球形封头开孔接管结构屈曲特性研究

针对外压作用下球形封头开孔接管结构,采用有限元非线性屈曲分析方法,探讨不同结构参数对其临界失稳压力Pcr的影响。研究结果表明,当球壳主体参数径厚比一定时,临界失稳压力削弱系数K随开孔率增大而下降,随接管与封头厚度比增大而增大。接管与封头厚度比较小时,计算模型失稳位置位于接管;接管与封头厚度比增至一定值时,计算模型失稳位置转移到封头。随着开孔率增大,失稳位置由接管与封头转到封头所需的接管与封头厚度比越大。针对本文计算参数,提出了临界接管与封头厚度比。实际工程设计中,当接管与封头厚度比取临界值时,可以在满足结构轻量化设计基础上,获得较优的结构承载能力。最后,建立了不同结构参数与临界失稳压力削弱系数K的分段经验关系式,且所得关系式具有较高预测精度。研究结果可为外压球形封头开孔接管结构稳定性研究及工程设计提供借鉴。     

内压标准椭圆封头弹塑性屈曲分析及失效载荷研究

采用有限元弹塑性屈曲分析,考虑椭圆封头的最大形状偏差并在过渡区施加局部厚度减薄缺陷,针对不同材料和厚径比δ_e/D_i,较为系统地讨论了内压标准椭圆封头结构屈曲载荷P_(cr)与极限载荷P_L的变化规律。研究结果表明,厚径比小于某临界值时,屈曲载荷低于极限载荷,分析模型发生屈曲破坏;厚径比大于某临界值时,屈曲载荷高于极限载荷,分析模型发生强度破坏。不同材料分析模型厚径比临界值存在一定差异,对高强钢13MnNiMoR材料而言,GB 150—2011标准防止标准椭圆封头内压弹性屈曲失效的厚径比规定偏于冒进。本文结果可为内压薄壁标准椭圆封头设计准则提供指导。     

正置正交加筋薄壁柱壳优化设计参数化有限元方法研究

利用有限元软件建立轴压正置正交加筋薄壁圆柱壳的参数化有限元分析模型,研究结构参数对薄壁加筋圆柱壳结构的临界载荷和屈曲模式的影响。随着蒙皮厚度的增加,结构的屈曲模式由局部屈曲逐步变化到总体屈曲,屈曲载荷上升;随着加筋厚度或宽度的增加,由总体屈曲变化到局部屈曲,屈曲载荷上升。通过等体积时的参数变化对屈曲载荷和屈曲模式的影响研究,表明在对应某体积的设计中,只有一种设计使结构屈曲载荷达到最大,而当此最大的屈曲载荷等于设计载荷时,是最轻重量的设计。在此基础上发展一种基于APDL(Ansys parametric design language)语言的薄壁加筋圆柱壳结构优化设计方法,利用该方法给出设计算例的优化结果。     

弹性圆柱壳的稳定性优化设计

研究任意轴对称边界条件下和受均布法向载荷作用圆柱壳的稳定性优化设计问题，即极大化屈曲临界载荷。利用能量原理分析轴对称变厚度圆柱壳的分支点屈曲，将求解屈曲临界载荷变成求解广义特征值方程，使圆柱壳稳定性优化设计成为极大化最小特征值问题。实际算例验证了本方法的有效性。研究结果可用于圆柱壳的加肋优化设计。     

碟形封头压力容器在内压作用下的弹塑性屈曲及后屈曲行为研究

基于ABAQUS对受内压碟形封头压力容器的弹塑性屈曲及后屈曲行为进行分析.通过非对称网格剖分技术诱发结构的屈曲行为,采用Riks算法捕捉完整的屈曲及后屈曲路径,分析屈曲载荷和后屈曲形态.计算结果表明,在内压作用下碟形封头压力容器过渡区域出现波状的分叉屈曲形态,随着加载的继续,过渡段将逐渐生成肉眼可视的褶皱,进入后屈曲阶段.后屈曲路径可以分为第一阶段与第二阶段.对引入初始厚度缺陷的结果分析可知,初始缺陷厚度的布置将对后屈曲路径产生影响,并降低结构的分叉屈曲载荷.     

凸面受压碟形封头的屈曲分析

利用有限元法和水压试验相结合的方法对凸面受压碟形封头的屈曲行为进行研究。基于ANSYS软件对凸面受压碟形封头进行了非线性有限元分析,采用特征值屈曲分析和非线性屈曲分析相结合的方法,并利用弧长法,计算出结构的临界屈曲载荷值,同时结合水压试验验证。研究结果表明,碟形封头发生了屈曲失效,发生屈曲的位置在靠近筒体纵焊缝的碟形封头上,并且水压试验的结果验证了有限元分析的可行性。屈曲分析的结果对碟形封头的优化设计具有指导意义。     

屏蔽电机主泵定子屏蔽套屈曲稳定性分析

屏蔽电机主泵定子屏蔽套的结构稳定性关系到其运行的安全性,基于薄壁圆筒外压屈曲稳定性理论对定子屏蔽套的失稳临界载荷进行了分析,采用Algor有限元软件分别计算了定子屏蔽套屈曲临界载荷和极限载荷,得到了定子屏蔽套屈曲临界载荷和极限载荷随其厚度、半径、长度以及初始缺陷变化的规律,结果表明,定子屏蔽套厚度是对结构稳定性影响最大的因素。     

波纹蒙皮结构屈曲性能研究

对两种加强槽的波纹蒙皮结构的屈曲性能进行了分析,讨论了加强槽的半径(宽度),加强槽深度,加强槽个数对临界屈曲载荷的影响,并对加强槽槽间距以及加工可行性对加强槽各个参数的取值约束进行了分析。分析结果表明,临界屈曲载荷随加强槽深度增加而增加。当加强槽深度一定时,存在一个加强槽半径(宽度)临界曲线,当处于该临界曲线左侧时,临界屈曲载荷随半径增加而增加,反之减小。当加强槽半径和深度一定时,存在一个加强槽个数的临界曲面,当处于该曲面下侧时,临界屈曲载荷随加强槽个数增加而增加。     

组合载荷作用下碟形封头的稳定性分析

对于受外压和局部载荷联合作用下的压力容器封头稳定性设计问题,以低温液化气体储罐的外筒体为例,采用有限元方法,对受外压及支座反力作用的碟形封头进行了线性和非线性稳定性分析,计算了封头的临界失稳外压和临界失稳轴向力并考察了支座垫板的作用。结果发现对于常见的3支座或4支座,支座的存在对封头的临界失稳外压几乎没有影响;封头因外压发生失稳和因轴向支座反力发生失稳是互相独立的;支座上有无垫板对封头的临界失稳外压影响不大,但垫板能够提高封头的临界失稳轴向力。此外,为便于工程设计,给出了不同直径和厚度的碟形封头临界失稳支座反力。     

在材料厚度临界值时封头设计厚度的选取

阐述了材料力学性能随板厚范围变化而变化的问题；举例说明当考虑封头加工成形减薄量而增加板厚时，在相同设计温度条件下，由于板厚的增加有些材料许用应力会相应降低，导致封头成形后的最小厚度不能满足强度要求。总结了当封头设计厚度处于相应材料厚度临界值时，设计人员应适当增加最小设计厚度、工艺人员应考虑尽量减小成形减薄量，以保证封头成形后的最小厚度仍能满足强度要求。     

加筋球壳结构稳定性及其优化研究

采用非弹性理论修正与有限元计算相结合的方法,进行加筋球壳结构的稳定性分析,得到加筋球壳结构的实际失稳压力;并通过改变球壳厚度、加强筋尺寸、加强筋布置形式等讨论球壳厚度、加强形式对加筋球壳结构稳定性的影响;同时考虑加筋球壳结构其他力学性能要求,进行加筋球壳结构的稳定性优化设计,给出加筋球壳结构合理的设计形式。研究表明,球壳厚度、加强形式对加筋球壳结构的稳定性有较大影响,增加球壳厚度、减小加强筋跨距可有效提高其实际失稳压力,改善其稳定性。     

Experiments on the buckling under internal pressure of thin torispherical ends of cylindrical pressure vessels

Ten cylindrical pressure vessels with torispherical ends, all of the same constant nominal thickness, were tested under internal pressure to observe the buckling behaviour of the toroidal knuckle. All specimens were of constant internal cylinder diameter to thickness ratio of 531·5. The sphere radius was equal to the cylinder diameter and only the torus radius was varied. Buckling was detected by rotating probes at the sphere/torus junction and at the mid-point of the torus. The buckling pressure increased with increasing torus radius and the two specimens with the largest torus radii did not buckle.For all specimens, the change of meridional shape with increase in pressure was measured. For one specimen, strain gauges were used to study the variation of circumferential strain on the inside and outside surface at the sphere/torus junction due to variation in thickness round the circumference.A simple theoretical expression for the buckling pressure, similar to the Rankine formula for a strut, is suggested.     

Preform design for large-scale bulkhead of TA15 titanium alloy based on local loading features

Large-scale TA15 (Ti–6Al–2Zr–1Mo–1V) titanium alloy bulkhead is a key lightweight load-bearing structure part in an aircraft, which has a large plane view and has a complex shape with high ribs and thin webs. In its forging process, the forming defects, such as folding and under-filling are prone to occurrence. The near-net shape forming with saving force of this large-scale complex component can be realized with proper preform design combining local loading condition. By analyzing isothermal local loading process characteristic of large-scale bulkhead, it indicates that the simple unequal-thickness billet is suitable for small lot manufacture of large-scale TA15 titanium alloy bulkhead. Considering the geometry and forming characteristics, such as large dimension, complex shape, mass data, etc., a design method of unequal-thickness billet using analytical analysis and numerical simulation is proposed. The preform for a large-scale TA15 titanium alloy bulkhead is designed by the proposed method. The basic three-dimensional shape of billet is determined by the analytical models based on local loading features, and the basic billet is modified according to numerical simulation result and considering the local loading forming characteristic, and then the preform without resulting in folding and under-filling can be obtained after two modifications.     

三种内夹层双层舱壁结构的数值仿真

反舰导弹在侵彻进入舰艇装甲内部时, 爆炸产生冲击波和飞散破片对人员和舰艇内部设备具有严重毁坏性. 研究了三种不同内夹层结构形式的双层舱壁结构: X型与六边形组合夹层结构、 十字型蜂窝夹层结构以及细胞增长型蜂窝夹层结构. 采用ANSYSY/LS-DYAN模拟了自锻破片对三种不同舱壁结构的侵彻过程. 根据破片的速度衰减和靶板的能量变化可知, 十字型蜂窝夹层结构的双层舱壁结构最适合作为舱壁的中间结构, 并对其动态响应特性进行了分析.     

多蛋交接耐压壳仿生研究

以鹅蛋壳为生物原型,开展了多蛋交接耐压壳仿生设计及性能研究工作。首先,通过蛋壳生物学试验,建立了蛋形函数;其次,对深海多蛋交接耐压壳进行设计,建立了蛋壳个数分别为2、3、4、5、6的数值模型,研究其临界屈曲载荷、极限强度载荷和储备浮力特性;最后,通过正交试验设计,分析了多蛋交接耐压壳主要几何参数对其性能的影响规律。结果表明：Kitching蛋形函数与鹅蛋经线的吻合程度最高,其长轴与偏心距之比取45,蛋形系数取0.69;深海多蛋交接耐压壳的临界屈曲载荷远大于极限强度载荷,即极限强度载荷为结构设计的主要因素;蛋形壳个数对极限强度载荷和浮力系数影响很小;蛋形壳厚度对极限强度载荷和浮力系数影响较大;加强肋对浮力系数影响较小,而对极限强度载荷影响较大。     

Nonlocal beam models for buckling of nanobeams using state-space method regarding different boundary conditions

Buckling analysis of nanobeams is investigated using nonlocal continuum beam models of the different classical beam theories namely as Euler-Bernoulli beam theory (EBT), Timoshenko beam theory (TBT), and Levinson beam theory (LBT). To this end, Eringen’s equations of nonlocal elasticity are incorporated into the classical beam theories for buckling of nanobeams with rectangular cross-section. In contrast to the classical theories, the nonlocal elastic beam models developed here have the capability to predict critical buckling loads that allowing for the inclusion of size effects. The values of critical buckling loads corresponding to four commonly used boundary conditions are obtained using state-space method. The results are presented for different geometric parameters, boundary conditions, and values of nonlocal parameter to show the effects of each of them in detail. Then the results are fitted with those of molecular dynamics simulations through a nonlinear least square fitting procedure to find the appropriate values of nonlocal parameter for the buckling analysis of nanobeams relevant to each type of nonlocal beam model and boundary conditions.analysis.     

A study of the relation between nozzle geometry,internal flow and sprays characteristics in diesel fuel injection systems

This study examines the influence of geometry on the internal flow and macroscopic behavior of the spray in Diesel nozzles. For this investigation, two bi-orifice nozzles were employed : one cylindrical and one conical. The first step is to use a non-destructive characterization method which is based on the production of silicone moulds so that the precise internal geometry of the two nozzles can be measured. At this stage the nozzles have been characterized dimensionally and therefore the internal flow can be studied using CFD calculations. The results gained from this experiment make it possible also to ascertain the critical cavitation conditions. Once the critical cavitation conditions have been identified, the macroscopic parameters of the spray can be studied in both cavitating and non-cavitating conditions using a test rig pressurized with nitrogen and with the help of a image acquisition system and image processing software. Consequently, research can be carried out to determine the influence that cavitation has on macroscopic spray behavior. From the point of view of the spray macroscopic behavior, the main conclusion of the paper is that cavitation leads to an increment of the spray cone angle. On the other hand, from the point of view of the internal flow, the hole outlet velocity increases when cavitation appears. This phenomenon can be explained by the reduction in the cross section of the liquid phase in the outlet section of the hole.     

含分层复合材料层合板剪切屈曲的实验研究

对含分层损伤的复合材料层合板在纯剪切条件下进行屈曲试验,并通过对试验载荷-应变曲线及损伤形貌的分析以及试验结果和有限元模拟结果的比较,得出复合材料层合板预制分层损伤面积对其剪切屈曲性能的影响.结果表明,试验件含分层损伤面积越大,其破坏载荷越大,而对应的破坏应变越大,因此分层损伤会降低复合材料层合板的承载力和刚度.含分层损伤的层合板试验件其屈曲临界载荷随着分层损伤面积的增加而减小,抗屈曲性能也随之降低.