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Abstract: The effect of strength mismatch for welded joints performed with different geometries on the yielding constraint has been investigated in the context of single-edged fracture-toughness specimens subjected to bending SE(B) using the finite-element method. The crack was located in the centre of the weld. Two geometri cal parameters have been identified as being the most important: the crack-Iength ratio a/W and the sIenderness of the welded joint (W-a)/H. They were systematically varied as follows: a/W = 0.1; 0.2; 0.3; 0.4; 0.5 and W = 2H, 4H, 8H, 16H, 24H. Basic equations and plane-strain finite-element solutions for the overmatched SE(B) specimen with all configuration combinations are given. The results are in good agreement with those in literature. This paper aims to establish yield-Ioad solutions for the same weldment configurations, but with materials dissimilarity present within the weld. This situation is usually encountered during repair welding. For this purpose, a practical combination of filler materials, with the same portion of overmatched part with M = 1.19 and undermatched part with M = 0.86, has been selected. Plane-strain solutions for the heterogeneous weld with the cracklocated in the overmatched half were obtained. The influence of the yielding-constraint key parameters has al so been evaluated. Yield-Ioad results for the specimens performed with different weld widths have the greatest scattering for the a/W = 0.5. The transition from the overmatched to the undermatched solution with increasing H is evident. On the other hand, the behaviour of the specimen with a shallow crack is dictated by the overmatch region ahead of the crack tip and depends very little on the weld slenderness. An approximated 3-D area of the yield-Ioad solutions depending ona/W and (W-a)lH has been proposed. Furthermore, the stress triaxility parameter h has been calculated using 2-D and 3-D finite-element analysis, and given as a field in the spec imen to get an insight into yielding-constraint regions. It was found that the 3-D yield-Ioad solutions are very close to the plane-strain solutions. Also, the effect of a/W on the yielding constraint is more significant than the effect of Mand (W-a)/H.
Keywords: welded structures, welded joints, fracture mechanics, cracks, SE(B) specimens, yielding load, yielding constraint parameters
Published in DKUM: 06.04.2017; Views: 1488; Downloads: 120
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Abstract: Ocenjeno je naraščanje prebivalstva na Zemlji v naslednjih desetletjih, sočasno naraščanje potreb po primarni energiji in napisani so možni nosilci primarne energije. Razložen je princip jedrske fuzije, navedeni so robni pogoji, pri katerih je zlitje jeder sploh mogoče, in opisana je razlika med jedrsko fisijo in fuzijo. V obeh primerih se skupna masa po končani jedrski reakciji zmanjša, del mase se namreč spremeni v energijo. Prikazani so doslej vloženi napori znanstvenikov, skupaj z najnovejšim projektom ITER. Projekt naj bi končno realiziral težko pričakovano samodejno reakcijo zlitja jeder vodika v jedro helija in s tem rešil problem preskrbe človeštva s primarno energijo.
Keywords: fisija, fuzija, ITER, naraščanje prebivalstva, oskrba s primarno energijo
Published in DKUM: 15.03.2017; Views: 1628; Downloads: 150
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Abstract: The distribution and amount of residual stresses can significantly contrubute to the fatigue fracture behaviour of welded joints in structures. Interior residual stresses, which interact with the plane strain state, are more dangerous than residual stresses at the surface of the welded joint. If the surface of the welded joint is mechanically treated (e.g. shapering), then significant differences between the stress stated at the surface and within the volume occur. Hence, different non-destructive methods (e.g. gamma radiation, neutron diffraction) have been developed to determine strains caused by residual stresses in the volume of polycrystalline materials. However, the measurement of strains caused by residual stresses becomes difficult for large samples. In this paper the measurement procedure on a sample taken from the weld joint is presented and the effecet of residual stresses on fatigue crack propagation is assessed for low and high cycle loading fatigue.
Keywords: zaostale napetosti, zvarni spoj, neutronski lom žarkov, utrujenostno širjenje razpoke, neutron diffraction method, residual stresses, fatigue crack propagation, weld joint
Published in DKUM: 10.07.2015; Views: 1308; Downloads: 35
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Abstract: In this investigation a high-strength low-alloyed (HSLA) steel of the 700-MPa strength class was used as a base material. A butt-welded joint with X grooves was produced with an overmatched weld metal that had a yield strength 23 % greater than that of the base material. Three-point bending B x 2B test specimens (thickness B = 36 mm) were extracted from the welded joints. The straight crack front (a0 = 35,571 mm) crosses different microstructures through the thickness of the specimen. Both fracture-mechanics tests and a 3D finite-element analysis were performed. The CTOD parameter of the fracture toughness was measured and calculated numerically. The loading level at which stable crack growth occurred was also determined. The comparison of the experimental and numerical values of the CTOD (bs) displacements showed good agreement. The principal stress, ▫$/delta_{y}$▫, the Mises equivalent stress, ▫$/delta_{eq}$▫. and the plastic equivalent strain, ▫$/epsilon_{pl, eq}$▫, at the moment of crack initiation were studied for six equidistant layers from the surface to the mid-thickness of the specimen. The dependence of the crack-opening stress (denoted as ax in this paper) on the local fracture-toughness value was considered as the parameter which determines the direction of the crack-front propagation. The results show that the lower strength of the base metal contributes to the crack-path deviation in the mid-thickness of the specimen. Both the crack-path deviation and the higher toughness of the base metal increase the critical fracture toughness value of the welded joint.
Keywords: trdnost spoja z večjo trdnostjo vara, razpoka, porazdelitev napetosti, porazdelitev deformacij, analiza končnih elementov
Published in DKUM: 10.07.2015; Views: 1377; Downloads: 110
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