Influence of the gear teeth profile shape and running-in on surface load capacity of cylindrical gear pairs

Ova doktorska disertacija se sastoji iz dva dela: prvi deo predstavljaju teorijska, a drugi eksperimentalna istraživanja uticaja oblika profila i uhodavanja zubaca na površinsku nosivost cilidričnih evolventnih zupčastih parova...This doctoral dissertation consists of two parts: the first part presents theoretical, and the second part presents experimental research on the influence of the gear teeth profile shape and running-in on the surface load capacity of cylindrical involute gear pairs..

Weibull probability distribution for reactor steel 20MnMoNi55 cleavage fracture in transition temperature

This paper presents the results and methods used for determining of fracture toughness of reactor steel, denoted as 20MnMoNi55, typically used for structures working at low temperatures, in transition temperature area. In addition, the effect of test specimen geometry and temperature on fracture toughness was investigated in order to predict the fracture behavior and probability of failure. Failure probabilities (i.e. cleavage fracture) in the function of J(c) for large test specimens, CT100 and CT200 were determined based on the results obtained by testing of small CT50 specimens, for the purpose of direct savings and decreased costs of specimen testing. Failure probability, represented using Weibull distribution of experimental data, will provide a clear insight into material behavior at different temperatures. Other factors affecting the obtained test results will also be discussed

Weibull probability distribution for reactor steel 20MnMoNi55 cleavage fracture in transition temperature

This paper presents the results and methods used for determining of fracture toughness of reactor steel, denoted as 20MnMoNi55, typically used for structures working at low temperatures, in transition temperature area. In addition, the effect of test specimen geometry and temperature on fracture toughness was investigated in order to predict the fracture behavior and probability of failure. Failure probabilities (i.e. cleavage fracture) in the function of J(c) for large test specimens, CT100 and CT200 were determined based on the results obtained by testing of small CT50 specimens, for the purpose of direct savings and decreased costs of specimen testing. Failure probability, represented using Weibull distribution of experimental data, will provide a clear insight into material behavior at different temperatures. Other factors affecting the obtained test results will also be discussed

Efficiency analysis of planetary gears

By kinematic combinations of toothed pairs with external and internal contacts, we can obtain planetary gears with a considerably improved performance than the corresponding ones with fixed axes, as well as planetary gears with notably poor performance regarding the efficiency. In regard to that, the reference literature and papers almost regularly emphasize that planetary gears, under the same technical conditions, have a smaller mass and a higher degree of efficiency than the ones with fixed axes. The main aim of this paper is to examine the above statement and to determine the scope of the gear ratios in which the planetary gears are more suitable than the fixed axes gears

Failure prediction of gas and oil drilling rig pipelines with axial defects

Working conditions of casing pipes in drilling rigs can significantly influence the initiation and development of damage in the material, and therefore also the safe service of the entire system. In this work, an integrity assessment of a steel pipe with initial defect (machined surface crack) is presented. The position of this defect is on the external surface; unlike transport pipes, where internal surface is often endangered due to the contact with the fluid, casing pipes are often exposed to damages at the external surface. Analyzed crack is in axial direction, bearing in mind that this type of defect most significantly decreases the load carrying capacity of the cylindrical pressurized components. A pipe segment exposed to internal pressure is analyzed experimentally and numerically, using the finite element method. The experimental setup included the tracking of crack mouth opening displacement (CMOD) values, as well as J integral, which is determined by application of direct measurement. Criteria for pipe failure are determined on finite element models of the pipe; fracture initiation and plastic collapse are considered as failure mechanisms. The size of the crack is varied in the finite element models; several 3D models with different crack sizes (length and depth) are evaluated. Dependence of maximum internal pressure on the defect size is obtained. 2D plane strain models are also examined, with an aim to determine the applicability limits of this simplified approach. Based on the obtained results, integrity assessment criteria for the analyzed geometries are discussed

Endoskopska antrostomija u lečenju dentogenog maksilarnog sinuzitisa

Introduction. Maxillary sinusistis of odontogenic origin is a wellknown condition that occurs due to close relationship of the maxillary posterior teeth to the maxillary sinus. We presented two patients with symptoms and signs of chronic inflammation of the maxillary sinus of odontogenic origin. Case report. In both patients, after clinical examination, microbiological testing, skin prick tests to inhalant allergens, and endoscopy of the nasal cavity, we performed the cone beam computed tomography (CBCT) of paranasal sinuses, which showed thickening of the mucosal lining of the maxillary sinus. The mucosal oedema resulted in obstruction of the osteomeatal complex in both patients. The presence of a foreign body in the right alveolar recess in the first case and in the left osteomeatal complex in the second case were noticed. The both foreign bodies had densities similar to bone. The alveolar recesses in both cases were below the level of the nasal cavity floor. The patients were treated by endoscopic approach, a combination of lower and middle meatal antrostomy. The thickened mucous membrane was removed in the region of the osteomeatal complex, and then the foreign bodies were removed in both cases. Histopathological analysis proved that both foreign bodies were tooth roots. Conclusion. This case report show how be able to successfully surgically remove foreign bodies from the maxillary sinuses using endoscopic approach, a combination of both, lower and middle meatal antrostomy.Uvod. Maksilarni sinuzitis dentogenog porekla je dobro poznato stanje koje nastaje zbog blizine korenova gornjih zuba i maksilarnog sinusa. Prikazali smo dva bolesnika sa simptomima i znacima hroničnog zapaljenja maksilarnog sinusa dentogenog porekla. Prikaz bolesnika. Kod oba bolesnika, nakon kliničkog pregleda, mikrobioloških ispitivanja, kožnih proba sa inhalacionim alergenima, kao i endoskopije nosne šupljine, urađena je kompjuterizovana tomografija konusnog zraka - [cone beam computed tomography (CBCT)], koja je pokazala zadebljanje sluznice maksilarnog sinusa. Otok sluznice doveo je do opstrukcije ostiomeatalnog kompleksa. Uočeno je prisustvo stranog tela u desnom alveolarnom recesusu u prvom, i u predelu ostiomeatalnog kompleksa, u drugom slučaju. Oba strana tela davala su senku sličnu koštanoj supstanci. Dno alveolarnog recesusa sinusa je u oba slučaja bilo ispod ravni poda nosne šupljine. Bolesnici su operisani endoskopskim pristupom, kombinacijom srednje i donje antrostomije. Odstranjena je zadebljala sluznica u predelu ostiomeatalnog kompleksa, a nakon toga su uklonjena strana tela. Histopatološka analiza je u oba slučaja pokazala da su strana tela bili korenovi zuba. Zaključak. Ovim prikazom se ukazuje na mogućnost uspešnog hirurškog uklanjanja stranih tela iz maksilarnog sinusa endoskopskim pristupom, kombinacijom srednje i donje antrostomije

RISK FACTORS AND BONE MINERAL DENSITY IN ATHLETES AND NON-ATHLETES

Risk factors are important aspects in the treatment of patients with lower bone mineral density (BMD).The objective of this study was to estimate the association between risk factors and BMD status of subjects.Forty subjects - athletes of first sub-sample, were recruited from a football club “Železničar” in Niš, while forty subjects - non-athletes of the second sub-sample, were recruited from the Faculty of Occupational Safety in Niš, totally 80 subjects of masculine sex. BMD was diagnosed by using Dual X-Ray Energy Absorptiometry (DEXA densitometer), in the lumbar region of the spinal column and region of the hip articulation, while the presence of risk factors was evaluated by the One-Minute Osteoporosis Risk Test, ie. questionnaire of the International Osteoporosis Foundation, just before the diagnostics of BMD. All subjects agreed with the terms of research, conducted in accordance with the Declaration of Helsinki.Among 80 subjects, in six (1 athlete and 5 non-athletes) athletes osteopenia was found in the lumbar region of the spinal column, and in three (non-athletes) osteopenia was found in the region of hip articulation. Based on the results of χ2 test, there was the association between the lack of physical activity as a risk factor and osteopenia in the lumbar region of the spinal column (BMDSPINE osteopenia), and between the lack of physical activity as a risk factor and osteopenia in the region of hip articulation (BMDHIP osteopenia), while the association significance between smoking as a risk factor and BMDSPINE osteopenia should be taken with caution, because it is approaching the critical value (p=0.056).Concerning this research, the risk factors had a considerably greater impact on low BMD in non-athletes, compared to athletes, ie., in patients who are smokers and lack physical activity

Comparison of 3D Printed Gear's Geometrical Characteristics

A study of the influence of extruded material type and layer thickness on the surface roughness and the geometry accuracy on a 3D printed gear tooth profile is presented in this paper. A whole set of samples with the same geometric characteristics is printed from two types of materials (PLA and ABS plastic) and with different layer thickness: 0.1; 0.2; and 0.3 mm. The results of roughness testing and uniformity of the layer thickness are presented in this paper. By comparing the results of samples testing from PLA and ABS plastics with the same 3D printing parameters, a certain conclusions are presented at the end of the paper

Procena rezerve organskog ugljenika u poljoprivrednom zemljištu Republike Srbije

This paper shows the assessment results of organic carbon stock in agricultural soils on the territory of the Republic of Serbia. The estimates for the calculation of content in t/ha were based on data from 577 sites and from 757 sites for calculation of the content in %. There are various types of soils, climate and altitude on a soil sampling sites. The results show that the average rate of soil organic carbon for the top 30 cm depth of the agricultural soils is 68.99 t/ha, or 1.58 %, that belongs to the class of low soil organic carbon content (1-2%). We estimated organic carbon stocks of the agricultural soils of the Republic of Serbia at 1.98% from the total estimated value of the contents on agricultural land in Europe. The methodology applied in this research allows an estimation that is comparable to the international level.U radu su prikazani rezultati procene rezerve organskog ugljenika u poljoprivrednom zemljištu na prostoru Republike Srbije. Procena je rađena na osnovu podataka sadržaja organskog ugljenika sa ukupno 577 lokaliteta za izračunavanje sadržaja u t/ha i 757 lokaliteta za izračunavanje sadržaja u %. Lokaliteti obuhvataju različite tipove zemljišta i pod uticajem su različitih klimatskih faktora i nadmorske visine. Rezultati istraživanja pokazuju da srednja vrednost sadržaja organskog ugljenika do 30 cm dubine u poljoprivrednom zemljištu iznosi 68,99 t/ha, odnosno 1,58 % što pripada klasi niskog sadržaja (1-2%). Procena sadržaja rezerve organskog ugljenika na ukupnoj površini poljoprivrednog zemljišta Republike Srbije iznosi 1,98% od ukupne procenjene vrednosti sadržaja za poljoprivredna zemljišta Evrope. Metodologija primenjena u okviru ovog istraživanja je omogućila dobijanje rezultata uporedivih na međunarodnom nivou