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Damage Models (damage + models)
Selected AbstractsA Study on the Effects of Damage Models and Wavelet Bases for Damage Identification and Calibration in BeamsCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 8 2007Vikram Pakrashi A numerical study has been performed in this article addressing these issues for single and multispan beams with an open crack. The first natural modeshapes of single and multispan beams with an open crack have been simulated considering damage models of different levels of complexity and analyzed for different crack depth ratios and crack positions. Gaussian white noise has been synthetically introduced to the simulated modeshape and the effects of varying signal-to-noise ratio have been studied. A wavelet-based damage identification technique has been found to be simple, efficient, and independent of damage models and wavelet basis functions, once certain conditions regarding the modeshape and the wavelet bases are satisfied. The wavelet-based damage calibration is found to be dependent on a number of factors including damage models and the basis function used in the analysis. A curvature-based calibration is more sensitive than a modeshape-based calibration of the extent of damage. [source] Void growth and damage models for predicting ductile fracture in weldsFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 2 2000Wilsius This study reports on a numerical and experimental investigation of ductile tearing using a local approach to fracture. Two models have been analysed: (i) the Rice,Tracey (RT) void growth model; and (ii) the Rousselier continuum damage theory. The effects of the model parameters, including the mesh size, on the crack growth behaviour have been analysed, and a significant influence on both the J -values and the slopes dJ/da has been noted. The crack propagation in an overmatched welded joint has also been investigated. For the RT model, crack propagation has been simulated using the release node technique. Because this method requires one to previously assign the crack propagation path, using such a model is somewhat restrictive. This problem vanishes when dealing with Rousselier's model (and more generally with coupled models) because the elements which are damaged automatically give the crack path. [source] Non-local damage modelling of concrete: a procedure for the determination of model parametersINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 7 2007Giang D. Nguyen Abstract This paper presents a procedure for the determination of parameters of non-local damage models. This is to assure a consistent response of a non-local damage model, as choice of the internal length and other parameters of the model are varied. Correlations between the internal length and other parameters governing the local constitutive behaviour of the model are addressed and exploited. Focus is put on the relationship between the internal length of the non-local model and the width of the fracture process zone. Numerical examples are used to demonstrate the rigour of the proposed method. Copyright © 2006 John Wiley & Sons, Ltd. [source] A new damage model based on non-local displacementsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 5 2005Antonio Rodríguez-Ferran Abstract A new non-local damage model is presented. Non-locality (of integral or gradient type) is incorporated into the model by means of non-local displacements. This contrasts with existing damage models, where a non-local strain or strain-related state variable is used. The new model is very attractive from a computational viewpoint, especially regarding the computation of the consistent tangent matrix needed to achieve quadratic convergence in Newton iterations. At the same time, its physical response is very similar to that of the standard models, including its regularization capabilities. All these aspects are discussed in detail and illustrated by means of numerical examples. Copyright © 2005 John Wiley & Sons, Ltd. [source] Non-local damage model based on displacement averagingINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 1 2005M. Jirásek Abstract Continuum damage models describe the changes of material stiffness and strength, caused by the evolution of defects, in the framework of continuum mechanics. In many materials, a fast evolution of defects leads to stress,strain laws with softening, which creates serious mathematical and numerical problems. To regularize the model behaviour, various generalized continuum theories have been proposed. Integral-type non-local damage models are often based on weighted spatial averaging of a strain-like quantity. This paper explores an alternative formulation with averaging of the displacement field. Damage is assumed to be driven by the symmetric gradient of the non-local displacements. It is demonstrated that an exact equivalence between strain and displacement averaging can be achieved only in an unbounded medium. Around physical boundaries of the analysed body, both formulations differ and the non-local displacement model generates spurious damage in the boundary layers. The paper shows that this undesirable effect can be suppressed by an appropriate adjustment of the non-local weight function. Alternatively, an implicit gradient formulation could be used. Issues of algorithmic implementation, computational efficiency and smoothness of the resolved stress fields are discussed. Copyright © 2005 John Wiley & Sons, Ltd. [source] Neuroprotective effects of atorvastatin against glutamate-induced excitotoxicity in primary cortical neuronesJOURNAL OF NEUROCHEMISTRY, Issue 6 2005Julian Bösel Abstract Statins [3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors] exert cholesterol-independent pleiotropic effects that include anti-thrombotic, anti-inflammatory, and anti-oxidative properties. Here, we examined direct protective effects of atorvastatin on neurones in different cell damage models in vitro. Primary cortical neurones were pre-treated with atorvastatin and then exposed to (i) glutamate, (ii) oxygen,glucose deprivation or (iii) several apoptosis-inducing compounds. Atorvastatin significantly protected from glutamate-induced excitotoxicity as evidenced by propidium iodide staining, nuclear morphology, release of lactate dehydrogenase, and mitochondrial tetrazolium metabolism, but not from oxygen,glucose deprivation or apoptotic cell death. This anti-excitototoxic effect was evident with 2,4 days pre-treatment but not with daily administration or shorter-term pre-treatment. The protective properties occurred independently of 3-hydroxy-3-methylglutaryl-CoA reductase inhibition because co-treatment with mevalonate or other isoprenoids did not reverse or attenuate neuroprotection. Atorvastatin attenuated the glutamate-induced increase of intracellular calcium, which was associated with a modulation of NMDA receptor function. Taken together, atorvastatin exerts specific anti-excitotoxic effects independent of 3-hydroxy-3-methylglutaryl-CoA reductase inhibition, which has potential therapeutic implications. [source] Determination of ion track and shapes with damage simulations on the base of ellipsometric and backscattering spectrometric measurementsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 5 2008O. Polgár Abstract On the base of geometrical and statistical considerations a damage simulator was created in order to determine the ion track-radius and -shape of ion-implantation caused damage in single-crystalline Si. Damage vs. dose curves calculated by spectroscopic ellipsometry (SE) and Rutherford backscattering/channeling spectrometry (RBS/C) measurements, using different doses of 100 keV Xe implantation, gave information about the damage profile in depth. Both methods are required, because of dose-dependent discrepancies of SE compared with RBS/C [Fried et al., Thin Solid Films 455/456, 404 (2004)]. Different kinds of damage models were investigated to calculate the ion track-radius and to describe the damages in depth and the shape of ion track. Comparing directly the simulated and the measured damage vs. dose curves, the damage function and the other simulation parameters were optimized and hence the ion track size and even the shape can be determined. The dose dependent mean size of the unchanged crystalline regions, obtained from the simulation was correlated with the complex dielectric functions, obtained from the SE analysis. The results clearly show the effect of decreasing size of the unchanged crystalline regions. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Local and non-local ductile damage and failure modelling at large deformation with applications to engineeringPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2003Bob Svendsen Prof. Dr. The numerical analysis of ductile damage and failure in engineering materials is often based on the micromechanical model of Gurson [1]. Numerical studies in the context of the finite-element method demonstrate that, as with other such types of local damage models, the numerical simulation of the initiation and propagation of damage zones is strongly mesh-dependent and thus unreliable. The numerical problems concern the global load-displacement response as well as the onset, size and orientation of damage zones. From a mathematical point of view, this problem is caused by the loss of ellipticity of the set of partial di.erential equations determining the (rate of) deformation field. One possible way to overcome these problems with and shortcomings of the local modelling is the application of so-called non-local damage models. In particular, these are based on the introduction of a gradient type evolution equation of the damage variable regarding the spatial distribution of damage. In this work, we investigate the (material) stability behaviour of local Gurson-based damage modelling and a gradient-extension of this modelling at large deformation in order to be able to model the width and other physical aspects of the localization of the damage and failure process in metallic materials. [source] | ||||||||||