桥墩在船舶撞击作用下的损伤仿真研究

评述了考虑应变率效应和材料损伤的HJC混凝土模型,就材料参数的取值进行了讨论。通过刚性球撞击混凝土板的例子,讨论了HJC模型中损伤参数的敏感性,并据此确定了计算中采用的HJC模型参数。对一艘万吨级的散货船与桥墩的碰撞过程进行了仿真,给出了船舶与桥墩的碰撞力时程以及桥墩损伤形态。结果表明,由于混凝土的破损,船舶对桥墩的撞击力峰值显著降低。为获得真实的结果,在船舶与薄壁桥墩碰撞的仿真分析中应考虑混凝土的动态损伤特征。     

Damage evaluation of concrete plates by high-velocity impact

This paper describes the evaluation of the local damage of concrete plates by the impact of high-velocity rigid projectiles. A new launching system of mushroom-shaped projectiles has been developed. Impact tests for concrete plates have been conducted by using the system to examine failure modes of the local damage of concrete plates. The damage or failure behavior has been discussed on the basis of the failure process captured by a high speed video camera and the strain histories obtained by strain gauges on the concrete plate. Numerical simulations have been also carried out in order to explain the mechanism of the local damage observed by the experiment. A reasonable numerical model has been discussed in terms of a constitutive model and strain rate effect of concrete material. Mechanism of the local damage of concrete plates has been illustrated schematically.     

基于能量耗散碾压混凝土重力坝地震损伤分析

摘　要：采用塑性损伤力学对混凝土重力坝进行非线性动力分析,通过研究塑性损伤本构中滞回曲线的特点以及地震中重力坝裂缝发展特征和结构能量耗散机理,建立了包含能量特性的大坝整体损伤评价指标。通过分析发现强震作用下坝体上部的损伤是结构的主要损伤,地震中的能量以结构阻尼耗散能量为主,混凝土损伤和塑性耗散的能量所占比例不大,但与裂缝的发展有直接关系。提出的大坝整体损伤指标可以综合的反应结构的整体损伤程度,以此对结构进行抗震设计,可以提高结构的抗震性能。     

混凝土结构三维损伤开裂破坏全过程非线性有限元分析

本文建立了损伤理论与强度准则相结合的本构模型,在宏观裂缝出现以前用损伤力学理论及宏观裂缝出现以后仍考虑损伤用强度理论进行从损伤→开裂→破坏的全过程三维非线性有限元分析。结合实例计算,所得结果与其它软件分析结果有较好的可比性。     

一种新的用于各向同性损伤模型的四参数等效应变

基于Hsieh-Ting-Chen强度破坏准则的思想,提出由于求解混凝土各向同性损伤模量的等效应变。首先通过混凝土试件材料特性以及强度试验资料来确定四参数,然后求解出由多轴应力状态下的应变退化得到的等效应变以及相应的损伤模量。对一混凝土立方体试件进行有限元分析,计算结果表明:采用该等效应变计算所得的应力应变曲线与试验曲线吻合性较好,从而说明了该等效应变的合理性,并且可说明利用该等效应变的损伤模型不但可以描述单轴应力状态下混凝土破坏的全过程曲线,而且能描述多轴应力状态下混凝土破坏的全过程曲线。该等效应变形式单一,计算简单。     

基于统计损伤理论的硫酸盐侵蚀混凝土本构模型研究

基于统计损伤理论及宏观试验现象,该文建立了考虑硫酸盐侵蚀影响的混凝土单轴、双轴压缩统计损伤本构模型。混凝土变形破坏被理解为细观断裂、屈服两种损伤模式的连续累积演化过程。硫酸盐侵蚀效应改变了混凝土微结构的组成成分和力学特征,进而改变了微裂纹萌生、扩展的形态以及损伤的累积演化过程,可通过改变断裂和屈服两种细观损伤机制演化过程的概率分布形态来模拟。分析结果表明:在硫酸盐侵蚀环境下,侵蚀程度的加深显著改变了混凝土细观损伤累积演化过程,最终导致混凝土宏观力学性能呈现先“强化”后“弱化”的现象。在此过程中,细观损伤演化过程呈现出明显地规律性,可由统计损伤模型中5个特征参数的变化规律表征。该文模型为复杂环境下侵蚀混凝土细观损伤过程预测和分析提供了新的方法和工具。     

混凝土弹塑性损伤帽盖模型参数确定研究

摘要:基于连续损伤力学和塑性力学理论形成的弹塑性损伤帽盖模型是一个高级混凝土本构关系模型,但模型涉及的参数过多却给运用造成了不便。本文对模型参数进行详细解释基础上,采用已有的混凝土材料试验数据给出了其子午线强度参数、帽盖参数、脆性损伤和延性损伤参数取值,大大方便了工程运用。最后以单轴拉伸和单轴压缩为例数值演示了模型基本力学特性。     

型钢混凝土异形柱框架地震损伤分析

为实现对型钢混凝土异形柱框架的地震损伤分析,采用加权系数法建立了能够反映构件损伤、楼层损伤和整体框架损伤三者迁移演化的地震损伤模型,并对两榀型钢混凝土异形柱框架进行了地震损伤试验及有限元模拟,获得了梁的弯矩-转角滞回曲线和柱的水平荷载-位移滞回曲线,进而对试件的地震损伤指数进行了计算分析。结果表明,构件、楼层和整体框架的损伤指数变化规律与试件的破坏发展历程较为吻合,说明所建立的型钢混凝土异形柱框架地震损伤模型是合理的。基于试件的破坏状态及地震损伤分析结果,提出了型钢混凝土异形柱框架对应5个性能水平的损伤指数范围,为该类结构的震后损伤评估提供了依据。     

NUMERICAL SMEARED FRACTURE ANALYSIS: NONLOCAL MICROCRACK INTERACTION APPROACH

A recently proposed new nonlocal concept based on microcrack interactions is discussed, its implementation in a smeared cracking finite element code for concrete is presented, numerical studies are reported, and comparisons with experimental results are made. The nonlocality is not merely a mathematical device to prevent excessive spurious localization into a zone of zero volume but is a necessary physical consequence of microcrack interactions. Since the constitutive law itself is strictly local, the new nonlocal concept can be combined with any type of constitutive law for strain-softening nonlocal damage, which is here chosen to be the microplane model. A simple method is formulated to approximately identify the material parameters in the model from the basic characteristics of concrete such as the tensile strength, fracture energy and maximum aggregate size. The results of finite element analysis are shown to be mesh insensitive, and good convergence is obtained. Cracking damage is found to localize into a volume whose size and shape depend on the macroscopic concrete properties as well as the current stress–strain state. Although the damage is considered to be tensile on the microlevel, due solely to mode I microcracks, the new nonlocal model can describe well not only mode I fracture tests but also complex shear-dominated and mixed-mode types of failure such a diagonal shear, and can do so for the same values of material parameters (which was not the case for previous nonlocal models). Most importantly, the new nonlocal model can correctly capture the size effect of quasibrittle fracture, in approximate agreement with Bažant's size effect law.     

基于损伤理论的钢筋混凝土拱结构破坏过程的数值模拟

从一服役28年的旧拱桥上拆下来两个钢筋混凝土拱肋,对其进行了静载破坏试验。将第一作者提出的弹性损伤理论与有限元法相结合,针对钢筋混凝土结构的破坏问题,建立了相应的损伤力学有限元数值计算方法,编制了相应的计算机程序。对钢筋混凝土拱肋的破坏过程进行了数值模拟计算。拱的破坏模式、位移与应变的理论计算结果与试验结果吻合良好。得出了混凝土材料损伤特性参数的数值,揭示了混凝土材料破坏过程中一些复杂的力学行为。在较大的荷载水平下,钢筋混凝土结构呈明显的非线性特征。研究表明,本文损伤模型可以较好地描述混凝土材料的损伤与破坏行为。     

An analysis methodology for failure in postbuckling skin–stiffener interfaces

Blade-stiffened structures have the potential to produce highly efficient structures, particularly when the large strength reserves available after structural buckling, in the postbuckling range, are exploited. In experimental tests of postbuckling stiffened structures made from fibre-reinforced composites, failure typically initiates at the interface of the skin and stiffener and leads to rapid and even explosive failure. A methodology has been developed for analysing collapse in postbuckling composite structures that involves predicting the initiation of interlaminar damage in the skin–stiffener interface. A strength-based criterion is monitored in each ply using a local model of the skin–stiffener interface cross-section. For the analysis of large structures, a global analysis is first run to obtain the complete postbuckling deformation field, which is then input onto a local model using a global–local analysis technique. The coordinates of the local model can easily be moved to rapidly assess failure initiation at numerous skin–stiffener interface locations throughout the global structure. The analysis methodology is compared to experimental results for two-dimensional T-section specimens and large, fuselage-representative stiffened panels and is shown to give accurate predictions of the failure load and failure mechanisms. The use of the approach for the analysis of postbuckling composite structures has application for the design and certification of the next generation of aircraft.     

CFRP加固钢筋混凝土梁极限承载力的三维非线性分析及试验研究

提出三维虚拟分块破坏分析方法,通过对单元中已破坏的材料分块进行弹模缩减技术处理,并对各载荷步通过迭代不断修正计算模型直至收敛。在对6组不同CFRP粘贴方式加固钢筋混凝土梁进行破坏加载试验研究的基础上,采用此法对结构从开裂直至完全破坏的受力-变形全过程和极限承载力进行了三维非线性分析,比较极限承载力的计算和试验结果表明,二者符合得令人满意。有关研究成果可为混凝土结构加固维修的施工和设计参考。     

混凝土正交各向异性动态损伤本构模型研究

为建立混凝土的正交各向异性动态损伤本构,首先采用动力放大系数的形式考虑材料的应变率效应,然后基于Sidoroff能量等价原理,建立动态条件下单元体的损伤刚度矩阵。同时在损伤演化模型中,采用Mazars损伤模型描述主轴方向的损伤变量。另外采用适用于正交各向异性的Hoffman屈服破坏准则,并考虑损伤及动力放大系数对强度的修正。以建筑结构受爆破震动荷载作用的实验资料,对本模型进行了验证     

基于隐式梯度公式的各向异性混凝土损伤研究

在空间复杂应力状态下,混凝土损伤表现出强烈的应力方向相关性,隐式梯度公式中标量形式的损伤变量,不能精确描述混凝土在复杂应力状态下失效问题.该文引入窄间有效损伤矩阵,构造一种基于隐式梯度公式的各向异性的非局部损伤模型,证明了其率平衡方程在损伤过程中类型保持不变,给出空间应力状态下基于该模型的有限元程序,并将该模型应用于空...     

Computational applications of a coupled plasticity-damage constitutive model for simulating plain concrete fracture

A coupled plasticity-damage model for plain concrete is presented in this paper. Based on continuum damage mechanics (CDM), an isotropic and anisotropic damage model coupled with a plasticity model is proposed in order to effectively predict and simulate plain concrete fracture. Two different damage evolution laws for both tension and compression are formulated for a more accurate prediction of the plain concrete behavior. In order to derive the constitutive equations and for the easiness in the numerical implementation, in the CDM framework the strain equivalence hypothesis is adopted such that the strain in the effective (undamaged) configuration is equivalent to the strain in the nominal (damaged) configuration. The proposed constitutive model has been shown to satisfy the thermodynamics requirements. Detailed numerical algorithms are developed for the finite element implementation of the proposed coupled plasticity-damage model. The numerical algorithm is coded using the user subroutine UMAT and then implemented in the commercial finite element analysis program Abaqus. Special emphasis is placed on identifying the plasticity and damage model material parameters from loading-unloading uniaxial test results. The overall performance of the proposed model is verified by comparing the model predictions to various experimental data, such as monotonic uniaxial tension and compression tests, monotonic biaxial compression test, loading-unloading uniaxial tensile and compressive tests, and mixed-mode fracture tests.     

Numerical Simulation of Brittle Damage in Concrete Specimens

A framework for damage mechanics of concrete is applied to simulate the nonlinear elastic deformation behavior of concrete using finite element method (FEM). A rather simple isotropic damage model containing essentially no adjustable parameters is shown to produce results in remarkably good agreement with sample experimental data: the damage law requires only the fracture energy to be defined completely. The model is achieved by introducing a damage surface that is similar to the yield function in the conventional theory of plasticity. A special form of damage surfaces is constructed to illustrate the application of the model. A new damage criterion, defined as an equivalent strain norm, is proposed, in order to take into consideration the asymmetric behavior of concrete. For verifying the FEM program including the model, deformations predicted by this model are compared with both the experimental ones for the concrete structural model and the ones calculated without application of the continuum damage mechanics.__________Translated from Problemy Prochnosti, No. 3, pp. 57 – 74, May – June, 2005.     

12Cr1MoV钢低周疲劳损伤研究

为了预测锅炉、压力容器的整体寿命,用连续介质损伤力学理论研究了工程材料的低周疲劳损伤演变过程.采用循环应力幅定义损伤变量D,根据有效应力概念,建立了低周疲劳各向同性连续损伤模型,并通过控制应变的疲劳试验,用该模型对锅炉常用材料12Cr1MoV钢试件进行了疲劳损伤的测量.研究表明,当循环进行到80%寿命时,损伤进入局部化阶段,宏观裂纹开始形成,较好地验证了损伤演变模型;所建立的模型形式简单,参数少,易测量,具有明确的物理意义,对锅炉的寿命估算有参考价值.     

钢筋混凝土桥梁疲劳累积损伤失效过程简化分析方法

为了有效预测疲劳损伤累积程度与桥梁剩余寿命,提出了钢筋混凝土桥梁结构在运营荷载下疲劳失效全过程数值模拟的简化方法。首先,根据混凝土及钢筋疲劳刚度退化、疲劳强度退化与疲劳残余变形演变规律,建立了混凝土及钢筋经历任意次数疲劳加载后的剩余强度包络线方程,基于混凝土单轴本构模型和钢筋理想弹塑性模型,建立了混凝土及钢筋疲劳本构模型;然后,在此基础上对文献提出的疲劳全过程分析法进行了改进,提出了疲劳损伤累积失效全过程数值分析法;最后,基于ABAQUS 软件平台和该文方法,对某钢筋混凝土简支梁算例进行疲劳全过程数值分析。结果表明:利用该文方法得到的模拟值与试验值的相对误差处于合理范围之内,验证了该文方法的可靠性和实用性。     

一种修正的混凝土弹性损伤本构模型及其应用

混凝土弹性损伤本构模型的模型参数少、标定简单、计算效率较高,适于工程应用。Faria和Oliver等人所提出的混凝土损伤模型,体现了混凝土弹性损伤本构模型的上述优点,但原模型对反复荷载作用下混凝土刚度恢复效应描述欠佳。针对此不足,该文做了修正。并以ABAQUS为平台编制了材料模型子程序UMAT。应用修正的模型对几个典型...     

Seismic damage assessment and basis for damage-limiting design

A seismic damage model is developed for reinforced concrete structures in which the structural damage is expressed as a linear combination of the maximum deformation and the hysteretic energy dissipation. From an extensive damage analysis of various reinforced concrete buildings, an intensity scale is derived to describe the potential destructiveness of ground motion. It is a simple function of the rms acceleration and strong-motion duration. The proposed damage model is calibrated with observed building damages from past earthquakes. On this basis, a design procedure is developed accordingly to limit the potential structural damage to a tolerable level.