45 research outputs found
Approximate method for stress intensity factors determination in case of multiple site damage
A simple and easy to use approximate procedure, for calculating stress intensity factors, was proposed. The procedure was developed based on existing solution for stress intensity factor in the case of two unequal cracks in an infinite plate subjected to remote uniform stress. The solution for this configuration was used for obtaining interaction effect coefficients which take into consideration the increase of stress intensity factor of analyzed crack tip due to interaction with existing adjacent crack. Accuracy and application of suggested procedure were verified through two different computer programs which are based on two different computational methods: finite element method (FEM) with singularity elements and extended finite element method (X-FEM). The analysis of the results has shown that a very good agreement between solutions was achieved, and that this method can provide stress intensity factors with acceptable accuracy
Approximate method for stress intensity factors determination in case of multiple site damage
A simple and easy to use approximate procedure, for calculating stress intensity factors, was proposed. The procedure was developed based on existing solution for stress intensity factor in the case of two unequal cracks in an infinite plate subjected to remote uniform stress. The solution for this configuration was used for obtaining interaction effect coefficients which take into consideration the increase of stress intensity factor of analyzed crack tip due to interaction with existing adjacent crack. Accuracy and application of suggested procedure were verified through two different computer programs which are based on two different computational methods: finite element method (FEM) with singularity elements and extended finite element method (X-FEM). The analysis of the results has shown that a very good agreement between solutions was achieved, and that this method can provide stress intensity factors with acceptable accuracy
Aerodynamic-structural optimization of aircraft lifting surfaces
Istraživanjem tokom izrade ove disertacije sprovedena je multidisciplinarna
studija kojom je izvrÅ”eno numeriÄko modeliranje interakcije fluid-struktura uzgonskih
porÅ”ina letelica. NumeriÄko modeliranje fenomena interakcije na relaciji fluid-struktura
sprovedeno je posrednim sprezanjem aerodinamiÄkih i strukturalnih proraÄuna, a sa
visokim stepenom pouzdanosti numeriÄkog predviÄanja. Primenom predloženog
algoritma postignuta je veÄa taÄnost aerodinamiÄko-strukturalnih analiza u odnosu na
postojeÄe postavke, dok je sama pouzdanost numeriÄkih proraÄuna utvrÄena u odnosu
na sprovedene aerodinamiÄke i strukturalne eksperimente.
U okviru definisanih karakteristiÄnih (kritiÄnih) režima tokom procesa
eksploatacije, izvrÅ”en je izbor optimalnog aerodinamiÄkog oblika koji ispunjava
taktiÄko-tehniÄke zahteve projektovanja, kao i propisana ograniÄenja, a na osnovu Äega
su aerodinamiÄko-strukturalne karakteristike letelice unapreÄene. Postupak optimizacije
je baziran na koriÅ”Äenju aproksimativnog modela, koji je opisan statistiÄkim metodima,
dok je sam optimajzer evolucionog tipa. Predloženo modularno okruženje predstavlja
osnovni metod multidisciplinarne optimizacije opslužen od strane jedinstvenog
optimajzera.
U okviru kreiranog monolitiÄkog okruženja sprovedena je optimizacija krila
balistiÄkog projektila kratkog dometa. Metodom meta-modeliranja prostora pretrage
znaÄajno je poveÄan broj moguÄih optimalnih geometrija koje zadovoljavaju i ciljeve i
ogreniÄenja. Osnovni doprinos predstavlja aerodinamiÄko-strukturalno unapreÄivanje
inicijalne geometrije analiziranog, realnog balistiÄkog projektila. Optimizacijom su
postojeÄe karakteristike i performanse projektila podignute na viÅ”i nivo, Äime je u
okviru realnih režima eksploatacije ostvareno poveÄanje finese, a time i dometa
projektila, dok je sa aspekta sigurnosti pouzdanost samog projektila poboljŔana. Ceo
postupak je doprineo da troÅ”kovi razvojnog programa budu znaÄajno umanjeni, a Å”to se posebno ogleda u uÅ”tedama na polju eksperimentalnih i numeriÄkih resursa. Ostvarenim
rezultatima analizirane letelice postignuti su realni uslovi za potencijalni razvoj jednog
takvog raketnog sistema, a sam razvojni program je u mnogome unapreÄen i može
poslužiti za razvoj i drugih letelica. Kreiranje numeriÄkog okruženja koje omoguÄava
ovakav vid analize predstavlja znaÄajan nauÄni i praktiÄni doprinos pri spregnutom
modeliranju ponaŔanja strukture izložene dejstvu fluida.In this research a multidisciplinary study of numerical modeling of fluidstructure
interaction phenomenon was carried out. Numerical modeling of fluidstructure
interaction of lifting surfaces was accomplished thru closely coupled
aerodynamic and structural computational domains, with high computational reliability
and accuracy which were established regarding conducted aerodynamic and structural
experiments. The proposed algorithm gives better numerical accuracy of aerodynamicstructural
analysis compared to existing similar methods.
Multipoint and multidiscipline aerodynamic shape optimization, with respect to
predefined objectives and constrains, was carried out in order to achieve the
improvement of initial aerodynamic-structural performances of aircraft. The
multidisciplinary feasible method proposed in this thesis, is a single level method driven
by meta-modeling based evolutionary optimizer.
The proposed monolithic environment was used for optimization of a realistic
short range ballistic missile fin. This kind of analysis enabled increased number of
feasible optimal geometries of fin, while its special feature was the overall improvement
of ballistic missile initial geometry. Within realistic multipoint regimes, the initial
performances of missile were optimized and upgraded, especially the missile fitness,
and therefore range. At the same time, the reliability of missile overall behavior was
improved. The whole procedure significantly decreased the costs of developing
program, especially in use of experimental and numerical resources. The achieved
results, regarding the ballistic missile, provide real conditions for potential development
of such and similar aircrafts, with upgraded developing program. The established multimodular
design optimization environment which enabled this kind of analysis presents
significant scientific and practical contribution of fluid-structure interaction numerical
modeling
3D finite element modeling of sling wire rope in lifting and transport processes
Paper explores some aspects of 3D modeling of āaircraft cableā as mostly used sling wire rope. First, the 1Ć19 stainless steel core of āaircraft cableā was investigated. The analysis was carried out by finite element method based computer program. The software used allowed two different types of contacts, including friction. The sling wire rope core was subjected to two different types of axial loading. The obtained results were compared with the solutions calculated from the literature (Costello 2012). Finally, using the advanced modeling techniques, the parametric 3D model of 7Ć19 āaircraft cableā was analyzed using finite element method, in order to provide a better understanding and, hence, prediction, of the mechanical behavior of the sling wire ropes in lifting processes.
First published online:Ā 16 Oct 201
Application of extended finite element method for fatigue life predictions of multiple site damage in aircraft structure
This paper presents an application of the extended finite element method (XFEM) to the modelling of the propagation of four cracks in a typical aircraft structural configuration. It is a thin plate with three holes subjected to uniform uniaxial tensile stress. Material of the plate is aluminium alloy Al-2024 T3. Short theoretical background information is provided on the XFEM as well as the representation of cracks and the stress intensity factors computation. The accuracy of these computations is verified through super-position based approximate procedure and through finite element method (FEM) with singularity elements. The numerical results illustrate that XFEM is efficient for the simulation of crack propagation in MSD (Multiple Site Damage) without the need to re-mesh during the propagation if the finite element mesh is well defined
Application of extended finite element method for fatigue life predictions of multiple site damage in aircraft structure
This paper presents an application of the extended finite element method (XFEM) to the modelling of the propagation of four cracks in a typical aircraft structural configuration. It is a thin plate with three holes subjected to uniform uniaxial tensile stress. Material of the plate is aluminium alloy Al-2024 T3. Short theoretical background information is provided on the XFEM as well as the representation of cracks and the stress intensity factors computation. The accuracy of these computations is verified through super-position based approximate procedure and through finite element method (FEM) with singularity elements. The numerical results illustrate that XFEM is efficient for the simulation of crack propagation in MSD (Multiple Site Damage) without the need to re-mesh during the propagation if the finite element mesh is well defined
Simulation of crack propagation in titanium mini dental implants (MDI)
UnapreÄenja u proizvodnji mini dentalnih implantata (MDI) su uglavnom usmerena ka poveÄanju njihove biokompatibilnosti i, u isto vreme, izdržljivosti i bezbednosti, ali i ka smanjenju njihovih dimenzija u odnosu na postojeÄe implantate. MeÄutim, tokom ugradnje MDI-a može doÄi do njegovog loma ili nastanka prsline koja kasnije može prouzrokovati lom. Da bi se analiziralo Å”irenje prsline u titanijumskom MDI-u, koriÅ”Äeni su softveri za primenu metode konaÄnih elemenata (MKE) ANSYS v13 i FRANC3D v5. KoriÅ”Äenjem FRANC3D programa izmodelirane su prsline razliÄitih veliÄina i oblika na 3D geometriji MDI-a i izvrÅ”eno je simuliranje njihovog Å”irenja. Na osnovu rezultata simulacije izraÄunat je približan zamorni vek oÅ”teÄenog MDI-a.Developments in mini dental implants (MDI) manufacturing are aimed at making them more biocompatible and, at the same time, lighter, more durable and simultaneously safer than the existing implants. But, occasionally, during installation the failure of MDI may occur or cracks may appear, which could lead to the later failure of MDI. In order to understand and assess crack growth in titanium MDI, Finite Element (FE) software packages ANSYS v13 and FRANC3D v5 have been used. Using FRANC3D software different crack sizes and shapes have been modeled and simulations of crack propagations in three-dimensional model of MDI have been performed. Based on simulation results, the approximate fatigue life of damaged MDI was calculated
Simulation of crack propagation in titanium mini dental implants (MDI)
UnapreÄenja u proizvodnji mini dentalnih implantata (MDI) su uglavnom usmerena ka poveÄanju njihove biokompatibilnosti i, u isto vreme, izdržljivosti i bezbednosti, ali i ka smanjenju njihovih dimenzija u odnosu na postojeÄe implantate. MeÄutim, tokom ugradnje MDI-a može doÄi do njegovog loma ili nastanka prsline koja kasnije može prouzrokovati lom. Da bi se analiziralo Å”irenje prsline u titanijumskom MDI-u, koriÅ”Äeni su softveri za primenu metode konaÄnih elemenata (MKE) ANSYS v13 i FRANC3D v5. KoriÅ”Äenjem FRANC3D programa izmodelirane su prsline razliÄitih veliÄina i oblika na 3D geometriji MDI-a i izvrÅ”eno je simuliranje njihovog Å”irenja. Na osnovu rezultata simulacije izraÄunat je približan zamorni vek oÅ”teÄenog MDI-a.Developments in mini dental implants (MDI) manufacturing are aimed at making them more biocompatible and, at the same time, lighter, more durable and simultaneously safer than the existing implants. But, occasionally, during installation the failure of MDI may occur or cracks may appear, which could lead to the later failure of MDI. In order to understand and assess crack growth in titanium MDI, Finite Element (FE) software packages ANSYS v13 and FRANC3D v5 have been used. Using FRANC3D software different crack sizes and shapes have been modeled and simulations of crack propagations in three-dimensional model of MDI have been performed. Based on simulation results, the approximate fatigue life of damaged MDI was calculated
Approximate determination of stress intensity factor for multiple surface cracks
U ovom radu koriÅ”Äena je jednostavna aproksimativna metoda za procenu faktora intenziteta napona za mod I tip optereÄenja, i to u sluÄaju viÅ”estrukih povrÅ”inskih prslina u trodimenzionalnom elastiÄnom telu, koje je podvrgnuto udaljenom jednoosnom optereÄenju. Navedena metoda koristi poznata reÅ”enja za 2D ili 3D konfiguracije koje sadrže samo jednu prslinu i uzima u obzir efekat interakcije izmeÄu istih. Ova metoda, inaÄe zasnovana na principu super-pozicije, konkretno je primenjena na konfiguraciji sa tri koplanarne polueliptiÄne prsline koje su umetnute u trodimenzionalno elastiÄno telo, a koje je podvrgnuto udaljenom jednoosnom naponu na zatezanje. Sve prsline se nalaze u istoj ravni na istim rastojanjima, u sredini tela, a primenjeni napon je upravan na ravan u kojoj prsline leže. Za potrebe verifikacije, faktori intenziteta napona su odreÄenii pomoÄu kompjuterskog programa baziranog na metodi konaÄnih elemenata. Sprovedena analiza pokazala je da je aproksimativna metoda pre svega brz i efikasan alat za procenu faktora intenziteta napona Äak i u sluÄaju 3D konfiguracija sa viÅ”estrukim prslinama. PoreÄenje rezultata pokazalo je i znaÄaj preciznog izraÄunavanja faktora intenziteta napona, kako bi se omoguÄilo bolje razumevanje i predviÄanje Å”irenja 3D prslina.In this paper a versatile and easy to use approximate procedure was used for the estimation of mode I stress intensity factors in case of multiple surface cracks in a three dimensional elastic body, subjected to remote uniaxial tensile loading. The mentioned method uses known solutions for either 2D or 3D configurations containing only one crack, and takes into consideration the interaction effect between cracks. This procedure, which is based on the principle of superposition, was applied on a configuration with three coplanar semi-elliptical cracks embedded in three dimensional elastic body, subjected to remote uniaxial tensile loading. All cracks are located in the same plane at the same distances, in the middle of the body and the applied stress is perpendicular to the cracks plane. For the verification purposes, the stress intensity factors solutions were obtained by using finite element method based computer program. The conducted analysis showed that approximate method is, above all, fast and efficient tool for stress intensity factors assessment even in the case of 3D configurations with multiple site damage. The comparison between results also showed the significance of accurate calculation of stress intensity factors, in order to provide a better understanding and prediction of 3D multiple cracks propagation
Numerical assessment of stress intensity factors at tips of multi-site cracks in unstiffened panel
The aim of this paper is to establish and demonstrate diverse capacity and performances of different numerical methods for calculating stress intensity factors' (SIFs) histories versus crack length for problems involving multiple, interacting cracks resulting from multiple site damage (MSD). A typical aero structural configuration is analysed: unstiffened flat panel made of aluminium Al 2024-T3, containing 11 holes, each of which is a site for crack growth. Analysed model makes a complex configuration with 22 cracks, propagating at the same time. The computations are carried out in FRANC2D software which is FEM based and with superposition based approximate method. The comparison of the results has shown that obtained solutions can be used for SIF predictions with acceptable accuracy