Elastic Wave Propagation in Sinusoidally Corrugated Waveguides

The ultrasonicwave propagation in sinusoidally corrugated waveguides is studied in this paper. Periodically corrugated waveguides are gaining popularity in the field of vibration control and for designing structures with desired acoustic band gaps. Currently only numerical method (Boundary Element Method or Finite Element Method) based packages (e.g., PZFlex) are in principle capable of modeling ultrasonic fields in complex structures with rapid change of curvatures at the interfaces and boundaries but no analyses have been reported. However, the packages are very CPU intensive; it requires a huge amount of computation memory and time for its execution. In this paper a new semi-analytical technique called Distributed Point Source Method (DPSM) is used to model the ultrasonic field in sinusoidally corrugated waveguides immersed in water where the interface curvature changes rapidly. DPSM results are compared with analytical solutions. It is found that when a narrow ultrasonic beam hits the corrugation peaks at an angle, the wave propagates in the backward direction in waveguides with high corrugation depth. However, in waveguides with small corrugation the wave propagates in the forward direction. The forward and backward propagation phenomenon is found to be independent of the signal frequency and depends on the degree of corrugation

A Hybrid Modeling of Soil Structure Interaction Problems

A hybrid method is proposed in this research for dynamic soil-structure interaction analysis of embedded structures within a multilayered elastic half-space. A near field region, containing the structure and a portion of soil surrounding it, is modeled by finite elements while the far field formulation is obtained through the classical wave propagation theory based on the assumption that the actual scattered wave fields can be represented by a set of line sources located at a depth corresponding to the center of mass of the structure under investigation. Traction reciprocity between the two regions is satisfied exactly while displacement continuity across the common interface is enforced in a least-squares sense. The two-dimensional system is excited by seismic body waves (P and SV) propagating with oblique incidence and harmonic time dependence

Elastic Wave Field Computation in Multilayered Nonplanar Solid Structures: A Mesh-Free Semianalytical Approach

Multilayered solid structures made of isotropic, transversely isotropic, or general anisotropic materials are frequently used in aerospace, mechanical, and civil structures. Ultrasonic fields developed in such structures by finite size transducers simulating actual experiments in laboratories or in the field have not been rigorously studied. Several attempts to compute the ultrasonic field inside solid media have been made based on approximate paraxial methods like the classical ray tracing and multi-Gaussian beam models. These approximate methods have several limitations. A new semianalytical method is adopted in this article to model elastic wave field in multilayered solid structures with planar or nonplanar interfaces generated by finite size transducers. A general formulation good for both isotropic and anisotropicsolids is presented in this article. A variety of conditions have been incorporated in the formulation including irregularities at the interfaces. The method presented here requires frequency domain displacement and stress Green’s functions. Due to the presence of different materials in the problem geometry various elastodynamic Green’s functions for different materials are used in the formulation. Expressions of displacement and stress Green’s functions for isotropic and anisotropicsolids as well as for the fluid media are presented. Computed results are verified by checking the stress and displacement continuity conditions across the interface of two different solids of a bimetal plate and investigating if the results for a corrugated plate with very small corrugation match with the flat plate results

An Experimental Investigation of Guided Wave Propagation in Corrugated Plates Showing Stop Bands and Pass Bands

Nonplanar surfaces are often encountered in engineering structures. In aerospace structures, periodically corrugated boundaries are formed by friction-stir-welding. In civil engineering structures, rebars used in reinforced concrete beams and slabs have periodic surface. Periodic structures are also being used to create desired acoustic band gaps. For health monitoring of these structures, a good understanding of the elastic wave propagation through such periodic structures is necessary. Although a number of research papers on the wave propagation in periodic structures are available in the literature, no one experimentally investigated the guided wave propagation through plates with periodic boundaries and compared the experimental results with theoretical predictions as done in this paper. The experimental results clearly show that elastic waves can propagate through the corrugated plate (waveguide) for certain frequencies called “pass bands,” and find it difficult to propagate for some other frequencies called “stop bands.” Stop bands are found to increase with the degree of corrugation. Experimental results are compared with the theoretical predictions, and good matching is observed for plates with small degree of corrugation. Only two parameters—the depth of corrugation and the wavelength of the periodicity—are sufficient for modeling the elastic wave propagation in slightly corrugated plates

Monitoring prestress in plates by sideband peak count-index (SPC-I) and nonlinear higher harmonics techniques

Propagating guided waves in a homogeneous, isotropic, prestressed, hyperelastic plate show nonlinear characteristics that depend on the state of initial prestress. These nonlinear phenomena include higher harmonic generation, occurring when Lamb wave modes of different frequencies (ωa and ωb) are allowed to mix within the material generating secondary waves at frequencies 2ωa, 2ωb and ωa ± ωb. Further, if prescribed internal-resonance conditions are satisfied, the amplitude of secondary waves increases in space, providing a response quantity which is dependent on prestress and easy to be observed. Using the finite element method, in this paper we investigatthe time and space evolution of higher harmonics arising in one-way wave mixing. The influence of prestress on the response is elucidated, observing the nonlinear parameter β. It is further shown that the nonlinear ultrasonic technique called Sideband Peak Count-Index (SPC-I) can provide an effective monitoring tool for prestress

Effect of carbonation on the linear and nonlinear dynamic properties of cement-based materials

[EN] Carbonation causes a physicochemical alteration of cement-based materials, leading to a decrease of porosity and an increase of material hardness and strength. However, carbonation will decrease the pH of the internal pore water solution, which may depassivate the internal reinforcing steel, giving rise to structural durability concerns. Therefore, the proper selection of materials informed by parameters sensitive to the carbonation process is crucial to ensure the durability of concrete structures. The authors investigate the feasibility of using linear and nonlinear dynamic vibration response data to monitor the progression of the carbonation process in cement-based materials. Mortar samples with dimensions of 40 x 40 x 160 mm were subjected to an accelerated carbonation process through a carbonation chamber with 55% relative humidity and >95% of CO2 atmosphere. The progress of carbonation in the material was monitored using data obtained with the test setup of the standard resonant frequency test (ASTM C215-14), from a pristine state until an almost fully carbonated state. Linear dynamic modulus, quality factor, and a material nonlinear response, evaluated through the upward resonant frequency shift during the signal ring-down, were investigated. The compressive strength and the depth of carbonation were also measured. Carbonation resulted in a modest increase in the dynamic modulus, but a substantive increase in the quality factor (inverse attenuation) and a decrease in the material nonlinearity parameter. The combined measurement of the vibration quality factor and nonlinear parameter shows potential as a sensitive measure of material changes brought about by carbonation. (C) 2015 Society of Photo-Optical Instrumentation Engineers (SPIE)The authors want to acknowledge the financial support of the Ministerio de Economia y Competitividad (MINECO), Spain, and FEDER funding (Ondacem Project: BIA 2010-19933). Jesus N. Eiras wants to acknowledge the financial support provided by Ministerio de Economia y Competitividad (MINECO), Spain, grant BES-2011-044624.Eiras Fernández, JN.; Kundu, T.; Popovics, JS.; Monzó Balbuena, JM.; Borrachero Rosado, MV.; Paya Bernabeu, JJ. (2016). Effect of carbonation on the linear and nonlinear dynamic properties of cement-based materials. Optical Engineering. 55(1):011004-1-011004-7. https://doi.org/10.1117/1.OE.55.1.011004S011004-1011004-755

A modified sideband peak count based nonlinear ultrasonic technique for material characterization

The ultrasonic Non-Destructive Testing and Evaluation (NDT&E) has been widely used for Structural Health Monitoring (SHM). The conventional linear ultrasonic technique which is suitable for detecting macro-scale defects is routinely used in industry; however, it often fails to detect the micro-scale defects. Generally, micro-defects in a material appear first due to dislocations at grain boundaries. These micro-defects then grow and coalesce to form macro-defects. The crack growth rate is much faster for macro-defects than micro-defects. Therefore, monitoring micro-defects is important to avoid catastrophic failures of structures. Nonlinear ultrasonic techniques help to detect micro-defects. A recently developed nonlinear ultrasonic technique called Sideband Peak Count - Index (SPC-I) technique has some inherent advantages over other nonlinear techniques for monitoring progression of micro-defects. In this research, the SPC-I technique is further modified. This modified technique, Sideband Peak Intensity (SPI) technique, is shown to be more robust and easier to implement. Both SPC-I and SPI techniques are used to monitor the damage progression in impact induced damages in metals. Similarities and dissimilarities between these two techniques are investigated. Then it is concluded that the SPI technique is good as a general-purpose robust damage monitoring tool that can be used by less skilled users while the SPC-I technique although requires more skills has more sensitivity and has the flexibility for an in-depth damage analysis in materials.24 month embargo; available online: 14 October 2022This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]