Search

Showing total 4 results
Start Over Topic elastic waves Publication Year Range Last 50 years
4 results

1. Shear Horizontal Wave Propagation Speed in Mylar Sheet and Coated Paper.

Author

Leppänen, M., Karppinen, T., Hæggström, E., and Stor-Pellinen, J.

Subjects
*SHEAR waves, *ELASTIC waves, *PAPER coatings, *PAPER finishing, *PROTECTIVE coatings, *POLYETHYLENE terephthalate
Abstract

Soft plate-like membranes find application e.g. as pill or paper coatings, bio-filter membranes, and gas seals in food products. For these applications the integrity and the mechanical properties of the membrane are important. Mechanical properties of these products can be determined by stretching or bending tests, but such methods can damage these fragile products. We propose a rapid nondestructive acoustic method to estimate mechanical film characteristics with shear horizontal (in-plane shear) waves. A 23 kHz, 1-cycle square signal was excited into a thin foil with a piezoceramic pickup and received with an inductive pickup. The SNR (power) was 20 dB in 1 kHz –50 kHz bandwidth. This actuation-detection scheme can be used to excite in-plane longitudinal, shear and even elliptic waves in a thin foil. The method was validated by measuring in-plane shear wave and longitudinal wave time-of-flight TOF at different actuator-receiver separations and calculating the corresponding longitudinal and shear modulus. The samples were Mylar® sheet and coated paper. The anisotropy of MOE for Mylar sheet was close to the manufacturer specifications. For coated paper a maximum shear modulus anisotropy of 5% and a shear modulus dependence on temperature of 0.7 MPa/°C were found. Laser doppler vibrometry showed that the excited waves were confined in-plane. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Published
2006
Full Text
View/download PDF

2. Imaging the anisotropic elastic properties of paper with the INEEL laser ultrasonic camera.

Author

Deason, V. A., Telschow, K. L., Schley, R. S., and Watson, S. M.

Subjects
*ELASTIC waves, *PAPER, *LAMB waves
Abstract

An important material property in the paper industry is the anisotropic stiffness distribution due to the fibrous microstructure of paper. Ultrasonic methods offer a means of determining the stiffness of sheets of paper from the anisotropic propagation characteristics of elastic Lamb waves along the machine direction (MD) and the cross direction (CD). Currently, piezoelectric ultrasonic methods are employed in the industry to measure the elastic polar diagram of paper through multiple contacting measurements made in all directions. This paper describes a new approach utilizing the INEEL Laser Ultrasonic Camera to provide a complete image of the elastic waves traveling in all directions in the plane of the paper sheet. This approach is based on optical dynamic holographic methods that record the out of plane ultrasonic motion over the entire paper surface simultaneously without scanning. The full-field imaging technique offers great potential for increasing the speed of the measurement and it ultimately provides a great deal of information concerning local property variations and flaws in the paper. This report shows the success of the method and the manner in which it yields the elastic polar diagram for the paper from the dispersive flexural or antisymmetric Lamb wave. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Published
2000

3. Richter's laws at the laboratory scale interpreted by acoustic emission.

Author

Carpinteri, A., Lacidogna, G., and Pugno, N.

Subjects
*ACOUSTIC emission, *MATERIALS testing, *STRESS waves, *ELASTIC waves, *METHODOLOGY, *PAPER, *THEORY of knowledge
Abstract

In the present work the acoustic emission (AE) technique is applied to examine some aspects influencing concrete failure in compression. By monitoring a structure by means of the AE technique, it proves possible to detect the occurrence of stress-induced cracks. Cracking, in fact, is accompanied by the emission of elastic waves that propagate within the bulk of the material. These waves can be received and recorded by transducers applied to the surface of the structural elements. This technique can be used for diagnosing structural damage phenomena. The current paper presents a mixed experimental and theoretical approach to evaluate the energy density dissipated during compression at each value of strain. Through this method, the two semi-empirical Gutenberg-Richter (GR) laws, well-known in seismology, are verified, the fractal interpretation results of which are very close to the essence of the AE phenomenon. Furthermore, the mentioned approach allows the parameter of ‘magnitude’ to be identified, appearing in the laws, with the number of oscillations larger than a given threshold measured in volts. Finally, the developed concepts are applied to the study of the compression phenomenon. In particular, by this approach, it is possible to distinguish between the energy progressively dissipated or stored in a compressed structural element. [ABSTRACT FROM AUTHOR]

Published
2006
Full Text
View/download PDF

4. Laser-induced elastic wave classification: thermoelastic versus ablative regimes for all-optical elastography applications

Author

Alexander Schill, Salavat Aglyamov, Kirill V. Larin, Chih-Hao Liu, and Susobhan Das

Subjects
Paper, Absorption (acoustics), Materials science, Physics::Medical Physics, Biomedical Engineering, Holography, 01 natural sciences, law.invention, 010309 optics, Biomaterials, Thermoelastic damping, Transition point, law, Elastic Modulus, 0103 physical sciences, medicine, Animals, General, optical coherence elastography, thermoelastic, medicine.diagnostic_test, Phantoms, Imaging, elastic waves, Mechanics, Laser, Atomic and Molecular Physics, and Optics, Biomechanical Phenomena, Electronic, Optical and Magnetic Materials, all-optical, Sound, Liver, Surface wave, Elasticity Imaging Techniques, Elastography, ablative, Chickens, Tomography, Optical Coherence, Coherence (physics)
Abstract

Significance: Shear wave optical coherence elastography is an emerging technique for characterizing tissue biomechanics that relies on the generation of elastic waves to obtain the mechanical contrast. Various techniques, such as contact, acoustic, and pneumatic methods, have been used to induce elastic waves. However, the lack of higher-frequency components within the elastic wave restricts their use in thin samples. The methods also require moving parts and/or tubing, which therefore limits the extent to which they can be miniaturized. Aim: To overcome these limitations, we propose an all-optical approach using photothermal excitation. Depending on the absorption coefficient of the sample and the laser pulse energy, elastic waves are generated either through a thermoelastic or an ablative process. Our study aimed to experimentally determine the boundary between the thermoelastic and the ablative regimes for safe all-optical elastography applications. Approach: Tissue-mimicking graphite-doped phantoms and chicken liver samples were used to investigate the boundary between thermoelastic and ablative regimes. A pulsed laser at 532 nm was used to induce elastic waves in the samples. Laser-induced elastic waves were detected using a line field low coherence holography instrument. The shape of the elastic wave amplitude was analyzed and used to determine the transition point between thermoelastic and ablative regimes. Results: The transition from the thermoelastic to the ablative regime is accompanied by the nonlinear increase in surface wave amplitude as well as the transformation of the wave shape. Correlation between the absorption coefficient and the transition point energy was experimentally determined using graphite-doped phantoms and applied to biological samples ex vivo. Conclusions: Our study described a methodology for determining the boundary region between thermoelastic and ablative regimes of elastic wave generation. These can be used for the development of a safe method for completely noncontact, all-optical microscale assessment of tissue biomechanics using laser-induced elastic waves.

Published
2020