【作者】 李新蕾；

【导师】 任尚坤；

【作者基本信息】 南昌航空大学 ， 测试计量技术及仪器， 2010， 硕士

【摘要】 本文以磁性物理学、技术磁学等理论为指导,以试验研究和数值仿真为手段,研究了不同铁磁材料在不同载荷下的磁记忆信号分布特征,并将金属磁记忆技术引入到疲劳损伤与寿命评估领域,探索疲劳损伤的磁记忆表征规律。根据应力的磁效应来源于应力的磁导率效应的理论,利用ANSYS有限元软件对20#钢小孔平板试样进行了力-磁效应的有限元仿真。提取数据并分析了磁场分布规律及检测路径、应力大小对表面漏磁场影响,对磁场强度法向梯度值进行了分析,绘制了法向梯度值的峰值幅度随应力的变化曲线。结果表明,在应力集中部位磁场强度法向分量过零点,切向分量出现最大值,磁力线在应力的加载过程中发生了反转,证明了力磁耦合模型的适用性。分析还表明,应力集中和漏磁场法向梯度值具有很强的相关性,应力分布决定了漏磁场梯度的分布。以45#钢为研究对象,分别对无预制缺陷及带缺口平板试样拉伸过程中的磁记忆信号进行了测量与分析。结果表明,在弹性阶段,磁记忆信号较小且分布杂乱,而当应力大于500MPa时,磁记忆信号明显增强。在磁记忆特征值提取方面,利用传统的磁场梯度极值|K|max可以有效的检验应力集中部位。同时本文提出一种新的基于磁记忆信号能量的检测特征值,实验证明可以通过此特征值对试样的安全性做出检测及评估。对比分析了45#钢与30CrMnSiNi2A钢拉伸过程中的磁记忆信号,结果表明,不同的铁磁材料在应力的作用下,其法向磁场梯度K值峰值变化规律不同,这与材料的力学性能以及材料的磁学参数有直接的关系。以40Cr钢三点弯曲SE(B)试样进行常温疲劳裂纹扩展试验,分别测量了试样在相同载荷条件下不同寿命N时的磁场数据。通过分析磁场数据与裂纹扩展寿命、累积疲劳损伤之间的关系,建立了基于磁记忆信号的损伤参量模型。利用该模型可以有效的评估材料的残余寿命,可为磁记忆检测技术在铁磁性材料早期损伤以及残余寿命评估方面的应用提供借鉴作用。更多还原

【Abstract】 In this paper, the distribution characteristics of magnetic memory signals of different ferromagnetic materials under different loads were studied by numerical simulation and experiments based on the magneto-physics and magnetic technology. The laws of fatigue damage and residual life assessment using magnetic memory signals were explored.According to theory of the stress effects magnetic permeability, the finite element analysis of stress-magnetization effect was done on 20# steel plate specimen with a hole using ANSYS. The magnetic field distribution was analyzed, also the influence of the detection path and the stress state on magnetic memory signal. The curve of the peak values of the normal gradient with the stress was drawn. Through the analysis result, the normal component of the magnetic field appeared a zero-crossing point, the tangential component reaches a maximum, and magnetic flux lines reversed in the stress loading process. It proved the applicability of the magneto-elastic coupling model. Through the analysis, the stress concentration has a strong correlation with the normal gradient of the magnetic field, the stress distribution determines the gradient distribution of leakage magnetic field.The magnetic field distributions under different tensile loads were measured for no pre-defect specimens and plate notched specimens of 45# carbon steel respectively. Through the analysis, the magnetic memory signal was small and irregular in the elastic phase, but it increased apparently when the stress is greater than 500MPa. In the aspect of eigenvalue extraction, the traditional magnetic field gradient|K|max can test the stress concentration area validity. A new eigenvalue based on MMM (metal magnetic memory) signal energy was proposed. The experiment confirms that this eigenvalue can effectively detect and evaluate the ferromagnetic items. Through comparative analysis of the magnetic memory signals for 45# steel and 30CrMnSiNi2A steel in the process of tensile loads, the magnetic field gradient K changes differently under the action of stress. It has a direct relationship with the mechanical properties and magnetic parameters of the material.The fatigue crack growth experiment was carried out at room temperature for the standard SE(B) specimens of 40Cr steel, the distribution of the surface magnetic field of the specimen was investigated under the same load and different cycle numbers (N). By analyzing relations between the magnetic memory signals and the crack propagation life, the cumulative fatigue damage, a new damage parameter model was established by using magnetic memory signals. According to this model, the residual life of ferromagnetic components can be evaluated excellently. It is a basic research for the application of magnetic memory testing technology in aspects of early damage and residual life assessment of ferromagnetic materials.更多还原