焊接裂纹金属磁记忆信号的神经网络识别

金属磁记忆检测技术是一种新型的利用铁磁材料内在信息对材料进行检测和评价的无损检测方法,对裂纹类缺陷进行早期检测具有潜在的优势.利用小波包分析技术,对水压试验条件下API 5L X70管线钢焊缝中有无焊接裂纹的金属磁记忆信号能量特征进行了分析,确定了焊接裂纹金属磁记忆信号的小波包能量特征,并利用其作为输入特征向量建立了BP(back propagation)神经网络,对焊缝中是否含有裂纹等缺陷进行智能识别.结果表明,利用小波包能量和神经网络技术可以较好的实现焊接裂纹的识别.     

金属磁记忆缺陷特征信号的研究

以45号冷轧钢为研究对象,对三种不同缺陷类型的平板进行了拉伸试验,提取了平板试样每条检测线上随着拉应力的增大过程中的磁记忆信号,获得了缺陷特征信号,并进行了对比分析。结果表明,缺陷异变磁记忆信号的变化可以反映载荷作用的历史和试件的应力和变形情况。     

基于微分方法的焊接裂纹金属磁记忆特征研究

针对金属磁记忆检测技术的瓶颈问题,以X70钢为研究对象,通过对预制焊接裂纹一阶微分处理后的金属磁记忆信号进行分析,可区别焊接裂纹引起的应力集中与其它缺口效应引起的应力,并可确定焊接裂纹存在的定位信号特征.现场检测表明,利用一阶微分处理后的磁记忆信号定位特征,可准确地对焊接裂纹进行检测.     

油气管道焊接裂纹金属磁记忆定量化分析系统

金属磁记忆检测技术是一种新型的无损检测方法,在焊接裂纹的检测和监测方面具有独特的优势.在提取焊接裂纹金属磁记忆信号特征的基础上,建立了用于焊接裂纹定量化分析识别的BP神经网络,利用Visual Basic和Matlab混合编程技术建立了焊接裂纹的金属磁记忆定量化分析软件.     

金属磁记忆检测技术的研究现状及发展

介绍金属磁记忆检测技术对铁磁构件疲劳失效和早期诊断的重要意义。通过分析比较,描述了金属磁记忆检测技术的独到优点、金属磁记忆检测机理以及检测仪器。重点介绍了目前金属磁记忆机理研究现状和国内外该技术的应用现状并给出了两个实例分析。最后,总结了金属磁记忆检测技术目前存在的问题和未来的发展方向。     

金属磁记忆检测信号的二维谱熵特征

金属磁记忆检测技术是能够对焊接裂纹进行早期诊断的最具有潜力的无损检测方法之一.以X70管线钢为主要研究对象,研究了其拉伸条件下金属磁记忆检测信号的二维特征谱熵分布规律,通过支持向量机模型,可以实现幅值谱熵和重心频率确定点的位置的分类,结合检测实例,得到了对焊缝中应力集中状态的诊断方法.结果表明,通过磁记忆信号二维特征谱熵的分布可以诊断出材料内部的应力集中状态,从而为利用金属磁记忆检测技术对裂纹萌生状态的诊断提供了依据.     

金属磁记忆法检测焊接裂纹的时间空间有效性

预制了焊接裂纹试板,在试板的不同空间区域,以及焊接之后的不同时刻进行了金属磁记忆检测.采用快速傅里叶变换对检测信号进行了特征分析,研究了焊接裂纹周围不同区域在不同时刻的金属磁记忆信号以及其傅里叶变换相位突变特征.结果表明,在焊接裂纹存在的70 mm范围内是金属磁记忆检测的空间有效区域.在焊接完成后,接头温度低于100 ℃以后的任何时间进行金属磁记忆检测,取得的结果都是有效的.     

非常规情况下金属磁记忆检测方法的研究

介绍了铁磁构件自身通入稳恒电流,外部存在稳恒干扰磁场以及当铁磁构件被交流磁化这三种非常规情况对铁磁构件金属磁记忆检测的影响。实验发现,1A以下稳恒电流的存在对于管道的金属磁记忆检测几乎没有影响,稳恒外磁场的存在对金属磁记忆检测影响是很大的,可能造成金属磁记忆信号整体的改变,而交流磁化则会完全破坏构件的自有漏磁场信息。     

焊接裂纹应力与磁记忆信号关系的实验研究

焊接裂纹产生的应力集中区是焊接构件在服役过程中最为危险的一个薄弱环节,对这个环节进行有效的安全评估,具有重要意义。金属磁记忆技术是近年来发展的一种全新的无损检测方法,它可以在地磁环境下检测铁磁构件的应力集中,从而诊断出产生（或可能产生）裂纹的危险区域。利用磁场中的高斯方程,对管线钢焊接裂纹的应力和金属磁记忆信号之间的关系模型进行了初步探讨,然后利用预制的焊接裂纹对此关系模型进行了研究预测,分析结果表明：此关系模型可满足应力检测的精度要求。     

铁道机车车辆轮心孔的磁记忆检测研究

金属磁记忆检测技术能检测出铁磁枸件的应力集中区，可以对铁磁构件的损伤进行早期诊断。研究了磁记忆检测技术在铁道机车承力部件上的应用，在对铁道机车车辆的轮心进行了磁记忆检测后，用磁粉检测进行了复检。结果表明，磁记忆检测可以有效发现表面裂纹等缺陷，并且能对机车轮心产生破坏的可能性进行预测。     

磁场对双丝间接电弧焊熔滴过渡的影响

对磁场作用下的双丝间接电弧气体保护焊熔滴过渡变化规律进行了研究,通过励磁线圈对间接电弧施加外部横向及纵向磁场,磁感应强度值由特斯拉计侧出,熔滴过渡过程借助于高速摄像系统拍摄,并由示波器同步记录下电流和电压值的变化.研究表明,随正向横向磁场强度增加,熔滴颗粒变细,过渡频率增加,随负向横向磁场强度增加,熔滴颗粒变大,过渡频...     

Research on methods of defect classification based on metal magnetic memory

Metal magnetic memory (MMM) technique can evaluate early damages of ferromagnets and search possible defect locations, while just classifies the defect types roughly. To promote study in this area, the magnetic gradient tensor (MGT) of the self-magnetic leakage field (SMLF) on the fracture zone of crack and stress concentration was measured using a tri-axis magnetometer. From measured results, both the plane and the vertical characteristics of SMLF distributions were discussed. To remove the influence of the measuring direction on experimental results, a new parameter of the analytical signal of magnetic gradient tensor (AMGT) was introduced to determine the location and boundary of the defect. Then, the vertical features were acquired by measuring the plane distributions of AMGT under different lift offs. Through analyzing the vertical features, it was concluded that change rule of the maximum AMGT can be used to predict the defect type. At last, the explanation of the relationship between the vertical feature and the defect type was discussed, which can give some useful inspirations to researchers on magnetic leakage field testing.     

20钢焊接缺陷磁记忆信号分析

对含有焊接缺陷的试块进行磁记忆检测,研究了金属磁记忆检测技术对裂纹、气孔、未焊透、未熔合、夹渣缺陷的检出能力,对裂纹、气孔、未焊透、未熔合、夹渣区域的磁场强度梯度平均值H_ave、最大值H_max、磁场强度梯度曲线围成的面积S(H)、磁场强度梯度平均值K_ave、最大值K_max、磁场强度梯度曲线围成的面积S(K)进行计算,并与无缺陷区域的参数进行对比分析.结果表明,焊缝中裂纹、气孔、未焊透、未熔合、夹渣区域的K_ave,K_max,S(K)明显区别于无缺陷区域,可以准确判定焊接缺陷位置;焊接缺陷和焊接残余应力虽然都会导致磁记忆信号的变化,但是二者具有本质不同.     

Influence of longitudinal magnetic field on metal transfer in MIG arc welding

Metal transfer is an important phenomenon in metal inert gas (MIG) arc welding with longitudinal alternating magnetic field. It is of great significance to observe the metal transfer modes under different excitatory currents and frequencies. However, it is very difficult to view the metal transfer process directly during welding, due to the strong interference from the arc light. To obtain the relationship between the metal transfer modes and the different magnetic fields, a high-speed video camera was used to acquire the images of globules. Different metal transfer modes under the conditions of different magnetic fields and welding parameters were studied. The experiment shows clear images of droplet transfer as well as influence of longitudinal magnetic field on both metal transfer and globule shape.     

Modelling the transverse magnetic field generated by equipment in arc welding

The design of equipment for generating the transverse magnetic field in arc welding can be optimised by modelling the direct magnetic field produced by the device for generating (GD) the transverse magnetic field (TMF) by the electric field of the current flowing in flat models made of electrically conducting materials. The lines of force of the electric field in the flow of the current in the modelling medium correspond to the lines of force (induction lines) of the magnetic field generated by GD TMF. Using these modelling methods, it is shown that to obtain the maximum values of the transverse component of the induction of the magnetic field in the zone of the welding arc of the electrode droplet and liquid metal of the weld pool, the optimum design of GD TMF is the one in which the angle of inclination of the bars to the vertical is equal to 45° and the end surfaces have chamfers parallel to the plane of the welded sheets.