Iskanje po katalogu digitalne knjižnice

Opis: Za določanje mehanskih lastnosti materiala pri torzijski obremenitvi izvajamo torzijske preizkuse, za le-te pa so običajno namenjeni posebni stroji. Izvajanje takih preizkusov pa je s prilagojeno napravo možno tudi v laboratoriju z enoosnim tlačno-nateznim preizkuševalnim strojem. V nalogi je predstavljeno konstruiranje naprave, ki nam omogoča da z enoosnim tlačnonateznim servo-hidravličnim strojem izvajamo tudi torzijske preizkuse na posebnih preizkušancih s kvadratnim vpetjem, in tako nadzorujemo preizkus z obstoječo krmilno konzolo za INSTRON-1255 z računalniškim vodenjem in zajemanjem podatkov. Naloga zajema primerjavo klasične analitične rešitve preizkusa, rešitev problema z računalniško simulacijo ter rezultati izvedenega preizkusa.
Ključne besede: vzvojno preizkušanje, torzija, strižna deformacija, strižni modul, utrujanje, simulacija preizkusa
Objavljeno v DKUM: 26.11.2012; Ogledov: 1968; Prenosov: 273
Celotno besedilo (2,86 MB)

Opis: Vsebina diplomske naloge opisuje konstrukcijo vetrnih elektrarn. Podrobna obravnava se nanaša na os vetrne elektrarne z direktnim pogonom, obremenitve na os, ki so posledica delovanja vetra, in lastnosti materiala osi. Cilj naloge je kontrola osi na ekstremne obremenitve in življenjsko dobo ter določitev primerjalne obremenitve, ki jo simuliramo pri izvajanju materialnega preizkusa. Pri reševanju problema upoštevamo standarde s tehničnega področja.
Ključne besede: vetrna turbina, vetrna energija, os elise, obratovalna trdnost, obremenitveni spekter
Objavljeno v DKUM: 20.11.2012; Ogledov: 2244; Prenosov: 308
Celotno besedilo (2,46 MB)

Opis: This paper provides yield load solutions for single edged fracture toughness specimen subjected to bending SE (B) with present X-shaped weld joint. The weld centre crack is located in the overmatch weld part. The corresponding fully plastic yield loads were obtained directly by plain strain FEM analysis for five characteristic a/W ratios: 0,1;0,2;0,3;0,4 and 0,5. Also, the influence of the sistematically varied weld root width 2H on the fracture behaviour has been evaluated. It was found that yield load decreases with the increasing weld root, because the undermatched region ahead the crack tip plays the dominant role.
Ključne besede: fracture mechanics, X-shaped welded joints, centre crack, strength mismatching, plastic yield load, constraint effects
Objavljeno v DKUM: 01.06.2012; Ogledov: 1794; Prenosov: 49
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Opis: High-alloyed Cr-Ni-based two-phase stainless steel (SS) cast alloys are commonly used in nuclear power plants. The mechanical equipment in these facilities can contribute to a reduction in its resistance to stable crack growth as a result of extended operating times and high temperatures. The toughness of these materials strongly depends on their delta (▫$/delta$▫) ferrite content, which spinodally decomposes into two phases with different ratios of Cr and Ni at a relatively low (slightly above 300 °C) temperature. This temperature is similar to the operating temperature of the vital parts, for example, the coolant system. The formation of two phases with the same crystalstructure but different lattice parameters causes internal elastic stresses that result in a hardness increase and an impact-toughness decrease. The result is an increased risk of crack formation in the stress-concentration zones such as the critical regions of different welded joints (e.g. "L, T, K and X" shapes). The values of the critical stress intensity factor change according to its position along the crack contour. Therefore, the aim of our study was to assess the influence of the materials' changes on the crack extension and the decrease of the primary pipeline's bearing capacity by taking account of the increased temperature and time of operation for the given loading conditions. The SINTAP (European Structural Integrity Assessment Procedure) was used for this assessment.
Ključne besede: welding, welded joints, pipelines, fracture toughness testing, structure integrity assessment procedure
Objavljeno v DKUM: 01.06.2012; Ogledov: 2032; Prenosov: 93
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Opis: This paper presents a case study, examining the influence of a sharp bimaterial interface on the effective crack driving force in a fracture mechanics specimen. The inhomogeneity of the elastic modulus in linear elasticand non-hardening and hardening elastic-plastic bimaterials is considered. The interface is perpendicular to the crack plane. The material properties and the distance between the crack tip and the interface are systematically varied. The effect of the material inhomogeneity is captured in form of a quantity called "material inhomogeneity term",▫$C_inh$▫. This term can be evaluated either by a simple post-processing procedure, following a conventional finite element stress analysis, or by computing the J-integral along a contour around the interface, ▫$J_int$▫. The effective crack driving force,▫$J_tip$▫, can be determined as the sum of ▫$C_inh$▫ and the nominally applied far-field crack driving force, ▫$J_far$▫. The results show that ▫$C_inh$▫ can be accurately determined by both methods even in cases where ▫$J_tip$▫-values are inaccurate. When a crack approaches a stiff/compliant interface,▫$C_inh$▫ is positive and ▫$J_tip$▫ becomes larger than ▫$J-far$▫. A compliant/stiff transition leads to a negative ▫$C_inh$▫, and ▫J_tip$▫ becomes smaller than ▫$J_far$▫. The material inhomogeneity term, ▫$C_inh$▫, can have the same order of magnitude as ▫$J_far$▫. Based on the numerical results, the dependencies of ▫$C_inh$▫ on the material parameters and the geometry are derived. Simple expressions are obtained to estimate ▫$C_inh$▫.
Ključne besede: mechanics of structures, fracture toughness, inhomogeneous materials, J-integral, crack driving force, interface, material force
Objavljeno v DKUM: 01.06.2012; Ogledov: 1720; Prenosov: 34
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