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1、大学本科生毕业设计外文翻译题 目：三辊卷板机辊子分析的实验验证1 .Roll bending experimentIn view of the crucial importance of the bending process, it is rather surprising to find that roller-bending process in the field has been performed in a very nonsymmetrical manner. Normal practice of the roller bending still heavily depends
2、upon the experience and skill of the operator. Working with the templates, or by trial and error, remains a common practice in the industry. The most economical and efficient way to produce the cylinders is to roll the plate through the roll in a single pass, for which the plate roller forming machi
3、ne should be equipped with certain features and material-handling devices, as well as a CNC that can handle the entire production process (Kajrup and Flamholz, 2003).Many times most of the plate bending manufacturers experience Low productivity due to under utilization of their available equipment.
4、The repeatability and accuracy required to use the one-pass production method has always been a challenging task。2. Bending analysis The plate fed by two side rollers and bends to a desired curvature by adjusting the position of center top roller in one or several passes. Bending analysis is based o
5、n some of the basic assumptions summarized below:The material is homogeneous and has a stable microstructure throughout the deformation process. Deformation occurs under isothermal conditions. Plane strain conditions prevail. The neutral axis lies in the mid-plane of the sheet. Bauschinger effect is
6、 neglected. Analysis is based on power law material model, Pre-strain is neglected. Change of material properties during deformation is neglected. Plate is with the uniform radius of curvature for supported length between bottom rollers. 2.1. Flexural strength testsThe specimens dimensions were meas
7、ured with a digital caliper (Mitutoyo Co., Kawasaki, Japan) before testing. The 3- and 4-point bending loads were applied using a universal testing machine DL2000 with a crosshead speed of 1mm/min (Fig. 1). The flexural strength () values were obtained from the 3PBT, in MPa, based on the following f
8、ormula:where P is the maximum load exerted on the specimen (N), L the distance between the supports (20mm), w the width (2mm) and b is the height of the specimen (2mm).The formula used for the 4-point flexural strength calculation was:where P is the maximum load (N), L the distance between the suppo
9、rts (20mm), w the width (2mm) and b is the height of the specimen (2mm).2.2. Fracture analysisThe fractured surfaces of the specimens were sputter coated with gold-palladium for 30s in a Denton Vacuum Desk II (serial no. 41878, Denton Vacuum Inc., NJ, USA) at a current of 45mA and a vacuum of 50mTor
10、r. They were observed in light microscopy (LM) at 60 magnification and scanning electron microscopy 2.3. Statistical analysisData obtained from the flexural tests were submitted to Students t-test for differences between composites in each flexural test and for the flexural test methods with the sam
11、e composite (=0.05). Weibull statistics were also carried out in order to obtain the shape (m) and scale (0) parameters of both composites.2.1. Geometry of bendingIn thin sheets, normal section may be considered to remain plane on bending and to converge on the center of curvature (Marciniak and Dun
12、can, 1992). It is also considered that the principal direction of forces and strain coincide with the radial and circumferential direction so that there is no shear in the radial plane and gradient of stress and strain are zero in circumferential direction. The middle surface however may extend. Fib
13、ers away from the middle surface are deformed as shown in Fig. 2. Initially the length of the fiber AB0 is assumed as l0 in the flat sheet. Then, under the action of simultaneous bending and stretching the axial strain of the fiber AB0 is of the form (1)where a is the strain associated with the exte
14、nsion of middle surface, b the bending strain and is the radius of curvature of the neutral surface.2.2. Moment per unit width for bending without tensionIn the case of simple bending without applied tension and where the radius of curvature is more than several times the sheet thickness, the neutra
15、l surface approximately coincides with the middle surface. If the general stressstrain curve for the material takes the form (2)Then, for the plastic bending, applied moment per unit width can be of the form (Marciniak and Duncan, 1992)2.3 Elastic spring back in plates formed by bendingIn practice,
16、plates are often cold formed. Due to spring back, the radius through which the plate is actually bent must be smaller than the required radius. The amount of spring back depends up on several variables as follows (Raval, 2002;Sidebottom and Gebhardt, 1979): Ratio of the radius of curvature to thickn
17、ess of plates, i.e. bend ratio. Modulus of elasticity of the material. Shape of true stress versus true strain diagram of the material for loading under tension and compression. Shape of the stressstrain diagram for unloading and reloading under tension and compression, i.e. the influence of the Bou
18、schinger effect. Magnitude of residual stresses and their distribution in the plate before loading. Yield stress (y). Bottom roller radius, top roller radius and center distance between bottom rollers. Bending history (single pass or multiple pass bending, initial strain due to bending during previo
19、us pass).Assuming linear elastic recovery law and plane strain condition (Marciniak and Duncan, 1992; Hosford and Caddell, 1993), for unit width of the plate, relation between loaded radius of curvature (R) and desired radius of curvature (Rf) can be given by3 Uncertainty analysisThe uncertainty ana
20、lysis is carried out in accordance with the McClintocks method with the following assumed uncertainties in the various parameters: Uncertainty in strain hardening exponent (n) =10%. Uncertainty in strength coefficient (K, N/mm2) =15%. Uncertainty in thickness of plate =0.29mm (5mmt 8 mm), 0.32mm (8m
21、mt10mm), 0.35mm (10mmt12mm) and 0.39mm (12mmt15mm). Uncertainty in center distance between bottom rollers (a) =1mm. Uncertainty in loaded radius (R, mm)=1%.4 ConclusionDeveloped analytical and empirical models were verified with the experiments on three-roller cylindrical bending. Following importan
22、t conclusions were derived out of the reported work: (1) For the small to medium scale fabricators, where the volume of production does not permit the acquisition of automated close loop control systems, developed models can be proved to be simple tool for the first hand estimation of machine settin
23、g parameters for required product dimensions.(2) Consideration of effect of initial strain and change of modulus of elasticity during deformation on spring back, in analytical/empirical model will further improve the accuracy of prediction of top roller position.(3) Further, empirical model based on
24、 the experimental loaded curvature distribution between roller supports would consider the top roller-plate contact point shift and will lead to more accurate prediction of top roller position.The Weibull statistics is considered to be an acceptable approach in engineering to evaluate the reliabilit
25、y of a material or component., Statistical parameters are commonly applied to data from mechanical strength tests to determine the level of structural reliability of the material strength. It provides a way of accessing the dependability of the material, disclosing the probability of failure at any
26、selected level of stress. As a measure of the variability of strength in a material and its dependence on crack size distribution.1 轧辊弯曲实验鉴于弯曲过程的至关重要性，轧辊弯曲过程使用一个非对称方式，这是相当令人吃惊的做法。轧辊弯曲的正常实践，仍主要取决于操作者的经验和技能。 与模板一起使用或经反复试验，在工业领域仍是一个普通的做法。最经济和最有效生产圆筒的方法，是钢板通过轧辊一次成型，其中根据钢板轧辊成型机的特点应配备一定物料搬运装置，以及数控系统能够处理整个
27、生产过程（kajrup和flamholz ， 2003年）。有经验的板弯曲制造商认为生产率低，是由于不能有效的利用设备。重复性和准确度，要求必须使用一次性成型的生产方式，这一直是一项具有挑战性的任务。钢板的进给由两个下辊完成，弯到一个期望的曲率，通过调整上辊的位置一次或多次滚弯。2 弯曲分析钢板的进给由两个下辊完成，弯到一个期望的曲率，通过调整上辊的位置一次或多次滚弯。弯曲的分析是基于一些基本的假设，归纳如下： 物质是均匀的，在整个变形过程有稳定的微观结构。变形发生在等温条件下以平面应变条件为准。 中性轴在板材的中间平面。 忽略Bauschinger效应 分析是基于幂律模型，即 忽略预应变。
28、忽略在变形中材料性能的改变。 下辊之间的负载长度有相同的曲率半径。2.1抗弯强度测试测试前先用数显卡尺（ mitutoyo公司，日本川崎）对样本的尺寸进行测量。 进行3 、4点弯曲载荷使用万能试验机DL2000上辊的下压速度为1mm/min（图1 ）。通过3pbt获得抗弯强度（ ）的数值，可以通过下列公式获得：其中p是施加给样本最大负荷（N）的，L为两个支撑点之间的距离（ 20mm） ，w是样本的宽度（ 2mm）和B是样本的厚度（ 2mm） 。使用四点抗弯强度的计算公式是：其中p是最大载荷（N）的，L是两个支点之间的距离（ 20mm） ，w样本的宽度（ 2mm）和B是样本的厚度（ 2mm）2.
29、2断裂分析对该样本的断裂表面进行溅射镀金，约30s、用Denton Vacuum Desk II机（型号 41878 ，Denton Vacuum Inc., NJ, USA）在目前为45马力和真空度50 摩尔 。将该断面放在在60 放大倍率的扫描电子显微镜下观察。2.3统计分析弯曲测试所得到的数据，提供给学生们让他们对不同的复合材料进行相同的弯曲试验都有相同的情况（ = 0.05 ）。威布尔统计也同样对形状系数（m）和规模系数（）进行了测试。2.1弯曲几何形状 在薄板材，正截面被认为是与弯曲面垂直并收敛于曲率中心。（marciniak和Duncan，1992年）。力和应变可分解为轴向和径向，
30、因此径向没有剪切分量，轴向应力梯度和应变为零。然而中性面可能延长。脱离中性面的变形如图2所示。最初在平板ABo的长短假定为l0根据同步弯曲和拉伸，ABo的轴向应变是 (1) a是中间面延伸的应变， b 中性面的弯曲应变，是中性面的曲率半径。 2.2无拉伸的单位弯曲宽度的弯矩 在没有拉伸的单纯弯曲的情况下，曲率半径是板厚的几倍，中性面近似为中间面。如果一般材料的应力应变曲线的形式 (2)那么，塑性弯曲单位宽度的弯矩，（ marciniak和duncan， 1992年） (3) 2.3弹性恢复在实践中，板经常由冷轧而成。由于回弹， 实际弯曲形成的半径小于要求的半径。回弹量取决以下几个参数（ rav
31、al ， 2002年; sidebottom和gebhardt ， 1979年）： 弯曲的比例即曲率半径与板材厚度的比。材料的弹性模量。 材料拉伸和压缩加载时实际应力应变。 材料拉伸和压缩卸载和再次加载时的应力-应变，即Bouschinger效应的影响。 在板加载之前残余应力的大小及分布。 y屈服应力。 下辊半径，上辊半径和下辊之间的中心距。 弯曲过程（单次或多次弯曲，初始应变由第一次弯曲引起）.假设线性弹性恢复规律和平面应变条件(Marciniak and Duncan, 1992; Hosford and Caddell,1993)，单位宽度的钢板，加载时的实际曲率半径和期望的曲率半径的关
32、系3 不确定性分析 不确定性分析，按照mcclintock的方法，具有下列各项参数的假设： 应变硬化指数不确定性，(n) = 10 。强度系数不确定性(K, N/mm2) =15%。 厚度的钢板不确定性= 0.29毫米(5mmt 8 mm), 0.32mm (8mmt10mm), 0.35mm(10mmt12mm) and 0.39mm (12mmt15mm).。 两下辊中心距的不确定性(a) =1mm.负载半径的不确定性(R,mm)=1% 。 4 结论对三辊卷板机辊子分析的实验验证，推导出以下重要结论： （1）对于中小型规模的生产厂家，由于其生产量小，所以不需要购买自动闭环控制系统，发展模式被证明是估算所需产品机械参数的最简便的工具。（2）在回弹过程，初应变和弹性模量变化的影响，分析/实证模型，将进一步提高上辊位置的计算精度。（3）实证模型在实验研究的基础上，考虑辊之间加载时的曲率分布及辊板接触点的偏移，将更准确地计算上辊位置。在工程中的应用，评估一个材料或元件的可靠性，威布尔统计，被认为是可以接受的办法。它提供了一个辨别的可靠性材料的方式，它披露失效概率在任何选定的水平的压力下都存在。作为衡量物理性能的量是一个物质和其依赖于裂纹尺寸分布， 即使是在形状系数较高时，平均断裂强度也可能略低，往往是较低的形状系数具有较高的平均断裂强度。
