Wyniki wyszukiwania - Biblioteka Nauki

1

Estimation of layer thickness by the cost function optimization: phantom study

100%

Tasinkiewicz J. , Podhajecki J. , Wojcik J. , Falińska K. , Litniewski J.

Hydroacoustics

|

2015

|

tom Vol. 18

161-166

EN

The aim of this work is to present preliminary results of the layer thickness assessment method based on optimization approach. The developed method is based on a multilayer model structure. The measured acoustic signal reflected from the layer is compared with a simulated signal on the basis of a multilayer model. The cost function is defined as the difference between the reflected signal measured using pulse echo approach and the simulated signal. The thickness of the solid layer is the parameter which minimizes the cost function yielding desired solution. Minimization of the cost function is performed with the simulated annealing algorithm. The results obtained with the developed method using measurement data of a custom design model are compared with the reference value and the accuracy of the method is checked. The relative error of the thickness estimation is 1.44%.

2

Spatial Resolution of Attenuation Imaging

100%

Klimonda Z. , Litniewski J. , Nowicki A.

Archives of Acoustics

|

2009

|

tom Vol. 34, No. 4

461-470

EN

The attenuating properties of biological tissue are of great importance in ultrasonic examination even though its anatomical variability limits diagnostics effectiveness. We are currently developing a technique for parametric imaging of attenuation and we intend to apply it for in vivo characterization of tissue. The diagnostic usefulness of the proposed technique crucially depends on the precision of the attenuation estimate and the resolution of the parametric image. These two parameters are highly correlated, since the resolution is reduced whenever averaging is used to minimize the errors introduced by the random character of the backscatter. Here we report on the results of numerical processing of both, simulated and recorded from a tissue-mimicking phantom echoes. We have analyzed the parameters of the estimation technique and examined their influence on the precision of the attenuation estimate and on the parametric image resolution. The optimal selection of attenuation image parameters depending on its intended diagnostic use, was also considered

3

Assessment of vacuum bag pressure impact on porosity of laminates made with VBO prepregs

75%

Czarnocki P. , Katz T. , Koperniak P.

Composites Theory and Practice

|

2015

|

tom R. 15, nr 3

141--145

EN

Vacuum bag only (VBO) prepregs allow for manufacturing composite airframe parts without the need for expensive autoclaves since such prepregs can be cured in ovens with the help of vacuum bags. However, the vacuum pressure must be kept at an acceptable level to obtain low porosity products. One of such prepregs is Cytec MTM46/HTS(12K)-150-35% RW carbon/epoxy VBO prepreg designed for airframe applications. The aim of the presented research was to determine an acceptable level of vacuum pressure in vacuum bags, in particular, and the effect it exerts on the porosity of laminates made with the aforementioned prepreg. For this purpose, UD laminate plates were manufactured under 10, 40, 60, 80 kPa and 96kPa vacuum pressure. Next, ultrasound attenuation displayed by every single plate during ultrasound C-scanning was defined in terms of the so-called full screen height percentage and presented in the form of coloured contour plots. Upon counting the pixels corresponding to each colour, it was possible to determine plate area fractions for each attenuation level. Next, a certain number of specimens was cut out of the plate regions that differed in their attenuation and these specimens were x-rayed with the help of a tomograph, then specialized software was used to determine their porosity. Finally, an experimental relationship between the ultrasound attenuation and specimen porosity was determined.

PL

Tak zwane „vacuum bag only” (VBO) preimpregnaty umożliwiają wytwarzanie struktur lotniczych bez potrzeby stosowania autoklawów. Prepregi takie mogą być utwardzane w piecach, z wykorzystaniem worków próżniowych. Jednakże, by uzyskać porowatość na akceptowalnym poziomie, ciśnienie w worku próżniowym musi być utrzymywane na odpowiednio niskim poziomie. Przedstawione badania dotyczą wpływu, jakie wywiera podciśnienie w worku próżniowym na porowatość wyrobu. W celu zbadania tej zależności wykonano jednokierunkowo wzmocnione płyty z wykorzystaniem prepregu VBO MTM46/HTS(12K)-150-35% RW firmy Cytec. Płyty utwardzano, stosując podciśnienia 10, 40, 60, 80 i 96 kPa, a następnie, wykonując C-skany, wyznaczono tłumienie sygnału ultradźwiękowego dla każdej z płyt. Jako miarę tłumienia przyjęto wielkość amplitudy odbitego sygnału wyrażoną w procentach wysokości ekranu skanera (w funkcji tzw. FSH). Uzyskane wyniki przedstawiono w formie kolorowych map warstwicowych. Licząc pixele odpowiadające każdej z barw, wyznaczono stosunki pól o wyselekcjonowanych wartościach tłumienia w odniesieniu do całkowitej powierzchni analizowanych płyt. Następnie, wykorzystując tomografię komputerową i specjalistyczne oprogramowanie, wyznaczono porowatości próbek wyciętych z wytypowanych obszarów badanych płyt. Umożliwiło to uzyskanie doświadczalnej zależności między tłumieniem fali ultradźwiękowej w badanym laminacie a jego porowatością.

4

Relationships between acoustical properties and stiffness of soft tissue phantoms

75%

Gambin B. , Kruglenko E. , Byra M.

Hydroacoustics

|

2016

|

tom Vol. 19

111--120

EN

Polyvinyl-alcohol cryogel is commonly used for soft tissue phantom manufacture. The gel formation from an aqueous solution of polyvinyl-alcohol takes place during the freezing and thawing cycle. The aim of this work was to assess the degree of gel solidification, hence the material stiffness, by means of quantitative ultrasound. We manufactured three phantoms which differed in the number of freezing/thawing cycles. First, tissue phantoms were examined with an elastography technique. Next, we measured the speed of sound and the attenuation coefficient. What is more, the inter structure variations in phantoms were assessed with the Nakagami imaging which quantifies the scattering properties of the backscattered ultrasound echo. Obtained results confirmed the connection between the number of freezing/thawing cycles and the solidification p rocess. We d efined th e bo undary layer as a region which has a different structure than the sample interior. Next, for each phantom this layer was extracted based on a Nakagami parameter map. We calculated that the thickness of the boundary layer was lower in samples which were subjected to a larger number of freezing/thawing cycles.

5

Evaluating the Attenuation in Ultrasonic Testing of Castings

63%

Boháčik M. , Mičian M. , Sládek A.

Archives of Foundry Engineering

|

2018

|

tom Vol. 18, iss. 2

151--156

EN

This paper considers the assessment of attenuation in aluminium alloys castings and in cast iron prepared by gravity casting method and by casting under pressure. The issue of ultrasound attenuation is important in setting the conditions of non-destructive (NDT) testing, especially in casted materials. The characteristics of the ultrasonic technique and ultrasonic attenuation and the calculation of the attenuation and the velocity of ultrasound are presented in the theoretical part of this paper. For experimental measurements, cylindrical castings from AlSi alloy (a hypoeutectic alloy with a silicon content of about 7% - AlSi7 and a eutectic alloy with a silicon content of about 12% - AlSi12) and from grey and ductile cast iron were made. The ultrasonic records of the casting control, the calculation of ultrasound attenuation for individual samples are listed and described in the experimental part. The evaluation of measurements and comparison of calculated ultrasound attenuation is at the end of this article.