Lamb mode diversity imaging for non-destructive testing of plate-like structures

Several Lamb wave modes can be coupled to a particular structure, depending on its geometry and transducer used to generate the guided waves. Each Lamb mode interacts in a particular form with different types of defects, like notches, delamination, surface defects, resulting in different information which can be used to improve damage detection and characterization. An image compounding technique that uses the information obtained from different propagation modes of Lamb waves for non-destructive testing of plate-like structures is proposed. A linear array consisting of 16 piezoelectric elements is attached to a 1 mm thickness aluminum plate, coupling the fundamental A0 and S0 modes at the frequencies of 100 kHz and 360 kHz, respectively. For each mode two images are obtained from amplitude and phase information: one image using the Total Focusing Method (TFM) and one phase image obtained from the Sign Coherence Factor (SCF). Each TFM image is multiplied by the SCF image of the respective mode to improve contrast and reduce side and grating lobes effects. The high dispersive characteristic of the A0 mode is compensated for adequate defect detection. The information in the SCF images is used to select one of the TFM mode images, at each pixel, to obtain the compounded image. As a result, dead zone is reduced, resolution and contrast are improved, enhancing damage detection when compared to the use of only one mode. © 2013 Elsevier Ltd.

A PZT-based technique for SHM using the coherence function

This paper presents a new approach for damage detection in structural health monitoring systems exploiting the coherence function between the signals from PZT (Lead Zirconate Titanate) transducers bonded to a host structure. The physical configuration of this new approach is similar to the configuration used in Lamb wave based methods, but the analysis and operation are different. A PZT excited by a signal with a wide frequency range acts as an actuator and others PZTs are used as sensors to receive the signal. The coherences between the signals from the PZT sensors are obtained and the standard deviation for each coherence function is computed. It is demonstrated through experimental results that the standard deviation of the coherence between the signals from the PZTs in healthy and damaged conditions is a very sensitive metric index to detect damage. Tests were carried out on an aluminum plate and the results show that the proposed methodology could be an excellent approach for structural health monitoring (SHM) applications.

Aplicação de sensor de deslocamento angular em fibra óptica para medição de concentração de líquidos via ondas acústicas guiadas

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Damage Detection in Flexible Plate Using Lamb Waves

This paper presents an experimental technique for structural health monitoring (SHM) based on Lamb waves approach in an aluminum plate using piezoelectric material as actuators and sensors. Lamb waves are a form of elastic perturbation that remains guided between two parallel free surfaces, such as the upper and lower surfaces of a plate, beam or shelf. Lamb waves are formed when the actuator excites the surface of the structure with a pulse after receiving a signal. Two PZTs were placed in the plate surface and one of them was used to send a predefined wave through the structure. Thus, the other PZT (adjacent) becomes the sensor. Using this methodology, this paper presents one case of damage detection considering the aluminum plate in the free-free-free-free boundary condition. The damage was simulated by adding additional mass on the plate. It is proposed two damage detection indexes obtained from the experimental signal, involving the Fast Fourier Transform (FFT) and the power spectral density (PSD) that were computed using the output signal. The results show the viability of the presented methodology to damage detection in smart structures

Damage Characterization Using Guided-Wave Linear Arrays and Image Compounding Techniques

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Uso das ondas de Lamb e Scholte para caracterização de líquidos

Pós-graduação em Engenharia Elétrica - FEIS

Analysis of the four wave mixing effect (FWM) in a dispersion decreasing fiber (DDF) for a WDM system

We did a numerical investigation of the propagation of short light pulses in the region of 1.55 mu m and the conversion efficiency (CE) for the four wave mixing generation (FWM) of ordinary and dispersion decreasing fibers for use in wavelength division multiplexing (WDM) systems, Our simulations studies three different profiles, linear, hyperbolic. and constant, One conclude that for all the profiles there is decrease of the conversion efficiency with the increase in the channel separation. The hyperbolic profile present a higher efficiency of around 1000 above in magnitude compared with the others profiles at 0.2 nm of channel separation. We calculate the conversion efficiency versus the fiber length for the three profiles. The conversion efficiency for the hyperbolic profile is higher when compared to the constant and linear profiles. The other interesting point of the hyperbolic profile is that the increase of the CE in the beginning of the fiber does not show my oscillation in the CE value (log eta), which was observed for the constant and linear profiles. For all the profiles there is an increase of the conversion efficiency with the increase of the pump power. The compression factor C-i for the generated FWM signal at omega(3) was measured along the DDF's and the constant profile fibers. One can conclude that with the use of decreasing dispersion profile (DDF) fibers one can have a control of the (CE) conversion efficiency and the compression factor of the four wave mixing (FWM) generation in WDM systems. (c) 2005 Elsevier B.V. All rights reserved.

Abundance of sedentary consumers and sessile organisms along the wave exposure gradient of subtropical rocky shores of the south-west Atlantic

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Fresh and matured lamb meat quality fed with sunflower seeds and vitamin E

O objetivo deste estudo foi avaliar a qualidade da carne de cordeiros Ile de France alimentados com dietas contendo grãos de girassol e vitamina E. Trinta e dois cordeiros pesando inicialmente 15kg foram alojados em baias individuais e abatidos ao atingir 32kg de peso corporal. Os tratamentos consistiram de quatro dietas experimentais: D1) cana-de-açúcar + concentrado sem grãos de girassol; D2) cana-de-açúcar + concentrado com grãos de girassol; D3) cana-de-açúcar + concentrado grãos de girassol, mais 1000mg de vitamina E kg-1 de matéria seca (MS) da dieta; e D4) cana-de-açúcar + concentrado com grãos de girassol e 1000mg de vitamina E dieta kg-1 de MS. Os parâmetros temperatura, pH, cor, perda de peso ao cozimento, força de cisalhamento e capacidade de retenção de água foram determinados nos tempos de maturação de 0, 7 e 14 dias no músculo Longissimus dorsi. As características qualitativas da carne não foram afetadas pelas dietas contendo grãos de girassol combinado com vitamina E, no entanto, pH 24 horas foi afetado (P<0,05) pela dieta contendo grãos de girassol com vitamina E. A perda de peso por cozimento não foi influenciada (P>0,05) pelos tempos de dieta ou de maturação, por outro lado, a força de cisalhamento e capacidade de retenção de água foi significativamente afetada (P<0,05). O uso da vitamina E resultou em carne com maior capacidade de retenção de água. O tempo de maturação influenciou nos parâmetros pH, cor e força de cisalhamento. Carne de cordeiro com 7 dias de maturação apresentou menor força de cisalhamento.

Incommensurate spin-density-wave and metal-insulator transition in the one-dimensional periodic Anderson model

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Material processing by plasma shock wave generated in an inverse Z-pinch plasma expander

The applicability of plasma shock wave for material processing was investigated using modified inverse Z-pinch device. Shock wave expanding speed and plasma spectral analysis were studied using an internal magnetic,probe and spatially collimated light spectroscopy. The material processing capability of the device was shown by many different surface analysis techniques such as AES, IRS, EPM and SEM. The interactions between a plasma shock wave of similar to4x10(6) cm/s speed with a Si substrate surface shows some ion implantation capability using a nitrogen plasma and thin film formation using a methane plasma.

Viscosity measuring cell using ultrasonic wave mode conversion

This work presents a cell to measure dynamic viscosity of liquids using ultrasonic wave mode conversion from longitudinal to shear wave. The strategy used to obtain the viscosity is based on the measurement of the complex reflection coefficient of shear waves at a solid-liquid interface. Viscosity measurements of automotive oils (SAE90 and SAE140) were obtained in the frequency range from 1 to 10 MHz. These results are compared with the Maxwell model with two relaxation times, showing the dependency of viscosity with frequency. Several parameters affecting viscosity measurements, including the solid material properties, liquid viscosity, and operating frequency are discussed.

Colombeau's theory and shock wave solutions for systems of PDEs

In this article we study the existence of shock wave solutions for systems of partial differential equations of hydrodynamics with viscosity in one space dimension in the context of Colombeau's theory of generalized functions. This study uses the equality in the strict sense and the association of generalized functions (that is the weak equality). The shock wave solutions are given in terms of generalized functions that have the classical Heaviside step function as macroscopic aspect. This means that solutions are sought in the form of sequences of regularizations to the Heaviside function that have to satisfy part of the equations in the strict sense and part of the equations in the sense of association.

Influence of feeding regime and finishing system on lamb muscle fiber and meat quality

Avaliou-se a influência dos níveis nutricionais da ovelha antes do parto, da idade à desmama e do sistema de terminação sobre as fibras musculares e a qualidade da carne dos cordeiros. Utilizaram-se matrizes mestiças Ile de France × Bergamacia criadas a pasto. As ovelhas foram divididas em dois grupos: um com suplementação alimentar 30 dias antes do parto e outro sem suplementação. Os animais (ovelha e cordeiros) foram subdivididos de acordo com a idade à desmama (45 ou 60 dias de idade) e os cordeiros desmamados foram submetidos a três sistemas de terminação: confinamento com dieta completa; confinamento somente com feno; e confinamento somente no pasto. O abate dos cordeiros foi realizado aos 30 kg de peso vivo ou aos 150 dias de idade. As características de carcaça analisadas foram morfofisiologia da fibra do músculo longissimus dorsi, fragmentação miofibrilar pós-morte (maturados nos dias 0, 3 e 7 pos mortem) e redução do pH e da temperatura da carne pós-abate. Não houve efeito da suplementação às ovelhas ou da idade à desmama sobre nenhuma das características avaliadas. A composição em fibras de contração lenta e oxidativa, contração rápida e oxidativa ou contração rápida e glicolítica não foi alterada pelos fatores em estudo, mas a área transversal das fibras foi menor nos cordeiros terminados com feno, assim como os valores de pH, temperatura e as medidas dos fragmentos de miofibrila. Com o aumento do tempo de maturação de 0 para 3 e 7 dias post mortem, houve redução do comprimento dos fragmentos de miofibrilas. O sistema de terminação de cordeiros em confinamento somente com feno interfere mais intensamente na qualidade da carne que o sistema de terminação a pasto ou em confinamento com dieta completa.