岩石破裂过程THMD耦合数值模型研究

从岩石的细观非均匀性特点出发,应用损伤力学、热力学和渗流力学理论,建立了岩体热(温度)-水(渗流)-岩(应力)-损伤耦合数值模型(THMD model),把岩石(体)THM耦合问题的研究从应力状态分析深入到损伤、破坏过程分析之中。探讨了THM耦合作用下岩石材料的细观结构损伤及其诱发的材料力学性能演化机制,并运用所提出方法计算温度-渗流-应力耦合作用下井筒近场围岩的稳定性,模拟得到的岩体破坏过程、应力分布、AE特性及渗流特性变化与现场标定结果有着一致的规律性,初步证明了该数值模型的合理性和有效性。THMD模型以简单的数值模型表征了岩石(体)中热、水、岩及损伤之间复杂的作用关系,为从细观损伤演化揭示宏观岩体温度-渗流-应力耦合破坏机制提供了一种新的数值分析方法。     

Micromechanical analysis of the fully coupled finite thermoelastic response of rubber-like matrix composites

A micromechanical analysis for the prediction of the coupled thermoelastic response of multiphase composites that include rubber-like phases is presented. Rubber-like solids are highly nonlinear thermoelastic materials that exhibit anomalous behavior referred to as the thermoelastic inversion effect. Results are presented which show that the derived micromechanical model is capable of predicting this effect in nylon/rubber composites subjected to appropriate thermal loadings assuming one-way coupling. For full thermomechanical coupling, the nonlinear response and induced temperatures under several types of mechanical loading are investigated.     

Elastic response of water-filled fiber composite tubes under shock wave loading

We experimentally and numerically investigate the response of fluid-filled filament-wound composite tubes subjected to axial shock wave loading in water. Our study focuses on the fluid–structure interaction occurring when the shock wave in the fluid propagates parallel to the axis of the tube, creating pressure waves in the fluid coupled to flexural waves in the shell. The in-house-developed computational scheme couples an Eulerian fluid solver with a Lagrangian shell solver, which includes a new and simple material model to capture the response of fiber composites in finite kinematics. In the experiments and simulations we examine tubes with fiber winding angles equal to 45° and 60°, and we measure the precursor and primary wave speeds, hoop and longitudinal strains, and pressure. The experimental and computational results are in agreement, showing the validity of the computational scheme in complex fluid–structure interaction problems involving fiber composite materials subjected to shock waves. The analyses of the measured quantities show the strong coupling of axial and hoop deformations and the significant effect of fiber winding angle on the composite tube response, which differs substantially from that of a metal tube in the same configuration.     

含损伤演化的TM耦合数值模型及其应用研究

基于生物力学中的Wolff法则，发展了一种连续体拓扑优化的新方法. 有待优化的结构 被看作是一块遵从Wolff法则生长的骨骼，把寻找其最优拓扑的过程比拟为骨骼的重建/生 长过程. 采用骨骼的重建/生长规律作为准则更新材料分布，直至达到一个平衡状态并由此 获得结构的最优拓扑. 算例表明了所提出方法的有效性.     

Modeling the response of nonlinear viscoelastic biodegradable polymeric stents

We analyze the response of nonlinear viscoelastic biodegradable polymers when subject to mechanical loading coupled with the diffusion of a fluid (water) through the polymers and the degradation that occurs over a period of time. We consider the quasi-linear viscoelastic (QLV) model introduced by Fung (1981) that has been found to be reasonably good in modeling tissues undergoing moderate deformations for modeling the nonlinear viscoelastic response of the biodegradable polymer that is being studied, i.e., poly-lactic acid (PLLA). We modify the QLV model to incorporate changes in the material parameters that are a consequence of the degradation that the polymers undergo. We assume that the rate of degradation increases with an increase in the magnitude of strains and concentration of water. We also assume that the degradation softens the polymers and that the rate of stress relaxation (or the rate of creep) of the polymer increases with degradation. Our primary intention is to examine the effect of viscoelasticity on the degradation in virtue of the time-dependent response of such bodies, and also due to the effect of the diffusion of water that leads to degradation. The problem leads to three different time histories associated with the strong coupling between the mechanical loading, diffusion of a fluid (water), and the degradation. As the biodegradable stent is placed inside a nonlinear viscoelastic arterial wall, we further examine the effect of the coupling between the response of the polymeric stent and arterial wall on the degradation of the biodegradable polymeric stent.     

气动加载与振动激励耦合试验方法研究

飞机结构在飞行过程中同时承受气动载荷和振动载荷的联合作用,这两种载荷的耦合加载试验对于飞机结构成为一项重要的研究内容,所以有必要对此类试验的可行性及其耦合加载方式进行研究。此次试验以气囊加载静载/常规疲劳载荷状态下试件的振动响应测试为目的,设计符合试验要求的试件和整套试验装置。得到了气囊5种不同加载情况下试件振动响应变化情况,并对此试验结果进行了理论分析,得出以下结论:a)气囊模拟静载/常规疲劳载荷加载不会大幅改变结构本身振动特性,此耦合试验方法所模拟环境比较接近飞机结构真实载荷环境;b)加载气囊的个数、部位及加载力的不同对试件结构的振动响应有一定影响,应增加气囊蓄能器或在试验前进行分析以选择合理的加载点。     

Some specific features and consequences of the thermal response of rubber under cyclic mechanical loading

The present paper deals with the specificities of the thermal response of rubber under cyclic mechanical loading at constant ambient temperature. This question is important, since the stabilized thermal response is used in fatigue life criteria, especially for the fast evaluation of fatigue life. For this purpose, entropic coupling in a thermo-hyperelastic framework is first used to predict the variation in the heat source produced or absorbed by the material during cyclic loading. The heat diffusion equation is then used to deduce temperature variations under adiabatic and non-adiabatic conditions. The influence of several parameters on the stabilized thermal response is studied: signal shape, frequency, minimum and maximum stretch levels, multiaxiality of the mechanical state. The results show that, in the steady-state regime, the mean value between the maximum and minimum temperature variations over a mechanical cycle is different from zero. This is due to the specific variation in the heat source, which depends on both the stretch rate and the stretch level. This result has numerous consequences, in particular for fatigue. Indeed, the stabilized mean value between the maximum and minimum temperature variations during fatigue tests does not reflect only fatigue damage, since the entropic coupling also leads to a value different from zero. This is a major difference with respect to materials exhibiting only isentropic coupling, such as metallic materials.     

A HYDRO-MECHANICAL-CHEMICAL COUPLING MODEL FOR GEOMATERIAL WITH BOTH MECHANICAL AND CHEMICAL DAMAGES CONSIDERED

A general framework of hydro-mechanical-chemical coupling model is proposed for geomaterial subjected to the dual effects of mechanical loading and chemical degradation. Mechanical damage due to microcracks in solid matrix and chemical damage induced by the increase of porosity due to dissolution of matrix minerals as well as their interactions are considered. A special model is proposed for sandstone. The reaction rate is formulated within the framework of mineral reaction kinetics and can thus take into account different dissolution mechanisms of three main mineral compositions under different pH values. The increase of porosity is physically defined by the dissolution of mineral composition and the chemical damage is related to the increase of porosity. The mechanical behavior is characterized by unified plastic damage and viscoplastic damage modeling. The effective stress is used for describing the effect of pore pressure. The elastic parameters and plastic evolution as well as viscoplastic evolution are dependent on chemical damage. The advection, which is coupled with mechanical damage and chemical damage, is considered as the dominant mechanism of mass transfer. The application of model proposed is from decoupled experiments to fully coupled experiment. The model offers a convenient approach to describing the hydro-mechanical-chemical coupled behavior of geomaterial.     

温度-随机载荷下CFL加固RC梁疲劳性能的实验研究

考虑亚热带地区公路桥梁的服役环境温度与车辆载荷的作用效应,本文以碳纤维薄板(CFL)加固钢筋混凝土(RC)桥梁结构为研究对象,利用本课题组构建的实验平台,提出了温度与车辆随机载荷耦合作用下CFL加固RC梁的疲劳实验方法。在3个温度和3个载荷水平下实施了温度-随机载荷耦合作用下的三点弯曲疲劳实验,初步探讨了温度-随机载荷作用下加固梁的疲劳破坏机理,并提出了温度-随机载荷耦合下加固梁疲劳寿命的半经验公式。     

Microstructural modeling of asphalt concrete using a coupled moisture–mechanical constitutive relationship

The coupled effect of moisture diffusion and mechanical loading on the microstructure of asphalt concrete is studied. The traditional Continuum Damage Mechanics (CDM) framework is modified to model detrimental effects of moisture and mechanical loading. Adhesive/cohesive moisture-induced damage constitutive relationships are proposed to describe the time-dependent degradation of material properties due to moisture. X-ray two-dimensional (2D) computed tomography-imaging technique is used to construct finite element (FE) microstructural representation of a typical dense-graded asphalt concrete. After being calibrated against pull-off experiments, the proposed moisture-induced damage constitutive relationship, which is coupled to thermo-viscoelastic–viscoplastic–viscodamage mechanisms, is used to simulate the microstructure of asphalt concrete. Simulation results demonstrate that the generated 2D FE microstructural representation along with the coupled moisture–mechanical constitutive relationship can be effectively used to model the overall thermo-hygro-mechanical response of asphalt concrete.     

On the direct interactions between heat transfer,mass transport and chemical processes within gradient elasticity

The behaviour of complex material systems often results from the combined effects of several multi-scale mechanisms and simultaneously occurring coupled physical processes. In this paper, we focus on such complex response of a class of geomaterials in which heat conduction, mass diffusion, chemical reactions and gradient-type elastic strain mechanisms interact. Our purpose is to develop within a formal thermodynamic framework a complete set of constitutive equations which account for most of the possible aforementioned direct couplings and the associated relevant size effects in a unified phenomenological way. For the sake of simplicity, the volume element is described at the macroscopic scale as a classical homogeneous continuous mixture of chemically active species. Based on theories of second-gradient elasticity endowed with the concepts of both nonlocality residual and constitutive insulation condition, a thermo-diffuso-chemo-elastic formulation is proposed in the restricted case of small perturbations. Coupling terms entering the relevant constitutive relations are discussed throughout the paper. Then, the model is applied to a simple one-dimensional situation, in which only the mechanical response is reported. The implementation of such modelling in a finite element code should enable us to address more specific problems, such as the stress solution phenomenon in hollow cylinders subjected to external loading.     

A coupled kinetic-constitutive approach to the study of high temperature crack initiation in single crystal nickel-base superalloys

A rate-dependent crystallographic constitutive theory coupled with a mass diffusion model has been used to study crack initiation in single crystal nickel-base superalloys, exposed to an oxidising environment and subjected to mechanical loading. The time to crack initiation under constant load has been predicted using a strain-based failure criterion. A notched compact tension (CT) specimen containing a single casting defect, idealised as a cylindrical void close to the notch surface, has been studied. Finite element analysis of the CT specimen revealed that, due to the strong localisation of inelastic strain at the void, a microcrack will initiate in the vicinity of the void rather than at the notch surface. The numerical results have also shown that the time to crack initiation depends strongly on the void location. The coupled diffusion-deformation studies have revealed that environmental effects reduce the time to crack initiation due to the oxidation-induced material softening in the vicinity of the notch and void. The applicability of a failure assessment approach, based on the linear elastic stress intensity factor, K, to predict the crack initiation time under creep loading is examined and a probabilistic framework for prediction of component lifetime is proposed.     

Interaction between diffusion of palm biodiesel and large strain in rubber: Effect on stress-softening during cyclic loading

In addition to fluctuating multiaxial mechanical loading, many engineering rubber components are exposed to hostile environments such as oil rich environment. In this case, the mechanical response of rubbers is affected by the interaction existed between mechanical loading and diffusion of liquid into the material. The present work attempts to investigate the above interaction and the resulting mechanical response under cyclic loading conditions in nitrile butadiene rubber (NBR) and chloroprene rubber (CR). More precisely, our focus is on the well-known stress-softening (Mullins effect) phenomenon classically observed in rubbers under cyclic loading conditions.     

Some transient coupled thermoelastic crack problems

This paper is concerned with determining the elastodynamic response of a plane strain medium containing a central crack deformed by the action of suddenly applied thermal and/or mechanical disturbances when the assumptions of the general theory of coupled thermoelasticity are assumed. Integral transform solution is employed to reduce the governing equations into integral equations of Fredholm type. A numerical inversion technique is used to compute the dynamic stress-intensity factors when the faces of the crack are subjected to constant heat flux and/or mechanical loading. Attention is focused on the overshoot in the stress-intensity factor and its time interval for non-stationary temperature fields, and to what degree it is influenced by the mutual dependence of the temperature and displacement fields inherent in the coupled theory of thermoelasticity.     

混凝土材料损伤-自愈行为的湿化力多场耦合分析

荷载与环境共同工作下的混凝土损伤-愈合力学行为具有典型的内在湿化力多场耦合特征．本文以混凝土中CaCO3 沉淀自愈机制为例,建立了一种湿-化-力多场耦合分析模型．通过引入一组扩散和化学反应方程,对材料微观结构层次的物理化学过程进行数学建模．随后,基于连续损伤愈合力学理论,将自愈效应引入混凝土损伤本构关系,发展出混凝土湿化力耦合分析模型并进行模型验证．针对单轴拉伸混凝土试样进行多场耦合数值分析,考察了关键参数对愈合过程的作用规律以及自愈进程对混凝土材料力学行为的影响．本文的研究为混凝土在运行环境下的损伤-愈合行为以及性能演变提供了定量分析方法．     

机械密封热力耦合有限元模型与密封性能分析

以接触式机械密封为研究对象,考虑密封环的热力变形和液膜温度、厚度等的耦合关系,建立了二维轴对称热力耦合计算模型,采用有限元与数值迭代技术实现了模型的数值解算,研究了密封端面热力变形规律,分析了不同密封压力下的密封性能.结果表明:热力耦合变形作用下,端面形成收敛型泄漏间隙,最小膜厚位于端面内靠近内径侧位置,最高温度位于最小膜厚处;随密封压力的增大,端面最小膜厚减小,端面最大温升、摩擦扭矩和泄漏率相应增大.采用的模型和计算方法可用于海洋装备用机械密封结构的优化设计.     

Dynamic analysis of a rotating rigid-flexible coupled smart structure with large deformations

Based on Hamilton's principle,a new kind of fully coupled nonlinear dynamic model for a rotating rigid-flexible smart structure with a tip mass is proposed.The geometrically nonlinear effects of the axial,transverse displacement and rotation angle are considered by means of the first-order approximation coupling(FOAC)model theory, in which large deformations and the centrifugal stiffening effects are considered.Three kinds of systems are established respectively,which are a structure without piezoelectric layer,with piezoelectric layer in open circuit and closed circuit.Several simulations based on simplified models are presented to show the differences in characteristics between structures with and without the tip mass,between smart beams in closed and open circuit, and between the centrifugal effects in high speed rotating state or not.The last simulation calculates the dynamic response of the structure subjected to external electrical loading.     

A single strain-based growth law predicts concentric and eccentric cardiac growth during pressure and volume overload

Adult cardiac muscle adapts to mechanical changes in the environment by growth and remodeling (G&R) via a variety of mechanisms. Hypertrophy develops when the heart is subjected to chronic mechanical overload. In ventricular pressure overload (e.g. due to aortic stenosis) the heart typically reacts by concentric hypertrophic growth, characterized by wall thickening due to myocyte radial growth when sarcomeres are added in parallel. In ventricular volume overload, an increase in filling pressure (e.g. due to mitral regurgitation) leads to eccentric hypertrophy as myocytes grow axially by adding sarcomeres in series leading to ventricular cavity enlargement that is typically accompanied by some wall thickening. The specific biomechanical stimuli that stimulate different modes of ventricular hypertrophy are still poorly understood. In a recent study, based on in vitro studies in micropatterned myocyte cell cultures subjected to stretch, we proposed that cardiac myocytes grow longer to maintain a preferred sarcomere length in response to increased fiber strain and grow thicker to maintain interfilament lattice spacing in response to increased cross-fiber strain. Here, we test whether this growth law is able to predict concentric and eccentric hypertrophy in response to aortic stenosis and mitral valve regurgitation, respectively, in a computational model of the adult canine heart coupled to a closed loop model of circulatory hemodynamics. A non-linear finite element model of the beating canine ventricles coupled to the circulation was used. After inducing valve alterations, the ventricles were allowed to adapt in shape in response to mechanical stimuli over time. The proposed growth law was able to reproduce major acute and chronic physiological responses (structural and functional) when integrated with comprehensive models of the pressure-overloaded and volume-overloaded canine heart, coupled to a closed-loop circulation. We conclude that strain-based biomechanical stimuli can drive cardiac growth, including wall thickening during pressure overload.     

On the constitutive modeling of coupled thermomechanical phase-change problems

This paper deals with a thermodynamically consistent numerical formulation for coupled thermoplastic problems including phase-change phenomena and frictional contact. The final goal is to get an accurate, efficient and robust numerical model, able for the numerical simulation of industrial solidification processes. Some of the current issues addressed in the paper are the following. A fractional step method arising from an operator split of the governing differential equations has been used to solve the nonlinear coupled system of equations, leading to a staggered product formula solution algorithm. Nonlinear stability issues are discussed and isentropic and isothermal operator splits are formulated. Within the isentropic split, a strong operator split design constraint is introduced, by requiring that the elastic and plastic entropy, as well as the phase-change induced elastic entropy due to the latent heat, remain fixed in the mechanical problem. The formulation of the model has been consistently derived within a thermodynamic framework. All the material properties have been considered to be temperature dependent. The constitutive behavior has been defined by a thermoviscous/elastoplastic free energy function, including a thermal multiphase change contribution. Plastic response has been modeled by a J2 temperature dependent model, including plastic hardening and thermal softening. The constitutive model proposed accounts for a continuous transition between the initial liquid state, the intermediate mushy state and the final solid state taking place in a solidification process. In particular, a pure viscous deviatoric model has been used at the initial fluid-like state. A thermomecanical contact model, including a frictional hardening and temperature dependent coupled potential, is derived within a fully consistent thermodinamical theory. The numerical model has been implemented into the computational finite element code COMET developed by the authors. Numerical simulations of solidification processes show the good performance of the computational model developed.