state,so the study on the influence of the pore water pressure on the static and dynamic mechanical properties of concrete material has important realistic meaning.With the support from National Nature Science Foundation of China under grants No.90510018 and 50679006,in-depth research was conducted regarding the meso-damage evolution mechanism of concrete and mechanical properties of saturated concrete.1.By comparing the basic theories of Continuum Damage Mechanics and Statistical Damage Mechanics,the defects and shortcomings of the existing damage mechanical models are pointed out.The influence of the meso-damage mechanism on the macroscopic mechanical properties of concrete materials is newly summarized into two aspects,rupture damage and yield damage.Based on the parallel bar system,combining with the synergetic method,the catastrophe theory and also the acoustic emission test,two new activated statistical damage models for quasi-brittle solid are developed,which could simulate the whole damage and fracture process of material when exposed to quasi-static uniaxial tensile traction.The whole damage course is newly divided into the statistical even damage phase and the local breach phase.The two characteristic states,the peak nominal stress state and the critical state are distinguished,and emphasize the critical state plays a key role during the whole damage evolution course.A physical mechanism existing in the fracture process zone during the local breach phase was assumed.The critical state is proposed as the final failure point in the compressive constitutive model.2.The failure process of solid is the trans-scales problem,for which the mechanics workers and the solid physicists have struggled for three and half centuries.To reveal the damage and failure mechanism of material is the persevering aim for the researchers both at home and abroad during the past several decades.Based on the damage evolution process of concrete under uniaxial tension described by the statistical damage model in this paper,a novel material failure theory,i.e.the exerting mechanism of internal mechanical capability of material is proposed.Combining with the viewpoint of the synergetic theory,the quasi-brittle material is regarded as the complicated system with the characteristics of active and self-organization behavior.The essence of the deformation and failure of solid materials is the self-organization behavior process to adapt the changes of the external load environment by the exerting and release of the potential mechanical capabilities the material owns by itself,at the cost of "damage",and the self-organization behavior obeys the exerting mechanism of intemal mechanical capability.By comparing the processes of the material damage evolution, the social advancement and the biological evolution which are the three typical nonlinear motion forms in the objective world,the correctness and rationality of this new fracture theory is proven.3.The dynamic mechanical properties of concrete material is remarkable different from the static state.The physical mechanism of the dynamic strain rate effect is usually divided into two aspects,the inertial effect and the viscous effect.The traditional phenomenological damage models couldn’t reflect the complicated meso-damage evolution mechanism,so they can’t describe the influence of the dynamic strain rate effect on the meso-damage evolution mechanism.The dynamic statistical damage models under uniaxial tension,which consider the inertial effect for dry concrete and the inertial and viscous combinated effect for the saturated concrete are proposed respectively.The result of the inertial effect leads to the change of the fracture form and the evolution process of the damage accumulation,and be simulated by adjusting the characteristic parameters of the evolution process of the two damage modes.The viscous effect of the pore water leads to the adjustment of the loading condition of the matrix,and be simulated by paralleling a damper with the static statistical damage model.The proposed models lively and vividly describe the damage evolution mechanism of dry and saturated concrete under dynamic loading case from the macroscopic-microscopic viewpoint.4.The failure of concrete specimen under uniaxial compression mainly contributes to the nucleation and growth of microcracks due to local tensile strain caused by the poisson effect. The traditional phenomenological damage models couldn’t reflect the tensile damage evolution mechanism in meso-scale.Based on the statistical damage model under uniaxial tension,a statistical damage model under uniaxial compression is further proposed.The damage evolutional law in the compressive direction is confirmed by the tensile damage evolution process of the lateral deformation due to the poisson effect,and then the compressive stress-strain relationship is defined.The comparisons between the theoretical results and the experiment results preliminarily verify the rationality and feasibility of understanding the failure mechanism of concrete through the statistical damage constitutional law.5.Most of the researches on the mechanical property of wet or saturated concrete are the description of the macroscopic phenomenon based on the experiment,but the influence mechanism of the pore water pressure has been seldom reported.Concrete is a porous material with two pore types,active pore and entrained non-active pore,and the former will be filled with water in moisture environment.Based on the effective inclusion theory,a double pore inclusion model is proposed to predict the influence of the pore and the pore water on the initial elastic modulus of moisture concrete.The two types of pore and the mortar are regarded as the equivalent matrix,the aggregate as the inhomogeneous inclusion,a kinds of double inclusion model is proposed;and an united compressive strength expression is established combining with the fracture mechanics method,which could consider the influence of the different volume fraction of kinds of phases,pore rate and the water saturation.The Terzaghi’s effective stress principle is introduced into the study of the mechanical properties of saturated concrete,and the specific expression of effective stress principle applicable to saturated concrete is established to investigate the influence mechanism of pore water pressure on the strength of concrete under complicated stress states. The relationship between strength,initial elastic modulus and saturation,loading rate of wet concrete are studied based on lots of test results in the literature.Combining with the constitutive relation of concrete suggested by the specification,the practical constitutive equations for wet concrete under static and dynamic uniaxial tension and compression are established,which considers the influence of the water content on the strength and the initial elastic modulus of concrete.更多还原