Random imperfection fields to model the size effect in laboratory wood specimens
Casciati S. and Domaneschi M. (2007). “Random imperfection fields to model the size effect in laboratory wood specimens”. Structural Safety, 29(4), 308-321. ISSN: 0167-4730.
DATA E LUOGO DI PUBBLICAZIONE: October 2007; Elsevier Science Bv, 1000 AE Amsterdam, Netherlands.
ABSTRACT. The composite nature of a wood continuum prevents one from extrapolating the results of laboratory tests on... more
ABSTRACT. The composite nature of a wood continuum prevents one from extrapolating the results of laboratory tests on standard wood specimens to structural elements of significant size. Therefore, these elements are usually tested under standardized loading conditions in order to detect a sort of average material behaviour.
In this paper, the initial step consists, instead, of testing the material specimens. The extension of the results to structural elements is then pursued by introducing a random field, or, in a discretized model, a random array of imperfections.
The calibration of the suitable spatial distribution of the imperfections is then investigated by a mixed experimental–numerical approach, for a reference beam. The analyses on the relative finite elements model are iterated to match the response of the full scale laboratory tests.
KEYWORDS: Biaxial tests; Finite element model; Imperfections; Laboratory tests; Random field; Wood specimens
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Seen by:Cohesive Crack Propagation in a Random Elastic Medium
Bruggi M., Casciati S., and Faravelli L. (2008). “Cohesive crack propagation in a random elastic medium”. Probabilistic Engineering Mechanics, 23(1), 23-35. ISSN: 0266-8920.
DATA E LUOGO DI PUBBLICAZIONE: January 2008; Elsevier Sci Ltd, Kidlington, Oxford OX5 1GB, Oxon, England.
ABSTRACT. The issue of generating non-Gaussian, multivariate and correlated random fields, while preserving the... more
ABSTRACT. The issue of generating non-Gaussian, multivariate and correlated random fields, while preserving the internal auto-correlation structure of each single-parameter field, is discussed with reference to the problem of cohesive crack propagation. Three different fields are introduced to model the spatial variability of the Young modulus, the tensile strength of the material, and the fracture energy, respectively. Within a finite-element context, the crack-propagation phenomenon is analyzed by coupling a Monte Carlo simulation scheme with an iterative solution algorithm based on a truly-mixed variational formulation which is derived from the Hellinger–Reissner principle. The selected approach presents the advantage of exploiting the finite-element technology without the need to introduce additional modes to model the displacement discontinuity along the crack boundaries. Furthermore, the accuracy of the stress estimate pursued by the truly-mixed approach is highly desirable, the direction of crack propagation being determined on the basis of the principal stress criterion. The numerical example of a plain concrete beam with initial crack under a three-point bending test is considered. The statistics of the response is analyzed in terms of peak load and load–mid deflection curves, in order to investigate the effects of the uncertainties on both the carrying capacity and the post-peak behaviour. A sensitivity analysis is preliminarily performed and its results emphasize the negative effects of not accounting for the auto-correlation structure of each random field. A probabilistic method is then applied to enforce the auto-correlation without significantly altering the target marginal distributions. The novelty of the proposed approach with respect to other methods found in the literature consists of not requiring the a priori knowledge of the global correlation structure of the multivariate random field.
KEYWORDS: Multivariate non-Gaussian random fields; Auto-correlation; Cohesive crack propagation; Truly-mixed finite element method; Monte Carlo simulations
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Seen by: and 14 moreThree-dimensional modeling to compute plastic zone in front of crack in compact tension sample of multiphase material
by Nazri Kamsah
Computational Materials Science, Volume 50, Issue 4, February 2011, Pages 1499-1503
Authors: Yunan Prawoto, Roslinda Idris, Nazri Kamsah, Nasir Tamin
Faculty of Mechanical Engineering, Universiti Teknologi Malaysia, Skudai, Johor, Malaysia
Two-dimensional modeling to compute plastic zone in front of a crack in a compact tension specimen of a multiphase... more
Two-dimensional modeling to compute plastic zone in front of a crack in a compact tension specimen of a multiphase material was published previously. This paper is the continuation of it, using the same concept, but in three dimensions. The heart of this study is to develop a simulation method to predict the effect of microstructural morphology in multiphase steel in three dimensions utilizing commercial software.
The object of the model, multiphase of ferrite and martensite, is known to benefit its fatigue performance by its high toughness yet maintains the high tensile properties due to controlled microstructure. Multiphase steel having a microstructure consisting of polygonal ferrite and martensite has received a great deal of attention due to their useful combination of high strength, high work hardening rate, and ductility. From the fracture mechanics point of view, the key to its fatigue performance is the large plastic zone size in front of the crack. In this research, a sub-modeling technique is used, by using three-dimensional modeling of cube with variation of ferrite fraction as local models. The global model, a compact tension specimen, is treated as a homogeneous material. The results show strong correlation and similarity with that of two-dimensional model. The analysis result shows the variation of the plastic zone sizes as the ferrite fraction varies and saturates at about 60% ferrite fraction.
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Seen by:Design of a microwave oven for the fabrication of transparent ceramic scintillators
by Wesley Hong
Stanford Photonics Research Center Symposium Technical Report
Microwave heating affords several advantages over traditional sintering methods that could ease the fabrication of... more Microwave heating affords several advantages over traditional sintering methods that could ease the fabrication of ceramic scintillators for nuclear detector applications. This work reports preliminary results on the design of a microwave cavity suitable for the sintering of air- and water-sensitive materials such as Eu2+:SrI2. This cavity will be used in the near future for investigating the possibility of inducing grain texture and producing transparent ceramics of birefringent scintillators.
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