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1.
On critical buckling load estimation for slender transversely cracked beam-columns by the application of a simple computational model
Matjaž Skrinar, 2008, original scientific article

Abstract: This paper brings new insights into the implementation of a simplified computational model in the prediction of buckling load Pcr for slender beam-type structures with a transverse crack. From among several approaches discussed, two of them produced applicable results exhibiting considerably good agreement with those values from more precise and complex computational models. In the first approach, the critical load value is obtained from numerical solutions of analytically expressed characteristic equations (obtained from governing differential equations). Although producing excellent results, this approach limits the application since an analytical solution of the governing differential equation can only be obtained for moderate structures. The second approach implements a new cracked beam-columnfinite element, derived at on the basis of a fairly accurate approximation of the governing differential equation's solution. It allows for flexible utilization and also yields the smallest compact computational model, thus exhibiting itself as very suitable for inverse identification problems. Numerical examples covering several structures with different boundary conditions are briefly presented in order to support the discussed approaches. The results obtained using the presented approaches are further compared with those values from either references or more complex models, thus clearly proving the quality of the presented compact FE model.
Keywords: beam columns, transverse cracks, stability problems, buckling load, computational model, finite element method
Published: 31.05.2012; Views: 1578; Downloads: 54
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2.
Analysis of cracked slender-beams on Winkler's foundation using a simplified computational model
Matjaž Skrinar, Boris Lutar, 2011, original scientific article

Abstract: This paper discusses the coupling of Winkler's soil model with a simplified computational model that is widely used for the calculation of transverse displacements in transversely cracked slender beams. The bending problem of a cracked beam embedded in Winkler's soil is addressed by means of an analytical approach. The solving of the corresponding differential equation solutions is studied in order to obtain exact analytical expressions for the transverse displacements of the simplified computational model. After the solutions for the displacements of the beam are obtained, the inner bending moment and the shear force distributions within the beam can be calculated, either by using known, established relationships from the Euler-Bernoulli beam theory or by implementing two mechanical equilibrium conditions. Numerical examples covering several load situations are briefly presented in order to support the discussed approach. The results obtained with the presented approach are then further compared with the values from huge 2D finite-element models, where a detailed description of the crack was achieved using the discrete approach. It is evident that any drastic difference in the computational effort is not reflected in the significant differences in the results between the models.
Keywords: beams with transverse cracks, simplified computational model, elastic foundation, Winkler's soil, transverse displacements, bending moment, shear forces
Published: 01.06.2012; Views: 1066; Downloads: 19
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3.
Crack tip shielding or anti-shielding due to smooth and discontinuous material inhomogeneities
N.K. Simha, Franz Dieter Fischer, Otmar Kolednik, Jožef Predan, G.X. Shan, 2005, original scientific article

Abstract: This paper describes a theoretical model and related computational methods forexamining the influence of inhomogeneous material properties on the crack driving force in elastic and elastic-plastic materials. Following the configurational forces approach, the crack tip shielding or anti-shielding dueto smooth (e.g. graded layer) and discontinuous (e.g. bimaterial interface)distributions in material properties are derived. Computational post-processing methods are described to evaluate these inhomogeneity effects.The utility of the theoretical model and computational methods is demonstrated by examining a bimaterial interface perpendicular to a crack in elastic and elastic-plastic compact tension specimens.
Keywords: fracture mechanics, fracture toughness, composite materials, layered material, inhomogeneity, cracks, finite element method, elastic bimaterials
Published: 01.06.2012; Views: 1093; Downloads: 46
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4.
On the application of a simple computational model for slender transversely cracked beams in buckling problems
Matjaž Skrinar, 2007, original scientific article

Abstract: This paper discusses the implementation of a simplified computational model that is widely used for the computation of transverse displacements in transversely cracked slender beams into the Euler's elastic flexural buckling theory. Two alternatives are studied instead of solving the corresponding differential equations to obtain exact analytical expressions for the buckling load ▫$P_{cr}$▫ due to the complexity of this approach. The first approach implements wisely selected polynomials to describe the behavior of the structure, which allows the derivation of approximate expressions for the critical buckling load. Although the relevance of the results strongly depends on the proper prime selection of the polynomial, it is shown that the later upgrading of the polynomials can lead to even more reliable results. The second approach is a purely numerical approach and presents the geometrical stiffness matrix for a beam finite element with a transverse crack. To support the discussed approaches, numerical examples covering several structures with different boundary conditions are briefly presented. The results obtained with the presented approaches are further compared with the values from enormous 2D finite elements models, where a detailed description of the crack was achieved with the discrete approach. It is evident that the drastic difference in the computational effort is not reflected in the significant differences in the results between the models.
Keywords: columns, transverse cracks, stability problems, buckling load, computational model, polynomial solutions, finite element method, geometrical stiffness matrix
Published: 01.06.2012; Views: 1289; Downloads: 50
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5.
New finite element for transversely cracked slender beams subjected to transverse loads
Matjaž Skrinar, Tomaž Pliberšek, 2007, original scientific article

Abstract: The paper covers the derivation of a new finite element for beams with transverse cracks. The derivation is based on a simplified computational model that has already proved itself suitable for the inverse identification of cracks. The model embodies all the necessary major information about the structure's response from the inverse identification point of view, where the presence and location and, if possible, the depth of the crack should be detected from the measured response, usually dynamic. In such situations the stress distributions obtained from 2D finite elements analysis are not as important as the computational model being capable of reliably describing the displacement of the structure. However, from numerical studies it also became evident that the relevance of the model decreases with element thickness. This indicated that shear forces should be included in the analysis process. Therefore, derivation of a new finite element with the inclusion of shear forces effect has been executed. The stiffness matrix for transversely cracked slender beams, as well as the derivation of interpolation functions is presented and all expressions are given in symbolic forms. The example shows that, although with significantly less computational effort than with 2D FE meshes, significant improvement in transverse displacements can be obtained with the presented beam finite element.
Keywords: beams, transverse cracks, computational model, finite element method, transverse displacements
Published: 01.06.2012; Views: 1152; Downloads: 58
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6.
Micromechanical analysis of constraint effect on fracture initiation in strength mis-matched welded joints
Miloš Dobrojević, Marko Rakin, Nenad Gubeljak, I. Cvijović, Milorad Zrilić, N. Krunich, Aleksandar Sedmak, 2007, original scientific article

Abstract: In this paper the micromechanical approach to ductile fracture was applied in a study of constraint effect crack growth initiation in mismatched welded joints. The single edged- notched bend specimens (precrack length ▫$a_o/W=0.32$▫) were experimentally and numerically analysed. The coupled micromechanical model prposed by Gurson, Tvergaard and Needleman was used. Constraint effect was tested by varying widths of the welded joints (6, 12 and 18 mm). HSLA steel was used as the base metal in a quenched and tempered condition. The flux-cored arx-welding process in shielding gas was used. Two different fillers were selected to obtain over- and undermatched weld metal. The micromechanical parameters used in prediction of the crack growth initiation on precracked specimen were calibrated on a round smmoth specimen. The difference in fracture behaviour between over- and undermatched welded joints obtained in experimental results was followed by numerical computationsof void volume fraction in front of the crack tip.
Keywords: fracture mechanics, ductile fracture, high strength low alloyed steel, cracks, micromechanical model, mismatched welded joints, constraint effect, void growth
Published: 01.06.2012; Views: 1079; Downloads: 51
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7.
The re-characterisation of complex defects
Boštjan Bezenšek, John. W. Hancock, 2004, original scientific article

Abstract: Defect assessment codes idealise complex defects as simple shapes which are amenable to analysis in a process known as re-characterisation. The present work examines the re-characterisation of complex defects which extend by fatigue, ductile tearing or cleavage. A family of representative defects were analysed numerically, while a related experimental programme investigated defect interaction and failure. Part I of the paper focuses on fatigue and ductile tearing. Part II examines cleavage. The numerical and experimental results are discussed within the context of the re-characterisation proceduresdescribed in BS 7910 (Guidance on methods for assessing the acceptability of flaws in metallic structures. London, UK: British Standard Institution; 1999 [Chapter 7] and R6/4 (Assessment of the integrity of structures containing defects. Gloucester: British Energy Generation Ltd.; 2001 [Revision 4, Chapters I and II.3]). The level of conservatism of the re-characterisation prpcedures for fatigue and ductile tearing are discussed. A possible non-conservatism of the re-characterisation for cleavage is discussed in Part II, within the framework of constraint based statistical fracture mechanics.
Keywords: fracture mechanics, structural elements, complex defects, recharacterisation, line-spring analysis, fatigue, ductile tearing, cracks, numerical analysis
Published: 01.06.2012; Views: 729; Downloads: 55
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8.
New linear spring stiffness definition for displacement analysis of cracked beam elements
Matjaž Skrinar, Tomaž Pliberšek, 2004, short scientific article

Abstract: The paper describes the reasons for the derivation of a new definition of a rotational spring that can be utilised in the simplified computational model for the computation of transverse displacements of cracked beam structures dueto transverse load. This definition plays an extremely important role in the inverse identification of cracks.
Keywords: linear springs, rotational spring, displacement analysis, transverse displacements, cracked beam structures, transverse load, inverse problems, transverse displacements, inverse identification of cracks
Published: 01.06.2012; Views: 1209; Downloads: 54
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9.
Factors influencing the yielding constraint by cracked welded components
Dražan Kozak, Jelena Vojvodič-Tuma, Nenad Gubeljak, Damir Semenski, 2005, original scientific article

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: 06.04.2017; Views: 596; Downloads: 48
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10.
Physical regularities in the cracking of nanocoatings and a method for an automated determination of the crack-network parameters
P. O. Maruščak, Vladimir Gliha, Igor Konovalenko, Tomaž Vuherer, Sergey Panin, 2012, professional article

Abstract: The regularities and spatial distribution of multiple cracking of a nanocoating are investigated. It is found that in the cracking zones the relaxation of the stresses accumulated in the coating takes place; moreover, the intensity of its failure is determined by the structural level of defect accumulation. A new algorithm for a digital identification of the elements of a crack network in a nanocoating is proposed, and its adequacy is checked.
Keywords: nanocoatings, cracks, materials testing
Published: 10.07.2015; Views: 438; Downloads: 43
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