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Title:Razvoj metode za spremljanje rasti razpoke na površini materiala med obratovanjem
Authors:Glaser, Bruno (Author)
Gubeljak, Nenad (Mentor) More about this mentor... New window
Predan, Jožef (Co-mentor)
Files:.pdf DOK_Glaser_Bruno_2018.pdf (7,99 MB)
MD5: B003F30B001C041E85F1FBF4109160F2
 
Language:Slovenian
Work type:Dissertation (m)
Typology:2.08 - Doctoral Dissertation
Organization:FS - Faculty of Mechanical Engineering
Abstract:Z namenom preprečitve porušitve konstrukcije zaradi razpoke, ki bi nastala med obratovanjem v linearno-elastičnem območju obremenjevanja, je bilo potrebno razviti metodo za spremljanje rasti razpoke na površini materiala. V okviru naloge sta bila razvita merilna elektronska sistema za merjenje deformacij Dynastrain, kot tudi stroj za dinamično ciklično utrujanje Rotech, ki je bil dodatno opremljen z večkanalnim merilnim sistemom National Instruments. V nalogi je analizirano utrujenostno obnašanje upogibnega nosilca z začetno površinsko razpoko, izdelanega iz konstrukcijskega jekla S690, ki se uporablja na visoko obremenjenih dinamičnih konstrukcijah. Spremembe deformacije v odvisnosti od števila ciklov in višine obremenitve so bile merjene z merilnimi lističi vzdolž roba razpoke. Zaradi utrujenostne rasti razpoke je prišlo do relaksacij deformacij, ki so bile zajete v analizo in konstrukcijo kalibracijske krivulje. Kalibracijska krivulja kaže višino relaksacije posameznega merilnega lističa oz. je definirana na posameznem mestu na površini v odvisnosti od položaja razpoke. Za potrditev rezultatov in primerjavo izmerjenih deformacij z merilnimi lističi smo numerično z metodo končnih elementov (MKE) izračunali deformacije v posameznih fazah rasti utrujenostne razpoke. Dodatno je bila narejena primerjava med rezultati deformacij iz analize MKE in rezultati posnetimi s stereo-optično metodo sistema ARAMIS, ki je tudi pokazala dobro ujemanje vseh treh načinov določanja deformacij v linearno-elastičnem območju obremenjevanja. Ugotovljeno je, da merilni lističi dajo verodostojne rezultate pri nizkih linearno-elastičnih obremenitvah, vendar v območju višjih cikličnih obremenitev, v bližini meje elastičnosti, rezultati ne kažejo več linearne odvisnosti. Nasprotno temu stereo-optična metoda v začetni fazi obremenjevanja pri nizkih obremenitvah kaže večji raztros vrednosti deformacij, ki se pri nadaljnjem obremenjevanju z višjimi obremenitvami zmanjšuje in dobimo primerljive rezultate deformacij, kot smo jih izračunali z analizami MKE na različnih delih površine. Razvita metoda merjenja relaksacij deformacij z merilnimi lističi omogoča spremljanje rasti utrujenostne razpoke v globino prereza nosilca med upogibnim obremenjevanjem na osnovi predhodno definirane kalibracijske krivulje. S tem je omogočeno pravočasno zaznavanje rasti utrujenostne razpoke za preprečitev nenadne porušitve nosilca.
Keywords:rast razpoke, uporovni merilni lističi, stereo-optične metode, digitalna stereo grametrija, utrujanje, utrujenostna rast razpoke
Year of publishing:2018
Publisher:[B. Glaser]
Source:Maribor
UDC:620.115:620.178.6(043.3)
COBISS_ID:298243328 New window
NUK URN:URN:SI:UM:DK:KNXHXXPG
Views:816
Downloads:140
Metadata:XML RDF-CHPDL DC-XML DC-RDF
Categories:KTFMB - FS
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Licences

License:CC BY 4.0, Creative Commons Attribution 4.0 International
Link:http://creativecommons.org/licenses/by/4.0/
Description:This is the standard Creative Commons license that gives others maximum freedom to do what they want with the work as long as they credit the author.
Licensing start date:21.08.2018

Secondary language

Language:English
Title:DEVELOPMENT OF METHOD FOR ONLINE CRACK GROWTH MONITORING ON THE SURFACE OF MATERIAL
Abstract:To prevent breaking of the component due to the crack, which could appear during the operation in linear-elastic loading, a method had to be developed to monitor crack growth on the surface of the material. As a part of doctoral dissertation investigations two electronic systems for deformation measurements were developed Dynastrain and device for dynamic cyclic fatigue loading Rotech, with additional National Instruments multi-channel measurement system. Fatigue behavior of specimen with initial surface crack made of construction steel S690 was described in dissertation, which is commonly used for high cycle dynamically loaded constructions. Changes in deformations in relation to number of cycles and loading were measured with the strain gauge measuring sensors installed near the crack. Relaxation of deformations occurred after crack growth, and were analyzed and used for calibration curve determination. Calibration curve show the level of relaxations of each strain gauge sensor and is defined for location of the measurement in relation to crack location. To prove results, the Finite Model Analyses (FME) was performed to compare measured and calculated deformations in different phases of crack growth. Additional comparison with stereo-optical measurement system ARAMIS results was done and demonstrated good matching of all three methods of deformations determination in linear-elastic region of loading. It was determined that strain gauge measurement give good results at lower linear-elastic loadings, but at higher loadings near yield stress, results are not proportional any more. Stereo-optical methods used for deformations measurements are sensitive at lower loadings because of noise, which is less contributing at higher loadings where results are well matching FME analyses results at different surface locations. Developed method for relaxations measurements with strain gauges assures monitoring of fatigue crack propagation during operations based on pre-determined calibration curve. This allows us to detect crack growth in time and avoid sudden construction failure.
Keywords:strain gauge, fracture, crack propagation, stereo-optical measurements, digital image correlation, fatigue, fatigue crack growth rate


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