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 izvršeno numeričko modeliranje interakcije fluid-struktura uzgonskih poršina letelica. Numeričko modeliranje fenomena interakcije na relaciji fluid-struktura sprovedeno je posrednim sprezanjem aerodinamičkih i strukturalnih proračuna, a sa visokim stepenom pouzdanosti numeričkog predviđanja. Primenom predloženog algoritma postignuta je veća tačnost aerodinamičko-strukturalnih analiza u odnosu na postojeće postavke, dok je sama pouzdanost numeričkih proračuna utvrđena u odnosu na sprovedene aerodinamičke i strukturalne eksperimente. U okviru definisanih karakterističnih (kritičnih) režima tokom procesa eksploatacije, izvršen je izbor optimalnog aerodinamičkog oblika koji ispunjava taktičko-tehničke zahteve projektovanja, kao i propisana ograničenja, a na osnovu čega su aerodinamičko-strukturalne karakteristike letelice unapređene. Postupak optimizacije je baziran na korišćenju aproksimativnog modela, koji je opisan statističkim metodima, dok je sam optimajzer evolucionog tipa. Predloženo modularno okruženje predstavlja osnovni metod multidisciplinarne optimizacije opslužen od strane jedinstvenog optimajzera. U okviru kreiranog monolitičkog okruženja sprovedena je optimizacija krila balističkog projektila kratkog dometa. Metodom meta-modeliranja prostora pretrage značajno je povećan broj mogućih optimalnih geometrija koje zadovoljavaju i ciljeve i ogreničenja. Osnovni doprinos predstavlja aerodinamičko-strukturalno unapređivanje inicijalne geometrije analiziranog, realnog balističkog projektila. Optimizacijom su postojeće karakteristike i performanse projektila podignute na viši nivo, čime je u okviru realnih režima eksploatacije ostvareno povećanje finese, a time i dometa projektila, dok je sa aspekta sigurnosti pouzdanost samog projektila poboljšana. Ceo postupak je doprineo da troškovi razvojnog programa budu značajno umanjeni, a što se posebno ogleda u uštedama na polju eksperimentalnih i numeričkih resursa. Ostvarenim rezultatima analizirane letelice postignuti su realni uslovi za potencijalni razvoj jednog takvog raketnog sistema, a sam razvojni program je u mnogome unapređen i može poslužiti za razvoj i drugih letelica. Kreiranje numeričkog okruženja koje omogućava ovakav vid analize predstavlja značajan naučni i praktični doprinos pri spregnutom modeliranju ponašanja 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 ‘aircraft cable’ as mostly used sling wire rope. First, the 1×19 stainless steel core of ‘aircraft cable’ 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 7×19 ‘aircraft cable’ 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: 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)

Unapređenja u proizvodnji mini dentalnih implantata (MDI) su uglavnom usmerena ka povećanju njihove biokompatibilnosti i, u isto vreme, izdržljivosti i bezbednosti, ali i ka smanjenju njihovih dimenzija u odnosu na postojeće implantate. Međutim, tokom ugradnje MDI-a može doći do njegovog loma ili nastanka prsline koja kasnije može prouzrokovati lom. Da bi se analiziralo širenje prsline u titanijumskom MDI-u, korišćeni su softveri za primenu metode konačnih elemenata (MKE) ANSYS v13 i FRANC3D v5. Korišćenjem FRANC3D programa izmodelirane su prsline različitih veličina i oblika na 3D geometriji MDI-a i izvršeno je simuliranje njihovog širenja. Na osnovu rezultata simulacije izračunat je približan zamorni vek oštećenog 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)

Unapređenja u proizvodnji mini dentalnih implantata (MDI) su uglavnom usmerena ka povećanju njihove biokompatibilnosti i, u isto vreme, izdržljivosti i bezbednosti, ali i ka smanjenju njihovih dimenzija u odnosu na postojeće implantate. Međutim, tokom ugradnje MDI-a može doći do njegovog loma ili nastanka prsline koja kasnije može prouzrokovati lom. Da bi se analiziralo širenje prsline u titanijumskom MDI-u, korišćeni su softveri za primenu metode konačnih elemenata (MKE) ANSYS v13 i FRANC3D v5. Korišćenjem FRANC3D programa izmodelirane su prsline različitih veličina i oblika na 3D geometriji MDI-a i izvršeno je simuliranje njihovog širenja. Na osnovu rezultata simulacije izračunat je približan zamorni vek oštećenog 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 korišćena je jednostavna aproksimativna metoda za procenu faktora intenziteta napona za mod I tip opterećenja, i to u slučaju višestrukih površinskih prslina u trodimenzionalnom elastičnom telu, koje je podvrgnuto udaljenom jednoosnom opterećenju. Navedena metoda koristi poznata rešenja za 2D ili 3D konfiguracije koje sadrže samo jednu prslinu i uzima u obzir efekat interakcije između istih. Ova metoda, inače zasnovana na principu super-pozicije, konkretno je primenjena na konfiguraciji sa tri koplanarne polueliptične prsline koje su umetnute u trodimenzionalno elastično 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 određenii pomoću kompjuterskog programa baziranog na metodi konačnih elemenata. Sprovedena analiza pokazala je da je aproksimativna metoda pre svega brz i efikasan alat za procenu faktora intenziteta napona čak i u slučaju 3D konfiguracija sa višestrukim prslinama. Poređenje rezultata pokazalo je i značaj preciznog izračunavanja faktora intenziteta napona, kako bi se omogućilo bolje razumevanje i predviđanje širenja 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