Local Buckling-Induced Forming Method to Produce Metal Bellows

A novel buckling-induced forming method is proposed to produce metal bellows.The tube billet is firstly treated by local heating and cooling,and the axial loading is applied on both ends of the tube,then the buckling occurs at the designated position and forms a convolution.In this paper,a forming apparatus is designed and developed to produce both discontinuous and continuous bellows of 304 stainless steel,and their characteristics are discussed respectively.Furthermore,the influences of process parameters and geometric parameters on the final convolution profile are deeply studied based on FEM analysis.The results suggest that the steel bellows fabricated by the presented buckling-induced forming method have a uniform shape and no obvious reduction of wall thickness.Meanwhile,the forming force required in the process is quite small.

Subsea Compensation of Pressure Based on Reducer Bellows

In this study,the pressure compensation mechanism of a reducer bellows is analyzed.This device is typically used to reduce the size of undersea instruments and improve related pressure resistance and sealing capabilities.Here,its axial stiffness is studied through a multi-fold approach based on theory,simulations and experiments.The results indicate that the mechanical strength of the reducer bellows,together with the oil volume and temperature are the main factors influencing its performances.In particular,the wall thickness,wave number,middle distance,and wave height are the most influential parameters.For a certain type of reducer bellows,the compensation capacity attains a maximum when the wave number ratio is between 6:6 and 8:4,the wall thickness is 0.3 mm,and the wave height is between 4–5 mm and 5–6 mm.Moreover,the maximum allowable ambient pres-sure of the optimized reducer bellows can reach 62.6 MPa without failure,and the maximum working water depth is 6284 m.

GENERAL SOLUTION FOR U-SHAPED BELLOWS OVERALL-BENDING PROBLEMS

The formulae for stresses and angular displacements of U-shaped bellows overall bending in a meridian plane under pure bending moments are presented based on the general solution for slender ring shells proposed by Zhu Weiping, et al. and the solution for ring plates. The results evaluated in this paper are compared with those on EJMA (standards of the expansion joint manufacturers association) and of the experiment given by Li Tingxilz, et al.

Application of Non-homogeneous Solution for Equations of Slender Ring Shells to Overall-Bending Problem of Ω-Shaped Bellows

A linear complex equation for slender ring shells overall bending in a meridian plane is given based on E. L. Axelrad's theory of flexible shells. And the non homogeneous solution is obtained from W. Z. Chien's solution for axial symmetrical slender ring shells to investigate the overall bending problem of Ω shaped bellows subjected to pure bending moments. The values calculated in the present paper are very close to the existing experiment. Thus Chien's work on axial symmetrical problems for ring shells has been extended to overall bending problems.

The Dynamical FSI Simulation for Bellows Inflating to Disperse Bomblets

According to the characteristics of fluid-structure interaction( FSI) in the process of metal bellows inflating to disperse bomblets,a 3D dynamical FSI model( W model) which describes the interaction between a viscous compressible flow and a structure undergoing large deformationis established. Then the dynamic characteristics of the metal bellows deformation,the changing law of the internal flow field and the motion law of the bombs are acquired.Where the internal pressure and bombs' moving law are approximate to interior ballistic results,which indicates the W model established reasonably. Besides,considering gaps existing atthe bellows' tow ends,the dynamical FSI modelcontaining gaps( Y model) is also built. The results of the W and Y models are compared and the results show that the existence of the gaps has little influence to the flow field and the stress distributionin the bellows,but obviously reduces the separation speed of the bomblets about 10%.

PROBLEMS OF U-SHAPED BELLOWS WITH NONLINEAR DEFORM TION OF LARGE AXISYMMETRICAL DEFLECTION(Ⅰ)--COUNTING NONLINEAR DEFORMATIONS OF RING SHELLS AND COMPRESSED ANGLE OF BELLOWS

This paper follows the work of[1,2].There are some progress in dealing with moderately small rotations(the squares of rotation angles are the order of magnitude of strains)of middle surface normals of inside and outside ring shells and compressed angle of bellows.Calculation results agree with experiments well.To bellow design,the method given in this paper is of practical value and the discussion of the influence of compressed angle on characteristic relation is helpful.

ON PROBLEMS OF U-SHAPED BELLOWS WITH NONLINEAR DEFORMATION OF LARGE AXISYMMETRICAL DEFLECTION(Ⅱ)——COUNTING VARIATION OF THICKNESS DISTRIBUTION

On the basis of paper[1],assuming the logarithm of thickness at arbitrary point on a U-shaped bellows meridian is linear with the logarithm of distance between that point and axis of symmetry,perturbation solutions of the corresponding problems of large axisymmetrical deflection are given.The effects of thickness distribution variation,which result from technology factors,on stiffness of bellows are discussed.

GENERAL SOLUTION OF THE OVERALL BENDING OF FLEXIBLE CIRCULAR RING SHELLS WITH MODERATELY SLENDER RATIO AND APPLICATIONS TO THE BELLOWS (Ⅱ)- CALCULATION FOR OMEGA-SHAPED BELLOWS

is one of the applications of (Ⅰ), in which the angular stiffness, the lateral stiffness and the corresponding stress distributions of Omega_shaped bellows were calculated, and the present results were compared with those of the other theories and experiments. It is shown that the non_homogeneous solution of (Ⅰ) can solve the pure bending problem of the bellows by itself, and be more effective than by the theory of slender ring shells; but if a lateral slide of the bellows support exists the non_homogeneous solution will no longer entirely satisfy the boundary conditions of the problem, in this case the homogeneous solution of (Ⅰ) should be included, that is to say, the full solution of (Ⅰ) can meet all the requirements.

GENERAL SOLUTION OF THE OVERALL BENDING OF FLEXIBLE CIRCULAR RING SHELLS WITH MODERATELY SLENDER RATIO AND APPLICATIONS TO THE BELLOWS (Ⅲ)-CALCULATION FOR C-SHAPED BELLOWS

This is one of the applications of Part (Ⅰ), in which the angular stiffness, the lateral stiffness and the corresponding stress distributions of C_shaped bellows were calculated. The bellows was divided into protruding sections and concave sections for the use of the general solution (Ⅰ), but the continuity of the stress resultants and the deformations at each joint of the sections were entirely satisfied. The present results were compared with those of the other theories and experiments, and are also tested by the numerically integral method. It is shown that the governing equation and the general solution (Ⅰ) are very effective.

GENERAL SOLUTION OF THE OVERALL BENDING OF FLEXIBLE CIRCULAR RING SHELLS WITH MODERATELY SLENDER RATIO AND APPLICATIONS TO THE BELLOWS (Ⅳ)-CALCULATION FOR U-SHAPED BELLOWS

This is one of the applications of Part (Ⅰ),in which the angular stiffness, and the corresponding stress distributions of U_shaped bellows were discussed. The bellows was divided into protruding sections, concave sections and ring plates for the calculation that the general solution (Ⅰ) with its reduced form to ring plates were used respectively, but the continuity of the surface stresses and the meridian rotations at each joint of the sections were entirely satisfied. The present results were compared with those of the slender ring shell solution proposed earlier by the authors, the standards of the Expansion Joint Manufacturers Association (EJMA), the experiment and the finite element method. It is shown that the governing equation and the general solution (Ⅰ) are very effective.

FINITE ELEMENT DISPLACEMENT PERTURBATION METHOD FOR GEOMETRIC NONLINEAR BEHAVIORS OF SHELLS OF REVOLUTION OVERALL BENDING IN A MERIDIONAL PLANE AND APPLICATION TO BELLOWS (Ⅰ)

In order to analyze bellows effectively and practically, the finite_element_displacement_perturbation method (FEDPM) is proposed for the geometric nonlinear behaviors of shells of revolution subjected to pure bending moments or lateral forces in one of their meridional planes. The formulations are mainly based upon the idea of perturba_ tion that the nodal displacement vector and the nodal force vector of each finite element are expanded by taking root_mean_square value of circumferential strains of the shells as a perturbation parameter. The load steps and the iteration times are not as arbitrary and unpredictable as in usual nonlinear analysis. Instead, there are certain relations between the load steps and the displacement increments, and no need of iteration for each load step. Besides, in the formulations, the shell is idealized into a series of conical frusta for the convenience of practice, Sander's nonlinear geometric equations of moderate small rotation are used, and the shell made of more than one material ply is also considered.

GENERAL SOLUTION OF THE OVERALL BENDING OF FLEXIBLE CIRCULAR RING SHELLS WITH MODERATELY SLENDER RATIO AND APPLICATIONS TO THE BELLOWS (Ⅰ)-GOVERNING EQUATION AND GENERAL SOLUTION

The overall bending of circular ring shells subjected to bending moments and lateral forces is discussed. The derivation of the equations was based upon the theory of flexible shells generalized by E.L. Axelrad and the assumption of the moderately slender ratio less than 1/3 (i.e., ratio between curvature radius of the meridian and distance from the meridional curvature center to the axis of revolution). The present general solution is an analytical one convergent in the whole domain of the shell and with the necessary integral constants for the boundary value problems. It can be used to calculate the stresses and displacements of the related bellows. The whole work is arranged into four parts: (Ⅰ) Governing equation and general solution; (Ⅱ) Calculation for Omega_shaped bellows; (Ⅲ) Calculation for C_shaped bellows; (Ⅳ) Calculation for U_shaped bellows. This paper is the first part.

Superplastic forming gas pressure of titanium alloy bellows

The complex superplastic forming (SPF) technology applying gas pressure and compressive axial load is an advanced forming method for titanium alloy bellows,whose forming process consists of the three main forming phases namely bulging, clamping and calibrating phase. The influence of forming gas pressure in various phases on the forming process was analyzed and the models of forming gas pressure for bellows were derived according to the thin shell theory and the plasticity deformation theory. Using the model values, taking a two-convolution DN250 Ti-6Al-4V titanium alloy bellows as an example, a series of superplastic forming tests were performed to evaluate the influence of the variation of forming gas pressure on the forming process. According to the experimental results these models were corrected to make the forming gas pressures prediction more accurate.

Research and Development of ITER Bellows Assemblies

In ITER facilities, there are some special expansion joints connected with the openings of cryostat. Expect for the assemblies connected with NB openings, others are rectangular section with big dimensions and severe working conditions and they are important for ITER safe runing.

基于ANSYS的波纹管波形参数对柱失稳影响分析

为了研究波纹管波形参数对波纹管柱失稳的影响,使用ANSYS Workbench对波纹管进行了模态分析与特征值屈曲分析。采用控制变量的方法,改变波纹管波形参数,分别进行有限元分析;并对相同波数下的复式波纹管进行有限元分析,且与单式波纹管稳定性做分析比较。有限元结果表明:在实际工作中,可通过增加波纹管壁厚、波距,或减小波高、减少波数的方法,减少波纹管柱失稳的发生;当波纹管长度较长、波数较多时,使用复式波纹管是更优的选择。

轴向拉压式U型厚壁金属波纹管阻尼器抗震性能研究

针对传统金属阻尼器承载力不足、极限变形较小等问题,提出一种新型轴向拉压式U型厚壁金属波纹管阻尼器。通过改变波纹管的壁厚、内径及波数等参数来调整阻尼器的承载力、初始刚度、极限变形及延性;采用有限元分析手段,对阻尼器的核心耗能元件进行单调及低周往复加载条件下的力学性能分析。研究核心耗能元件的内径、壁厚、波纹平均半径、U型波纹直边长度、材料屈服强度及波数这6个独立变量对其力学性能的影响关系,提出阻尼器极限位移的计算方法,给出阻尼器受拉屈服后刚度与屈服前刚度之比的拟合公式,揭示出新型阻尼器的受力机理,建立阻尼器的恢复力模型。同时,针对U型波纹管建立考虑边波效应的修正简化计算方法,并与规范法进行比较。研究结果表明:修正后的简化分析方法与规范法相比具有更高的精度;阻尼器滞回曲线饱满、耗能能力强、变形大、延性高;金属波纹管的刚度、屈服荷载、屈服后刚度及极限荷载均随壁厚的增加而显著增大;随着波数的增加,核心耗能元件的极限变形、延性及累积耗能显著提高,但受拉屈服后刚度降低;建议阻尼器设计时波纹平均径厚比不大于3.8,最大设计工作位移不大于极限位移的0.8倍。

波纹管最大压缩位移及疲劳寿命分析

为解决某GIS母线中波纹管的最大压缩位移和疲劳寿命究竟能否同时满足工程指标的难题,应用工程计算和有限元分析分别加以计算,然后通过两种计算结果和实验验证进行比较,以期获得哪种方法更精确可靠。为达此目的,文中给出了工程计算和有限元建模的详细过程。按工程计算方法得到的最大压缩位移结果无法满足工程指标,而有限元分析计算方法,却可以达到工程指标,且有较大的安全裕度。有限元分析还揭示了满足大压缩位移的机理,计算结果符合某GIS工程同时需要的压缩位移和疲劳寿命。经型式试验也验证了模拟的正确性。充分证明了有限元分析方法是比按工程计算方法更为先进和准确的设计手段。

弯曲状态电沉积波纹管疲劳寿命影响因素分析

为了研究弯曲状态下电沉积波纹管疲劳寿命的影响因素,文中使用弯曲测试工装,开展了相应的旋转弯曲疲劳实验,对实验结果进行了分析。结果表明:在弯曲疲劳实验中,电沉积波纹管断裂位置出现在波谷处,且均为韧性断裂;随着电沉积波纹管壁厚减小、波高增加,疲劳寿命提高;与弯曲极限角度相比,电沉积波纹管在正常工况角度时,疲劳寿命增大6.8倍。实验表明:壁厚为0.03 mm、波高为2.3 mm、工作弯曲角度为110°的多层电沉积波纹管的疲劳性能最优。

电阻缝焊在多层波纹管膨胀节制造中的非典型应用

因薄壁多层的波纹管刚度小,补偿量大,寿命长而得到广泛应用。但薄壁多层的波纹管与其连接件的环缝焊接难度较大。为了方便多层波纹管的环缝焊接,多采用电阻缝焊将波纹管的直边段封焊在一起。电阻焊缝普遍存在2种状态,即熔合状态和塑性粘合状态。在生产实践中和通过试验研究发现,塑性粘合状态的电阻焊缝大量存在,但并没有显著影响环缝的焊接,采用分散热输入的多层焊是可以克服的。此种电阻缝焊的目的和要求与通常意义上的2层电阻缝焊不同,不要求有承压强度和密封性,只要将多层波纹管端部塑性粘合成整体,当波纹管与连接件焊接时,使下层起到对上层的衬垫作用,不致烧穿即可。此处电阻焊缝是工艺过程焊缝,不是终极焊缝,是在波纹管膨胀节制造过程中的非典型应用。生产实践中不分层的塑性粘合状态的电阻焊缝也可以满足环缝焊接。

弹簧刚度对敏感波纹密封件特性影响的分析

对某些特殊性能的波纹管,可以采取在波纹管内腔或外部配置圆柱螺旋弹簧的方式。本文通过对弹簧数据、p-w曲线特性数据的分析,包括均布力刚度、压力灵敏度、重复性误差、迟滞误差、最大量程等数据,同时通过Ansys软件对密封组件进行受力分析,探究弹簧对测量类敏感类波纹管组件的影响。结果表明,加入弹簧后,波纹管组件特性有改善,均布力刚度下降,压力灵敏度升高,重复性误差、迟滞误差、最大量程等减小,并且通过选择合适刚度的弹簧,可以使组件性能达到最佳。