Numerical analysis of static performance comparison of friction stir welded versus riveted 2024-T3 aluminum alloy stiffened panels

Most researches on the static performance of stiffened panel joined by friction stir welding（FSW） mainly focus on the compression stability rather than shear stability. To evaluate the potential of FSW as a replacement for traditional rivet fastening for stiffened panel assembly in aviation application, finite element method（FEM） is applied to compare compression and shear stability performances of FSW stiffened panels with stability performances of riveted stiffened panels. FEMs of 2024-T3 aluminum alloy FSW and riveted stiffened panels are developed and nonlinear static analysis method is applied to obtain buckling pattern, buckling load and load carrying capability of each panel model. The accuracy of each FEM of FSW stiffened panel is evaluated by stability experiment of FSW stiffened panel specimens with identical geometry and boundary condition and the accuracy of each FEM of riveted stiffened panel is evaluated by semi-empirical calculation formulas. It is found that FEMs without considering weld-induced initial imperfections notably overestimate the static strengths of FSW stiffened panels. FEM results show that, buckling patterns of both FSW and riveted compression stiffened panels represent local buckling of plate between stiffeners. The initial buckling waves of FSW stiffened panel emerge uniformly in each plate between stiffeners while those of riveted panel mainly emerge in the mid-plate. Buckling patterns of both FSW and riveted shear stiffened panels represent local buckling of plate close to the loading corner. FEM results indicate that, shear buckling of FSW stiffened panel is less sensitive to the initial imperfections than compression buckling. Load carrying capability of FSW stiffened panel is less sensitive to the initial imperfections than initial buckling. It can be concluded that buckling loads of FSW panels are a bit lower than those of riveted panels whereas carrying capabilities of FSW panels are almost equivalent to those of riveted panels with identical geometries. Finite elem     

基于等效理论的多夹心层蜂窝板模态分析

研究蜂窝板的三明治等效理论,应用该等效理论对蜂窝板夹芯进行等效计算得其等效参数,建立多夹心层蜂窝板的有限元模型,完成不同算例在不同边界条件下的模态分析,解决了通用有限元程序如NASTRAN等不能直接计算蜂窝板的动、静力学性能问题.将计算结果与解析解对比,说明等效方法是合理的,适用于多夹心层蜂窝板结构的有限元分析.     

金属软管的网套及端部过渡波的有限元研究

对金属软管的网套进行非线性有限元分析，由于网套在受力时可以在波纹管上面既滚动又滑动，因此采用空间梁单元Beam189来表征网套的受力特性。将过渡波引入金属软管的有限元模型，对模型的端部进行修正，在此模型上，进行网套的静态特性分析，分析结果与试验结果符合较好，说明了有限元建模的有效性。     

Buckling analysis of laminated composite rectangular plates reinforced by SWCNTs using analytical and finite element methods

In this paper, the buckling analysis of laminated composite plates reinforced by single-walled carbon nanotubes (SWCNTs) is carried out using an analytical approach as well as the finite element method. The developed model is based on the classical laminated plate theory (CLPT) and the third-order shear deformation theory for moderately thick laminated plates. The critical buckling loads for the symmetrical layup are determined for different support edges. The Mori-Tanaka method is employed to calculate the effective elastic modulus of composites having aligned oriented straight nanotubes. The effect of the agglomeration of the randomly oriented straight nanotubes on the critical buckling load is also analyzed. The results of analytical solution are compared and verified with the FEM calculations The critical buckling loads obtained by the finite element and the analytical methods for different layup and boundary conditions are in good agreement with each other. In this article, the effects of the carbon nanotubes (CNTs) orientation angle, the edge conditions, and the aspect ratio on the critical buckling load are also demonstrated using both the analytical and finite element methods.     

复合材料蜂窝夹层板低速冲击损伤模拟及实验研究

复合材料蜂窝夹层板因其良好的力学特性及质量轻等优点在工程中得到了广泛应用,但其抗冲击能力较差。本文研究了复合材料蜂窝夹层板受低速冲击后的变形和损伤情况,采用光滑粒子动力学结合有限元数值模拟方法分析了复合材料蜂窝夹层板受不同能量冲击后的响应,并通过试验和模拟计算结果对比分析,给出了不同冲击能量下复合材料蜂窝夹层板的位移和损伤。研究结果表明:给出的复合材料蜂窝夹层板冲击数值模型能够合理的模拟低速冲击行为,能为工程中复合材料蜂窝夹层板结构受冲击损伤的测定提供参考依据。     

铝合金搅拌摩擦焊接加筋板剪切稳定性能研究

对2024-T3铝合金搅拌摩擦焊接加筋壁板的剪切稳定性能进行试验研究,得到该结构的剪切失稳形式及屈曲载荷、承载能力及破坏形式。应用有限元法对该焊接加筋壁板结构进行简化建模,对该结构的稳定性和承载能力进行计算,将计算结果与试验结果进行比较。试验及有限元计算结果表明,结构的剪切失稳形式表现为筋条间平板的局部屈曲;屈曲后结构进入张力场受力状态,破坏形式主要表现为平板的塑性变形和边缘撕裂、筋条的弯扭变形以及焊接区的局部脱焊;出现脱焊现象的试验件其承载能力较未出现脱焊现象的试验件下降7.7%;线性和非线性屈曲计算所得屈曲载荷分别比试验平均值高出18.4%和26.2%,而非线性计算所得承载能力比试验平均值高出5.7%,焊接引起的初始缺陷对结构承载能力的影响小于对屈曲载荷的影响;有限元分析得到的结构屈曲形式和失效形式与试验现象吻合,验证了有限元模型的合理性,但其仍需要进一步改进以考虑初始缺陷来减小计算误差。     

盲孔法测量焊接残余应力应变释放系数的有限元分析

为探讨简单易行的盲孔法测量焊接残余应力应变释放系数A、B的标定方法，根据盲孔法测量残余应力时应变释放系数A、B试验标定原理和强度理论，建立三维有限元模型，分别对盲孔法测量92lA钢焊接残余应力应变释放系数进行有限元标定和孔边应力集中有限元塑性修正．并由此得出应变释放系数随孔深与孔径比值的关系式和应变释放系数随形状改变比能参量S变化的塑性修正公式；将有限元标定结果与试验标定结果、通孔应变释放系数理论解进行比较，结果表明，有限元标定结果与试验结果、通孔应变释放系数理论值有较好的一致性，经塑性修正，计算结果与试验测量结果的偏差大大减小，建立适当有限元模型，用有限元法标定释放系数和进行孔边塑性变形修正是可行的。     

基于蜂窝加肋板结构参数匹配抑制光学卫星随机响应

以结构参数的最优匹配为设计目标,提出了一种改善光学卫星振动环境的新思路。针对某光学卫星振动试验中出现的蜂窝顶板随机振动响应过大的问题,研究了加强肋在降低简支蜂窝板随机振动响应中的作用。分析了该光学卫星蜂窝板结构的特点,探讨了它的随机载荷以及在其激励下蜂窝板式结构的动力学响应。结合卫星自身结构上的需要,提出了一种通过添加特定截面H型加强肋的方法来降低蜂窝板的响应。利用有限元法对外形尺寸为1 000mm×1 000mm×30mm的蜂窝板模型进行随机振动分析验证,结果显示:H型加强肋能显著降低蜂窝板的振动响应,有明显减振效果。最后,根据整星振动试验结果对卫星力学模型进行了修正,并利用该方法对修正后的模型进行动力学分析和优化,分析结果表明顶板响应降幅达到了40%,为系统可接受范围,证明了提出的方法很好地抑制了结构的随机振动响应。     

Manufacturing Error Effects on Mechanical Properties and Dynamic Characteristics of Rotor Parts under High Acceleration

Stress, strain and vibration characteristics of rotor parts should be changed significantly under high acceleration, manufacturing error is one of the most important reason. However, current research on this problem has not been carried out. A rotor with an acceleration of 150,000 g is considered as the objective, the effects of manufacturing errors on rotor mechanical properties and dynamic characteristics are executed by the selection of the key affecting factors. Through the force balance equation of the rotor infinitesimal unit establishment, a theoretical model of stress calculation based on slice method is proposed and established, a formula for the rotor stress at any point derives. A finite element model (FEM) of rotor with holes is established with manufacturing errors. The changes of the stresses and strains of a rotor in parallelism and symmetry errors are analyzed, which verify the validity of the theoretical model. The pre-stressing modal analysis is performed based on the aforementioned static analysis. The key dynamic characteristics are analyzed. The results demonstrated that, as the parallelism and symmetry errors increase, the equivalent stresses and strains of the rotor slowly increase linearly, the highest growth rate does not exceed 4%, the maximum change rate of natural frequency is 0.1%. The rotor vibration mode is not significantly affected. The FEM construction method of the rotor with manufacturing errors can be utilized for the quantitative research on rotor characteristics, which will assist in the active control of rotor component reliability under high acceleration.     

Prediction enhancement of the J-lead interconnection reliability of land grid array sockets

The solder joint is a key component in land grid array (LGA) sockets. A simplified solder joint has been widely used in finite element model (FEM) computations because the J-lead interconnection solder joint is relatively complex. Therefore, there are discrepancies between the physical phenomenon and FEM simulations. In this study, an alternative method to simulate the J-lead interconnection solder joint through an interface program using surface evolver software is presented. Simulations of the J-lead interconnection solder joint were improved to reduce the mismatch between the actual physical shape and the simplified finite element models that are typically used to predict component reliability. To perform these simulations, an interface program capable of simulating solder interconnections for twelve different pad–solder combinations was developed. Predictions of J-lead interconnection solder joints were carried out using the interface program. Geometric comparisons between experimental data and predictions showed good agreement, with the exception of wetting height. To evaluate the prediction accuracy of the simulated J-lead solder joints, FEM analysis was performed for the static load and the thermal cycle.

     

负泊松比蜂窝芯非线性等效弹性模量研究

设计并加工了一种负泊松比蜂窝结构,采用柔性悬臂梁模型,对蜂窝壁板大变形条件下的弯曲变形进行分析,给出了蜂窝芯面内等效弹性模量理论计算公式。通过有限元仿真和力学实验的对比分析,验证了非线性理论计算公式的正确性。得出了等效弹性模量的非线性特性及相同方向和不同方向弹性模量的变化特性。研究结果为柔性蜂窝芯层的工程实用化提供了参考。     

蜂窝材料超声波切割声学系统研究

根据超声波加工原理,设计了一种新型Nomex蜂窝材料数控超声波切割主轴。采用四端网格法对变幅杆进行了有限元分析和位移节点修正。建立了超声波切割声学系统有限元模型,并进行了模态分析。从振型图可以看出变幅杆法兰盘处位移变化较小,输出端振幅较大。利用激光位移传感器测量了刀具的振动位移,圆形刀振幅a=22.37μm,满足加工要求。利用超声波切割主轴对Nomex蜂窝材料进行了大量切割实验,取得了加工表面平整光滑、加工精度高、切削过程中没有粉尘污染等显著效果。     

Theoretical and Finite Element Analysis of Static Friction Between Multi-Scale Rough Surfaces

The current work considers the multi-scale nature of roughness in a new model that predicts the static friction coefficient. This work is based upon a previous rough surface contact model, which used stacked elastic–plastic 3-D sinusoids to model the asperities at multiple scales of roughness. A deterministic model of a three-dimensional deformable rough surface pressed against a rigid flat surface is also carried out using the finite element method (FEM). The accuracy of the deterministic FEM model is also considered. At the beginning of contact, which is surface-point contact, the asperities or peaks are isolated, sharp, and the contact areas consist of an inadequate number of elements and sources of error. In this range of contact, the results are not presented as real or accurate. As the normal load increases, the number of the contact elements become larger, and thus, the results become more accurate. That is, the deterministic FEM results are most accurate at high loads. Spectral interpolation is used to smooth the geometry in between the original measured nodes. The effects of normal load and plasticity index on static friction are then analyzed. The results predicted by the theoretical model are also compared to other existing rough surface friction contact models and the FEM results. They are in a good qualitative agreement, especially for higher loads and higher plasticity indices. The FEM model also has significant error, but it is more accurate at higher loads where the proposed multi-scale static friction model and FEM model are in better agreement.     

Free vibration and buckling response of hat-stiffened composite panels under general loading

The paper presents finite element free vibration and buckling analysis of laminated hat-stiffened shallow and deep shells using arbitrarily oriented stiffener formulation. Modified approach for modelling the curved stiffener is implemented using necessary transformations. A simplified stiffener formulation is presented to accommodate various shapes of stiffener shapes in developing the rigidity matrix for the finite element formulation. Investigation has been carried out on free vibration and buckling analyses of laminated composite stiffened shell structures with laminated open section (rectangular or ‘T’ shaped) and closed section (‘hat’ shaped) stiffeners. Parametric study on the hat-stiffened panels for the free vibration and buckling analyses confirms that the closed section stiffener being torsionally rigid is found to show better performance over open section stiffeners.     

The analytical solution of the buckling of composite truncated conical shells under combined external pressure and axial compression?

The objective of this research is determining the buckling load of composite truncated conical shells under external loading by theoretical and numerical methods. The boundary conditions are assumed to be clamped. At first, basic equations and stability relations of conical shells were derived. The analysis is carried out using Donnel-type stability equations for thin cross-ply conical shells. By applying Galerkin??s method, these equations are converted to a system of ordinary time dependent differential equations. Ritz method is employed for finding the dynamic stability load. Finally, the critical static and dynamic buckling loads and the corresponding wave numbers have been found analytically. Then comparison of results is considered. Results of analytical calculations are compared with numerical results and with other researchers?? analytical results. The effects of geometric parameters, the cone semi-vertex angle, number of layers and material of fibers on buckling loads are discussed.     

Buckling analysis of filament-wound thick composite cylinder under hydrostatic pressure

Underwater vehicles that operate in deep waters require a pressure hull to maintain the sufficient strength and stiffness against external hydrostatic pressure. We investigated the validity of the finite element method (FEM) that is applied to a buckling analysis of the filament-wound composite cylinder, subjected to an external hydrostatic pressure. Two methods were suggested for the buckling analysis of a filament-wound thick composite cylinder under hydrostatic pressure: using the equivalent properties of the composite, and using stacking sequence. The hydrostatic pressure test was conducted to verify the FEA. Test results were compared with the previous results obtained by FEM on the buckling of a filament-wound composite cylinder under hydrostatic pressure. FEM analysis results were in good agreement with the test results. The difference between FEM results and the test results was approximately 1∼5%.     

直角切口柔性铰链串联支链的屈曲分析

利用材料力学弯曲变形理论的挠曲线近似微分方程,建立计算直角切口柔性铰链串联支链屈曲临界力的数学模型,在建模过程中定义平均屈曲临界挠度系数并给出其确定方法.采用商用有限元软件ANSYS8.0对大量不同参数的串联支链模型进行有限元屈曲分析,分析结果与根据数学模型计算得到的屈曲临界力十分接近,说明了所建数学模型的正确性.研制测试柔性铰链串联支链屈曲临界力的专用试验装置,针对加载载荷尺寸对柔性支链屈曲的影响,提出载荷等效长度的概念.试验结果表明:屈曲临界力的试验值与理论计算值相吻合,从而验证所建数学模型具有较高的参考价值,可以作为柔性铰链串联支链屈曲优化设计的指导理论.     

高精度反射器面板柔性复合成形数值模拟

建立了双曲率蜂窝夹层板在“点阵钉模、真空负压”条件下成形的有限元分析模型。对双曲率蜂窝夹层板的柔性复合成形过程进行了数值模拟，研究了板料在成形过程中薄膜力及型面误差分布。通过分析得到了反射面型面精度的影响因素，优化了反射面结构形式。实验得到的反射面天线具有很高的型面精度和结构稳定性，实际型面精度和数值模拟结果十分接近，表明该模型能够有效地分析蜂窝夹层板的成形问题。     

大型轴流压缩机焊接机壳的静态有限元分析

在建立大型轴流压缩机焊接机壳有限元模型的基础上,对联接螺栓台阶面与上机壳法兰面和上下机壳法兰面之间的接触问题,以及螺栓的预紧问题进行了处理,应用有限元分析软件对模型进行了分析计算.结果表明,所设计焊接机壳静态下的应力和变形均在允许范围内.可进一步对焊接机壳进行动态特性分析,以便为改进设计提供更可靠的理论依据.     

蜂窝夹芯胞元壳的屈曲特性研究

以正六边形蜂窝夹芯的胞元壳为例,将Euler细长杆的稳定理论与板壳力学中的稳定理论相结合,提出了薄壁胞元壳轴向受压临界载荷的计算公式和屈曲模态的三重级数表达式。根据胞元壳不同的失效形式,将其分成了短胞元壳、长胞元壳和特长胞元壳,确定了不同类型胞元壳的临界载荷控制方程和其对应的一阶屈曲模态,在此基础上提出了胞元壳临界载荷总图。用3D有限元数值模拟技术,通过对铝质正六边形蜂窝胞元壳进行模拟,将其结果与公式的计算结果相比,两者非常接近,证实了理论分析的有效性。其结论对蜂窝夹层结构和薄壁棱柱壳的理论研究有重要的指导意义。