基于金属磁记忆检测技术对Q235钢应力集中的研究

发布时间：2018-04-08 14:58

本文选题：应力集中　切入点：金属磁记忆检测　出处：《天津科技大学》2017年硕士论文

【摘要】：应力集中一直是工程界普遍关注的问题。构件存在应力集中会造成其承载能力降低,严重时会使运行中的承载构件突然断裂,导致灾难性事故的发生。因此,最好的解决办法是可以对工作中的构件进行实时监测,及时发现应力集中及早期损伤,降低突发性事故的发生率。传统的无损检测技术虽然已经在工程中得到了广泛的应用,但主要的检测对象是构件上已经存在的缺陷,对于那些由于应力集中等引起的早期损伤并不能检测出来。金属磁记忆检测技术的出现,使铁磁构件的早期诊断成为可能,该技术是利用地磁场环境,通过检测构件由于应力集中引起的表面漏磁场变化来判断损伤部位以及损伤程度。由于发展时间较短,该技术还不是很成熟,且检测过程中受到的影响因素较多,目前只是作为判断铁磁构件应力集中位置的一种初步检测方法,还需要其他检测方法进行复检,且不能提供量化结果。在该技术中,常用的磁参数是自有漏磁场法向分量以及其在长度方向上的梯度值。在现阶段大多数的实验研究中,主要是对试件表面应力集中区域上所作的一些测量线进行检测并研究磁记忆信号变化情况,并通过法向磁记忆信号曲线过零点来判断应力集中位置,但一些实验研究也表明,通过此方法来判断试件的应力集中位置不是十分准确。针对此问题,本文首先对不同直径的中心小孔试件加载并进行磁记忆检测,研究试件表面小孔附近测量线上法向磁记忆信号变化过程,并进行力学仿真分析磁记忆信号与应力集中的关系;其次,分别对预制中心圆孔和两半圆槽试件进行磁记忆检测,提出了通过法向磁记忆信号在两个方向上的梯度来判断试件应力集中位置的方法,主要内容和结论包括:(1)对一系列不同直径中心小孔试件拉伸加载并进行磁记忆检测,观察试件经拉伸后法向磁记忆信号变化情况,并进行力学仿真得到受载试件在不同拉伸载荷下,不同位置应力集中系数相同而磁记忆信号过零点位置不同的现象,得出仅根据法向磁记忆信号过零点判断受载试件应力集中位置方法欠妥的结论。(2)在弹性阶段内,对中心圆孔试件表面划分网格后进行拉伸,对不同载荷下试件表面上的网格点进行磁记忆信号采集,提出了通过法向磁记忆信号在检测平面长和宽两个方向上的梯度来判断试件应力集中位置的方法。此外,利用COMSOL软件对试件在弹性阶段内的受力情况进行了仿真,发现应力与法向磁记忆信号梯度成正比关系,得出可通过法向磁记忆信号在两个方向上的梯度判断受载试件的应力集中位置。(3)对两半圆槽试件加载并进行磁记忆检测,该实验与中心圆孔试样的实验方法完全相同,进一步验证了通过法向磁记忆信号在试件长和宽两个方向上的梯度来判断应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.
【学位授予单位】：天津科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG142.15

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