Modeling of the matrix porosity influence on the elastic properties of particulate biocomposites

Porozni materijali se koriste za široki spektar inženjerskih struktura napravljenih na bazi keramike, poroznih legura sa memorijskim efektom, penastih struktura, termički zaštitnih filmova. U skorije vreme primena poroznih biokompozita u inženjerstvu tvrdih tkiva kao i implanata kod koštanih defekata privlači posebnu pažnju. Uticaj matrične poroznosti na karakteristike elastičnosti čestičnih biokompozita analiziran je primenom metode konačnih elemenata upotrebom dvofaznog i trofaznog modela napravljenog na bazi reprezentativnog zapreminskog elementa - RZE. Razvijen je trofazni model RZE sa čestičnim ojačanjem raspoređenim u površinski centrirano kubnom rasporedu sa matričnom poroznošću oblika sfere, čiji su rezultati upoređeni sa jednostavnim analitičkom modelima. Primećeno je da matrična poroznost značajno utiče na karakteristike elastičnosti ovih vrsta kompozita. Rezultati dobijeni na osnovu dvofaznog modela imaju više vrednosti od onih dobijenih na osnovu trofaznog modela u skoro celom analiziranom opsegu usled fizičke granice za zapreminski udeo poroziteta kod trofaznog modela koja je očigledno određena vrednošću zapreminskog udela čestice ojačanja.For a wide range of engineering structures such as ceramics, porous shape memory alloys, foam-like structures and thermal spray deposits, porous materials have been used. Recently, porous biocomposites for the applications to bone implants and hard tissue engineering have become increasingly important. The effect of matrix porosity on the elastic properties of particulate biocomposite was studied by two-and three-phase unit cell finite element models. A 3D FCC unit cell model of particulate composite with included matrix porosity is developed and compared with the simple theoretical models. It is found that the matrix porosity has noticeable influence on the composite elastic properties. The two-phase predictions overestimate the three-phase ones because of the physical threshold for three-phase model determined by the particle content

Considerations of various moving load models in structural dynamics of large gantry cranes

Rad se bavi problematikom pokretnog opterećenja kod portalnih dizalica visokih performansi. Usvojen je kombinovani pristup, koji podrazumeva primenu metode konačnih elemenata u kombinaciji sa jednačinama analitičke mehanike, za formiranje matematičkih modela portalne dizalice. Model kolica je razmatran kroz nekoliko modela: pokretna sila, pokretna masa, pokretni oscilator i pokretni oscilator sa klatnom. Svaki od modela ima svoje dinamičke karakteristike koje profilišu dinamički odziv strukture dizalice. Rešenja su dobijena numerički, metodom direktne integracije, razmatranjem ravanskog ramovskog konačno elementnog modela strukture pod dejstvom ekvivalentnog pokretnog opterećenja na osnovu postavljenog sistema diferencijalnih jednačina drugog reda sa promenljivim koeficijentima. Prikazana je problematika koja nastaje pri povećanju broja parametara pri formiranju dinamičkog modela-postavci matematičkog modela. Na realnom primeru dizalice su dati dinamički odzivi različitih modela koji mogu poslužiti kao preporuka za izbor modela u zavisnosti od važnosti željenih dinamičkih parametara u fazi projektovanja kontejnerskih dizalica.The paper deals with the moving load problems within the structural dynamic analysis of a large gantry crane as high-performance machine. The emphasis is placed on combined method approach, i.e. finite element method and analytical postulations, to obtain the mathematical model of crane. Moving trolley is considered throughout several models: moving force, moving mass, moving oscillator and moving oscillator with swinging object. Each model has characteristics which determine the responses of the crane structure, along with its dynamic properties. The title problem is solved by calculating the forced vibration responses of the two-dimensional framework with time-dependent property matrices and subjected to an equivalent moving load. Improving the moving load models increases complexity as well for postulating as for obtaining the solutions from overall crane model. Comparative presentation of models is shown here with conclusion that leads to an appropriate way of model selection prior to crane problem postulation

Modeling of the matrix porosity influence on the elastic properties of particulate biocomposites

Porozni materijali se koriste za široki spektar inženjerskih struktura napravljenih na bazi keramike, poroznih legura sa memorijskim efektom, penastih struktura, termički zaštitnih filmova. U skorije vreme primena poroznih biokompozita u inženjerstvu tvrdih tkiva kao i implanata kod koštanih defekata privlači posebnu pažnju. Uticaj matrične poroznosti na karakteristike elastičnosti čestičnih biokompozita analiziran je primenom metode konačnih elemenata upotrebom dvofaznog i trofaznog modela napravljenog na bazi reprezentativnog zapreminskog elementa - RZE. Razvijen je trofazni model RZE sa čestičnim ojačanjem raspoređenim u površinski centrirano kubnom rasporedu sa matričnom poroznošću oblika sfere, čiji su rezultati upoređeni sa jednostavnim analitičkom modelima. Primećeno je da matrična poroznost značajno utiče na karakteristike elastičnosti ovih vrsta kompozita. Rezultati dobijeni na osnovu dvofaznog modela imaju više vrednosti od onih dobijenih na osnovu trofaznog modela u skoro celom analiziranom opsegu usled fizičke granice za zapreminski udeo poroziteta kod trofaznog modela koja je očigledno određena vrednošću zapreminskog udela čestice ojačanja.For a wide range of engineering structures such as ceramics, porous shape memory alloys, foam-like structures and thermal spray deposits, porous materials have been used. Recently, porous biocomposites for the applications to bone implants and hard tissue engineering have become increasingly important. The effect of matrix porosity on the elastic properties of particulate biocomposite was studied by two-and three-phase unit cell finite element models. A 3D FCC unit cell model of particulate composite with included matrix porosity is developed and compared with the simple theoretical models. It is found that the matrix porosity has noticeable influence on the composite elastic properties. The two-phase predictions overestimate the three-phase ones because of the physical threshold for three-phase model determined by the particle content

Closed-form solution for the free axial-bending vibration problem of structures composed of rigid bodies and elastic beam segments

In this paper, the coupled axial-bending vibration of planar serial frame structures composed of rigid bodies and Euler-Bernoulli beam segments is considered. The corresponding mode orthogonality conditions for this kind of structures are derived. It is assumed that the mass centers of rigid bodies have both the transverse and the axial eccentricity with respect to beam neutral axes and that the mass centers are located in the plane in which the rigid bodies perform planar motion. The system responses to initial excitation in the case of distinct as well as repeated natural frequencies are considered. Theoretical considerations are accompanied by four numerical examples.This is the peer reviewed version of the article: Tomović, A.; Šalinić, S.; Obradović, A.; Grbović, A.; Milovančević, M. Closed-Form Solution for the Free Axial-Bending Vibration Problem of Structures Composed of Rigid Bodies and Elastic Beam Segments. Applied Mathematical Modelling 2020, 77, 1148–1167.[https://doi.org/10.1016/j.apm.2019.09.008

Numerical Modeling of the Porosity Influence on Strength of Structural Materials

The effect of micro-scale structural low-level porosity on strength of structural materials was studied using the three-dimensional Unit Cell Numerical Model - UCNM. A comparison between proposed UCNM and available experimental data in literature was done by comparing obtained values for stress concentration factor - SCF for different sizes and shapes of pore. Results for normalized strength obtained by proposed UCNM model are in agreement with available experimental data published in literature. It was confirmed that material porosity in form of closed pores, regarding pores' size (volume fraction) and shape, has note cable influence on strength of structural material. Less porosity in the material microstructure generally leads to higher values of material strength. For fixed porosity volume fraction, shape of pores has an impact on strength of structural material

Stress field analysis around optical fiber embedded in composite laminae under transverse loading

U ovome radu analiziran je uticaj ugrađenog optičkog vlakna na naponsko stanje transferzalno opterećene kompozitne lamine. Ugrađeno optičko vlakno ima primetan uticaj na naponsko polje kompozitne lamine. Vrednosti komponentnih napona u lamini sa ugrađenim optičkim vlaknom imaju i do 40% veće vrednosti od nominalnih. Za razmatrani slučaj opterećenja optičko vlakno ugrađeno u kompozitnu laminu jeste generator primetnih ali ne i značajnih koncentracija napona u poređenju sa onima koje, na primer, mogu da se jave usled geometrije oblika.The influence of embedded optical fiber on stress state of transversally loaded composite laminae was analyzed in this paper. The optical fiber interaction with the host material (composite) has noticeable effect on the stress field of laminae. For considered load case, values of the component stresses in laminae with embedded optical fiber have values up to 40% higher than the nominal ones. For the observed loading scenario, optical fibers are acting as generators of evident but not significant stress, comparing to the stress concentrations that could arise, for instance, as a consequence of the shape geometry

Numerical Modeling of the Porosity Influence on Strength of Structural Materials

The effect of micro-scale structural low-level porosity on strength of structural materials was studied using the three-dimensional Unit Cell Numerical Model - UCNM. A comparison between proposed UCNM and available experimental data in literature was done by comparing obtained values for stress concentration factor - SCF for different sizes and shapes of pore. Results for normalized strength obtained by proposed UCNM model are in agreement with available experimental data published in literature. It was confirmed that material porosity in form of closed pores, regarding pores' size (volume fraction) and shape, has note cable influence on strength of structural material. Less porosity in the material microstructure generally leads to higher values of material strength. For fixed porosity volume fraction, shape of pores has an impact on strength of structural material

Osnovi otpornosti konstrukcija, osnovni udžbenik, 298 strana

Овај уџбеник је првенствено намењен студентима прве године Основних академских студија машинства на Машинском факултету Универзитета у Београду. Књига је настала као последица дугогодишњег извођења наставе из области Отпорности конструкција на различитим нивоима студија и у оквиру различитих предмета на Машинском факултету у Београду, а уједно и као скуп наставничких искустава аутора. Истиче се да је овај уџбеник по свом обиму намењен и студентима треће године Основних академских студија који би желели да раде Завршни рад из ове области, тако да су поједина Поглавља књиге проширена и томе прилагођена. Даље, аутори желе да нагласе да је књига настала и као део резултата рада на пројектима Министарства просвете, науке и технолошког развоја Републике Србије (ТР35006, ТР35011 и ТР35040) у периоду од 2011. године до данас. Аутори посебну захвалност изражавају рецензентима проф. др Ташку Манеском, проф. др Зорану Петковићу, проф. др Игору Балаћу и проф. др Момчилу Дуњићу на сугестијама, предлозима и коментарима који су допринели квалитету ове књиге. У Београду, децембра 2019. годин