Characterization of Delamination in Beams Using Flexural Wave Scattering Analysis

2001 ◽  
Vol 123 (4) ◽  
pp. 421-427 ◽  
Author(s):  
S. I. Ishak ◽  
G. R. Liu ◽  
S. P. Lim ◽  
H. M. Shang
Keyword(s):  
Wave Propagation ◽  
Wave Scattering ◽  
Beam Theory ◽  
Flexural Wave ◽  
Laser Vibrometer ◽  
Beam Model ◽  
Harmonic Load ◽  
Beam Displacement ◽  
Flexural Wave Scattering

An analytical model for the characterization of delamination in beams using flexural wave scattering analysis is presented. In the beam model of wave propagation, the beam is divided into four regions; to each of them the beam theory of wave propagation is applied to obtain the wave fields excited by a harmonic load on the beam surface. The solution for the entire beam is obtained in terms of the solution for the respective regions using continuity conditions at the junctions. Numerical results on beam displacement for various delamination sizes, materials and excitation frequencies are presented. Experiments using a scanning laser vibrometer on specimens containing simulated delamination are also conducted. The results are then verified by comparing with those obtained by the Strip Element Method (SEM) and experiment. Good agreement is observed between the present model with SEM and experiment.

Effect of van der Waals force on wave propagation in viscoelastic double-walled carbon nanotubes

2018 ◽  
Vol 32 (24) ◽  
pp. 1850291
Author(s):  
Yugang Tang ◽  
Ying Liu
Keyword(s):  
Carbon Nanotubes ◽  
Wave Propagation ◽  
Van Der Waals ◽  
Van Der Waals Force ◽  
Strain Gradient Theory ◽  
Flexural Wave ◽  
Gradient Theory ◽  
Beam Model ◽  
Double Walled Carbon Nanotubes ◽  
Walled Carbon Nanotubes

In this paper, the influence of van der Waals force on the wave propagation in viscoelastic double-walled carbon nanotubes (DWCNTs) is investigated. The governing equations of wave motion are derived based on the nonlocal strain gradient theory and double-walled Timoshenko beam model. The effects of viscosity, van der Waals force, as well as size effects on the wave propagation in DWCNTs are clarified. The results show that effects of van der Waals force on waves in inner and outer layers of DWCNTs are different. Flexural wave (FW) in outer layer and shear wave (SW) in inner layer are sensitive to van der Waals force, and display new phenomena. This new finding may provide some useful guidance in the acoustic design of nanostructures with DWCNTs as basic elements.

Bandgap of flexural wave in periodic bi-layer beam

2016 ◽  
Vol 24 (14) ◽  
pp. 2970-2985 ◽  
Author(s):  
Zhiwei Guo ◽  
Meiping Sheng
Keyword(s):  
Wave Propagation ◽  
Floquet Theory ◽  
Wave Attenuation ◽  
Vibration Reduction ◽  
Single Layer ◽  
Beam Theory ◽  
Flexural Wave ◽  
Transmission Characteristic ◽  
Beam Structure ◽  
Software Simulation

A periodic bi-layer beam structure is proposed and the bandgap characteristic of flexural wave is studied in this paper. The single cell is made up of two bi-layer beams with four components. For the infinite structure, the flexural wave bandgap frequency algorithm is theoretically derived through Timoshenko beam theory, Hamilton principle, Bloch-Floquet theory and transfer matrix method. An analytical example is presented to illustrate the bandgap characteristic and FEA software simulation is conducted to demonstrate the validation of the algorithm. For the finite structure, the vibration transmission characteristic is studied with FEA software to show the flexural wave attenuation behavior of the periodic bi-layer beam. The results reveal that, the flexural wave is attenuated gradually in the stopband along the direction of wave propagation, while in the passband, it will propagate without attenuation. Comparisons with periodic single layer beam are studied to verify the convenience and flexibility of bi-layer beam. Finally, parametric influences on bandgaps are discussed, which will help the designers to make a better design for vibration reduction.

Flexural Wave Scattering by Double Elliptic Holes in an Infinite Thin Plate

2011 ◽  
Vol 488-489 ◽  
pp. 37-40
Author(s):  
Hong Liang Li ◽  
Jing Guo ◽  
Xiao Hua Shao
Keyword(s):  
Stress Concentration ◽  
Thin Plate ◽  
Displacement Field ◽  
Wave Scattering ◽  
Aerospace Engineering ◽  
Theoretical Research ◽  
Flexural Wave ◽  
Algebraic Equations ◽  
Local Complex ◽  
Flexural Wave Scattering

In mechanical engineering and aerospace engineering, thin plate structure is used widely. For the sake of fixing bolt, it often design open holes in the plate. Sometimes elliptic holes should be used inevitably. When the plate is overloaded or the load is changed regularly, flexural wave is propagating in the plate. Because there are holes, it can cause stress concentration. Stress concentration could decrease the bearing capacity of structure, and reduce the service life of structure. The problem of flexural wave scattering by holes in the plate is one of the important and interesting questions in aerospace engineering for the latest decades. There are lots of materials obtained by theoretical research and experimental investigation. The problem is complicated, because there are many factors influenced. It is hard to obtain analytic solutions except for several simple conditions. In this paper, based on the theory of elastic thin plate, by using wave function expansion method and multi local complex coordinates, scattering of flexural wave and dynamic stress concentration by double elliptic holes in the thin plate are investigated. In the complex plane, the displacement field aroused by incident wave and the scattering displacement field impacted by double elliptic holes comprised of Fourier-Bessel series with undetermined coefficients are constructed. Through applying the method of multi local complex coordinates, the equations with unknown coefficients can be obtained by using the stress-free condition of the double elliptic holes in the radial direction. According to orthogonality condition for trigonometric function, these equations can be reduced to a series of algebraic equations. Then the value of the unknown coefficients can be obtained by solving these algebraic equations. So the analytical solution of this problem is obtained. By using the displacement and stress expressions, an example is provided to show the effect of the change of relative location of the elliptic holes.

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