20.500.12556/DKUM-96483 Zagotavljanje integritete zvarnih spojev na jeklih za protibalistično zaščito doktorska disertacija Ensuring the integrity of welded joints on armoured steels Zvarni spoji in vsi njihovi konstrukcijski elementi predstavljajo velik problem v vseh konstrukcijah v obratovanju, vključno z jekli, katerih glavna funkcija je protibalistična zaščita. Jekla za protibalistično zaščito, ki se uporabljajo večinoma v vojaške namene, imajo kot glavno funkcijo absorpcijo energije izstrelka in ohranjenje celovitosti konstrukcij. Danes na svetu obstajajo različni proizvajalci jekla za protibalističnu zaščito z različnimi komercialnimi imeni in razredi trdote. V tej doktorski disertaciji so bila uporabljena štiri protibalistična jekla dveh različnih proizvajalcev. Komercialni imeni jekla SA 500 in SA 600 sta iz skupine jekel Swebor Armor iz Švedske, medtem ko se jekli P 500 in P 600 iz skupine jekel Protac proizvajata v slovenski železarni Acroni d.o.o. Jesenice. Njihove številke v imenu določajo razred trdote po Brinellu, kar kaže, da spadajo med ultra trde in visoko trdne materiale. Jekla istega razreda trdote imajo precej podobno kemijsko sestavo, mehanske lastnosti in majhne razlike v toplotni obdelavi. Problem takšnih jekel je zvarni spoj iz več razlogov. Prvi razlog je njihova kemijska sestava, ki glede na izračun ogljikovega ekvivalenta uvršča ta jekla med težko varljiva. Drugi razlog je, da z varjenjem presežemo njihovo temperaturo toplotne obdelave (nizkotemperaturno popuščanje), kar vodi do mehčanja materiala v področju TVP-ja. Prav tako je zelo pomembna izbira dodajnega varilnega materiala, da se izpolnijo različni standardi glede mehanskih lastnosti, hkrati pa se ne ogroža glavna funkcija jekla - neprebojnost. Za varjenje takšnih jekel se najpogosteje uporabljajo avstenitni nerjavni dodajni materiali. Ta disertacija predstavlja drugačen pristop in kot dodajni material uporabimo visokotrdnostno varilno žico, s katero smo želeli doseči in približno izenačiti mehanske lastnosti zvarnega spoja in osnovnih materialov ter izboljšati celovitost same konstrukcije. Ker so jekla v utrjenem stanju in nizko temperaturno popuščana, je bila tehnologija varjenja (predgrevanje, vnos toplote in redosled gradnje varkov) optimizirana tako, da ne bi prišlo do pretiranega mehčanja materiala v toplotno vplivnem področju in da bi imel zvarni spoj kot celota izboljšano integriteto. V V doktorski disertaciji je bilo varjenje izvedeno z robotsko MAG tehnologijo in predstavljen je niz eksperimentalnih preizkusov. Zaostale napetosti v zvarnem spoju so bile izmerjene s tremi različnimi metodami, kjer smo dobili enako porazdelitev napetosti po merilnih točkah z manjšimi odstopanji v rezultatih zaradi različnosti metod. Nato so bili izdelani različni vzorci (iz področja osnovnega materiala, TVP-ja in vara) za določitev mehanskih in lomnomehanskih lastnosti ter hitrosti rasti razpok. Meritve trdote, natezni in Charpyjev preizkus so nam omogučili, da smo vzpostavili korelacijo med trdoto in trdnostjo na eni strani ter žilavostjo na drugi strani. Pričakovano je bilo v področju TVP-ja, na materialih zabeleženo znižanje trdote ob povečani žilavosti, medtem ko je na področju vara trdnost dosegla več kot 1000 MPa, trdota pa okoli 350 HB. Lomna mehanika je bila analizirana z vidika vpliva razpok v strukturi na SENB vzorcih, pa je bil določen kritični faktor intenzivnosti napetosti (KJIC). Najbolj žilavo obnašanje pri preizkusu lomne mehanike je pokazalo področje TVP-ja, varovi so dosegli približno 100 MPa∙m1/2 lomne žilavosti, medtem ko so osnovni materiali pokazali izrazito krhko obnašanje. S Parisovo in McEvilyjevo enačbo so predstavljena obnašanja hitrosti rasti razpoke pri utrujitvenih obremenitvah vseh področja zvara in nato primerjana. Na koncu lahko rečemo, da nam je eden od glavnih preizkusov – balistični preizkus, izveden na pločevinah SA 500 in SA 600 po standardu STANAG 4569 – nivo 1, pokazal neprebojnost vseh preizkušenih področjih, kar je pripeljalo do zaključka, da je uporabljena tehnologija varjenja lahko uporabna v industriji, ki se ukvarja z jekli za protibalistično zaščito. Welded joints and all their structural elements represent a major problem in all structures in service, including steels whose main function is ballistic protection. Armour steels, which are used mainly for military purposes, have as their main function the absorption of projectile energy and the preservation of structural integrity. Today, there are various manufacturers of armoured steels in the world with different commercial names and hardness classes. Four armoured steels from two different manufacturers were used in this doctoral dissertation. The commercial names of the steels SA 500 and SA 600 are from the Swebor Armor steel group from Sweden, while the steels P 500 and P 600 from the Protac steel group are produced in the Slovenian ironworks Acroni d.o.o. Jesenice. Their numbers in the name determine the Brinell hardness class, which indicates that they belong to the ultra-hard and high-strength materials. Steels of the same hardness class have quite similar chemical composition, mechanical properties and small differences in heat treatment. The problem with such steels is the welded joint for several reasons. The first reason is their chemical composition, which, according to the calculation of the carbon equivalent, classifies these steels as difficult to weld. The second reason is that by welding we exceed their heat treatment temperature (low-temperature tempering), which leads to softening of the material in the HAZ area. The choice of filler material is also very important in order to meet various standards regarding mechanical properties, while at the same time not compromising the main function of the steel - bulletproofness. Austenitic stainless filler materials are most often used for welding such steels. This dissertation presents a different approach and uses high-strength welding wire as a filler material, with which we wanted to achieve and approximately equalize the mechanical properties of the welded joints and the base materials and improve the integrity of the structure itself. Since the steels are in a hardened state and low-temperature tempered, the welding technology (preheating, heat input and sequence of welding passes) was optimized so that excessive softening of the material in the heat affected zone would not occur and that the welded joint as a whole would have improved integrity. In the doctoral dissertation, welding was performed using robotic MAG process and a series of experimental tests are presented. Residual stresses in the welded joint were measured using three different methods, where we obtained the same stress distribution across the measurement points with minor deviations in the results due to the differences in the methods. Then, different specimens (from the base material, HAZ and weld) were manufactured to determine the mechanical and fracture mechanical properties and fatigue crack growth rates. Hardness measurements, tensile and Charpy tests allowed us to establish a correlation between hardness and strength on the one hand and toughness on the other. The HAZ area was tested, and a decrease in hardness was recorded in the materials with increased toughness, while in the weld area the strength reached more than 1000 MPa, and the hardness was around 350 HB. Fracture mechanics was analyzed from the perspective of the influence of cracks in the structure on SENB specimens, and the critical stress intensity factor was determined. The HAZ area showed the most ductile behavior in the fracture mechanics test, the welds reached approximately 100 MPa∙m1/2 of fracture toughness, while the base materials showed a distinctly brittle behavior. The behavior of the crack growth rate under fatigue loads of all weld areas is presented using the Paris and McEvily equations and then compared. In conclusion, we can say that the main test - the ballistic test, carried out on SA500 and SA600 plates according to the STANAG4569 - Lev. 1 standard, showed us the bulletproofness of all tested area. zvarni spoj jeklo za protibalistično zaščito mehanske lastnosti lomna žilavost hitrost rasti razpok zaostale napetosti balistični preizkus. welded joint armoured steel mechanical properties fracture toughness fatigue crack growth rate test residual stresses ballistic test. true true false M. Manjgo Slovenski jezik Angleški jezik Doktorsko delo/naloga 2026-01-13 15:38:04 2026-06-21 16:12:39 2026-07-15 09:10:12 0000-00-00 00:00:00 2026 0 Maribor 0 Maribor XXXI, 203 str. 0000-00-00 NiDoloceno NiDoloceno NiDoloceno 0000-00-00 0000-00-00 0000-00-00 620.17/.18:621.791.053(043.3) 284023299 DOK_Manjgo_Mirza_2026.pdf DOK_Manjgo_Mirza_2026.pdf 1 8529158DCC945F93EC9EE05BC72B85A0 971d624b1cb5f710afaeb8d577188bd3ec6154b366dd492fb22d2f57da31b1f2 3b2bba50-68a0-11f1-bd95-00155d580e34 https://dk.um.si/Dokument.php?lang=slv&id=207137 Fakulteta za strojništvo 0 0 0