混凝土楔入劈拉破坏的损伤塑性模拟

针对混凝土在微观上产生的损伤或者断裂,长期积累下来会导致在宏观上破坏的问题,基于试件表面的数字图像,建立反映真实骨料形状和分布的二维有限元模型,并通过混凝土损伤塑性模型进行楔入劈拉试验中混凝土非线性破坏的数值模拟.模拟结果与试验结果非常吻合,很好地反映混凝土试件的破坏区域和损伤发展的路径.     

微平面模型与经典混凝土理论模型的比较

针对在混凝土非线性分析时所采用的宏观本构模型中,没有考虑混凝土软化阶段或考虑不当,以及在多轴受力情况下宏观模型不能很好地模拟混凝土受力状态的问题,基于微平面理论,利用MATLAB编写混凝土材料的非线性本构关系程序,从理论和计算结果两方面与经典的基于应力张量及其不变量的本构模型进行比较.比较结果表明,在弹性变形阶段,经典理论模型和微平面模型计算结果与试验结果无明显区别;在非弹性变形阶段,经典理论模型与微平面模型有较大的差异,后者与试验结果吻合较好.微平面理论在混凝土三向受力和软化阶段更能准确地描述混凝土材料本构关系,且本构关系更简单、清晰.     

混凝土板裂纹扩展的态型近场动力学模拟

构建考虑混凝土拉压异性和宏观断裂特征的混凝土类材料非局部态型近场动力学本构模型,并通过引入动态松弛、系统失衡判断和力边界等效等算法,构建适于分析混凝土类材料和结构变形破坏过程的态型近场动力学数值模拟体系.通过分组模拟和定量计算,分析算法的收敛性、计算精度和效率等问题;在此基础上开展含不同角度中心裂纹混凝土板的破坏模拟.     

T形异形柱的非线性有限元分析

分析了T形异形柱的受力问题,利用ABAQUS有限元软件对T形异形柱进行了弹塑性非线性有限元分析.着重从混凝土的非线性本构关系和破坏准则,受拉开裂后的行为,钢筋的本构关系几方面进行分析,通过计算绘制出了梁柱混凝土的应力云图、裂缝图及钢筋的应力云图.用ABAQUS计算所得的裂缝图与拟静力试验结果裂缝进行比较,两者结果吻合.结果表明:应用ABAQUS对异形柱进行非线性分析是可靠的,从而论证了软件的实际应用能力,也为进一步进行更复杂的非线性分析打下了基础.     

泡沫铝填充在轿车B柱中的侧面耐撞性研究

为了提高轿车侧面耐撞性,设计耐撞性能强的B柱成为主要课题之一.目前的优化方法很难将B柱侵入量和侵入速度同时控制在理想范围内.因此,提出泡沫铝材料填充在汽车B柱内代替B柱加强板的方法,缓冲侧面碰撞冲击.通过建立泡沫铝有限元模型与材料特性分析,确定仿真泡沫铝主要材料参数.进而根据中国新车评价规程C-NCAP要求,建立轿车整车侧面碰撞有限元模型,采用LS-DYNA软件进行仿真分析.结果表明,泡沫铝填充后的B柱侵入量和侵入速度都有明显降低.泡沫铝材料塑性变形和整体弯曲变形能够吸收1.51kJ的能量,是B柱加强板的3倍.填充泡沫铝前后仿真结果表明,轿车B柱填充泡沫铝是一种提高轿车侧面耐撞性的方法.     

泡沫铝部分填充薄壁梁弯曲吸能特性研究

为了研究泡沫铝填充帽型薄壁梁横向弯曲时的吸能特性,建立了泡沫铝填充双帽型薄肇粱的有限元模型,采用非线性有限元软件LS-DYNA进行了横向弯曲工况下的仿真.首先进行了空心帽型薄壁梁和泡沫铝填充帽型薄壁梁的横向弯曲仿真,分析了材料参数、几何参数对其比吸能(单位质量吸收的能量)的影响;然后为降低结构重量并保持薄壁梁吸能效果,对部分填充泡沫铝薄壁梁进行了横向弯曲仿真,考察了不同泡沫铝填充长度对结构吸能特性的影响.研究结果表明:填充泡沫铝后,帽型薄壁梁在横向弯曲中吸能特性有明显的改善;在吸收相同的能量时,泡沫铝填充薄壁梁的质量要比空心薄壁梁的质量少.     

分数阶微积分流变模型在岩体结构加速流变破坏分析中的应用

针对采用常用的元件模型较好地拟合试验结果时需要的参数较多的缺点,将分数阶微积分理论应用于岩体结构的流变分析.将分数阶微积分的黏弹性模型和黏塑性模型的一维本构关系推广为三维本构关系,推导流变应变增量计算公式.然后将分数阶微积分流变模型应用于不同岩体结构的加速流变破坏分析.结果表明：改变分数阶次时,岩体结构加速流变性态将发生较大变化,分数阶微积分流变模型可较好地描述岩体结构不同的加速流变破坏过程,且模型简单实用.     

形变体仿真中材质本构模型的应用与设计综述

本构模型是形变体仿真中最重要的因素之一,现有的基本的本构模型的应力应变关系具有一定的局限性,形变行为比较单一.近年来,很多研究工作探讨如何设计更加复杂并满足设计师需求的材质模型.本文将材质模型分为三类,传统的具有单一材质属性的均质材质、具有复合结构的非均质材质以及根据基本材质模型通过编辑材质参数和结构以及编辑形变行为的材质模型.此外,我们梳理近年来材质本构模型方面的研究成果,分类总结相关技术及其优缺点,最后讨论并指出形变体仿真中本构模型应用与设计领域主要的技术挑战和需要进一步探索的方向.     

含孔复合材料层合板累积损伤仿真分析

针对面内静拉伸纤维增强复合材料含中孔层合板,发展了一种参数化三维逐渐损伤模型,并结合有限元三维逐渐损伤分析技术即应力分析、失效判定准则及损伤过程中材料性能退化等,对含孔层合板损伤扩展进行了仿真分析.本模型可以模拟含中孔层合板损伤起始、发展及最终结构破坏整个过程,并能较好地预测含孔层合板的破坏模式和破坏强度.该文同时对含孔层合板的损伤基本机理、类型及其相互关联作用进行了分析探讨,该文计算结果与文献实验结果非常吻合.     

材料中应变率力学性能测试数据处理与表征方法

针对材料的中应变率力学性能测试数据,为数据处理与本构表征设计专用的分析软件。给出了载荷测量和应变测量方法,梳理了从测试数据到本构参数所历经的数据处理流程和方法,按照逻辑程序和功能模块化设计,基于MATLAB GUI平台编制了数据处理软件。利用该软件处理了S580B合金钢的测试数据,得到3种动态本构模型对应的应变强化参数和应变率敏感性参数,结果表明,Johnson-Cook模型相对于Cowper-Symonds模型和塑性随动模型更适合反映S580B合金钢的动态力学性能,拟合曲线和试验结果较为吻合。利用该专用软件,处理手段和过程完整可追溯,本构参数更容易获得,很大程度地提高了中应变率动态力学性能测试工作的效率和规范性,为冲击动力学数值仿真提供了重要的数据支持。     

Numerical simulations of oblique penetration into reinforced concrete targets

A dynamic constitutive model based on the tensile and the compressive damage models for concrete was developed and implemented into the three-dimensional finite element code, LS-DYNA. Numerical simulations of oblique penetration into reinforced concrete targets were performed using LS-DYNA. On the basis of the proposed model, the tensile and compressive damages of reinforced concrete after oblique penetration were observed and the deformation of reinforcing steel bars was obtained. Moreover, the depths of penetration for different oblique angles were obtained. The numerical results for the depth of penetration are in good agreement with existing experimental data.     

Efficient numerical integration of an elastic–plastic damage law within a mixed velocity–pressure formulation

This study focuses on numerical integration of constitutive laws in numerical modeling of cold materials processing that involves large plastic strain together with ductile damage. A mixed velocity–pressure formulation is used to handle the incompressibility of plastic deformation. A Lemaitre damage model where dissipative phenomena are coupled is considered. Numerical aspects of the constitutive equations are addressed in detail. Three integration algorithms with different levels of coupling of damage with elastic–plastic behavior are presented and discussed in terms of accuracy and computational cost. The implicit gradient formulation with a non-local damage variable is used to regularize the localization phenomenon and thus to ensure the objectivity of numerical results for damage prediction problems. A tensile test on a plane plate specimen, where damage and plastic strain tend to localize in well-known shear bands, successfully shows both the objectivity and effectiveness of the developed approach.     

Constitutive models for concrete

In a recent work, the strain-hardening theory of plasticity has been utilized to formulate a complete stress-strain relationship for concrete material under general three-dimensional stress states up to the ultimate stress condition. No attempt has been made to model more accurately the behavior of fractured concrete, once the ultimate condition or fracture criterion is exceeded. Herein, an extended formulation which includes the constitutive relationships of fractured concrete is described. The extension considers both the kinematics of crack development under a tensile type of failure and the limited plastic flow before crush under a compressive type of failure. The dual representation of concrete behavior in terms of stresses as well as strains at the ultimate or fracture state along with a sudden stress drop which results in local stress redistribution after cracking or crushing are the essential features of this continued development.     

Continuum damage model for orthotropic materials: Application to masonry

This paper contributes to the formulation of continuum damage models for orthotropic materials under plane stress conditions. Two stress transformation tensors, related to tensile and compressive stress states, respectively, are used to establish a one-to-one mapping relationship between the orthotropic behaviour and an auxiliary model. This allows the consideration of two individual damage criteria, according to different failure mechanisms, i.e. cracking and crushing. The constitutive model adopted in the mapped space makes use of two scalar variables which monitor the local damage under tension and compression, respectively. The model affords the simulation of orthotropic induced damage, while also accounting for unilateral effects, thanks to a stress tensor split into tensile and compressive contributions. The fundamentals of the method are presented together with the procedure utilized to adjust the model in order to study the mechanical behaviour of masonry material. The validation of the model is carried out by means of comparisons with experimental results on different types of orthotropic masonry at the material level.     

An elastic plastic damage formulation for concrete: Application to elementary tests and comparison with an isotropic damage model

Pure elastic damage models or pure elastic plastic constitutive laws are not totally satisfactory to describe the behaviour of concrete. They indeed fail to reproduce the unloading slopes during cyclic loading which define experimentally the value of the damage in the material. When coupled effects are considered, in particular in hydro-mechanical problems, the capability of numerical models to reproduce the unloading behaviour is essential, because an accurate value of the damage, which controls the material permeability, is needed. In the context of very large size calculations that are needed for 3D massive structures heavily reinforced and pre-stressed (such as containment vessels), constitutive relations ought also to be as simple as possible. Here an elastic plastic damage formulation is proposed to circumvent the disadvantages of pure plastic and pure damage approaches. It is based on an isotropic damage model combined with a hardening yield plastic surface in order to reach a compromise as far as simplicity is concerned. Three elementary tests are first considered for validation. A tension test, a cyclic compression test and triaxial tests illustrate the improvements achieved by the coupled law compared to a simple damage model (plastic strains, change of volumetric behaviour, decrease in the elastic slope under hydrostatic pressures). Finally, one structural application is also considered: a concrete column wrapped in a steel tube.     

An elasto-plastic damage model cast in a co-rotational kinematic framework for large deformation analysis of laminated composite shells

This paper presents an elasto-plastic damage model that is based on irreversible thermodynamics and internal state variable formalism for the analysis of multi-layered composites. The model is based on a damage surface that is defined in terms of an internal damage variable of energy, along with a set of rate-independent elasto-plastic constitutive equations defined in an effective stress–strain space. Employing the operator splitting methodology, a three-step predictor/multi-corrector algorithm is developed that includes an elastic predictor, a plastic corrector, and a damage corrector. The constitutive model is cast in a co-rotational kinematic framework for damage analysis in laminated plates and shells undergoing large deflections. Numerical examples are presented to demonstrate the accuracy and range of applicability of the proposed model.     

A plastic damage approach for confined concrete

There are many situations in which it is necessary to increase the capacity of structures in use. This need maybe either for a change of use or because the structures have suffered some damage or have shown little resistance in case of extreme loads such as earthquakes. The most common methods for repair and retrofit of reinforced concrete columns are concrete jacketing, steel jacketing and fiber wrapping. This last type of reinforcement has many advantages as it offers a high-strength, low-weight and corrosion-resistant jacket with easy and rapid installation. The reinforcement with composite materials improves shear and compression strength and ductility as a result of concrete core confinement. The present analytical and numerical ability to quantify the efficiency of fiber confinement is rather limited, especially with respect to ductility.A constitutive model that approximately reproduces the behavior of structural concrete elements under confinement is developed in this paper. The model allows the assessment of concrete columns and bridge piles repaired and/or reinforced with fiber reinforced composites (FRP). The model presented is a modification of an existing coupled plastic damage model. A new definition for the plastic hardening variable and a new yielding surface with curved meridians are proposed. Both improvements enable the adequate reproduction of concrete behavior in high confinement conditions.The comparison of numerical and experimental results shows the model capacity to simulate concrete behavior under triaxial compression conditions like the ones present in concrete columns confined with fiber reinforced composites.     

Coupled simulation of wave propagation and water pumping phenomenon in driven concrete piles

The purpose of the paper is to simulate the water pumping phenomenon that may cause damage to driven concrete pile below water. The cracked concrete is modeled as water saturated porous media, where the cracked region is given a high permeability. A FE program based on a coupled hydro-mechanical theory has been developed to perform simulations. The simulations clearly demonstrate the water pumping phenomenon, where water is pressed out from the crack by the compressive wave induced by the pile driving hammer, and then sucked back again by the following tensile wave. Further, the principal tensile stress distribution indicates that further cracking is likely to occur at the surface of the pile around the crack, which is in agreement with the damages seen on piles in reality.     

The application of a meshless method to consolidation analysis of saturated soils with anisotropic damage

This paper explores the applicability of a novel meshless method, namely the radial point interpolation method (RPIM), to the numerical simulation of consolidation of saturated soils with anisotropic damage. Firstly, an elastic constitutive relationship for the anisotropically damaged soil is derived. The RPIM is subsequently presented. Then, the damage constitutive equation is implemented into the RPIM code, in which the displacement and excess pore water pressure are spatially approximated by the same shape functions and the time domain is discretized by fully implicit integration scheme. At last, the effect of anisotropic damage on soil consolidation process is explored numerically. The results reveal that the established numerical scheme incorporating the constitutive model with anisotropic damage and the RPIM meshless method is very effective in simulating the soil–water coupling problem with good accuracy. Besides, the effects of the magnitude and direction of anisotropic damage are found to exert significant influences on the evolution of settlement and the excess pore water pressure.