1. Factors influencing the yielding constraint by cracked welded componentsDražan 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 v DKUM: 06.04.2017; Ogledov: 1488; Prenosov: 119
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2. Application of the european SINTAP procedure to the failure analysis of a broken forkliftNenad Gubeljak, Uwe Zerbst, Jožef Predan, Maks Oblak, 2004, izvirni znanstveni članek Opis: The recently developed European flaw assessment procedure SINTAP was applied to the failure analysis of a broken fork of a forklift. Based on the service load at failure, critical crack sizes were determined at different analysis levels of the procedure. It was shown in the present case study that the failure was caused by defective design.
Ključne besede: structural integrity, mechanics of structures, forklift, fracture mechanics, critical crack size, failure analysis, SINTAP procedure, load bearing capacity
Objavljeno v DKUM: 01.06.2012; Ogledov: 2294; Prenosov: 92
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3. Efficient handling of stability problems in shell optimization by asymmetric "worst case" shape imperfectionMarko Kegl, Boštjan Brank, Boštjan Harl, Maks Oblak, 2008, izvirni znanstveni članek Ključne besede: mechanics of structures, optimization of structures, stability, shells, imperfection, shape design
Objavljeno v DKUM: 01.06.2012; Ogledov: 2429; Prenosov: 111
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4. On fracture behaviour of inhomogeneous materials - a case study for elastically inhomogeneous bimaterialsOtmar Kolednik, Jožef Predan, G.X. Shan, N.K. Simha, Franz Dieter Fischer, 2005, izvirni znanstveni članek 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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5. Thermal post-impact behaviour of closed-cell cellular structures with fillersMatej Vesenjak, Andreas Öchsner, Zoran Ren, 2007, izvirni znanstveni članek Opis: The study describes the behavior of regular closed-cell cellular structure with gaseous fillers under impact conditions and consequent post-impact thermal conduction due to the compression of filler gas. Two dependent but different analyses types have been carried out for this purpose: (i) a strongly coupled fluid-structure interaction and (ii) a weakly coupled thermal- structural analysis. This paper describes the structural analyses of the closed-cell cellular structure under impact loading. The explicit code LS-DYNA was used to computationally determine the behavior of cellular structure under compressive dynamic loading, where one unit volume element of the cellular structure has been discretised with finite elements considering a simultaneous strongly coupled interaction with the gaseous pore filler. Closed-cell cellular structures with different relative densities and initial pore pressures have been considered. Computational simulations have shown that the gaseous filler influences the mechanical behavior of cellular structure regarding the loading type, relative density and type of the base material. It was determined that the filler's temperature significantly increases due to the compressive impact loading, which might influence the macroscopic behavior of the cellular structure.
Ključne besede: mechanics, cellular structures, closed cells, gas fillers, impact loading, fluid-structure interaction, dynamic loads, LS-DYNA, ANSYS CFX 10.0, computational simulations
Objavljeno v DKUM: 31.05.2012; Ogledov: 1851; Prenosov: 36
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6. Shape optimization of truss-stiffened shell structures with variable thicknessMarko Kegl, Boštjan Brank, 2006, izvirni znanstveni članek Opis: This paper presents an effective approach to shape optimal design of statically loaded elastic shell-like structures. The shape parametrization is based on a design element technique. The chosen design element is a rational Bézier body, enhanced with a smoothly varying scalar field. A body-like designelement makes possible to unify the shape optimization of both pure shells and truss-stiffened shell structures. The scalar field of the design element is obtained by attaching to each control point a scalar quantity, which is an add-on to the position and weight of the control point. This scalar field is linked to the shell thickness distribution, which can be optimized simultaneously with the shape of the shell. For linear and non-linear analysis of shell structures, a reliable 4-node shell finite element formulation is utilized. The presented optimization approach assumes the employment of a gradient-based optimization algorithm and the use of the discrete method of direct differentiation to perform the sensitivity analysis.Four numerical examples of shell and truss-stiffened shell optimization are presented in detail to illustrate the performance of the proposed approach.
Ključne besede: mechanics of structures, shape optimization, shells, trusses, Bézier body, numerical methods, optimum design
Objavljeno v DKUM: 30.05.2012; Ogledov: 2136; Prenosov: 120
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