基于磁记忆的建筑钢结构应力表征技术研究

发布时间：2018-07-18 07:49

【摘要】：常规钢结构无损检测技术只能对宏观缺陷进行检测,对未形成明显物理不连续的隐性损伤无法识别。金属磁记忆检测技术(MMMT)作为一门新兴的无损检测技术,可利用地磁场的特殊反应特性有效检测铁磁材料内部微观缺陷和局部应力集中,以进行隐性损伤检测。然而该技术研究仅仅局限于材性试件的单轴拉伸试验,受力形式单一,无法满足钢结构中主要承重结构检测的要求。因此,本文将理论与试验相结合,重点研究了基于材性的钢平板试件三点受弯试验和基于构件的钢梁四点受弯试验,分析不同应力作用下的磁记忆信号变化规律,提出适用于建筑钢结构受弯构件的应力表征参数。主要进行了以下工作:(1)通过理论与模型分析,解释了金属磁记忆检测技术对钢结构隐性损伤进行检测的原因,探讨了常规应力表征参数在建筑钢结构检测中的适用性。表明:由于磁机械效应存在,使得铁磁构件的磁记忆信号与其应力应变之间存在必然联系;法向磁场Hp(y)过零点仅能反应试件在断裂后的应力状态,对弹塑性阶段的磁记忆信号变化趋势不明显。(2)通过对Q235B钢平板试件三点受弯试验,研究了基于材性的建筑钢结构应力表征参数。结果表明:随着横向荷载的增大,磁记忆信号强度Hp(y)也逐渐增大并在应力集中部位出现“波峰”或者“波谷”现象;磁记忆信号梯度K在应力集中部位出现“峰-峰”值变化且过零点,可用来判断试件的应力集中区域,实现早期损伤定位的初步判断。受拉面的Hp(y)??曲线在屈服强度附近迅速增长并出现“拐点”,而受压面的Hp(y)??曲线呈线性增大关系,无明显“拐点”,借助Hp(y)??曲线的“拐点”所对应的应力,可以表征受弯试件受拉边的屈服强度。(3)通过对Q235B钢梁四点受弯试验,研究建筑钢结构磁场表征应力参数,对受弯试件不同部位的应力集中进行有效评判。磁记忆信号曲线形状变化趋势与试件在竖向荷载作用下的弯曲图具有较强的相似性,可利用磁记忆信号在检测线上的变化曲线预测受弯试件的弯矩分布情况。“过零点”现象可近似确定翼缘屈曲后应力集中的位置,但存在“零点漂移”现象。腹板磁记忆信号峰值评判试件的应力集中区,峰值越大,表明试件应力集中程度越高,已发生屈曲的可能性越大,其梯度曲线峰-峰值maxK可作为构件屈曲前危险时刻的判断依据。(4)磁记忆信号与弯曲拉应力之间存在必然的联系,试件翼缘表面的Hp(y)??曲线与试件的应力应变曲线表现出相似的变化趋势,随着试件翼缘受力状态的不同,磁记忆信号表现出与之对应的状态。腹板表面磁记忆信号与其水平压应力之间呈线性关系,无明显的拐点。相同应变下,磁记忆信号强度存在差值,目前仅适用于定性评判。
[Abstract]:The conventional nondestructive testing technique of steel structure can only detect macroscopic defects, but can not identify the hidden damage without obvious physical discontinuity. As a new nondestructive testing technique, metal magnetic memory testing (MMMT) can effectively detect the microscopic defects and local stress concentration in ferromagnetic materials by using the special response characteristics of geomagnetic field to detect hidden damage. However, the study of this technique is limited to uniaxial tensile test of material specimens, and the stress form is single, which can not meet the requirements of the main load-bearing structures in steel structures. Therefore, combining theory with experiment, this paper focuses on the three-point bending test of steel plate specimen based on material property and the four-point bending test of steel beam based on component, and analyzes the variation rule of magnetic memory signal under different stress. The stress characterization parameters suitable for bending members of steel structures are presented. The main works are as follows: (1) through theoretical and model analysis, the reasons of metal magnetic memory testing technology for detecting hidden damage of steel structures are explained, and the applicability of conventional stress characterization parameters in the detection of building steel structures is discussed. The results show that due to the existence of magneto-mechanical effect, there is an inevitable relationship between magnetic memory signal and stress and strain of ferromagnetic component, and the normal magnetic field HP (y) zero crossing point can only reflect the stress state of the specimen after fracture. The change trend of magnetic memory signal in elastic-plastic stage is not obvious. (2) based on the three-point bending test of Q235B steel plate specimens, the structural stress characterization parameters based on material properties are studied. The results show that with the increase of transverse load, the intensity of magnetic memory signal HP (y) increases gradually, and the phenomenon of "wave peak" or "trough" appears in the stress concentration area. Magnetic memory signal gradient K has a "peak-peak" change and a zero crossing point in the stress concentration area, which can be used to judge the stress concentration area of the specimen and to realize the initial judgment of early damage location. HP (y)? The curve increases rapidly near yield strength and appears "inflection point", while HP (y)? The curve showed a linear increase relationship, no obvious "inflection point", with the help of HP (y)? The stress corresponding to the "inflection point" of the curve can be used to characterize the yield strength of the tensile edge of the bending specimen. (3) through the four-point bending test of Q235B steel beam, the magnetic field of the building steel structure is studied to characterize the stress parameters. The stress concentration in different parts of bending specimens is evaluated effectively. The variation trend of magnetic memory signal curve is similar to the bending diagram of the specimen under vertical load. The curve of magnetic memory signal on the detection line can be used to predict the bending moment distribution of the bending specimen. The "zero crossing point" phenomenon can approximately determine the position of stress concentration after flange buckling, but there exists "zero drift" phenomenon. The higher the peak value of the stress concentration, the higher the degree of stress concentration and the greater the probability of buckling. The gradient curve peak maxK can be used as the basis for judging the dangerous moment before buckling. (4) there is an inevitable relationship between magnetic memory signal and bending tensile stress. The stress-strain curve of the specimen shows a similar change trend, and the magnetic memory signal shows the corresponding state with the different stress state of the flange of the specimen. There is a linear relationship between the magnetic memory signal on the surface of the web and the horizontal compressive stress, and there is no obvious inflection point. At the same strain, there is a difference in the intensity of the magnetic memory signal, so it is only suitable for qualitative evaluation.
【学位授予单位】：西安建筑科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TU391;TU317

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