基于塑性铰理论的车身概念设计正碰分析与优化方法

在概念设计阶段,车身碰撞安全性能评价是一个难点问题,需要详细的结构模型,本文基于塑性铰理论提出采用梁单元简化模型对框架车身进行概念设计阶段的耐撞性评估和优化设计方法。首先,介绍了关于箱型截面薄壁梁弯曲特性研究的理论模型与计算过程,接着赋予梁单元塑性铰的特性,模拟薄壁梁变形,再对框架车身进行了碰撞仿真。将仿真结果与详细模型对比,以分析简化模型的精度及可靠性。最后,以此为基础对框架车身进行耐撞性优化。结果表明,该简化模型易于创建,且有较高的精度,可用于概念设计阶段梁结构的设计工作。     

超静定连续梁弹塑性过程分析的单位荷载法

讨论了分析超静定连续梁弹塑性受力和变形全过程的单位荷载法,运用该方法分析了集中荷载作用下一次超静定两跨连续梁的弹塑性加载和变形全过程．根据受力变形的特点,集中荷载作用下两跨连续梁的弹塑性加载过程可分为四个阶段,分别是弹性阶段、集中荷载作用点附近塑性区扩展阶段、集中荷载作用点保持为塑性铰而附近区域线性卸载阶段、两跨连接点附近塑性区扩展直至形成第二个塑性铰阶段．给出了加载过程中各阶段的弯矩内力和竖向位移随外荷载而变化的解析公式．研究结果表明：在相同的单跨荷载工况下,连续梁的变形过程不同于单跨一次超静定梁,其塑性铰形成顺序不同,静定结构形成顺序不同,但塑性极限破坏荷载相同．     

DYNAMIC RESPONSE OF A RIGID,PERFECTLY PLASTIC FREE-FREE BEAM STRUCK BY A PROJECTILE ATANY CROSS-SECTION ALONG ITS SPAN

I. INTRODUCTION The dynamic plastic response of free-free beams subjected to intense dynamic loading is a subject ofinterest for aerospace engineering applications. For example, when a rocket is attacked by a missile, itslarge plastic deformation behav…     

Elastic–plastic behavior of a semicircular frame being pressed against a rigid plane

As a simplified structural model, a semicircular frame is used to study the crashworthiness behavior of an aircraft fuselage. The quasi-static large elastic-plastic deformation of a semicircular frame in the process of its being pressed against a rigid ground is analyzed. First, based on the linear elastic assumption, the quasi-static large deformation contact process of the frame can be divided into three phases, i.e., point contact, line contact and post-buckling. By means of a shooting method, the relations between the displacement and contact force as well as the distribution of bending moment in the three phases are obtained. Then, by assuming an elastic, perfectly-plastic moment-curvature relationship for the semi-circular frame, the contact process is analyzed in detail to reveal the plastic collapse mechanism, the traveling of plastic hinge and the force-displacement relationship. In order to verify the analysis, a preliminary experiment was conducted, in which two types of half rings with clamped ends were pressed by a rigid plate. In addition, a numerical simulation is also conducted by employing ABAQUS to analyze both rectangular cross-sectional beam and I-beam. Finally, the theoretical predictions are compared with the experimental results and numerical solutions, showing that the elastic-plastic analysis can predict the contact process very well.     

钢框架抗震耗能节点梁的极限承载力分析1）

为提高结构的抗震性能,框架结构中以翼缘削弱型节点为代表的延性耗能节点逐渐代替传统节点,为研究翼缘削弱型节点框架梁在单向比例加载时的极限载荷,对削弱梁极限状态进行了分析,判定极限状态下削弱梁塑性铰生成的位置并计算极限载荷,将计算结果和普通梁进行对比.分析结果表明：削弱梁越长承载力下降越明显,对短梁需要选择合适的削弱参数,才能避免塑性铰出现在梁端.研究结果可为削弱梁塑性设计提供依据,同时拓展结构力学极限载荷学习内容.     

钢框架抗震耗能节点梁的极限承载力分析

为提高结构的抗震性能,框架结构中以翼缘削弱型节点为代表的延性耗能节点逐渐代替传统节点,为研究翼缘削弱型节点框架梁在单向比例加载时的极限载荷,对削弱梁极限状态进行了分析,判定极限状态下削弱梁塑性铰生成的位置并计算极限载荷,将计算结果和普通梁进行对比.分析结果表明：削弱梁越长承载力下降越明显,对短梁需要选择合适的削弱参数,才能避免塑性铰出现在梁端.研究结果可为削弱梁塑性设计提供依据,同时拓展结构力学极限载荷学习内容.     

An experimental study of the large deformation of plastic hinges

Recent applications of structural plasticity to areas such as vehicle crashworthiness has led to interest in the large deformation plastic collapse of general frames. Even when displacements are comparable to the original structural dimensions, the plasticity is confined to localized regions or “hinges”. This paper reports an experimental study of the behavior of such hinges in thin walled structural members. Due to local deformation the load carrying capacity of the hinge significantly decreases at large rotations. In a companion paper [4] a structural constitutive theory is proposed to account for this behavior. Numerical data for this theory is obtained in the present paper. Finally test results are given for a large deformation combined loading test designed to validate the theory of [4]. The experimental results are in good agreement with the theoretical predictions.     

哈大客运专线沈阳高铁站弹塑性时程分析

以哈大客运专线沈阳站为工程背景,对该结构进行罕遇地震作用下的弹塑性时程分析。通过SAP2000有限元软件研究结构的动力特性、变形状况、基底剪力时程曲线,分析了框架梁、柱的塑性损伤发展历程、拱桁架的塑性铰出铰机制以及关键框架梁、柱构件的塑性损坏状态。结果表明:结构在7度罕遇地震作用下基底剪力与多遇地震下比值最大为5.69;框架梁的损伤比框架柱严重,已进入"极限承载力"状态,仅有少量框架柱进入塑性变形阶段,结构满足"强柱弱梁"的设防要求;关键梁、柱构件损坏程度为79%和68%,仍有较大的富余度。结构薄弱区集中在顶层商业层区域,由于屋面和框架柱的连接效应,柱顶率先出现塑性铰,致使顶层位移角增大。     

端部受斜撞击作用悬臂梁的弹塑性动力响应模式

基于大变形动力控制方程并利用有限差分离散分析,研究了斜撞击作用下弹塑性悬臂梁的动力响应.通过对屈服函数以及弯矩、轴力在动力响应过程中分布规律的分析,阐明了斜撞击下悬臂梁的弹塑性动力响应模式和斜撞击的轴向分量对变形机制的影响.研究表明,弹塑性响应过程可划分为四个阶段,对应的变形模式为:"压缩塑性区扩展"模式,"广义移行塑性铰"和"压缩塑性区收缩"混合模式,"驻定塑性铰"模式,"弹性自由振动"模式.与刚塑性分析所假定的两相变形模式比较,弹塑性响应分析证实了响应早期的瞬态轴向压缩模式和梁根部"驻定塑性铰"模式的存在性,肯定了刚塑性分析所假定变形模式的主要特征.斜撞击的轴向分量在撞击发生的瞬时主导了梁的变形,使梁呈现同承受横向冲击明显不同的变形规律.随着响应的深入,轴向分量迅速衰减,其对截面屈服的贡献非常微弱,由横向分量引起的弯曲挠动在大部分时间内主导和控制梁的变形.数值计算结果表明,斜撞击载荷的质量、撞击速度和角度是影响梁动力响应的重要因素.     

刚塑性自由梁中部在横向冲击下的初始变形模式

研究了均匀矩形截面刚塑性自由梁中部在小尺寸、平头、圆柱形刚性弹体撞击下的三种变形模式,即梁的刚体平动、单铰变形模式和三铰变形模式。考虑了刚性子弹冲击后在梁上形成的剪切冲塞,分析了子弹通过冲塞作用在梁中部的剪切力可能引起的梁的弯曲变形,找出了梁的初始变形模式对子弹大小、梁的尺寸和材料性能的依赖关系。     

双轴反复荷载作用下钢筋混凝土空间框架结构滞回全过程分析

实际地震中结构所承受的地震作用是多维的。结构的恢复力特性是反映其抗震性能的一个重要属性。对地震作用下钢筋混凝土柱、梁塑性铰区的计算模型进行了分析,给出了塑性铰区等效长度的简便计算公式;建立了“有限纤维”空间线性梁单元模型并推导出了其刚度矩阵;使用“弥散法”来考虑梁锚固钢筋在结点区的粘结滑移对结构整体变形的影响。最后使用空间杆系模型对一承受双向反复荷载的框架结构进行了计算分析。分析表明所建立的计算模型是精确有效的。     

冲击载荷下软钢梁早期响应的数值模拟和简化模型

冲击载荷作用下，梁的早期响应既有弹性变形也有塑性变形，两者相互耦合．有限元数值模拟的结果表明，弹性弯曲波的传播是梁早期变形的主要机制，刚塑性简化理论预言的初始阶段中梁的“移行塑性铰”实际上是不存在的．本文提出的弹性 理想塑性简化模型可以很好地模拟固支软钢梁的早期响应     

横截面参数化网格变形算法及耐撞性优化应用

薄壁梁结构是汽车等运载工具的主要承载构件,提高该类结构的耐撞性对乘员安全具有重要意义。然而,形状优化设计要求多组有限元模型与仿真分析,因此需要特定的建模技术或人工交互。本文提出了一种基于横截面形状的参数化网格变形方法,以实现已有有限元模型的有效重用。以给定有限元模型为输入,采用基于各向异性径向基函数网格变形方法,并结合骨架内嵌空间,可快速生成适用于仿真分析的有限元模型变体。以S形梁轴向冲击耐撞性设计为例,采用所提方法改变构件塑性铰区域的横截面形状,可快速（低于4 s）获取100组局部变形有限元模型,并采用代理模型技术和多目标遗传算法优化结构耐撞性。数值结果显示,构件耐撞性获显著提高,验证了所提参数化变形方法的有效性,展示了与一般形状优化框架的可集成性。     

THE ANALYSIS OF THE ENTIRE ELASTO-PLASTIC PROCESS OF A BEAM WITH ONE DEGREE OF INDETERMINACY UNDER A CONCENTRATED LOAD

对跨中集中载荷作用下一次超静定梁的弹塑性加载和变形全过程进行了分析。根据受力变形特点,集中载荷作用下一次超静定梁的加载过程可分为4 个阶段,分别是弹性阶段、固支端附近塑性变形区扩展阶段、固支端和集中载荷作用点附近塑性变形区双扩展阶段、固支端保持为塑性铰同时附近卸载而集中载荷作用点附近塑性变形区继续扩展直至形成第2 个塑性铰阶段。在弹性阶段,弯矩内力和挠度与外载荷是线性比例关系,在第2,3 两个阶段,弯矩和挠度与外载荷是复杂的非线性关系,在第4 阶段,弯矩与外载荷是线性关系但不是比例关系而挠度与外载荷是更为复杂的非线性关系。给出了全过程任意点的弯矩和挠度计算公式,可供结构设计参考应用。     

自由梁受集中质量两点撞击的刚塑性动力响应

对矩形截面自由梁在两端同时受到完全相同的集中质量横向撞击问题进行了理论上的研究 ,通过采用刚塑性的材料模型得到了其动力响应完全解。结合数值方法给出了梁的瞬态变形 ,并讨论了输入能量、质量比等参数对梁的最终变形、能量耗散的影响。针对典型算例将完全解的结果与MSC/Dytran的计算结果进行了比较 ,两者具有合理的近似 ,但理论预测的结果略高估计了梁的最终变形。     

The rapidly heated rigid-plastic cantilever

The concept of the expanding and contracting hinge produced by rapid thermal curvature is applied to the detailed analysis of a cantilever. In addition to a general study of the modes of deformation, the accelerations velocities and displacements are determined for a specific case. Although for the example chosen, less than 10% of the final plastic curvature occurs in the root hinge, a greatly simplified “strong beam” analysis which constrains all plastic deformation to the root hince gives a tip deflection only 6% less than the original value. The paper includes a discussion of the conditions which must be satisfied such that longitudinal inertia effects and elastic deflexions do not invalidate the analysis when it is applied to real materials.     

Biaxial Vibrations of an Elasto-Plastic Beam with a Prescribed Rigid-Body Rotation Including the Effect of Stiffening

In the present work, we study biaxial vibrations of elasto-plastic beamswith a prescribed rigid-body motion. Exemplarily, we treat the case of ahinged-hinged beam with a rotation about a fixed hinge. Such a problemis frequently to be encountered in machine dynamics. The deformations ofthe beam are assumed to remain small. In order to describe the beamvibrations, we utilize the Bernoulli–Euler beam theory. Axial vibrationsof the beam are neglected. We study cases, in which the flexuralstiffness of the beam is considerably lowered due to catastrophicenvironmental influences, such that the deformations relative to therigid-body motion, albeit small, reach the plastic regime. In thepresent paper, special emphasis is laid upon including the effect ofgeometric stiffening due to a comparatively fast rigid-body rotation.The equations of motion are derived by Hamilton's principle. The biaxialdeflections are discretized in space by means of Legendre polynomials.The plastic strains are discretized over length, height and width of thebeam by small plastic cells. Galerkin's procedure, together with aproper implicit midpoint rule is used for integration of the equationsof motion. The plastic strains are computed in every time-step by asuitable iterative procedure. Linear elastic/perfectly plastic behavioris exemplarily treated in a numerical study.     

Plastic modal approximations in analyzing beam-on-beam collisions

Dynamic behavior of a moving free–free beam striking the tip of a cantilever beam, as a typical example of collision between two deformable structures, is analysed by employing modal approximation techniques. The applicability of both rigid-plastic and elastic–plastic mode approximations is examined in predicting the energy partitioning between the two colliding beams.Three rigid-plastic modes (RP-Modes) are considered and the Lee’s functional is applied to select the appropriate mode. It is found that one of the beams would absorb all the initial kinetic energy, unless a higher-order RP-mode is adopted.To incorporate the effect of elastic deformation into the modal solution, an elastic, perfectly plastic mode (EP-Mode) approximation for the same problem is proposed. By replacing each of the plastic hinges in the RP-Mode with a nature hinge and an elastic–plastic rotational spring, the fundamental features of the dynamic elastic–plastic behavior of the two colliding beams are revealed. Both beams participate in energy dissipation, while the structural and geometrical parameters greatly influence the energy partitioning. It is shown from numerical examples that the EP-Mode solution provides a fairly good approximation compared with the RP complete solution and finite element simulation.     

Determination of the microscale stress–strain curve and strain gradient effect from the micro-bend of ultra-thin beams

A simple method is established to determine the microscale uniaxial stress–strain curve from the load and deflection data for a doubly clamped beam. The method is based on the fact that, for beam deflection much larger than the beam thickness, the axial stretching dominates the deformation in the doubly clamped beam and the doubly clamped beam behaves like a simple plastic hinge. The microscale uniaxial stress–strain curve, together with the cantilever beam experiments, is used to determine the strain gradient effect in Au thin beams. The effect of finite rotation is also discussed.     

梁中复合应力波的传播

采用有限差分法讨论了梁中复合应力波的传播．给出了粘塑性悬臂梁当自由端受突加弯矩载荷作用时梁内复合应力波传播的基本图象。指出，在冲击早期响应阶段．截面横向转动惯性效应起着重要作用，是不可忽视的。标志弹塑性边界的塑性效，一开始由自由端向固定端运动，但在反射卸载波的迎面作用下，会出现回退现象。在波动早期阶段，固定端主要处于弹性变形状态。此外，还对弹塑性梁中复合应力波的控制方程进行了必要的讨论。