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Gear root load-carrying capacity is primarily influenced by fillet geometry. Many different fillet geometries and optimization approaches have been tried to increase gears' load-carrying capacity. One such approach was proposed by Akpolat and Yilmaz et al. Authors proposed using an asymmetric root profile to minimize root stresses in spur gears. Such a method is reported to improve the load- carrying capacity by up to 12%. Root stress was determined in using static FE analysis by applying load to the highest point of single tooth contact. In this research, the effect of asymmetric fillet geometry on root fatigue life was investigated. Moreover, the effect of the adjacent tooth was also explored.

In this paper the authors conducted a numerical investigation of residual stress distribution on two butt-welded plates. Subsequently, they incorporated the obtained residual stresses into a welded model that included a hypothetical semielliptic crack. The stress intensity factors (SIFs) were calculated using the eXtended Finite Element Method (X-FEM). The obtained SIFs results match very well with the analytical results of the API 579-1 standard with the biggest difference being 6.73%. Similar differences can be noticed in the comparison between X-FEM and the results obtained by the conventional Finite Element Method (FEM), where the biggest difference between these two results is 6.75%.

U sklopu suradnje s tvrtkom INA d.d. provedeno je tenzometarsko mjerenje vibracija na vratilu elektromotora. Izmjereni su momenti savijanja i uvijanja na kritičnom dijelu vratila za vrijeme rada elektromotora pod opterećenjem, usporedo je mjerena i brzina vrtnje vratila.

In recent years, growing demand for light-weight, efficient and quiet transmissions, fueled by the introduction of electric vehicles is observed. This calls for simultaneous gear optimization regarding efficiency, mass, and NVH (noise vibration harshness). Herewith gear macro-geometry was optimized for efficiency and mass using pressure and helix angles, gear width, modulus, tooth count, addendum, dedendum and root radius coefficients as variables. Optimization was carried out using NSGA-II. The optimization algorithm results have shown that a clear trade- off between weight and efficiency exists, as previously reported by other authors. Since the third axis of solution space, the transmission error, was not implemented yet the algorithm will tend to minimize addendum coefficient values so as to minimize sliding. In-turn, this will worsen the NVH (noise vibration harshness) behavior of the gear pair. Consequently, minimum transverse and axial contact ratio value constraints were implemented to ensure that the algorithm returns a solution with decent NVH behavior. On the other hand, such constraints will prevent the algorithm from finding the actual global optimum of the original objective function. This was implemented to prepare the algorithm for the future introduction of the third objective, which is the transmission error. With the current setup of constraints, the resulting gearing will always fall in the category of high contact ratio gearing.

Zupčanici se nalaze među najčešće korištenim strojnim elementima za prijenos snage i gibanja. Zubi zupčanika u zahvatu su podvrgnuti klizno- valjnom kontaktu u uvjetima elastohidrodinamičkog podmazivanja (EHL). Nakon određenog broja ciklusa na zubima zupčanika u zahvatu javljaju se različiti zamorni mehanizmi kao što su rupičenje, trošenje, zamor u korijenu zuba, itd… Eksperimentalna istraživanja su pokazala da je rupičenje statistički najčešći oblik zamora koji se javlja na zubima zupčanika u klizno- valjnom kontaktu. Dosadašnje metode, koje su korištene za numeričko modeliranje rupičenja na boku zuba zupčanika, ne opisuju precizno taj zamorni mehanizam. Cilj ovog istraživanja je razvijanje novog numeričkog modela za opisivanje procesa rupičenja. Raspodjela opterećenja, kao posljedica kontaktnog pritiska, modelirana je prema Hertzovoj teoriji. Za modeliranje zamornog opterećenja je korištena metoda faznog polja, koja uključuje dodatnu varijablu koja opisuje prelazak iz neoštećenog u potpuno oštećeno stanje materijala.

U inženjerskoj praksi prilikom dinamičkog opterećenja zupčanika dolazi do pojave zamornog oštećenja. Jedan od najčešćih oblika zamornog oštećenja zupčanika tokom klizno-valjnog kontakta u prisutnosti maziva je proces rupičenja. Zbog toga znanstvena istraživanja su već dugi niz godina usmjerena na pronalazak čim preciznijeg postupka za određivanje broja ciklusa opterećenja zupčanika do nastanka rupičenja kako bi se na vrijeme poduzele mjere sprečavanja. Metoda konačnih elemenata je značajno doprinijela rješavanju tog problema. U području metode konačnih elemenata razvijeni su razni pristupi za određivanje nastanka i propagacije pukotine uslijed čega dolazi do rupičenja. Za eksperimentalno ispitivanje pojave rupičenja kod klizno-valjnog kontakta zupčanika na rupičenje najčešće se koriste cilindrični valjci, čiji je radijus ekvivalentan kružnicama zupčanika u zahvatu. U ovom radu prikazan je pregled dosadašnjih istraživanja i numeričkih metoda za određivanje nastanka rupičenja.

Bending fatigue in spur gears, which transpires due to cyclic and variable tooth root stresses, is one of the main reasons for gear failure. Bending fatigue can bring about crack initiation, propagation and possible complete failure of the gear tooth. To investigate and possibly prevent such occurrence, single tooth bending fatigue tests are often used to obtain statistically significant bending fatigue data at a comparatively low price. In material fatigue, relatively minor change of nominal stress results can produce significant shift in fatigue lives. Hence, to accurately interpret and apply single tooth bending fatigue results on a running gear pair, it is of great importance to properly consider the effect of friction forces on gear load capacity. In this paper, numerical investigation of tooth flank friction effect on gear load capacity during single tooth bending fatigue test is conducted. Finite element analysis, whilst considering various friction coefficients and test fixture dimensions, is carried out to obtain nominal tooth root stresses. The aim of the research is to optimize the rigidity of the experimental fixture to minimize the influence of friction forces on nominal tooth root stress results. Confirmation of the aforestated goal is insinuated by the preliminary results of the numerical investigation.

Surface hardened spur gears are one of the most commonly used machine elements regarding the power transmission. During gear service life, variable and cyclic nature of the stresses at the tooth root may lead to material fatigue, commonly known as bending fatigue. The bending fatigue may cause crack initiation and consequently propagation at the tooth root fillet, eventually resulting in a tooth breakage. In this paper, the authors presented a computational model for predicting the number of cycles required for crack initiation. Two cases of driven gears are considered. Elastic finite element analysis is used to generate the numerical models which accounts for the nominal tooth root stress change during the gear meshing. Additional effects due to friction and centrifugal force are also considered. Fatigue models are generated using the strain-life approach and finite element analysis results. Mean and residual stresses, along with the local plastic deformation effects, are also considered. The bending fatigue life results are in good agreement with the experimental data from the available literature for the first case and conservative for the second.

U ovom radu izrađena je programska procedura za parametarsko modeliranje dvodimenzijskog modela zupčanika s evolventnim ozubljenjem u čeonoj ravnini. Za izradu programske procedure korišten je VBA modul u sklopu programskog paketa AutoCAD 2014. Opisan je proces izrade programske procedure uz teorijski opis nekih pojmova evolventnog ozubljenja i objašnjenje pojedinih pojmova vezanih uz teoriju i primjenu zupčanika. Programskom procedurom je omogućeno dvodimenzijsko parametarsko modeliranje cilindričnog zupčanika s ravnim i kosim, simetričnim i asimetričnim zubima. Parametri obuhvaćeni programskom procedurom su normalni modul, broj zubi, faktor pomaka profila, kut nagiba boka zuba i profil ozubljenja.

The primary objective of the STF test is to generate bending fatigue data at a comparatively low price. Assuming negligible effects of friction on fatigue data, it is commonly performed under dry conditions. The aim of this study is to evaluate the effects of friction on tooth bending fatigue lives in a simulated STF test of steel spur gear. The fatigue lives are determined using the strain-life approach within the framework of the finite element method (FEM). Two load models are considered. With the increase in the coefficient of friction, the results showed increase in the fatigue lives with significant differences between considered load models.

A numerical model, based on the finite element and the strain-life methods, is proposed to estimate tooth bending fatigue life of case- carburized steel spur gear from number of cycles required to initiate surface fatigue crack at the tooth root fillet. The fatigue life estimates were found to correlate very well with the available experimental lives from pulsator testing. The model is used then to correlate fatigue life estimates for two load cases: the first one in which the gear tooth is loaded with pulsating load acting at the outer point of single pair tooth contact, and the second one in which quasi-static meshing of the gears is considered.

U e-biblioteci Terminološki rječnici Strune objavljuju se terminološke zbirke koje su nastale kao rezultat pojedinih projekata u okviru programa Izgradnja hrvatskoga strukovnog nazivlja – Struna. Struna je terminološka baza Instituta za hrvatski jezik i jezikoslovlje u kojoj se terminografski i jezično obrađuje nazivlje raznih struka radi stvaranja, usklađivanja i usustavljivanja nazivlja na hrvatskom jeziku. Od 2012. godine baza se može pretraživati na internetskoj adresi http://struna.ihjj.hr/. Cilj je ove biblioteke učiniti pojedinačne terminološke zbirke Strune dostupnima i u cjelovitu tekstualnom obliku koji je moguće pretraživati po raznim kriterijima i po potrebi otisnuti. U ovom se svesku donosi nazivlje obrađeno u okviru projekta Hrvatske zaklade za znanost Hrvatsko nazivlje strojnih elemenata koji je vodio prof. dr. sc. Božidar Križan.

U radu su dati rezultati ispitivanja prirubničkih spojeva plinskih cijevi glede potrebnih unesenih momenata pritezanja radi ostvarenja funkcije brtvljenja. Ispitivan je jedan konkretan problem iz eksploatacije.

Numerical model for bending fatigue crack initiation life prediction in spur gear tooth root is presented. Stresses are determined from two-dimensional finite element model, assuming plane stress conditions. The material, case carburized 14NiCrMo13-4 steel, is assumed to be homogenous, isotropic and linear elastic. Neuber’s rule is used to account plasticity effects. The bending fatigue crack initiation life is predicted using a strain-life approach including: surface finish, mean stress and residual stress effects. Assuming that fatigue cracks are initiated on a component’s surface, analysis is performed for all the nodes in the root fillet of the loaded tooth side. Node with the smallest life is regarded as location of potential crack initiation. Two load cases are investigated: the first one in which gear tooth is loaded with a normal cyclic load acting at the highest point of single tooth contact, and the second one in which actual gear operation is considered.

This paper presents an experimental and a finite element analysis which are conducted to determine the allowable and failure pressures in unflawed valve housing (designation DN100 PN40). Extensive three-dimensional non-linear finite element analyses are performed to obtain the plastic limit, collapse and instability loads for the valve housing under internal pressure and to predict the burst pressure obtained by experimental tests. Finite element results show that the failure pressures obtained by the limit load analyses give conservative results, except those obtained by using the ultimate tensile stress as the flow stress. It is shown that the plastic collapse pressure results obtained by a real strain hardening material model agree well with the experimental results.

Numerical analyses of rim thickness effect on bending fatigue crack initiation life of thin-rim gears manufactured from case carburized 14NiCrMo13-4 alloy steel taking into account actual gear operation are performed. Thin-rim gears are often used in aircraft applications in order to reduce weight. Rim deflections have significant effect on stress amplitudes in the tooth root which may lead to bending fatigue problems. Generally, fatigue process can be divided into two main stages: crack initiation and crack propagation. Since crack initiation stage usually accounts for most of the load cycles to gear failure, especially in high-cycle fatigue, a simplification that failure has occurred when a crack has initiated can be adopted. Service life of gear, according to ISO, can be estimated from tooth bending life factor. For surface-hardened steels, this factor is given with respect to the experimentally obtained number of load cycles required to initiate bending fatigue crack in gear tooth root from pulsator testing and therefore does not take into account fact that in actual thin-rim gear operation a significant reversed stress occurs at the root of the tooth adjacent to the loaded tooth. A proposed numerical model is based on the continuum mechanics approach and on the assumption that fatigue cracks are initiated on the component’s surface. Material is assumed to be homogenous, isotropic and linear elastic. Commercial finite element package ABAQUS/Standard is used to determine stresses in gear. Two-dimensional finite element model is created, assuming plane stress conditions and uniformly distributed load on the tooth flank. Elastic strains are calculated from obtained stresses and corrected using Neuber’s rule to account plasticity effects. The number of load cycles required to initiate fatigue crack is calculated using strain-life approach based on principal strain criterion. Strain-controlled fatigue properties of the material are approximated from hardness. The mean stress as well as residual stress effects are included through Morrow’s mean stress correction. Analysis is performed for all the nodes in the root fillet region of the loaded tooth side. Node with the smallest number of load cycles required to initiate fatigue crack is regarded as location of potential crack initiation. Numerical model is validated by comparison with available experimental data from literature and used for parametric studies of thin-rim gears. Predicted numbers of load cycles required to initiate potential bending fatigue crack as well as its location in tooth root fillet region are presented with respect to the evaluated rim thickness.

Thin-rim gears are often used in applications where light weight and compact design are demanded. Since the gear rim is more rigid in the area of the gear web, this influences the load as well as the contact stress distribution along the tooth face width. Conventional standard procedures for gear design assume uniform rigidity along the face width and therefore are not fully applicable to the thinrim gears tooth contact stress calculation. The objective of this paper is to evaluate effect of web arrangement on a thin-rim gear tooth contact stresses using advanced engineering tools for a numeric analysis. Three-dimensional parametric finite element model of thin-rim gear engaged with a solid gear is created. The gear pair contact position is chosen to load the thin-rim gear (the wheel) at the highest point of single tooth contact assuming small sliding and dry frictionless contact. Commercial finite element package Abaqus/Standard is used to determine contact stresses assuming small displacement hypothesis. The material is considered homogenous and isotropic with a linear elastic behavior. Obtained tooth contact stress contour lines as well as the maximum tooth contact stress values for various thin-rim gear web arrangements are presented.

In the process industry, globe valves are used to shut off and regulate fluid flow in pipelines. The main valve component carrying the internal pressure is the valve body. For safe exploitation, the valves are designed with the allowable internal pressure taken into consideration. The aim of this paper is to investigate the influence of the wall thickness on the allowable and failure pressures of two- and tree-way globe valve bodies, DN50 and DN100 respectively. Twice-elastic-slope (TES) and the tangent intersection (TI) methods are used to obtain the plastic collapse pressures at the critical location which is determined at the location where maximum equivalent plastic strain throughout the valve body thickness reaches the outer surface. Obtained values are used subsequently to calculate corresponding allowable pressures according to the limit design method, while the failure pressure at the same location is determined as the highest point from the load-displacement curve. Calculated allowable pressure values, for both valve bodies, are compared with the corresponding ones that are obtained using the EN standard.

U radu je provedena trodimenzijska numerička analiza nastanka zamorne pukotine u korijenu strane zuba zupčanika na kojoj djeluje opterećenje. Usporedo je provedena i analiza najvećeg glavnog naprezanja. Predmet istraživanja su cilindrični zupčanici s tankim vijencem i vanjskim evolventnim ozubljenjem ravnim zubima. Istražen je utjecaj položaja diska, debljine vijenca, okretnog momenta te brzine vrtnje, odnosno centrifugalne sile. Najveće glavno naprezanje kao i njegovo mjesto u korijenu zuba određeni su primjenom elastične analize pomoću metode konačnih elemenata. Utjecaj slike nošenja uzet je u obzir modeliranjem kontakta između zubi u zahvatu. Numerički model je verificiran eksperimentalnim ispitivanjem pomoću metode tenzometrije, a iskorišten je i za određivanje povijesti stanja naprezanja u korijenu zuba zupčanika. U obzir je uzeta činjenica da se opterećenje prenosi s pogonskog na gonjeni zupčanik mijenjajući svoj pravac djelovanja, položaj i intenzitet zbog čega je stanje naprezanja neproporcionalno. Na osnovu poznatih cikličkih karakteristika materijala, potencijalno mjesto i vrijeme do nastanka zamorne pukotine određeni su numeričkim izračunom pomoću metode ovisnosti amplitude deformacije o vremenu do nastanka pukotine u kombinaciji s metodom kritične ravnine. Izračun je verificiran usporedbom s numeričkim i eksperimentalnim rezultatima drugih autora. Pokazano je da iznos i mjesto najvećeg glavnog naprezanja u korijenu zuba, kada opterećenje djeluje u vanjskoj točki jednostrukog zahvata, ovise o opterećenju, centrifugalnoj sili, debljini vijenca te položaju diska. Dobiveni rezultati odstupaju od istih izračunanih pomoću konvencionalnog proračuna. Potencijalno mjesto nastanka zamorne pukotine znatno se razlikuje od mjesta najvećeg glavnog naprezanja. Za analizirani materijal zupčanika, čelik C45E, ovisi o debljini vijenca i položaju diska. Životni vijek zupčanika s obzirom na nastanak zamorne pukotine, ovisi o opterećenju, debljini vijenca te položaju diska, dok centrifugalna sila, pri brzinama vrtnje karakterističnim za prijenosnike opće namjene, ima neznatan utjecaj na njega. Pretpostavkom da zamorna pukotina nastaje na mjestu najvećeg glavnog naprezanja čini se nekonzervativna greška u njegovom određivanju. Trajna dinamička čvrstoća korijena zuba zupčanika s tankim vijencem razlikuje od one kod punih zupčanika, a ovisi o debljini vijenca i položaju diska. Primjenom numeričkog modela te rezultata iz ovog rada može se pouzdanije i točnije procijeniti životni vijek te nosivost korijena zuba zupčanika s tankim vijencem.

Reuse and recycling have become crucial because the rapid advancement in technology has led to the accelerated obsolescence of electronic equipment. Disassembly is the first stage in the recycling process. Manual disassembly has proven to be the most efficient method. Automated systems find their implementation only when relatively uniform-type equipment or assemblies are disassembled. Layout changes can enhance the disassembly speeds by efficient material movement. A new disassembly workstation layout concept introduces solutions for the known problems in the existing layouts.

Provedene su opsežne eksperimentalne i numeričke analize za dobivanje dopuštenog opterećenja i opterećenja plastičnog kolapsa kućišta ventila oznake DN100 PN40. Nelinearnom numeričkom analizom određeno je opterećenje plastičnog tečenja, plastičnog kolapsa te plastične nestabilnosti kućišta uslijed unutarnjeg tlaka. Pokazano je da se numerički rezultati dobiveni realnim materijalnim modelom dobro poklapaju s eksperimentalnim. Za određivanje tlaka plastičnog kolapsa primijenjena je metoda dvostrukog elastičnog nagiba i metoda sjecišta tangenti, dok je definiranje dopuštenog tlaka provedeno pomoću metode graničnog projektiranja. Osim toga, primjenom norme EN12516-dobiven je dopušteni tlak koji se dobro podudara s numeričkim rješenjem.

Provedeno je mjerenje naprezanja pomoću tenzometarske metode na glavnim osima, cirkularno i aksijalno, na cijevi spcifiriranoj prema API spec 5L, materijal PSL2 X70, dimenzija 609, 6 x 7, 9 mm. Izmjerena naprezanja na površini cijevi na tri mjerna mjesta tijekom tlačne probe na 113 bara nisu prešla granicu tečenja RP0, 5 za navedeni materijal. Prema navedenom nije došlo do plastične deformacije uslijed narinutog unutarnjeg ispitnog tlaka. Potrebno je napomenuti da je na ispitivanom modelu bilo prisutno i savijanje uslijed vlastite težine cijevi i težine vode u ispitivanom sklopu, čiji utjecaj nije obuhvaćen ovim mjerenjem.

This paper introduces the concept of disassembly line for liquid crystal display (LCD) monitors remanufacturing and recycling. By the end of 2004 it is estimated that LCD monitors will surpass CRT monitors in worldwide unit sales. Currently the only methods used to deal with the end-of-life LCD units are incineration or landfill. Both are expensive and environmentally harmful because LCD monitors contain hazardous materials. The European Commission Directive 2002/96/EC on WEEE requests disassembly of LCD monitors with a surface greater than 100 cm2. Disassembly in the recycling process provides the means to efficiently remove the components containing hazardous materials and extract valuable components or metals.

U ovom radu dan je teoretski pristup proračunu nosivosti i gubitaka snage prema Hertz-ovoj teoriji kontaktnih pritisaka. Na osnovu ovih teoretskih postavki definiran je izraz za proračun stupnja iskoristivosti ozubljenja pužnih prijenosnika. Za proračun dodirnih linija i klizno-valjane omjere u zahvatnom polju kao i drugih parametara neophodnih za proračun iskoristivosti ozubljenja razmatranih profila puža u ovom radu korišten je vlastiti računalni program. Rezultati teoretskih razmatranja iskoristivosti provjereni su na ispitnom postolju, s realnim prijenosnicima za dvije ulazne brzine vrtnje i različita izlazna opterećenja. Prijenosnik je podmazivan mazivom mineralnog i sintetskog porijekla.

Na osnovi izvorne konstrukcije izvršena je strukturalna anliza jednog elemta transformatora - poklopca kotla. Metodom konačnih elementa izvršen je proračun čvrstoće prilikom djelovanja sila u postupku transporta transformatora.

Saint-Venant's principle is in engineering procedures the fundamental basis for static mechanical tests of material properties. But traditional applications of Saint-Venant's principle require major modifications when strongly anisotropic and composite materials are of concern. Cortical bone at the macrolevel can be considered as a composite with a hydroxyapatite matrix reinforced with collagen. The measurement of the pressure distribution and the subsurface stress field developed on the polished cortical bone surface in contact with pressuresensitive films, can be carried out with high accuracy. This phenomenon has important practical consequences in many fields of biomechanics - in the mechanical testing of bone material and implants, appropriate specimen sizes and strain gauge placement etc.

Reuse and recycling have become crucial because rapid advance in technology have led to accelerated obsolescence of electronic equipment. Disassembly is the first stage in recycling process. Manual disassembly has proven to be the most efficient although cost-effective. Automated systems find implementation only when relatively uniform-type equipment or assemblies are disassembled. Layout changes can enhance the disassembly speeds by efficient material movement. New disassembly workstation layout concept introduces solutions for known problems in existing layouts.

Rad se temelji na projektu uvođenja informacijskog sustava u konstrukcijski ured. Primjenom web tehnologije nastojalo se omogućiti korištenje sustava u mrežnom okolišu. Na konkretnom primjeru sastvanice energetskog transformatora prikazane su mogućnosti kao i nedostaci takvog pristupa. Pri izradi programskog sustava, koncipiran je relacijski model podataka opće sastavnice transformatora pri čemu je projektirana i realizirana relacijska baza podataka.

Rad ukratko opisuje postupak nastanka pređe i osnovne oblike trenja koji su od interesa za ovaj rad. Zatim se opisuju metode za testiranje faktora trenja između pređe i čvrstog materijala prema normi ASTM D3108. Korištena metoda naziva se indirektna metoda te se za njezinu konstrukciju odabiru pojedine komponente usvojene iz postojećih rješenja sličnih uređaja i standardne komponente. Konstrukcijsko rješenje uređaja za određivanje faktora trenja je razrađeno do razine radioničkih crteža te je izvršen i proračun čvrstoće, brzine vrtnje i momenta sile kritičnih komponenti. Konstrukcija je osmišljena tako da je moguće dodavanje maziva na bazi parafina u svrhu smanjenja utjecaja trenja. Na kraju je opisan i postupak mjerenja koristeći konstruirani uređaj. This paper briefly describes the process of yarn creation and the basic forms of friction that are of interest for this paper. Methods for testing the coefficient of friction between yarn and solid material according to ASTM D3108 are then described. The method used is called the indirect method, and individual components adopted from existing solutions of similar devices and standard components are selected for its construction. The construction solution of the device for determining the coefficient of friction has been worked out to the level of workshop drawings, calculation of the strength, speed of rotation and moment of force of critical components has also been carried out. The construction is designed in such a way that it is possible to add a paraffin-based lubricant in order to reduce the impact of friction. Finally, the measurement procedure using the constructed device is described.

U ovome radu konstruiran je mjerni uređaj za mjerenje statičkog torzijskog momenta. Okretni moment mjeriti će se indirektno primjenom tenzometara na pretvorniku na koji će se izvor momenta moći spojiti. In this paper we will design torque measuring device based on aplication of strain gages. Strain gages will by mounted on a transducer to which a sorce of the torque will be connected.

Spur gears are one of the most commonly employed machine elements for power transmission. During their operating life, they are subjected to variable and cyclic loading. Consequently, material fatigue may occur in the tooth root region, more commonly referred to as bending fatigue. Steel gears are typically subjected to heat treatment processes such as carburizing to reduce wear. Additionally, the gears may be shot peened to induce a beneficial, fatigue-resistant surface layer of compressive residual stresses. However, this may result in bending fatigue crack initiation below the surface, i.e., subsurface bending failure. This type of crack is hardly detectable during regular service intervals. Hence, it may often go unnoticed, grow, and propagate rapidly through the brittle carburized layer, resulting in tooth breakage and gear failure. This doctoral thesis establishes a computational model for predicting the bending fatigue crack location (surface vs. subsurface) and the required number of cycles for surface-hardened spur gears. Due to the relative complexity of the gear’s geometry and loading conditions, the finite element method is employed to obtain load-induced stresses and strains. The multilayer method is employed to account for inhomogeneous material, while the strain life approach (ε – N) is used to predict the bending fatigue life. The research is divided into multiple stages. During the initial stages, bending fatigue with surface/subsurface crack initiation is investigated on relatively simple geometry, such as surface-hardened gear steel specimens. Then, the model is gradually upgraded to account for more complex loading conditions, residual stress distributions, and inhomogeneous material until the final model applicable to the running gear pair is acquired. According to the obtained numerical results and confirmed by the experimental investigations from the available literature, subsurface bending fatigue crack initiation tends to occur only in carburized and additionally shot-peened gears. The critical region for subsurface failure is located in the proximity of sharp loss of compressive residual stresses and still relatively high load-induced stresses. The probability of subsurface crack initiation can be reduced by modifying the gear’s geometry (choosing a smaller normal module) or increasing the beneficial compressive residual stresses by prolonging the carburization time. Zupčanici su jedni od najčešće korištenih strojnih elemenata u prijenosnicima snage i gibanja. Vođeni strogim proračunskim kriterijima prema relevantnim standardima kao što je ISO 6336, čelični zupčanici s ravnim zubima u pravilu zadovoljavaju minimalni očekivani radni vijek. Međutim, postojeći standardi ne uzimaju u obzir zajednički utjecaj dodatnih postupaka površinskog otvrdnjavanja, kao što su cementiranje i sačmarenje, na pojavu zamora materijala u korijenu zuba. U takvim slučajevima, javlja se potreba za računskim modelom koji može procijeniti ne samo broj ciklusa do pojave zamorne pukotine, već i mjesto nastanka spomenute pukotine (površinski naspram potpovršinski nastanak). Mjesto nastanka zamorne pukotine od posebne je važnosti zbog njene otežane detekcije tijekom redovnih servisnih intervala. U okviru rada razvijen je računski model temeljen na metodi slojeva (eng: multilayer method) te metodi konačnih elemenata (eng: finite element method – FEM) koji predviđa mjesto te broj ciklusa do nastanka zamorne pukotine u korijenu zuba zupčanika. Zbog relativne kompleksnosti modela, istraživanje je započeto na uzorcima izrađenim od materijala tipično korištenim za izradu čeličnih zupčanika. Predloženi model postepeno je unaprijeđen kako bi se simulirala stvarna geometrija te opterećenje zupčanog para.

Odgovarajućom nosivošću zupčanih parova osigurava se da ne dođe do nastanka oštećenja koja mogu utjecati na normalan rad unutar predviđenog životnog vijeka. S obzirom da se opterećenje s pogonskog na gonjeni zupčanik prenosi na način da mijenja svoj pravac djelovanja, položaj i intenzitet, mijenja se i naprezanje u korijenu zuba zupčanika koje može izazvati lom zuba uslijed zamora materijala. U radu je primjenom metode konačnih elemenata pomoću programskog paketa Abaqus određen ciklus naprezanja u korijenu zuba. Pretpostavljeno je da su oba zupčanika izrađena od istog materijala te da je materijal homogen, izotropan i linearno elastičan. Analizirani su cilindrični zupčanici s ravnim simetričnim i asimetričnim zubima te je provedena usporedba njihovih ciklusa naprezanja. Kako bi sama računalna simulacija što realnije odgovarala stvarnim uvjetima rada zupčanog para, u obzir su uzeti i faktori poput centrifugalnog opterećenja i/ili trenja te je analiziran i njihov utjecaj. Određeno je mjesto maksimalnog naprezanja u korijenu zuba, tj. kritični presjek te je uspoređeno s mjestom maksimalnog naprezanja prema normi HRN EN ISO 6336-3. By choosing the appropriate load capacity of gear pairs it is ensured that no damage occurs which could affect normal operation within the expected service life. Since the load from the operating to the driven gear is transferred in a way that it changes it's direction, position and intensity, the tooth root stress also changes, which can cause breakage of the teeth due to bending fatigue. In thesis, the tooth root stress cycle was determined using finite element method and Abaqus software package. It s assumed that both gears are made of the same material which is considered to be homogenous, isotropic and linearly elastic. Cylindrical gears with symmetric and assymetric involute teeth were analyzed and their stress cycles were compared. In order to conduct the simulation as accurately as possible, factors such as centrifugal load and/or friction were taken into account and their influence on the tooth root stress cycle was analyzed. The place of maximum principal stress in tooth root, i.e. the critical cross section, was determined and compared with the place of maximum stress according to the standard HRN EN ISO 6336-3.

Kako bismo izbjegli oštećenja zubi zupčanika, potrebno je točno odrediti dopuštenu opteretivost istih te određene parametre koji utječu na propagaciju oštećenja. Pri radu, kada se prelazi maksimalna nosivost cilindričnih zupčanika, mogu se pojaviti oštećenja kao što su lom zubi, oštećenje bokova zubi, deformacije zubi, habanje te oštećenje neke komponente sustava koje naposljetku dovodi do nefunkcionalnosti samog zupčanog prijenosnika. Detaljna analiza postojećih uređaja na tržištu i postupka ispitivanja maziva prema normi ISO 14635-1:2000, otkrila je neka zadovoljavajuća rješenja koja su odgovarala određenim zahtjevima dodijeljenog zadatka. Na temelju postojećih rješenja i aktualne norme za ispitivanje maziva, nastala su tri koncepta te je odabran onaj optimalan među njima. Odabrani koncept je detaljnije razrađen kroz proračun i tehničku dokumentaciju. In order to avoid the damage of the gear teeth, it is necessary to accurately determine the load capacity of the gears and the parameters that affects the propagation of the crack and the damage to the material. During operation, when the maximum load capacity of the cylindrical gears is exceeded, it causes damage as tooth breakage, damage of the tooth flanks, tooth deformation, abrasive wear and at the end it can cause damages of some components that leads to dysfunctional gear transmission. This thesis describes the development and construction of the device used for measuring of the load-carrying capacity of the cylindrical gears and is also used as gear lubricant test rig. A detailed analysis of the existing devices on the market and according to the ISO 14635-1:2000 standard it came to some solutions that satisfy the specific requirements of this assignment. Based on the existing solutions and the current standard that is used for lubricant testing, it came into creation of the three concepts and it was chosen the optimal among them for subsequent construction that was fully elaborated in a form of both calculation and technical documentation.