曲加筋条壁板优化设计研究

针对多设计变量的新型曲加筋条壁板(curvilinearly stiffened panels)优化问题,提出了一种参数化设计方法。该方法以加筋壁板的重量最小为目标,以加筋壁板屈曲、von Mises应力和筋条压损等为约束条件,通过MSC.Patran/Nastran进行参数化建模并获得结构响应,采用非劣分层遗传算法Ⅱ(NSGA-Ⅱ)实施结构优化。为了合理、简洁地描述曲加筋条的几何形状,采用B样条定义曲加筋条的轴线,并取其起点、终点和控制点坐标为位置/形状设计变量。利用单级优化策略,同时对位置/形状变量和包括筋条高度、筋条厚度以及平板厚度在内的尺寸变量进行优化。采用该设计方法,在结构承受面内压缩和剪切载荷以及四边简支的条件下,分别对采用直/曲加筋条的壁板进行了轻量化设计。结果表明,复杂载荷作用下,采用相同数目的曲加筋条能够提高结构效率,实现结构减重。     

大型设备顶部板式工装吊耳的分析设计

对垂向载荷与横向载荷共同作用下的大型设备顶部板式工装吊耳的强度设计方法进行了研究,采用Abaqus软件对卸扣销轴与吊孔的挤压截面A-A处进行极限载荷分析,对连接吊耳与筋板的焊缝进行应力强度评定,确保了整个吊耳的安全性,为设备的顺利制造提供了保证。     

原位压痕仪机械载荷分析与控制方法设计

以提高对产品材料硬度及其抗形变能力的测量效果,本研究首先分析了金属压痕仪的测量原理,发现影响其极限机械载荷控制的因素与压头形状与表面粗糙程度有关.因此,通过应力响应系数分析压头过渡圆角半径、过渡角度与极限载荷的关系.然后在加载平衡的约束下,以材料截面中心为加载中心获取极限机械载荷,再通过控制拉伸与弯曲载荷实现对压痕仪极...     

机械装备构件轻量化主要技术途径的探讨

在对机械装备构件轻量化的基本原则和主要技术依据进行概括的基础上,就机械装备构件轻量化强度设计技术进行探讨,分别在简单拉伸、弯曲、扭转、疲劳等受力状态下,对简单形状构件轻量化强度设计判据进行分析,并进一步得到构件轻量化强度设计通用判据;对铁、钛、铝、镁、钴等金属基体合金轻量化性能指标进行比较,并进一步提出逐步建立构件轻量化材料性能指标体系的设想;对机械装备构件轻量化成形工艺和表面改性技术的作用进行概括,并提出通过工艺技术提高构件材料的强度(或屈服强度)、提高构件截面形状的抗弯截面系数(或抗扭截面系数)、提高表面层材料的强度(或屈服强度)和改变构件表面为压应力状态等工艺途径来达到构件轻量化目的。     

考虑残余应力的金属波纹垫压缩-回弹性能有限元分析

为探讨金属波纹垫模压成型过程的残余应力和应变强化对垫片压缩-回弹性能的影响,在试验的基础上,建立考虑制造残余应力的金属波纹垫压缩回弹有限元分析方法,并将分析结果与试验结果进行对比。结果表明:有限元计算结果与试验结果吻合较好,两者的垫片最大压紧载荷误差为1. 30%,压缩率误差为9. 08%,回弹率误差为13. 90%。根据有限元计算结果将金属波纹垫的变形历程分成3个阶段,对其变形机制进行分析,研究轴向载荷作用下金属波纹垫的压缩-回弹过程。研究表明:轴向载荷作用下金属波纹垫依次发生弹性变形、塑性屈服和弹性恢复阶段。     

Pro／E中可变剖面扫描功能在设计中的应用

Pro／E的可变剖面扫描功能是通过控制截面的方向和形状，使截面沿着一条或多条选定轨迹线扫描来创建实体或曲面，本文介绍了在可变剖面扫描过程中通过轨迹线和截面参数变化来控制截面的方法，用实例说明了可变剖面扫描功能在设计中的应用。     

高强钢板DP590温热环境下屈服准则适用性分析

板料成形过程中温度的变化会影响其塑性流动行为。以先进高强钢板DP590为研究对象,通过不同温度下单拉试验和不同温度不同加载比例双拉试验得到其在温热环境下的试验屈服轨迹,结果显示温度不仅会影响DP590钢板屈服轨迹的大小,而且影响屈服轨迹的形状。将试验屈服轨迹和几种理论屈服轨迹进行对比分析,表明Yld2000-2D屈服准则与试验结果吻合较好,同时等效应力应变点分析也显示出Yld2000-2D屈服准则满足塑性力学的单一曲线假设规律。针对Yld2000-2D屈服准则,采用不同温度下的试验数据计算出不同温度下的各向异性参数,通过拟合获得各向异性参数与温度的四次多项式函数关系,建立温度相关Yld2000-2D屈服准则,并与常规Yld2000-2D屈服准则对比分析,结果显示温度相关Yld2000-2D屈服准则更加适合描述DP590钢板温热环境下的屈服行为。     

时速400公里高速列车底架拓扑优化

运用OptiStruct软件,针对400km/h高速列车车体,计算其在重要载荷作用下的结构强度、刚度以及模态分析后,以列车的底架作为研究对象,对其进行拓扑优化设计.结合OptiStruct中的OSSmooth模块和SOLIDWORKS软件,总结分析不同载荷方式作用下得出的拓扑优化结果,确定车体底架结构内筋的分布,得出最佳截面形状,并对优化后的底架结构及车体进行静强度以及模态分析比较.对比得出,优化后底架结构减重6.82％,满足车体强度、刚度及模态频率等性能要求的同时,改善了结构的应力分布.     

汽车后桥壳弹塑性有限元分析

对我国生产的一种汽车后桥壳进行了大位移、大应变弹塑性有限元模拟分析，求得了加载点的载荷-位移变化曲线、最大应力点的弹塑性应变-载荷变化曲线、危险截面的弹塑性应力-载荷变化曲线、危险截面达到全面屈服时的屈服载荷等，为汽车后桥的强度评价及疲劳寿命估算提供了有关数据。     

复杂循环载荷条件下金属的应力、应变规律

在各向同性循环强化模型基础上 ,通过屈服面及极限面形状、方向及面积的变化 ,分析了拉 -扭非比例循环载荷下金属的双表面各向异性强化模型 [1 ] ,并用BT9钛合金 [3 ] 及 30 4不锈钢 [3～ 5] 的试验结果检验了该模型的可行性。采用了塑性应变历程非比例参数来描述非比例载荷下材料的循环强化程度。研究了材料的横向强化及附加强化效应。结果表明 :本模型能很好地描述非比例载荷下金属的一系列主要应力、应变规律     

The effect of strut geometry on the yielding behaviour of open-cell foams

A micromechanical analysis was carried out to investigate the effect of strut geometry on the yielding behaviour of open-cell foams. Different strut cross sections, in rectangular, circular and equilateral triangular shapes, were investigated. It was found that the strut geometry significantly affects the plastic-yielding behaviour of open-cell foams. The shape of the plastic-yield surface was found to depend not only on relative density but also on the cross-sectional shape of the struts. Numerical results show that even though the material of the struts is perfectly plastic, open-cell foams with asymmetrical sectional struts will exhibit different tensile and compressive collapse strength.     

The effect of doubly tapered strut morphology on the plastic yield surface of cellular materials

Although the literature on the mechanics of cellular materials is vast, there is no theoretical model to account for the effects of axial yielding of struts aligned to the applied loading direction on the plastic yield surface under multiaxial loading conditions. An anisotropic hexagonal model having tapered strut morphology is developed to show these effects on the plastic yield surface under multiaxial tensile loading condition. This model covers several types of cellular structure such as two-dimensional (2D) hexagonal and square cellular materials, and three-dimensional (3D) hexagonal and rhombic cellular materials of rod-like columnar structure. A tetrahedral element with tapered strut morphology is also used for a foam model to illustrate these effects on the yield surface under axisymmetric loading condition. Plastic collapse due to bending moment in the inclined struts is a dominant mode. However, under multiaxial tensile loading, the collapse due to axial yielding of struts parallel to the loading direction is found to be an important mode. The shape of plastic yield surface was found to depend not only on relative density but also on the strut morphology.     

Stress analysis of two-dimensional cellular materials with thick cell struts

Finite element analyses (FEA) were performed to thoroughly validate the collapse criteria of cellular materials presented in our previous companion paper. The maximum stress (von-Mises stress) on the cell strut surface and the plastic collapse stress were computed for two-dimensional (2D) cellular materials with thick cell struts. The results from the FEA were compared with those from theoretical criteria of authors. The FEA results were in good agreement with the theoretical results. The results indicate that when bending moment, axial and shear forces are considered, the maximum stress on the strut surface gives significantly different values in the tensile and compressive parts of the cell wall as well as in the two loading directions. Therefore, for the initial yielding of ductile cellular materials and the fracture of brittle cellular materials, in which the maximum stress on the strut surface is evaluated, it is necessary to consider not only the bending moment but also axial and shear forces. In addition, this study shows that for regular cellular materials with the identical strut geometry for all struts, the initial yielding and the plastic collapse under a biaxial state of stress occur not only in the inclined cell struts but also in the vertical struts. These FEA results support the theoretical conclusion of our previous companion paper that the anisotropic 2D cellular material has a truncated yield surface not only on the compressive quadrant but also on the tensile quadrant.     

Indentation of foamed plastics

When a low density foam is indented, it is found that the indentation hardness is about equal to the yield strength of the foam in compression. In this, foams differ from fully dense materials which, when plastic, exhibit a hardness which is about three times larger than the yield strength. This is because the foam is compressible: under the indent, a column of foam collapses, in a way which is hardly influenced by the surrounding material. This paper reports analyses of the indentation of compressible foams by cylindrical and spherical indenters, which reasonably account for measurements of the indentation hardness and the shape of the plastic zone beneath the indenter, in polyurethane foams. The results are relevant to the understanding of low density foams and woods, be they elastic, plastic or brittle.     

Yield and buckling behavior of Kelvin open-cell foams subjected to uniaxial compression

This study analyzes the yield and buckling behavior of Kelvin open-cell foams subjected to uniaxial compression. A homogenization theory of the updated Lagrangian type is applied to cubic unit cells and cell aggregates in the Kelvin foam model. Macroscopic instability and microscopic bifurcation are thus incrementally examined under uniaxial compression. The analysis is performed by taking into account the non-uniformity of strut cross-sectional areas and the strain hardening-softening behavior of struts that were observed in experiments on open-cell 6101-T6 aluminum alloy foams. It is shown that macroscopic instability primarily occurs as a consequence of the strain hardening-softening behavior of struts. It is further shown that the macroscopic instability stress obtained has (3/2)th power dependence on relative density as predicted in the Gibson-Ashby relation.     

A general constitutive relation for linear elastic foams

A three-dimensional linear elastic constitutive relation is formulated based on a representative unit cell of foam using elasticity theory and micromechanics homogenization scheme. The displacement and strain fields of the unit cell are obtained from elasticity theory and used to derive the macroscopic strain field defined on the outer surface of unit cell through homogenization scheme. By assuming a uniform macroscopic stress on the unit cell surface and the existence of strain energy potential, the constitutive relation of linear elastic foams is obtained. The newly derived constitutive relation is a function of mechanical property of solid constituent, the geometry of cell struts, and the porosity of foams and is able to characterize the anisotropic behavior of foams due to non-uniform strut geometry. The linear elastic response of open-celled foams with both low- and medium-relative densities can be studied using the derived constitutive relation. The effective elastic modulus for uniform strut geometry is reduced from the constitutive relation and agrees well with Gibson and Ashby's semi-empirical equation, Warren and Kraynik's, and Zhu's analytical models within relative density ranging from 0 to 0.35. For non-uniform strut geometry, the calculated effective elastic moduli in three axial directions are different and the material displays anisotropic behavior. The bulk modulus shows less dependence on the variation of the strut geometry. Poisson's ratios are also reduced from the compliance matrix.     

Influence of strut cross-section of stents on local hemodynamics in stented arteries

Stenting is a very effective treatment for stenotic vascular diseases, but vascular geometries altered by stent implantation may lead to flow disturbances which play an important role in the initiation and progression of restenosis, especially in the near wall in stented arterial regions. So stent designs have become one of the indispensable factors needed to be considered for reducing the flow disturbances. In this paper, the structural designs of strut cross-section are considered as an aspect of stent designs to be studied in details. Six virtual stents with different strut cross-section are designed for deployments in the same ideal arterial model. Computational fluid dynamics(CFD) methods are performed to study how the shape and the aspect ratio(AR) of strut cross-section modified the local hemodynamics in the stented segments. The results indicate that stents with different strut cross-sections have different influence on the hemodynamics. Stents with streamlined cross-sectional struts for circular arc or elliptical arc can significantly enhance wall shear stress(WSS) in the stented segments, and reduce the flow disturbances around stent struts. The performances of stents with streamlined cross-sectional struts are better than that of stents with non-streamlined cross-sectional struts for rectangle. The results also show that stents with a larger AR cross-section are more conductive to improve the blood flow. The present study provides an understanding of the flow physics in the vicinity of stent struts and indicates that the shape and AR of strut cross-section ought to be considered as important factors to minimize flow disturbance in stent designs.     

A continuum plasticity model for the constitutive and indentation behaviour of foamed metals

A yield surface is proposed that can be fitted to the plastic flow properties of a broad class of solids exhibiting plastic compressibility and different yield points in tension and compression. The yield surface is proposed to describe cellular solids, including foamed metals, and designed to be fitted to three experimental results: (1) the compressive stress–strain response (including densification), (2) the difference between the tensile and compressive yield points and (3) the degree of compressibility of the foam, as measured by the lateral expansion during a uniaxial stress compression test. The model is implemented using finite elements and used to study the effects of plastic compressibility on two problems: the compression of a doubly notched specimen and indentation by a spherical indenter. The model is then fitted to the properties of a typical closed cell aluminum foam and used to study indentation into a dense aluminum face sheet on a foam foundation. The dependence of the indentation load–displacement curve on the relevant material and geometric parameters is determined, and a single load–displacement relation is presented which approximates the behaviour of a wide range of practical designs. These results can be used to design against indentation failure of sandwich panels.     

Plastic collapse of cellular structures comprised of doubly tapered struts

In this paper, micro-structural models are developed to examine the effects of tapered strut morphology on the plastic collapse of cellular structures. The analytical models are for materials that fail by plastic yielding and cover several types of columnar structure (e.g. hexagonal and square honeycombs, and hexagonal and rhombic cellular materials of rod-like columnar structure). The results indicate that the plastic collapse of hexagonal cellular materials is dependent not only on the relative density but also on the strut morphology. The presence of taper in struts can increase or decrease the plastic collapse strength of cellular materials, depending on the strut morphology.     

The microtextured plastic moldings to control human tactile sense: The texture effect enhancement due to apical shape and material frictional properties

The purpose of this study is to develop a plastic molding with a distinguishing tactile character for various industrial applications. In the present paper, we investigated the effects of the apical shape of the texture and the frictional properties of the plastic material on the tactile sense of the textured plastic molding in order to enhance the texture effect. Based on the analyses conducted, it was found that both the apical shape and the material frictional properties affect the particular tactual sensation of the plastic molding. The “Uneven” and similar trend sensations, which are mainly dominated by the fluctuation of friction, were dependent on the apical shape due to the sticking characteristics of the fingerprint. The strength of these sensations was caused by the sharper apical shape. The “Sticky” sensation was dominated by the complex effect of the fluctuation of friction and the frictional properties of the plastic material. The larger texture effect elicited for “Slick” sensations was obtained at round and sharp textures with a pitch of 120 μm. The enhanced texture effect of material frictional properties was observed at the apical shapes with large contact area, and it was obtained at the round texture. However, flat texture elicited a similar sensation to that elicited by the nontextured surface as a result of the small texture effect and large contact area. These results indicate that control of the apical shape and material frictional properties is effective in enhancing the texture effect of the plastic molding surface.