基于磁记忆的淬火45钢拉伸性能的评估

以工业中常用的45钢作为研究对象,并针对不同淬火的45钢试样进行拉伸试验,研究拉伸过程的阶段性磁记忆信号特征,揭示拉伸过程磁记忆表征规律,明确磁记忆信号与力学性能参数的关系,建立基于磁记忆的淬火45钢力学损伤的评估方法,为磁记忆技术用于评估淬火钢力学损伤程度奠定基础。研究结果表明,磁记忆检测能准确判断淬火钢拉伸过程应力状态及损伤程度,实现评估力学损伤的目标。     

疲劳损伤金属磁记忆二维信号评估

研究疲劳后期(累积损伤严重期)金属磁记忆信号随疲劳加载的变化规律,构建了有效的评估方法。研究表明:表征二维磁记忆信号曲线相似程度的相关系数ρ可以很好地反应铁磁性材料的疲劳损伤程度。     

基于磁记忆检测方法的45钢应力集中评价

在离线情况下,利用金属磁记忆二维扫查装置测量45钢试样的磁记忆信号二维分量。通过对磁记忆信号二维分量进行微分处理得到相关分量的梯度,进而合成磁记忆信号的李萨如图形。通过分析李萨如图形区域面积与拉伸载荷之间的变化特性,对材料中应力集中进行定量评估。试验结果表明:对试样进行拉伸时,缺口处磁记忆信号变化特征比较显著,有利于对应力集中位置的确定;切向分量的信号峰值与拉伸载荷之间的相关性更好;李萨如图形区域面积大小与拉伸载荷呈正相关变化趋势,通过对李萨如图形面积大小进行非线性拟合可得到材料的应力集中定量评估判定曲线。     

金属磁记忆检测技术用于再制造毛坯寿命预测的试验研究

为探讨金属磁记忆无损检测技术预测再制造毛坯的剩余寿命,采用金属磁记忆技术检测了拉-拉疲劳过程中45钢光滑试件和预制缺陷试件表面的磁记忆信号变化规律.结果表明45钢光滑试件疲劳试验过程中,在试件断裂之前,随疲劳载荷作用循环次数的增加,试件表面磁信号的分布规律变化不大,试件断裂后断口处磁信号发生激变;表面预制槽型缺陷的45钢试件在疲劳试验过程中,其表面磁信号在预制缺陷扩展后发生变化,且缺陷部位磁信号峰峰值随裂纹长度增加而持续增大.研究分析认为,金属磁记忆检测技术对疲劳裂纹的扩展情况有较好的反映,有望通过建立磁记忆信号峰峰值--疲劳裂纹长度a的关系模型,实现金属磁记忆技术对再制造毛坯剩余寿命的定量方法.但是,采用金属磁记忆技术预测疲劳裂纹萌生前铁磁材料的损伤程度尚需进一步探索.     

不同载荷对无取向硅钢试件表面漏磁场的影响

利用电子拉伸试验设备和弱磁场测量系统,对受静拉伸载荷的试样表面漏磁场进行测量,研究了试件在弹性阶段、均匀变形阶段和非均匀变形阶段磁记忆信号随载荷大小不同的变化规律;最后,根据试验现象,结合晶粒滑移理论基础对静载荷下磁记忆检测的机理作了解释。试验和理论研究的结果表明:采用磁记忆方法对承载疲劳载荷铁磁构件由应力集中造成的早期损伤进行检测是可行的。     

环境磁场对磁记忆信号的影响

金属磁记忆检测技术是一种可早期准确判断构件的应力集中位置和评估疲劳损伤程度的无损检测技术新方法,而磁记忆信号的存在离不开环境磁场。为探讨环境磁场对磁记忆信号的具体影响,在不同环境磁场下,对45钢进行静载拉伸试验,测量在相同环境磁场下不同应力作用下的磁记忆信号。试验结果表明:环境磁场不能改变磁记忆信号曲线的形状,但可以改变磁记忆信号值的大小;在一定的磁场范围内,磁记忆信号值随环境磁场的增加而增加,但当环境磁场超过某一临界值时,磁记忆信号值反而随环境磁场的增加而减少;若环境磁场为零或完全被抵消,应力则不能产生磁记忆信号。故在磁记忆检测实践中,特别是在定量检测应用中必须考虑环境磁场的影响。     

金属磁记忆技术用于去应力退火评估的可行性研究

本文基于磁致伸缩效应的新型金属磁记忆无损检测技术,利用金属磁记忆信号与应力大小严格的对应关系,对金属磁记忆检测技术用于去应力退火进行评估,进行可行性研究.通过研究分析发现,金属磁记忆信号与45钢的去应力退火程度有一致的单调性,通过检测金属磁记忆信号磁场的强度,可实现对去应力退火工艺的评估.     

磁记忆切向分量信号的检测研究

针对金属磁记忆切向信号难以提取的问题,提出采用矢量合成法提取金属磁记忆切向分量,并通过ANSYS仿真软件验证其有效性;通过铁磁性金属构件拉伸试验对磁记忆切向分量信号与应力集中部位和应力集中程度的关系进行研究,并对磁记忆切向分量信号的K曲线进行分析.结果表明:采用矢量合成法能有效提取金属磁记忆切向信号;金属磁记忆切向分量...     

金属磁记忆检测技术用于再制造毛坯寿命预测的试验研究

为探讨金属磁记忆无损检测技术预测再制造毛坯的剩余寿命，采用金属磁记忆技术检测了拉－拉疲劳过程中45钢光滑试件和预制缺陷试件表面的磁记忆信号变化规律。结果表明：45钢光滑试件疲劳试验过程中，在试件断裂之前，随疲劳载荷作用循环次数的增加，试件表面磁信号的分布规律变化不大，试件断裂后断口处磁信号发生激变；表面预制槽型缺陷的45钢试件在疲劳试验过程中，其表面磁信号在预制缺陷扩展后发生变化，且缺陷部位磁信号峰峰值随裂纹长度增加而持续增大。研究分析认为，金属磁记忆检测技术对疲劳裂纹的扩展情况有较好的反映，有望通过建立磁记忆信号峰峰值——疲劳裂纹长度a的关系模型，实现金属磁记忆技术对再制造毛坯剩余寿命的定量方法。但是，采用金属磁记忆技术预测疲劳裂纹萌生前铁磁材料的损伤程度尚需进一步探索。     

磁记忆对45号钢回火效果及力学性能的评估

研究了回火温度对45号钢磁记忆信号及其力学性能的影响,记录回火钢拉伸过程的各阶段磁记忆信号表征,建立磁记忆信号与力学性能参数的关系,阐明不同回火试件拉伸过程磁记忆信号变化机理。结果表明,磁记忆作为一种新兴无损检测方法能够快速、有效的评价回火效果,并能对回火钢拉伸过程各阶段的损伤程度进行判断。     

Magnetic field variation induced by cyclic bending stress

Metal magnetic memory technique has provided a new arena for assessing stress status, especially for detecting early damage in ferromagnetic materials. To investigate the magnetomechanical effect of metal magnetic memory phenomenon, the rotary bending fatigue experiments under different stress levels were conducted. The normal components of magnetic field intensities induced by cyclic bending stresses on the surfaces of 45-steel specimens were measured throughout the fatigue process. The results show that surface magnetic fields generated contains reversible and irreversible process prior to failure, while there is a substantial increase just before fracture. Possible reasons for the variations of magnetic fields and corresponding signal characteristics to identify damage zones were discussed.     

旋转弯曲疲劳件的法向磁信号分布

为对旋转弯曲疲劳过程中的磁记忆信号进行分析,从磁记忆的物理基础出发,把旋转弯曲疲劳试验件看成一个磁体,试件的疲劳破坏过程就是试件由一个磁体变成两个磁体的过程。指出在试件表面检测到的磁场是环境磁场、试件的磁感应磁场和漏磁场的叠加,并分析了沿试件轴向的法向磁信号的分布变化。最后通过旋转弯曲疲劳试验,验证了理论分析结果。理论分析和试验结果均显示,疲劳破坏前法向磁信号出现显著的异常特征,可用其进行疲劳损伤诊断。     

铁磁材料疲劳损伤的磁性无损检测技术

疲劳破坏是铁磁材料构件主要的失效形式，评价铁磁材料的疲劳损伤在工程实践中具有重要的意义。磁性无损检测新技术在判断铁磁材料的疲劳损伤领域具有广阔的应用前景。综述了磁巴克豪森噪声技术（MBN）、磁声发射技术（MAE）和磁记忆技术（MMM）的检测原理、特点和应用情况，提出了三种新技术目前存在的问题和未来的发展。     

30CrMnSiNi2A钢疲劳损伤二维磁记忆检测的试验研究

选取不同厚度30CrMnSiNi2A平板缺口试样在0.7σs应力水平下进行低周疲劳试验,并实施磁记忆二维检测,研究不同厚度、不同循环周次下的磁记忆信号变化规律。研究结果表明:随着循环次数的增加,局部应力集中部位的磁记忆信号特征越来越明显,信号幅值也越来越大,并在裂纹失稳断裂前出现明显的法向分量过零而切向分量具有最大值的特征;法向分量和切向分量微分后合成的李萨如图形的封闭区域大小随循环周次呈现Logistic曲线变化,可定量分析构件疲劳损伤程度。该研究结果可为进一步进行磁记忆二维检测研究提供技术支撑。     

基于磁记忆机理的焊缝疲劳累积损伤特征

通过20号钢焊接平板试件的拉-拉疲劳试验,研究了在单周期和多周期循环载荷下焊缝疲劳累积损伤的磁记忆信号特征。结果表明,由于试件内部初始状态下各处应力分布不均匀,焊缝原始磁信号表现为起伏较大;随着循环周次的增加,试件内部应力集中重新分布,信号趋于稳定;在周期累积循环试验中,磁记忆信号随着循环周次的增加出现螺旋上升的趋势,呈现出磁弹性效应变化特征;通过建立磁记忆信号与损伤度函数的模型,可根据磁记忆信号的变化准确判断裂纹扩展趋势,用于焊缝剩余寿命的预测。     

The effect of residual stresses induced by prestraining on fatigue life of notched specimens

The effect of tensile prestraining-induced residual stress on the fatigue life of notched steel parts was investigated. The study was performed on AISI 4140 steel. Rotating bending fatigue tests were carried out on semicircular notched specimens with different notch radii in the as-quenched and tempered conditions. Metallography of the specimens was performed by means of light optical microscopy. The finite-element method was used to evaluate the residual stress distribution near the notch region. Fatigue tests revealed fatigue life improvement for notched specimens, which changes depending on the notch radii and applied stress. Scanning electron microscopy was used to examine the fracture surfaces of the specimens.     

Fatigue-life prediction of SiC aluminum composite using a Weibull model

The feasibility of the acoustic emission technique in predicting the residual fatigue life of 6061-T6 aluminum matrix composite reinforced with 15 vol.% SiC particulates (SiC_p) is presented. Fatigue damages corresponding to 40, 60 and 80% of total fatigue life were induced at a cyclic stress amplitude. The specimens with and without fatigue damage were subjected to tensile tests. The acoustic emission activities were monitored during tensile tests. The number of cumulative AE events increased exponentially with the increase in strain during tensile tests. This exponential increase occurred when the material was in the plastic regime and was attributed mainly to SiC particulate/matrix interface decohesion. Cumulative events during post fatigue tensile tests reduced with a decrease in the residual fatigue life. Based on the high cycle fatigue damage accumulation model, a Weibull probability distribution model is developed to explain the post fatigue AE activity of specimens during tensile tests. Using the model, the residual fatigue life can be predicted by testing the specimen in tension and monitoring the AE events. In high cycle fatigue, it was observed that the residual tensile strengths of the material did not change significantly with prior cyclic loading damages since the high cycle fatigue life was dominated by the crack initiation phase.     

Study on magnetic memory signals of medium carbon steel specimens with surface crack precut during loading process

Static tensile test and tensile-tensile fatigue test of medium carbon steel sheet specimens with surface crack precut were performed on MTS810 hydraulic testing machine to clear the meaning of the point of Hp( y ) value zero. Magnetic memory signals were measured during the test process. The results show that only one point of Hp( y ) zero value exists in all measured magnetic signal curves during the loading process, which should be a sign of intersection of positive-negative magnetic poles after magnetic ordered state appears and does not indicate the position of surface crack precut. The analysis shows that the surface crack precut can not interrupt the magnetic ordered state occurred during the test completely, hence its Hp( y ) value is not zero. However, the crack extending to a penetrated defect at the instant of specimen's fracture leads to the discontinuance of magnetic ordered state.     

拉保持对316L奥氏体不锈钢焊接接头低周疲劳循环应力响应及损伤机制的影响

在873 K温度下对316L奥氏体不锈钢母材和焊缝分别进行连续和拉保持低周疲劳试验,使用光学显微镜(OM)和透射电镜(TEM)对试样位错微观结构和裂纹扩展形貌进行观察,分析拉保持对母材和焊缝低周疲劳循环应力响应及损伤机制的影响.结果表明,母材在连续和拉保持低周疲劳试验初期都发生循环硬化,焊缝在连续低周疲劳试验中发生连续循环软化,而在拉保持试验后期则出现明显循环稳定阶段;母材和焊缝试样拉保持低周疲劳寿命低于其连续低周疲劳寿命;母材和焊缝在连续低周疲劳试验中裂纹主要以穿晶方式扩展,而在拉保持试验中焊缝是以沿晶或混合方式扩展.