Large deformation pure bending of an elastic plastic power-law-hardening wide plate: Analysis and application

The large deformation pure bending of a wide plate made of a power-law-hardening material is solved. The deformation theory, the flow theory with either isotropic hardening or kinematic hardening, and the shell theory (which ignores the transverse stress) have been used in the respective analyses and their results have been compared. The solutions reveal that large curvature bending can result in a significant thickness reduction of the bent plate, and therefore the non-dimensional bending moment initially increases with the non-dimensional bending curvature, reaches a peak point, and then drops with the further increment of the non-dimensional bending curvature. When a metallic honeycomb is in-plane crushed, the maximum non-dimensional bending curvature in the cell walls (plates) can well exceed 1.5, the external energy is mainly absorbed by the plastic-hinges whose size is within the order of the cell wall (plate) thickness.     

Buckling of elastic—plastic square tubes under bending

This paper addresses the response, buckling and collapse of long, thin-walled, seamless steel square tubes under pure bending using a combined experimental and analytical approach. All tubes tested had nominal cross-sections with height equal to 1 in. (25.4 mm) and ranged in height-to-thickness ratios (h/t) from 15.4 to 28.6. The experiments were conducted under curvature control. It was found that the deformation of the cross-section that accompanied bending was uniform along the tubes for low values of curvature. At higher values, periodic ripples with wavelengths approximately equal to the width of the cross-section appeared on the compression flange. These ripples increased in amplitude with further bending. For tubes with higher h∼ the increase was more pronounced. Tubes with lower h/t showed more moderate increases in ripple amplitude but developed regions spanning several ripples in which the cross-section deformation was more pronounced. In all cases, collapse occurred when a kink formed on the compression flange of the tube.Rayleigh—Ritz type formulations based on the principle of virtual work were developed to predict the response and buckling of the tubes. Results include predictions of the response considering the effect of uniform cross-section deformation and predictions of the critical curvature at which the ripples appear. The numerical results are in good agreement with experimental observations.     

机械构件的弯曲变形与弯曲刚度

分析了影响构件弯曲变形的主要因素及弯曲刚度与弯曲变形的联系和区别。对其在概念上的不同进行论述,并分析影响机械构件弯曲的主要因素,找出提高构件刚度的有效措施是零件结构设计的主要内容。     

An exact solution for the elastic/plastic bending of anisotropic sheet metal under conditions of plane strain

A theoretical analysis for the elastic/plastic bending of sheet metal exhibiting a state of normal anisotropy is considered in this paper, assuming a plane strain condition to exist in the deformation process. The material is supposed to yield according to Hill's quadratic yield criterion and its associated normality rule of plastic flow. The relationship between the bending couple and the curvature of the bent sheet is presented in a graphical form that reveals the influence of anisotropy and strain-hardening on the bending characteristic of the sheet metal. The results indicate that the elementary bending theory significantly overestimates the magnitude of the bending couple to produce a given elastic/plastic curvature of the bent sheet.     

Plane strain elastic–plastic bending of a strain-hardening curved beam

Elastic–plastic analysis of plane strain pure bending of a strain-hardening curved beam has been presented. Only a linear hardening case has been analyzed as the nonlinear equations for a general hardening case could not be solved analytically. A numerical scheme for the computation of stresses and displacements in different stages of deformation has been given and limited FEM verifications have been presented.     

Large deflection analysis of elastoplastic plate in steady continuous four-roll bending process

This paper presents a mathematical model to simulate the mechanics in a steady continuous bending mode for four-roll thin plate bending process. The differential equations governing the large deflection bending of elastic-perfectly plastic thin plate are derived by modelling the loading and unloading deformation of the operational process. Through a semi-analytical solution of the system equations, the physical quantities of (i) the deformation and stress resultants of bend plate, (ii) the springback, (iii) the shift of contact-angle of bend plate with rolls, (iv) the applied forces on rolls, (v) the bending torque and power, and (vi) the position of the operative side roll, etc., associated with bending of a plate to an anticipated curvature, for single-pass bending operation, are predicted and discussed.     

工业构件塑变校正系统的自适应模糊控制

利用金属塑性变形后产生残余变形的原理对需校正工件主动加载,可实现工业构件的塑变校正.但塑性变形受工件的长度、直径、材质等非线性因素影响,难以建立精确的解析模型进行控制.文中在总结人工操作经验的基础上,设计了以需校正构件的塑性变形量及其变化量为输入、加载量为输出的具有自学习功能的二维模糊控制器,以达到减小误差和提高工效的目的.校正原理样机实验证明,塑变控制精度可达到0.04 mm.     

定径带长度对花键轴冷挤压弯曲变形的影响

基于刚塑性有限元技术,使用Deform-3D仿真软件模拟花键轴冷挤压过程,分析不同凹模定径带长度对挤压件弯曲变形的影响,获得了弯曲变形量随凹模定径带长度的变化规律,从而优化出最佳定径带长度。     

弹性体材料微塑性变形与称重传感器非线性

本文提出了弹性体材料微观组织的微塑性变形是产生传感器非线性的原因之一的新观点。通过对载荷、微塑性变形、应变、输出之间的关系在原理上进行分析,探讨了弹性体材料微塑性变形对称重传感器非线性的影响规律以及进程输出曲线的形状特点,并指出控制钢材成份和改进热处理工艺以减少软质相是缩小非线性的途径。     

基于误差修正模型的机翼风洞试验弯扭变形测量方法

风洞试验中,机翼在高速气流下产生弯曲、扭转变形,本文提出一种基于误差修正模型的机翼弯扭变形测量方法。 首 先,利用基于摄影测量的相机标定方法求得相机畸变参数,采用数字图像相关法定位与追踪荧光点的无畸变像素坐标。 然后根 据摄影测量技术建立气流坐标轴系标定板,并利用气流坐标轴系标定板标定相机外参及求取机翼上荧光标记点的 Y 坐标。 最 后,根据标记点已知的 Y 轴向约束,建立单双目测量系统各自的三维重建模型及弯扭变形的误差修正模型,并以模型迎角为 0° 水平时为基准状态计算吹风状态下机翼弯扭变形。 经试验验证,本文提出的机翼扭转变形测量误差小于 0. 01°,机翼弯曲变形 测量误差小于 0. 15 mm/ m。 该方法可为飞行器设计提供可靠及鲁棒的实验数据。     

利用数字全息干涉术测量电路板的连续弯曲形变

采用离轴菲涅耳数字全息干涉术实现了对电路板表面的连续弯曲形变测量。在电路板两端依次施加0.01mm至15mm位移载荷过程中,记录了1 501幅全息图。通过相邻两幅全息图数值重建的复振幅相位分布相减得到干涉相位差,根据相位差与离面位移的关系计算得到照明测量区域的离面位移,通过累加获得了施加1～15mm位移载荷时电路板表面的弯曲形变测量结果。由5块相同规格电路板上照明测量区域中同一电容中心点的离面位移,计算得到测量结果的A类不确定度不超过0.008mm,加载夹具引起的测量结果的B类不确定度为0.003 5mm,测量结果的合成不确定度不超过0.008 7mm。实验表明这种利用离轴菲涅耳数字全息干涉术测量物体大位移连续弯曲形变的方法具有良好的重复性和稳定性。     

激光冲击软模大面积微弯曲成形方法

为了实现金属箔板大面积微弯曲成形,本文结合激光冲击微弯曲成形技术与软模成形技术的优点,提出了激光冲击软模大面积微弯曲成形方法。 该方法是在脉冲激光冲击波压力下,将软模作为柔性冲头作用于金属箔板来实现工件成形的。实验中使用了Innolas Gmbit公司生产的Spitlight 2000 THG脉冲激光器,将250 μm厚的聚氨酯橡胶薄膜作为软模,采用德国LPKF-ProtoMat-C60型雕刻机在印刷电路板上加工出深度为120 μm的U型多槽模具,实现了在厚度为30 μm的铜箔板上一次性对3个U型凹槽冲击成形。用KEYENCE VHX-1000C超景深三维显微系统进行工件观测,结果显示工件上的微成形槽具有良好的轮廓质量。以ANSYS/LS-DYNA为平台,使用有限元建模（FEM）方法对微弯曲过程进行了数值模拟。实验和模拟结果均表明,加载软模的工件与模具的U型凹槽特征在形状上更加接近,成形工件更加均匀,而且具有较好的表面质量,其最大平均成形深度可达110 μm,大于激光直接冲击成形的最大深度（88 μm）,说明使用软模提高了充型能力。     

电磁声谐振对Q235钢压缩形变评价研究

结构件塑性变形检测是设备安全运维中值得注意的重要问题。针对常见的Q235钢材料塑性变形问题,提出了一种基于电磁换能器谐振模式的非接触超声检测的方法。有别于传统的超声回波反射时差法测距原理,共振所产生的谐振超声能够显著增强电磁声谐振点的声波幅值,利用超声波在试件内共振方式实现更高精确的厚度检测。通过双波压缩叠加法及双波压缩叠乘法能够有效改善电磁声谐振信噪比并实现谐振点的提取。通过对标准试件的厚度测量,其厚度测量绝对误差控制在0. 2%以下,最后利用电磁声谐振实现对不同轴向压力载荷下Q235试件的形变测量。     

On the load distribution of thin-walled beams subjected to bending with respect to the cross-section distortion

The paper deals with the estimation of the load distribution under which distortion of the cross-sections of thin-walled beams subjected to bending cannot occur. It is assumed that beam walls are hinged along their longitudinal edges. Beams with closed and open rectangular cross-sections, with three or two cells, with two or one axis of symmetry are considered. It is shown that the problem can be treated by two equivalent beams, defined by the shear flow zero points of the beam with rigid cross-section. The beam load must be distributed in the plane of beam walls, proportionally to the cross-section moments of inertia of the equivalent beams. Some illustrative examples are given.     

Influence of plastic deformation and prolonged ageing time on microstructure of a Haynes 242 alloy

The material used in this study was a commercial HAYNES® alloy 242? with a nominal composition of Ni‐25% Mo‐8% Cr (in wt.%). In the standard heat treatment, the 242 alloy is annealed at a temperature between 1065 and 1095 °C and then water quenched. The ageing treatment is carried out at 650 °C for 24 h in order to develop the long‐range‐order strengthening. The alloy in the conventionally aged condition was additionally cold rolled to 50% reduction in thickness and subsequently subjected to prolonged ageing at 650 °C for 4000 h. The enhanced diffusion resulted in the decomposition of the Ni₂(Mo,Cr) metastable phase into the stable Ni₃Mo‐based phase. The presence of the new stable phase increased the yield and tensile strengths but deteriorated the ductility of the alloy at both room and 650 °C temperatures.     

Al2O3陶瓷薄片CO2连续激光弯曲试验研究

脆性材料的激光弯曲成形技术是激光快速成形技术的重要应用,有着广阔的应用前景。本文通过改变激光功率、扫描速度等工艺参数,利用CO2连续激光对氧化铝陶瓷薄片进行弯曲试验,同时引入线能量密度来寻求适合弯曲的最佳工艺参数,并结合氧化铝陶瓷的高温性能分析了其激光弯曲特点。试验结果表明：采用CO2连续激光可以对氧化铝陶瓷薄片进行弯曲,弯曲角度可达2°;氧化铝陶瓷的激光弯曲过程具有强烈的温度敏感性,当试样表面温度大于临界温度时,弯曲角度迅速增加;适合弯曲的最佳线能量密度范围为17～24 J/mm 。     

Tribological properties of the AZ91D magnesium alloy hardened with silicon carbide and by severe plastic deformation

Results of investigation of the tribological contact characteristics of R18 tool steel in interface with AZ91D magnesium alloy hardened with SiC disperse powder filler and by severe plastic deformation (SPD)—specifically, equal-channel angular pressing (ECAP)—are presented. It is established that introduction of the SiC powder filler into the magnesium alloy increases the friction coefficient and reduces the wear rate. The size and volume of the powder filler particles, the normal load, and the relative sliding velocity influence these tribological characteristics. SPD of the original material leads to reduction of the molecular component of the friction coefficient.     

基于微塑性变形的振动时效激振力的选择

振动时效使残余应力峰值降低并得到均化的主要原因是材料内部微塑性变形的局部性。本文分析了静载荷及循环载荷下的微塑性变形行为,认为振动时效动应力的选择应以材料的疲劳极限作为依据。     

股骨颈密质骨和松质骨抗弯变形的测量方法与初步分析

提出一种新的方法,对股骨颈部位总体、密质骨和松质骨的承载特点进行分析,为今后探求这些特点与股骨颈骨折愈合关系提供基础。通过粘贴应变片和将股骨颈剖开,分别测量不同载荷下股骨颈在保持和去除松质骨时的弯曲变形。结果证明,载荷与应变成线性关系;股骨颈处有、无松质骨在同样载荷和弯曲方向时的应变之比在50％～70％之间。尽管股骨颈部位由松质骨和密质骨组成,且几何形状不规则,受力复杂,但通过粘贴应变仍可测量出股骨颈总体、密质骨和松质骨各自的承载特点：股骨颈处密质骨和松质骨总体为线弹性性质;股骨颈处密质骨的承载能力大于松质骨0～20％。