铝合金型材拉弯成形回弹的有限元模拟

对回弹进行有效预测与控制是提高型材弯曲件精度的关键.为了分析轴向作用力对拉弯制件回弹的影响,采用动力显式有限元仿真软件Pam-Stamp2000对中空矩形截面铝型材AA6082(T5)转臂式拉弯成形过程进行了数值模拟,并与实验结果进行了对比.结果表明:增加预拉可以减小制件的回弹,但预拉达到一定水平后,继续加大预拉力对减小回弹将基本不起作用;当预拉不充分时,增加补拉同样有利于减小制件的回弹,但过大的补拉力对于减小回弹几乎没有任何帮助.可见,型材拉弯成形制件的回弹不仅与加载顺序及加载程度密切相关,同时也受到材料应变硬化特性的制约.     

型材拉弯的力学与回弹分析

回弹是弯曲成形中普遍存在的现象,是由卸载过程中内力重新分布引起的,回弹的存在直接影响弯曲件的成形精度.本文针对转台拉弯成形过程,对等边型材等曲率拉弯进行了应力-应变分析,并按照卸载预拉力与不卸载预拉力两种情况对工件回弹进行了研究与探讨,得到两组半径回弹率理论曲线.通过与试验结果对比,不卸载拉力计算的结果与试验值比较吻合.     

复杂截面型材力控制拉弯成形数值模拟分析

复杂截面挤压型材的高精度拉弯成形是制造框架式车身的关键技术.本文基于动态显式有限元软件PAM-STAMP,针对一种典型的框架武车身用复杂截面挤压型材,对其力控制方式的直进台面式拉弯成形进行了数值模拟研究,对比分析了两种截面形状的型材截面畸变和回弹随补拉力增大的变形规律,并得到了摩擦系数对成形精度的影响.数值模拟结果表明,增加型材截面的变形刚度,可以显著地减小截面畸变和回弹;增加补拉力,增大了截面畸变但减小了回弹;增大摩擦系数,截面畸变量减小而回弹增加.     

平面应变板料拉弯成形回弹理论分析

基于平面应变假设,采用服从Hill平方屈服准则和指数强化材料模型,建立了板料拉弯成形回弹量预测的理论模型。应用该模型计算了一个拉弯成形回弹实例,分析了单位宽度切向拉力、凸模圆角半径、摩擦因数及各向异性参数对板料回弹量的影响。分析结果表明,只有当中性层偏移距离超过板厚的四分之一时,增大切向拉力才能有效地控制板料回弹量,而且弯曲半径越大,增大切向拉力控制板料的回弹量越为有效,然而拉力不能无限制的增大,它的计算准则为板料最外层的等效应变应不大于极限应变。同时还表明,摩擦因数对板料回弹量的影响随切向拉力的增大变得更为显著,而各向异性参数对板料拉弯成形回弹量的影响也较为明显。与有限元数值模拟预测结果的对比表明,理论模型预测板料拉弯成形回弹量与有限元数值模拟结果很接近。     

铝合金矩形管拉弯成形过程的数值模拟

采用动力显式有限元程序Pam-Stamp2000对铝合金矩形管的一种拉弯成形过程进行了模拟,分析了模具最大作用力、管材截面畸变、成形件回弹的变化规律.模拟结果和文献给出的实验结果相当吻合,即模具最大作用力、管材截面畸变均随预拉力的增加而增加,而成形零件的回弹随预拉的增加而减小;相同预拉状况下,增加壁厚有利于减小截面畸变.此外,数值模拟给出了模具对管材作用力及管材夹持端轴向拉伸作用力随模具行程的变化规律,揭示了本文的拉弯实质上是一种非恒定轴向作用力(呈渐增趋势)的拉弯成形方式,这与本文的解析结果高度一致.     

不锈钢车顶弯梁拉弯成形研究

利用ABAQUS软件,对某轨道车辆的不锈钢车顶弯梁的拉弯成形过程进行了模拟研究,分析了L形型材拉弯后截面畸变及回弹的影响因素及控制方法。结果表明:模具立边深度对截面畸变的影响较大,拉伸量对其影响相对较小;包覆拉伸量对回弹时发生的截面扭曲的影响最大,补拉量对回弹时发生的侧面弯曲的影响最大;采用模具型面补偿法可以有效减小回弹,提高轮廓精度。实验证明,当预拉量和补拉量为1%、包覆拉伸量为7.5%和模具立边深度为H-0.5mm并且模具型面补偿量为最大回弹量的1.1倍时,可以制造出高质量的不锈钢型材拉弯件。     

钢筋混凝土矩形截面拉弯扭构件极限扭矩的试验分析

本文在８根钢筋混凝土截面在较大轴拉力以及弯矩，扭矩共同作用下的极限抗扭强度的试验基础上，对拉弯扭构件的破坏形态，纵筋及筋的应力应变规律，极限状态下斜裂缝的倾角等问题进行了分析研究，作者以变角桁架理论为基础，推导出拉弯扭构件拉力，弯矩，扭矩的相关方程，提出了计算轴拉力较大情况下拉弯扭构件及极限矩的实用公式，公式逻辑关系清晰，概念明确，与试验结果吻合良好，可供工程设计时参考。     

均布荷载作用下工字形截面单跨超静定深梁应力计算方法研究

工字形截面单跨超静定深梁因截面形式复杂目前其应力计算仍无解析方法。该文对均布荷载作用下工字形截面单跨超静定深梁应力计算进行研究,通过引入合理的参数并对工字形截面作恰当的拆分和组合及合理假设,建立了力学模型,应用半逆解法求解,并考虑了弯剪耦合效应,给出了各应力分量的计算公式。分析了弯应力沿梁高及跨长的分布规律及剪力对弯应力的影响,结果表明剪力对弯应力的影响较大,这种影响随跨高比的减小或翼缘与腹板面积比的增大而增大。结果可为工字形截面单跨超静定深梁的设计提供概念明确的理论计算方法。     

不同材料型材拉弯成形性的比较

介绍了型材拉弯成形性的比较方法,通过数值模拟,建立不同型材的拉弯成形性图,用于评估截面畸变等缺陷产生的难易;以某轿车门框复杂截面型材为例,进行了AA6060-T4和TRIP800两种型材拉弯成形性的对比,表明铝合金型材比钢型材具有更好的拉弯成形性,可得到较高的成形精度,有利于轿车车身轻量化设计.     

抽芯对H96薄壁矩形波导管绕弯成形回弹的影响

基于ABAQUS软件平台,建立了考虑弹性模量变化的H96薄壁矩形管绕弯回弹预测模型,模拟研究了考虑弹性模量随塑性变形的变化和不考虑弹性模量变化对回弹预测精度的影响,并试验验证了模型的可靠性.基于所建模型,模拟研究了抽芯参数对H96黄铜薄壁矩形管绕弯成形回弹角的影响规律及抽芯前后截面尺寸的变化规律.结果表明:采用变弹性模量的回弹预测模型可有效提高回弹预测精度14.9%;随着芯棒与管坯摩擦系数增大,回弹角减小;抽芯次数增加,回弹角先减小后趋于稳定;抽芯速度增大,回弹角先减小后趋于稳定;抽芯后的截面回弹有助于使各截面变化量趋于均匀.     

Finite element analysis on the coined-bead mechanism during the V-bending process

The coined-bead technique is commonly applied to solve the spring-back problem in the V-bending process. However, the coined-bead mechanism on the spring-back/spring-go feature has not been clearly identified yet. In this study, the finite element method (FEM) and laboratory experiments were used to investigate the coined-bead mechanism and its effects on the spring-back/spring-go feature. The features were clearly identified using a stress distribution analysis. The results revealed that the mechanism of the coined-bead technique not only increases the compressive stress on the bending allowance zone, where the spring-back feature decreases, but also increases the reversed bending zone on the leg of the workpiece, where the spring-go feature increases. Therefore, after compensating for the increases in the compressive stress and the reversed bending feature, the amount of spring-back on the bent part was decreased. The FEM simulation bending force and bending angle results were agreed with those from the experimental results.     

帽形型材绕弯件的曲率一致性

在工业部门广泛应用的各种异型断面的框类零件,由于成形后的弹复变形引起的曲率变化和断面形状畸变等缺陷严重影响制件的质量.此外,沿周向曲率的不均匀性使制件的圆度下降,影响制件的装配性及被加强构件的使用性能.因此,也是这类零件成形时不可忽视的重要问题.本文采用带张力绕弯方法,通过对LY12M帽形材的绕弯试验与分析,得到了主要工艺参数相对弯曲半径R/H、侧压力P、后张力(摩擦力)F对绕弯件曲率不一致性的影响规律.这对提高型材绕弯精度提供了有效的途径.     

The prediction of spring-back and residual stress in coiled strip

Cold-rolled, heat-treated strip has tensile and compressive stress-strain characteristics which approximate to those of an ideal elastic-perfectly plastic material. The paper describes the use of Gardiner's¹ equation for spring-back following pure bending and its application to a rapid method of determining the ratio of the Young's modulus to the yield stress of the material. If, as is often the case, tension is applied to the strip during coiling, the spring-back equations of Woo and Marshall² are applied. Woo and Marshall's equations for residual stress are used in non-dimensional form for both pure bending and bending under tension.     

Forming of the titanium elements by bending

Titanium alloys are superior to nearly all metals in terms of a combination of high mechanical strength and low weight. Therefore, titanium is used whenever the construction weight and its strength are essential. Bending is one of the most frequently used methods for forming titanium elements. However, current knowledge of titanium and its alloys forming by cold working is insufficient. Many phenomena, such as spring-back, need to be investigated and explained.This study was undertaken in order to investigate the titanium bending process. A numerical simulation of the bending of a Ti6Al4V ELI titanium alloy bar was carried out with the Adina System, based on the finite element method. The influence of bar diameter, bending radius and bending angle on the strain and stress distribution in the deformed element was analysed. The numerical calculations demonstrated that the spring-back was dependent on the size of the middle material zone, which remained in an elastic state during bending process. This in turn was dependent on the value of the bending radius, bending angle and diameter/thickness of the bent element. Knowledge of the spring-back is very important because it essentially decreases the forming accuracy of the bent elements. This is especially important when vital titanium elements, such as: body implants or aircraft elements, are bent. Therefore, the calculation results were validated experimentally.     

Investigation of spring-go phenomenon using finite element method

Bending is an application used in the sheet metal forming processes in many industries. One of the main problems of the bending process is the occurrence of spring-back/spring-go. Past research has investigated the spring-back problem. However, the spring-go problem was rarely investigated. In this study, the spring-go phenomenon was investigated using the finite element method (FEM) on the V-bending process. The FEM simulation results clearly and theoretically clarified the spring-go phenomenon on the material flow analysis and stress distribution. The comparison between the spring-back and spring-go phenomena was also clarified.     

材料参数对3A21矩形管弯曲回弹的敏感性分析

为了解材料参数波动对3A21铝合金薄壁矩形管弯曲回弹的影响,基于动态显式有限元软件ABAQUS,借助多因素敏感性分析方法,建立了薄壁矩形管弯曲回弹敏感性分析模型,对材料参数影响回弹的规律进行了敏感性分析.结果表明：弹性模量是影响3A21薄壁矩形管回弹最敏感的因素,其次分别为强度系数、初始屈服应力及硬化指数;弹性模量对回...     

芯棒对铝合金矩形管绕弯回弹作用的数值模拟

为掌握芯棒参数对薄壁矩形管绕弯成形回弹的影响规律,从而为芯棒参数的选取与设计提供依据,基于ABAQUS有限元软件建立了3A21铝合金薄壁矩形管弯曲成形及回弹三维有限元模型,试验验证了所建模型的可靠性.基于所建模型,研究了芯棒参数如芯棒/芯头与管坯摩擦(μm)、芯棒/芯头与管坯间隙(δm)、芯头个数(n)及芯棒伸出量(em)对回弹角的影响.结果表明:抽芯是一个应力预卸载过程,可显著减小回弹;随着芯棒/芯头与管坯摩擦系数(μm)的增加,回弹减小;随着芯棒/芯头与管坯间隙(δm)的增加,回弹增加;随着芯头个数(n)的增加,回弹减小;随着芯棒伸出量(em)的增加,回弹先增大后减小.     

Simulations of stress distributions in crankshaft sections under fillet rolling and bending fatigue tests

The residual stresses due to fillet rolling and the bending stresses near the fillets of crankshaft sections under bending fatigue tests are important driving forces to determine the bending fatigue limits of crankshafts. In this paper, the residual stresses and the bending stresses near the fillet of a crankshaft section under fillet rolling and subsequent bending fatigue tests are investigated by a two-dimensional plane strain finite element analysis based on the anisotropic hardening rule of Choi and Pan [Choi KS, Pan J. A generalized anisotropic hardening rule based on the Mroz multi-yield-surface model for pressure insensitive and sensitive materials (in preparation)]. The evolution equation for the active yield surface during the unloading/reloading process is first presented based on the anisotropic hardening rule of Choi and Pan (in preparation) and the Mises yield function. The tangent modulus procedure of Peirce et al. [Peirce D, Shih CF, Needleman A. A tangent modulus method for rate dependent solids. Comput Struct 1984;18:875–87] for rate-sensitive materials is adopted to derive the constitutive relation. A user material subroutine based on the anisotropic hardening rule and the constitutive relation was written and implemented into ABAQUS. Computations were first conducted for a simple plane strain finite element model under uniaxial monotonic and cyclic loading conditions based on the anisotropic hardening rule, the isotropic and nonlinear kinematic hardening rules of ABAQUS. The results indicate that the plastic response of the material follows the intended input stress–strain data for the anisotropic hardening rule whereas the plastic response depends upon the input strain ranges of the stress–strain data for the nonlinear kinematic hardening rule. Then, a two-dimensional plane-strain finite element analysis of a crankshaft section under fillet rolling and subsequent bending was conducted based on the anisotropic hardening rule of Choi and Pan (in preparation) and the nonlinear kinematic hardening rule of ABAQUS. In general, the trends of the stress distributions based on the two hardening rules are quite similar after the release of roller and under bending. However, the compressive hoop stress based on the anisotropic hardening rule is larger than that based on the nonlinear kinematic hardening rule within the depth of 2 mm from the fillet surface under bending with consideration of the residual stresses of fillet rolling. The critical locations for fatigue crack initiation according to the stress distributions based on the anisotropic hardening rule appear to agree with the experimental observations in bending fatigue tests of crankshaft sections.