【作者】 龙盛蓉；

【导师】 钟毓宁； 刘莹；

【作者基本信息】 南昌大学 ， 机械设计及理论， 2014， 博士

【摘要】 磁致伸缩导波检测传感器作为一种新型的超声波检测装置实现了非接触式的高效无损检测，常用于铁磁性管道等结构的健康监测，但其较低的信噪比及非线性力磁耦合特性造成输出信号多变等不足限制了其应用。因此探索力磁耦合作用下磁致伸缩导波检测技术机理和传播特性，明确影响磁致伸缩传感器的主要因素对于提升磁致伸缩导波检测效率有着重要的意义。本论文采用仿真计算和物理实验相结合的方法，针对磁致伸缩导波检测技术机理和力磁作用下的磁致伸缩导波传播特性及其影响因素进行了研究。首先，以电磁学、弹性力学及电动力学等经典理论为基础，应用动量守恒定理的方法，推导了基于Lorentz力、磁化力和磁致伸缩力的磁致伸缩导波检测系统控制方程，详细阐述了磁致伸缩导波检测系统的换能机理。依据磁致伸缩导波检测的工作原理，将其分成三个相互关联的场，即电磁场、电磁场与物质相互作用的力场和超声波场，并给出了相应的数学描述，得到了磁致伸缩导波检测系统完整方程式。在此基础上，分析了磁致伸缩力和Lorentz力之间的关系，确定了磁致伸缩力在基于磁致伸缩效应导波检测中的主导地位，说明偏置磁场平行于检测工件的情况下，磁致伸缩力的变化对磁致伸缩导波的检测效率有直接影响。其次，针对以磁致伸缩效应为主要机理传感器的研究，在过去一般将材料的非线性磁致伸缩关系假定为线性关系，而该线性模型只适用于在偏置磁场附近狭小的线性范围，并不能满足实际的工作条件。为了真实的反映非线性力耦作用下磁致伸缩导波传感器的工作机理，本文利用磁致伸缩导波检测系统中电磁场及力场的数学方程式，建立了导波的磁致伸缩式纵向模态激励传感器非线性动力学模型，并以此模型为基础，针对影响磁致伸缩导波检测传感器力磁耦合转换效率的静态偏置磁场、交流磁场及激励频率进行了研究。分析表明，在考虑频散特性的情况下，通过降低激励电流频率、提高其电流强度，并将偏置磁场设定于磁致伸缩曲线中切线斜率最大处等方法可以有效的提高磁力转换效率。再次，传统的磁致伸缩导波检测中忽略了力磁作用对导波传播的影响，造成缺陷定位的不准确。基于此不足，本文从磁致伸缩材料的非线性本构模型出发，建立了磁场、应力场与铁磁性材料弹性模量之间的关系，讨论了磁场及应力场对磁致伸缩材料特性的影响，并采用有限元分析软件进行了模拟，得到了力磁作用下磁致伸缩导波的传播特性。计算表明在磁场或应力场的作用下磁致伸缩导波群速度会发生改变，从而影响到检测中缺陷的定位。最后，采用虚位移方法推导了在轴对称坐标下，永磁体、线圈的脉冲涡流场及被测试样的平衡运动方程的弱形式方程，得到了对磁致伸缩导波检测有着重要影响的磁致伸缩力和磁致伸缩电流密度的计算公式。从磁致伸缩导波检测系统优化的角度出发，建立了其有限元仿真模型，针对影响其检测性能的偏置磁场强度及均匀性、激励电流特性等因素进行了优化设计，并采用实验方法进行了验证。更多还原

【Abstract】 Magnetostrictive sensor of guided wave is a new type of ultrasonic testingdevice which is useful for the structural health monitoring (SHM) of systems. Thetraditional NDT tools, such as magnetic flux leakage testing, piezoelectric ultrasonictesting and X-ray testing, have shortcomings, it is slowly and costing. Whilemagnetostrictive sensor of guided wave have overcome these defects and realize theefficient nondestructive testing which is non-contact. While the shortcoming ofmagnetostrictive sensor of guided wave, such as low SNR and the output affected bythe nonlinear magneto-mechanical coupling performance under magnetic field, canlimit the use of it. In order to solve this problem, the magnetostrictive guided wavestesting mechanism and propagation characteristic for steel tubes were analyzed.Making clear of main influence factors of sensor can improve the energy transitionefficiency. By the method of simulation and experiment, the mechanism ofmagnetostrictive guided waves testing and propagation characteristics of guidedwaves which under stress and magnetic are studied.Firstly, using the law of conservation of momentum, the governing equations ofmagnetostriction guided wave sensor are got which basing on the Lorentz force,magnetizing force and magnetostrictive force. And all these are deduced from theclassical theory such as electro-magnetics, mechanics of elasticity andelectrodynamics and so on. By electromagnetic field, force field and ultrasonic field,the working principle of magnetostrictive guided waves sensor is got andcorresponding mathematical description is given. The relationship betweenmagnetostrictive force and Lorentz force is discussed by the equations given before.And the leading role of the magnetostrictive force in magnetostrictive guided wavessensor is determined. The result is that with the change of the magnetostrictive force,the efficiency of magnetostrictive guided waves sensor is much affected when thebias magnetic paralleled the surface of pipe.Secondly, the research on the magnetostrictive guided waves sensor was usually regarded the material constitutive as linear which could only suit the bias magneticnear the linear range. So these models can’t satisfy the actual working conditions. Inorder to solve this problem, the paper set up the dynamics mechanical model formagnetostrictive guided wave sensor generation on the nonlinearmagneto-mechanical coupling performance of ferromagnetic. The effect of the biasmagnetic field, excitation frequency and excitation current on the particle amplitudewas analyzed. The difference of particle amplitude between nonlinear and linearmodel was discussed, which proved the applicability of the model further. Theanalysis indicates that by increasing of excitation current or decreasing of excitationfrequency and setting the bias magnetic around the biggest tangent slope of themagnetostrictive curve can improve the magnetic conversion efficiency.Thirdly, in past research the effect of stress or magnetic on the guided waves isneglected which caused the inaccurate in defect locational. So, according to thenonlinear constitutive equations of magnetostrictive material, in the free constraincondition, the effect of magnetic and stress on the material is studied. The relationshipbetween magnetic, stress and elastic modulus of ferromagnetic materials is set up. ByFEM software, the propagation characteristics of magnetostrictive guided wave undermagnetic or stress is simulated. The result is the group velocity of magnetostrictiveguided wave is changed which can influence the defect location.At last, the weak form of balance equations for permanent magnet, pulsed eddycurrent by coil and the test sample under axisymmetric coordinates are got by thevirtual displacement method. At the same time, the formulas of the magnetostrictiveforce and magnetostrictive current density are deduced which having effect on themagnetostrictive guided wave system. In order to optimize the system, a FEM modelis set up. Using the model, the factors, such as the strength and uniform of biasmagnetic and the characteristics of excitation current, are analyzed. All these resultsare verified by experiments.更多还原