SQUID结合涡旋电流法用于铍材残余应力检测的可行性研究

【作者】 史鹏；

【导师】 李炬；

【作者基本信息】 中国工程物理研究院 ， 核燃料循环与材料， 2007， 硕士

【摘要】 金属铍材性脆，在机加焊接时很容易产生残余应力，而这可能进一步发展成裂纹等缺陷，引起材料失效，因而希望有种无损检测手段，具有一定探测深度且能快速实施对铍材残余应力状态的监测。而Barkhausen、XRD、锥孔法等常用残余应力监测手段都不能满足要求。因此，我们采用电磁场有限元计算方法，依据SMM-601型无损检测仪构建计算模型，初步研究了SQUID结合涡旋电流法对铍材内部残余应力引起的材料电导率变化的响应程度和关系，从理论上初步论证了SQUID用于铍材残余应力检测的可能性。金属材料都具有压电效应，残余应力的存在会引起电磁学属性的改变。涡旋电流法通过激发涡旋电磁场探测材料内部畸变，但传统涡旋检测法没有足够灵敏度用于残余应力检测。超导量子干涉仪直接对磁场通量强度实施测量，因而灵敏度高，此外还具有工作频带宽等优点，这为用于材料残余应力检测提供了可能性。对不同激发频率下的电磁场分布的研究结果显示：涡旋电流法的检测深度和激励频率相关，激励频率低，电磁场透入深度大，能够探测区域大，反之亦然。相应地，要检测较深区域的残余应变，激励频率需要向低频扩展。对残余应力的计算结果表明：模拟条件下，铍材单位MPa应力强度变化引起的SQUID磁通改变幅度为1.194×10^-16Wb／MPa，SQUID磁场测量灵敏度优于10^-14T／Hz^1/2，对应的磁通测量灵敏度可达10^-20Wb／Hz^1/2·mm²，本模型中SQUID梯度计的线圈半径为1.728mm，而SQUID在低频情况下仍具有较高信躁比，从测量仪器的绝对灵敏度判断SQUID梯度计能够响应残余应力的变化。该结果还显示，磁场通量的变化和材料内残余应力的强度近似成线性关系，这为实际测量时从SQUID信号进行反演获取残余应力信息提供了基础。对影响SQUID其他因素初步的研究表明：提离效应对测量结果的影响较大，这一计算结果同G.Y.Tian等人的实验结果相吻合，而温漂是另外一个需要考虑的干扰因素。此外，本文对这两种烦扰的抑制方法进行了初步讨论。初步的研究结果表明从理论上SQUID结合涡旋电流法有可能为铍材残余应力的无损检测提供一种新途径。但是要将该方法实际应用，面临的问题众多而复杂，涉及到材料、力学、电磁学、低温学等诸多领域，因此还需开展进一步的研究工作。更多还原

【Abstract】 Non-ferrous metal Beryllium was widely used in many fields for its special characters,Due to its brittleness, the beryllium components might be damaged by the residual stresscaused during machining and welding. Accordingly, itis important to examine the statusof residual stress in Be components. While industrial CT, XRD（X-Ray Diffraction） andBarkhausen methods failed to accomplish, it was needed to find a new way.Eddy Current was a NDE（Non-Destructive Evaluation） method based on testingthe changes of electromagnetic property. And,SQUID（Superconducting QUantum Inter-ference Device） has been extended to NDE since 1980s. Different from the conventionalelectromagnetical detecting method, the magnetic flux density B was directly examined bySQUID. Besides, SQUID has some other better capabilities: a wider operating frequencybandwidth, from dc to MHz, and higher sensitivity.In this paper, A method based on SMM-601 by Tristan Company was developed tomodel SQUID. The magnetic flux change in the SQUID detection coil was calculated byFinite Element Method. The dependence of residual stress on magnetic flux was com-puted. In addition, the interval effect and temperature alteration effect were discussed.What’s more, the ways to restrain the foregoing two side effects were listed and takeninto account.According to the computed results: the dependence of axial residual stress on mag-netic flux of SQUID was 1.194×10^-16Wb/MPa, and the radius of SQUID in our modelwas 1.728mm. While the sensitivity of SQUID was 10^-20Wb/Hz^1/2·mm². Therefore thischange of residual stress was measurable by SQUID. In addition, the magnetic flux changeis nearly in linear with residual stress intension.In a word, a new method based on SQUID and eddy current to examine residualstress in beryllium components was feasible. While there were still much difficulty on theway to be realized. A thorough research is needed.更多还原