高温超塑性拉伸大变形测量装置与方法研究

发布时间：2018-06-23 18:04

本文选题：视觉测量 + 超塑性拉伸　；参考：《吉林大学》2017年硕士论文

【摘要】：超塑性拉伸试验一直以来是进行超塑性研究的重要基础,是研究材料超塑性、测定材料参数和性能指标等最普遍、最简单的实验方法,也是进一步揭示超塑性变形本质与变形规律,连接超塑性微观变形机制与宏观变形规律的重要方法和途径。在超塑性拉伸试验中,由于试样是在高温炉内被拉伸,无法使用引伸计来测量其伸长量ΔL,一般均将活动横梁的位移作为ΔL,并以此来计算应力、应变和应变速率等力学参数,这在均匀变形阶段基本可满足精度要求。但当试样进入几何失稳而产生颈缩时,试样上各处的变形并不均匀,此时继续用横梁位移ΔL来推算力学参数将会产生较大的误差。此外,横梁位移并不能准确反映ΔL,它把试样上标距以外部分的变形、夹具与试样夹持部分可能产生的打滑、以及试验机力传递环节间可能存在的某些间隙等都包含其中,这对一些延伸率很小的材料在拉伸时将产生较大的误差。因此,要获得准确的试验结果,就必须能够精确测量试样标距范围内的变形,包括横截面变化。此外,由于无法测量拉伸过程中试样颈缩的产生与发展,对于超塑性拉伸失稳尤其是断裂的研究,一直是个难点,未能有大的突破。因此本文设计一种适用于高温超塑性拉伸试验大变形非接触测量装置和方法。其组成,工作原理,应用和误差分析如下:(1)该装置由计算机、十字工作台和立柱、两台性能相同的数字摄像机、可调云台、条形光源组成,其中立柱和条形光源垂直固定在十字工作台台面上,两台摄像机与可调云台一体,安装在立柱上,且摄像机间的距离可调。(2)基于上述装置,运用小孔成像原理进行摄像机标定和图片拼接。应用摄像机对拉伸试验过程进行连续拍摄,同时应用Halcon软件对这些图片进行保存、提取、处理操作,最终输出试样轮廓坐标进而测算试样纵向和横向变形,颈缩产生、移动和发展过程。(3)应用上述方法对圆棒和板试样在常温拉伸实验过程中的形变进行测量,计算出常温颈缩位置和变化情况,测量精度较横梁位移法有大幅度提升。(4)总结分析常温实验中误差产生的原因,结合高温超塑性拉伸试验高温和大变形特点针对系统误差推导出修正公式,提出相应的自标定拼接方法;针对随机误差提出相应的解决办法。(5)提出网格化测量方法并针对棒料和板材推导出相应的超塑性力学参数的求解公式。
[Abstract]:Superplastic tensile test has always been an important basis for superplasticity research. It is the most common and simple experimental method to study material superplasticity, measure material parameters and performance index, etc. It is also an important method and way to reveal the nature and law of superplastic deformation and to connect the microscopic deformation mechanism of superplastic deformation with the macroscopic deformation law. In the superplastic tensile test, because the specimen is drawn in a high temperature furnace, it is impossible to measure the elongation 螖 L by extensometer. Generally, the displacement of the moving beam is taken as 螖 L, and the mechanical parameters such as stress, strain and strain rate are calculated. This can basically meet the precision requirement in the uniform deformation stage. However, when the specimen is subjected to geometric instability and necking occurs, the deformation of the specimen is not uniform. In this case, the calculation of mechanical parameters by the displacement of the beam 螖 L will cause great errors. In addition, the displacement of cross beam can not accurately reflect 螖 L, it includes the deformation of the part outside the upper distance of the specimen, the possible slip of the clamping part between the fixture and the specimen, and some possible gaps between the force transfer link of the testing machine, etc. This will result in a large error in drawing for some materials with low elongation. Therefore, in order to obtain accurate test results, it is necessary to accurately measure the deformation within the range of sample spacing, including cross-section changes. In addition, it is difficult for the study of superplastic tensile instability, especially for fracture, because it is impossible to measure the occurrence and development of specimen necking in tensile process, and there is no great breakthrough. Therefore, a non-contact measuring device and method for large deformation in high temperature superplastic tensile test is designed in this paper. Its composition, working principle, application and error analysis are as follows: (1) the device consists of a computer, a cross table and a pillar, two digital cameras with the same performance, a adjustable cloud head and a strip light source. The upright column and the strip light source are perpendicular to the cross table, the two cameras are integrated with the adjustable cloud head and are mounted on the column, and the distance between the cameras is adjustable. (2) based on the above device, Camera calibration and image stitching are carried out by using the principle of pinhole imaging. The video camera is used to continuously shoot the tensile test process. At the same time, Halcon software is used to store, extract, process and operate the images. Finally, the contour coordinates of the sample are output, and then the longitudinal and transverse deformation of the specimen is measured and the necking is produced. (3) the deformation of round rod and plate specimen during tensile test at room temperature was measured by using the above method, and the necking position and change at room temperature were calculated. The accuracy of measurement is much higher than that of beam displacement method. (4) the causes of errors in room temperature experiment are summarized and the correction formula is deduced according to the characteristics of high temperature superplastic tensile test and large deformation. The corresponding self-calibration splicing method and the corresponding solution to the random error are proposed. (5) the gridding measurement method and the corresponding formula for solving the superplastic mechanical parameters are derived for the bar and sheet metal.
【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TB302.3

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