Ultrasonic prediction ofR-value in deep drawing steels

The textures of five types of deep drawing steels were measured and analyzed using the series expansion method. Electromagnetic acoustic (EMAT) techniques were employed to determine the elastic anisotropy in terms of the angular variation of the ultrasonic velocities. The series expansion formalism was employed for predicting the elastic and plastic anisotropies from texture data. Comparison with the experimental measurements of Young's modulus indicates that the elastic energy method can accurately reproduce the elastic anisotropy if the single crystal elastic constants are appropriately chosen. The angular variation of ther-value in the rolling plane was calculated from the ODF coefficients by means of the pancake relaxed constraint model using an appropriate CRSS ratio for glide on the {112} 111 and {110} 111 slip systems. The fourth order and first sixth order ODF coefficients were calculatednondestructively from the anisotropy of the ultrasonic velocities. The calculated pole figures based on the ODF coefficients obtained in this way are similar to those derived from complete X-ray data. It is shown that the plastic properties of commercial deep drawing steels are predicted more accurately when the 4th-and 6th-order ODF coefficients are employed than when only the 4th-order ones are used.     

The influence of the drawing parameters and temperature rise on the prediction of chevron crack formation in wire drawing

The objective of the present work is to predict the formation of chevron crack in copper wire drawing process. The first part of this paper is to determine the chevron crack formation initiated by a central burst inside the wire material using experimental tests. These results are compared with results from a series of numerical simulations using the Cockcroft?CLatham fracture criterion. The second part of this work concerns the determination of a curve that divides the chevron and safe zones for a better wire drawing process. The conditions of central burst defects formation along the wire axis depend on drawing parameters and friction coefficient between the die and the wire. The friction coefficient is defined as a linear function of temperature rise which is measured close to the wire-die interface. The obtained results show that the friction coefficient depending on temperature rise during wire drawing has an impact on the damage of copper wire.     

Springback prediction in sheet metal forming of high strength steels

Both increased weight reduction and improved passive safety have been simultaneously required for components of new vehicle generation. Thus, advanced high strength Dual Phase (DP) steels have been progressively used when making automotive parts. During each sheet metal forming process the high strength steels exhibit distinct springback effect, which is governed by strain recovery of material after load removal. The springback is variably sensitive to materials and process parameters. Considering springback occurred in a formed part is significant for designing tools and dies. In this work, both experiments and Finite Element Analyses (FEA) of a U-shape forming test were performed and compared for investigating the springback effect. Two DP steels (JSC590R and JSC780Y) with different strengths and a mild steel (JSC270C) were taken into account. The planar anisotropic material model according to Hill’s 1948, Barlat’s yield 2000, and Yoshida–Uemori kinematic hardening model were applied in the simulations. Various mechanical testing as hydraulic bulge test, disk compression test, and in particular cyclic test under tension and compression load were carried out in order to determine required materials parameters of the models. Obviously, steel with higher yield and tensile strength definitely showed an increasing in magnitude of both springback and curling. All presented material models restricted ability to predict springback effect of the examined steels, although the Yoshida–Uemori criterion provided more accurate results than other ones. The model is therefore preferred for describing the strain recovery mechanism of high strength steels, while parameter determination plays a decisive role. The cyclic test was verified to successfully describe the kinematic behaviour of material.     

无应力氧化下C/SiC复合材料弹性性能模拟及验证

结合复合材料氧化质量损失率模型和混合率公式, 发展了单向C/SiC复合材料在无应力氧化下的弹性模量预测方法。对400~700 ℃和700~900 ℃两种氧化机制下C/SiC复合材料的弹性模量进行了预测, 分析了氧化温度、氧化时间和纤维体积含量对C/SiC复合材料弹性模量的影响。开展了单向C/SiC复合材料在650 ℃和800 ℃空气环境下的无应力氧化试验, 建立了复合材料质量损失率与氧化时间的变化关系, 得到了氧化后材料拉伸应力-应变曲线。同时, 将理论预测值与试验结果进行对比, 发现理论值与试验值基本吻合, 从而验证了该方法能够有效地预测无应力氧化下陶瓷基复合材料的弹性性能。     

Hot deep drawing of titanium sheet

Abstract

Commercial purity titanium (IMI 125) and a Ti–Cu alloy (IMI 230) in sheet form have been deep drawn at room temperature and at elevated temperatures. Cylindrical cups drawn at room temperature and at temperatures up to about 550°C develop four ear peaks at about 45° to the rolling direction (RD). When drawing is carried out at temperatures above 600°C, two ear peaks are formed at 90 and 270° to RD. The change in anisotropy is attributed to the temperature dependence of crystallographic slip modes, the high temperature behaviour being associated with basal plane slip. Drawing with a temperature gradient (cold punch, heated die) enables high drawing ratios to be achieved.

MST/1352     

Influence of tool geometry variations on the limiting drawing ratio in micro deep drawing

In this study, the impact of different tool geometries on the limiting drawing ratio (LDR) in micro deep drawing was investigated. Experimental micro deep drawing tests to determine the limiting drawing ratios were carried out for a variation of the punch diameter, the die radius and the die clearance. In order to assess the impact of the material properties on the process limits the foil materials Al99.5 and E-Cu58, both with a thickness of 20 μm, and the stainless austenitic nickel-chromium steel 1.4301 (X5CrNi18-10) with a thickness of 25 μm were investigated. The results reveal an increase of the limiting drawing ratio with increasing die radius size for the foil materials E-Cu58 and austenitic steel. For a decrease of the die clearance to values smaller than 1.25 times the foil thickness an increase of the limiting drawing ratio was determined for all three materials.     

小直径厚壁管材变曲率弯曲回弹预测

为快速、准确地预测管材变曲率的弯曲回弹,建立变曲率弯曲回弹预测的解析模型.基于ABAQUS平台建立小直径厚壁管材变曲率弯曲成形及回弹数值模拟模型,通过试验验证了所建模拟方法的可靠性.将变曲率回弹问题转化为离散定曲率回弹问题进行研究,通过近似纯弯曲回弹实验,建立管材定曲率弯曲回弹前后半径之间的函数关系式,将变曲率弯管轴线双圆弧拟合逼近离散,针对离散化的回弹弯管进行G1连续拼接,依据轴线复杂程度,构建拼接修正函数,建立管材变曲率弯曲回弹预测解析模型.通过2个试验算例验证该解析模型能够有效预测小直径厚壁管材平面变曲率弯曲回弹.回弹的准确预测是有效控制弯管回弹缺陷的前提,用于指导后续模具型面修正,补偿回弹误差,保证弯管几何精度.     

基于Yoshida-Uemori材料模型的汽车结构件冲压回弹分析

Yoshida-Uemori随动硬化材料模型能够准确描述应变路径发生变化时材料性能的改变,从而较好地反映复杂加载情况下材料的各向异性.本文基于JSTAMP件分别采用Yoshida-Uemori随动硬化材料模型和各向同性硬化材料模型对汽车高强钢结构件的冲压成形进行了仿真分析与回弹预测,研究了不同材料硬化模型对回弹预测精度...     

Analysis of sheet steel fracture during deep drawing

Low-carbon steel sheet used for the fabrication of automotive brake components was tearing during deep drawing. The associated mill certificates revealed that the coil met the specified chemical composition and mechanical properties. Metallographic evaluation revealed a severe variation with respect to grain size through the thickness of the steel sheet, as well as a slight segregation of pearlite. Insufficient temperature during hot rolling in combination with a high coiling temperature resulted in the observed microstructural gradient. The anisotropic mechanical properties were amplified by the slight carbon segregation.     

简单形状零件拉深成形智能化控制技术研究

板材成形智能化是冲压工艺的一项新技术.以圆锥形件和锥壁盒形件为研究对象,分别讨论了实现实时监测、实时识别、实时预测和实时控制所需的关键技术,逐步形成了拉深成形智能化控制的理论基础.在实时识别和实时预测阶段采用人工神经网络,在压边力控制阶段采用基于破裂临界曲线的控制方法,能够得到较满意的结果.研究过程中开发了智能化拉深实验系统,实验证明识别、预测精度较好.     

Experimental validation of numerical sensitivities in a deep drawing simulation

Deep drawing of a benchmark B-pillar is numerically modelled and experimentally performed with varying blankholder force and several blank shape parameters. The most influential parameters are selected for optimisation. Direct application of Autoform sigma software was used to determine sensitivities, as well as indirect application using response surfaces. Interesting nonlinear sensitivities were found that will be missed with simple linear screening techniques.     

The manufacture of ultra-high modulus polyethylenes by drawing through a conical die

Various grades of linear polyethylene have been drawn through a heated conical die at 100° C. It was found that after a suitable start-up procedure, continuous drawing was possible in all cases with a stable neck region extending beyond the die exit. The degree of deformation attainable was found to depend strongly on the draw velocity. Very high deformation ratios could be obtained and the Young's moduli of the die-drawn products were comparable to those of similar products obtained by solid state extrusion and tensile drawing, reaching values as high as 60 GPa. The effects of molecular weight and co-polymerization are substantial, but not exactly analogous to those previously observed in hydrostatic extrusion and tensile drawing. This is probably due to the non-isothermal nature of the final stage of deformation in the case of die drawing.     

Systematic back-calculation protocol and prediction of resilient modulus for MEPDG

A research focusing on the characterisation of representative local material properties was conducted to facilitate the full implementation of the Mechanistic-Empirical Pavement Design Guide for roadway designs in Wyoming. As part of the test program, falling weight deflectometer deflection data were collected from 25 test sites in Wyoming for back-calculation of subgrade resilient modulus. Also, subgrade materials from these test sites were sampled for laboratory resilient modulus measurement in accordance with the AASHTO T 307. The back-calculation is a user-dependent procedure and produces a non-unique resilient modulus estimation. To alleviate this limitation, this paper focuses on the recent development of a systematic back-calculation protocol for subgrade resilient modulus using MODCOMP6 software. The protocol is intended for use on a flexible pavement with a crushed base. The proposed procedure discusses pre-analysis checks, seed modulus adjustment, pavement structure adjustment and program termination criteria. A correlation study was conducted to correct back-calculated resilient modulus to laboratory-equivalent values. The results conclude that a non-zero intercept linear regression model provides a better correlation than the widely used zero intercept linear regression model. Furthermore, better correlations are achieved when the back-calculated resilient modulus of a lower subgrade layer and resilient modulus measured at higher laboratory test sequences Nos. 11 to 15 are considered. The non-zero model based on M_r test sequence No. 14 and lower subgrade layer yields the best correlation. For the zero model, a C-factor of 0.645 based on M_r test sequence No. 15 and lower subgrade layer yields the best correlation.     

复合泡沫塑料模量和屈服强度的理论预测

基于广义自洽原理,利用四相球模型研究了复合泡沫塑料在拉伸加载下的力学性能,并对其可能发生的破坏进行了分析,发现模型退化后给出的泡沫材料强度预测结果与实验值符合较好。通过分析微珠与基体界面的法向应力集中系数和基体相的von Mises应力分布,可以发现,当微珠壁极薄时,微珠的力学行为与实心柔性粒子相似,随着微珠壁厚的增加,微珠对材料整体力学行为的影响与实心刚性粒子的影响接近相同。通过引入破坏影响因子,对复合泡沫塑料的强度预测进行研究,提出了一种有效的预测方法。     

Allocation of variance reduction targets under the influence of supplier interaction

A common quality improvement strategy used by manufacturers is to periodically allocate quality improvement targets among their suppliers. We propose a formal modelling and optimization approach for assessing quality improvement targets for suppliers. In this approach it is understood that a manufacturer's quality improvement results from reductions in supplier process variances, which occurs only through investments in learning. A constrained nonlinear optimization model is developed for determining an optimal allocation of variance reduction target that minimizes expected total cost, where the relationship between performance measures and the set of design parameters is generally represented by second-order polynomial functions. An example in the fabrication of a tyre tread compound is used both to demonstrate the implementation of our proposed models as well as to provide an empirical comparison of optimal learning rates for different functional relationships between the performance measures and the set of design parameters.     

Explicit FEM analysis of the deep drawing of paperboard

An explicit finite element model of the deep-drawing of paperboard has been developed utilizing a custom yet simple material model which describes the anisotropy and plasticity of paperboard. The model was verified with a variety of tests and was then utilized to compare the punch force that was measured during the deep-drawing experiments to the punch force that was calculated during the deep-drawing simulations. All material parameters were calibrated based on individual experiments; thus, no parameter fitting was utilized to match the experimental deep-drawing results. The model was found to predict the experimental results with reasonable accuracy up to the point when wrinkling began to dominate the material response. Since most failures during paperboard deep-drawing occur before wrinkling begins to play a major role, this model can probably be utilized to study and predict the failure of deep-drawn paperboard cups. The overall trends and the effects of major process parameters are predicted by the model. The process parameters that were varied and compared for both experiments and simulations were: blankholder force, die temperature, and thickness. The model was utilized to discover that friction of the blankholder and die have significant effects on the punch force and thus the stress, implying that low-friction dies and blankholders can considerably reduce the failure probability and thus also improve the quality of deep-drawn paperboard cups.     

Numerical analysis of hydroforming deep drawing of conical cup

Aided by the FE-code, analysis is carried to find the proper hydroforming deep-drawing condition for the perfect forming of a conical cup that can not be drawn successfully by conventional deep drawing method. Hydraulic counter pressure must be reasonably controlled, otherwise defects such as fracture and wrinkling can not be avoided. Therefore, the forming procedure is divided into three stages, and the counter pressure is adjusted intentionally to make the blank clamped onto the punch at a suitable time, then deformation at dangerous area is resisted by the effect of the counter pressure and the conical cup can be formed without defects.     

Blank design optimization on deep drawing of square shells

A numerical scheme for improving the drawability in the deep drawing of square shells by blank design optimization is presented. The numerical scheme is formulated as an optimization problem whose objective is to maximize the drawability, subject to the constraint that fracture failure and draw-in failure do not occur. Appropriate blank design parameters are used as the design variables of the formulation. To enable the numerical scheme to work models predicting the onset of fracture failure and draw-in failure are required. Numerical models simulating the onset of these failures under the given process conditions are thus discussed. Optimal designs for three cases are then presented. Finally, by considering both the drawability and the non-uniformity of the final flange profile it is shown that the circular profile can be considered to be the optimal blank shape for square cup drawing.