METODA NAPOVEDOVANJA NASTANKA TERMIČNIH RAZPOK NA TORNI POVRŠINI AVTOMOBILSKIH ZAVORNIH DISKOV

Pevec, Miha

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Title:	METODA NAPOVEDOVANJA NASTANKA TERMIČNIH RAZPOK NA TORNI POVRŠINI AVTOMOBILSKIH ZAVORNIH DISKOV
Authors:	ID Pevec, Miha (Author) ID Potrč, Iztok (Mentor) More about this mentor... ID Šraml, Matjaž (Comentor)
Files:	DR_Pevec_Miha_2013.pdf (14,48 MB) MD5: 52FF03979C9D0570F414EFFD80F79F48
Language:	Slovenian
Work type:	Dissertation
Typology:	2.08 - Doctoral Dissertation
Organization:	FS - Faculty of Mechanical Engineering
Abstract:	V predloženi doktorski disertaciji je razvita metoda za določitev dobe trajanja zavornih diskov zaradi termičnih razpok na torni površini. Po avtorjevem vedenju je to prvo delo, ki sistematično obravnava vsa področja, ki vplivajo na določitev dobe trajanja pri znanih obremenitvah. Tako razvita metodologija bo služila znanstvenikom ter zavornim inženirjem kot orodje pri optimizaciji geometrije zavornega diska ter materialov. Določitev dobe trajanja zavornih diskov je izredno multidisciplinarno raziskovalno področje, saj zajema znanje iz testiranj, materialov, mehanike, numeričnih metod, prenosa toplote ter dimenzioniranja na dobo trajanja. V doktorskem delu so najprej povzeti rezultati dosedanjih rezultatov iz posameznih področij, po kritični analizi dosedanjih del pa so izpostavljene opažene pomanjkljivosti, ki so v nadaljevanju podrobno obdelane. Za potrebe določitve natančnega temperaturnega polja je predstavljena numerična metoda za določitev faktorja prestopa toplote, ki upošteva realne pogoje med testiranji. Ugotovljeno je, da se rezultati predlagane metode razlikujejo z do sedaj objavljenimi analitičnimi ter numeričnimi metodami, ki ne morejo upoštevati vpliv vpihovanja hladilnega zraka med izvajanjem testa. Poleg tega je predstavljena tudi predlagana metoda za določitev emisijskega koeficienta sevanja zavornega diska med obratovanjem, katere rezultati se razlikujejo tudi za do 47 % od trenutno javno objavljenih. Opravljena je bila podrobna analiza temperaturno odvisnih fizikalnih lastnosti sive litine EN-GJL-250, kot so toplotna prevodnost, specifična toplota ter temperaturna razteznost. Ugotovljeno je bilo, da se nekatere lastnosti razlikujejo od javno objavljenih tudi za do 48 %. S pomočjo numerične analize po metodi končnih elementov so bila določena temperaturna ter deformacijska polja med predstavljenim obremenitvenim ciklom. Za natančno določitev deformacijskega polja je bila opravljena podrobna analiza mehanskih lastnosti sive litine EN-GJL-250. Predstavljeni so rezultati nateznih in tlačnih preskusov pri sobni temperaturi ter povišanih temperaturah. Rezultati so statistično obdelani z Weibullovo verjetnostno teorijo. Na osnovi zahtev računskih modelov za izračun dobe trajanja po izbrani deformacijski metodi je bila v sklopu doktorske naloge opravljena podrobna analiza lastnosti utrujanja obravnavane sive litine. Nizkociklični preskusi utrujanja so bili izvedeni pri sobni temperaturi ter povišanih temperaturah. Določeni so bili parametri utrujanja, ki so potrebni za izračun dobe trajanja, ter izrisane deformacijske krivulje zdržljivosti. Na koncu je po izbranih hipotezah določena doba trajanja zavornega diska, ki je primerjana z rezultati eksperimenta. Eksperiment zajema pet obravnavanih zavornih diskov, ki so bili testirani po obravnavanem testu na odpornost proti utrujenostnim razpokam na zavornem dinamometru. Ugotovljeno je, da se rezultati eksperimenta ter predlagane metodologije odlično ujemajo, kar kaže na nujnost celovite obravnave problema, kot je to prikazano v predloženi doktorski disertaciji.
Keywords:	avtomobilski ventiliran zavorni disk, siva litina, termične razpoke, torna površina, doba trajanja, nizkociklično utrujanje, parametri utrujanja materiala, deformacijska metoda, metoda končnih elementov, testiranje na dinamometru
Place of publishing:	[Maribor
Publisher:	M. Pevec]
Year of publishing:	2013
PID:	20.500.12556/DKUM-41954
UDC:	629.3.018.4(043.3)
COBISS.SI-ID:	17386774
NUK URN:	URN:SI:UM:DK:GS2O6RZQ
Publication date in DKUM:	09.12.2013
Views:	2620
Downloads:	360
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Categories:	KTFMB - FS
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Secondary language

Language:	English
Title:	PREDICTION METHOD OF THERMAL FATIGUE CRACK INITIATION ON AUTOMOTIVE BRAKE DISC RUBBING SURFACE
Abstract:	In this doctoral thesis, the method of service life determination for brake discs due to thermal cracks on the rubbing surface is developed and presented. To the author’s knowledge, this is the first published work that systematically discusses all the areas that influence the service life assessment at known loadings. The presented methodology will serve scientists and development engineers as a tool for optimizing the geometry and materials of the brake discs. Service life determination is a particularly multidisciplinary research field, as it combines the knowledge areas of testing, materials, mechanics, numerical methods, heat transfer and service life prediction theories. The beginning of the thesis focuses on the analysis of the results of previous research done in the discussed fields and discovered imperfections that are in the continuation handled in detail. Based on the requirements of the accurate temperature field determination, the numerical method for predicting convective cooling coefficient, which considers the real test conditions, was presented. It was discovered that the results of the presented method differentiate from the results of the presently published analytical and numerical methods that cannot consider the influence of the cooling air blowing during the experiment. In addition, the method for radiation emission coefficient of the brake disc during the operation prediction was presented. The results obtained with the method showed the deviation of 47 % regarding the presently published results. Detailed analysis of the temperature dependent physical material characteristics (such as thermal conductivity, specific heat and thermal expansion) of the lamellar grey cast EN-GJL-250 was made. It was ascertained that some of the results deviate from the presently published results up to 48 %. Temperature, stress and strain fields generated during the presented loading cycle were analysed with finite element method. For the accurate determination of the stress and strain fields the detailed analysis of the mechanical material properties of the EN-GJL-250 grey cast iron was made. The results of tensile and pressure tests at room temperatures and at increased temperatures are presented. The results are statistically treated with the Weibull probability theory. Based on the requirements of the computational models for service life assessment, a detailed analysis of the low-cycle fatigue parameters of the used grey cast was made. Low-cycle fatigue parameters were conducted at room temperatures and at increased temperatures. Strain-life curves were obtained and low-cycle fatigue parameters were determined. Based on the numerical results, service life was calculated using the presented hypothesis and compared with the experiment results. The experiment was conducted on a brake dynamometer on five brake discs that were tested according to the analysed testing procedure for fatigue crack resistance. It was established that the agreement of the experimental results and the results of the presented methodology was 94 %, which confirms the accuracy of the research presented in this doctoral thesis.
Keywords:	automotive ventilated bake disc, grey cast iron, thermal cracking, rubbing surface, service life, low cycle fatigue, material fatigue parameters, strain method, finite element method, brake dynamometer testing

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