水下爆炸载荷作用下加筋圆柱壳的响应分析

运用MSC．DYTRAN软件，首先比较了网格划分密度的改变，耦合法的选取及边界条件对计算的影响。并在合理的网格划分和耦合方法选用的基础上，设置符合实际的边界条件，在壳体的迎爆面，侧爆面和背爆面各选取一个点，在分析光壳的响应的基础上，详细计算了加筋圆柱壳对水下爆炸冲击波的响应。比较分析了不同的尺寸参数对结构抗爆性能的影响，并做了综合讨论，计算中考虑了材料的应变率强化效应。在此基础上验证了增加壳体厚度，减小加筋间距和增加加筋高度等有利于提高加筋圆柱壳抗爆性能的方法，同时得到了一个适合本例计算的较优化模型。     

关于圆柱壳在水下爆炸冲击波作用下二次加载现象的数值模拟研究

运用大型商业有限元程序MSC．DYTRAN数值模拟了水下爆炸冲击波载荷作用下自由环肋圆柱壳的非线性动态响应．采用一般耦合算法(general coupling)模拟流体与结构的耦合效应，计算中考虑了材料的应变率强化效应，几何非线性的影响，分析了空穴现象的产生和二次加载对结构响应的影响．仿真结果表明，相同工况和厚度下的无限自由平板和自由环肋圆柱壳，后者的空化时间比前者长，而壳体运动的最大速度后者比前者低．     

考虑应变率效应的钢筋混凝土结构非线性地震灾变过程模拟

为研究应变率对钢筋混凝土结构非线性地震灾变过程的影响,采用钢筋、混凝土单轴动态本构关系及加卸载准则,基于纤维梁理论开发了ABAQUS显式动力分析材料子程序。通过对3层偏心钢筋混凝土框-剪结构振动台试验的数值模拟,验证了该程序用于钢筋混凝土结构非线性地震反应分析的准确性和有效性。通过在材料子程序中定义钢筋、混凝土材料失效破坏判别准则,实现了地震作用下考虑应变率效应的钢筋混凝土结构连续倒塌破坏全过程模拟。分别对振动台试验模型结构和钢筋混凝土框架结构的倒塌破坏模式进行了预测,初步探讨了应变率对钢筋混凝土结构地震反应与连续倒塌破坏过程的影响。结果表明:该程序能够准确模拟钢筋混凝土结构的非线性地震灾变过程,可用于考虑材料应变率效应的钢筋混凝土结构抗震设计与分析中。     

一种考虑应变率效应的结构非线性时程分析方法

提出了一种在非线性时程分析中考虑材料应变率效应的近似方法：首先,对结构进行不考虑应变率效应的非线性时程分析;然后,根据第一次分析的结果可以得到关键位置在与结构最大顶点位移对应的前1/4循环内的平均应变率,根据这些点的平均应变率对进入非线性构件材料的本构关系进行修正;最后,对结构进行第二次分析。文中给出了该方法的力学解释,并通过数值模拟对该方法进行了验证。结论：本文提出的方法具有较高的精度,可以作为一种在非线性时程分析中考虑应变率效应的有效方法。     

复合材料纵横加筋圆柱壳自由振动分析

使用能力法分析了两端简支复合材料纵横加筋圆柱壳的自由振动特性,从Love’s理论出发,分别计算壳体面板和纵横加筋结构的应变能和动能,在计算加筋结构应变能和动能时,将加筋结构的作用影响平均在整个壳体区域。然后代入Lagrange方程得到频率方程。通过比较,计算方法所得到的结果与文献比较吻合。采用平均法计算的结果比采用离散方法计算的结果偏小。还研究了壳体和加筋结构参数的变化对圆柱壳自由振动频率的影响。     

GSQ24壳体单元用于板壳结构的几何非线性分析

在考虑剪切变形的Von Karman大变形小应变假设下,基于全Lagrange描述方法,将平面内带有旋转自由度的GSQ24壳体单元用于板壳结构的几何非线性分析,给出了板壳结构大变形下的小位移刚度矩阵、初应力刚度矩阵、初位移刚度矩阵有限元列式。同时,文中也给出了既考虑材料非线性,又考虑几何非线性的强非线性问题的板壳结构分析时的有限元列式。数值算例与变分法和级数解结果比较,表明本文方法的可行性。     

基于分层壳单元的现浇混凝土空心楼板数值模拟

现浇混凝土空心楼板中由于存在不连续的孔洞,目前常采用的实体单元分析既复杂且计算效率低。分层壳单元根据组成材料的不同将壳分成多层,可考虑面内弯曲-面内剪切-面外弯曲之间的耦合作用,能够较全面地反映壳体结构的空间力学性能。该文在分层壳单元的基础上,通过设置2条对称的连续"空心层",根据面积和刚度相等原则,经计算得到"空心层"厚度和距截面中性轴的距离,并以此对分层壳单元各组成材料进行划分。通过与试验进行对比,数值模拟结果与试验结果吻合良好,表明该文提出的"空心层"分层壳单元具有较高的精度,能较准确的模拟混凝土空心楼板各项非线性力学性能,且建模方便具有很好的实用性,可运用于实际工程。     

圆柱壳在水下爆炸载荷下的流-固耦合响应分析

研究了无限域流场中两端简支圆柱壳受球形炸药爆炸冲击载荷作用的响应特性。运用Hamilton变分原理,推导出了考虑流固耦合作用圆柱壳受水下爆炸冲击载荷作用的运动方程,并分别展开成Fourier级数的形式,最后在时域上差分离散,用Galerkin方法求解,得到了在水下爆炸冲击载荷下圆柱壳的响应分析。文章着重就圆柱壳在迎爆面和背爆面的不同位置的变形位移和变形速度进行了对比分析,同时还比较了流体动压力对结构响应的影响。并将分析结果与有限元计算软件MSC.DYTRAN计算结果比较,验证了算法的可靠性。     

钢筋混凝土剪力墙应变率效应试验与基于动力塑性损伤模型的模拟

应变率对混凝土材料的力学性能有着重要影响。该文在对2 片剪力墙构件进行快速加载试验的基础上,在混凝土塑性损伤模型中引入应变率效应,建立了考虑应变率效应的塑性损伤模型。应用该模型对该文所描述的快速加载下的剪力墙构件以及在拟静力作用下的另外3 个构件进行了有限元模拟,结果表明考虑应变率效应的混凝土塑性损伤模型较好地描述了钢筋混凝土剪力墙在快速加载下的非线性行为。最后,运用所建立的考虑应变率效应的混凝土塑性损伤模型对不同轴压比和加载速率下剪力墙构件的非线性性能进行了模拟与分析。     

静水压下含缺陷中厚复合材料圆柱耐压壳的极限强度

为探究静水压下含缺陷中厚复合材料圆柱耐压壳的极限强度，以湿法缠绕工艺制备中厚玻璃纤维增强树脂基复合材料(GFRP)圆柱耐压壳结构模型，对其初挠度进行测试，并开展静水压破坏试验，分析了结构的极限承载能力、应变响应和破坏模式。基于实测初挠度及破坏模式，建立含缺陷复合材料圆柱壳的非线性分析有限元模型，同时考虑壳体几何缺陷及承压过程中的复合材料面内损伤，编制ABAQUS接口子程序USDFLD，对模型的损伤过程进行数值模拟，获得静水压下含缺陷中厚复合材料圆柱壳的渐进失效过程，并与试验结果对比验证。研究表明：在静水压下中厚GFRP圆柱壳结构在破坏前载荷几乎呈线性增加，最终破坏模式为材料的压缩破坏，整体屈曲破坏模式不明显。考虑结构的几何缺陷和材料损伤演化后，采用非线性有限元模拟得到的壳体极限强度与试验结果吻合良好，可以作为预测含缺陷中厚复合材料圆柱壳极限强度的方法。采用该方法对影响中厚复合材料圆柱耐压壳极限强度的关键参数进行了研究，为深海复合材料耐压壳的研究设计提供参考。     

Ultra high molecular weight polyethylene deformation and fracture behaviour as a function of high strain rate and triaxial state of stress

The dynamic response and fracture characteristics of Ultra High Molecular Weight Polyethylene (UHMWPE) were investigated both experimentally and numerically. The strain rate sensitivity of the material was studied by carrying out tensile tests on smooth cylindrical specimens over a range of high strain rate conditions using the purpose built `flying wedge' testing machine at separation velocities up to 9 m/s. The effect of the initial stress triaxiality conditions on the material's ductility at different strain rates was studied using pre-notched cylindrical specimens with different notch radii. The true stress-strain results indicated that the tested material is highly sensitive to strain rate changes. Post-fracture geometric measurements of the fractured specimens indicated that the ductility of UHMWPE is strongly dependent on both the initial stress triaxiality conditions and the strain rate. Numerical simulations of the quasi-static and high strain rate tests were used to predict, for different notch radii, variation of the centre-most element radial strain and stress triaxiality factor with the average radial strain. Based on the combined numerical and experimental results, a simple relation for the ductile fracture of UHMWPE was derived as a function of stress triaxiality and strain rate.     

Strength and ductility of Weldox 460 E steel at high strain rates, elevated temperatures and various stress triaxialities

Strength and ductility data at high strain rates for Weldox 460 E steel was obtained from tensile tests with axisymmetric specimens. The tests were performed in a Split Hopkinson Tension Bar and the initial temperature was varied between 100 and 500 °C. The combined effect of high strain rate, elevated temperature and stress triaxiality on the behaviour was studied by testing both smooth and pre-notched specimens. It was found that the influence of temperature on the stress-strain behaviour differs at high strain rates compared with quasi-static loading conditions. The true fracture strain depends considerably on the stress triaxiality, which is governed by the notch geometry, while the influence of strain rate and temperature is less clear. Numerical simulations with the explicit finite element code LS-DYNA were performed using a model of elasto-viscoplasticity and ductile damage, which is based on the constitutive relation and fracture criterion of Johnson and Cook. The numerical simulations compare reasonably well with the experiments with respect to strength and ductility for both smooth and notched specimens at elevated temperatures.     

An unsymmetric 8-node hexahedral solid-shell element with high distortion tolerance: Geometric nonlinear formulations

A recent distortion-tolerant unsymmetric 8-node hexahedral solid-shell element US-ATFHS8, which takes the analytical solutions of linear elasticity as the trial functions, is successfully extended to geometric nonlinear analysis. This extension is based on the corotational (CR) approach due to its simplicity and high efficiency, especially for geometric nonlinear analysis where the strain is still small. Based on the assumption that the analytical trial functions can properly work in each increment during the nonlinear analysis, the incremental corotational formulations of the nonlinear solid-shell element US-ATFHS8 are derived within the updated Lagrangian (UL) framework, in which an appropriate updated strategy for linear analytical trial functions is proposed. Numerical examples show that the present nonlinear element US-ATFHS8 possesses excellent performance for various rigorous tests no matter whether regular or distorted mesh is used. Especially, it even performs well in some situations that other conventional elements cannot work.     

Degenerated shell element with composite implicit time integration scheme for geometric nonlinear analysis

A degenerated shell element with composite implicit time integration scheme is developed in the present paper to solve the geometric nonlinear large deformation and dynamics problems of shell structures. The degenerated shell element is established based on the eight‐node solid element, where the nodal forces, mass matrices, and stiffness matrices are firstly obtained upon virtual velocity principle and then translated to the shell element. The strain field is modified based on the mixed interpolation of tensorial components method to eliminate the shear locking, and the constitutive relation is modified to satisfy the shell assumptions. A simple and practical computational method for nonlinear dynamic response is developed by embedding the composite implicit time integration scheme into the degenerated shell element, where the composite scheme combines the trapezoidal rule with the three‐point backward Euler method. The developed approach can not only keep the momentum and energy conservation and decay the high frequency modes but also lead to a symmetrical stiffness matrix. Numerical results show that the developed degenerated shell element with the composite implicit time integration scheme is capable of solving the geometric nonlinear large deformation and dynamics problems of the shell structures with momentum and energy conservation and/or decay. Copyright © 2015 John Wiley & Sons, Ltd.     

A refined non‐linear non‐conforming triangular plate/shell element

A refined non‐conforming triangular plate/shell element for geometric non‐linear analysis of plates/shells using the total Lagrangian/updated Lagrangian approach is constructed in this paper based on the refined non‐conforming element method for geometric non‐linear analysis. The Allman's triangular plane element with vertex degrees of freedom and the refined triangular plate‐bending element RT9 are used to construct the present element. Numerical examples demonstrate that the accuracy of the new element is quite high in the geometric non‐linear analysis of plates/shells. Copyright © 2003 John Wiley & Sons, Ltd.     

飞机风挡夹层结构耐撞性数值分析

用LS-DYNA3D软件,建立了由钢化玻璃和PU、PVB塑料薄膜组成的风挡夹层结构鸟撞数值模型。鸟体采用ALE格式和与应变率相关的随动硬化材料模型,夹层结构用Lagrange格式和双线性材料模型,对11种风挡夹层结构进行了数值计算,分析了撞击过程的损伤和应力,讨论了夹层结构耐撞性的评估方法,为风挡夹层结构设计提供理论依据。     

Numerical implementation of strain rate dependent thermo viscoelastic constitutive relation to simulate the mechanical behavior of PMMA

In this work, a nonlinear viscoelastic constitutive relation was implemented to describe the mechanical behavior of a transparent thermoplastic polymer polymethyl methacrylate (PMMA). The quasi-static and dynamic response of the polymer was studied under different temperatures and strain rates. The effect of temperature was incorporated in elastic and relaxation constants of the constitutive equation. The incremental form of constitutive model was developed by using Poila–Kirchhoff stress and Green strain tensors theory. The model was implemented numerically by establishing a user defined material subroutine in explicit finite element (FE) solver LS-DYNA. Finite element models for uniaxial quasi-static compressive test and high strain rate split Hopkinson pressure bar compression test were built to verify the accuracy of material subroutine. Numerical results were validated with experimental stress strain curves and the results showed that the model successfully predicted the mechanical behavior of PMMA at different temperatures for low and high strain rates. The material model was further engaged to ascertain the dynamic behavior of PMMA based aircraft windshield structure against bird impact. A good agreement between experimental and FE results showed that the suggested model can successfully be employed to assess the mechanical response of polymeric structures at different temperature and loading rates.     

Modelling delaminations in postbuckling stiffened composite shear panels

 A method has been developed to predict the effect of delaminations in a postbuckling stiffened structure manufactured from laminated composite materials. The emphasis of the technique, driven by aircraft certification requirements, was towards establishing whether delamination growth would initiate under given loading conditions. A geometric nonlinear finite element analysis was used to calculate the strain energy release rate around the circumference of a circular delamination using the virtual crack closure technique. In order to deal with the complex structural response in a computationally efficient manner, the structure was modelled using plate elements with two layers of plate elements used in the delaminated region. The effect of delamination size on the strength of postbuckling panels was shown to be a complex phenomenon in which trends were difficult to predict. Large delaminations could significantly affect the global and sub-laminate buckling modes and therefore be less critical than smaller delaminations. It was concluded that the method could accurately predict the load and location at which delamination growth would initiate, given suitable critical strain energy release rate data. Received 16 February 2000     

A nine node finite element for analysis of geometrically non-linear shells

A nine node finite element is presented for the analysis of thin shell structures undergoing large deflection. The finite element formulation is based on the concept of degenerate solid shell element and the Hellinger-Reissner principle with independent strain. Three versions of assumed independent strain are selected to suppress spurious kinematic modes. One version leads to a finite element model which is kinematically stable at element level while the other two give globally stable models. Numerical tests indicate that the finite element model which is stable at element level may reveal the locking effect in certain cases. However, the other two models are free of locking.