Al/Cu双金属管内旋压增量成形有限元数值模拟与分析

目的 分析Al/Cu双金属管在内旋压增量成形时应力、应变、剪切结合强度的分布情况,研究主要工艺参数对双金属管剪切结合强度的影响规律。方法 基于有限元模拟软件,对Al/Cu双金属管内旋压成形过程进行有限元数值模拟;研究了内旋压增量成形时工艺参数：内管减薄率ψ、两管之间的初始间隙c、旋轮进给比f对剪切结合强度的影响。结果 随着工艺参数内管减薄率ψ、两管之间的初始间隙c、旋轮进给比f的增大,剪切应力数值也随着增大;基管与衬管的高剪切应力值主要集中在旋压结束部分,衬管的长度被拉长,模拟与实验的剪切应力在旋压成形的末端数值明显增大。结论通过有限元数值模拟分析,得出不同的工艺参数对成形质量的影响规律,对实际成形有重要的作用。     

高钢级厚壁直缝埋弧焊管JCO成型下压量的有限元模拟及理论计算

采用有限元方法研究分析了φ1 219 mm×33 mm规格X80高钢级厚壁直缝埋弧焊管JCO成型过程中的应力和应变分布。结果表明:在该过程中,应力和应变均以钢板与上模具下压点为中心呈左右对称分布,最大等效应变和最大等效应力均位于弯曲处内外表面;随着位移载荷绝对值的增加,最大等效应变和最大等效应力也随之增加,当位移载荷h=18 mm时,模型最大等效应变达到屈服状态。采用理论计算方法得到该规格钢管的理论成型下压量h=17.8 mm,与有限元模拟计算结果非常接近。     

焊管冷弯回弹曲线方程构建及工艺优化

目的 研究316L奥氏体不锈钢板材JCOE弯曲卸载回弹和应力分布特征,对预弯曲量实施相应补偿,以提高弯曲成形精度。方法 基于弹塑性变形理论,利用有限元模拟研究各关键成形参数对板材弯曲卸载回弹的影响规律,将影响指标线性/非线性拟合叠加,构建回弹曲线方程。结果 板料回弹量与上模下压量、下模开口量呈线性关系,与上模下行速度、摩擦因数呈指数关系。结论 优化后的最佳冷弯成形工艺参数如下：上模下压量为12 mm,下模开口量为150 mm,上模下行速度为4 mm/s,摩擦因数为0.15。对于径壁比值≤10的板料成形,理论计算得到的弯曲回弹量与实测平均值吻合较好,构建的模型可以为实际生产奠定理论基础。     

皮带轮圆筒形凸台多道次拉深成形工艺研究

目的研究皮带轮圆筒形凸台多道次拉深成形工艺过程。方法根据拉深系数计算拉深道次,并采用有限元模拟软件模拟分析多道次拉深成形过程。结果根据计算,需采用八道次拉深成形筒形凸台,成形过程中最大等效应力、应变分布在凸模、凹模圆角位置处及筒壁外表。随着道次增多,坯料内累积的等效应力应变值增大。结论八道次拉深成形后,坯料内累积的应力应变值较大,筒形凸台尺寸符合要求,成形质量较好,根据模拟结果成功进行了生产试制。     

不锈钢/铝/不锈钢复合板拉深工艺及有限元数值模拟

目的研究各工艺参数对复合板拉深成形工艺的影响,以指导实际生产。方法以不锈钢/铝/不锈钢三层复合板为研究对象,探究了复合板拉深工艺数值模拟的关键技术;结合有限元数值模拟和试验验证,预测了复合板在拉深成形中的缺陷,研究了凹模圆角半径、凸凹模间隙、压边力、拉深速度对最大减薄率的影响规律,并利用正交试验对这4种工艺参数进行了优化。结果有限元模拟中,分层复合板模型比整体模型准确度高。最大减薄率随凹模圆角半径的增大而减小,随着凸凹模间隙的增大而先减小后增大,随拉深速度的增大而增大,随着压边力的增大而增大。各成形工艺参数影响最大减薄率的主次顺序是:凹模圆角半径压边力模具间隙拉深速度。结论有利于减小最大减薄率的工艺参数优化组合为:凹模圆角半径为21 mm,模具间隙为3.2 mm,压边力为50 k N,拉深速度为10 mm/s。     

基于六边界优化角度函数的多道次辊弯成形研究

目的 为了提高多道次辊弯成形中板材的成形质量、减少板材纵向弯曲缺陷的产生,提出一种基于新型六边界成形角度分配函数的多道次辊弯成形优化方法。方法 根据翼缘端部水平面投影五次曲线推导出最优辊弯成形角度公式,结合COPRA研究板件峰值纵向应变,以确定最佳成形角度分配区间;在相同条件下,利用Abaquse模拟与实验研究不同成形角度对帽形件辊弯成形纵向弯曲缺陷的影响,并分析辊弯成形工艺参数对板材辊弯过程中应力-应变的影响。结果 新型六边界成形角度分配函数的多道次辊弯成形方法可有效改善板材纵向弯曲缺陷;应力随着成形角度增量的增加而增大,等效塑性应变随成形角度和成形角度增量的增加而增加;实验与模拟结果基本吻合,验证了模拟结果的正确性。结论 优化成形角度分配函数的多道次辊弯成形方法可有效改善板材纵向弯曲缺陷,为提高辊弯工艺精度与板材质量提供一定的理论指导。     

反向压力对板材粘性介质压力胀形的影响研究

为研究带有反向压力粘性介质压力胀形过程中接触条件对板材成形性的影响规律,利用DEFORMTM-2D结合韧性断裂准则对覆层板粘性介质压力胀形过程进行有限元分析.结果表明:接触表面无摩擦单纯依靠反向压力能够提高板材成形极限,随着接触表面摩擦系数增大,板材壁厚分布愈均匀,板材的破裂位置由试件顶端转移到凹模圆角处,板材成形极限显著提高.因此,在三维应力状态下有效控制板材所受法向压力和界面摩擦力可以提高板材成形性.     

双金属复合板材辊式矫直的数值模型

将弯曲分层矫直数值计算和实验验证相结合,研究了双金属复合板材辊式矫直过程中的连续弯曲变形和力能参数。结果表明,使用弯曲分层矫直计算模型是计算双金属复合板材矫直过程的有效方法,分层算法的结果与实验数据有较好的一致性;双金属复合板材弯曲应变的中性层与几何中间层产生偏离,中性层位置随弯曲程度和材料比例而变化;同时,由于材料的力学性能不同,在同一弯曲单元内各组元材料的塑性层比例也不同;计算模型所给出的在双金属复合板材矫直过程中应力应变的演化,与单一材料有明显的不同;在不考虑原始曲率的前提下,矫后残余应力随着弯曲单元的增加而减小。     

铝合金壳体精密成形回弹控制工艺优化

目的 精确控制铝合金壳体成形回弹角度,对铝合金壳体成形工艺进行优化。方法 针对影响回弹角度的多个成形工艺参数（保温成形温度、模具间隙、摩擦因数和压边力）进行单变量逐步优化研究。结果 随着保温成形温度的升高,壳体回弹角度因流变应力的降低和校正力的升高而逐渐降低;随着模具间隙的增大,可变动模具的圆角半径增大,板材贴合模具程度降低,壳体回弹角度逐渐增大;随着摩擦因数的增大,板材加工的形状与模具更契合,成形后回弹的角度降低;随着压边力的增大,板材内/外表面间的应力差大大降低,回弹角度逐渐降低。结论 通过多个参数的逐步优化,获得最终优化工艺参数如下：保温成形温度为310℃,摩擦因数为0.15,模具间隙为1.1 mm,压边力为12 kN,对应的回弹角度为7.027°。     

Cu/Al双金属复合管旋压复合成形规律研究

目的 探究双金属管材在复合过程中的受力变化以及关键工艺参数对覆管和基管壁厚分布的影响。 方法 通过有限元仿真技术和实验相结合,对铜和铝两种材料的双金属管进行旋压复合成形过程受力情况以及壁厚变化进行研究。结果 覆管由于受力面积小于基管,导致各自承受的应力具有明显差异。另外,在双金属管旋压复合时,覆管屈服强度需大于基管,否则基管不会发生减薄塑性变形。在Cu/Al双金属管旋压过程中,随着压下量的减少,双金属管的减薄以覆管为主;随着旋轮安装角的减小,双金属管的减薄以基管为主。结论 通过对压下量和旋轮安装角的优化,可实现对覆管和基管壁厚分布的良好控制。     

Study on the microstructure and mechanical properties of explosive welded 2205/X65 bimetallic sheet

In this study, microstructural inhomogeneity and mechanical properties of explosive welded 2205 stainless steel/X65 pipe steel bimetallic sheets were investigated. The explosion-bonded 2205/X65 bimetallic sheets had good shear strength. The tensile shear fracture primarily occurred in the interior of X65 material and primarily exhibited dimple morphology. Fine crystal grains in the 0.5–2 μm range were found all over the narrow localized melted zone near the 2205/X65 interface, whereas a coarse columnar crystal structure growing along the perpendicular direction to the interface formed in the wider localized melted zone. Quasi-cleavage fracture morphology was observed in the coarse columnar crystal region after the stratified tensile test. The junction of the three regions near the interface with large differences in morphology was the weak point in the bimetallic sheet, where Y-shaped cracking easily occurred under a loading force. Stratified tensile test and micro-hardness tests for the explosively welded bimetallic sheet showed that severe hardening occurred in the 2205 cladding, and the most severe metal hardening occurred near the interface. Tests for 45° face bending and root bending tests were conducted under extreme conditions. The results showed that voids were prone to appeared in the peninsula and island morphologies near the interface.     

Microstructure and mechanical properties of CP-Ti/X65 bimetallic sheets fabricated by explosive welding and hot rolling

CP-Ti/X65-pipe-steel bimetallic sheet was fabricated by explosive welding and hot rolling (W&R). Trace of the wavy CP-Ti/X65 interface formed from explosive welding was observed along the straight CP-Ti/X65 interface of bimetallic sheet fabricated by W&R. The microstructure and component analysis showed the following. (i) The cross-section of the X65 zone consisted of a 2–5 μm-wide Ti diffusion layer next to the interface, a 150–200 μm-wide decarbonization layer, and the rest area with a banded structure morphology. (ii) There were numerous voids and a slight C element enrichment at the interface. (iii) The section of the CP-Ti zone consisted of a 10–50 μm-wide Fe diffusion zone next to the interface, a residual adiabatic shear band zone next to Fe diffusion zone, and the rest region composed of the α-Ti microstructure. The micro-hardness profile across CP-Ti/X65 interface was measured. The variation patterns of the mechanical properties of the bimetallic sheet in the thickness direction were obtained from stratified tensile tests. The shear test proved that the CP-Ti/X65 bimetallic sheet produced by W&R had acceptable shear bond strength. The microstructure and alloy element distribution across the TA1/X65 interfaces of as-welded, heat treated and extruded TA1/X65 bimetallic sheets were studied and compared.     

Analysis of thick orthotropic laminated composite plates based on higher order shear deformation theory

A two-dimensional finite element model is presented to perform the linear static analysis of laminated orthotropic composite plates based on a refined higher order shear deformation theory. The theory accounts for parabolic distributions of transverse shear stresses and requires no shear correction factors. A finite element program is developed using serendipity element with seven degrees of freedom per node. The present solutions are compared with those obtained using three-dimensional elasticity theory and those obtained by other researchers. The theory accurately predicts displacements and transverse shear stresses compared to previously developed theories for thick plates and are very close to three-dimensional elasticity solutions. The effects of transverse shear deformation, material anisotropy, aspect ratio, fiber orientation and lamination sequence on transverse shear stresses are investigated. The error in values of transverse shear stresses decreases as the number of lamina increases, for a plate of same thickness. An increase in degree of anisotropy results in lower values of deflection in the plate. For cross-ply plate an increase in anisotropy results in an increase in effective stress whereas for angle-ply plate the effect is almost negligible. Through thickness variation of transverse shear stresses are independent of anisotropy. The maximum effective stress increases exponentially at lower values of anisotropy and reaches to an asymptotic value at higher values. The stacking sequence has a significant effect on the transverse deflections and shear stress. Rectangular plates experience less effective, in-plane and transverse shear stresses compared to square plates.     

6A02铝合金异形截面小弯曲半径薄壁管液压成形工艺研究

目的 研究6A02铝合金异形截面薄壁管的液压成形过程,改进管件的成形质量。方法 使用Abaqus软件进行数值模拟,通过考察管件壁厚分布情况、管件轴线的最小弯曲半径及管壁与模具贴合情况,研究了内压、轴向进给量、加载路径及合模过程中的内压与进给对成形质量的影响,并提出了合模力–轴向进给–内压三者同时配合的加工方法。结果 通过数值模拟确定了无轴向进给情况下管件薄弱处发生破裂时的内压为7.5 MPa,发生起皱前的最大轴向进给量为2 mm,最低整形内压为80 MPa。确定了在合模过程中进给0.75 mm、合模后继续按照特定加载路径进行内压提升和轴向进给、最后施加80 MPa的整形压力的情况下成形效果最好。通过此路径加工出的管件最小壁厚为0.42 mm,最大减薄率为16%,轴线最小弯曲半径为1.258 mm,与模具间隙面积为0.065 mm²。结论 适当的内压–轴向进给可以实现较好的成形质量。在合模过程中,施加与合模力相配合的轴向进给和内压能增加管件弯曲处薄弱部分的补料量,改善管件在合模后的壁厚分布情况,进一步提升管件最终成形质量。     

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。     

Creep properties of a U‐type notch plate in Ni‐based superalloy

In the present investigation, the effect of notch on creep rupture behavior and creep rupture life of a Ni‐based superalloy has been assessed by performing creep tests on smooth and U‐notched plate specimen under 0°C. The finite element analysis coupled with continuum damage mechanics are carried out to understand the stress distribution across the notch throat and the creep damage evolution under multi‐axial stress state. The creep rupture life of U‐notched specimen is much larger than that of plane plate specimen under the same stress condition, indicating that there is a strengthening effect on notch specimen. Creep rupture life increases with increasing the notch radius, the smaller notch radius can induce the creep rupture easier. The effect of notch on the creep damage is also studied. It is found that the location of the maximum creep damage and the maximum equivalent creep strain initiates first at the notch root and gradually moves to the inside as the notch radius increases.     

Effect of die design parameters on the deformation behavior in pure shear extrusion

Influences of die design parameters in terms of diameter ratio and length of the deformation zone on the distribution of effective strain, filling fraction of the die exit channel and pressing load in pure shear extrusion (PSE) are studied using finite element method (FEM). Dimensional stability, pressing load and hardness measurements are used to validate the predictions of the simulation. Acceptable agreements between the predictions of simulation and experimental results are observed. It is found that strain is inhomogeneously distributed which increases from the center to the corners. Effective strain, inhomogeneity of strain, filling fraction of the die exit channel and pressing load are increased with increasing diameter ratio. In addition, the work-piece is deformed more homogeneously at lower pressing load by increasing the length of deformation zone. However, filling fraction of the die exit channel initially increases by the length of the deformation zone up to 60 mm after which it reduces. The optimum die design parameters covering a range of acceptable effective strain and strain homogeneity, filling fraction of the die exit channel and pressing load are proposed as being 60 mm and 2 for length of the deformation zone and diameter ratio, respectively.     

JCOE成型的X80输油钢管开裂分析

在JCOE成型过程中一根X80输油钢管母材发生纵向开裂,裂纹长度达到了700 mm。通过化学成分分析、力学性能测试、断口分析及金相检验等方法分析了钢管的开裂原因。结果表明:大尺寸外来非金属夹杂物的存在导致了钢板在连铸或轧制过程中产生裂纹。而较低的断裂韧度为裂纹进一步扩展创造了条件,在成型拉应力的作用下微裂纹扩展并延伸。     

交叉缩放椭圆管冷压成形的数值模拟

对新型强化换热管——交叉缩放椭圆管的冷压成形过程进行了有限元数值模拟。计算了成形后交叉缩放椭圆管的残余应力分布并比较了三个典型截面上的残余应力状况。分析了模具过渡段倾斜角对成形的影响。结果表明残余应力最大值出现在换热管过渡段的内壁面;模具过渡段倾斜角较小时将使换热管表面的残余应力显著增大。分析结果有利于加工过程中控制参数的合理选择。综合考虑交叉缩放椭圆管的换热性能和加工后的残余应力状况,给出了模具过渡段倾斜角的参考值。