长梯形截面钢板弯曲成形工艺的数值模拟

使用Dynaform 5.7软件对长梯形截面钢板弯曲成形的2种工艺方案进行了数值模拟,并对结果进行了分析比较.采用简单V形模具分步冲压工艺得到的工件形状误差较大,而采用整体模具先弯曲中间部位后弯曲两头的成形方案效果较好.     

炭基复合材料与人骨的力学性能对比分析

选用3种炭基复合材料,分别为采用化学气相沉积（CVD）工艺和CVD/浸渍复合工艺制备的2种C/C复合材料以及采用CVD/熔融渗硅（MSI）工艺制备的C/C-SiC复合材料,通过对比分析3种炭基复合材料与人骨的微观结构和力学性能,研究了所选用的3种炭基复合材料作为新型骨折内固定材料的可行性。结果表明:3种炭基复合材料与人骨均具有纤维增强、多孔基体的微观结构形态。在力学性能方面,3种炭基复合材料的弹性模量与人骨都较为接近,其中C/C-SiC复合材料的力学性能与人骨最为接近,分别为弯曲强度213.0 MPa、剪切强度19.3 MPa、压缩强度228.1 MPa,有望成为理想的接骨板材料。CVD和CVD/浸渍工艺制备的C/C复合材料,弯曲强度分别仅为161.8 MPa和174.6 MPa,低于人骨的弯曲强度,后期可通过改进坯体结构和制备工艺等方法来使其力学性能与人骨相匹配。      

平面变曲率管件成形工艺获取策略研究

目的 获取平面管件在弯曲成形过程中的初始工艺参数。方法 基于平面圆弧管件弯曲成形原理,将成形管件划分为稳定段和过渡段。针对稳定段,分析了平面圆弧管件的弯曲半径与弯曲模偏移量之间的映射关系,并通过二次曲线拟合得到非线性方程,以方便预测管件稳定区的成形工艺参数;针对过渡段,通过分析不同时间内不同模式下弯曲模偏移量对整体管件成形的影响,以确定最佳过渡方式。基于管件成形工艺知识库,提出了平面管件弯曲成形工艺参数的规划与预测方法,并通过成形实例管件进行了验证。结果 整个管件的逼近残差为0.230 1 mm,最大偏差为0.390 7 mm,逼近残差和最大偏差与管件总长度的比值分别为0.127 4%和0.216 2%。结论 所提出的方法可以有效获取平面变曲率管件的成形工艺参数。     

网格式整体壁板增量弯曲工艺知识库研究

针对网格式整体壁板数字化加工制造的需求,建立了自适应增量弯曲工艺知识库系统,阐述了系统的体系结构与实现方法.基于增量成形以及自适应控制的基本理论,提出了自适应增量弯曲成形工艺知识库参数获取方法(直接法、单特征法、双特征法、三特征法、多点回归求解法),在此基础上,建立了一种基于工艺特征方程的自适应增量弯曲工艺知识库系统.研究表明,所设计的系统能够按照一定的计算法则,给出待加工零件的弯曲工艺参数,实现了网格式整体壁板增量弯曲成形过程中的工艺参数自动预测与调整,并在实际应用中进行了验证.     

MoSi2-SiC 抗氧化涂层对碳/碳复合材料弯曲性能的影响

在C/C 复合材料表面制备了MoSi₂-SiC 抗氧化涂层, 分析了涂层工艺对C/C 复合材料组织的影响, 测试了材料的室温弯曲力学性能。结果表明, 该工艺在C/C 复合材料表面生成抗氧化涂层的同时, 基材内部的层间和纤维束界面, 以及孔隙周围也被硅化。C/C 复合材料经涂层工艺处理后, 弯曲断裂行为发生改变, 弯曲强度明显升高,塑性有一定程度的降低。      

温湿度和紫外老化对纸浆模塑材料性能的影响

目的 研究温度、湿度和紫外老化对脱木素和未脱木素纸浆模塑材料性能的影响,定量地对比不同因素作用下2种材料的力学性能差异。方法 以废纸浆为原料,经打浆、脱木素、湿成型、热压等工艺制得脱木素和未脱木素等2种纸浆模塑材料;模拟不同的温湿度和紫外老化环境,测试2种纸浆模塑材料物理力学性能的变化。结果 在同等条件下,脱木素材料的拉伸强度与弯曲强度均高于未脱木素材料;2种材料的拉伸强度、弹性模量和弯曲强度随着含水率升高而大幅降低;当温度为20 ℃、含水率为0~40%时,脱木素材料的拉伸强度下降了45 MPa,未脱木素材料的拉伸强度下降了35 MPa。当温度为0 ℃、含水率为0~40%时,脱木素材料的弯曲强度下降了70 MPa,未脱木素材料的弯曲强度降低了62 MPa;当含水率低于20%时,脱木素材料的拉伸性能和弯曲性能更易受到温度影响;虽然2种材料的拉伸性能和弯曲性能均随着紫外老化时间的延长而不断降低,但其影响程度远小于温湿度。结论 湿度对材料的力学性能影响最大,其次是温度和紫外老化;脱去木素有利于提高纸浆模塑材料的力学性能和抗紫外老化性能。     

复杂空间弯管三维自由弯曲成形有限元模拟及试验

目的以一复杂空间弯管为例,开展三维自由弯曲成形实验研究。方法首先提出三维自由弯曲成形工艺解析方法,然后通过有限元模拟与实际试验相结合的方法进行研究。结果有限元模拟所得到的弯管与CAD模型相比,弯曲半径偏差值不超过2%,吻合度较高。实际成形出的弯管与CAD模型对比显示,第1个弯曲段的实际弯曲半径为118 mm,设计值为120 mm,实际值与设计值偏差1.67%;第2个弯曲段的实际弯曲半径为133 mm,设计值为130 mm,实际值与设计值偏差2.30%,2个弯曲半径的偏差值均不超过3%。结论验证了三维自由弯曲成形工艺解析方法的可靠性,有限元模拟较好地指导了实际成形试验。     

异形闭合件弯曲成形模的设计与制造

根据一种异形闭合件的产品要求,对其弯曲工艺作了具体分析,克服了技术难点,设计制造了一套简单实用的弯曲成形模,达到了产品质量要求,也为类似形状制件的弯曲成形模的设计提供了一种新方法.     

碳纤维增强羟基磷灰石/环氧树脂复合材料的制备与力学性能

采用树脂传递模塑(RTM)工艺制备了碳纤维增强环氧树脂以及碳纤维增强羟基磷灰石(HA)/环氧树脂两种复合材料，并测试了其力学性能。结果表明，RTM工艺可以基本保证环氧基体均匀浸入碳纤维织物内部。碳纤维增强HA，环氧复合材料的冲击韧性高于碳纤维增强环氧复合材料，而弯曲强度和弯曲模量低于碳纤维增强环氧复合材料。两种复合材料的弯曲强度远高于人体皮质骨，弯曲模量与皮质骨非常接近。动态力学分析(DMA)表明加入HA后，复合材料的贮存模量和内耗降低，玻璃化转变温度升高。     

影响弯曲件展开料尺寸计算的几个因素

实际工作中,常常会发现有的弯曲件经模具弯曲后的实际尺寸与预先计算的展开料尺寸有较大偏差.针对这一问题,从中性层弯曲半径的计算公式及中性层的位移、几种弯曲工艺方案的比较和不同弯曲模具结构的选择等方面,分析了造成这种偏差、影响弯曲件展开料尺寸计算准确性的几个因素.     

医用接骨板选型的数值模拟研究

随着医疗器械行业的快速发展,对于医用接骨板,国际上相关机构制定了ISO 9585、ASTM382等行业标准来规定接骨板弯曲强度和刚度的测试方法,而测试的主要方法就是四点弯曲实验。所以两个标准中主要阐述的是如何设置实际实验以及实验的方法和要求。而本文的目的,是根据实际的实验情况,以有限元仿真的手段来模拟实验,从而得到不同型号接骨板的力-位移曲线,进而得到计算弯曲强度所需要的屈服载荷,再与已知的跨距算出不同型号接骨板的弯曲强度。通过比较弯曲强度的大小来选出最差的型号。     

Eccentric compression stability of multi-walled carbon nanotubes embedded in an elastic matrix

This paper reports the results of an investigation on the eccentric compression stability of multi-walled carbon nanotubes embedded in an elastic matrix. Based on continuum modeling, a multilayer shell model is presented for the eccentric compression buckling of multi-walled carbon nanotubes embedded in an elastic matrix, in which the effect of van der Waals forces between two adjacent tubes is taken into account. The critical bending moment and the eccentric compression mode for three types of multi-walled carbon nanotubes with different layer numbers and ratios of radius to thickness are calculated. Results obtained show that the eccentric compression buckling mode corresponding the critical bending moment is unique, and is different from the purely axial compression buckling of an individual multi-walled carbon nanotube. For different types of multi-walled carbon nanotubes, the effect of matrix stiffness on the critical bending moment of multi-walled carbon nanotubes under eccentric compression loading is obviously different, and is dependent on the innermost radius and layer numbers of the multi-walled carbon nanotubes. The critical bending stress exerted on the center tubes of nearly solid multi-walled carbon nanotubes does not change as the ratio of the axial compression loading to the bending membrane force increases. The new features and meaningful numerical results in this paper are helpful for the application and the design of nanostructures in which multi-walled carbon nanotubes act as basic elements.     

Bending of simply-supported,antisymmetrically laminated rectangular plate under transverse loading

The deformation of antisymmetric angle-ply laminated plate under transverse loading is analysed using the bending theory of laminated plate presented by Ren.^1,2 By expanding the load in a double Fourier series, a closed-form solution is obtained for special types of simply-supported boundary condition. The results are compared with similar results from the classical laminated plate theory and Mindlin theory. This shows that the theory presented by Ren is suitable not only for cylindrical bending but also for general bending problems.     

广义康托洛维奇法解任意四边形板的弯曲问题

本文从变分原理和双线性坐标变换出发,采用基于三次B样条函数的广义康托洛维奇法得到了带有各种边界条件任意四边形板弯曲的近似解答。样条函数广义康托洛维奇法是一种数值型的康托洛维奇法,因而它既能化二维问题为一维同题,同时又具有样条函数法收敛快、精度高、处理边界条件方便等优点。推导出的计算格式适用于各种边界条件,使梯形板、平行四边形板和矩形板的弯曲问题为本文的特殊情况。本文方法与通常有限元法相比,具有计算量小、精度高等显著特点,且通用性强,是一种很有前途的计算方法。     

Nonlinear oscillations in a thin ring — I. Three-wave resonant interactions

Summary Nonlinear resonant interactions between planar waves in a thin circular ring are investigated. It is found that a high-frequency azimuthal wave is unstable against a pair of secondary low-frequency waves. The secondary waves are of two types; either two bending or azimuthal and bending. These are in phase with the primary wave. All three together compose a resonant triad. Such kind of instability causes the stress amplification in the ring. The stress growth constant and the period of energy exchange between the waves are estimated based on analytical solutions to the evolution equations driving the triad. The lowest-order nonlinear approximation analysis predicts stability for bending waves. A good qualitative agreement of the obtained results with some known experimental data is observed.     

拉弯联合载荷下弹塑性J积分估算方法研究

基于计算J积分的等效原场应力方法,利用等效原场应力σeff只有外加载荷意义而不再具有拉伸或者弯曲等载荷类型方面的属性,提出了利用现有含裂纹结构的纯拉伸以及纯弯曲J积分全塑性解直接计算拉弯联合载荷下的J积分简化估算方法。该方法可以直接利用已经存在的J积分纯拉伸和纯弯曲全塑性解来计算拉弯联合载荷下的J积分,简化了拉弯联合载荷下J积分全塑性解的计算;并且可以应用于任意应力-应变材料,包括Ramborg-Osgood关系的材料和任意单调加载非R-O关系材料。计算过程简便。并通过与有限元计算结果对比对之进行验证,说明其工程实用性,为对含裂纹结构进行弹塑性断裂评定奠定基础。     

Bending stiffness of composite plates with delamination

Cross-ply GFRP circular plates have been impacted repeatedly at increasing input energies. The global bending stiffness of each plate was measured before and after each impact through quasi-static bending tests. The effects of local thickening as well as matrix cracking and delamination on global bending stiffness have been discussed. Approximate analytical solutions for bending of damaged and undamaged plates under uniform ring load have been obtained. Two types of models have been used to separate the effects of changes in material and geometrical properties on global bending stiffness. The trends of bending stiffness changes have been successfully simulated by analytical calculations.     

Edge effects of uniformly loaded cross-ply composite laminates

Interlaminar stresses resulting from bending of rectangular cross-ply composite laminates are determined using a layer wise laminate theory. Two types of laminates are considered. First a fully simply supported laminate subjected to bi-directional bending is analyzed. The results obtained from this theory are compared with those of the published three-dimensional elasticity solutions to verify the validity and accuracy of the present theory. Then laminates with two edges simply supported and the other two edges free are examined. The results indicate the presence of significant interlaminar stresses near the free edges.     

Bending instability and vibration of plates and shallow shells

In the equations of the general theory of shells, the nonlinear terms accounting for membrane strains are accompanied by large coefficients (describing the extensional stiffness of the shell). Although formally infinitesimals of the second order, in the case of small but finite displacements these terms can be commensurate with, or even exceed in magnitude, the first-order terms. Disregarding such nonlinear terms can be debilitating to the linearized theory. For example, it will not reflect the fact that a plate or shell in bending prefers a deflection mode not accompanied by midsurface stretching (so-called isometric bending) and can switch to such a mode more or less abruptly, exhibiting the phenomenon of bending instability

In this study, bending instability and vibration of plates and shallow shells are investigated by simple analytical and numerical means, having in mind certain types of layered, sandwich, and truss-like structures.     

Bending properties of epoxy resin matrix composites filled with Ni-Mn-Ga ferromagnetic shape memory alloy powders

Two types of epoxy resin matrix composites filled with Ni-Mn-Ga ferromagnetic shape memory alloy powders, with and without magnetic field during curing, were prepared, aiming to create anisotropic and isotropic alignments of the Ni-Mn-Ga particles. The bending properties of the composites are found to be significantly influenced by the distribution of Ni-Mn-Ga particles in the epoxy matrix. The composites without magnetic field during curing exhibit larger bending strength and fracture strain than the composites with magnetic field during curing. The fractography reveals that the Ni-Mn-Ga particle chains formed in the composites with magnetic field during curing facilitate the initiation and propagation of cracks, thus weakening the bending properties.