Research of Elastic and Elastic-Plastic Deformation on Bending Problems of Variable Stiffness Beams

A novel variable stiffness model was proposed for analyzing elastic-plastic bending problems with arbitrary variable stiffness in detail.First,it was assumed that the material of a rectangular beam is an ideal isotropic elastic-plastic material,whose elastic modulus,yield strength,and section height are functions of the axial coordinates of the beam respectively.Considering the effect of shear on the deformation of the beam,the elastic and elastic-plastic bending problems of the axially variable stiffness beam were studied.Then,the analytical solutions of the elastic and elastic-plastic deformation of the beam were derived when the cross-section height and the elastic modulus of the material were varied by special function along the length of the beam respectively.The elastic and elastic-plastic analysis of the variable stiffness beam was carried out using Differential Quadrature Method(DQM)when the bending stiffness varied arbitrarily.The influence of the axial variation of the bending stiffness on the elastic and elastic-plastic deformation of the beam was analyzed by numerical simulation,DQM,and finite element method(FEM).Simulation results verified the practicability of the proposed mechanical model,and the comparison between the results of the solutions of DQM and FEM showed that DQM is accurate and effective in elastic and elastic-plastic analysis of variable stiffness beams.

Theoretical analysis on springback of L-section extrusion in rotary stretch bending process

The theoretical analysis of springback in rotary stretch bending process of L-section extrusion was studied. The models for characterizing the springback angle after unloading were established based on the stress and strain distributions in the cross-section of the part. With the proposed model, analysis of the effect of pre-stretch force and post-stretch force on springback angle shows that springback decreases as the pre-stretch force or post-stretch force increases. Comparative study with experiments clearly demonstrates that the prediction of springback can resort to the current model without the loss of accuracy.

Effect of bending and tension deformation on the texture evolution and stretch formability of Mg-Zn-RE-Zr alloy

Bending and tension deformations were performed on Mg-1.3 wt%Zn-0.2 wt%RE-0.3 wt%Zr(ZEK100)alloy sheets that initially had a transverse direction(TD)-split texture.The effects of bending and tension deformations on the texture formation and room-temperature formability of specimens were investigated.The specimen subjected to 3-pass bending and tension deformations exhibited an excellent Erichsen value of 9.6 mm.However,the Erichsen value deterioration was observed in the specimen subjected to 7-pass deformations.The rolling direction-split texture developed on the surface with an increasing pass number of deformations.Conversely,the clear TD-split texture remained at the central part.As a result,a quadrupole texture was macroscopically developed with an increasing pass number of deformations.The reduction in anisotropy by the formation of the quadrupole texture is suggested to be the main reason for the improvement in stretch formability.By contrast,the generation of coarse grains near the surface is suggested to be the direct cause for the deterioration of the stretch formability of the specimen subjected to 7-pass deformations.

Numerical analysis of dimension precision of U-shaped aluminium profile rotary stretch bending

In order to enhance the dimension precision of bent part, advanced bending technologies is requested recently. Rotary stretch bending(RSB) is a suitable technology to realize high precision of bent part. The effect of processing parameters, namely the side pressure and the stretching force, on the dimension precision of aluminium profile RSB part was studied by finite element method. The numerical simulation of the U-shaped aluminium profile RSB was carried out, and the validity of the simulation was checked. Parametric analysis shows that the section distortion of the U-shaped profile LY12M bent part decreases with the increasing of the side pressure, whereas the springback of curvature increases, and that both of the section distortion and the springback of curvature decrease with the increasing of the stretching force, moreover, the uniformity of curvature of the bent part is clearly enhanced with the increasing of the stretching force. The results above prove that RSB technology can better improve the dimension precision of aluminium profile bent part.

Determining knots by optimizing the bending and stretching energies

For a given set of data points in the plane, a new method is presented for computing a parameter value（knot） for each data point. Associated with each data point, a quadratic polynomial curve passing through three adjacent consecutive data points is constructed. The curve has one degree of freedom which can be used to optimize the shape of the curve. To obtain a better shape of the curve, the degree of freedom is determined by optimizing the bending and stretching energies of the curve so that variation of the curve is as small as possible. Between each pair of adjacent data points, two local knot intervals are constructed, and the final knot interval corresponding to these two points is determined by a combination of the two local knot intervals. Experiments show that the curves constructed using the knots by the new method generally have better interpolation precision than the ones constructed using the knots by the existing local methods.

Analysis of plane strain bending of a strain hardening curved beam based on unified yield criterion

The analysis of plane strain elastic-plastic bending of a linear strain hardening curved beam with a narrow rectangular cross section subjected to couples at its end is conducted based on a unified yield criterion. The solutions for the mechanical properties of plane strain bending are derived, which are adapted for various kinds of non-strength differential materials and can be degenerated to those based on the Tresca, von Mises, and twin-shear yield criteria. The dependences of the two critical bending moments, the radii of the interfaces between the elastic and plastic regions and the radial displacements of the points at the symmetrical plane on different yield criteria and Poisson’s ratios are discussed. The results show that the influences of different yield criteria and Poisson’s ratio on the two critical bending moments, the radii of the interfaces between the elastic and plastic regions and the radial displacements of the points at the symmetrical plane of the curved beam are significant. Once the value of bis obtained by experiments, the yield criterion and the corresponding solution for the materials of interest are then determined.

An elastic-plastic analysis of short-leg shear wall structures during earthquakes

Short-leg shear wall structures are a new form of building structure that combine the merits of both frame and shear wall structures. Its architectural features, structure bearing and engineering cost are reasonable. To analyze the elastic-plastic response of a short-leg shear wall structure during an earthquake, this study modified the multiple-vertical-rod element model of the shear wall, considered the shear lag effect and proposed a multiple-vertical-rod element coupling beam model with a new local stiffness domain. Based on the principle of minimum potential energy and the variational principle, the stiffness matrixes of a short-leg shear wall and a coupling beam are derived in this study. Furthermore, the bending shear correlation for the analysis of different parameters to describe the structure, such as the beam height to span ratio, short-leg shear wall height to thickness ratio, and steel ratio are introduced. The results show that the height to span ratio directly affects the structural integrity; and the short-leg shear wall height to thickness ratio should be limited to a range of approximately 6.0 to 7.0. The design of short-leg shear walls should be in accordance with the ＂strong wall and weak beam＂ principle.

Mechanical Analysis of Stretch-Bend Process

Describing stretch-bend process quantitatively is a need of the operator of tension leveller.Based on the research results of stretch-bend deformation mechanism,the mechanical behavior of stretch-bend process is analysed.

ANOMALOUS BEHAVIOR REVISITED:DYNAMIC RESPONSE OF ELASTIC-PLASTIC STRUCTURES

Based on the minimum principle of acceleration in the elastic-plastic continua under finite def ormation, the dynamic response of an elastic-perfectly plastic pin-ended beam subjected to rectangular impulse loading is studied with the help of a numerical approach. The calculated results once again show the anomalous behavior of the beam during its response process, which was previously found in [1]. By carefully analyzing the instantaneous distribution of the bending moment, the membrane force, the curvature and displacement during the response process, it is concluded that the interactive effect between the geometry and materials nonlinearities of the structure is the key reason for leading to the anomalous behavior. This will be helpful for clarifying some misunderstandings in explaining the problem before.

Stretchy Electronic Devices Assembled in a Lego-like Way

Stretchable electronics,which can function under mechanical deformations such as stretching,bending,or twisting,are comprised of various functional modules.However,the connections between these modules are often fragile,limiting the device’s overall robustness.

T型截面铝合金型材零件成组加工技术研究与应用

针对目前飞机T型材零件单件弯曲成形效率低成形精确差的问题,提出了T型材弯曲件成组拉弯成形的成组加工方法。基于截面尺寸、引导线的曲率半径等信息建立了成组分析算法,对T型材进行分组,使用长型材拉弯成形后切割分段得到符合精确外形要求的T型材零件。通过理论计算、模拟分析和拉弯试验,验证了T型材拉弯成形成组加工技术的可行性,该方法提高了零件的制造效率和成形精度,可以大幅度降低人工矫正的工作量和加工成本。

有限元分析技术在织物力学性能领域的应用

随着计算机和软件技术的快速发展,有限元分析技术展现出越来越大的潜力,已成为纺织服装领域进行力学性能研究的重要手段。为促进有限元分析技术在织物力学性能中的有效应用,更好地解决生产实践中的问题,首先从实验图像和物理几何手段两方面,阐述了目前织物几何模型的构建方法;梳理了织物材料连续模型、离散模型、半离散模型等本构模型的研究进展;其次,归纳了目前常用有限元分析软件的应用领域及优缺点,概括了有限元技术在织物拉伸、撕裂、防弹冲击、弯曲等力学性能领域的应用现状;最后指出当前研究存在模型精度不足、材料参数难确定、边界条件设置困难等不足,后续可以从应用多尺度分析方法、开发高精纺织检测仪、进行多物理场耦合模拟等方面展开研究。研究结果可用于指导生产实践,更好地解决织物力学性能的相关问题。

乳化沥青冷再生混合料材料组成对其低温抗裂性能影响研究

为解决就地冷再生混合料低温抗裂性能不足的问题,通过间接拉伸(IDT)、半圆弯曲(SCB)等试验方法研究了矿粉、机制砂和9.5 mm~19 mm粗集料对冷再生混合料低温抗裂性能的影响。研究表明:1)IDT试验断裂功(W)与SCB试验断裂能(G_(f))可较好区分不同类型冷再生混合料的低温性能,且数据变异性小(分别为12%和15%左右);2)矿粉掺量为3%时,相较不掺矿粉,W、G_(f)分别提高了116%、45%;3)机制砂掺量为20%~30%时,相较不掺机制砂,W、G_(f)可分别提高45%、37%;4)9.5 mm~19 mm粗集料掺量为10%~30%时,相较不掺粗集料,W、G_(f)可分别至少提高92%~130%、38%~50%。综上,建议冷再生混合料中9.5 mm~19 mm粗集料掺量为10%~30%、机制砂掺量为20%~30%、矿粉掺量为3%。

拉弯矫清洗设备改造升级和高效清洗工艺

对1950 mm拉弯矫机列的清洗系统现状进行阐述,对铝板带清洗质量不高的原因进行分析,并提出提高拉弯矫机列清洗质量和能力的有效清洗工艺和设备改造升级方案。

THE ELASTIC-PLASTIC BENDING AND WRINKLING OF THIN CIRCULAR PLATES

Ⅰ. INTRODUCTIONThin circular plates, a kind of the basic structural element widely used in engineering,are of the simplest plane-stress mechanical model with double curvatures. Hence, the investigation on the fundamental mechanical properties of the thin circular plates has been attracting great attention and brought about many results. Due to the difficulties

Modified couple stress and thickness-stretching included formulation of a sandwich micro shell subjected to electro-magnetic load resting on elastic foundation

This paper studies electromagnetoelastic static investigation of a sandwich doubly curved microshell subjected to multi-field loading based on a new thickness stretching included refined higher order shear/normal deformable model.Modified-couple-stress-theory(MCST)is used for accounting small-scaledependency.The numerical results are derived using an analytical method.The effect of small scale parameter in micro scale,initial electric and magnetic potentials and foundation parameters is studied on the electromagnetoelastic bending results.It is confirmed an enhancing in stiffness of small scale shell with an increase in micro length scale parameter.

钛合金型材多点三维热拉弯成形工艺及其微观组织演化

为解决钛合金等难加工材料型材的三维弯曲成形问题,提出了多点三维热拉弯成形工艺并研制了成形装备。通过成形试验探索了预拉伸量、补拉伸量和成形温度等工艺参数对TC4钛合金L形截面型材的三维热拉弯成形规律,其中成形温度是影响回弹变形的最主要因素,当温度一定时,采用预拉伸量为100%ε_(s)、补拉伸量为20%ε_(s)时(ε_(s)为屈服应变参数),型材达到最佳的成形状态。基于成形试验和材料力学性能测试结果建立了预测多点三维热拉弯成形工艺成形过程和回弹过程的有限元仿真模型,回弹预测误差小于15%,验证了模型的有效性。此外,对成形前后的TC4钛合金进行了微观组织观测,研究结果表明,与初始未变形样件相比,三维热拉弯成形后的TC4钛合金产生了相变,(101-0)晶面织构强度显著提高,两相晶粒尺寸均有所减小,TC4钛合金成形件的塑性变形能力得到了提高,且几何必需位错密度有所增大。

攀门拽伸法联合双侧椎弓根穿刺经皮椎体成形术治疗骨质疏松性椎体压缩骨折患者疗效分析

目的研究攀门拽伸法联合双侧椎弓根穿刺经皮椎体成形术(PVP)对骨质疏松性椎体压缩骨折(OVCF)患者疗效的影响及其影响因素分析。方法选择120例OVCF患者作为研究对象,将其均分为对照组与观察组。所有患者均进行双侧椎弓根穿刺PVP治疗,观察组患者在术前采取攀门拽伸法治疗。比较两组患者的手术指标、治疗效果、康复效果。结果观察组患者的手术时间、术中骨水泥灌注量高于对照组(P<0.05);观察组治疗后VAS评分、ODI指数低于对照组,cobb角高于对照组;观察组临床优良率高于对照组(P<0.05)。结论攀门拽伸法联合双侧椎弓根穿刺PVP能升高OVCF患者骨折椎体高度,降低后凸角度及降低ODI指数。

拉弯机控制系统及其多轴同步运动控制算法

针对汽车零部件的复杂拉弯工艺需求,以稳定可靠、多轴同步运动和末端速度均匀可控为目标,采用工控机和运动控制卡设计了一种双六轴的伺服拉弯机控制系统。系统软件依据MVC设计模式进行设计开发,系统硬件以运动控制卡为核心,通过EtherCAT总线对电机进行实时控制。将虚拟主轴策略引入多轴同步运动控制算法,并通过运动仿真与试验验证了控制系统的可行性。

对双峰织构类型AZ31镁合金板材力学性能各向异性的分析

目的制备双峰织构类型的AZ31镁合金板,以改善板材微观组织和弱化基面织构,研究微观组织对力学性能各向异性的影响规律,以提高镁合金板材的成形性能。方法通过弯曲限宽矫直技术对0°、30°和60°轧向切样的板材进行热加工以预制拉伸孪晶,获得双峰织构类型的AZ31镁合金板材,通过EBSD获取板材的微观组织。对RD、45°和TD方向的原始板材进行室温单向拉伸实验,获得板材的工程应力-应变曲线及力学性能参数,并计算r值(塑性应变比)与n值(应变硬化指数)。结果弯曲限宽矫直技术可诱发大量拉伸孪晶形成ED偏转织构,将偏转织构与基面织构共存的板材称为双峰织构类型AZ31镁合金板材。拉伸孪晶的出现显著细化了晶粒,弱化了基面织构强度,使板材的屈服强度下降,极大提升了材料塑性。其中30°轧向切样的板材ND面塑性力学性能各向异性的改善效果最好,其r值最小、n值最大。结论双峰织构类型能够弱化AZ31镁合金板材基面的织构强度,提高材料塑性。拉伸孪晶含量越高,板材的强度与塑性越好,力学性能各向异性的改善效果也越显著。