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1.
According to the principle of synchronous demodulation,the modulation information in the output signal of vibro-acoustic modulation test was investigated and the nonlinear interaction of sound and vibration with the crack interface in a metallic rod was analyzed.A swept signal excitation was used to obtain a proper high frequency parameter in the test of aluminum rod samples with different sizes of cracks and the modulation information in the output signal was analyzed.It was found that the ultrasound wave in the structure can be separated into two parts.One is the wave which passes through the crack interface modulated by the low frequency vibration,and other wave has no any changes.The nonlinear modulation model was modified and a quantitative method for crack detection was proposed.It is demonstrated by comparing with the ultrasonic C-scanning that this method can be used to estimate the fatigue crack size in the metallic rod.  相似文献   

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In this paper a new continuous model for flexural vibration of rotors with an open edge crack has been developed. The cracked rotor is considered in the rotating coordinate system attached to it. Therefore, the rotor bending can be decomposed in two perpendicular directions. Two quasi-linear displacement fields are assumed for these two directions and the strain and stress fields are calculated in each direction. Then the final displacement and stress fields are obtained by composing the displacement and stress fields in the two directions. The governing equation of motion for the rotor has been obtained using the Hamilton principle and solved using a modified Galerkin method. The free vibration has been analyzed and the critical speeds have been calculated. Results are compared with the finite element results and an excellent agreement is observed.  相似文献   

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Steel 09G2S specimens are subjected to cyclic tests, and real-time monitoring of the initiation of a fatigue crack and its growth kinetics is performed by dynamic speckle interferometry. The time averaging of speckles are used to reveal a relation between the parameters that characterize random and deterministic changes in the relief height and speckle images of the surface near the notch during crack initiation.  相似文献   

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圆截面弹性螺旋杆的稳定性与振动   总被引:2,自引:0,他引:2       下载免费PDF全文
刘延柱  盛立伟 《物理学报》2007,56(4):2305-2310
基于Kirchhoff理论讨论圆截面弹性螺旋杆的动力学问题.以杆中心线的Frenet坐标系为参考系,建立用欧拉角描述的弹性杆动力学方程.讨论其在端部轴向力和扭矩作用下保持的无扭转螺旋线平衡状态.在静力学和动力学领域内讨论其平衡稳定性问题.还讨论了弹性杆平衡的Lyapunov稳定性和欧拉稳定性两种不同稳定性概念之间的区别和联系.在一次近似意义下证明了螺旋杆在空间域内的欧拉稳定性条件是时域内Lyapunov稳定性的必要条件.导出了解析形式螺旋杆三维弯曲振动的固有频率,为螺旋线倾角和受扰挠性线波数的函数. 关键词: 弹性螺旋杆 Kirchhoff动力学比拟 Lyapunov稳定性 欧拉稳定性  相似文献   

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朱广平  王成  门伟  赵宿辰 《应用声学》2021,40(3):433-439
簧片是笙等中国传统簧管类乐器的核心部件之一.通过点簧工艺可调整簧片振动频率,点簧簧片的差异对整体乐器的声音效果具有重要影响.针对点簧簧片的振动特性问题,对其建立非均匀截面并具有质量负载的振动模型,采用有限元方法计算点簧簧片的固有频率.大量算例分析了点簧质量、位置以及簧片的边界条件对振动频率的影响,研究发现:若点簧质量不...  相似文献   

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The relative stability of exo-and endohedral lithium complexes with the C60 fullerene was estimated using quantum chemistry and molecular-dynamics methods. Endohedral compounds were shown to have a higher stability. The possible maximum filling of the C60 inner sphere by lithium was estimated theoretically. The interaction of metallic lithium with the C60 fullerene and a C60 + C70 mixture was studied using DTA and EPR and established to proceed in several stages.  相似文献   

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The interaction between ultrasound and macroscopic defects in solids is considered using the nonlinear theory of elasticity. It is shown that, due to the resonance nature of the vibrations of the defect, considerable anharmonism occurs even when the intensity of the ultrasonic wave is weak. Because of this, effective conversion of the ultrasonic wave into internal vibrational states of the macrodefect occurs.V. D. Kuznetsov Siberian Physico-Technical Institute, Tomsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 3–9, November, 1994.  相似文献   

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