Wyniki wyszukiwania - BazTech

1

Bounds of the effective elastic moduli of nanoparticle-reinforced composites based on composite sphere assemblage and interface stress model

Tang Z., Ye W.

Archives of Mechanics

|

2022

|

Vol. 74, nr 4

283--317

EN

Three different approaches are formulated to obtain the bounds of the effective elastic moduli of nanoparticle-reinforced composites based on the CSA and the interface stress model. It is found that the effective bulk modulus can be obtained by all three different approaches but the effective shear modulus can be obtained only by the energy approach. The bounds of the effective bulk modulus coincide and depend only on the interface bulk modulus, while those of the effective shear modulus are distinct and depend on two interface elastic constants. Furthermore, limit analysis discloses that the bounds of the effective bulk modulus of nanoparticles coincide but deviate from the bulk modulus of particle in the classical case, and the bounds of the effective shear modulus are distinct in contrast to the effective bulk modulus of nanoparticles or both effective moduli of conventional composites.

2

Wpływ zailenia na wartości parametrów sprężystych w osadach miocenu

Lis-Śledziona Anita, Mroczkowska-Szerszeń Maja

Nafta-Gaz

|

2020

|

R. 76, nr 1

18--21

PL

Parametry sprężyste minerałów ilastych są słabo rozpoznane głównie z powodu niewielkich rozmiarów ziaren tych minerałów i trudności w wyizolowaniu pojedynczych kryształów tak, aby pomierzyć ich własności akustyczne. Do tej pory własności sprężyste minerałów ilastych określano za pomocą obliczeń teoretycznych lub przez połączenie wyników badań eksperymentalnych i obliczeń teoretycznych. Celem artykułu było określenie wpływu zawartości minerałów ilastych na wartości prędkości fali P oraz fali S. Jak wiadomo, wartości parametrów sprężystych ściśle zależą od porowatości. Jednak niebagatelny wpływ na te wartości ma także zawartość minerałów ilastych. W badanym ośrodku do głównych minerałów ilastych zaliczamy: illit (25–30%), minerały mieszanopakietowe illit/smektyt (5–10%) oraz kaolinit (0,5–1,3%). Występują także krzemiany warstwowe w postaci chlorytu (2–9%). Pierwszym etapem pracy było przeprowadzenie badań laboratoryjnych na dziewięciu próbkach pochodzących z osadów miocenu z profilu odwiertu R-1. Pomiary zawartości poszczególnych minerałów wykonano metodą spektroskopii w podczerwieni FTIR (Fourier-transform infrared spectroscopy) za pomocą przystawki ATR (attenuated total reflectance). Ponadto przeprowadzono pomiary prędkości fali P i fali S. Z uwagi na wysoką kruchość badanych próbek pomiary prędkości wykonano w warunkach statycznych. Na podstawie otrzymanych prędkości policzono wartości modułów sprężystości. W oparciu o pomierzone parametry zbudowano model mineralogiczny oraz wyliczono porowatość. Pomierzone statyczne wartości prędkości fal P i S przeliczono do wartości dynamicznych. Korzystając ze wzoru Castagny, obliczono wartości prędkości fali S. Finalnym etapem pracy było określenie zależności pomiędzy zawartością minerałów ilastych a wartościami prędkości fali P, prędkością fali S oraz modułami sprężystości: modułem Younga i modułem sprężystości objętościowej. Przedstawiono także zależność prędkości fali P od wartości prędkości fali S dla różnych zakresów zawartości materii ilastej przy wykorzystaniu modelu Greenberga–Castagny dla utworów piaszczysto-ilastych.

EN

The elastic parameters of clay minerals are poorly recognized mainly due to the small size of clay minerals and the difficulty in isolating individual crystals to measure their acoustic properties. So far the effective elastic properties of clays have been derived either by theoretical computation, or by a combination of theoretical and experimental investigations on clay mixtures. The aim of the article was to determine the effect of clay mineral content on the values of P-wave velocity and S-wave velocity. In the research area, the main clay minerals are: illite (25–30%), interstratified clay minerals illite/smectite (5–10%) and kaolinite (0.5–1.3%). There are also silicates present in the formation in the form of chlorite (2–9%). The first stage of the work consisted in laboratory tests on nine samples from Miocene deposits from the R-1 well. The FTIR (Fourier Transformed Infrared Spectroscopy) was used to measure the content of individual minerals using ATR (Attenuated Total Reflectace) technique. In addition, P- and S-waves velocity measurements were performed. Due to the high brittleness of the tested samples, the velocity measurements were performed under static conditions. The values of the elastic modulus were calculated based on measured velocities. The mineralogical model was built and calibrated based on the measured clay content and porosity was calculated. As is well known, the values of elastic parameters are closely related to the porosity. However, the content of clay minerals also has a considerable impact on the values of elastic parameters. Static values of P-wave and S-wave velocity were converted to dynamic values. Using the Castagna formula, the values of S-wave velocity were calculated. The final stage of the work consisted in determining the relationship between the clay mineral content and P-wave velocity values, S-wave velocity and elastic moduli: the Young modulus, the bulk modulus. The relationship between P-wave velocity and S-wave velocity for different ranges of clay content was presented using the Greenberg–Castagna model for clastic silicate rocks.

3

Elastic properties of self-compacting concrete modified with nanoparticles: Multiscale approach

Stefaniuk D., Niewiadomski P., Musial M., Lydzba D.

Archives of Civil and Mechanical Engineering

|

2019

|

Vol. 19, no. 4

1150--1162

EN

Advances in cementitious composites and nanotechnologies have led to the development of self-compacting concrete (SCC) modified with nanoparticles. SCC with Al2O3 nanoparticles was used in this study. In addition, a reference sample of SCC without an addition of nanoparticles was investigated. First, the micro-mechanical properties of each phase of the composites were examined using the statistical nanoindentation techniques and deconvo-lution. Then, the interfacial transition zone (ITZ) was investigated using line indentation and X-ray microCT. The results indicated that the ITZ played no significant role in the compo-sites. Subsequently, modified Mori–Tanaka and self-consistent homogenization schemes, accounting for random variability of constituent properties, were applied to evaluate the overall elastic properties of the composites. Then, macroscale laboratory (uniaxial compres-sion) tests were carried out to verify the adopted approach. The results of the micro- and macroscale tests showed that the proposed laboratory investigation procedure and homog-enization approach were proper. Finally, the modified Mori–Tanaka scheme was used to verify the influence of material composition on the effective elastic modulus of SCC with Al2O3 nanoparticles.

4

Effects of porosity and composition on seismic wave velocities and elastic moduli of lower cretaceous rocks, central Lebanon

Salah M. K., Alqudah M., El-Aal A. K. A, Barnes C.

Acta Geophysica

|

2018

|

Vol. 66, no. 5

867--894

EN

We collected 40 rock samples from the Cretaceous strata exposed at central Lebanon in order to study the effects of porosity and rock composition on their seismic wave velocities and elastic moduli. Several sedimentological and mineralogical studies were conducted to evaluate the rock composition, provenance, depositional conditions, and the diagenetic history of the studied rocks. Porosity, bulk and grain densities and seismic wave velocities were measured for 35 drilled core samples at ambient conditions in the laboratory. Velocity measurements were conducted on the dry core samples utilizing the pulse transmission technique. Petrographically, four lithofacies have been identified under the polarizing microscope. From oldest to youngest, these comprise arenitic sandstone, lithic limestone, oolitic limestone, and micritic limestone. Investigations of representative rock samples under the SEM revealed that a number of diagenetic processes have impacted the studied rocks, and thereby affected their petrophysical properties. The XRD analysis, on the other hand, revealed that quartz and calcite are the dominant minerals in the sandstones of the Chouf Formation and the limestones of the Abeih and Mdairej Formations, respectively. The measured porosity, bulk density, and compressional and shear wave velocities of the investigated rocks vary, respectively, between 2.14–10.05%, 2.41–2.67 g/cm3, 3885–6385 m/s and 2246–3607 m/s. The grain density was calculated from the measured porosity and bulk density data and varies narrowly between 2.64 and 2.78 g/cm3. We further calculated the Poisson’s ratio and the moduli of shear, bulk, and Young from the measured bulk density and seismic wave velocities. Calculated values of these parameters vary between 0.18–0.28, 1.23–3.43 × 1010 Pa, 2.03–6.18 × 1010 Pa and 3.06–8.69 × 1010 Pa, respectively. The generalized mixture rule is used to provide a unified description of the physical properties of the studied rocks regarding their component properties, volume fractions, and microstructures. We constructed a number of relationships between the measured petrophysical and elastic properties to evaluate the mutual interdependence of these parameters and assess the effects of porosity and rock type on these important rock characteristics.

5

On shape and material optimization of isotropic bodies

Czarnecki S., Lewiński T., Wawruch P.

Engineering Transactions

|

2017

|

Vol. 65, iss. 1

3--9

EN

This paper deals with the free material design and its two constrained versions constructed by imposing isotropy with (i) independent bulk and shear moduli, and (ii) fixed Poisson’s ratio. In the latter case, the Young modulus is the only design variable. The moduli are viewed as non-negative, thus allowing for the appearance of void domains within the design domain. The paper shows that all these methods reduce to one stress-based problem in which the norm involved reflects the type of the constraints imposed.

6

Elastic moduli of carbon nanotubes with new geometry based on FEM

Fereidoon A., Rajabpour M., Hemmatian H.

Journal of Theoretical and Applied Mechanics

|

2014

|

Vol. 52 nr 1

235--245

EN

In this paper, the elastic moduli of elliptic single walled carbon nanotubes (ESWCNTs) are described. A three-dimensional finite element (FE) model for such carbon nanotubes is proposed. The covalent bonds are simulated by beam elements in the FE model. The elastic moduli of beam elements are ascertained from a linkage between molecular and continuum mechanics. The deformations of the FE model are subsequently used to predict the elastic moduli of ESWCNTs. In order to demonstrate the FE performance, the influence of length, chirality, diameter and cross sectional aspect ratios on the elastic moduli (Young’s modulus and shear modulus) of ESWCNTs is investigated. It is found that the cross sectional aspect ratio of ESWCNTs significantly affects the elastic moduli. With increasing cross sectional aspect ratio, the Young’s modulus and shear modulus decrease. As a result, every change in geometry operates as a defect and decreases the elastic moduli. With increasing the length, Young’s modulus increases and the shear modulus decreases.

7

Evaluation of material parameters, texture and stress of a prestressed polycrystalline aggregate from ultrasonic measurements

Lewandowski J.

Archives of Acoustics

|

2001

|

Vol. 26, no. 4

305-329

EN

The propagation of ultrasonic plane waves in a polycrystalline aggregate (steel) is considered for a bulk sample of the material with plane initial (residual) stress, the material being made of cubic crystals of the highest symmetry. Some effective stiffness moduli of the bulk sample and the components of the initial stress are found as functions of the propagation velocities of the respective ultrasonic plane waves. Moreover, the use is made of Jaynes' principle of maximum Shannon entropy and the averaging procedure proposed by Voigt. In this way, the probability density function of the crystallite orientation (texture) and the effective stiffness moduli of a single crystallite of the polycrystalline aggregate are evaluated numerically for the initial plane stress increasing from zero up to about 300\,MPa (in the range of elasticity). The numerical analysis shows that while the effect of the initial stress on the results of these calculations increases with increasing initial stress, the changes in the texture and effective stiffness moduli of a single crystallite are inconsiderable in the region of the values of the initial stress taken in to account.

8

Methods of determination of elastic moduli of particulate materiais - brief review

Świdziński W.

Archives of Hydro-Engineering and Environmental Mechanics

|

2000

|

Vol. 47, nr 1-4

27-50

EN

The methods of determination of elastic moduli for particulate materials with special attention to non-cohesive soils are discussed. Various experimental techniques to isolate elastic response of tested materials are described and analysed. Some short-comings are indicated and any inconsistencies with cIassical theory of elasticity are discussed. Attention is focused on the methods that can be applied using conventional laboratory apparatuses. In addition, some models that allow for calculation of elastic moduli are also presented.

9

Determination of elastic moduli of sands from triaxial compression test

Świdziński W.

Archives of Hydro-Engineering and Environmental Mechanics

|

2000

|

Vol. 47, nr 1-4

51-73

EN

In the paper an empirical method of determination of elastic constants of non-cohesive soils on the basis of the experimental data from conventional triaxial com-pression tests, is proposed. The method is based on a new interpretation of triaxial tests during which samples of dry sands are subjected to several cycles of loading and unloading. The test results of all strain and stress components measured in the experiment are presented in terms of deviatoric stress versus deviatoric strain and mean effective pressure versus volumetric strain diagrams. It is assumed that after any stress reversals the material exhibits purely elastic response that obeys Hooke's linear law. Elastic moduli are determined from the first stage of unloading, which is different from the other methods commonly accepted in soil mechanics. The main advantage of the method proposed was isolating linear behaviour of the material that corresponds to elastic response and including in the analysis the lateral deform-ation of a sample. In the paper several examples of test results for various confining pressures and initial void ratios are presented and analysed. Comparison with other methods is made and discussed.