轴向冲击圆柱壳非弹性响应

简要论述承受轴向冲击载荷圆柱壳非弹性动屈曲响应的研究进展。采用Ｋａｒｍａｎ－Ｄｏｎｎｅｌｌ运动方程研究轴向流固冲击载荷作用下的圆柱壳轴对称弹塑性动屈曲问题。本构关系采用增量理论，借助增量数值方法求解动力方程组。研究不同边界条件对屈曲的影响，以及径向外压力在不同边界条件下对屈曲的影响。     

复杂载荷作用下圆柱壳的弹塑性动力屈曲研究

对复杂载荷作用下圆柱壳的弹塑性动力屈曲问题进行了研究。基于Hamilton变分原理导出圆柱壳的运动方程 ,本构关系采用增量理论 ,借助增量数值算法求解动力方程组。结果表明 ,均匀径向外压对圆柱壳的轴向冲击的过程或冲击性态有较大的影响 ,并讨论了径向压力与轴向冲击载荷的幅值对结构临界动力屈曲载荷和临界动力失效载荷的影响。     

两参数轴向冲击载荷作用下圆柱壳弹塑性动力屈曲

研究圆柱壳在两参数轴向冲击载荷下的弹塑性动力屈曲问题，基本控制方程由弹塑性连续介质中关于加速度的最小原理获得，本构关系采用增量理论。研究表明：屈曲过程可划分为两相，两相之间由临界时间ｔ表征，并分别讨论了应力波对屈曲的影响，压缩波与弯曲波的相互作用及几何尺寸，材料参数，初始缺陷，载荷峰值及持续时间等诸多因素与动力屈曲的关系。     

冲击载荷作用下矩形薄板的弹性动力屈曲

为了研究冲击载荷作用下考虑应力波效应弹性矩形薄板的动力屈曲,根据动力屈曲发生瞬间的能量转换和守恒准则,导出板的屈曲控制方程和波阵面上的补充约束条件,真实的屈曲位移应同时满足控制方程和波阵面上的附加约束条件。满足上述条件,建立了该问题的完整数值解法,对屈曲过程中冲击载荷、屈曲模态和临界屈曲长度之间的关系进行研究,定量计算了横向惯性效应对提高薄板动力屈曲临界应力的贡献。研究表明:板的厚宽比一定时,临界屈曲长度随冲击载荷的增大而减小;由于屈曲时的横向惯性效应,应力波作用下薄板一阶临界力参数是相应边界板的静力失稳临界力参数的1.5倍;随着边界约束逐渐减弱,板临界力参数逐渐减小,动力特征参数逐渐增大。     

初曲矩形薄板的非线性动力屈曲研究

对两参数冲击载荷面内压缩作用下初曲矩形薄板的非线性动力屈曲问题进行了理论研究。首先采用双重余弦函数的组合确定了面内冲击矩形薄板的艾雷应力函数和中面力的分布；其次根据伽辽金法求得了初曲矩形薄板非线性动力屈曲问题的控制方程，基于巴拿赫压缩映象原理，采用逐次逼近方法求解了该控制方程。最后，应用本文发展的理论，给出了面内两参数冲击载荷作用下初曲矩形薄板动力屈曲响应的计算实例，计算结果与已有的实验结果较吻合     

外压对环肋圆柱壳轴向弹塑性动力屈曲的影响

采用增量理论,借助增量数值解法研究了复合加载（轴向流－固冲击载荷＋径向均匀外压）条件下环肋圆柱壳的弹塑性动力屈曲,采用类似B－R准则和Southwell方法来确定临界载荷,讨论了径向均匀外压对结构动力性态及抗轴冲击能力的影响。     

水下爆炸载荷作用下环肋加筋圆柱壳结构的弹塑性动力屈曲

为研究水下爆炸载荷作用下潜艇结构的动力屈曲现象,以潜艇耐压结构的简化模型环肋加筋圆 柱壳结构为研究对象,建立流固耦合有限元分析模型,应用瞬态有限元分析程序MSC.Dytran对该结构在水 下爆炸冲击载荷作用下的弹塑性动力屈曲行为进行研究,基于Budiansky-Roth准则和Southwell方法确定环 肋加筋圆柱壳结构的临界屈曲载荷,讨论结构动力屈曲的影响因素如载荷强度、网格密度、径厚比、长径比、加 筋截面间距、加筋尺寸等对环肋加筋圆柱壳结构动屈曲模态和临界屈曲载荷的影响。结果表明:采用建立的 流固耦合有限元分析模型,应用动力瞬态有限元软件MSC.Dytran可以对加筋圆柱壳结构的动力屈曲行为进 行模拟,模型网格尺寸大小、结构几何参数对结构的动力屈曲临界载荷都有一定的影响,其中加筋圆柱壳结构 的径厚比对结构的动力屈曲临界载荷影响最为显著。     

面内阶跃载荷下矩形薄板的塑性动力屈曲

对于面内阶跃载荷作用下矩形薄板的塑性动力屈曲问题,将临界应力和屈曲惯性项指数参数作为双特征参数求解。由相邻平衡准则导出失稳控制方程,由动力屈曲发生瞬间的能量转换和守恒准则,导出波阵面上的屈曲变形补充约束条件。失稳控制方程、边界条件、塑性波阵面上的连续条件和补充约束条件构成了定量求解两个特征参数和动力屈曲模态的完备条件。研究了矩形薄板塑性动力屈曲过程中板的厚宽比、冲击载荷大小、屈曲模态和临界屈曲长度之间的关系。     

Hamilton体系下功能梯度梁的热冲击动力屈曲分析

在Hamilton体系下,基于Euler梁理论研究了功能梯度材料梁受热冲击载荷作用时的动力屈曲问题;将非均匀功能梯度复合材料的物性参数假设为厚度坐标的幂函数形式,采用Laplace变换法和幂级数法解析求得热冲击下功能梯度梁内的动态温度场:首先将功能梯度梁的屈曲问题归结为辛空间中系统的零本征值问题,梁的屈曲载荷与屈曲模态分别对应于Hamilton体系下的辛本征值和本征解问题,由分叉条件求得屈曲模态和屈曲热轴力,根据屈曲热轴力求解临界屈曲升温载荷。给出了热冲击载荷作用下一类非均匀梯度材料梁屈曲特性的辛方法研究过程,讨论了材料的梯度特性、结构几何参数和热冲击载荷参数对临界温度的影响。     

圆柱壳撞水时的弹塑性动力屈曲研究

本文研究圆柱壳在流固中冲击载荷下的弹塑性动力曲问题。建立了液体－气体－固体三相的数学模型。其中结构部分控制方程由弹塑性力学中关于加速度的最小原理获得，本构关系采用增量理论，液体假设为不可压缩，空气层认为最等熵压缩。分别讨论了不同冲击高度时压力变化规律，屈曲对载荷的影响。屈曲沿壳长的分布及发展规律等。     

Influence of ice conditions on the effectiveness of the resonant method of breaking ice cover by submarines

This paper describes a numerical model for analyzing the stress-strain state of ice cover which has fractures of various widths caused by hydrodynamic loads due to submarine motion. Calculations and experiments were performed using the model of unbreakable ice, and the results were used to obtain dependences of the amplitude of deflections and stress in ice cover on the width of the ice fracture. The behavior of ice cover under wave loading was studied.     

正交各向异性地基平面问题动力响应研究

以位移分量为基本未知量,在直角坐标系下建立正交各向异性地基的平面应变问题动力偏微分方程．采用Laplace-Fourier变换和逆变换方法,引入初始条件和边界条件,推导了任意形式表面动荷载作用下正交各向异性地基平面问题在时域内动力反应的积分形式解．基于理论解,编制了相应的计算程序,并对正交各向异性土
体表面作用线性移动谐振荷载进行了算例分析,研究了土体参数、荷载移动速度、荷载频率不同而导致的土体表面各点竖向位移幅值的变化规律,以及荷载速度对竖向应力分量的影响规律．数值分析结果表明：土体的各向异性、荷载频率和移动速度对表面位移幅值有较大影响,土体阻尼比对于荷载中心点附近的位移幅值影响较小;荷载移动速度对于竖向应力分量有较大影响,这对工程实践具有重要指导意义．     

Experimental Investigation of Fracture Process Zone in Rocks Damaged Under Cyclic Loadings

Compared with other materials, most rocks generally fail in a brittle fashion rather than exhibiting yielding or purely plastic deformation. However, the initiation and coalescence of micro-cracks in the nonlinear region, known as the ‘fracture process zone’ (FPZ), are the primary reason for fracture propagation in rocks. Different elasticity-related models proposed for determining the features of the FPZ have not achieved an adequate understanding of its various fracture patterns. Based on previous experiments and numerical models, micro-crack density has been shown to be a function of loading history and to vary depending on whether the loading is monotonic or cyclic. The aim of the study reported here was to examine the different patterns of the FPZ under various types of cyclic loading and to quantitatively define damage and fracture patterns through the grains or rock matrix. Considerable laboratory testing was conducted, and fractured samples were investigated by computerised tomography scanning, supported by thin-section analysis. In the study, two different types of cyclic loading were tested: stepped and continuous. A diametral compressive loading was applied at predetermined amplitude and frequency with the continuous cyclic loading. The applied cyclic diametral compressive load was returned to the original level after each step, and at the next step, the amplitude started from zero, with stepped cyclic loading (SCL). An average 30 % strength reduction was found due to the SCL and emergence of high micro-fracture density in the FPZ. We presume that hard rock breakage techniques will be improved, especially for rock-cutting technologies, such as drag bits and oscillating disc cutting, by understanding the effects of cyclic loading on rock strength.     

轴向变速运动正交各向异性板的动态稳定性

研究面内载荷作用下轴向变速运动正交各向异性薄板的横向振动及其稳定性。利用Galerkin法与平均法,在激励频率为2倍固有频率或为两阶固有频率之和附近时得到自治的常微分方程组;在参数激励频率和激励振幅平面上,分析由共振引发的失稳区域。数值算例验证了面内载荷、轴向速度、加速度参数对失稳区域的影响。     

周期荷载作用下煤岩声发射特征的颗粒流模拟

为研究周期荷载应力水平对煤样声发射特征的影响,采用PFC数值软件开展了 3种不同应力水平的等幅周期荷载数值模拟试验,分析了周期荷载应力水平对煤样破坏循环次数、声发射计数及损伤演化特征的影响.研究结果表明:周期荷载作用下,煤样破坏过程中的声发射活动呈现初始、相对平静和活跃三阶段演化规律,且在煤样破坏前的周期荷载卸载阶段及...     

Asymptotic and numerical study of a surface breaking crack subject to a transient thermal loading

An asymptotic algorithm is applied to the problem of a finite, thermo-elastic solid containing a surface breaking crack, when the exterior surface is subjected to oscillatory thermal loading. This algorithm involves the study of a model problem. An analytical and numerical study of this model problem of a thermo-elastic half space containing a surface breaking crack and subjected to oscillatory thermal loading is presented. The crack surface is traction free. In particular, the amplitude of the stress intensity factor at the crack vertex is found as a function of the crack depth and the frequency of thermal oscillation.     

Finite amplitude oscillations of a hyperelastic spherical cavity

We present numerical results for the finite oscillations of a hyperelastic spherical cavity by employing the governing equations for finite amplitude oscillations of hyperelastic spherical shells and simplifying it for a spherical cavity in an infinite medium and then applying a fourth-order Runge-Kutta numerical technique to the resulting non-linear first-order differential equation.The results are plotted for Mooney-Rivlin type materials for free and forced oscillations under Heaviside type step loading. The results for Neo-Hookean materials are also discussed. Dependence of the amplitudes and frequencies of oscillations on different parameters of the problem is also discussed in length.     

Frictional Hertzian contact problems under cyclic loading using static reduction

In this study we investigate an axisymmetric Hertzian contact problem of a rigid sphere pressing into an elastic half-space under cyclic loading. A numerical solution is sought to obtain a steady state, which demands a large amount of computer memory and computing speed. To achieve a tractable problem, the current numerical model uses a “static reduction” technique, which employs only a contact stiffness matrix rather than the entire stiffness of the problem and is more accurate than the approach used by most finite element codes. Investigation of the tendency of contact behavior in the transient and steady states confirms that a steady state exists, showing converged energy dissipation. The dependence of dissipation on load amplitude shows a power law of load amplitude less than 3, which may explain some deviations in the experimental findings.     

冲击加载下样品软回收过程中的侧向稀疏效应

通过数值模拟, 计算冲击加载下样品经历一维应变加载过程和侧向稀疏过程产生的塑性功, 给出试样内部从冲击加载开始到进入回收桶前全过程的应力随时间变化的历程。结果表明:侧向稀疏过程开始后,样品在径向汇聚波的作用下受循环拉、压载荷作用,拉压循环的振幅在中等冲击压力下达到最大。如果振幅超过了材料的层裂强度,样品中心将发生拉伸破坏不能完整回收。侧向稀疏与一维应变加载产生的塑性功之比随冲击速度的增加而减小。在冲击速度为某临界值时,侧向稀疏产生的塑性功与一维应变加载产生的塑性功相等。在一定的冲击速度下,采用低初始屈服应力的材料可减轻侧向稀疏效应。对理想塑性材料的理论分析表明,侧向稀疏与一维应变加载产生的塑性功之比随冲击速度与屈服强度比值的增大而减小,与数值模拟结果一致。     

相变复合波在伪弹性TiNi合金薄壁管中的传播

相变可以改变材料的性质,从而严重影响波在介质中传播的结构。采用考虑静水压力和偏应力联合作用的增量型相变本构模型,研究了在拉(压)-扭联合作用下半无限长TiNi合金薄壁管内相变复合波的传播规律。基于广义特征理论分析了相变复合波的特征波速及简单波解的基本性质。利用数值方法研究了两种典型情况下管内相变耦合波传播的规律,管内传播的应力路径和波的结构与初始状态及加载幅值有关,展现出和普通弹塑性材料截然不同的性质。