Contact stresses in gear teeth due to tip relief profile modification

In this paper the linear tip relief profile modification has been observed. This kind of modification has been considered to be potentially dangerous considering micro-pitting initiation as a consequence of contact pressure increase. The amount of tip relief profile modification depends on the elastic gear tooth deflection that needs to be compensated. The standard gear model without linear tip relief profile modification, as well as the modified one, has been discretized by finite elements and analyzed using the finite element method to compare Hertz contact stresses on tooth flank, as influenced by the mentioned profile modification

CALIBRATION OF MATERIAL MODELS FOR THE HUMAN CERVICAL SPINE LIGAMENT BEHAVIOUR USING A GENETIC ALGORITHM

Research of biomaterials in loading conditions has become a significant field in the material science nowadays. In order to provide better understanding of the loading effects on material structures, complex material models are usually chosen, depending on their applicability to the material under consideration. In order to provide as accurate as possible the material behavior modeling of the human cervical spine ligaments, the procedure for calibration of two material models has been evaluated. The calibration of material models was based on the genetic algorithm procedure in order to make possible optimization of material parameters identification for the chosen models. The influence of genetic algorithm operators upon the results in evaluated procedure has been tested and discussed here and the simulated behavior of the material has been compared to the experimentally recorded stress stretch relationship of the material under consideration. Since various influential factors contribute to the genetic algorithm performance in calibration of complex material models and identification of material parameters, additional possible improvements have been suggested for further research

SOME CONSIDERATIONS ON THE LOAD CAPACITY OF INTERNAL HIGH TRANSVERSE CONTACT RATIO INVOLUTE GEARING

Evolventni zupčanici s velikim stupnjem prekrivanja profila (VPP) nude određene prednosti u odnosu na standardno evolventno ozubljenje, poput povećane nosivosti, jednoličnijeg prijenosa okretnog momenta, smanjenog šuma zahvata te povećane trajnosti. Kako je unutarnje ozubljenje važno za konstrukciju mjenjača brzina i mehanizama za okretanje dizalica, analizirana je nosivost unutarnjeg VPP ozubljenja te je istražen problem raspodjele opterećenja kod unutarnjeg VPP ozubljenja. Na temelju rezultata ove analize izračunato je naprezanje u korijenu zuba i Hertzovo naprezanje uzduž zahvatnog puta zupčanika. Najveće naprezanje uzduž zahvatnog puta kao referentna vrijednost uspoređeno je s vrijednostima naprezanja zuba izračunatim prema standardu DIN 3990, čime se pokazalo da proračun prema DIN 3990 daje vrijednosti koje poprilično odstupaju od izračunatih, iako je pogreška na strani sigurnosti.High transverse contact ratio (HCR) involute gears present advantages in relation to standard involute gears, such as improved load capacity, smoother torque transfer, reduced meshing noise and extended gear life. As internal gearing is important for the design of gearboxes and crane rotation mechanisms, the load capacity of internal HCR gearing has been analyzed and the problem of load distribution in internal HCR gearing researched. Based on the results of this analysis, tooth root and Hertzian stresses along the path of contact have been calculated. The maximum stresses along the path of contact were used as a reference value and compared to results of tooth stress calculations according to the DIN 3990 standard. Research has shown that the calculation according to DIN 3990 provides rather inaccurate results for internal HCR gearing, although with higher safety factors

SURFACE ROUGHNESS OF Ti6Al4V ALLOY PRODUCED BY LASER POWDER BED FUSION

Controlling the surface roughness of materials manufactured by laser powder bed fusion (L-PBF) is critical for achieving functional performance of components and improving their mechanical properties. This is important for components whose surfaces cannot be post-treated using subtractive methods. In this study, the surface roughness has been investigated by applying different laser power and scanning speed combinations. Furthermore, potential effects of different locations on the build platform have been considered as well. The regression models have been developed using significant predictor variables, with their levels defined using face-centered central composite design. The analysis of variance (ANOVA) procedure has been used to evaluate the statistical significance of factors and model performances for each prediction variable. It has been found that the average surface roughness of L-PBF Ti6Al4V alloy can be described with high fitting accuracy using laser power and scanning speed as predictor variables. The position of specimens on the build platform showed no statistically significant effect on the average surface roughness. The experimental research and statistical analysis reported in this paper will contribute to a better understanding of how position, laser power, and scanning speed influence the average surface roughness of L-PBF Ti6Al4V alloy

MONOTONIC BEHAVIOUR OF NORMALISED AND QUENCHED AND TEMPERED STEEL 42CrMo4

U radu je predstavljeno na eksperimentu zasnovano utvrđivanje ponašanja normaliziranoga i poboljšanoga niskolegiranog čelika 42CrMo4 (AISI4140) izloženog djelovanju monotonoga aksijalnog vlačnog opterećenja te njegova karakterizacija putem odgovarajućih monotonih parametara. Eksperimenti su izvođeni na ispitnim tijelima standardnog oblika i dimenzija uz korištenje servohidrauličkog stroja pri sobnoj temperaturi. Analizirano je i uspoređeno ponašanje materijala različitih tvrdoća. Određene su vrijednosti osnovnih monotonih parametara materijala te je utvrđena i jednostavnim izrazima okarakterizirana veza između vrijednosti granice tečenja i lomne čvrstoće te temperature popuštanja odnosno postignute tvrdoće materijala.The presented work is concerned primarily with experimental determination of the behaviour of normalised and quenched and tempered low-alloy steel 42CrMo4 (AISI4140) subjected to monotonic uniaxial tensile loading and determination of its monotonic parameters. Experiments were performed on standard specimens using a servo-hydraulic testing machine at room temperature. The behaviours of materials with differing hardnesses were analyzed and compared. After determination of principal monotonic parameters values, correlation was confirmed to exist between tempering temperature, i.e. achieved materials’ hardness, and the monotonic yield strength as well as the ultimate strength. Simple expressions are proposed for fast estimation of cited monotonic properties from hardness

CRITICAL POSITION OF HCR GEAR\u27S TEETH WITH REGARD TO PITCH ERROR

Iako su vrlo osjetljivi na nepravilnosti nastale u proizvodnji, zupčanici s velikim stupnjem prekrivanja profila (HCR, engl. high transverse contact ratio) u sve su češćoj upotrebi zbog povećane nosivosti u odnosu na zupčanike s niskim stupnjem prekrivanja profila. Procedura izračuna raspodjele sile na parove zuba u istodobnom zahvatu izvedena za HCR zupčanike s odstupanjem koraka na zahvatnoj crti bitno ovisi o položaju parova zuba u zahvatu s obzirom na vrijednosti odstupanja. Kritični položaj parova zuba u zahvatu koji izaziva najveći porast naprezanja u odnosu na naprezanja geometrijski točnih zupčanika, definiran je u ovom radu.High transverse contact ratio (HCR) gears are more frequently in use because of their increased load-carrying capacity compared to low contact ratio gears, although they are very sensitive to manufacturing errors. The calculation procedure of load distribution, established for HCR gears with pitch errors, depends on the position of tooth pairs, with regard to pitch error. The critical position of tooth pairs, which causes the maximum stress increase, compared to geometrically ideal gears, is defined in this paper

Rolling-sliding-contact fatigue damage of the gear tooth flanks

Bokovi zuba evolventnih zupčanika izloženi su tijekom zahvata cikličkom djelovanju kontaktnih pritisaka te kombinaciji kotrljanja i klizanja. Spomenuto opterećenje može izazvati specifičnu vrstu zamora materijala koja se naziva kotrljajno-klizno-kontaktni zamor. U radu su opisane faze procesa zamaranja materijala izloženog djelovanju cikličkih opterećenja. Klasificirana su zamorna oštećenja boka zuba zupčanika te su za svaku vrstu navedeni njezini uzroci i značajke. Navedene informacije mogu poslužiti kao pomoć pri sprečavanju ili naknadnoj identifikaciji i uklanjanju problema sa zamornim oštećenjima zupčanika u prijenosnicima snage.During the meshing of involute gears, their teeth flanks are subjected to cyclic contact pressure loading and simultaneous rolling and sliding. The mentioned loading can induce a specific type of material fatigue that is commonly denoted as rolling-sliding-contact fatigue. In this work, individual phases of fatigue occurring due to the cyclic loading are described. Furthermore, different types of fatigue damage of gear teeth flanks are classified and for each type, its causes and features are given. The information presented can be used for prevention or subsequent identification and remedial action in the case of fatigue damage of gears in power transmissions

Oštećenje korijena zuba zupčanika zbog niskocikličnog zamora materijala : doktorska disertacija

Kratkotrajna vršna opterećenja zupčanika u zahvatu uzrok su pojave i akumulacije oštećenja u korijenu zuba, odnosno niskocikličnog zamora materijala. Za karakterizaciju ponašanja materijala pri niskocikličnom zamoru u radu odabran je takav materijalni model kojim se uzima u obzir izotropno i kinematsko očvršćivanje i/ili oslabljivanje materijala te pojava i razvoj oštećenja u materijalu. Budući da se radi o materijalnom modelu koji je izrazito nelinearan, u cilju ostvarenja optimalnih vrijednosti parametara ponašanja materijala razvijen je automatizirani sustav koji se temelji na modernim numeričkim metodama, između ostalih genetski algoritam. Simulacijom odziva materijala pri cikličnom opterećenju i usporedbom s eksperimentalnim vrijednostima naprezanja i deformacija kalibrirani su parametri ponašanja materijala konačnog elementa. Metodom konačnih elemenata je uz primjenu kalibriranih parametara ponašanja materijala diskretiziran model zuba zupčanika. Analizom odziva materijala u korijenu zuba zupčanika pri cikličnom opterećenju te analizom pojave i razvoja oštećenja utvrđene su granice opteretivosti zupčanika obzirom na niskociklični zamor materijala te je dana procjena njihovog životnog vijeka.Short–time overloads in meshing gears cause low–cycle fatigue damage in the material, which means nucleation and accumulation of damage in gear tooth root. In this work the material behavior in low–cycle fatigue regime is characterized by material model that in addition to isotropic and kinematic hardening and/or softening includes also damage occurrence and accumulation. Since the material model is highly non–linear, the automated system for optimal material parameter identification is developed, based on modern numerical methods, among others genetic algorithm. The material parameters are calibrated within the finite element by simulating material response under cyclic loading and comparing results with the experimental stress and strain data. The gear tooth is discretized by using finite element method with elements that have integrated calibrated material parameters. The material response in tooth root under cyclic loading and occurrence and evolution of damage are analyzed to establish the load boundaries of gears with regard to low–cycle fatigue and its service life estimation

Oštećenje korijena zuba zupčanika zbog niskocikličnog zamora materijala : doktorska disertacija

Kratkotrajna vršna opterećenja zupčanika u zahvatu uzrok su pojave i akumulacije oštećenja u korijenu zuba, odnosno niskocikličnog zamora materijala. Za karakterizaciju ponašanja materijala pri niskocikličnom zamoru u radu odabran je takav materijalni model kojim se uzima u obzir izotropno i kinematsko očvršćivanje i/ili oslabljivanje materijala te pojava i razvoj oštećenja u materijalu. Budući da se radi o materijalnom modelu koji je izrazito nelinearan, u cilju ostvarenja optimalnih vrijednosti parametara ponašanja materijala razvijen je automatizirani sustav koji se temelji na modernim numeričkim metodama, između ostalih genetski algoritam. Simulacijom odziva materijala pri cikličnom opterećenju i usporedbom s eksperimentalnim vrijednostima naprezanja i deformacija kalibrirani su parametri ponašanja materijala konačnog elementa. Metodom konačnih elemenata je uz primjenu kalibriranih parametara ponašanja materijala diskretiziran model zuba zupčanika. Analizom odziva materijala u korijenu zuba zupčanika pri cikličnom opterećenju te analizom pojave i razvoja oštećenja utvrđene su granice opteretivosti zupčanika obzirom na niskociklični zamor materijala te je dana procjena njihovog životnog vijeka.Short–time overloads in meshing gears cause low–cycle fatigue damage in the material, which means nucleation and accumulation of damage in gear tooth root. In this work the material behavior in low–cycle fatigue regime is characterized by material model that in addition to isotropic and kinematic hardening and/or softening includes also damage occurrence and accumulation. Since the material model is highly non–linear, the automated system for optimal material parameter identification is developed, based on modern numerical methods, among others genetic algorithm. The material parameters are calibrated within the finite element by simulating material response under cyclic loading and comparing results with the experimental stress and strain data. The gear tooth is discretized by using finite element method with elements that have integrated calibrated material parameters. The material response in tooth root under cyclic loading and occurrence and evolution of damage are analyzed to establish the load boundaries of gears with regard to low–cycle fatigue and its service life estimation