兰州大学机构库 >土木工程与力学学院
基于数字图像相关法的材料低温下断裂特性及超导带材失超实验研究
Alternative TitleExperimental Study on Fracture Characteristics and Quench Behaviors of Superconducting Tapes under Cryogenic Temperature Using DIC
王淑丹
Thesis Advisor王省哲
2018-04-08
Degree Grantor兰州大学
Place of Conferral兰州
Degree Name硕士
Keyword数字图像相关方法 低温环境 超导材料 断裂力学 应力强度因子 过电流失超
Abstract

极端复杂环境下材料的多场性能及力学变形测量是当前实验技术研究领域面临的基础难题与挑战。数字图像相关(Digital image correlation DIC)方法是通过图像区域的相关性来获取、分析物体位移、应变等力学量的一种光学测试方法,其具有非接触、全场以及抗电磁干扰等显著优点近年来备受关注。基于DIC 测试方法,本文开展了低温环境下材料的断裂特性及超导带材过载流失超现象的实验研究。
首先,针对典型的断裂力学基本问题——带有中心裂纹的巴西圆盘,开展了圆盘径向压缩下的断裂实验研究。基于I 型裂纹的应力强度理论,并结合DIC 测试图像,获得了圆盘变形特征以及裂纹尖端处的应力强度因子等,实验测试结果与经典理论预测结果吻合良好,验证了DIC 测试方法在结构断裂测试中的有效性。其次,为了实现可视化的低温测试环境,自主试制了可视化低温测试杜瓦(基于热传导冷却模式,可实现293K~77K 变温), 采用DIC 测试方法,开展了带有单边裂纹的金属铜带材的力学拉伸实验研究,测量了其低/变温环境下的力学行为(包括全场位移、应变等)与温度的依赖关系等,分析获得了其裂纹尖端处的应力强度因子等断裂特性。进一步地, 基于有限元软件Comsol, 对上述实验过程进行了相应的数值仿真研究,获得的定量仿真结果与实验测试结果吻合良好。最后,基于非接触的DIC 测试方法,开展了高温超导带材过电流失超情形下的力学特性研究,获得了超导带材从超导态到正常态演化过程中的全场应变云图。结果表明:DIC 测试方法能够清晰、直观地呈现高温超导带材整个失超过程中应变的变化特征,并有望成为一种基于全场应变的超导结构失超非接触检测新方法。通过将失超发生时的应变信号与电压测试信号进行对比和分析,提出了全场应变判断失超的临界判据。考虑到理想超导带材过电流失超发生时其失超触发位置具有随机性,我们采用中心开洞的超导带材进行了过电流失超实验。研究结果表明:失超发生时圆孔附近的应变先增大,并逐渐向周边传播,该方法能够直观地表征其失超传播的特性。本文的实验研究与探索可望为超导材料低温多场下力学性能测试,特别是超导失超过程中的全场应变测试提供一种新的方法与技术。

Other Abstract

The measurement of multi-field performance and mechanical deformation of materials in extremely complex environments are the main challenges faced by current experimental technology research. The digital image correlation (DIC) method is a new optical test method for obtaining mechanical quantities such as displacements and strains through the correlation of image region. It has attracted a lot of attention due to its remarkable advantages such as non-contact, full-field and anti-electromagnetic interference. Based on the DIC test method, this paper carried out the
experimental research on the fracture characteristics of materials under low temperature as well as the phenomenon of overcurrent  quench of superconducting tapes.
First of all, aiming at the basic problem of fracture mechanics, i.e., the Brazilian disc with a central crack, the fracture test under radial compression of the disc was carried out. Based on the
I-type crack stress intensity theory and combined with the DIC optical measurement method, the disc deformation characteristics and the stress intensity factor at the crack tip were obtained. The
experimental results agree well with the theoretical prediction results, which confirm the effectiveness of the DIC method in the fracture test.Secondly, in order to achieve visualized low-temperature test environment and facilitate the application of DIC optical measurement methods, we have independently produced a visualized low-temperature test named Dewar (based on a heat conduction cooling mode, whose temperature interval is 293K to 77K).Experiments on the mechanical properties of metallic copper strips under different low/varied temperature environments has been done. The DIC method was used to test the external full-field displacement and strain information of the metal strip under external load and low-temperature environment, and the fracture characteristics such as stress intensity factor at the crack tip were obtained. Furtherly, the corresponding numerical simulation was carried out by using the finite element software of Comsol. The quantitative simulation results are in accordance to the experimental test results.Finally, based on the non-contact and full-field strain test of the DIC photometric method,mechanical properties of the high-temperature superconducting tape under the over-current quenching was studied, and the full-field strain map of the superconducting tape during evolution from the superconducting state to the normal state was obtained. The results indicate that the DIC test method can clearly and intuitively present the characteristics of the strain change during the entire quenching.process of the high temperature superconducting tape, which is expected to be a novel non-contactquenching method for superconducting structures based on the full field strain. By comparing and analyzing the strain signal with the voltage test signal at the time of the occurrence of quench, the critical criterion for judging the quench of the full-field is proposed. Considering the randomness of the ideal superconducting tape start position at the time of the over-current quench, superconducting tape with a center opening was used. The quenching experiment showed that the strain near the round hole increased firstly when the quench occurred, followed by the deformation of the surrounding area and then gradually expanded to the surroundings, thus  characteristics of superconducting quench propagation could be visually demonstrated.A new method and technique for superconducting material’s multi-field mechanical properties testing under low-temperature is proposed in this paper, especially for superconductor quenching.

URL查看原文
Language中文
Document Type学位论文
Identifierhttps://ir.lzu.edu.cn/handle/262010/226249
Collection土木工程与力学学院
Recommended Citation
GB/T 7714
王淑丹. 基于数字图像相关法的材料低温下断裂特性及超导带材失超实验研究[D]. 兰州. 兰州大学,2018.
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