1. Modified coefficient of subgrade reaction to laterally loaded pilesAyhan Gurbuz, 2018, izvirni znanstveni članek Opis: An accurate prediction of the load capacity of a laterally loaded pile at a permissible displacement is an important concern at the design stage. In contrast to many sophisticated methods, Broms’ method based on moment equilibrium has been preferred by engineers to predict the load capacities of laterally loaded piles due to both its simplicity and because it is established on a way of hand calculation. However, Broms’ method typically overestimates a pile’s lateral load capacity as it requires a constant coefficient of horizontal subgrade reaction (nh) into analyses, regardless of the magnitude of the pile’s top displacement. In this study, modified coefficients of subgrade reactions(nh*) that are sensitive to the pile’s top displacement in cohesionless soils are first proposed to improve the performance level of Broms’ method for the prediction of the load capacity of a laterally loaded pile as the pile’s top displacement increases. The modified values of nh* are calibrated using 45 independently freehead, singledriven, fullscale pile tests from 23 sites in cohesionless soils. It is demonstrated that Broms’ method with nh* would correctly estimate a pile’s lateral loaddeflection behavior with accuracy levels similar to more complicated methods. Ključne besede: Broms' method, coefficient of horizontal subgrade reaction, py curves, strain wedge model Objavljeno: 11.10.2018; Ogledov: 663; Prenosov: 329 Celotno besedilo (735,27 KB) Gradivo ima več datotek! Več...

2. Prediction of standard lactation curves for primiparous Holstein cows by using corrected regression modelsJanez Jeretina, Drago Babnik, Dejan Škorjanc, 2015, izvirni znanstveni članek Opis: Prediction of the expected milk yield is important for the management of the primiparous cows (PPC) with a few or no data on their own milk productivity. We developed a system of regression equations for predicting milk yields in standard lactation. The models include the systematic effects of the calving season, the fiveyear rolling herd average of milk yield of PPC, the breeding values of the parents for milk production, and daily milk recordings. A total of 21,901 lactations of Holstein PPC were collected during the regular monthly milk recordings of cows in the Republic of Slovenia. By including daily milk recordings in the model, the coefficients of determination of regression models for the prediction of milk yield increase: without known recordings (M0) R 2 =0.80; with one recording (M1) R 2 =0.82; with two first consecutive recordings (M2) R 2 =0.86; and with three recordings (M3) R 2 =0.89. Deviations of milk yield up to 500 kg in a standard lactation (<1.6 kg/day) were as follows: with the model M0, they occurred in 53.4% of PPC; with M1, they occurred in 56.3% of PPC; with M2, they occurred in 64.5% of PPC; and with M3, they occurred in 70.9% of PPC. We concluded that the developed system of regression models is an appropriate method for milk yield prediction of PPC. Ključne besede: primiparous cows, milk yield, prediction, lactation curves, regression equations Objavljeno: 24.07.2017; Ogledov: 703; Prenosov: 407 Celotno besedilo (497,85 KB) Gradivo ima več datotek! Več...

3. Fracture toughness of a highstrength lowalloy steel weldmentJelena VojvodičTuma, Nenad Gubeljak, Borivoj Šuštaršič, Borut Bundara, 2006, izvirni znanstveni članek Opis: The use of highstrength lowalloy steels for highperformance structures, e.g., pressure vessels and pipelines, requires often highstrength consumables to produce an overmatched welded joint. This globally overmatched welded joint contains local mismatched regions, which can affect the unstable fracture behaviour of the welded joint and the welded structure itself. If local mismatched regions are present in the vicinity of a crack tip, then the fracture toughness of the weld metal can be significantly lower than that of the base metal. In this paper, the influence of the weldmetal microstructure on the fracture behaviour is estimated enabling an evaluation of the resistance to stable crack growth through different microstructures. The lower bound of the fracture toughness for different microstructures was evaluated using a modified Weibull distribution. The results, obtained using specimens with a through thickness crack front, indicated a low fracture toughness, caused by the strength mismatching interaction along the crack front. In the case of throughthethickness specimens, at least one local brittle zone (LBZ) or a local soft region is incorporated into the process zone in the vicinity of the crack tip. Hence, an unstable fracture occurred with small stable crack propagation, or without it. Despite the fact that the differences between the impact toughness of the weld metal and the base metal can be insignificant, the fracture toughness of a weld metal can be significantly lower. Ključne besede: fracture mechanics, welded joint, cracktip opening displacement, resistance curves Objavljeno: 16.03.2017; Ogledov: 676; Prenosov: 62 Celotno besedilo (502,10 KB) Gradivo ima več datotek! Več...

4. Fracture behaviour of thin sheet stainless steelNenad Gubeljak, Darko Jagarinec, Jožef Predan, John Landes, 2012, objavljeni znanstveni prispevek na konferenci Opis: The differences in fracture behavior between the compact tension C(T) and the middle tensile M(T) specimens make structure integrity assessment uncertain. Two different types of specimens C(T) and M(T) specimens made from stainless steel have been used for fracture toughness testing at the room temperature by the principles of the ASTM 182005 standard procedure. Stable crack initiation and crack propagation occurred for the C(T) specimens at lower values of crack driving force than for the M(T) specimens. Crack tip opening displacementCTOD has been directly measured on the surface of specimens by using a stereooptical grading method. The critical crack tip opening displacement at crack initiation CTODi has been measured as a plastic Stretch Zone Width (SZW) during a post test fractographic inspection. Comparison between the CTODR curves of both types of specimens shows some difference between the C(T) and the M(T) specimens, but a more significant difference appeared in the crack driving force, as consequence of different constraint (triaxiality) of the C(T) versus the M(T) specimens. Therefore, the result obtained by test on laboratory C(T) specimens cannot be directly used as fracture toughness material properties in a structure integrity assessment, except as a conservative lower bound estimate. Ključne besede: stainless steel, compact tension specimen, middle tension specimen, CTODR curves Objavljeno: 10.07.2015; Ogledov: 797; Prenosov: 68 Povezava na celotno besedilo 
5. Improving centrifugal pump by adding vortex rotorTihomir Mihalić, Zvonimir Guzović, Stanislav Sviderek, 2011, izvirni znanstveni članek Ključne besede: centrifugal vortex pump, hydrodynamic phenomena, energy transformation, unsteady flow, pump performance curves, energy efficiency, computational fluid dynamics Objavljeno: 05.06.2012; Ogledov: 1276; Prenosov: 36 Povezava na celotno besedilo 
6. Determination of lower bound fracture toughness of a high strength low alloy steel welded jointNenad Gubeljak, 2005, izvirni znanstveni članek Opis: The use of highstrength lowalloy steels for high performance structures (e.g. pressure vessels and pipelines) requires high strength consumables to produce an overmatched welded joint. This globally overmatched multipass welded joint contains two significantly different microstructures, as welded and reheated. In this paper, the influence of weld metal microstructure on fracture behaviour is estimated in comparison with the fracture behaviour of composite microstructures (as welded and reheated). The lower bound of fracture toughness for different microstructures was evaluated by using the modified Weibull distortion. The results, obtained using specimens with crack front through the thickness, indicated low fracture toughness, caused by strength mismatching interaction along thevcrck front. In the case of through thickness specimens, at least one local brittle microstructure is incorporatedin the process zone at the vicinity of the crck tip. Hence, unstable fracture occurred with small or without stable crack propagation. Despite the fact that the differences between the impact toughness of a weld metal and that of base metal are insignificant, the future toughness of a weld metal can be significantly lower. Ključne besede: welded joints, fracture mechanics, Crack tip opening displacement, high strength seeel weld, mismatch effects, fracture toughness, resistance curves Objavljeno: 01.06.2012; Ogledov: 1641; Prenosov: 87 Povezava na celotno besedilo 