Influence of Pre-Deformation on Springback Effect of Advanced High Strength Steel

In sheet metal forming process of automotive components,the springback effect is significant,in particular for Advanced High Strength Steels (AHSS),for example the Dual Phase (DP) steel.Most of construction parts of modern vehicles have very complex shapes and therefore multi-step procedures are necessary to form such a part.Steel sheets,which firstly undergo pre-deformation,can show considerable change in mechanical behavior during the forming process.However,at present there are limited sufficient data concerning pre-deformation effect on the springback available.In this work,a study of influences of different pre-strain levels on the springback of steel sheet made of AHSS materials has been carried out.The sheet specimens were firstly pre-stretched on a tensile testing machine and the pre-strain values were calculated based on the engineering strain.Furthermore,the steel sheets prepared parallel,transverse,and 45° to the rolling direction have been investigated.A modified U-shape forming was used to evaluate the degree of springback of the steel sheets under various conditions.In parallel,FE simulation of the U-shape forming was performed.Both isotropic model using stress-strain responses from tensile test of specimens with different directions and anisotropic Hill’s 48 model have been applied.The experimental results are compared with the sheet metal forming FE simulations.The primarily aim is to basically understand the springback mechanism by means of the simple models.And finally,conclusions with regard to the springback modeling will be presented.     

高精度黄铜接插件铜带生产技术的研究

论述生产高精度H65黄铜接插件铜带在铸造、铣面、轧制、酸洗等关键工序的工艺过程及其特点，并重点分析探讨了如何控制和提高该产品质量的措施和途径．     

Study of effect of load on springback in sheet metal bending

Springback remains a major concern in sheet metal bending in fabricating any final product within the permissible tolerance. Apart from the geometrical and material parameters, springback is significantly affected by the forming load also and the present study is focused on it. Sheet metal bending process involves large rotation and strain as well as large springback due to elastic recovery of the material. Therefore, a large deformation algorithm based Finite Element software was used to model a typical sheet metal bending process employed in manufacturing cylindrical structures. A Total-Elastic-Incremental-Plastic (TEIP) algorithm has been incorporated in an in-house software to handle large deformation and the elastic recovery during the unloading process. In addition, experiments have been performed on aluminum, brass, copper and mild steel sheets and substantiated with the FEM analysis.     

Springback in simple axisymmetric stampings

A series of experiments was conducted to measure springback (calculated from dome height measurements) in a simple, stretched sheet metal part formed using a 50.8-mm-radius hemispherical punch. Parts were formed from three materials [5182-0 aluminum, 2036-T4 aluminum, and aluminum-killed (AK) steel] using three different binder geometries (lockbead, stinger, flat), and punch penetration was varied between 1.27 and 21.6 mm, limited by failure of the aluminum sheet. The steel and 5182-0 aluminum were chosen to possess similar gage and tensile properties to highlight the effect of elastic modulus, while the 5182-0 and 2036-T4 aluminum were chosen to possess similar gage and modulus but different tensile behavior to highlight the effect of strength differences. Springback increased with increasing strength and decreasing modulus. A major finding was that, for a specific material, a primary factor influencing spring-back was the binder geometry, with the lockbead showing the least springback and least variation with punch penetration: by contrast, the stinger and flat binders exhibited much greater springback, and the magnitude of the springback was strongly influenced by the extent of punch penetration. In the worst case, the springback was more than 30 pct of punch penetration. The effect of binder region restraint on springback was evaluated by comparing the part geometry both before and after strain-free removal of the binder region by electrodischarge machining. The magnitude and sign of the binder region restraint depended on binder geometry and punch penetration but was always less than the springback observed in removing the part from the die initially.     

时效工艺对非调质钢螺栓组织和性能的影响

研究了不同时效工艺对螺栓组织和性能的影响。采用热处理加热装置进行系列工艺试验研究时效规律,借助光学显微镜、扫描电镜、拉伸试验机等设备,分析时效工艺对材料组织及性能的影响。研究结果表明:提高时效温度和延长时效时间皆使硬度升高;适合生产的最佳时效工艺为250~300℃,2.5 h,时效工艺和表面处理工艺可以同时进行;柯氏气团、铁素体中亚晶的形成和弥散碳、氮化合物析出是时效强化的主要原因。     

Experimental Analysis on the Frictional Behaviour of Drawbeads in Sheet Metal Forming

In sheet metal forming, drawbeads are commonly used to control uneven material flow, which may cause defects such as wrinkles, fractures, surface distortion and springback. Although friction may not directly change the limiting strain of steel sheets, the tribological conditions in the contact zone between the sheet surface and the tool surface play an important role in determining the limits of the forming process. Friction in the drawbead contact zones affects the flow of the material in the tool and is used deliberately to control the stamping process. Therefore in this study, the frictional behaviour of drawbeads is experimentally investigated by the drawbead friction test. To characterize the effect of processing variables on the friction coefficients, tests are performed for various sheets, lubricants and bead materials suffering different surface treatments. The results obtained from the drawbead friction test show that the friction and drawing characteristics of deforming sheets were strongly influenced by the strength of sheet, viscosity of lubricant and hardness of bead surface.     

热等静压技术新进展

目前热等静压技术已广泛应用于航空、航天、能源、运输、电工、电子、化工和冶金等行业,用于生产高质量产品和制备新型材料.为了探讨和交流各国在热等静压设备、工艺研究及应用的发展动态,从1987年开始召开国际热等静压会议.2008年5月在美国加利福尼亚召开了第九届国际热等静压会议,本文就此次会议所报道的热等静压技术、应用及发展情况进行了概述,特别是对美国和俄罗斯热等静压技术作了介绍.     

Microstructure and Properties of Hot Rolled Ti23Al17Nb Alloy Sheets

 Microstructure and tensile properties of the Ti-23Al-17Nb alloy sheets rolling at （α2＋B2＋O）phase field with the various heat treatments were studied. Before rolling the microstructure of B2 phase particles embedded in O phase continuity matrix is acquired. The B2 phases deform more greatly and recrystallize more easily than α2/ O phases during the same rolling step. The (α2＋B2) two-phase equiaxed microstructure is obtain by solution treatment at (α2＋B2) phase field. The B2 phases become the continuity matrix by recrystallization and growing up of B2 grains and the anisotropy caused by rolling disappears. The microstructure obtained by solution treatment has more excellent tensile properties than the microstructure gained by subsequent aging treatment at (O＋B2) phase field because the O phases precipitate as the block structure during aging and the B2 matrix continuity is broken down.     

稀土硅铁孕育对高铬合金白口铸铁性能的影响

本文对稀土硅铁、钒铁、钛铁的不同加入量对高铬合金白口铸铁性能的影响进行了实验研究。结果表明，当稀土硅铁的加入量为１．２～１．５％时，冲击韧性达到最大值，硬度也有提高。稀土硅铁孕育可以显著改善碳化物的形态和分布，细化基体组织。当加入量为０．９～１．５％时，大部分碳化物断网，呈孤立状态分布。钒铁的加入量为０．２％时，即可起到明显的孕育作用，机械性能得到提高。     

Microstructure and Properties of Hot Rolled Ti-23Al-17Nb Alloy Sheets

Microstructure and tensile properties of Ti-23Al-17Nb (at%) alloy sheets rolled in (α2+B2+O) phase field with the various heat treatments were studied.Before rolling the microstructure of the billet is B2 phase particles embedded in O phase continuity matrix.The B2 phases are deformed more greatly than α2/O phases during the same rolling step.The (α2+B2) two-phase equiaxed microstructure can be obtained by solution treatment in (α2+B2) phase field.The B2 phases become the continuous matrix by recrystallizat...     

Increasing Rigidity and Strength using Local Effects of Bead‐on‐Plate Laser Welding Seams

In order to achieve graded strength properties and to improve the rigidity of metallic materials, side effects of the laser joining process are used. Local physical and geometrical effects which have only been observed as side effects are to be used purposefully. The investigations take place in context of the SFB 675 “high‐strength metallic structures and joints by setting up scaled local material properties”. The energy needed to produce bead‐on‐plate welding seams can be limited to a small area of the workpiece by using a focused laser beam with a diameter of tenths of a millimetre. The heat affected zone of a laser beam is very small. In comparison to other welding procedures, lower heat input is the main reason that basic material characteristics remain unaffected after welding. The progressive development of laser beam sources to higher available laser output power has extended their spectrum of use in the field of joining technologies [1, 2]. It should be pointed out that local physical and geometrical effects can be used to achieve specific material characteristics. Bead‐on‐plate laser welding seams were produced to demonstrate that strength and rigidity can be increased in metal sheets. First investigations are carried out on the micro‐alloyed high‐strength steel H340LAD. The sheets were tested using tensile tests and also with 3‐point and 4‐point bending tests. Six different specimens were investigated, one without welding seams and five with different laser based welding seam types. The tensile and bending tests showed that higher forces were needed to rupture or to bend the laser welded specimens. Furthermore, the investigations showed that the strength of the specimens was increased in comparison to the specimens without welding seam.     

一种远程高压电机绝缘测试装置的开发研究

介绍了一种远程高压电机绝缘测试装置。根据系统需求,独自研发了一种加入了RS-485通信模块和控制模块的新一代电子式电阻表。基于西门子S7-200型PLC对高压电机绝缘监测设备、高压继电器、机械抓进行控制。建立了触摸屏、PLC、绝缘检测仪之间的通讯,实现了高压电机绝缘的远程测量功能。通过运用本装置,提高了高压电机绝缘检测的自动化水平,降低了设备维修频率,并保障了工人的人身安全。     

试样对纯净钢元素分析影响浅析

随着钢质纯净度的不断提高,需要分析的钢中气体元素含量以及部分低碳钢的碳含量越来越低,分析精度要求越来越高.对大生产中分析气体氢使用的真空玻璃吸管棒样以及分析氧和碳使用的扁平样和双厚度样进行了分析,认为上述取样器用于氢、氧和碳分析时波动较大,精度不能满足要求,而对氮的分析没有影响;同时认为在线定氢仪和TOS取样器取出的试样成分稳定,具有很好的代表性;研究表明不同的加工方式对试样的分析精度也会产生较大的影响.     

Analytical Solution of Two-Layer Beam Taking into Account Nonlinear Interlayer Slip

This paper presents a fully developed nonlinear analytical (exact) model for analyzing composite beams under transverse bending load. The model reproduces the elements responsible for the relative slip between the layers (shear connectors and interface) with an elastoplastic strain-softening interlayer. Further than the slip, the model predicts stresses due to a given load and ultimate load for debonding of bilayered composite beams. All the details on the mathematical development are presented. This paper advances the state of the art, since the last development available in literature is an analytical (nonexact) linear model. A number of parametric studies are conducted to evaluate the influence of various geometrical and material parameters, the main results of which are presented together with the interpretation, e.g., the dependence of load-carrying capacity, stresses, and deflection on the local nonlinear load-slip relationship. The research proves as well that the shear connection lower and upper bounds (respectively, totally flexible and infinite rigid shear connectors) do not imply any lower and upper bound for the response.     

Plastic Localization Phenomena in a Mn-Alloyed Austenitic Steel

A 0.5 wt pct C, 22 wt pct Mn austenitic steel, recently proposed for fabricating automotive body structures by cold sheet forming, exhibits plastic localizations (PLs) during uniaxial tensile tests, yet showing a favorable overall strength and ductility. No localization happens during biaxial Erichsen cupping tests. Full-thickness tensile and Erichsen specimens, cut from as-produced steel sheets, were polished and tested at different strain rates. During the tensile tests, the PL phenomena consist first of macroscopic deformation bands traveling along the tensile axis, and then of a series of successive stationary deformation bands, each adjacent to the preceding ones; both types of bands involve the full specimen width and yield a macroscopically observable surface relief. No comparable surface relief was observed during the standard Erichsen tests. Because the stress state is known to influence PL phenomena, reduced-width Erichsen tests were performed on polished sheet specimens, in order to explore the transition from biaxial to uniaxial loading; surface relief lines were observed on a 20-mm-wide specimen, but not on wider ones.     

ARefined Model of Three-roller Elastoplastic Asym-metrical Pre-bending of Plate

The geometry of plate after edge pre-bending mode is compared with that after roll-bending mode and the relationship among edge pre-bending angle, pre-bending edge length, and cylindrical desired radius is presented for a three-roller plate bender with bottom rollers adjustable horizontally. The analytical moment-curvature model and springhaek model for pure bending are established, assuming that the stress-strain relationship of material is linear, and the material is in plain strain and yields according to Mises yield criterion. The mathematical model for three- roller edge pre-bending of plate is developed considering the effect of pre-bending edge length, bottom roller radius, friction between plate and roller, etc. The plate tensile test and plate bending test are done and the numerical results agree well with the test data. The results are shown graphically and analyzed in the following aspects： （1） the error between numerical results and test data of top roiler force; （2） the influence of bottom roller radius, relative curva- ture, and bending arc length on springback angle; （3） the relationship between springhack ratio and edge pre-ben- ding angle.     

Experimental Bond Behavior of FRP Sheets Glued on Brick Masonry

This paper deals with the experimental characterization of the mechanical tensile and shear bond behavior of fiber-reinforced polymer (FRP) sheets externally glued on masonry prisms, in terms of load capacity and stress distribution along the bonded length. The brick masonry adopted tries to replicate ancient brick masonry, by using handmade low-strength solids bricks and low-strength lime-based mortar. Key parameters relative to the FRP-masonry interface response, particularly bonded length, FRP materials, anchor scheme adopted, and shape of masonry substrate, were studied. Finally, an analytical bond stress-slip formulation was developed, allowing deducing local bond stress-slip curves directly from the experiments.     

弹性连接器组件研究现状及进展

弹性连接器常用于电流和信号的传输，在现代电子通讯领域被广泛应用。其制备过程中的冲压工艺，受到包括冲压方向、冲压角度、冲压宽度、最小相对弯曲半径等因素影响。其制备材料的导电率、摩擦系数、耐腐蚀性将影响弹性连接器的接触阻抗，同时材料本身的弹性模量、强度、抗热应力松弛率、摩擦系数等，将影响弹性组件的可靠性，而接触阻抗和可靠性将直接影响弹性连接器通讯电讯号的传输。本文从选材的角度，针对电力传输用连接器的电导率、弹性模量、强度、摩擦磨损性能、冲压性能和抗热应力松弛性能，信号传输用连接器的弹性模量、强度、冲压性能、表面电导率，以及高温下长周期服役用连接器的抗热应力松弛性能和耐腐蚀性，反复插拔用连接器的接触组件表层的耐摩擦磨损性能等分别进行了综述，同时从加工的角度提出弹性连接器需要结合设计考虑不同冲压方向、冲压角度、冲压厚度、冲压宽度下的最小相对弯曲半径。     

异步轧制AZ31镁合金板材的晶粒细化及性能

采用上下轧辊速比1.125的异径异步轧制方法对AZ31镁合金板材进行轧制。采用光学显微镜、X射线衍射仪和电子拉伸机等设备分析轧制前后AZ31镁合金板材的微观组织和力学性能。结果表明:AZ31镁合金热挤压板坯在加热到350℃后,经一道次38%压下率的异步轧制,可获得平均晶粒尺寸为2.8μm的等轴晶粒,板材轧制方向的伸长率和抗拉强度显著增加;轧制过程中形成了非基面晶粒取向;伸长率的增大与晶粒细化和非基面织构的形成有关,抗拉强度的增大归因于晶粒的显著细化效应。     

Springback behavior of tailor rolled blank in U-shape forming

The springback of tailor rolled blanks with quenching and partitioning steels was investigated.In order to find out the springback behavior and related influence factors for the novel sheets,both experimental and simulation methods have been used to compare and analyze the springback characteristics of equal thickness blanks and tailor rolled blanks in U-channel forming.From the results,the overall springback angles of tailor rolled blanks at thin and thick sides are respectively 106.79° and 99.705°,which are both lower than those of the corresponding equal thickness blanks.Due to the existence of the thickness transition zone,the stress distribution in thin and thick sides of blanks is changed.The location of dangerous region in thin side of tailor rolled blanks is closer to the end of side,and the thick side moved to the middle of straight wall,which are different with the equal thickness blanks.Afterwards,the released quantitles of tangential stress and strain per unit section of blank are adopted to calculate relative springback angles and give novel evaluation criteria for qualitatively analyzing the amount of springback angles.By comparing the results,it shows that the tangential strain method is more suitable for the actual situation.