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1.
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: 1100; Downloads: 47
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2.
On fracture behaviour of inhomogeneous materials - a case study for elastically inhomogeneous bimaterials
Otmar Kolednik, Jožef Predan, G.X. Shan, N.K. Simha, Franz Dieter Fischer, 2005, original scientific article

Abstract: 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$▫.
Keywords: mechanics of structures, fracture toughness, inhomogeneous materials, J-integral, crack driving force, interface, material force
Published: 01.06.2012; Views: 786; Downloads: 9
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3.
Application of material forces to fracture of inhomogeneous materials : illustrative examples
Franz Dieter Fischer, Jožef Predan, Otmar Kolednik, N.K. Simha, 2007, original scientific article

Abstract: The material forces concept has become an elegant tool in continuum mechanics for the calculation of the thermodynamic driving force of a defect. Based on this concept, we have recently shown that inhomogeneities essentially shield or anti-shield crack tips from applied far-field stresses. The goal of this paper is to illustrate this by considering the model example of a crack in a CT-type specimen that contains a bimaterial interface. The crack driving force is calculated as the sum of the far-field driving force and the crack-tip shielding or anti-shielding. Several cases of inhomogeneity in either thermal or elastic properties are considered. Rather simple hand calculations are provided in addition to numerical results to illustrate the advantages of using the material forces concept.
Published: 01.06.2012; Views: 667; Downloads: 44
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