地下开采过程损伤场演化与地表变形的时变分析

以形状随时间变化的物体——时变体为研究对象,将损伤理论与时变力学结合,引入与时变过程相关的损伤参数,形成损伤时变力学分析方法。针对岩石介质特性给出了弹性损伤时变力学本构方程,并利用虚功原理建立相应数值化方法和分析过程。利用损伤时变力学分析方法对某地下煤层开采过程进行计算机仿真分析,给出形状时变引起的损伤场与地表移动的动态演化过程,并对比了非时变以及施工分析结果。研究表明,损伤时变分析可得到连续变化的位移及损伤演化图,相比非时变的常规分析和施工分析能更好地模拟连续施工,为工程施工分析与预测提供更加科学和有效的手段。为实现开采过程的经济和安全,应该采用损伤时变力学的分析方法。     

滑移爆轰驱动钢管的层裂

将VG损伤模型推广到二维情况,考虑了最大主应力方向对损伤演化的影响,并使用显式断裂算法对20钢管在GI-920炸药滑移爆轰驱动下层裂的问题进行二维数值模拟。分析了一维内爆和滑移爆轰两种加载方式下作用于钢管外表面的压力及钢管内部受力状态的区别,考察了滑移爆轰加载方式下钢管外表面的受力随炸药厚度变化的规律,进而研究了钢管内损伤的分布和演化,以及裂纹的产生和扩展现象。计算得到的层裂片初始厚度随炸药厚度的变化规律与实验结果符合较好。     

45#钢的损伤演化方程和层裂准则研究

通过唯象分析和细观物理统计相结合的方法建立了一种韧性材料的损伤演化方程。在试验结果和内变量理论的基础上得到了45#钢的含损伤热—粘塑性本构关系。用有限差分方法计算了45#钢平板撞击所产生的应力波传播规律、损伤演化规律及层裂进程。通过自由面速度历史的数值模拟,并基于计算结果与试验结果间的最佳一致性,得到了损伤演化方程中的材料参数和极限损伤数值,并以此为依据建立了材料的应力率层裂准则。     

强动载作用下孔洞汇合对延性金属层裂损伤演化过程的影响

针对强动载作用下延性金属的层裂问题,在分析孔洞之间几何关联的基础上,定义了一个新的耦合损伤及孔洞几何信息的孔洞汇合判定方法,同时,基于能量守恒原理,解析了孔洞汇合对损伤快速增长影响的物理机理.通过分析数值计算结果和对比相关文献的实验可知:孔洞汇合后不仅引起损伤增长,而且导致了损伤材料内部微孔洞数目的减少、孔洞平均尺寸的增加。     

改进SPH方法在陶瓷材料层裂数值模拟中的应用

为了探讨铝飞片撞击陶瓷材料时的层裂现象,采用改进SPH方法模拟应力波在陶瓷材料中的传播。结果表明,当离散粒子分布不均匀时,数值模拟计算的自由面速度时程曲线与实测曲线吻合良好。对比CSPM方法,改进SPH方法的精度更高。提出适用于数值模拟的陶瓷材料损伤演化方程,对脉冲载荷下陶瓷/钢层合板层裂的破坏过程进行数值模拟,结果表明,由于陶瓷的波阻抗高于钢的,且抗压强度远高于抗拉强度,因此拉应力引起的层裂破坏是主要的。即使在材料内部传播的只是弹性压缩波,当弹性波到达材料界面时,由界面反射引起的卸载波也能导致陶瓷发生层裂破坏。     

An energy formulation of continuum magneto-electro-elasticity with applications

We present an energy formulation of continuum electro-elasticity and magneto-electro-elasticity. Based on the principle of minimum free energy, we propose a form of total free energy of the system in three dimensions, and then systematically derive the theories for a hierarchy of materials including dielectric elastomers, piezoelectric ceramics, ferroelectrics, flexoelectric materials, magnetic elastomers, magnetoelectric materials, piezo-electric–magnetic materials among others. The effects of mechanical, electrical and magnetic boundary devices, external charges, polarizations and magnetization are taken into account in formulating the free energy. The linear and nonlinear boundary value problems governing these materials are explicitly derived as the Euler–Lagrange equations of the principle of minimum free energy. Finally, we illustrate the applications of the formulations by presenting solutions to a few simple problems and give an outlook of potential applications.     

高应变率下计及损伤演化的材料动态本构行为

材料在高速变形过程中常常伴有不同形式的内部缺陷或微损伤的演化。大量的实验观察表明,损伤演化同时依赖于应变、应变率和温度,而且高应变率和低温之间有某种等价性。由此基于热激活机制,提出了同时依赖于应变率和应变的微损伤演化律,及相应的计及损伤弱化效应的率型本构关系。以聚丙烯/尼龙（PP/PA）共混高聚物为例,具体研究了其计及损伤演化的ZWT本构关系,并区分其率相关的本构响应及率相关的损伤演化响应。     

On coupled gradient-dependent plasticity and damage theories with a view to localization analysis

Combinations of gradient plasticity with scalar damage and of gradient damage with isotropic plasticity are proposed and implemented within a consistently linearized format. Both constitutive models incorporate a Laplacian of a strain measure and an internal length parameter associated with it, which makes them suitable for localization analysis.The theories are used for finite element simulations of localization in a one-dimensional model problem. The physical relevance of coupling hardening/softening plasticity with damage governed by different damage evolution functions is discussed. The sensitivity of the results with respect to the discretization and to some model parameters is analyzed. The model which combines gradient-damage with hardening plasticity is used to predict fracture mechanisms in a Compact Tension test.     

A study on the damage evaluation of weld heat affected zone

From the micro- and macroscopic points of view, the damage evolution of weld-simulated heat affected zone (HAZ) is studied. In the framework of continuum damage mechanics (CDM), the ductile and low cycle fatigue (LCF) damage evolution laws of HAZ have been examined. Two alternative laws of damage are proposed in this paper, which may meet the need for describing damage evolution of ductile rupture and LCF fracture, respectively.     

高应变率大变形下的聚丙烯/尼龙共混高聚物损伤型本构特性

对两种采用不同相容剂的聚丙烯（PP）和尼龙（PA）共混高聚物材料在大变形下的粘弹性力学行为进行研究,着重考察应变率效应和损伤的演化,从而分析不同的界面分子设计对共混体系材料宏观性能的作用。在准静态及冲击实验研究的基础上,基于ZWT非线性粘弹性模型,并结合了遗传算法,分别得到了能有效描述两种共混高聚物大变形阶段计及损伤的非线性粘弹性本构关系。两种材料在不同加载条件下表现出明显不一致的性能,原因在于其损伤演化的率相关性,且两种材料的大变形机制存在一定的差别,能用ZWT方程进行描述的范围也不一样。     

Lagrangian formulation of continuum with internal long-range interactions

Based on a new definition of nonlocal variable, this paper establishes the Lagrangian formulation for continuum with internal long-range interactions. Distinguished from the existing theories, the nonlocal term in the Lagrangian formulation automatically satisfies the zero mean condition determined by the action and reaction law. By this formulation, elastic wave in a rod with the internal long-range interactions is investigated. The dispersion of the elastic wave is predicted.     

接触面损伤演化过程的数值模型

结合接触面在细观尺度上的非均匀性及其损伤演化规律,提出了一种可以考虑接触面损伤演化过程的数值模型.数值模拟得到的剪切应力-剪切位移关系表明:随着剪切位移的增加,接触面上产生的损伤单元导致曲线斜率逐渐降低;当接触面被完全剪断后,模型中的剪切应力出现了一定程度的下降,此后的剪应力在摩擦力的作用下基本保持不变.模型所能承受的...     

损伤演化对韧性金属碎裂过程的影响

固体在冲击拉伸载荷作用下会断裂成多个碎片,基于线性内聚力断裂假设的Mott-Grady模型能较好地预测碎裂过程所产生的平均碎片尺度的下限。然而实际上,韧性金属的损伤演化是多元化的,为此通过数值模拟方法研究了不同损伤演化规律对韧性碎裂过程的影响。利用ABAQUS/Explicit动态有限元软件数值再现了韧性金属杆（45钢）在高应变率下拉伸碎裂的过程,分析了线性和非线性损伤演化对韧性碎裂过程的影响规律。结果表明：损伤演化规律对韧性金属的碎裂过程具有显著影响,非线性指标α越大,碎裂过程产生的碎片数越少;Grady-Kipp碎裂公式仍能在一定范围内预测韧性碎裂过程中产生的碎片尺寸;当非线性指标α远大于零时,在较低冲击拉伸载荷作用下,数值模拟结果和Grady-Kipp模型预测值偏差较大,随着应变率增大,数值模拟结果与Grady-Kipp模型预测值吻合较好。

     

Nonlinear free vibration analysis of piezoelastic laminated plates with interface damage

This paper presents a nonlinear model for piezoelastic laminated plates with damage effect of the intra-layers and inter-laminar interfaces. Discontinuity of displacement and electric potential on the interfaces are depicted by three shape functions. By using the Hamilton variation principle, the three-dimensional nonlinear dynamic equations of piezoelastic laminated plates with damage effect are derived. Then, by using the Galerkin method, a mathematical solution is presented. In the numerical studies, effects of various factors on the natural frequencies and nonlinear amplitude-frequency response of the simply-supported peizoelastic laminated plates with interfacial imperfections are discussed. These factors include different damage models, thickness of the piezoelectric layer, side-to-thickness ratio, and length-to-width ratio.     

Microstructure evolution of compressible granular systems under large deformations

We report three-dimensional particle mechanics static calculations that predict the microstructure evolution during die-compaction of elastic spherical particles up to relative densities close to one. We employ a nonlocal contact formulation that remains predictive at high levels of confinement by removing the classical assumption that contacts between particles are formulated locally as independent pair-interactions. The approach demonstrates that the coordination number depends on the level of compressibility, i.e., on Poisson's ratio, of the particles. Results also reveal that distributions of contact forces between particles and between particles and walls, although similar at jamming onset, are very different at full compaction. Particle–wall forces are in remarkable agreement with experimental measurements reported in the literature, providing a unifying framework for bridging experimental boundary observations with bulk behavior.     

粘塑性变截面杆中冲击波的演化

讨论了粘塑性变截面杆中的一维应力波传播规律。在粘塑性本构理论框架的基础上,利用特征关系和冲击波阵面上的突跃条件,得出了冲击波在传播过程中的演化规律,包括其微分方程和解析表达式,并对Bodner和Johnson-Cook材料和不同收缩形式的杆中冲击波的演化规律进行了讨论,同时计算和讨论了杆中冲击波后方应力波传播规律的特点。     

Nonlinear dynamic response and fatigue damage evolution for piezoelectric laminated plates with matrix cracks

Based on the Talreja’s damage model with tensor valued internal state variables, considering the effects of piezoelectricity, geometrical nonlinearity and the constitutive relations of the composite uni-ply plate with matrix cracks, the nonlinear dynamic equations of piezoelectric laminated plates with damage are established and the problems are solved by using the finite difference method. In numerical calculating examples, the nonlinear dynamics responses and the fatigue damage evolution curves of the plates are obtained, and the effects of piezoelectric materials, damage and external load on the nonlinear dynamic response and fatigue damage evolution of the plates are discussed.     

Generalization of a new parametric formulation of mechanics for systems with variable mass

In this paper a new parametric formulation of mechanics, formulated by the author himself and based on the separation of the double role of time (independent variable and a parameter) with the aid of a family of varied paths, is extended to the arbitrary rheonomic systems with variable mass. For such systems d'Alembert–Lagrange's principle, general Hamilton's principle, and the corresponding Hamiltonian formalism are formulated, as well as the energy relations with energy change law. The obtained results are illustrated by a simple, but characteristic example.     

损伤围岩中爆炸应力波动的数值模拟

应用有限元方法分析了硐室损伤围岩中爆炸应力波的传播和应力分布特征,通过引入JHC本构模型和岩石损伤变量D探讨了应力波作用下岩体的损伤演化模式。研究表明：围岩初始损伤对后续爆炸应力波的波动性质、作用范围和围岩应力分布具有不同程度的影响。当初始损伤超过某临界值后会显著地影响应力波的波动范围和围岩应力分布;在一定爆炸当量下,爆炸应力存在一个有效作用范围Lp,该范围塑性区以内,爆炸应力对岩体的损伤随围岩初始损伤增大而增大;有效作用范围Lp以外,围岩初始残余非弹性变形积累和单元残余拉应力可以平衡爆炸应力波动产生的损伤叠加效应,耗散了爆炸应力作用和波动能量。分析了产生在这种现象的原因。给出了有效作用范围Lp与围岩初始等效应力p之间的经验关系。     

Experimental investigation into plastic damage of microvoids with interaction

A mechanism of plastic flow localization in ductile matter near microvoids is studied. The voids with the size-scale of micromillimeter exist in sheet specimens under tensile loading, and the plastic strain field around voids is obtained by digital image processing of deformed grids. The size growth of the microvoids, the spacing change of the neighboring voids, and the development of shear bands in the ligament between the voids, are presented by experimental results accompanied with the plastic strain distribution, that gives good interpretation to the process of void growth and coalescence with the flow localization in the ligaments. The project supported by the National Natural Science Foundation of China