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Numerical study of the dynamic active lateral earth pressure coefficient of cohesive soils
Mehrab Jesmani, Hossein Alirezanejad, Hamed Faghihi Kashani, Mehrad Kamalzare, 2017, izvirni znanstveni članek

Opis: Retaining walls are proposed in many projects, such as bridges, coastal structures, road constructions and wherever lateral support is required for the vertical surface of an excavation. The active lateral pressure coefficient of soil, Ka , is an important parameter for studying the static and dynamic behaviors of these retaining walls. Many studies have evaluated this coefficient in static situations, but in most previous dynamic studies, researchers have worked on the behavior of cohesionless backfill soil or made simplifying assumptions (e.g., pseudo-static status) for cohesive soils as backfill soil. In this study, the size of the active lateral earth pressure coefficient (Ka) was studied in a full dynamic situation (Kae). A retaining wall with cohesive backfill soil is evaluated using the finite-difference method (FDM) and the effects of important soil and loading properties are assessed. The model is based on Mohr-Coulomb failure criteria under seismic loading. The results show that the value of Kae at the top of the wall, where it is highly sensitive to any variation in the soil and loading properties, is greater than one due to the high pressure value induced by the horizontal dynamic acceleration and the presence of tension cracks.
Ključne besede: dynamic active lateral earth pressure coefficient (Kae), cohesive backfill soil, finite difference method (FDM), tension cracks, retaining wall, seismic loading
Objavljeno: 18.06.2018; Ogledov: 660; Prenosov: 46
.pdf Celotno besedilo (3,26 MB)
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The importance of tensile strength in geotechnical engineering
Ivan Vaníček, 2013, izvirni znanstveni članek

Opis: Many Soil mechanics textbooks contain only limited information about tensile characteristics. Šuklje’s “Rheological aspects of soil mechanics” [1] is an exception, as he devoted a special chapter to this problem “Tensile and Bending Strength of Soils”. Therefore, it is not a great surprise that the subject of the 13th Šuklje’s Lecture is devoted to soil behaviour in tension. Tensile tests are briefly described, some results as well, with a distinction between undrained and drained tests. Practical examples of the application of the results are discussed, firstly in cases where the development of tensile cracks can be expected. Because the results of the drained tests give more information about the bonds between individual particles, some theoretical aspects of these tests are discussed as well.
Ključne besede: tensile cracks, tensile strength, bending, triaxial drained tensile test
Objavljeno: 14.06.2018; Ogledov: 649; Prenosov: 46
.pdf Celotno besedilo (549,04 KB)
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Factors influencing the yielding constraint by cracked welded components
Dražan Kozak, Jelena Vojvodič-Tuma, Nenad Gubeljak, Damir Semenski, 2005, izvirni znanstveni članek

Opis: 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.
Ključne besede: welded structures, welded joints, fracture mechanics, cracks, SE(B) specimens, yielding load, yielding constraint parameters
Objavljeno: 06.04.2017; Ogledov: 836; Prenosov: 71
.pdf Celotno besedilo (793,79 KB)
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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, strokovni članek

Opis: 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.
Ključne besede: nanocoatings, cracks, materials testing
Objavljeno: 10.07.2015; Ogledov: 635; Prenosov: 72
.pdf Celotno besedilo (260,70 KB)
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New linear spring stiffness definition for displacement analysis of cracked beam elements
Matjaž Skrinar, Tomaž Pliberšek, 2004, kratki znanstveni prispevek

Opis: 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.
Ključne besede: linear springs, rotational spring, displacement analysis, transverse displacements, cracked beam structures, transverse load, inverse problems, transverse displacements, inverse identification of cracks
Objavljeno: 01.06.2012; Ogledov: 1512; Prenosov: 77
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The re-characterisation of complex defects
Boštjan Bezenšek, John. W. Hancock, 2004, izvirni znanstveni članek

Opis: 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.
Ključne besede: fracture mechanics, structural elements, complex defects, recharacterisation, line-spring analysis, fatigue, ductile tearing, cracks, numerical analysis
Objavljeno: 01.06.2012; Ogledov: 985; Prenosov: 79
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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, izvirni znanstveni članek

Opis: 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.
Ključne besede: fracture mechanics, ductile fracture, high strength low alloyed steel, cracks, micromechanical model, mismatched welded joints, constraint effect, void growth
Objavljeno: 01.06.2012; Ogledov: 1422; Prenosov: 77
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New finite element for transversely cracked slender beams subjected to transverse loads
Matjaž Skrinar, Tomaž Pliberšek, 2007, izvirni znanstveni članek

Opis: 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.
Ključne besede: beams, transverse cracks, computational model, finite element method, transverse displacements
Objavljeno: 01.06.2012; Ogledov: 1482; Prenosov: 91
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On the application of a simple computational model for slender transversely cracked beams in buckling problems
Matjaž Skrinar, 2007, izvirni znanstveni članek

Opis: 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.
Ključne besede: columns, transverse cracks, stability problems, buckling load, computational model, polynomial solutions, finite element method, geometrical stiffness matrix
Objavljeno: 01.06.2012; Ogledov: 1549; Prenosov: 79
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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, izvirni znanstveni članek

Opis: 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.
Ključne besede: fracture mechanics, fracture toughness, composite materials, layered material, inhomogeneity, cracks, finite element method, elastic bimaterials
Objavljeno: 01.06.2012; Ogledov: 1568; Prenosov: 73
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