Biomaterials: Joints and problems of contact interfaces

Intenzivan razvoj savremenih materijala omogućava njihovu sve širu primenu u biomedicinskom inženjerstvu. Da bi razmatrani materijal mogao da se primeni kao bimaterijal, potrebno je da se obezbedi biokompatibilnost sa organskim materijalom. Jedan od problema koji se javlja pri projektovanju spojeva implanta u ljudskom organizmu je problem dodirnih površina izazvan velikom razlikom u mehaničkim osobinama materijala koji čine spoj. Stoga je dobro razumevanje ove problematike od izuzetnog značaja u sprečavanju prevremenih otkaza konstrukcija u biomedicinskom inženjerstvu.Intensive development of modern materials enables their increasing application in biomedical engineering. To make the material under consideration applicable, it should be made biocompatible with organic material. One of the problems encountered in design of the implant joints in a human body is the problem of the interfaces in contact, caused by significant difference in mechanical properties of the materials applied. Good understanding of these problems is of immense significance in prevention of premature failures of the structures in biomedical engineering

Consideration of a moving mass effect on dynamic behaviour of a jib crane structure

U radu se razmatra dinamičko ponašanje ravninske konstrukcije stupne konzolne dizalice izložene djelovanju gibanja kolica elektromotornog vitla koje nosi teret. Dinamički odzivi konstrukcije, u vertikalnom i u horizontalnom pravcu, dobiveni su uporabom metode konačnih elemenata i metode direktne integracije. Umjesto konvencionalnog pristupa uporabe modela pokretne sile, u ovom su radu obuhvaćeni utjecaji inercije masa kolica, vitla i tereta. Radi toga, koncept matrice pokretne mase je implementiran u matrici masa cijelog sustava. Određene su prinudne oscilacije konstrukcije stupne konzolne dizalice zbog djelovanja ekvivalentnog pokretnog opterećenja pri čemu je matrica masa sustava promjenjiva u vremenu. Razmatran je utjecaj intenziteta, brzine i ubrzanja pokretnog opterećenja. Rezultati daju korisne zaključke za konstruiranje konzolnih dizalice.This work examines the dynamics of a two-dimensional jib crane structure subjected to a moving trolley with hoist and payload. Dynamic responses of the structure, both in the vertical (Y) and horizontal direction (X), are calculated using the finite element method and the direct integration method. Instead of the conventional moving force problem, this paper deals with the two-dimensional inertial effects due to the masses of trolley, hoist and payload. For this purpose, the moving mass matrix has been used to give contribution to the overall mass matrix of the entire system. The title problem was solved by calculating the forced vibration responses of the jib crane structure with time-dependent overall mass while subjected to an equivalent moving force. Factors as magnitude, speed and acceleration of the moving trolley were studied as well. Numerical results reveal that the approach used herein is usefull and can be used to draw conclusions for the structural design purposes of jib cranes

An overview of application of micromechanical models in ductile fracture analysis of welded joints

Fracture of welded joints has been an important research and industrial topic for a long time, having in mind the key role of welded joints in ensuring the safe operation and integrity of welded structures. This work contains an overview of application of micromechanical models to ductile fracture of welded joints. The main benefit of these models, in comparison with the classical fracture mechanics approach, is consideration of the local quantities (stress and strain) in prediction of damage development. The damage is quantified through the value of the damage parameter, which is typically related to the void nucleation, growth and coalescence for ductile fracture of metallic materials, i.e. the description of the material can be related to the actual material behaviour during fracture. Most of the presented studies, including those published by the present authors, are performed on steel as the base material, and the rest deal with aluminium alloys

Micromechanical modelling of ductile fracture - local approach

Micromechanical modelling of ductile fracture by using the local approach has been presented as the review of previously obtained results for welded joints made of low alloyed high strength steel. Experimental work was performed on 3PB specimens and tensile panels, which were then modelled by finite element method, using two- and three-dimensional meshes, respectively. The local approach was used to simulate both for crack initiation and growth during ductile fracture process

Numerical simulation for studying constraint effect on ductile fracture initiation using complete Gurson model

Nastanak žilavog loma u zavarenim spojevima niskolegiranog čelika povišene čvrstoće je predviđen primenom mikromehaničkog kompletnog Gursonovog modela (CGM). Ograničeno deformisanje oko vrha prsline (eng. 'constraint') i promena troosnosti napona u ligamentu su razmatrani na epruvetama za savijanje u tri tačke SE(B) i na kompaktnim epruvetama za zatezanje C(T), uzimajući u obzir uticaj razlike u mehaničkim osobinama (eng. 'mismatch') i širine metala šava. Analizirana je prenosivost parametra koji odgovara nastanku prsline, u zavisnosti od troosnosti napona ispred njenog vrha i zaključeno je da se dobijene vrednosti korišćenog parametra mogu koristiti za obe geometrije razmatrane u radu.Ductile fracture initiation in high-strength low alloyed welded steel joints is predicted using micromechanical complete Gurson model (CGM). The crack tip constraint and variation of stress triaxiality in ligament are considered on single-edge notch bend SE(B) and compact tension C(T) specimens, including the effect of strength mismatching and different weld metal width. According to the analysis of stress triaxiality in front of the crack tip, transferability of fracture initiation parameter was studied. As a result of the analyses on specimens, fracture initiation parameter determined by using CGM can be transferred from one geometry to another if their triaxial conditions are found to be similar

Numerical simulation of the plunge stage in friction stir welding alloys EN AW 2024 T 351 and EN AW 7049A T 652

Tema ovog rada je proučavanje faze probijanja korišćenjem numeričkog modela. Analizirana je promena temperature i sile probijanja u toku faze probijanja postupka zavarivanja trenjem mešanjem za legure aluminijuma visoke čvrstoće EN AW 2024 T 351 i EN AW 7049A T 652, pri različitim brzinama rotacije alata. Numerički rezultati pokazuju da maksimalne temperature u postupku zavarivanja trenjem mešanjem mogu biti povećane sa povećanjem brzine rotacije alata i da su temperature manje od temperature topljenja materijala koji se zavaruje. Pri istim brzinama rotacije alata, registrovana je veća temperatura kod legure aluminijuma EN AW 2024 T 351 i veća sila probijanja - otpor materijala kod legure EN AW 7049A T 652. Sa povećanjem brzine rotacije alata, sila probijanja može biti smanjena. Trodimenzionalni model konačnih elemenata faze probijanja je razvijen korišćenjem ABAQUS programskog paketa za proučavanje termomehaničkih procesa faze probijanja. Spregnuti termo-mehanički model konačnih elemenata koristi proizvoljnu Lagranž-Ojlerovu formulaciju, Džonson-Kukov zakon i Kulonov zakon trenja. U ovoj analizi se temperatura, pomjeranje i mehaničke reakcije posmatraju istovremeno. Generisanje toplote u postupku zavarivanja trenjem mešanjem se može podeliti na tri dela:generisanje toplote trenjem od čela alata, generisanje toplote trenjem od trna alata i generisanje toplote od plastičnih deformacija u blizini trna alata.This paper investigates the plunge stage using numerical modeling. Change of temperature and plunge force have been analyzed during the plunge stage of the FSW procedure for high hardness aluminum alloys EN AW 2024 T 351 and EN AW 7049A T 652, at different speed of tool rotation. Numerical results indicate that the maximum temperature in the FSW process can be increased with the increase of the rotational speed and that temperature is lower than the melting point of the welding material. Higher temperature was registered at the aluminum alloy EN AW 2024 T 351 at the same speed of tool rotation, and higher plunge force - resistance of material was registered at the alloy EN AW 7049A T 652. When the rotational speed is increased, the plunge force can be reduced. A three-dimensional finite element model (FEM) of the plunge stage was developed using the commercial code ABAQUS to study the thermo-mechanical processes involved during the plunge stage. A coupled thermo-mechanical 3D FE model using the arbitrary Lagrangian-Eulerian formulation, the Johnson-Cook material law and the Coulomb's Law of friction. In this analysis, temperature, displacement and mechanical responses are determined simultaneously. The heat generation in FSW can be divided into three parts: frictional heat generated by the tool shoulder, frictional heat generated by the tool pin, and heat generated by material plastic deformation near the pin region

Numerical simulation of the plunge stage in friction stir welding alloys EN AW 2024 T 351 and EN AW 7049A T 652

Tema ovog rada je proučavanje faze probijanja korišćenjem numeričkog modela. Analizirana je promena temperature i sile probijanja u toku faze probijanja postupka zavarivanja trenjem mešanjem za legure aluminijuma visoke čvrstoće EN AW 2024 T 351 i EN AW 7049A T 652, pri različitim brzinama rotacije alata. Numerički rezultati pokazuju da maksimalne temperature u postupku zavarivanja trenjem mešanjem mogu biti povećane sa povećanjem brzine rotacije alata i da su temperature manje od temperature topljenja materijala koji se zavaruje. Pri istim brzinama rotacije alata, registrovana je veća temperatura kod legure aluminijuma EN AW 2024 T 351 i veća sila probijanja - otpor materijala kod legure EN AW 7049A T 652. Sa povećanjem brzine rotacije alata, sila probijanja može biti smanjena. Trodimenzionalni model konačnih elemenata faze probijanja je razvijen korišćenjem ABAQUS programskog paketa za proučavanje termomehaničkih procesa faze probijanja. Spregnuti termo-mehanički model konačnih elemenata koristi proizvoljnu Lagranž-Ojlerovu formulaciju, Džonson-Kukov zakon i Kulonov zakon trenja. U ovoj analizi se temperatura, pomjeranje i mehaničke reakcije posmatraju istovremeno. Generisanje toplote u postupku zavarivanja trenjem mešanjem se može podeliti na tri dela:generisanje toplote trenjem od čela alata, generisanje toplote trenjem od trna alata i generisanje toplote od plastičnih deformacija u blizini trna alata.This paper investigates the plunge stage using numerical modeling. Change of temperature and plunge force have been analyzed during the plunge stage of the FSW procedure for high hardness aluminum alloys EN AW 2024 T 351 and EN AW 7049A T 652, at different speed of tool rotation. Numerical results indicate that the maximum temperature in the FSW process can be increased with the increase of the rotational speed and that temperature is lower than the melting point of the welding material. Higher temperature was registered at the aluminum alloy EN AW 2024 T 351 at the same speed of tool rotation, and higher plunge force - resistance of material was registered at the alloy EN AW 7049A T 652. When the rotational speed is increased, the plunge force can be reduced. A three-dimensional finite element model (FEM) of the plunge stage was developed using the commercial code ABAQUS to study the thermo-mechanical processes involved during the plunge stage. A coupled thermo-mechanical 3D FE model using the arbitrary Lagrangian-Eulerian formulation, the Johnson-Cook material law and the Coulomb's Law of friction. In this analysis, temperature, displacement and mechanical responses are determined simultaneously. The heat generation in FSW can be divided into three parts: frictional heat generated by the tool shoulder, frictional heat generated by the tool pin, and heat generated by material plastic deformation near the pin region

Micromechanical modelling of ductile fracture – local approach

Micromechanical modelling of ductile fracture by using the local approach has been presented as the review of previously obtained results for welded joints made of low alloyed high strength steel. Experimental work was performed on 3PB specimens and tensile panels, which were then modelled by finite element method, using two- and three-dimensional meshes, respectively. The local approach was used to simulate both for crack initiation and growth during ductile fracture process