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1

Relationships between acoustical properties and stiffness of soft tissue phantoms

Gambin B., Kruglenko E., Byra M.

Hydroacoustics

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2016

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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.

2

Differentiation of random structure properties using wavelet analysis of backscattered ultrasound

Gambin B., Wojcik J., Doubrovina O.

Hydroacoustics

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2016

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Vol. 19

121--128

EN

The aim of this work was to find the differences between random media by analyzing the properties of the ultrasound signals backscattered from the inhomogeneities. A numerical model is used to generate two types of random media. The first has the randomness in scatterers’ positions and the second has the randomness in the size and acoustical properties of scatterers. The numerical model of wave scattering has been used to simulate the RF (radio frequency) signals caused by the incident pulse traveling as a plane wave. The markers of randomness type differences between the scattering media were obtained with the help of the spectral and wavelet analysis. The effect of differences in randomness type is more spectacular when the wavelet analysis is performed.

3

Application of ultrasound to noninvasive imaging of temperature distribution induced in tissue

Karwat P., Kujawska T., Secomski W., Gambin B., Litniewski J.

Hydroacoustics

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2016

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Vol. 19

219--228

EN

Therapeutic and surgical applications of High Intensity Focused Ultrasound (HIFU) require monitoring of local temperature rises induced inside tissues. It is needed to appropriately target the focal plane, and hence the whole focal volume inside the tumor tissue, prior to thermo-ablative treatment, and the beginning of tissue necrosis. In this study we present an ultrasound method, which calculates the variations of the speed of sound in the locally heated tissue. Changes in velocity correspond to temperature change. The method calculates a 2D distribution of changes in the sound velocity, by estimation of the local phase shifts of RF echo-signals backscattered from the heated tissue volume (the focal volume of the HIFU beam), and received by an ultrasound scanner (23). The technique enabled temperature imaging of the heated tissue volume from the very inception of heating. The results indicated that the contrast sensitivity for imaging of relative changes in the sound speed was on the order of 0.06%; corresponding to an increase in the tissue temperature by about 2 °C.

4

Ultrasonic Measurement of Temperature Rise in Breast Cyst and in Neighbouring Tissues as a Method of Tissue Differentiation

Gambin B., Byra M., Kruglenko E., Doubrovina O., Nowicki A.

Archives of Acoustics

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2016

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Vol. 41, No. 4

791--798

EN

Texture of ultrasound images contain information about the properties of examined tissues. The analysis of statistical properties of backscattered ultrasonic echoes has been recently successfully applied to differentiate healthy breast tissue from the benign and malignant lesions. We propose a novel procedure of tissue characterization based on acquiring backscattered echoes from the heated breast. We have proved that the temperature increase inside the breast modifies the intensity, spectrum of the backscattered signals and the probability density function of envelope samples. We discuss the differences in probability density functions in two types of tissue regions, e.g. cysts and the surrounding glandular tissue regions. Independently, Pennes bioheat equation in heterogeneous breast tissue was used to describe the heating process. We applied the finite element method to solve this equation. Results have been compared with the ultrasonic predictions of the temperature distribution. The results confirm the possibility of distinguishing the differences in thermal and acoustical properties of breast cyst and surrounding glandular tissues.

5

Theoretical results and numerical study on the nonlinear reflection and transmission of plane sound waves

Wojcik J., Gambin B., Litniewski J.

Hydroacoustics

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2015

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Vol. 18

181-192

EN

The comparison between theoretical and numerical solutions of the reflection/transmission problem for the acoustic plane wave normally incident on the discontinuity surface between two nonlinear lossy media was presented. Numerical calculations made under the assumption that the two media have the same impedance, allow to single out the effect of nonlinearities in the description of the reflection and transmission phenomena, so they agreed with theoretical predictions. It was shown that theoretically obtained and numerically calculated results mutually confirmed themselves.

6

Temperature detection based on nonparametric statistics of ultrasound echoes

Byra M., Gambin B.

Hydroacoustics

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2015

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Vol. 18

17—23

EN

Different ultrasound echoes properties have been used for the noninvasive temperature monitoring. Temperature variations that occur during heating/cooling process induce changes in a random process of ultrasound backscattering. It was already proved that the probability distribution of the backscattered RF (radio frequency) signals is sensitive to the temperature variations. Contrary to previously used methods which explored models of scattering and involved techniques of fitting histograms to a special probability distribution two more direct measures of changes in statistics are proposed in this paper as temperature markers. They measure the ''distance'' between the probability distributions. The markers are the Kolmogorov Smirnov distance and Kulback-Leiber divergence. The feasibility of using such nonparametric statistics for non- invasive ultrasound temperature estimation is demonstrated on the ultrasounds data collected during series of heating experiments in which the temperature was independently registered by the classical thermometer or thermocouples.

7

Relationship between thermal and ultrasound fields in breast tissue in vivo

Gambin B., Kruglenko E., Wójcik J.

Hydroacoustics

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2015

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Vol. 18

53--58

EN

The study shows the direct relationship between the temperature field and the parallel changes that are taking place in backscattered ultrasonic signals from the breast tissue in vivo when heated to the temperature of approximately 42 deg. C. The non-uniform temperature field inside the heating tissue was determined by the numerical model using FEM. It is shown that the spatial distribution of intensities of the backscattered signals coincides with the temperature distribution field predicted by the numerical model in some areas. The result indicates the possibility of the indirect measurement of the temperature rise in the breast tissue in vivo by measuring the intensity variations of the ultrasound echo.

8

Macroscopic thermal properties of quasi-linear cellular medium on example of the liver tissue

Gambin B., Kruglenko E., Gałka A. A., Wojnar R.

Computer Assisted Methods in Engineering and Science

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2015

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Vol. 22, no. 4

329--346

EN

There are two main topics of this research: (i) one topic considers overall properties of a nonlinear cellular composite, treated as a model of the liver tissue, and (ii) the other topic concerns the propagation of heat in the nonlinear medium described by the homogenised coefficient of thermal conductivity. For (i) we give a method and find the effective thermal conductivity for the model of the liver tissue, and for the point (ii) we present numerical and analytical treatment of the problem, and indicate the principal difference of heat propagation in linear and nonlinear media. In linear media, as it is well known, the range of the heat field is infinite for all times t > 0, and in nonlinear media it is finite. Pennes’ equation, which should characterize the heat propagation in the living tissue, is in general a quasi-nonlinear partial differential equation, and consists of three terms, one of which describes Fourier’s heat diffusion with conductivity being a function of temperature T. This term is just a point of our analysis. We show that a nonlinear character of the medium (heat conductivity dependent on the temperature) changes in qualitative manner the nature of heat transfer. It is proved that for the heat source concentrated initially (t = 0) at the space point, the range of heated region (for t > 0) is finite. The proof is analytical, and illustrated by a numerical experiment.

9

Temperature level and properties of wavelet approximations of backscattered ultrasound

Doubrovina O., Gambin B., Kruglenko E.

Hydroacoustics

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2014

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Vol. 17

37--46

EN

The aim of the paper is to find links between the dynamics of changes of statistical parameters and changes in spectral properties of the signal envelope of backscattered RF signals during the thermal process. We have shown previously that by using wavelet approximations these tendencies are better recognized in the case of the heating of a phantom sample than in the parallel analysis performed for a full signal envelope. Here we are currently expanding this statement to the case of heating a soft tissue sample in vitro. The shape parameter of the K- distributed random variable is considered as a statistical marker of temperature level changes. Additionally, the spectral properties of different levels of wavelet approximations are calculated and their sensitivity to temperature increase and decrease is demonstrated. Both approaches registering changes in temperature, are used in the case of the pork loin tissue sample in vitro, heated by an ultrasound beam with a different power.

10

RF signal amplitude statistics during temperature changes in tissue phantoms

Kruglenko E., Gambin B.

Hydroacoustics

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2014

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Vol. 17

115--122

EN

Two heating protocols for soft tissue phantoms have been performed. An Agar-Gel-Oil (AGO) mixture has been heated locally by applying ultrasonic beams and a Poly Vinyl Alcohol-cryogel (PVA-c) has been heated “globally” by a water bath with a controlled temperature rise. The RF signals were collected during heating by an ultrasound transducer to ensure no interference from waves from the heating transducer. Independently, the thermocouples' measurement has been used to obtain temperature as a function of time in the AGO case. At first, a compensation of attenuation was performed and normalized envelopes of signals were used as data for statistical analysis. It is shown that random the values of the backscattered amplitude are close to Rayleigh and K-distributed random variables for AGO and PVA-c, respectively. Temperature is linked to the scale parameter of Rayleigh distribution for the AGO, and the shape parameter of K-distribution for PVA-c were calculated and discussed in the context of their suitability for the acoustic measurement of temperature.

11

Ultrasonic Synthetic Apertures: Review

Nowicki A., Gambin B.

Archives of Acoustics

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2014

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Vol. 39, No. 4

427--438

EN

In the paper the concept of synthetic aperture used for high resolution/high frame rate ultrasonic imaging is reviewed. The synthetic aperture technique allows building extended “virtual” apertures, synthesized from smaller real aperture resulting in improved lateral resolution along full penetration depth without sacrificing the frame rate. Especially, four methods, synthetic aperture focusing (SAF), multi-element synthetic aperture focusing (M-SAF), synthetic receive aperture (SRA) and synthetic transmit aperture (STA) are addressed. The effective aperture function, describing two-way, far field radiation is a useful tool in beam pattern analysis. Some basic notations, which are used to calculate the effective aperture are introduced in Appendix.

12

Statistical properties of wavelet transform coefficients of backscattering signal from soft tissues and their phantoms

Gambin B., Doubrovina O.

Hydroacoustics

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2013

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Vol. 16

59--66

EN

The paper contains the wavelet approach to registered backscattered RF signals from two different cases. First, the wavelet analysis has been performed for RF signals registered from soft tissue phantoms. The second case is the wavelet analyses of RF scattered signals from regions of healthy and BCC changed human skin. The three phantoms made from tissuemimicking material with different structures have been measured. We claim that there are visible differences in the statistical parameters of wavelets coefficients of signals between healthy and BCC changed skin regions as well as between phantoms without scatterers and with different number of strong small scatterers.

13

Soft tissue-mimicking materials with various number of scatterers and their acoustical characteristics

Kruglenko E., Gambin B., Cieślik L.

Hydroacoustics

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2013

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Vol. 16

121--128

EN

For the study of the temperature increase in the soft tissues irradiated by a low-power ultrasound [1], soft tissue-mimicking materials can be used. The phantoms have been produced based on an aqueous solution of agar, oil, and glass beads microparticles. The RF signals collected in the experiments enabled evaluation of the acoustic properties of phantoms with different number of strong scatterers (concentration varied from 0 to 30 pcs/mm3). Speed of sound (SOS) determined for the phantoms was similar to the value typical of soft tissue (about 1540 m/s). To determine attenuation coefficient the semi-transmission method has been used. Attenuation coefficient value varied from 0.5 to 1.1 dB/(MHz cm), depending on the number of scatterers. It was shown that the phantoms stored for 6 months preserved their acoustical properties and were usable for further experiments. It was found that within the total attenuation, the part corresponding to scattering can be distinguished.

14

Incompressible limit for a magnetostrictive energy functional

Gambin B., Bielski W.

Bulletin of the Polish Academy of Sciences. Technical Sciences

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2013

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Vol. 61, nr 4

1025--1030

EN

The modern materials undergoing large elastic deformations and exhibiting strong magnetostrictive effect are modelled here by free energy functionals for nonlinear and non-local magnetoelastic behaviour. The aim of this work is to prove a new theorem which claims that a sequence of free energy functionals of slightly compressible magnetostrictive materials with a non-local elastic behaviour, converges to an energy functional of a nearly incompressible magnetostrictive material. This convergence is referred to as a Γ -convergence. The non-locality is limited to non-local elastic behaviour which is modelled by a term containing the second gradient of deformation in the energy functional.

15

BEM and Shear lag method for interface problem of bi-material structure under static loading

Valeva V., Ivanova J., Gambin B.

Journal of Theoretical and Applied Mechanics

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2011

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Vol. 49 nr 1

17-29

EN

The behaviour of the interface of a pre-cracked bi-material ceramic-metal structure under static axial loading is an object of interest in the present paper. To solve the problem for interface delamination of the structure and to determine the debond length along the interface, a 2D BEM code was created and applied. The interface plate is assumed as a very thin plate comparing with the others two. The parametric (geometric and elastic) analysis of the debond length and interface shear stress is done. First, the obtained numerical results are compared with analytical ones from 1D. Shear lag analysis of the considered structure. The respective comparison is illustrated in figures and shows a good agreement. The comparison between the calculated using 2D BEM code elastic-brittle debond lengths with Song's experimental data for the bi-material structure Zinc/Steel as well as with respective results from FEM simulation shows good coincidence.

PL

W pracy badano zachowanie się na granicy pomiędzy warstwami metalu i ceramiki pod wpływem statycznego obciążenia przyłożonego w kierunku równoległym do połączenia pasm, w przypadku istnienia początkowego nacięcia w jednej z warstw prostopadłego do powierzchni połączenia. W celu rozwiązania zagadnienia delaminacji wzdłuż powierzchni łączącej oba materiały i wyznaczenia długości odspojenia został stworzony i zastosowany kod Metody Elementów Brzegowych – zagadnienie 2-wymiarowe. Warstwa łącząca dwa materiały została potraktowana jako bardzo cienka płyta, w porównaniu do grubości obu warstw materiałowych. Przeprowadzono parametryczną (geometrycznaą i sprężystą) analizę długości odspojenia (delaminacji) i naprężenia stycznego. Otrzymane rezultaty numeryczne porównano z analitycznymi rozwiązaniami 1-wymiarowej analizy tzw. metodą "shear lag". Otrzymane wyniki, zilustrowane na rysunkach, wykazują wzajemną zgodność. Pokazano również, że wyniki uzyskane przy użyciu Metody Elementów Brzegowych są zgodne z wynikami eksperymentu Song'a przeprowadzonego dla dwuwarstwowego elementu kompozytowego pomiędzy warstwą cynku i stali, a także z wynikami uzyskanymi w Metodzie Elementów Skończonych.

16

Some aspects of numerical modeling of temperature increase due to ultrasound beam irradiation of rat liver

Kruglenko E., Gambin B.

Hydroacoustics

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2011

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Vol. 14

99-110

EN

Some aspects of FEM modeling of hyperthermia, the procedure of tissue temperature rise above 37 oC inside the living organism, as a treatment modality, are studied. Low intensity focused ultrasound (LIFU) beam has been used as a source of temperature rise in the liver tissue during performed experiments in vitro. The comparison of the FEM model of the corresponding heating process and the experimental results has been presented in [1]. In the paper, the FEM model of heating scheme of the rat liver tissue in vivo irradiated by the same ultrasound transducer is formulated. At first, the existence of blood perfusion is taken into account in the model equation. Secondly, the thermal and acoustical properties, which are the input parameters of the numerical model, are taken from the published data in literature. Here, the size and the intensity of heat sources are modeled in two ways on the basis of acoustic nonlinear equation solutions in 3 layers attenuating medium. We demonstrate how the results of FEM model in the case of in vitro and in vivo heating, depend on the assumed power density of heat sources, as well as on the size of the heated area. The results are compared and discussed. The influence of different models on temperature rise profiles are demonstrated.

17

Applying crystallography in analysis of trabecular bone backscatter

Wojcik J., Litniewski J., Nowicki A., Gambin B.

Hydroacoustics

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2011

|

Vol. 14

255-266

EN

Some important details of the Backscatter Effective Cross-Sections obtained for random scattering structures (like trabecular bone) are explain by comparison with the results obtained by means of the simplified theoretical model. The simplified model was (establish) and justified on the basis of the structural analysis of the results obtained for exact model of the field scattering on complex structures. The simplified model is commonly used in description of the scattering on the regular structures like crystal. Comparison with experimental results for the trabecular bone is also presented. The results allowed to conclude that crystallographic methods could be potentially useful for extracting characteristic features of trabecular bone.

18

Temperature Fields Induced by Low Power Focused Ultrasound in Soft Tissues During Gene Therapy. Numerical Predictions and Experimental Results

Gambin B., Kujawska T., Kruglenko E., Mizera A., Nowicki A.

Archives of Acoustics

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2009

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Vol. 34, No. 4

445-459

EN

The aim of this work is twofold. Firstly, to verify a theoretical model which is capable of predicting temperature fields appearing in soft tissues during their ultrasound treatment. Secondly, to analyze some aspects of the dynamics of Heat Shock Response induced by the heating process in the context of therapeutic treatment. The theoretical investigations and quantitive analysis of temperature increments at any field point versus time of heating process, depending on the heat source power, spatial distribution and duration as well as on the tissue thermal properties, has been carried out by Finite Element Method (FEM). The validation of the numerical model has been performed by comparison of the calculation results with the experimental data obtained by measuring in vitro of the 3D temperature increments induced in samples of the turkey and veal liver by the circular focused transducer with the diameter of 15 mm, focal length of 25 mm and resonance frequency of 2 MHz. Various ultrasonic regimes were considered. They were controlled by adjusting ultrasound power and exposure time. The heat shock proteins (HSP) and misfolded proteins (MFP) levels during the proposed cyclic sonification are presented.

19

Wpływ mikorstruktury na własności kompozytów sprężystych, piezoelektrycznych i termosprężystych

Gambin B.

Prace Instytutu Podstawowych Problemów Techniki PAN

|

2006

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nr 12

1-183

PL

Celem pracy jest przedstawienie wyników badań własnych autorki dotyczących wyznaczania efektywnych własności materiałów kompozytowych: sprężystych, piezoelektrycznych i termosprężystych. Pojęcie materiału kompozytowego (złożonego) zdefiniowano zgodnie z matematyczną teorią homogenizacji. Dzięki tej teorii można określić w sposób jednoznaczny związek pomiędzy mikrostrukturą i makroskopowymi (efektywnymi, zastępczymi) własnościami materiału. Badania, oparte o różne metody teorii homogenizacji i przedstawione w rozprawie, dotyczą następujących klas materiałów. Kompozyty sprężyste. Wyprowadzone zostaną nielokalne związki konstytutywne dla liniowego ośrodka sprężystego, w których nielokalność jawnie zależy od rozmiarów mikrostruktury. Pokazany będzie wpływ mikrostruktury na zmianę profilu fali przejścia przez warstwę z materiału typu FGM oraz opisane będzie zachowanie się makroskopowe ośrodka o periodycznie-stochastycznym rozkładzie szczelin. Kompozyty piezoelektryczne. Dzięki wprowadzeniu nowych pojęć i udowodnieniu kilku ważnych twierdzeń, możliwe będzie wyznaczenie własności fizycznie nieliniowych kompozytów piezoelektrycznych, dokonanie analizy zagadnień projektowania optymalnego piezoelektrycznych kompozytów gradientowych, podanie nowych charakterystyk sprzężenia elektromechanicznego, a także sfrormułowanie pewnych nowych ograniczeń na liniowe własności piezoelektryczne i obliczenie efektu warstwy brzegowej. Zostaną także wyprowadzone formuły typu Murata na tzw. laminację wielokrotną. Kompozyty termosprężyste. Zastosowanie metod homogenizacji stochastycznej oraz wprowadzenie nowego funkcjonału, który opisuje fizycznie nieliniowe oddziaływanie pól sprężystych z dodatkowym polem skalarnym, umożliwi znalezienie formuł opisujących efektywne stałe termosprężyste. Otrzymane wyniki teoretyczne będą wyjaśnione i zilustrowane przykładami numerycznymi. Merytorycznie rozprawa jest jednorodna tematycznie wszystkie rozdziały związane są z modelowaniem wpływu mikrostruktury na zachowanie się kompozytów. Z punktu widzenia metod użytych do wykonania postawionego celu należy wydzielić Rozdział 6, w którym użyto metod homogenizacji stochastycznej. Z powodu specyfiki języka używanego w metodzie stochastycznej homogenizacji, rozdział ten zawiera dużo nowych definicji i pojęć niezbędnych do zrozumienia przedstawionych wyników. Ze względu na szeroki zakres analizowanych zagadnień, literatura stanowiąca podstawę przeprowadzonych badań będzie omówiona w odpowiednich rozdziałach. Treść rozprawy jest w dużej części podsumowaniem oryginalnych wyników badań autorki prowadzonych w Instytucie Podstawowych Problemów Techniki PAN w latach 1989-2006. Część wyników opublikowano w pracach, których współautorami byli koledzy z Pracowni Metod Wariacyjnych i Biomechaniki.

20

Influence of anisotropy induced by microcracks on effective elastic properties

Gambin B, Gałka A., Telega J. J., Tokarzewski S.

Engineering Transactions

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2005

|

Vol. 53, iss. 4

363-374

EN

The influence of microcracks distribution on macroscopic elastic properties of composites with a specific structure is studied. The model predicts the properties of laminates made of materials in which fracture process leads to appearance of many microcracks distributed practically uniformly. The method of solution is based on the so-called reiterated homogenization with two different scales of inhomogeneities. The smaller scale is connected with microcracks size. After homogenization performed with the help of FEM an anisotropic homogeneous elastic material is obtained. The anisotropy is implied by directional distribution of microcracks. On the second larger scale, random mixture of two or more different anisotropic elastic materials is considered.