1,720,961 research outputs found
Interphase Model and Phase-Field Approach for Strain Localization
No full textQuasi-brittle materials subjected to a high level of mechanical solicitations see the development in relatively narrow zone of micro-cracks that coalesce into stress free cracks. In this work, the problem
of strain localization in elastoplastic materials exhibiting softening has been approached by applying the interphase model together with the phase-field theory. In particular, the narrow zone where strains concentrate, usually named process zone or localization band, is kinematically modeled using the interphase model, while the phase-field variable is introduced to regularize the contact strains at the interface between the plastic strain band and the surrounding material. This corresponds to
diffuse the interphase in the volume of the solid body.
The formulation of the problem has been developed in a classical way using the principles of thermodynamics. A key point consists in a Reuss/Sachs type homogenization of the inelastic contact strains through a weak Dirac delta function which takes the shape of the Mumford-Shah
functional. The introduction of this kinematical hypothesis consistently leads to the complete set of the governing equations for a localized body.
The model has been tested by means of analytical applications. The results show that the introduced strain regularization does not affect substantially the structural behavior, also the model can be easily used to replicate experimental results.
The application of the proposed model may involve different contexts as the strain localization in soil mechanics, plastic hinge formation in reinforced concrete frames and delamination in composite materials. It should be noted that the calibration of model parameters for the comparison between numerical end experimental results can be performed easily, since no additional mechanical parameters are needed with respect to those that characterize the elastoplastic behavior
Ultrasonic inspection for the detection of debonding in CFRP-reinforced concrete
No full textFibre-reinforced plastic (FRP) composites are extensively used to retrofit civil structures. However, the
quality and the characteristics of the bond between the FRP and the structure are critical to ensure the
efficacy of the retrofit. For this reason, effective non-destructive evaluation (NDE) methods are often
necessary to assess the bonding conditions. This article presents an ultrasonic technique for detecting
defects at the FRP-substrate interface. The technique uses the Akaike Information Criterion, to detect
automatically the onset of the ultrasonic signals, and the novel Equivalent Time Lenght (ETL) parameter, to
quantify the energy of the propagating ultrasonic signals along the interface between FRP and concrete. The
uniqueness of the ETL is that it is not affected by the coupling conditions between the ultrasonic probes and
the structure. The proposed NDE technique has been tested numerically by performing 2D Finite-Element
analysis and experimentally on reinforced concrete samples. The results show that the method is robust
and cost-effective
Assessment of bonding defects in FRP reinforced structures via ultrasonic technique
Get PDFFiber reinforced polymer (FRP) composite systems are widely used for the rehabilitation
of concrete structures such as building that need to resist to seismic loads,
bridges that have to carry heavier traffic loads. The technique consists in bonding the
composite plate to the concrete surface element in order to increase the flexural capacity.
A proper attachment of the FRP plate to the concrete surface is necessary for
the efficiency of the load transfer between the reinforcement and the substrate. In
this work, the quality of composite bonding is characterized through ultrasonic testing.
The proposed technique is relative to a time domain analysis of the ultrasonic
signals and couples the Akaike Information Criterion (AIC), used as automatic onset
signal detection, and the Equivalent Time-Length (ETL), used as an indicator of the
quantity of energy propagating through the bonding. It has been tested both numerically
and experimentally, in vitro, using samples with imposed well- known defects
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Fractional Viscoelastic Transversally Isotropic Timoshenko Beam
No full textIn this paper the viscoelastic behavior of pultruded beams has been examined. Pultruded beams are constituted by a polymer infilled with reinforcement in longitudinal direction, while in the orthogonal direction no fiber are present for technological reasons. As a consequence the material has two different behaviors in longitudinal and in orthogonal directions. It follows that pultruded beams are transversally isotropic, and the shear deformation may not be neglected. Based upon the previous observations and assuming for Creep and/or Relaxation test the power law, the constitutive equations are ruled by fractional operators. From constitutive laws, and assuming the Timoshenko beam theory to account for the shear, the equations of the beam are derived. Experimental test performed on the specimen of the pultruded beam have been carried out confirming the validity of the fractional differential equations here derived
A New Meta-Heuristic Multi-Objective Approach For Optimal Dispatch of Dispersed and Renewable Generating Units in Power Distribution Systems
No full textThe application of stochastic methods in engineering research and optimization has been increasing over the past few decades. Ant Colony Optimization, in particular, has been attracting growing attention as a promising approach both in discrete and continuous domains. The present work proposes a multi-objective Ant Colony Optimization for continuous domains showing good convergence properties and uniform coverage of the non-dominated front. These properties have been proved both with mathematical test functions and with a complex real world problem. Besides the second part of the chapter presents the application of the new algorithm to the problem of optimal dispatch of dispersed power generation units in modern electrical distribution networks. The issue is intrinsically multi-objective and the objectives are calculated based on the solution of the power load flow problem. The performances of the algorithm have been compared to those of the Non-dominated Sorting Genetic Algorithm II on all applications. The chapter is organized as follows, in the introductory part, the relevance of multi-objective optimization problems to modern power distribution operation is outlined. Then the Non-dominated Sorting Genetic Algorithm II is described as well as the proposed Multi-objective Ant Colony Optimization algorithm in details. Both approaches are compared on a test suite of mathematical test functions. Finally, an interesting case study in the field of modern electrical distribution systems management is proposed.</jats:p
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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