热驱动型SMP材料加热过程中激光超声衰减特性研究
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摘要
本文采用有限元方法分别建立了常温和加热情况下脉冲激光线源在热驱动型SMP材料(形状记忆高分子聚合物)中激发声表面波的数值模型,并在此基础上开展对激光在热驱动型SMP材料中激发超声表面波波形及传播特性的数值模拟及实验的研究。
从激光超声的激发机制出发,分别介绍声表面波的基本性质和激光声表面波常用的检测方法。随后重点论述了脉冲激光线源分别作用于室温态和加热态的样品上时激发超声波的解析模型,分析两种模型各自的特点,为进一步的理论研究奠定基础。
在不考虑粘性劲度系数的情况下,基于平面应变的弹性理论,建立了脉冲激光在热驱动型SMP材料表面激发Rayleigh波的有限元模型。与考虑粘性劲度系数的模拟结果相比较,分析了随传播距离增加,Rayleigh波振幅衰减的原因。基于平面热粘弹理论、结合激光脉冲能量的空间分布特征和热驱动型SMP材料板材变温时的各向同性粘弹性特征,建立起脉冲激光激发热驱动型SMP材料产生声表面波的有限元模型,重点研究热驱动型SMP材料中激发点和探测点之间局域加热的过程中声表面波衰减特性。建立了利用PVDF传感器接收经过三倍频所得的紫外波长激光激发的声表面波的实验装置,分析了去噪后的实验结果,并与数值模拟结果作比较,发现随材料升温,材料的粘性特征变得明显的同时,弹性性能不断减弱,表现为材料升温至玻璃化温度附近时,声表面波形衰减至几乎消失。可见,对弹性性能的研究可以作为评价材料粘性特征的有效手段。
超声衰减是声学特性及无损检测的重要参量,本文研究的热驱动型SMP材料中激光声表面波衰减特性的数值模拟与实验测量的结果,为开展应用激光超声技术检测新型复合材料的物理特性和检测材料内部缺陷的研究提供了理论依据。
In this paper, the finite element method (FEM) is applied to simulate the physical processes, which include the generation and propagation of the surface acoustic wave (SAW) in the SMP(Shape Memory polymer composite material) material on the condition of the room and rising temperature respectively. Then, waveforms and its propagation characteristics of SAWs excited by thermoelastic laser in the SMP material are studied by computer simulation combining with experiment.
From the excitation mechanisms of laser ultrasound, the physical properties of SAWs and the detection methods used in laser-generated SAWs are introduced in a common manner. Subsequently, two main analytical models of the laser-generated ultrasound are given, constructed by line source irradiating on the sample at room temperature and rapid rising temperature respectively. The features of each model are also analyzed. All these works are preparations for the further theoretical study.
Without considering viscosity modulus, in order to simulate the laser-generated SAWs, the finite element models of the line source irradiating on. the plate of SMP material is established by the elastic theory of plane strain. Compared with the results calculated by means of fitting viscosity modulus, the causes of amplitude attenuation of laser-generated Rayleigh waves with increasing propagation length are analyzed in this paper. Then, combined with the spatial distribution characteristics of laser pulse energy density and isotropic viscoelastic characteristics of the SMP material under varied temperatures, based on the thermoviscoelasticity of plane strain, the finite element method is employed to simulate the interactions of the laser-generated Rayleigh waves with the material, while the area of SMP material between excite point and detect point is heated to produce phase transformation. More important of all, the attenuation characteristics of the SAWs are studied by using FEM method when heating material is taken into account. Finally, the excitation and detection systems according to the acoustic principle are set up. After serials of ultrasound pulses frequencies are multiplicated, SAWs signals excited by ultraviolet line source can be detected by PVDF (polyvinylindene fluoride) transducer at the same point of the sample surface. The de-noised experimental results are consistent with simulation analysis, which demonstrates that the more viscous material becomes, the less elastic it will reflect, along with the temperature rising. When the temperature is about to reach glass transition temperature, the SAWs almost disappear. Thus, we can obtain that elastic behavior can represent physical characteristics of viscosity effectively.
Ultrasound attenuation plays a vital role in the evaluation of ultrasonic properties and nondestructive testing technology. The results of this paper may provide theoretical and experimental references for SAWs attenuation measurement using laser ultrasound, and accelerate the development and application of laser ultrasonic nondestructive testing technology for the new composite materials.
从激光超声的激发机制出发,分别介绍声表面波的基本性质和激光声表面波常用的检测方法。随后重点论述了脉冲激光线源分别作用于室温态和加热态的样品上时激发超声波的解析模型,分析两种模型各自的特点,为进一步的理论研究奠定基础。
在不考虑粘性劲度系数的情况下,基于平面应变的弹性理论,建立了脉冲激光在热驱动型SMP材料表面激发Rayleigh波的有限元模型。与考虑粘性劲度系数的模拟结果相比较,分析了随传播距离增加,Rayleigh波振幅衰减的原因。基于平面热粘弹理论、结合激光脉冲能量的空间分布特征和热驱动型SMP材料板材变温时的各向同性粘弹性特征,建立起脉冲激光激发热驱动型SMP材料产生声表面波的有限元模型,重点研究热驱动型SMP材料中激发点和探测点之间局域加热的过程中声表面波衰减特性。建立了利用PVDF传感器接收经过三倍频所得的紫外波长激光激发的声表面波的实验装置,分析了去噪后的实验结果,并与数值模拟结果作比较,发现随材料升温,材料的粘性特征变得明显的同时,弹性性能不断减弱,表现为材料升温至玻璃化温度附近时,声表面波形衰减至几乎消失。可见,对弹性性能的研究可以作为评价材料粘性特征的有效手段。
超声衰减是声学特性及无损检测的重要参量,本文研究的热驱动型SMP材料中激光声表面波衰减特性的数值模拟与实验测量的结果,为开展应用激光超声技术检测新型复合材料的物理特性和检测材料内部缺陷的研究提供了理论依据。
In this paper, the finite element method (FEM) is applied to simulate the physical processes, which include the generation and propagation of the surface acoustic wave (SAW) in the SMP(Shape Memory polymer composite material) material on the condition of the room and rising temperature respectively. Then, waveforms and its propagation characteristics of SAWs excited by thermoelastic laser in the SMP material are studied by computer simulation combining with experiment.
From the excitation mechanisms of laser ultrasound, the physical properties of SAWs and the detection methods used in laser-generated SAWs are introduced in a common manner. Subsequently, two main analytical models of the laser-generated ultrasound are given, constructed by line source irradiating on the sample at room temperature and rapid rising temperature respectively. The features of each model are also analyzed. All these works are preparations for the further theoretical study.
Without considering viscosity modulus, in order to simulate the laser-generated SAWs, the finite element models of the line source irradiating on. the plate of SMP material is established by the elastic theory of plane strain. Compared with the results calculated by means of fitting viscosity modulus, the causes of amplitude attenuation of laser-generated Rayleigh waves with increasing propagation length are analyzed in this paper. Then, combined with the spatial distribution characteristics of laser pulse energy density and isotropic viscoelastic characteristics of the SMP material under varied temperatures, based on the thermoviscoelasticity of plane strain, the finite element method is employed to simulate the interactions of the laser-generated Rayleigh waves with the material, while the area of SMP material between excite point and detect point is heated to produce phase transformation. More important of all, the attenuation characteristics of the SAWs are studied by using FEM method when heating material is taken into account. Finally, the excitation and detection systems according to the acoustic principle are set up. After serials of ultrasound pulses frequencies are multiplicated, SAWs signals excited by ultraviolet line source can be detected by PVDF (polyvinylindene fluoride) transducer at the same point of the sample surface. The de-noised experimental results are consistent with simulation analysis, which demonstrates that the more viscous material becomes, the less elastic it will reflect, along with the temperature rising. When the temperature is about to reach glass transition temperature, the SAWs almost disappear. Thus, we can obtain that elastic behavior can represent physical characteristics of viscosity effectively.
Ultrasound attenuation plays a vital role in the evaluation of ultrasonic properties and nondestructive testing technology. The results of this paper may provide theoretical and experimental references for SAWs attenuation measurement using laser ultrasound, and accelerate the development and application of laser ultrasonic nondestructive testing technology for the new composite materials.
引文
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[2]C. J. Hellier,戴光译.无损检测与评价手册.北京：中国石化出版社,2006
[3]袁易全等.近代超声原理与应用.第1版.南京：南京大学出版社,1996
[4]C. B. Scruby. Some applications of Laser ultrasound. Ultrasonics.1989(27):56～209
[5]C. B. Scruby. Laser generation of ultrasound in metals. Research Techniques in NDT. 1982(5):281-327
[6]陆建等.激光与材料相互作用物理学.第一版.北京：机械工业出版社.1996
[7]张淑仪.激光超声与材料无损评价.应用声学.1992(11)：1-6
[8]刘贵明.无损检测技术.第一版.北京：国防工业出版社,2006
[9]J. W. Wagner. Generation of ultrasound by repetitively Q-switching a pulsed Nd:YAG laser. Appl. Applied Optics.1988(27):4696～4698
[10]V. V. Kozhushko, P. Hess. Laser-induced focused ultrasound for nondestructive testing and evaluation. J. Appl. Phys.2008(12):186-190
[11]A. K. Kromine, P. A. Fomitchov, S. Krishnaswamy, J. D. Achenbach. Applications of scanning laser source technique for detection of surface-breaking defects. Proceedings of SPIE.2000(4):252～552
[12]S. Younghoon, S. K. Interaction of a scanning laser-generated ultrasonic line source with a surface-breaking flaw. J.Acoust.Soc.Am.2004(12):172～181
[13]I. Arias, J. D. Achenbach. A model for the ultrasonic detection of surface-breaking cracks by the scanning laser source technique. Wave Motion.2004(3):61～69
[14]J. W. Wagner. Generation of ultrasound by repetitively Q-switching a pulsed Nd:YAG laser. Appl. Applied Optics.1988(27):4696～4698
[15]P. Hess. Determination of linear and nonlinear mechanical properties of diamond by laser-based surface acoustic waves. Diamond & Related Materials.2009(15):186-190
[16]T. Ohki, Q. Q. Ni, N. Ohsako. Mechanical and shape behavior of composites with shape memory polymer.Journal. Composites.2004(35):1065-107
[17]G. L Carlo and J. R. Glenn.Solution of the Rayleigh Eigenproblem in Viscoelastic Media.Bulletin of the Seismological Society of America.2002(92):2297-2309
[18]M. Nicos, J. Zhan. Time-domain viscoelastic analysis of earth structures. Earthquake Engineering and Structural dynamics.2000(29):745-768
[19]T. Bohlen etc. Rayleigh-to-shear wave conversion at the tunnel face:From 3D-FD modeling to ahead-of-drill exploration. Geophysics.2007(67):72-78
[20]岳庆霞.地下综合管廊地震反应分析与抗震可靠性研究.硕士学位论文.同济大学,2007
[21]D. Fei, X. R. Zhang, C. M. Gan, S. Y. Zhang. Study on SAW attenuation of PMMA using laser ultrasonic technique. Review of Progress in Quantitative Nondestructive Evaluation.1994(14):577-583
[22]韩庆邦,钱梦騄.激光激发粘弹表面波特性分析.声学学报.2007(4)：338-342
[23]孙宏祥等.激光激发黏弹表面波有限元数值模拟.物理学报.2009(9)：6344-6349
[24]L. F. Bresse, D. A. Hutchins. Transient generation by a wide thermoelastic source at a solid surface. Journal of Applied Physics.1989(65):1441～1446
[25]T. Sanderson, C. Ume, J. Jarzynski. Longitudinal wave generation in laser ultrasonics. Ultrasonics.1998 (35):553～561
[26]L. R. F. Rose. Point-Source representation for laser-generated ultrasound. J. Acoust. Soc. Am..1984(75):723～732
[27]J. J. Wang, Z. H. Shen, B. Q. Xu, X. W. Ni, J. F. Guan, J. Lu. Numerical simulation of laser-generated ultrasound in non-metallic material by the finite element method. Optics & Laser Technology.2007(4):806-813
[28]R. Mittall, G. Rus, R. Gallego, S. Y. Lee, T. Park. Mechanical constants characterization of thin layers by low frequency ultrasonics. CMNE/CILAMCE.2007(2): 13～15
[29]A. Christine, H. Hennion, R. Bossut. Time analysis of immersed waveguides using the finite element method. J. Acoust. Soc. Am..1998(1):64-71
[30]A. Oishi, K. Yamada, S. Yoshimura, G. Yagawa, S. Nagai, Y. Matsuda. Neural network-based inverse analysis for defect identification with laser ultrasonics. Research in Nondestructive Evaluation.2001(2):79-96,
[31]B. Q. Xu, Z. H. Shen, X. W. Ni, et. Finite element modeling of laser-generated ultrasound in coating-substrate system. Journal of Applied Physics.2004 (4):2106～211
[32]童世虎.基于形状记忆高分子复合材料结构的半主动减振控制.硕士学位论文.南京理工大学,2009
[33]Y. F. Shi, Z. H. Shen, X. W. Ni, J. Lu. A novel differential optical beam deflection system for measuring laser-generated surface acoustic waves. Proc of SPIE.2007(5): 111-118
[34]John D. Ferry. Viscoelastic properties of polymers.1st edition. Canada:John Wiley
&Sons,1980
[35]孙宏祥,许伯强,徐晨光,徐桂东,王峰.横观各向同性材料中激光超声谱有限元数值模拟.光子学报.2009(5)：1041-1046
[36]J. C. Cheng, S. Y. Zhang. Quantitative theory for laser-generated Lamb waves in orthotropic thin plates. Appl. Phys. Lett.1999(5):2087-2089
[37]陆明万,罗学富.弹性理论基础.第2版.北京：清华大学出版社,2001
[38]Girault, Vivette, Raviart, Pierre Arnaud. Finite element methods for Navier-Stokes equations:Theory and algorithms. Berlin and New York:Springer Series in Computational Mathematics,1986
[39]P. A. Doyle.C. M. Scala. Near-field ultrasonic Rayleigh waves from a laser line source. Ultrasonics.1996
[40]G. A. Antonelli, P. Zannitto, H. J. Maris. New method for the generation of surface acoustic waves of high frequency. Physical B:Condensed Matter.2002(2):377-379
[41]M. Beh, A. Lendlein. Shape-memory polymers. Materials today.2007(4):20-28
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