發(fā)布時間：2018-04-08 14:58

  本文選題：應力集中　切入點：金屬磁記憶檢測　出處：《天津科技大學》2017年碩士論文

【摘要】：應力集中一直是工程界普遍關注的問題。構件存在應力集中會造成其承載能力降低,嚴重時會使運行中的承載構件突然斷裂,導致災難性事故的發(fā)生。因此,最好的解決辦法是可以對工作中的構件進行實時監(jiān)測,及時發(fā)現(xiàn)應力集中及早期損傷,降低突發(fā)性事故的發(fā)生率。傳統(tǒng)的無損檢測技術雖然已經在工程中得到了廣泛的應用,但主要的檢測對象是構件上已經存在的缺陷,對于那些由于應力集中等引起的早期損傷并不能檢測出來。金屬磁記憶檢測技術的出現(xiàn),使鐵磁構件的早期診斷成為可能,該技術是利用地磁場環(huán)境,通過檢測構件由于應力集中引起的表面漏磁場變化來判斷損傷部位以及損傷程度。由于發(fā)展時間較短,該技術還不是很成熟,且檢測過程中受到的影響因素較多,目前只是作為判斷鐵磁構件應力集中位置的一種初步檢測方法,還需要其他檢測方法進行復檢,且不能提供量化結果。在該技術中,常用的磁參數(shù)是自有漏磁場法向分量以及其在長度方向上的梯度值。在現(xiàn)階段大多數(shù)的實驗研究中,主要是對試件表面應力集中區(qū)域上所作的一些測量線進行檢測并研究磁記憶信號變化情況,并通過法向磁記憶信號曲線過零點來判斷應力集中位置,但一些實驗研究也表明,通過此方法來判斷試件的應力集中位置不是十分準確。針對此問題,本文首先對不同直徑的中心小孔試件加載并進行磁記憶檢測,研究試件表面小孔附近測量線上法向磁記憶信號變化過程,并進行力學仿真分析磁記憶信號與應力集中的關系;其次,分別對預制中心圓孔和兩半圓槽試件進行磁記憶檢測,提出了通過法向磁記憶信號在兩個方向上的梯度來判斷試件應力集中位置的方法,主要內容和結論包括:(1)對一系列不同直徑中心小孔試件拉伸加載并進行磁記憶檢測,觀察試件經拉伸后法向磁記憶信號變化情況,并進行力學仿真得到受載試件在不同拉伸載荷下,不同位置應力集中系數(shù)相同而磁記憶信號過零點位置不同的現(xiàn)象,得出僅根據(jù)法向磁記憶信號過零點判斷受載試件應力集中位置方法欠妥的結論。(2)在彈性階段內,對中心圓孔試件表面劃分網格后進行拉伸,對不同載荷下試件表面上的網格點進行磁記憶信號采集,提出了通過法向磁記憶信號在檢測平面長和寬兩個方向上的梯度來判斷試件應力集中位置的方法。此外,利用COMSOL軟件對試件在彈性階段內的受力情況進行了仿真,發(fā)現(xiàn)應力與法向磁記憶信號梯度成正比關系,得出可通過法向磁記憶信號在兩個方向上的梯度判斷受載試件的應力集中位置。(3)對兩半圓槽試件加載并進行磁記憶檢測,該實驗與中心圓孔試樣的實驗方法完全相同,進一步驗證了通過法向磁記憶信號在試件長和寬兩個方向上的梯度來判斷應力集中位置方法的可行性。
[Abstract]:Stress concentration has always been a common concern in engineering circles.The stress concentration of the member will lead to the decrease of its bearing capacity, and when it is serious, it will suddenly break the bearing member in operation and lead to the occurrence of catastrophic accident.Therefore, the best solution is to monitor the components in real time, to find stress concentration and early damage in time, and to reduce the incidence of sudden accidents.Although the traditional nondestructive testing technology has been widely used in engineering, the main detection object is the existing defects on the components, which can not be detected for the early damage caused by stress concentration.The appearance of metal magnetic memory detection technology makes it possible for the early diagnosis of ferromagnetic components. The technique uses geomagnetic field environment to judge the damage location and damage degree by detecting the change of magnetic field leakage on the surface of the components due to stress concentration.Because of the short development time, the technology is not very mature, and there are many influencing factors in the testing process. At present, it is only a preliminary detection method to judge the stress concentration position of ferromagnetic components, and other detection methods are needed for re-examination.And can not provide quantitative results.In this technique, the commonly used magnetic parameters are the normal component of the self-leakage magnetic field and its gradient value in the length direction.In most of the experimental studies at present, some measuring lines in the stress concentration area of the specimen surface are detected and the changes of the magnetic memory signal are studied.The zero-crossing point of the normal magnetic memory signal curve is used to determine the stress concentration position, but some experimental studies also show that it is not very accurate to judge the stress concentration position of the specimen by this method.To solve this problem, this paper first loads the specimen with different diameter and carries on the magnetic memory detection, studies the change process of the normal magnetic memory signal on the measuring line near the small hole on the surface of the specimen.The relationship between the magnetic memory signal and the stress concentration is analyzed by mechanical simulation. Secondly, the magnetic memory test of the prefabricated central circular hole and the two semicircular groove specimens are carried out respectively.A method is proposed to determine the stress concentration position of the specimen by the gradient of the normal magnetic memory signal in two directions. The main contents and conclusions include: 1) tensile loading and magnetic memory detection of a series of specimens with different diameter center holes.The change of normal magnetic memory signal after tensile is observed, and mechanical simulation results show that the stress concentration coefficient is the same at different positions and the crossing position of magnetic memory signal is different under different tensile loads.It is concluded that only the zero crossing point of normal magnetic memory signal is used to determine the stress concentration position of loaded specimen. The conclusion is that in the elastic stage, the surface of the specimen with a central circular hole is meshed and stretched.The magnetic memory signal was collected from the grid points on the surface of the specimen under different loads. A method to determine the stress concentration position of the specimen was proposed by measuring the gradient of the normal magnetic memory signal in the direction of the length and width of the plane.In addition, the stress of the specimen during the elastic stage is simulated by COMSOL software. It is found that the stress is proportional to the gradient of the normal magnetic memory signal.It is concluded that the stress concentration position of loaded specimen can be determined by the gradient of normal magnetic memory signal in two directions) and the magnetic memory test can be carried out on two semicircular grooves. The experimental method is identical to that of the specimen with central circular hole.The feasibility of the method to determine the stress concentration position is further verified by the gradient of the normal magnetic memory signal in both the length and width directions of the specimen.
【學位授予單位】：天津科技大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TG142.15

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