Optimization on springback reduction in cold stretch forming of titanium-alloy aircraft skin

An optimization method was presented for cold stretch forming of titanium-alloy aircraft skin to determine process parameters and to reduce springback.In the optimization model,a mathematical formulation of stress difference was developed as an indicator of the degree of springback instead of implicit springback analysis.Explicit finite element method(FEM)was used to analyze the forming process and to provide the stress distribution for calculating the amount of the stress indicator.In addition,multi-island genetic algorithm(MGA)was employed to seek the optimal loading condition.A case study was performed to demonstrate the potential of the suggested method.The results show that the optimization design of process parameters effectively reduces the amount of springback and improves the part shape accuracy.It provides a guideline for controlling springback in stretch forming of aircraft skin.     

NUMERICAL SIMULATION OF TEMPERATURE FIELD ON FLASH BUTT WELDING FOR HIGH MANGANESE STEELSF

An axial symmetry finite element model coupled with electricity-thermal effect was developed to study the temperature field distribution in process of the flash butt welding （FBW） of frog highmanganese steel. The influence of temperature dependent material properties and the contact resistance were taken into account in FEM ＇simulation. Meanwhile, the lost materials due to .splutter was resolved by using birth and death element. The result of analyzing data shows that the moddel in the FBW flashing is reasonable and feasible, and can exactly simulate the temperature field distribution. The modeling provides reference for analysis of welding technologies on the temperature field of high-manganese steel in FBW.     

在数值模拟基础上利用神经网络进行缺陷预测

利用体积可压缩的刚塑性有限元法,对多孔体材料镦粗成形过程进行了数值模拟计算,并结合Ｌｅｅ－Ｋｕｈｎ提出的极限压缩应变准则得到了坯料鼓形表面出现裂纹的一系列极限参数。     

NUMERICAL SIMULATION OF TEMPERATURE FIELD ON FLASH BUTT WELDING FOR HIGH MANGANESE STEELS

1. IntroductionW ith the developm entofrailw ay tow ard high-speed,heavy-load,trans-regionaland seam less,high-erperform ancessuch aslongerservice life, betterfatigue-resistance and w ear-resistance are desired forthe frog system on the railw ay.M eanw hi…     

Numerical and experimental study of thermally induced residual stress in the hybrid laser-GMA welding process

A model based on a double-ellipsoidal volume heat source to simulate the gas metal arc welding (GMAW) heat input and a cylindrical volume heat source to simulate the laser beam heat input was developed to predict the temperature field and thermally induced residual stress in the hybrid laser-gas metal arc (GMA) welding process. Numerical simulation shows that higher residual stress is distributed in the weld bead and surrounding heat-affected zone (HAZ). Effects of the welding speed on the isotherms and residual stress of the welded joint are also studied. It is found that an increase in welding speed can reduce the residual stress concentration in the as-weld specimen. A series of experiments has been performed to verify the developed thermo-mechanical finite element model (FEM), and a qualitative agreement of residual stress distribution and weld geometrical size is shown to exist.     

Void closure prediction in cold rolling using finite element analysis and neural network

Cold rolling is used to eliminate void defects in cast materials thus improving the material performance during service. A comprehensive procedure is developed using finite element analysis and neural network to predict the degree of void closure. A three-dimensional nonlinear dynamic finite element model was used to study the mechanism of void deformation. Experiments were conducted to investigate void closure during the cold flat rolling process. Experimental results are compared to the three-dimensional finite element predictions to validate the model. The void reduction predictions from finite element analysis are in good agreement with experimental findings. Plastic strain, principal stress distribution around the void and void reduction ratio are presented for various case studies. As finite element simulation is time-consuming, a back-propagation neural network model is also developed to predict void closure behavior. Based on the correlation analysis, the reduction in sheet thickness, the dimension of the void and the size of the rollers were selected as the inputs for the neural network. The neural network model was trained based on results obtained from finite element analysis for various simulation cases. The trained neural network model provides an accurate and efficient procedure to predict void closure behavior in cold rolling.     

Numerical simulation of temperature fields for T-joint during TIG welding of titanium alloy

Three-dimensional finite element model was established to simulate temperature fields of T-joint titanium sheets during TIG welding with finite element method （FEM） software. Temperature dependent material properties and the effect of latent heat were considered. A technique of element birth and death was used to simulate the process of welded metal filling. Dynamic variation process of temperature fields during T1G welding was achieved. The simulated results agreed well with the measured results.     

高强钢精密冲压件回弹量预测及控制研究

运用Dynaform软件建立高强钢板DP590的U形件有限元模型,进行了恒定压变力、恒定冲压速度条件下的回弹预测,并通过相同条件下的实验验证了回弹预测的准确性。为实现高强钢精密冲压件回弹的智能控制,进行了变冲压速度和变压边力条件下的U形件的拉深试验。其试验结果表明,采用变压力技术比变冲压速度技术更能有效地控制高强钢精密冲压件的回弹。     

Modeling and FE Simulation of Quenchable High Strength Steels Sheet Metal Hot Forming Process

High strength steel (HSS) sheet metal hot forming process is investigated by means of numerical simulations. With regard to a reliable numerical process design, the knowledge of the thermal and thermo-mechanical properties is essential. In this article, tensile tests are performed to examine the flow stress of the material HSS 22MnB5 at different strains, strain rates, and temperatures. Constitutive model based on phenomenological approach is developed to describe the thermo-mechanical properties of the material 22MnB5 by fitting the experimental data. A 2D coupled thermo-mechanical finite element (FE) model is developed to simulate the HSS sheet metal hot forming process for U-channel part. The ABAQUS/explicit model is used conduct the hot forming stage simulations, and ABAQUS/implicit model is used for accurately predicting the springback which happens at the end of hot forming stage. Material modeling and FE numerical simulations are carried out to investigate the effect of the processing parameters on the hot forming process. The processing parameters have significant influence on the microstructure of U-channel part. The springback after hot forming stage is the main factor impairing the shape precision of hot-formed part. The mechanism of springback is advanced and verified through numerical simulations and tensile loading-unloading tests. Creep strain is found in the tensile loading-unloading test under isothermal condition and has a distinct effect on springback. According to the numerical and experimental results, it can be concluded that springback is mainly caused by different cooling rats and the nonhomogengeous shrink of material during hot forming process, the creep strain is the main factor influencing the amount of the springback.     

基于刚黏塑性本构关系的钛合金空心整体结构成形过程三维有限元分析

建立了钛合金空心整体结构成形过程的三维有限元模型.采用刚黏塑性本构关系,基于Marc有限元程序,分析了工艺参数对成形的影响.研究表明,扭转速度的提高使扭矩仅有较小的变化;当模具速度和应变速率提高时,热成形的成形力和超塑性成形的气压将提高.随成形温度降低,成形力显著提高,当温度高于900℃时,扭转成形的扭矩、热成形的成形力和超塑性成形的气体压力随温度的变化均不明显.在有限元分析的基础上,选取合适的工艺参数制备了钛合金空心整体结构模拟件,成形后的钛合金空心整体结构件面板厚度的实测值和模拟计算值具有相同的变化趋势,两者吻合良好.     

基于ANSYS的铸造过程热应力双向耦合模拟

为提高铸造过程温度场和应力场的模拟精度,开发了基于ANSYS的铸造过程热应力双向耦合模拟的FEM/FEM集成系统.系统使用接触单元处理铸件·铸型间的相互作用,采用一致的有限元网格模型模拟温度场和应力场,并实现了温度场-应力场的相互影响.最后使用该系统进行了应力框铸件的实例验算,模拟结果与实验结果吻合良好.     

Prediction of wear properties in A356 matrix composite reinforced with B4C particulates

In the present study, wear properties of A356 unreinforced alloy and composites with different vol.% of boron carbide particles were investigated. It is noted that composites exhibit better wear resistance compared to unreinforced alloy. According to the differences in wear rates of the composites, two separate wear rate were identified as low and high wear rate regimes. A combination of artificial neural network (ANN) and finite element technique (FEM) was implemented in order to predict the composites wear behavior. The FEM method is used for discretization and to calculate the transient temperature field of quenching. It is observed that predictions of ANN are consistent with experimental measurements for A356 composite and considerable savings in terms of cost and time could be obtained by using neural network model.     

基于正交试验和神经网络的激光拼焊板回弹预测

准确预测和有效控制拼焊板成形回弹,研究各因素的影响及其交互作用具有重要意义。以U形件拼焊板为研究对象,通过数值模拟、正交试验和神经网络相结合的方法,考察多个工艺参数对拼焊板回弹的交互作用,建立拼焊板回弹的BP神经网络预测模型,对U形件拼焊板的回弹进行预测和控制。结果表明,板料参数、焊缝位置、压边力、模具间隙、凹模圆角等均对拼焊板回弹有重要的影响,并存在交互作用;建立的BP神经网络模型能很好地预测U形件拼焊板在各参数影响下的回弹变化趋势,和给定一组工艺参数下的拼焊板回弹量,为拼焊板的回弹控制提供了可靠的依据。神经网络技术在拼焊板回弹预测中的应用,为拼焊板成形优化研究提出了新思路。     

宽板V型自由弯曲回弹的有限元模拟

当前 ,开发准确、高效的回弹算法及提高回弹过程数值模拟的精度是亟待解决的问题 ,也是研究的热点。本文利用自主开发的二维弹塑性有限元程序 ,针对宽板V型自由弯曲的特点 ,采用无模法求解回弹。加载时基于弹塑性有限元法 ,卸载时基于弹性有限元法 ,均采用静力隐式算法。实验表明 :该程序对宽板V型自由弯曲回弹的模拟是高效、可靠的。特别是采用随塑性变形而发生变化的弹性模量 ,会进一步提高回弹模拟的精度     

基于直流电位法的泡沫金属定量无损检测方法

提出一种基于直流电位法的泡沫金属定量无损检测方法。该方法采用主元分析前馈神经网络求解逆问题,对内部缺陷进行定量。正问题求解采用有限元方法。为解决三维直流电场分析中庞大的节点数及神经网络所需大量训练数据带来的计算资源问题,开发了一种基于知识库的快速直流电位分布计算方法。算例结果表明,神经网络可有效用于泡沫金属的定量无损检测;所提出的快速算法可大大缩短计算时间且具有较高计算精度。     

Dynamic simulation of resistance spot welding of zinc-coated steels

A model was developed to simulate the temperature distribution and nugget formation during resistance spot welding （ RS1V） of zinc-coated steels. It employs a coupled thermal-electrical-mechanical analysis simulating the dynamic RSW process. Temperature-dependent thermal-electrical-mechanical material properties were considered including contact-resistance. The contact area was determined from a coupled thermal-mechanical analysis. A layer of transition elements was used to represent the change of contact area by killing or activating elements. The heat generation and temperature field were computed in a coupled thermal-electrical model. All these analyses were solved using the commercial finite element method （FEM） based on ANSYS code, and some advanced functions were used by writing a paragraph of codes by the authors. Compared with the results from only coupled thermal-electrical model in which contact area was uniform during the whole process, the result matches better to the experimental results.     

H96黄铜薄壁矩形管绕弯回弹和截面畸变对工艺参数的敏感性(英文)

为了研究工艺参数对回弹和截面畸变的作用,结合多参数敏感性分析法和回弹/截面畸变预测三维有限元模型,建立敏感性分析系统模型,并利用此模型研究回弹和截面畸变对工艺参数的敏感性。结果表明:回弹最敏感的工艺条件是助推速度和助推压力,截面变形最敏感的工艺条件是芯头的个数;当夹紧力、助推速度与助推压力被用来控制绕弯过程的截面畸变时,必须同时考虑这些参数对回弹的影响;在任何情况下利用工艺参数控制绕弯过程回弹都必须同时考虑截面畸变。     

TC4钛合金神经网络本构模型及在有限元模拟中应用

利用Zwick/Roell Z100材料试验机,对TC4钛合金进行等温恒应变速率下的单向拉伸试验。基于获得的试验数据,采用BP神经网络技术建立了该合金的高温本构关系模型,并对其预测性能进行分析。基于ABAQUS/Explcit平台进行材料子程序二次开发,将神经网络本构模型嵌入到有限元计算中,实现了TC4钛合金高温变形的数值模拟。结果表明,神经网络本构模型预测精度很高,可以准确地描述TC4钛合金在热态下的动态力学性能。神经网络本构模型应用于有限元模拟可行且有效。     

板料的渐进弯曲成形及其研究

介绍了一种板料渐进弯曲成形的方法及其设备,并运用有元元法对板料的渐进弯曲成形过程进行了较为全面的研究,主要分析了渐进弯曲过程中的回弹问题。以模切板刀片的渐进弯曲成形为例,分别建立了外环转角与板料弯曲角,板料弯曲回弹角度的关系。通过控制弯曲成形过程中不同的工艺参数,对渐进弯曲成形过程进行了有限元仿真。     

工艺参数对转子屏蔽套真空热胀形影响的模拟

建立了转子屏蔽套真空热胀形过程的二维轴对称有限元模型。借助非线性有限元软件MSC.Marc的二次开发功能,将Hastelloy C-276合金的蠕变本构模型与真空热胀形过程的有限元模型相结合,模拟了转子屏蔽套的真空热胀形过程。计算了真空热胀形过程中转子屏蔽套和模具内部的瞬时温度场和径向位移场,预测了转子屏蔽套的胀形量。研究了模具厚度、保温时间和保温温度等工艺参数对转子屏蔽套真空热胀形胀形量的影响。开展了真空热胀形工艺实验,模拟结果与实验结果吻合较好。