拉应力对不同厚度Q345钢磁记忆信号的影响

为明确磁记忆信号与拉应力之间的对应关系和几何尺寸对试件表面磁场的影响,对Q345低合金钢不同厚度板状试件进行静载拉伸实验.利用TSC-1M-4型磁检测仪,研究3种厚度的光滑试件表面磁记忆信号在不同拉应力下的变化规律.结果表明:弹性阶段磁记忆信号与拉应力之间有较好的相关性,塑性阶段两者相关性较弱;切向磁记忆信号对试件局部屈服的表征比法向磁记忆信号更敏感,利用切向磁场的畸变性可预判试件的早期塑性变形和应力集中区;同一应力水平下,试件表面磁场强度随厚度增加而减小,但不影响其变化规律.     

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.     

塑性变形条件下拉伸构件的磁记忆效应

通过对经退磁处理的光滑和切口试件在不同程度拉伸变形下的在线磁信号的测量,研究了塑性变形对磁记忆效应的影响.光滑试件在弹性和均匀塑性流动阶段磁场分布近似为斜直线,仅到颈缩后才在应力集中部位产生明显的磁场畸变;切口试件在屈服以后即出现畸变特征,基于位错理论分析了异常波波高增加的原因,利用磁信号水平线图可定性判断应力集中区破...     

金属磁记忆检测技术机理模型

研究了铁磁构件在应力和地磁场共同作用下的磁记忆检测机理,从磁记忆的原理出发,根据铁磁材料所具有的自发磁化和磁畴的特点以及磁的产生机制,提出一种新的磁记忆检测技术的机理模型.以此模型为基础,得出试件表面所测得的磁场是缺陷处产生的漏磁场、试件本身感应磁场以及环境磁场矢量叠加的结果,并以矩形槽为例用matlab对磁场进行了仿真,很好的解释了磁记忆检测过程中的现象.     

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.     

静态磁场谐振磁传感器设计

为了解决磁致伸缩/压电复合磁传感器测量静态磁场时需要交变激励磁场以及磁电电压输出低等问题,提出了一种改进结构的磁致伸缩/压电/音叉复合谐振磁传感器,采用COMSOL有限元仿真软件对传感器的应力与应变分布以及音叉的振动模态进行仿真.结果表明,传感器的谐振频率随着磁场强度的增加近似线性递增;在0～1 000 Oe磁场范围内,灵敏度达1. 750 5 Hz/Oe,是改进前的7倍,验证了传感器改进结构的有效性.     

钢结构对接焊缝隐性损伤的磁记忆检测试验研究

通过施加拉伸及弯曲荷载,分析了未焊透缺陷及无缺陷的对接焊缝钢构件的磁记忆信号.发现漏磁场强度与外应力存在一定的对应关系,磁场强度随拉应力的增大而增大,随压应力的增大而减小,在应力集中区磁记忆曲线出现波峰或波谷.进入塑性阶段以后磁记忆曲线产生巨大突变,磁场强度突变时刻可用于判断焊缝试件即将破坏的临界状态,梯度峰值可用于表征未焊透缺陷试件的应力集中程度.     

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.     

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.     

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.     

水-温循环作用下千枚岩的动态拉伸特性

为研究水-温耦合作用下0°层理倾角千枚岩的动态拉伸特性变化规律,分别对3组试样进行0、1、3、5、7、8、11次温度循环自然降温、温度循环冷水降温、干湿循环后,采用霍普金森杆试验装置对0°层理倾角千枚岩试样开展动态巴西劈裂试验,从动态拉伸应变曲线、动态峰值抗拉强度、动态弹性模量、能量分析与宏观破坏5个角度研究水、温劣化条件下千枚岩的动态拉伸特性。结果表明：千枚岩应力应变曲线包括极速弹性变形阶段、屈服变形阶段、破坏变形阶段;随着水-温循环次数的增加,千枚岩应力-应变曲线极速弹性变形阶段逐渐缩短,屈服变形阶段的应变增长率不断增大;千枚岩动态峰值抗拉强度呈负指数函数关系变化,耗散能比不断减小;水-温耦合条件下,千枚岩峰值抗拉强度、耗散能比普遍小于温度循环自然降温时;动态冲击下,千枚岩发生贯穿层理的张拉破坏,主要破碎为2块;随着水-温循环次数的增加,千枚岩主碎块发生沿层理面的张拉与穿层理面的剪切复合破坏,千枚岩碎块的平均尺寸不断减小;温度循环冷水降温条件下,千枚岩碎块的平均尺寸更小,且降幅最为显著。     

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。