环境磁场对磁记忆检测信号的影响

通过对一铁磁性试件进行磁记忆检测实验,选择手机信号作为干扰源,研究不同环境磁场下试件磁记忆检测信号的变化情况.同时,对试验过程中的环境磁场对磁场强度变化的影响进行了机理分析.研究结果表明:对不同程度的环境磁场干扰,检测得到的试件磁记忆信号差别显著;周围有放置手机但不通话时,环境磁场的干扰程度不大;随着周围环境的通话手机数量逐渐增多,环境磁场的干扰程度不断加大直至足以影响检测精度.     

Metal magnetic memory signals from surface of low-carbon steel and low-carbon alloyed steel

In order to investigate the regularity of metal magnetic signals of ferromagnetic materials under the effect of applied load, the static tensile test of Q235 steel and 18CrNiWA steel plate specimens were conducted and metal magnetic memory signals of specimens were measured during the test process. The influencing factors of metal magnetic memory signals and the relationship between axial applied load and signals were analyzed. The fracture and microstructure of the specimens were observed. The results show that the magnetic signals corresponding to the measured points change linearly approximately with increasing axial load. The microstructure of Q235 steel is ferrite and perlite, whereas that of 18CrNiWA steel is bainite and low-carbon martensite. The fracture of these two kinds of specimens is ductile rupture; carbon content of specimen materials and dislocation glide give much contribution to the characteristics of magnetic curves.     

Residual Tensile Strength of Plain Concrete Under Tensile Fatigue Loading

The functional relation between the residual tensile strength of plain concrete and number of cycles was determined. 99 tappered prism specimens of plain concrete were tested under uniaxial tensile fatigue loading. Based on the probability distribution of the residual tensile strength, the empirical expressions of the residual tensile strength corresponding to the number of cycles were obtained. The residual tensile strength attenuating curves can be used to predict the residual fatigue life of the specimen under variable-amplitude fatigue loading. There is a good correlation between residual tensile strength and residual secant elastic modulus. The relationship between the residual secant elastic modulus and number of cycles was also established.     

Variation regularity of metal magnetic memory signals with inspecting time-interval and location

Influences of inspecting time-interval and location on varying behavior of metal magnetic memory （MMM） signals of defects were studied. Different areas in two precracked weldments were inspected at different time-intervals by type TSC-1M-4 stress-concentration magnetic inspector to obtain MMM signals. Mechanisms of MMM signals varying behavior with inspecting time and space were analyzed and discussed respectively. It is found that MMM signals don＇t change with inspecting time-interval, since stress field and magnetic leakage field maintain unchanged at any time after welding. On the other hand, MMM signals differ greatly for different inspecting locations, because stress field and magnetic leakage field are unevenly distributed in defective ferromagnetic materials.     

水平稳恒磁场下Cu-12%Fe合金的凝固组织

研究了施加磁感应强度1 T的水平磁场对Cu-12%Fe合金凝固过程中Fe枝晶形貌、XRD及显微硬度的影响.表明,施加1 T水平稳恒磁场后,Fe枝晶显著细化,这主要是由于洛伦兹力和热磁对流竞争作用的结果;XRD分析的结果表明,Cu（111）晶面和Cu（200）晶面所对应的峰值强度均明显大幅度增加;显微硬度的测试表明由于Fe枝晶的细化致使施加磁场后样品的显微硬度小幅度增加.     

静电场和磁场对碳钢表面结垢和腐蚀的影响

在模拟循环冷却水系统中研究了高碱度、高含盐量、高硬度水质条件下 ,静电场和磁场对碳钢表面结垢和腐蚀的影响 .研究表明 ,静电场对结垢有明显的抑制作用 ,强磁场对结垢虽有一定的抑制作用 ,但是还存在不利的因素 .它们对碳钢腐蚀性能的影响主要与对沉积物的影响有关     

Ratcheting led surface failure of medium carbon bainitic steel under mild operation conditions

The behavior of rolling contact fatigue (RCF) of medium carbon bainitic back-up roll steel was investigated under its actual work conditions. A kind of asperity-scale surface originated cracks, which is lying parallel or at an acute angle to the surfaces, initiated after unidirectional plastic flow of the material in thin surface layer had occurred. Theoretical analysis indicates that they nucleate due to plastic ratcheting induced by asperity contact stresses, and consequently are named as ratcheting cracks. After nucleating and initially propagating, they arrest at some depth and resume propagating till about 70%-80% of the RCF failure life by initially turning parallel to contact surfaces. Their behavior of initiation and propagation is confined to a thin layer prior to the formation of surface distress. According to the critical principle of the preventive grinding strategy, removing the asperity influenced surface layer at about 70%-80% of the RCF failure life can effectively prevent the ratcheting cracks from developing into surface distress, which can lead to the formation of macro-RCF failure soon.     

Metal magnetic memory testing for early damage assessment in ferromagnetic materials

In order to investigate the physical mechanism of metal magnetic memory testing, both the influences of earth magnetic field and applied stress on magnetic domain structure were discussed. Static tension and fatigue tests for low carbon steel plate specimens were carried out on hydraulic servo testing machine of MTS810 type and magnetic signals were measured during the processes by the type of EMS-2003 instrument. The results indicate that the initial magnetic signals of specimens are different before loading. The magnetic signals curves are transformed from initial random to regular pattern due to the effect of two types of loads. However, the shape and distribution of magnetic signal curves in the elastic region are different from that of plastic region in tension test. While in fatigue test those magnetic signals curves corresponding to different cycles are similar. The Hp (y) value of magnetic signals on the fracture zone increases dramatically at the breaking transient time and positive-negative magnetic poles occur on the two parts of fracture zone.     

Metal magnetic memory testing for early damage assessment in ferromagnetic materials

In order to investigate the physical mechanism of metal magnetic memory testing, both the influences of earth magnetic field and applied stress on magnetic domain structure were discussed. Static tension and fatigue tests for low carbon steel plate specimens were carried out on hydraulic servo testing machine of MTS810 type and magnetic signals were measured during the processes by the type of EMS-2003 instrument. The results indicate that the initial magnetic signals of specimens are different before loading. The magnetic signals curves are transformed from initial random to regular pattern due to the effect of two types of loads. However, the shape and distribution of magnetic signal curves in the elastic region are different from that of plastic region in tension test. While in fatigue test those magnetic signals curves corresponding to different cycles are similar. The H _p(y) value of magnetic signals on the fracture zone increases dramatically at the breaking transient time and positive-negative magnetic poles occur on the two parts of fracture zone. Foundation item: Project(50235030) supported by the National Natural Science Foundation of China     

Application of empirical mode decomposition in early diagnosis of magnetic memory signal

In order to eliminate noise interference of metal magnetic memory signal in early diagnosis of stress concentration zones and metal defects, the empirical mode decomposition method combined with the magnetic field gradient characteristic was proposed. A compressive force periodically acting upon a casing pipe led to appreciable deformation, and magnetic signals were measured by a magnetic indicator TSC-1M-4. The raw magnetic memory signal was first decomposed into different intrinsic mode functions and a residue, and the magnetic field gradient distribution of the subsequent reconstructed signal was obtained. The experimental results show that the gradient around 350 mm represents the maximum value ignoring the marginal effect, and there is a good correlation between the real maximum field gradient and the stress concentration zone. The wavelet transform associated with envelop analysis also exhibits this gradient characteristic, indicating that the proposed method is effective for early identifying critical zones.     

拉伸实验中的金属磁记忆信号总体特征研究

为了确定构件承载应力与金属磁记忆信号之间关系,以推进金属磁记忆法在构件检测中的应用,制备了不同尺寸和结构的拉伸试件,在试件承受不同拉伸载荷的情况下,进行了金属磁记忆检测,分析了金属磁记忆信号的总体特征Deta.研究表明:Deta作为金属磁记忆检测信号的特征量可以描述构件承载水平的高低;随着构件承载增加,Deta将逐渐减小,在达到材料屈服极限后,Deta保持在一定水平波动;对应材料X70屈服极限的Deta值是79.27A/m,高于该值时,X70构件是安全的.     

Analysis on the deformation and fracture behavior of carbon steel by in situ tensile test

1. IntroductionIn materials science, the emphasis is on the under-lying relationship between the microstructure andproperties of materials. Materials science and engi-neering has since long times aimed to develop the accu-rate relationship between the pro…     

磁控形状记忆合金执行器迟滞非线性模型

针对磁控形状记忆合金执行器的迟滞非线性,利用PI模型建模思想,采用线性Play算子建立磁控形状记忆合金执行器迟滞非线性模型。根据其模型结构与神经网络结构十分相似的特点,引入神经网络进行权值训练。为了提高系统的实时性,采用遗忘因子递推最小二乘法训练权值。试验结果显示:本文方法对输出位移的最大预测误差为0.0015mm,均方差为2.2931×10-4,最大误差率为0.1593%,表明该方法能够有效地建立磁控形状记忆合金(MS-MA)执行器的迟滞非线性模型,并可以获得较高的模型精度。     

中碳钢温变形过程的流变应力

为了制定中碳钢温轧工艺,利用Gleeble-3500热模拟试验机对中碳钢进行温压缩试验,研究其在不同变形温度(550～700℃)和应变速率(0.001～10s-1)下的流变行为,讨论温变形过程流变应力的影响因素。研究结果表明:中碳钢温变形过程由铁素体动态回复、铁素体动态再结晶、渗碳体球化和稳态变形4个阶段构成,其软化机理主要有铁素体动态再结晶和珠光体动态球化。     

Q345钢在低温下的力学性能研究

船用集装箱锁具中的锁轴原为 4 5钢 ,在低温 ( - 2 0℃ )下其性能尤其是冲击值达不到用户 2 7J的要求 ,航行时容易产生脆断。选用Q345钢 ,通过采用适当的锻造工艺和热处理工艺 (正火处理 ) ,锁轴拉伸、冲击性能在低温下使用有了很大的改善 ,延长了使用寿命 ,满足了用户的要求。     

Martensitic transformation and magnetic properties of aged Ni-Fe-Ga-Ti shape memory alloy

This article reports the effect of ageing on the microstructure, martensitic transformation, magnetic properties, and mechanical properties of Ni51FelsGa27Ti4 shape memory alloy. There are five specimens of this alloy aged at 573 up to 973 K for 3 h per each. This range of ageing temperature greatly affects the microstructure of the alloy. As the ageing temperature increased from 573 up to 973 K, the microstructure of Ni51FelsGa27Ti4 alloy gradually changed from the entirely martensitic matrix at 573 K to the fully austenitic microstructure at 973 K. The volume fraction of precipi- tated Ni3Ti particles increased with the ageing temperature increasing from 573 to 773 K. Further increasing the ageing temperature to 973 K decreased the content of Ni3Ti in the microstructure. The martensitic transformation tempera- ture was decreased steadily by increasing the ageing temperature. The magnetization saturation, remnant magnetization, and coercivity increased with the ageing temperature increasing up to 773 K. A further increase in ageing temperature decreased these raagnetic properties. Moreover, the hardness values were gradually increased at first by increasing the ageing temperature to 773 K, and then dramatically decreased to the lowest value at 973 K.     

Adsorption Capacity of Kaolinite for Copper （Ⅱ） under Magnetic Field

The adsorption of Cu^2 on kaolinite under magnetic field was studied at 25℃.The magnetic effects were investigated by designing the variation of exposure time, rnagnetie flux density and the method of magnetic exposure. The results from these study show that the magnetic treatment significaatly enhance the fraction of adsorption of Cu^2 ,the adsorption of Cu^2 by kaolinite increases with the increase of pH value from 2 to 6. Both the magnetic exposure time and the magnetic flux density promote the fruetion of adsorption Cu^2 on kaolinite.     

基于磁记忆机理的铁磁材料弯曲变形状态研究

利用磁记忆方法,采用自行研制的多通道磁记忆采集系统,研究铁磁材料在三点弯曲复杂应力状态下,0～250 kN不同试验载荷作用下的弯曲变形状况与磁记忆信号的对应关系,首次给出了三点弯曲复杂应力状态下磁记忆信号Hp(y)的分布规律与特点．实验发现：未加载时,Hp(y)呈无序状态；加载到50 kN时,试件受拉层Hp(y)开始变为负值,同时受压层Hp(y)信号全部变为正值,受拉层与受压层符号相反,表明不同层所受的正应力不同；加载到250 kN时,受拉层Hp(y)出现零点,表明应力集中的形成,中性层中心切应力最大处随载荷的增加Hp(y)过零梯度变大,反映了三点弯曲切应力的变化规律．最后应用NASTRAN有限元软件进行试验载荷下的应力状态仿真,结果验证了磁记忆方法对三点弯曲变形状态研究的有效性．     

采动影响下厚湿陷性黄土层拉伸裂缝预测研究

在受到采动影响下,为了预计湿陷性黄土地表生成裂缝的区域,提出了湿陷性黄土极限抗拉强度与采动影响而形成的拉伸变形相结合的方法,判断地表生成裂缝的区域.如果在采动影响下的拉伸变形量大于湿陷性黄土极限抗拉强度,则在该区域生成地表裂缝,否则不生成裂缝.利用概率积分法求得移动变形分量,并推导出了最大拉伸变形和最小压缩变形;根据黄土的力学参数,求得地表产生裂缝的极限抗拉变形.以常村矿为例,得到在该工程地质条件下,地表产生最小拉伸变形为3.9 mm/m,裂缝角为60°.