多种截面形状薄壁管轴向冲击吸能特性对比研究及优化设计

利用经过台车碰撞试验验证的铝合金薄壁管材料参数对比研究了方形、六边形、八边形和圆形的多种不同截面形状薄壁管在轴向动态冲击下的吸能特性。结合多目标优化算法对吸能特性较好的八边形多胞管进行了参数优化,并提出了一种新的优化设计方案。该方案将多胞管外管、肋板和内管的厚度分别作为优化设计变量,通过与将多胞管取统一厚度作为设计变量的传统方案进行对比发现,采用该方案对八边形多胞管进行优化后明显提高了其在相同压缩力峰值下的能量吸收效率。     

STACER伸展变形的一种计算方法

STACER是一种航天器上广泛应用的伸展机构,其储能部件由薄壁钢带经冷加工涡卷最终成型为螺旋管状.由于伸展长度可达装载高度的几十倍,钢带在展开过程中呈现为大挠度、大应变形变,机构伸展力的计算必然涉及强非线性问题;同时,钢带的构型、边界条件在伸展过程中不断变化,这些因素又增加了问题的难度,致使常用的商业软件已无法直接处理此类问题.此研究工作应用变分方法的思想,以研究钢带变形的几何特性为基础,构造出钢带构型恰当的可能函数空间,并利用形状函数随伸展长度的变化规律求出钢带的主应变以及变形能,再利用势能极小原理,确定出钢带的真实构型以及相应的变形能,最终利用变形能和虚功原理得出伸展力.这一方法既可以简化计算又可以得到钢带形状函数、伸展力的近似解析式,为伸展力影响因素的定量分析提供了条件.     

平面应力下薄壁管材连续矫直压弯量力学模型与数值解法

薄壁管材在连续矫直过程中,各矫直辊组的压弯量作为核心工艺参数直接决定了薄壁管材的矫直精度。而目前现场仍沿用经验图表结合人工经验和反复试矫对其进行估定,亟待建立针对性的压弯量数学模型以指导生产。为此从薄壁管材的结构特点和矫直辊系组成出发,构建了针对压弯量计算的简化悬臂结构模型,基于相关假设和弹塑性相关理论,分别确定了平面应力状态下弹性区和弹塑性区管材横截面的弯矩模型,运用虚功原理建立了矫直辊压弯量力学模型,并给出了数值计算方法,完成了程序开发。经有限元动态仿真试验证明了模型的正确性和适用性,通过对典型管材数据的计算绘制了一系列工艺参数曲线,得到管材轴线弯曲半径和压弯量随管材直径、壁厚和屈服极限的变化关系,为现场压弯量的调整提供理论依据。     

用统一分析梁与有限节线法分析弹性薄壁截面构件

传统薄壁截面梁理论不仅与梁的长细比有关,还强烈地依赖于其横截面的形状和荷载的作用方式.为了解决任意长细比、任意形状弹性薄壁截面杆状类结构构件或结构体系受任意荷载作用的力学分析问题,提出了一种新的梁模型——统一分析梁,一种结构数值分析新方法——有限节线法.利用统一分析梁模型和有限节线法不仅可以分析任意弹性薄壁杆状类结构构件的力学行为,而且当问题的性质与传统梁理论的前提条件一致时,会得出同样精度的解答.算例计算结果证明了统一分析梁的合理性与有限节线法的正确性.     

Elastic-plastic secondary indeterminate problem for thin-walled pipe through the inner-wall loading by three-point bending

The inner-wall loading by three-point bending about thin-walled pipe is an elastic-plastic secondary indeterminate problem in the symmetrical three-roller setting round process. In this study, the shifting of the tangent point between the pipe and lower roller is ignored. The bilinear hardening material model is adopted, and the static equilibrium condition, physical relationship of elastic-plastic deformation, and deformation compatibility condition are taken into account. Based on the geometrical discrete idea, a semi-circular pipe is meshed equably into N micro-pipe-wall elements with same geometric parameters along the circumferential direction. Deformation characteristics of each element are calculated, and then the deformation history response of the whole pipe is resolved by the load increment method. The finite element model of static bending in three-roller setting round process is established by using the software package ABAQUS. The theoretical and simulated results show that the cross section of pipe has two positive bending regions and two reverse bending regions; the maximum bending curvature appears in the bottom section of pipe, the minimum bending curvature appears in the section corresponding to the tangent point of the pipe and lower roller. The quantitative relationships between the upper roller load, maximum(minimum) bending curvature and reduction are given. Finally, the reliability of theoretical calculation is proved by numerical simulation.     

Free torsion of thin-walled structural members of open- and closed-sections

Free torsion of thin-walled structures of open- and closed-sections is a classical elastic mechanics problem, which, in literature, is often solved by the method of membrane analogy. The method of membrane analogy, however, can be only applied to structures of a single material. If the structure consists of both open- and closed-sections, the method of membrane analogy is difficult to be applied. In this paper, a new method is presented for solving the free torsion of thin-walled structures of open- and/or closed- sections with multiple materials. By utilizing a simple statically indeterminate concept, torsional equations are derived based on the equilibrium and compatibility conditions. The method presented here not only is very simple and easy to understand but also can be applied to thin-walled structures of combined open- and closed-sections with multiple materials.     

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以当前车架前纵梁薄壁吸能管为依据,制作了普通单、双帽薄壁管以及单、 双帽冲压筋薄壁管试件,并依次进行了轴向准静态压缩试验,来研究这些管件的轴向压缩吸 能特性. 试验发现：添加冲压筋之后,单、双帽薄壁结构的轴向吸能特性都得到了很大提高, 但冲压筋对帽型薄壁结构稳定性的提高不明显. 试验结果表明,在不增加材料的前提下,通 过改变吸能元件的截面结构可以提高其碰撞吸能特性.     

开孔薄壁钢梁-轻骨料混凝土组合楼板火灾后受力性能研究

针对一种由冷弯卷边H型开孔薄壁钢梁和轻骨料混凝土预制板装配而成的新型轻质组合楼板, 对一组两端简支的组合楼板试件开展了烃类火灾作用后的力学性能试验研究. 结果表明, 承担2kN?m-2均布荷载的组合楼板试件在遭受600℃烃类火灾作用后, 仍具有较高的承载能力和整体刚度. 在4kN?m-2的均布荷载作用下, 火灾后损伤最严重的组合楼板试件的跨中挠度仍小于L/400, 且未见混凝土的进一步开裂. 试验结果表明, 薄壁钢梁腹板开孔形式及抗剪键的数量对火灾后组合楼板的整体刚度和受力性能有明显影响, 从提高组合楼板整体刚度的角度考虑, 对主钢梁腹板的开孔宜首选孔径大、数量少的分布形态, 同时适当增加抗剪键数量.     

The application of graph theory to the limit analysis for torsion of thin-walled bars with complex cross-sections

Graph theory is employed in this paper as a means to establish the topological model of complex thin-walled cross-sections. On this basis, the upper and lower bound theorems of the plastic limit analysis are applied to the analysis of the plastic limit shear flows on the cross-section of thin-walled bars under St. Venant torsion. Corresponding mathematical programming problems are formulated and their duality is shown. After solving the linear programming problem corresponding to the lower bound theorem, the limit torsional moment of a thin-walled cross-section can be calculated according to the shear stress distribution in the limit state. The formula for calculating the limit torsional moment is given. Furthermore, the limit state of thin-walled cross-sections under St. Venant torsion is also discussed and the concept of the limit tree is introduced. A computer program has been developed by the author. Results calculated by the program for typical complex cross-sections are given.     

Time to Creep Failure of Thin-Walled Cylindrical Pipes under Torsion

The time to creep failure is calculated for rectilinear thin-wall pipes subjected to pure torsion, torsion with uniaxial tension, and torsion with internal pressure. The problem is solved using the concept of equivalent stress. The equivalent stresses are found from the generalized mixed failure criterion whose form depends on the signs of the principal stresses. The criterion relates the maximum normal stress and the intensity of shear stress if the signs coincide, and the maximal shear stress and the octahedral shear stress if the signs are opposite. A technique for determining the material constants is developed. The calculated and experimental data are compared and found to be in satisfactory agreement