铁磁材料表面硬度无损测量方法的研究

通过实验研究了巴克豪森噪声强度与铁磁材料表面硬度之间的关系,结果表明,随材料硬度的降低巴克豪森器材怕的强度逐渐升高,因此可以利用巴克豪森噪声强度对材料的表面硬度进行无损测量。     

巴克豪森效应在铁磁材料残余应力测量中的应用

因巴克豪森效应在试样表面接收线圈中产生的电压脉冲和噪声称为巴克豪森噪声。根据铁磁学理论介绍了巴克豪森噪声产生的机制，并研制出巴克豪森信号传感器及信号采集处理系统。通过试验给出了SM570钢焊接部分热处理前后巴克豪森信号功率谱和方均根(RMS)强度的变化。同时通过盲孔法确定实际材料热处理前后的残余应力变化。试验结果给出了一些有用信息，但该巴克豪森信号系统只能定性地给出应力的大小和热处理效果，要达到定量的目的还需进一步研究。     

基于巴克豪森效应的铁磁性材料硬度检测

根据巴克豪森效应,铁磁性材料在外部交变磁场的影响下会产生周期性的噪声信号。采用该种基于巴克豪森效应的检测方法,通过检测在同等试验条件下不同硬度45钢试件接收到的巴克豪森信号,分析了信号各特征值与试件硬度的关系。试验结果表明:巴克豪森信号与硬度具有较高的相关性,巴克豪森法可用于检测铁磁性材料表面硬度。     

高Co-Ni超高强度钢残余应力的巴克豪森信号表征

采用四点弯曲的加载方式,通过巴克豪森检测方法表征高Co-Ni超高强度钢不同热处理状态的残余应力以及微观组织状态.分析得出残余应力以及微观组织与巴克豪森信号的对应关系.结果表明,高Co-Ni超高强度钢表层应力和材料微观组织与巴克豪森信号值相关性较好,在弹性极限范围内,巴克豪森噪声值(BN)随拉应力的增大而增大,随压应力的增大而减小;退火处理状态下BN值最高,淬火态次之,回火状态下最低.     

磁巴克豪森噪声技术在应力评估中的研究进展

磁巴克豪森噪声(MBN)技术可以探测铁磁性材料由于应力作用而发生的微观结构变化,进而评估材料受力和失效情况。基于金属磁畴理论和磁化理论,从微观上对MBN现象进行解释,并结合Jiles-Atherton磁化模型定量分析应力对MBN信号的影响,介绍应力作用下金属材料在弹性变形阶段和塑性变形阶段的MBN信号变化特点,分析材料所受载荷压力和残余应力在本质上对材料磁畴结构、晶粒易磁化轴、晶粒各向异性等微观结构的影响,指出应力既会促使材料内部产生缺陷从而阻碍巴克豪森跳跃,也会促进相邻磁畴壁的融合,进而增加巴克豪森跳跃,最终的MBN信号是应力对巴克豪森跳跃阻碍作用和促进作用相互博弈的结果。最后,还总结了MBN技术在应力评估方面的优势、不足及未来可开展的研究方向。     

巴克豪森应力检测中激励方式的影响

巴克豪森效应是电磁方式检测材料微观结构和应力的基础。通过试验方法分析不同激励频率、激励电压和激励波形下巴克豪森噪声信号的时域、频域特征,研究激励信号参数对材料应力检测的巴克豪森信号特征值的影响,并探究现象的微观解释。     

基于巴克豪森效应预测烧伤齿轮显微组织的变化

齿轮是机械传动的关键零部件,齿轮的磨削烧伤会影响其传动的稳定性和疲劳寿命。通过材料中马氏体含量的变化判定齿轮的烧伤程度,利用磁巴克豪森噪声检测装置对激光模拟烧伤齿轮进行测试,采集烧伤齿面的巴克豪森噪声信号;通过巴克豪森噪声信号的包络与切向磁场的关系曲线提取特征值(包括峰值,峰值位置,半峰宽),利用自适应模糊神经网络进行训练,建立材料马氏体含量的预测模型。试验结果表明,该方法具有检测和表征微观金相组织中马氏体深度的能力,同时可以避免激励频率对巴克豪森噪声信号输出的影响。通过拟合优度参数R~2=0.964 1和均方根误差R_(MSE)=16.981 7进一步验证了自适应模糊神经网络模型具有较高的准确性,可用于预测齿轮烧伤的程度。     

利用巴克豪森效应测量铁磁材料的晶粒大小

研究了铁磁材料的晶粒芳与巴克豪森噪声的强度和波形特征参数之间的关系。利用波形的半主同宽占空比作为测量参数,能良好地反映材料的晶粒大小。结果表明可以利用巴克豪森噪声来测量铁磁材料的晶粒大小。     

钢板应力检测中的巴克豪森信号分析

针对铁磁性材料由于应力集中导致的断裂等问题,分析了铁磁性材料在磁化过程中激励频率对巴克豪森信号的影响,分析了应力与巴克豪森信号的关系及特性。采用检测线圈与激励线圈共同缠绕于同一磁芯的方式来接收信号,并通过高通滤波电路得到巴克豪森信号。实验结果表明,激励频率在20Hz时,巴克豪森信号较强较稳定,并且随铁磁性材料中拉应力增大而增大。通过检测巴克豪森信号的大小实现铁磁性材料的应力检测,有效地预防因应力过大造成的工件损坏问题。     

9310钢磨削烧伤的巴克豪森噪声法检测

介绍了利用巴克豪森噪声法检测磨削烧伤的工作原理,研究了应用巴克豪森噪声法检测9310钢磨削烧伤的关键参数(磁化电压和特征磁致弹性参数M_P值)的确定方法。首先制备含不同程度磨削烧伤的试样,并通过酸蚀检测法按程度对磨削烧伤进行分级,然后将巴克豪森噪声法所测得的M_P值与不同的磨削烧伤级别建立对应关系,最后根据特征值随磁化电压和烧伤程度的变化规律来确定检测所需的磁化电压和M_P值。     

Influence of uniaxial plastic deformation on magnetic Barkhausen noise in steel

Magnetic Barkhausen noise (MBN) measurements were made on hot-rolled mild steel samples uniaxially deformed to differing magnitudes of plastic strain, to study the dependence of MBN activity on plastic strain. The results indicated an initial increase in MBN energy with increasing plastic strain followed by a decrease at higher plastic deformations. At still higher plastic deformations, the MBN energy was found to be almost independent of plastic strain. The results are explained in terms of different mechanisms of interaction of domain walls with dislocations, with increasing plastic strain. The behavior of MBN energy with plastic strain was found to be anisotropic and the angular MBN measurements indicated that the deformation-induced easy axis of magnetization changed direction with increasing plastic strain. At higher deformations, the MBN activity was largely controlled by the deformation-induced anisotropy, due to residual stress.     

Plastic versus elastic deformation effects on magnetic Barkhausen noise in steel

A study was performed to differentiate the effects of elastic and plastic deformation on magnetic Barkhausen noise (MBN) signals. Linear and angular MBN measurements were made on a number of mild steel plate samples subjected to varying degrees of uniaxial elastic and plastic deformation up to ∼40% strain. Elastic strain effects on the MBN_energy were determined to be far more significant than plastic strain effects. MBN_energy increases in the early plastic deformation region were attributed to a slight increase in elastic strain due to work hardening. Magnetic anisotropy studies indicated that elastic strain significantly alters the magnetic anisotropy (α) in the sample, but changes the isotropic signal (β) very little. Plastic deformation has a smaller, but apparently opposite effect, in that it appears to change β but has little influence on α. As plastic deformation levels become large, however, behaviour becomes more complex and is less well understood.     

304不锈钢相变条件下涡流检测频率选取仿真

304奥氏体不锈钢由于其本身组织特性,在制造和在役过程中会产生部分铁素体和马氏体并析出,使其具有一定的磁性,即相对磁导率肼大于1,试验测试结果表明：当不锈钢件形变量在20％以内,随着形变量的增加,试件的磁导率增加,并逐渐开始具有铁磁材料的磁特性,导致不锈钢涡流检测集肤深度降低,也改变了检测的最佳激励频率。此外,通过比较2种不同激励频率的选取方法可得,在不锈钢形变量20％以内,不锈钢形变量增大,其最佳检测频率倾向于降低,且小于100kHz。试验和仿真结果表明,304不锈钢压力容器最佳检测频率范围为40—100kHz。     

铁素体/贝氏体(F/B)双相钢组织调控及其抗变形行为分析

本文针对低C,高Mn和高Nb化学成分,采用轧后弛豫控制相变的组织调控技术得到5种不同铁素体/贝氏体（F/B）体积含量的双相组织钢.用改进的C-J分析方法分析了软相（铁素体）含量,研究了晶粒尺寸对加工硬化性能的影响,以及以铁素体和贝氏体为主的软硬相混合组织的塑性变形协调关系.并用电子背散射（EBSD）技术验证了双相组织在均匀塑性变形阶段的协调变形行为.结果表明,软硬相的合理比例有利于提高加工硬化程度(高Rt_1.5/Rt_0.5),降低屈强比,同时能保证较高的均匀变形能力.铁素体与贝氏体之间的协调变形是提高双相组织钢应力比和均匀伸长率的主要机制.     

基于瞬态A_r方程的非线性涡流无损评价数值模拟

就一简化的三维磁性材料数值计算模型,对其非线性涡流信号进行了数值模拟试验。基于变形磁矢量位(Ar)低频涡流场的控制方程改良并开发了用于计算非线性涡流检测信号的数值模拟程序,得出非线性涡流检测信号与磁性材料因塑性变形而产生的磁导率变化之间的相关性,开发了非线性涡流信号数值模拟程序,利用开发的数值模拟程序计算非线性涡流检测信号,采用不同初始磁导率等效模拟试件不同塑性变形程度,得出了模拟信号的谐波幅值与塑性变形的关联性。对比非线性涡流数值模拟结果和试验检测结果,证明了塑性变形导致的磁导率变化是非线性涡流检测信号变化的直接诱因。     

Magnetic properties of cementite and the coercive force of carbon steels after plastic deformation and annealing

Magnetic hysteresis properties of cementite obtained by the method of mechanical alloying have been studied. It is shown that the strongly deformed cementite is in a low-coercivity state, and the cementite annealed at 500°C is in a high-coercivity state. The need to allow for the contribution of the coercivity of cementite to the coercive force of high-carbon steel is shown. Taking into account this point of view, the behavior of the coercive force depending on the degree of cold plastic deformation by drawing is explained for a number of carbon steels with a structure of fine platelike and globular cementite.     

Unwrapping the influence of multiple parameters on the Magnetic Barkhausen Noise signal using self-organizing maps

The main advantage of Magnetic Barkhausen Noise as a non-destructive testing method is its sensitivity to several parameters such as microstructure, applied tension and plastic deformation. However, this noticeable property of the MBN sometimes could be a drawback. Usually, in measurements of industrial steel samples the variation of parameters occurs simultaneously. Then it is difficult to separate the influence of multiple parameters from the raw signal. This work proposes a method using trajectories traced in a type of neural network known as Self-Organizing Maps, in order to separate the influence of varying parameters on the Magnetic Barkhausen Noise row signal.     

A study of plastic deformation around a defect using the magnetic Barkhausen noise in ASTM 36 steel

The present work presents the measurements of the magnetic Barkhausen noise (MBN) in ASTM 36 steel samples around a pit under plastic deformation. The contour maps obtained from these Barkhausen noise measurements are compared with the finite element analysis of the ideal plastic deformation. Also, a parameter of the Barkhausen signal to detect the plastic deformation around the pit in ASTM 36 steel is obtained. Additionally to that, we propose another MBN parameter to estimate the pit width using the Barkhausen noise.     

无镍高氮奥氏体不锈钢的脆韧转变

研究了无镍高氮奥氏体不锈钢的脆韧转变(BDT)。在176 K、273 K和336 K进行的落锤试验结果表明,尽管Fe-25Cr-1.1N(质量分数,%)是面心立方结构的奥氏体合金钢,但仍展现出显著的脆韧转变现象。对冲击试验试样的塑性变形观察表明,BDT是由于低温下差的延展性所致,这与铁素体钢的情况是一致的。为了测量BDT的激活能,利用4点弯曲试验研究了应变速率与BDT温度的关系。研究发现,BDT温度与应变速率之间的依赖关系不显著,且BDT温度对应变率的Arrhenius曲线表明Fe-25Cr-1.1N钢BDT的激活能比低碳铁素体钢的高得多。从滑移位错与溶质氮原子发生交互作用导致低温下位错可动性降低这一角度,本文探讨了高氮钢特有的BDT及其高激活能的本质原因。     

磁巴克豪森残余应力测量技术在热处理工艺评估中的应用

磁巴克豪森噪讯（Magnetic Barkhausen Noise,即MBN）方法是残余应力无损检测中的一门新技术。通过结合虚拟仪器技术,实现了巴克豪森噪讯的采集和实时处理,并应用于铁磁材料热处理后残余应力分析。通过与盲孔法的比较,验证了SM570板材焊缝区在热处理前后MBN噪讯与残余应力的相应变化。