大型管件管端过弯矫圆三步法控制策略

管端过弯矫圆工艺是保证大型管件产品质量的重要工序之一.管端矫圆是一个局部弹塑性变形过程,采用传统的弹塑性理论对其变形本质的精确解析存在一定困难,而合理的矫圆控制策略是提高生产效率的有效手段.本文首先采用物理实验的方法验证了管端矫圆与压扁之间的等价关系,进而通过分析管端压扁过程的弹复规律建立了"三步法"控制策略,从而为后续的过弯矫圆智能化控制系统的奠定了基础.最终的验证实验表明,该控制策略可有效地将管件的管端椭圆度控制在0.5%以下.     

电磁缩径中集磁器参数和铝合金管件参数对变形的影响

管件电磁缩径是高端智能制造的一个新方向，缩径成形质量好坏主要与集磁器线圈参数、管件自身参数和放电能量大小有关，研究集磁器和管件工艺参数对电磁力和成形性能的影响尤为重要。针对3003和6063铝合金管件，本文结合实验研究和数值仿真方法，讨论了集磁器结构和管件参数等对电磁力的影响，研究了放电电压、管件金属材料类型、管件长度对最终管件成形的影响规律，并探究了影响管件成形均匀性的原因，可为合理制定管件电磁成形工艺方案提供一定技术参考。研究结果表明：集磁器内斜面角度变化对磁场力有明显影响，且角度为40°比较合理；3003铝合金管成形性较好，最大缩径率31.2%，塑性变形影响区域长度7.0 mm～15.5 mm，在5000 V～6000 V放电电压时成形均匀度φ≦18%，但是放电电压达到6500 V时出现失稳现象；6063铝合金管强度较高，最大缩径率16.2%，塑性变形影响区域长度5.3 mm～9.4 mm，管件变形均匀φ<14%。     

薄壁管材连续矫直压扁量力学模型研究

针对薄壁管材在连续矫直过程中大弯曲变形产生的截面扁化,需对管材截面进行压扁矫圆。在分析压扁矫圆变形过程和成形机理的基础上,结合薄壳弹塑性理论及其相关假设,确定了变形区的周向应变模型,进而完成了周向弯曲力矩的解析,运用经典卸载规律建立了薄壁管材截面矫圆的压扁量数学模型方程。通过有限元仿真分析证明了该模型的正确性和有效性,同时得到用初始截面径向最大位移量的2倍近似估算压扁量的方法,为继续深入研究矫直相关工艺参数的合理设置、完善薄壁管材矫直理论体系奠定基础。     

内高压成形合模力对变径管尺寸精度的影响

目的 在内高压成形过程中,合模力加载不合理不仅会导致模具寿命降低,而且容易引起管件截面精度超差,需探究合模力对管件截面尺寸的影响以改善这一缺陷。方法 以低碳钢和铝合金变径管为例,采用内高压成形实验与数值模拟的方法,在两种不同的加载条件下分析合模力对管件截面尺寸精度的影响规律。结果 变径管内高压成形时,模腔上、下侧的等效应力高于左、右侧,模腔顶部的径向位移最小,分型面附近的径向位移最大。模腔在合模力的作用下被压扁,导致卸载内压和合模力后管件截面竖直方向的直径始终小于水平方向,存在一定的不圆度。SAPH440低碳钢和6063铝合金变径管的截面最大不圆度分别为0.27%和0.26%。结论 在内高压成形过程中,合模力对截面精度的影响不可避免,需通过增大模具尺寸或采用可变合模力的加载方式以减小其影响。     

薄壁管壳体环矢挤压缩径工艺仿真分析与研究

目的 针对空心薄壁件在缩径成形工序中力学性质难以观测且缩径成形加工效率较低的问题,提出一种使用18瓣环矢挤压模具进行环矢挤压一次性成形的缩径工艺,并研究了该工艺下薄壁管壳体的弹塑性变形规律。方法 以外径6.3 mm、壁厚2 mm、颈缩宽度1 mm的小尺寸薄壁管壳体（Q255材料）为研究对象,基于Barlat''96屈服准则和M–K沟槽理论,结合L.H.Donnell理论,建立管壳体环矢挤压缩径的塑性微元应力模型,通过ANSYS软件建立环矢挤压缩径工艺有限元模型,并进行数值模拟分析,获得管壳体环矢挤压过程中内壁面和颈缩区厚度方向的应力分布规律;最后进行实验验证,利用千分尺测量外径,采用应力测定仪测量中心位点应力,验证了该工艺下仿真结果的准确性。结论 颈缩区域宽径比越大,缩径成形越远离弹性区;内壁面的应力整体呈凸状分布;卸载后,壁厚方向的残余应力呈从外壁到内壁逐渐增大的线性分布趋势,缩径区中心点最大残余等效应力为319.76 MPa,分布在挤压部位的内表面;经实验验证,内壁面中心位点的最大残余应力为183 MPa,其与仿真分析结果（202.5 MPa）的吻合度高达91.5%,验证了仿真结果的准确性。该环矢挤压模具能够有效进行空心薄壁管壳体的一次性缩径成形,提高制造效率,该研究结果可为薄壁管件环矢挤压缩径成形的工艺设计及工程应用提供参考。     

金属棒材拉丝应力统一解

材料拉压强度不相等时棒材拉丝问题的应力解答是研究材料成形工艺人员所关心的问题。根据统一强度理论,分析了棒材拉丝问题,得到考虑材料拉压比影响的棒材拉丝应力统一解和最大截面缩减率统一解。分析过程中引入一个反映棒材拉制和压制工艺的系数,将棒材拉丝问题的拉制解和压制解统一起来。当材料拉压强度相同时,棒材拉丝应力的Mises解答是棒材拉丝应力统一解的特例。在拉丝过程中,棒材拉丝问题的最大截面缩减率随材料拉压比变化而变化。当材料的拉压强度相等时,棒材拉丝最大截面缩减率的Mises解答是最大截面缩减率统一解的特例,也是它的最大值。     

补料量对管材充液剪切弯曲成形精度的影响

充液剪切弯曲方法能够整体成形相对弯曲半径小于0.5的极小半径管,内压和补料量对其成形精度有着重要的影响.采用实验的方法研究了在恒定内压下,不同补料量对5A02铝合金管材充液剪切弯曲成形过程截面畸变、圆角大小和壁厚分布影响,并通过数值模拟深入研究了补料量对厚向应变的影响.研究结果表明:补料比(补料量和切向位移之比)小于1.2时可以成形管件精度良好.补料比为1.3时,靠近第一弯角的位置产生截面畸变,不圆度为2.2%.补料比对第一弯角外侧圆角影响明显,当补料比由1提高到1.2时,圆角减小50%由4.5 mm减小至2.25 mm.随着补料比的增加,内外侧壁厚均增大.内外两侧最大增厚分别由27.47%和26.67%增加到38%和34.67%,最大减薄分别由14.53%和6.64%降低到8.73%和5.8%.补料比对外侧壁厚影响大于内侧.由此可知,补料量增加,有利于外侧圆角的成形和改善成形管件的壁厚分布,但补料量过大,易造成截面畸变.     

结构参数对费马型线柔性弹簧性能的影响分析

基于一种费马曲线的柔性弹簧,设计出不同略角、厚度、弹簧臂数和槽首尾封闭方式的多种柔性弹簧.利用ANSYS软件对多种几何参数的费马型线柔性弹簧进行了有限元分析,通过分析不同参数的费马型线柔性弹簧的最大应力值和径、轴向刚度的变化特性,总结了略角、厚度等结构参数对费马曲线柔性弹簧性能的影响规律;通过改变槽首尾端封闭方式实现了...     

460MPa高强钢箱形截面轴压柱局部稳定有限元分析和设计方法研究

为研究460MPa高强度钢材等边箱形截面轴心受压柱的局部稳定受力性能和设计方法, 该文采用有限元软件ANSYS建立有限元模型, 考虑残余应力和局部初始几何缺陷的影响, 对3组共10个460MPa等边箱形截面轴心受压短柱的局部屈曲进行了有限元分析, 并将极限承载力计算值与试验实测值进行对比, 结果证明该模型能够准确分析计算460MPa高强度钢材等边箱形截面轴心受压柱的局部屈曲受力性能。利用该模型进行有限元参数分析, 与钢板的宽厚比相比, 钢板厚度、钢板长宽比、残余压应力值和局部初始几何缺陷幅值等因素对局部屈曲受力性能的影响都很小。将试验实测值和参数分析的结果与中国、美国和欧洲钢结构设计规范中箱形截面局部稳定设计曲线进行对比, 表明现行规范的设计方法不够安全。该文提出的建议设计公式适用于460MPa高强度钢材等边箱形截面轴心受压柱局部屈曲极限应力的设计计算。     

加载路径对不锈钢球形件内高压成形过程影响

为了研究加载路径对不锈钢球形件内高压成形过程的影响,采用实验方法分析了加载路径对成形过程中缺陷形式的影响,获得了80%膨胀率成形管件的壁厚分布规律.结果表明:当初始内压与屈服强度比值小于0.21时,管坯形成两个皱纹,在整形阶段发生开裂;当初始内压与屈服强度比值大于0.25时,管坯在轴向进给阶段即发生开裂.在初始内压与屈服强度比值为0.21～0.25时,可以成形出合格管件,合格管件最大减薄点位于球形件的最大截面处,最大减薄率为24.5%.本文所成形不锈钢球形件内高压成形区间,合理初始内压与屈服强度比值范围为0.21～0.25.     

Mechanical behaviour analysis of a buried steel pipeline under ground overload

Ground overload is one of the most important factors that threaten the safe operations of oil and gas pipelines. The mechanical behaviour of a buried pipeline under ground overload was investigated using the finite element method in this paper. The effects of the overload parameters, pipeline parameters and surrounding soil parameters on the stress–strain response of the buried pipeline were discussed. The results show that the maximum von Mises stress appears on the top of the buried pipeline under the loading area when the ground load is small, and the stress distribution is oval. As the ground load increases, the maximum stress increases, and the high stress area extends. The von Mises stress, plastic strain, plastic area size, settlement and ovality of the buried pipeline increase as the ground load and loading area increase. The buckling phenomenon of the no-pressure buried pipeline is more serious than the pressure pipeline. As the internal pressure increases, the high stress area and the maximum plastic strain of the buried pipeline first decrease and then increase, the settlement of the buried pipeline increases, and the ovality decreases. The von Mises stress, maximum plastic strain, settlement and ovality of the buried pipeline decrease with increasing buried depth, the surrounding soil's elasticity modulus, Poisson's ratio and cohesion. The maximum von Mises stress, high stress area, the maximum plastic strain, plastic area and ovality increase as the diameter–thickness ratio increases. The critical diameter–thickness ratio is 60, and the settlement of the buried pipeline first increases and then decreases as the diameter–thickness ratio increases. Finally, a protective device of the buried pipeline is designed for preventing ground overload. It can be repaired in a timely manner without stopping the transmission of oil and gas and widely used in different locations because of its simple structure and convenient installation.     

基于全量流动理论的管材弯曲过程失稳分析研究

目的 基于全量流动理论,研究管材弯曲成形过程中的外侧破裂和内侧起皱,分析其产生的原因及控制方法.方法 采用理论解析方法,建立了管材弯曲变形应力、应变计算公式,推导管材外侧破裂和内侧起皱发生的判据,并试验验证了预测公式的可靠性.结果 基于推导的应力、应变计算公式,依据临界许用变形程度,建立了管材外侧破裂判据;采用能量准则,提出了管材弯曲过程起皱发生公式,确定了起皱失稳计算公式的各个边界参数.结论 试验与理论结果表明,构建的最小壁厚下许用R/r(弯曲半径与管材平均半径的比值)计算公式、基于起皱失稳计算的许用R/r(弯曲半径与管材平均半径的比值)计算公式均有较高精度,可用于指导弯管工艺参数设计与优化.     

考虑大变形和排水条件时柱孔扩张问题统一解析

将柱孔周围土体中的应力分布分为弹性区和塑性区,在弹性区中采用小变形理论,在塑性区中采用大变形理论和统一强度准则。根据柱孔扩张问题排水条件时的应力平衡方程、应力和应变连续的边界条件,推导出考虑土体剪胀、大变形、排水条件和中主应力等因素的柱孔扩张问题塑性区半径和极限扩孔压力的理论解答,同时也获得了弹塑性区中的应力和应变场分布规律。理论计算结果与现场实测结果较为接近,初步说明该理论具有一定的工程应用价值。对比分析表明:扩孔压力和塑性区半径受土体剪胀的影响要比b值显著。     

Finite element analysis of frictionless contact between a sinusoidal asperity and a rigid plane: Elastic and initially plastic deformations

A series of finite element simulations of frictionless contact deformations between a sinusoidal asperity and a rigid flat are presented. Explicit expressions of critical variables at plastic inception including interference, contact radius, depth of first yielding, and pressures are obtained from curve fitting of simulation results as a function of material and geometrical parameters. It is found Hertz solution is not applicable to the critical contact variables at plastic inception for sinusoidal contact, although contact responses of initially plastic deformation follow the same trend as that of purely elastic deformation. The contact pressure at incipient plasticity, which is defined as yield strength, is dependent on Poisson’s ratio, yield stress, and geometrical parameters, but independent of elastic modulus. It is not yield stress, but yield strength that correlates with indentation hardness. The results yield the insight into the specification of material properties to realize elastic contact. A larger ratio of yield stress to elastic modulus is beneficial to sustain a larger load before plastic deformation.     

带筋管整体成形力学条件研究

目的掌握带筋管整体成形的工艺条件。方法实验研究了带筋管坯整体成形易出现的缺陷形式,并分析了影响筋板整体成形的力学条件。结果实验结果表明:对于一定高径比范围内的带筋管可整体成形,但当高径比超出临界值时,易发生起皱和倾倒缺陷。起皱主要发正在曲率半径增大的部位,倾倒则发生在曲率半径减小的部位。起皱发生的原因是曲率半径增大导致筋板中性层外侧形成了较大的压应力,倾倒则是非均匀分布的拉应力形成了弯矩,进而导致了失稳的发生。结论带筋管内部施加支撑压力能同时降低压应力和弯矩,避免起皱和倾倒的发生。最终成功成形出了椭圆度为1.5和2的整体带筋管件。     

Flux Pinning-Induced Stress in a Long Hollow Cylindrical Superconductor Restricted by a Metal Tube

The tensile stress in a hollow cylindrical superconductor completely restricted by a metal tube in a parallel magnetic field is investigated. Using the plane strain approach, analytical expressions for the stress distribution of the superconductor and the contact stress between the metal tube and the superconductor are obtained and show that both the ratio of Young’s modulus and thickness ratio of the high-temperature superconductors and the metal tube significantly affect the stress distribution in the superconductor explicitly. In addition, the flux pinning-induced stress in the above-mentioned superconductor is systematically studied by the exponential critical state model during the field cooling process. The results indicate that the metal tube can reduce effectively the tensile stress in the hollow cylindrical superconductor during the magnetization process. The findings suggest that the appropriate selection of material parameters and size of the metal tube can improve superconductor performance efficiently.     

管材弯曲中应力中性层位移计算与影响因素分析

为研究管材弯曲成形过程中应力中性层位移及影响因素,基于塑性力学全量理论,分析了管材弯曲的应力应变规律,在考虑材料硬化特性和壁厚变化的情况下推导出应力中性层位移的近似计算公式,并利用正交设计法对应力中性层位移的影响因素进行了敏感性分析,认为相对弯曲半径和硬化指数是影响应力中性层位移最敏感的因素,其它参数无显著影响.通过与数值模拟结果对比,证明了理论分析的正确性和有效性.     

Buckling behavior under radial loading of orthotropic oval cylindrical shells with parabolically varying thickness

In this article, the framework of the Flügge's shell theory, the transfer matrix approach, and the Romberg integration method have been employed to investigate the buckling analysis of a radial loaded oval cylindrical shell with parabolically varying thickness along its circumference. Trigonometric functions are used to form the modal displacements of the shell and Fourier's approach is used to separate the variables. The mathematical analysis is formulated to overcome the difficulties related to mode coupling of variable curvature and thickness of the shell. Using the transfer matrix of the shell, the buckling equations of the shell are reduced to eight first-order differential equations in the circumferential coordinate and rewritten in a matrix form and solved numerically. The proposed model is adopted to get the critical buckling loads and the corresponding buckling deformations for the symmetrical and antisymmetrical modes of buckling. The influences of the shell geometry, orthotropic parameters, ovality parameter, and thickness ratio on the buckling parameters and the bending deformations are presented for different type-modes of buckling.     

Thermal deformation of glass backplanes during Joule-heating induced crystallization process

Large area crystallization of amorphous silicon (a-Si) thin-films on glass backplanes is one of key technologies in manufacturing flat displays of commercial scales. Among various crystallization technologies, Joule-heating induced crystallization (JIC) has been recently introduced and considered as the highly promising one since the whole film of a-Si on glass backplane can be crystallized within tens of microseconds. Based on theoretical investigation accompanied by in-situ and ex-situ experimentations, this study clarified the critical mechanism of the glass backplane deformation during the JIC process. Simulation using a commercial FEM code with one-dimensional conduction and viscoelastic models showed that the local region of which temperature was larger than the glass softening point undergoes structural shrinkage due to stress relaxation and this shrinkage remained permanently even after the process. As a quantification factor for such plastic deformation, the radius of curvature was estimated and compared to the experimental observation. Consequently the pulse duration should be decreased for larger display applications, because the radius of curvature could be considerably increased as the pulse duration was decreased for the same peak temperature of the JIC processes.     

汽车车门把手气辅成型工艺CAE优化研究

目的 针对传统汽车车门把手成型工艺在实际应用中塑件收缩变形量大、无法有效控制等问题,开展汽车车门把手气辅成型工艺优化研究。方法 通过确定基于计算机辅助工程的塑件成型方式、设置改造后汽车车门把手塑件结构、优化注塑和注气参数,提出一种针对汽车车门把手气辅成型的工艺优化方案。结果 与优化前成型工艺相比,采用优化后成型工艺得到的汽车车门把手塑件的收缩变形量明显降低,汽车车门把手塑件的收缩变形量均能够控制在0.45%以下。结论 引入计算机辅助工程优化分析技术对实现汽车车门把手整体制件结构设计具有更高的实际应用价值,有利于提升汽车车门把手设计、生产和加工的效率。