【作者】 邵俊华；

【导师】 李友荣； 王涛；

【作者基本信息】 武汉科技大学 ， 机械设计与理论， 2018， 博士

【摘要】 螺栓联接作为一种最基本的紧固件联接结构形式,从小型工具到大型设施,从日常民用到先进科技装备等被广泛应用于国民生产生活的众多领域。螺栓联接结构在冲击、振动及交变荷载的长期作用下,会逐渐产生松动脱落甚至断裂,而某些关键部位的螺栓联结结构一旦松动或脱落,将可能导致重大安全事故。本论文利用压电阻抗技术,结合理论分析、有限元仿真分析与实验验证,系统地研究了螺栓联接状态的监测机理及方法,主要研究内容及主要结论如下:(1)基于压电材料自身的高频谐振特性,建立了压电材料自身及压电材料与基体结构耦合系统的压电阻抗高频理论模型,由逐点动态刚度理论,揭示了基体结构工作状态改变对其局部动力学特性(结构的局部谐振频率)的影响,即当基体结构的工作状态发生变化时,其机械阻抗会随之发生变化,导致结构局部阻抗比或刚度比发生变化,并由压电材料输出阻抗/导纳谱反映出来,通过压电输出导纳信号,便可确定结构的健康状态。基体结构局部的刚度变化仅影响基体结构局部动态特性,从结构整体进行测试很难检测到该变化,而压电阻抗技术采用高频激励与传感时,测量安装位置基体结构局部的动力学特性变化,能有效检测到这种初始变化,这是其它结构健康监测方法难以实现的。(2)基于单轴拉压一维构件波动方程,推导了单轴拉压一维构件轴向载荷变化与结构固有频率之间的函数关系,即结构横向振动模态的固有频率会随轴向拉伸载荷(拉应力)的增加而近似线性增大,随轴向压缩载荷(压应力)增加而线性减小;而纵向振动模态频率则基本保持不变。鉴于结构的每一阶振动模态都会在压电阻抗/导纳信号中以谐振形式出现,因此,在结构压电耦合系统输出的阻抗/导纳谱中,通过观察导纳谱峰、谷值对应频率发生的相应偏移,便可以确定结构的应力变化状态,实现对结构工作应力状态的监测。(3)基于压电阻抗谐振频率的变化量与结构外部载荷变化量两者间的线性关系,提出将压电阻抗谐振频率的变化量作为特征参量来对螺栓的联接状态进行监测。针对螺栓联接件的结构特征及使用环境,设计了螺栓杆部集成压电材料、螺栓头部端面集成压电材料及螺母侧面集成压电材料的三种螺栓联接状态监测方案:(a)螺栓杆部集成压电材料的螺栓联接状态监测实验结果表明,耦合结构的阻抗/导纳谱谐振频率随螺栓轴向拉伸载荷的增大而近似线性增大;(b)螺栓头部端面集成压电材料的螺栓联接状态监测实验结果表明,压电导纳谱中谐振峰值频率随螺栓预紧力的增加而近似线性递减,即当螺栓发生松动,预紧力减小时,其谐振峰值频率近似线性增大。在洁净环境和油污环境下的对比实验测试结果还表明,油污环境对谐振峰值频率影响较小,因此,基于谐振频率变化的螺栓联接状态监测方法抗干扰能力强;(c)螺母侧面集成压电材料的螺栓联接状态监测实验结果表明,在预紧力作用下,螺母外侧面靠近自由端面部分处于拉应力状态,接近被联接件部位呈现压应力状态,因此,螺母侧面集成压电材料所得到的导纳谐振峰值频率与螺栓预紧力的大小、压电片的集成位置有关,但阻抗谱中谐振频率该变量与预紧力变化之间呈现出的线性关系与理论分析符合。实验分析还发现,压电片几何尺寸越小,耦合结构阻抗谐振峰值频率越大,且压电片横向粘贴时谐振频率随载荷变化更明显。当将压电材料分别集成在螺栓杆部、螺栓头部端面与螺母外侧面上形成智能螺栓结构时,可将阻抗/导纳谱中谐振频率峰值作为特征值来对螺栓预紧力及联接状态进行在线监测,该方法抗噪性能好,应用范围广。更多还原

【Abstract】 As one of the most basic fastener connection structures,bolt connection is widely used in many fields of national production and life;From small tools to large facilities as well from daily civilian to advanced scientific and technological equipment.Under the long-term impact,vibration and alternating load,the bolted structure will loosen and even break.Once the bolted structure in some key parts is loosened or falls off,it may lead to major safety accidents.In this paper,piezoelectric impedance technology,combined with theoretical analysis,finite element simulation analysis,and experimental verification,systematically studied the monitoring mechanism and method of bolt connection state.The main research contents and main conclusions are as follows:Based on the high-frequency resonance characteristics of piezoelectric materials,the high-frequency theoretical models of the piezoelectric impedance of piezoelectric materials and the coupling system of piezoelectric materials and substrate structures are established.Based on the point-by-point dynamic stiffness theory,the influence of the change of the working state of the matrix structure on its local dynamic characteristics(local resonance frequency of the structure)is revealed,that is,the mechanical impedance changes accordingly when the working state of the matrix structure changes,resulting in changes in the local impedance ratio or stiffness ratio of the structure,which is reflected by the output impedance/admittance spectrum of piezoelectric materials.Through the piezo output impedance/admittance signal,the health state of the structure can be determined.The local stiffness change of the matrix structure only affects the local dynamic characteristics of the matrix structure.It is difficult to detect the change by testing the whole structure;However,when piezoelectric impedance technology uses high-frequency excitation and sensing,it can measure the local dynamic characteristics of the base structure in the installation position,which can effectively detect the initial changes,which is difficult to achieve by other structural health monitoring methods.Based on the wave equation of uniaxial tension-compression one-dimensional members,the functional relationship between the change of axial load and the natural frequency of the structure is derived.The natural frequency of the transverse vibration mode of the structure increases approximately linearly with the increase of the axial tension load(tensile stress)and with the increase of the axial compression load(compressive stress).While the linear frequency decreases,while the longitudinal vibration modal frequency basically remains unchanged.In view of the fact that every vibration mode of the structure will appear in the form of resonance in the piezoelectric impedance/admittance signal,the stress state of the structure can be determined by observing the corresponding frequency shift of the peak and valley of the admittance spectrum in the impedance/admittance spectrum of the piezoelectric coupling system.Monitoring of stress state.Based on the linear relationship between the variation of piezoelectric impedance resonance frequency and the variation of the external load of the structure,the variation of piezoelectric impedance resonance frequency is proposed as the characteristic parameter to monitor the bolt connection state.Aim to the structural characteristics and application environment of bolted joints,three monitoring schemes for bolted joints are designed,i.e.bolt-rod integrated piezoelectric material,bolt-head integrated piezoelectric material,and nut-side integrated piezoelectric material.(a)The state monitoring results of bolted joints with integrated piezoelectric materials in the bolt rod show that the impedance/admittance spectrum resonance frequency of the coupling structure increases approximately linearly with the increase of the axial tension load of the bolt.(b)The experimental results show that the peak resonance frequency of the piezoelectric admittance spectrum decreases linearly with the increase of pre-tightening force,that is,when the bolt loosens and the pre-tightening force decreases,the peak resonance frequency increases linearly.The comparative test results in the clean environment and oil pollution environment also show that oil pollution environment has little effect on resonance peak frequency.Therefore,the bolt joint condition monitoring method based on resonance frequency variation has the strong anti-interference ability.(c)The experimental results of the bolt joint condition monitoring of the integrated piezoelectric material on the side of the nut turned out that under the pretension force,the part of the outer side of the nut near the free end face is in the tensile stress state,and the part near the joint part is in the compressive stress state.Therefore,the peak admittance resonance frequency of the integrated piezoelectric material on the side of the nut is related to the bolt.The size of the preload is related to the integrated position of the piezoelectric chip;However,the linear relationship between the resonance frequency and the change of preload force in impedance spectroscopy agrees with the theoretical analysis.It is also found that the smaller the size of piezoelectric patches,the larger the peak frequency of impedance resonance of the coupling structure.For the same load,the change of resonant frequency with load is more obvious when piezoelectric patches are transversely bonded.When the piezoelectric material is integrated into the bolt rod,the end face of the bolt head and the outer side of the nut to form an intelligent bolt structure,the peak value of resonance frequency in the impedance/admittance spectrum can be used as the eigenvalue to monitor the bolt preload and the connection state online.The method has good anti-noise performance and also a wide application range.更多还原