26 KB782 KB31 KB199920252006Bazaras, ŽilvinasKrenevičius, AlgimantasLeonavičius, MindaugasPetraitis, GediminasStupak, StanislavŠukšta, Marijonas10 straniletnik:52številka:9str. 558-567ISSN:0039-2480COBISSID:9714203URN:URN:NBN:SI:doc-YVMZO0RBenAssociation of Mechanical Engineers and Technicians of Slovenia et al.Zveza strojnih inženirjev in tehnikov Slovenije et al.Strojniški vestniklito železolom materialovmehanske lastnostinormalizacijarazpoketrdnostutrujanje materialovThe strength of as cast iron and normalized cast iron subjected to cyclic loading|This paper presents the results of an experimental and analytical investigation of the high-cycle fatigue of special as-cast and normalized irons, which later in the text are referred to as GI (grade iron) and SGI (spherical graphite iron). Well-known types of cast iron have been modified toachieve better mechanical properties and an improved resistance to crack formation and development as well as propagation. The defined values of the mechanical properties show that the normalizing changes the microstructure, enlarges the plasticity and makes uniform the limits of yield and strength. The microstructures of the investigated as-cast irons include graphite of different sizes, which, after the heat treatment, acquire a spherical shape, unify and reduce in size, and the whole microstructure becomes finer. After testing the compact eccentric tension CT (ASTM) specimens, the crack-growth rate versus the stress intensity factor range for the fatigue diagrams were constructed, and the threshold stress intensity ranges were determine for GIas cast iron dKth = 6.5 to 8.6 MPa; for GI normalized cast iron dKth = 8.2 to 10.3 MPa; for SGI as cast iron dKth = 8.0 to 9.6 MPa, and for SGI normalized cast iron dKth = 8.7 to 9.8 MPa. The significant differences in the threshold stress intensity factors were determined and related to the structural imperfections at the different sites of specimens formed during themanufacturing and normalization process. For specimens of as-cast and normalized cast iron, the dependence of DKth on the crack size was observed. An additional investigation and the fracture analysis show that it was influenced by the absence of structural uniformity. The suggested analytical expression of the DKth and the dependence of the mechanical properties can be applied for calculating the strength of cyclically loaded large-sized partsV prispevku so predstavljeni rezultati eksperimentalnih in analitičnih raziskav pogosto se ponavljajoče utrujenosti posebnega litega in normaliziranega zeleza, ki ju kasneje v besedilu imenujemo GI (stopenjsko zelezo) in SGI (krogelno grafitno zelezo). Uveljavljeni vrsti zeleza smo spremenili, da bi dosegli boljse mehanske lastnosti in izboljšali odpornost proti nastajanju razpok, prav tako pa tudi njihovemu širjenju. Iz določenih mehanskih lastnosti vidimo, da normaliziranje spremeni mikrosestavo, poveča plastičnost in izenači meje proznosti in trdnosti. V mikrosestavi opazovanega litega zeleza je vključen tudi grafit različnih velikosti, ki po toplotni obdelavi, pridobi krogelno obliko, poenoteno in manjšo velikost, tako da celotna mikrosestava postane bolj drobna. Po preizkušanju "kompaktne" izsrednenapetosti CT (ASTM) na vzorcih smo za diagrame utrujenosti oblikovali območje faktorja razmerja rasti razpoke glede na jakost napetosti. In sicer za: GI lito zelezo dKth = 6,5 do 8,6 MPa; za GI normalizirano lito zelezo dKth= 8,2 do 10,3 MPa; zaSGI lito zelezoi dKth = 8,0 do 9,6 MPa in za SGI normalizirano lito železo dKth = 8,7 do 9,8 MPa. Pri mejnih vrednostih faktorjev jakosti napetosti smo ugotovili opazne razlike ter jih povezali z nepravilnostmi v sestavi na različnih straneh vzorcev, ki so nastale med izdelavo in postopkom normalizacije. Opazovali smo tudi vpliv dKth na velikost razpok vzorcev litega in normaliziranega litega zeleza. Nadaljnje raziskave in analiza razpok so pokazale vpliv premajhne enotnosti sestave. Predlagan analitični izraz za dKth in odvisnost mehanskih lastnosti lahko uporabimo za izračun trdnosti izmenično obremenjenih velikih kosovTEXTznanstveno časopisjejournalsSlovenian National E-content AggregatorNational and University Library of SloveniaUniverza v Ljubljani, Fakulteta za strojništvo