共查询到19条相似文献,搜索用时 156 毫秒
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1 磁粉探伤中的磁导率概念电磁学理论中,磁导率μ的定义是磁感应强度(磁通密度)B与磁场(磁化力)H之比。μ的物理意义反映村料被磁化的难易程度。由于B与H是非线性函数关系,磁导率不是一个常数,而是一个变量,磁粉探伤中各种含义的磁导率有不同的物理意义和用途。1.1 材料磁导率μ材料磁导率μ是指在周向磁化(没有反磁场的影响)下,工件材料内部的磁导率。由材料磁导率建立的B-H磁化曲线和磁滞回线(图1),均为材料本身的标准曲线,反映材料真实的磁特性。在磁粉探伤中根据材料磁化曲线和磁滞回线选择正确的周向磁化规范,以及确定检验方法(剩、连)的依据。1.2 起始磁导率起始磁导率是指磁感应强度(磁通密度)与磁场(磁化力)初始线性变化区域的磁导率(即图2中1的斜率)。此时B与H的变化是可逆的呈线性的。在磁粉探伤中,初始磁导率是决定磁粉性能的十分重要因素之一。 相似文献
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法向漏磁通随外磁化场和矩形槽尺寸的变化 总被引:1,自引:0,他引:1
用磁偶极子模型讨论法向漏磁通随外磁化场和矩形槽尺寸的变化.法向漏磁通的蜂-峰值随外磁化场强度或有效磁感应强度的变化有相似的趋势;法向漏磁通的峰-峰值随矩形槽深度的变化受铁磁材料磁化状态影响;在不同的提离高度时,法向漏磁通的峰-峰值随矩形槽宽度的变化趋势不同;法向漏磁通的峰-峰间隔受提离高度以及矩形槽深度和宽度影响,提离高度>1mm时,法向漏磁通的峰-峰间隔随提离高度线性增加,矩形槽宽度的影响已不明显. 相似文献
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针对铁磁性承压设备脉冲涡流热成像(ECPT)缺陷检测过程中,拉应力对铁磁材料磁导率的影响被忽略而引起的缺陷量化精度不高的问题,结合力磁耦合关系、电磁感应定律、焦耳定律仿真探究弹性拉应力对ECPT量化不同方向、不同深度缺陷的影响。结果表明,不同方向缺陷的最大磁导率随着弹性拉应力的增加而增加,同一应力作用下,缺陷处的最大磁导率随着横向缺陷深度的增加而增加,但最大磁导率对竖直缺陷深度的变化不敏感;在ECPT缺陷量化过程中,基于温差特征的横向缺陷的深度量化曲线的斜率随应力的增加而增加,且横向缺陷深度量化拟合曲线的标准差低于0.3℃,可决系数达95%,拟合效果好;基于温差特征的竖直缺陷深度量化曲线受应力的影响较小。 相似文献
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在脉冲强磁场中测量了Gd1-xLaxMn2 Ge2 (x =0 .0 6 ,0 .0 7)化合物在不同温度下的磁化曲线。结果表明 ,当这些化合物处于反铁磁状态的温度范围内时 ,Mn次晶格中发生了场诱导的从反铁磁状态到铁磁状态的一级磁相变。随着温度的降低 ,相变临界磁场逐渐增大 ,达到最大值后 ,随着温度的进一步降低 ,临界磁场很快减小 ;随La含量的增加 ,相变临界磁场也很快减小。在交换相互作用的分子场模型基础上 ,考虑层面间Mn Mn交换作用随晶格常数a以及温度的变化 ,从理论上计算了这种场诱导的反铁磁→铁磁一级磁相变所对应的临界磁场 ,理论计算结果较好地描述了临界磁场随温度的变化规律。理论模型也较好地解释了在这些化合物中发生的从亚铁磁结构到反铁磁结构再到铁磁结构的一级自发磁相变 相似文献
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磁致伸缩和磁记忆问题研究 总被引:9,自引:1,他引:9
从铁磁性材料的基本特性和最小自由能原理出发,探讨了应力和外磁场对磁性材料磁化状态的不同影响,讨论了磁致伸缩现象的规律和特点。用磁致伸缩方程组详细研究了磁记忆现象产生的条件和规律,分析了应力和地磁场在磁记忆现象中的不同作用。结论认为应力可改变材料的磁特性,地磁场则可改变材料的压磁性,两者共同作用产生净磁场,磁记忆现象不仅与应力和材料的磁特性有关,而且还与工件在空间的位置和方向有关。 相似文献
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The investigation described in this paper focuses on the velocity effect of dynamic magnetization and magnetic hysteresis due to rapid relative motion between magnetizer and measured specimens in high-speed magnetic flux leakage (MFL) inspection. Magnetization intensity and permeability of ferromagnetic materials along with the duration of dynamic magnetization process were analyzed. Alteration of the intensity and distribution of magnetic field leakage caused by permeability of specimen were investigated via theoretical analysis and finite-element method (FEM) combined with the actual high-speed MFL test. Following this, a specially designed experimental platform, in which motion velocity is within the range of 5 m/s–55 m/s, was employed to verify the velocity effect and probability of a high-speed MFL test. Preliminary results indicate that the MFL technique can achieve effective defect inspection at high speeds with the maximum inspection speed of about 200 km/h being verified under laboratory conditions. 相似文献
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金属磁记忆法诊断的理论基础——铁磁性材料的弹—塑性应变磁化 总被引:22,自引:6,他引:16
电磁感应定律证明,铁磁性材料在地球磁场中的自发磁化来源于定向应力作用下材料本身的应变和交变应力作用下材料的非对称弹-塑性应变。某种铁磁性材料的自发磁化过程可由该材料的磁化和退磁曲线来估计,由此推得的磁弹性现象图与实验结果相一致。 相似文献
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K. Proke Th. Wand A.V. Andreev M. Meissner F. Honda V. Sechovský 《Journal of Alloys and Compounds》2008,460(1-2):47-53
Specific heat of a single crystalline URhSi was measured by a relaxation method in a temperature range 0.3–25 K in magnetic fields up to 8 T applied along the two of the principal axes. The low-temperature specific heat exponentially decays with magnetic field. The decay is much faster in fields applied along the easy magnetization direction (the c-axis) than for the hard axis (the a-axis) case. A strong upturn in cp/T versus T below 0.6 K that disappears with application of magnetic field is observed suggesting possible magnetic or superconducting phase transition at lower temperatures. The electrical resistivity in the vicinity of the ferromagnetic phase temperature is found to be reduced by more than 50% upon application of magnetic field of 8 T applied along the c-axis. URhSi represent an itinerant ferromagnetic system with influence of spin fluctuations. 相似文献
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《Intermetallics》2016
We have investigated dc magnetization, magneto-transport and magnetostriction of C15 Laves phase 4f ferromagnetic compound NdRu2 as a function of temperature and applied magnetic field. We find that the magnetic properties of this compound can not be explained within a simple model based on localized magnetic moment even though Nd based compounds and alloys are usually considered as localized magnetic moment systems. Our experimental results on temperature dependence of magnetization, electrical resistivity and magnetoresistance suggest the existence of spin fluctuations in the paramagnetic state of NdRu2. This compound shows unusually high and non-linear forced magnetostriction. We conjecture the hybridization of Nd 4f states with valence electrons as one of the possibilities for explaining the experimental results. 相似文献
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磁场干摩擦主要是研究磁场强度参量对材料干摩擦磨损性能的影响机理和规律。系统综述了金属材料直流磁场干摩擦的研究过程、研究方法和相应研究成果。阐述了不同磁属性(抗磁性、顺磁性和铁磁性)材料的磁场干摩擦特性及其机理,得出材料磁导率与其磁场干摩擦学特性有一定对应关系,材料磁导率越大,磨损率和摩擦系数的减小趋势越明显,并指出了试验研究中遇到的问题,如应关注摩擦副材料选配、磁场施加装置、摩擦接触方式及装卡装置等。为了避开材料化学成分不同造成的干扰,设计了三种制备方案,发现通过热处理工艺改变微观组织相含量或添加铁、钴、镍等铁磁性元素进行化学成分设计等常规的材料制备方法,难以达到目的。最终利用奥氏体不锈钢1Cr18Ni9Ti较大的冷加工硬化特性,采用常温下锻造工艺制备了不同磁导率的几种相同成分材料,使磁导率成为关键变量。研究了磁场强度、材料磁导率与其磁场干摩擦特性的交互影响情况和规律,并展望了未来需要开展的研究方向。 相似文献
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介绍了铁磁性物质静置于地磁场中产生的自发磁化和退磁的原因,主要有以下三点:一是磁时效—铁磁性物质的磁性和磁畴的空间排列都滞后于施加于其上的磁化场;二是地磁场强度大小和方向随着时间推移而发生的周期性变化;三是金属的时效—材料中机械应力随着时间流逝导致其磁化曲线和金相组织的改变以及延迟裂纹的出现等。 相似文献
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《Intermetallics》2015
In this study we report detailed magnetic property of the 4f-3d pseudo-quaternary Tb0.2Pr0.8(Fe0.4Co0.6)1.88C0.05 compound by detailed magnetization measurements. Very sharp magnetization jumps across the antiferromagnetic–ferromagnetic transition are observed below 3.0 K, and the number of jump-like transitions increases with decreasing temperature. The time-dependent magnetic relaxation, field sweep rate and cooling field dependence of magnetization jumps resemble the martensitic scenario. The number and occurrence of magnetization jumps are mainly determined by the competitions between the thermal fluctuation energy, elastic energy and Zeeman energy, and the field-induced antiferromagnetic to ferromagnetic phase transition at low temperatures is of first-order in nature. 相似文献