横观各向同性松质骨撞击动力响应数值分析

本文基于对松质骨结构特征的观察,考虑固体骨质为横观各向同性多孔材料,引入了描述松质骨的流固两相多孔弹性模型。采用Ｇａｌｅｒｋｉｎ加权残值法,通过在连续方程中引入压力ｐ与罚参数β之比项,消去控制方程中的压力项,导出了松质骨在撞击载荷作用下的动力响应的罚有限元公式。用编制的有限元程序计算了松质骨平面问题的撞击动力响应。结果表明,由于松质骨中液体组分的扩散和流动,引起固体骨质和液态骨髓间的相互作用,使得松质骨呈现出一种强烈的表观粘弹性行为以及能量耗散性质。     

鸟撞45#钢平板动响应试验研究

采用动态数据采集系统,对45#钢平板在不同撞击速度下的鸟撞动响应全过程进行了详细研究,得到了撞击过程中平板上三个点位移和四个点的应变、撞击方向4个支反力等物理量随时间变化历程,同时利用高速摄像系统记录了鸟撞过程中鸟体及平板动态变形的全过程。对重复试验的结果进行比较,二者良好的一致性表明试验结果的可靠性,在此基础上分析了平板动响应及鸟体破碎随撞击速度的变化规律。发现,位移及撞击支反力峰值随撞击速度的提高而线性增大;撞击速度越高,鸟体的流体特性越明显,表明高速撞击数值模拟中鸟体应采用描述流体行为的本构模型。该试验结果对建立合理的鸟体本构模型及验证鸟撞有限元计算方法具有重要意义。     

带有沙漏控制的相对自由度壳元

针对一点积分的八节点相对自由度壳单元存在的沙漏现象，提出采用拟应变法解决该问题的方法，并对锁死问题进行研究。给出了带有沙漏控制的八节点相对自由度壳元内的坐标、位移插值公式，推导了拟应变的表达式，通过Hu-Washizu变分原理，建立了有限元求解方程。利用Wilson非协调位移模式，单元的计算精度得到了明显改善。算例表明：基于八节点相对自由度壳单元，本文给出的沙漏控制算法能够有效的解决线性静力问题，并且具有较高的计算精度。     

能量有限元方法在复合材料层合梁耦合结构振动分析中的应用

以能量有限元方法(EFEM)建立控制方程,研究了复合材料层合梁受激励时的横向振动问题。该方法以结构中的能量密度作为变量,根据波动理论中功率流与能量密度的平衡关系建立了与傅里叶热传导方程类似的二阶偏微分方程组,通过有限元离散得到结构单元节点的能量密度矩阵形式方程。根据耦合连续平衡条件,建立耦合单元节点矩阵,从而对总矩阵方程进行组集及求解,得到结构中能量密度的分布。通过数值算例与传统有限元方法(FEM)结果做了对比,取得了较好的一致性。     

舰载超近程反导弹药冲击引爆战斗部的研究

建立了舰载超近程反导智能弹药毁伤元撞击反舰导弹战斗部的理论模型和有限元模型,计算了不同速度下舰载超近程反导智能弹药毁伤元冲击引爆反舰导弹战斗部的可能性,然后利用有限元方法进行了仿真计算,仿真结果与理论分析吻合较好。研究结果表明:当毁伤元材料采用93#钨、速度大于1.80km/s时,撞击产生的冲击波压力理论计算值和数值模拟结果均大于5.63GPa,说明舰载超近程反导智能弹药毁伤元的高速撞击可以引爆加装Comp.B炸药的反舰导弹战斗部。     

舰载超近程反导弹药冲击引爆战斗部的研究

建立了舰载超近程反导智能弹药毁伤元撞击反舰导弹战斗部的理论模型和有限元模型,计算了不同速度下舰载超近程反导智能弹药毁伤元冲击引爆反舰导弹战斗部的可能性,然后利用有限元方法进行了仿真计算,仿真结果与理论分析吻合较好。研究结果表明:当毁伤元材料采用93#钨、速度大于1.80km/s时,撞击产生的冲击波压力理论计算值和数值模拟结果均大于5.63GPa,说明舰载超近程反导智能弹药毁伤元的高速撞击可以引爆加装Comp.B炸药的反舰导弹战斗部。     

抗事故包装箱的跌落冲击分析技术

目的研究抗事故包装箱冲击分析技术,实现抗事故包装箱设计的高速碰撞分析。方法基于对抗事故包装箱冲击响应的初步认识,确定冲击跌落的计算方法。深入研究冲击跌落计算方法中接触、沙漏等问题,确定避免接触失效和沙漏能偏大的计算方法。针对不同的材料类型确定对应的本构关系。建立模型试验,校验跌落冲击分析方法中的接触控制技术、沙漏控制技术和材料本构模型。结果建立了抗事故包装箱的冲击分析技术,获得了抗事故包装箱模型件高速碰撞时的动力学响应。结论模型试验及其数值分析表明此方法切实可行。     

PAM-CRASH碰撞模拟中主要控制参数影响的分析

在汽车耐撞性研究中有限元模拟计算已成为主要的研究手段。本文基于非线性显式有限元软件PAM－CRASH对某车车架前部碰撞过程的模拟计算，分析了有限元模型的主要控制参数对计算结果和效率的影响，其中包括网格尺寸、沿单元厚度的积分点个数、单元类型和沙漏（Hourglass)控制。比较了采用不同控制参数对计算结果的载荷－时间曲线、时间和沙漏能量等的影响。确定该车架的模拟计算控制参数选择范围。     

空间碎片高速撞击的数值模拟方法评述

计算机数值模拟是实现空间碎片撞击效应地面模拟的重要手段之一。撞击速度增加,撞击的物理机制和效应将发生改变,计算机数值模拟方法也应随之丰富和全面。介绍了基于有网格和无网格方法的高速撞击数值模拟发展历程,并针对数值模拟中常用的有限元法和SPH法进行了分析比较,阐述了高速撞击计算机模拟中无网格法的计算优势,并提出量子力学在未来无网格法数值模拟中的可能应用。为空间碎片高速撞击更加真实可靠的数值模拟提供参考。     

箱形柱与工字梁连接节点翘曲变形的传递分析

箱形柱与工字形梁刚性连接节点是钢结构建筑中最常用的节点形式之一.通过对采用这种节点形式的梁柱节点处的梁柱构件之间的翘曲位移传递的研究,提出了这种节点处梁柱的翘曲位移的简单关系,并推导了在常用薄壁构件空间框架梁单元有限元模型中的实现方法.通过与壳体单元有限元的分析结果进行比较,发现壳体有限元与提出的方法结果非常吻合,同时...     

纤维增强复合材料层板高速倾斜冲击损伤数值模拟

根据复合材料三维黏弹性本构关系, 建立了纤维增强复合材料层板高速倾斜冲击损伤的数值分析模型。该模型在复合材料层间引入界面单元模拟层间分层, 结合三维Hashin失效准则进行单层板面内损伤识别, 引入材料刚度折减方案, 采用非线性有限元方法, 研究高速倾斜冲击下复合材料层板的破坏过程和损伤特性。研究结果表明: 层板的主要损伤形式是层间分层、 基体微裂纹和纤维断裂; 冲击速度不变而入射角度增大时, 剩余速度减小, 层板损伤面积在一定入射角度范围内有明显变化; 入射角度不变而冲击速度增大时, 剩余速度增大, 层板损伤面积在一定速度范围内也有明显变化。     

Numerical analysis of oblique impact on reinforced concrete

This study proposes a simple but efficient methodology based on the equivalent inclusion method and finite element analysis. Oblique impacting is considered to investigate the residual velocity and ricochet limit of an ogive-nose steel projectile with various impact velocities against a reinforced concrete slab. The computational results are compatible with Tate’s formula for the ricochet limit as a function of the impact velocity. The proposed methodology is useful for designing defense structures, and the ricochet limit is one of the important parameters that govern the performance of a weapon system. The methodology can be further developing for designing the protection of military structures and nuclear power plants against high velocity projectiles.     

A hybrid element formulation for the three‐dimensional penalty finite element analysis of incompressible fluids

This work presents a hybrid element formulation for the three‐dimensional penalty finite element analysis of incompressible Newtonian fluids. The formulation is based on a mixed variational statement in which velocity and stresses are treated as independent field variables. The main advantage of this formulation is that it bypasses the use of ad hoc techniques such as selective reduced integration that are commonly used in penalty‐based finite element formulations, and directly yields high accuracy for the velocity and stress fields without the need to carry out smoothing. In addition, since the stress degrees of freedom are condensed out at an element level, the cost of solving for the global degrees of freedom is the same as in a standard penalty finite element method, although the gain in accuracy for both the velocity and stress (including the pressure) fields is quite significant. Copyright © 2007 John Wiley & Sons, Ltd.     

Transient response of pretwisted delaminated stiffened shell under low velocity impact

The paper presents the study of low velocity impact response of delaminated composite stiffened shell with pretwist employing finite element method for different combination of stiffeners. An eight noded isoparametric shell element along with a three noded isoparametric beam element are employed to model the shell and the stiffener, respectively. The modified Hertzian contact law is considered to compute the contact force, while the Newmark's time integration algorithm is used to solve the time dependent equations of both impactor and shell. The multipoint constraint algorithm is used to model delamination. Finally, the parametric studies are reported.     

利用SMA的SME特性改善复合材料板低速冲击响应性能的研究

本文将具有一定塑性应变的形状记忆合金(SMA)纤维埋设在复合材料板中，利用其形状记忆功能(SME)改善复合材料板的低速冲击响应性能。研究中，应用有限元法对SMA杂交复合材料板的低速冲击响应进行了分析，其中，SMA中产生的恢复应力通过实验得出的应力-温度关系确定，冲击接触力通过修正的Hertzian接触定律求得；研究结果表明具有形状记忆功能的SMA能有效地改善复合材料的低速冲击响应性能。     

基于多尺度模型的RC框架撞击倒塌响应数值分析

为了在保证计算精度的同时提高撞击荷载作用下RC框架结构连续倒塌分析的计算效率,本文基于有限元软件LS-DYNA,建立了撞击响应分析的多尺度模型。针对该模型分别采用拆除构件法和撞击全过程分析法分析了撞击荷载下框架结构的连续倒塌动力响应。结果表明：拆除构件法在分析撞击作用下结构的连续倒塌时,由于忽略了撞击力及其对周围结构造成的初始损伤、初始位移和初始速度,低估了结构的动力响应,不能合理反映撞击作用下框架结构的破坏模式;多尺度模型能够准确模拟撞击作用下框架结构的动力响应和破坏模式,同时计算时间仅为精细模型的三分之一,满足整体结构系统撞击倒塌分析的需要。     

Spectral strip analysis for composite cylinders subjected to lateral impact

An efficient computational method, combining the spectral element and the finite-strip method (spectral-strip) is developed in order to obtain numerical results to time dependent problems of cylindrical composite structures subjected to lateral impact, within moderate CPU times. The finite strip method is applied to cylindrical structures uses global interpolation in the circumferential direction, and spectral emenents in the meridional cross section. A term superposition solution is obtained, where every iteration refines the solution and is independent of former iterations. In this manner, a full three-dimensional solution to the problem of the dynamic response of cross-ply cylindrical composite shells subjected to a lateral impact, is obtained. The stability and the accuracy of the method are examined. The main goal is to predict the damage caused by a high velocity non penetrating impact of microparticles. Two types of shells are studied—thin and thick cross-ply laminates. The effect of curvature on a high velocity impact is studied. Also, the stress field obtained by the finite element code is investigated and damage evaluation is discussed. The present work focuses on moderate and high velocity impacts and therefore the force duration is of the order of the through-the-thickness propagation time, causing the imapct region to be in tension due to the reflected stress wave. The results demonstrate the dilatational compression wave traverses the shell thickness as a result of the impact and the dilatational tension wave reflected from the interior free surface as well as the propagation of shear waves in different directions. Using failure criteria, one can find that the compressive stress wave causes matrix cracking and the tensile stress wave causes both delamination and matrix cracking. It is shown that for a thin cylinder, the impact phenomenon is concentrated near the striking region while for a thick-walled cylinder the results of the impact are visible in points far from the striking point as well. The interference of the stress waves that circumevent the cylinder create other points of local maxima for the equivalent stresses. The code written for the finite element solution embloys the object oriented programming through the C++ language. A special matrix class is developed to perform various linear algebra operations. Dedicated to the memory of Professor Joab J. Blech (1934–1996)     

Effects of Stacking Sequence and Impactor Diameter on Impact Damage of Glass Fiber Reinforced Aluminum Alloy Laminate

The methods of numerical simulation and test are combined to analyze the impact behavior of glass fiber reinforced aluminum alloy laminate (GLARE). A new failure criteria is proposed to obtain the impact failure of GLARE, and combined with material progressive damage method by writing code of LS-DYNA. Low velocity impact test of GLARE is employed to validate the feasibility of the finite element model established. The simulation results have been shown that progressive damage finite element model established is reliable. Through the application of the finite element model established, the delamination of GLARE evolution progress is simulated, various failure modes of GLARE during impact are obtained, and the effects of stacking sequence and impactor diameter on the impact damage of GLARE are obtained.