An approximation of deflection line function at the rod loaded by buckling under self-weight

Rad se bavi aproksimacijom točne funkcije linije otklona za štap opterećen izvijanjem zbog vlastite težine pomoću funkcije, što je najbolje prikazano točnim oblikom ovog štapa. U ovom radu predlažemo metode derivacije kritične duljine izvijanja pomoću točnog rješenja i pomoću metode energije. Za zamjenske funkcije linije otklona su izabrane varijante goniometrijskih funkcija i polinomi. Pojedinačni koeficijenti funkcija su izabrani na temelju postojećih rubnih uvjeta i u slučaju nedovoljnog broja, oni su izabrani kako bi se izrazio točan oblik linije otklona štapa na najprikladniji način, koji je prenesen iz konkretnog primjera rješenja pomoću softvera SolidWorks. Rad prikazuje pogreške kritičnog izračuna duljine izvijanja nasuprot točnom rješenju, kao i maksimalna apsolutna i relativna odstupanja kod bočnog pomicanja za odabranu funkciju. Od pojedinačnih zamjenskih funkcija je naknadno izabrana ona koja ispunjava uvjet za opće korištenje i ima najmanja odstupanja od točnog rješenja.The paper deals with an approximation of the exact deflection line function at a rod loaded by self-weight buckling via the function, which is best-presented by the exact shape of this rod. In this paper, we suggest the methods of derivation of the critical buckling length by the exact solution and by the energy method. For the substitute functions of deflection line, the variants of goniometric functions and polynomials are chosen. Individual coefficients of the functions are chosen on the basis of existing boundary conditions and in the case of their insufficient count, they are chosen in order to express the exact rod deflection line shape in the most suitable way, which was transposed from the concrete example solution by SolidWorks Simulation software. The paper shows the errors of critical buckling length calculation against the exact solution, as well as the maximum absolute and relative deviations in the lateral displacement for the chosen function. From the individual substitute functions, one function that meets the condition for general use and has the lowest deviations from the exact solution, is subsequently chosen

Effect of machining parameters on jet lagging in abrasive water jet cutting

Glavne karakteristike površine obrađene abrazivnim mlazom vode su razlike u hrapavosti površine na vrhu i na dnu reza i pojava zakrivljenih linija-brazgotina koje su karakteristične za sve procese obrade s koncentriranim tokom velike energije. Zakrivljenost ovih linija je posljedica zaostajanja mlaza. Zaostajanje mlaza je uzrok grešaka pri rezanju radijusa i oštrih kutova. Parametri obrade imaju značajan utjecaj na ovu pojavu. Iz tog razloga nužno je poznavati i definirati utjecaj parametara obrade na ovu pojavu. Cilj ovog rada je istražiti utjecaj parametara obrade na zaostajanje mlaza, odnosno geometriju reza. Uzorci od AISI 304 obrađeni su abrazivnim mlazom vode različitim posmičnim brzinama, radnim tlakovima i protocima abraziva. Zaostajanje mlaza mjereno je na 10 mjernih mjesta preko dubine reza. Na temelju tih rezultata, formiran je odnos između zaostajanja mlaza i parametara obrade.The main characteristics of the surface machined with the abrasive water jet are the differences in surface roughness at the top and bottom of the cut and the appearance of curved lines-striations, which are characteristic for all machining processes with the concentrated stream of high energy. The curvature of these lines is the consequence of jet lagging. Jet lagging is the cause of errors in cutting of radius and sharp corners. The machining parameters have a great influence on this phenomenon. Therefore, it is necessary to know and to define the influence of machining parameters on this phenomenon. The aim of this paper is to investigate the effect of machining parameters on the jet lagging, i.e. cut front geometry. The specimens of AISI 304 were machined by the abrasive water jet under varying traverse speeds, operating pressures and abrasive mass flow rates. The jet lagging was measured at ten monitoring points by the depth of cut. Based on these results, the relationship between the jet lagging and machining parameters has been formed

Utjecaj triboloških procesa mehanizma slobodnog hoda na radne karakteristike impulsnih tarnih varijatora

The impulsive friction variators are very specific transmitters. They are characterised by the periodical impulse transmission of power and motion. For research purposes, the device was made to simulate wear of the tribomechanical system: external envelope (coulisse) – roller and roller-shaft in the free motion mechanism with use of the impulsive friction variators. Monitoring of the elements of tribomechanical system was conducted by recording the changes of dimensions depending on the investigation time. Roughness parameters were measured and wear traces of the tribomechanical system were recorded. It was concluded that at the shaft (star), a dominant mechanism of wear is pitting, and that destruction of the oil film precedes the damage at the coulisse (roller). By analysing the change of the gap and influence of the change of wedging angle, it is determined that the period of intensive wear at the beginning and the period of constant wear can be differentiated. It was concluded that the change of the gap clearly represents theImpulsni tarni varijatori su vrlo specifični prijenosnici. Karakterizira ih impulsni periodični prijenos snage i gibanja. U cilju istraživanja izrađen je ispitni uređaj za simuliranje trošenja tribosustava: vanjski prsten (kulisa) - valjčić i vratilo - valjčić u mehanizmu slobodnog hoda pri radu impulsnih tarnih varijatora. Praćenje elemenata tribosustava vršeno je snimanjem promjena dimenzija u ovisnosti o trajanju ispitivanja. Mjereni su parametri hrapavosti i snimani tragovi trošenja elemenata tribosustava. Zaključeno je da je kod vratila (zvijezde) dominantni mehanizam trošenja pitting, a da oštećenju vanjskog prstena (valjčića) prethodi razaranje uljnog filma. Analizom promjene zazora i utjecaja promjene kuta zaklinjavanja utvrđeno je da se mogu razlučiti period početnog intenzivnog trošenja i period ustaljenog trošenja. Zaključeno je da promjena zazora jasno prikazuje krivulje trošenja triboelemenata. Povećanje zazora direktno utječe na promjenu kuta zaklinjavanja, a samim time i na povećanje neravnomjernosti rotacije izlaznog vratila

Examination of welding parameters’ influence on stud arc welding process

In this paper, the influence of two selected parameters (the welding time and the presence of the activating flux on the surface of the base metal) on the weld joint at Stud Arc Welding process is investigated. In the experimental part of the paper, the drawn arc stud welding process with the ceramic ferrule is applied with the different welding time and the application of the activating flux for ATIG process. In order to evaluate the influence of the welding time and the activating flux on the weld characteristics, the cast zone width and Vickers hardness HV 0.2 are measured