1,721,061 research outputs found
Influence of hygrothermal ageing on the mechanical properties of CFRP-concrete joints and of their components
No full textExternally bonded (EB) fiber reinforced polymer (FRP) composites have been effectively employed to strengthen existing reinforced concrete (RC) structures. However, relatively limited information is available regarding the long-term behavior of FRP-concrete joints. In this paper, different experimental tests are employed to investigate the effect of hygrothermal ageing on the bond behavior of a carbon FRP composite applied to a concrete substrate and on the mechanical properties of the epoxy resin and FRP composite considered. The experimental campaign includes tensile tests of epoxy resin, carbon FRP (CFRP) coupon, pull-off tests of the CFRP bonded to the concrete substrate, and single-lap direct-shear tests of CFRP-concrete joints. Specimens were conditioned in warm water (38 ± 2 °C) for 500, 1000, and 1500 h to accelerate the possible degradation induced by a simulated high-moisture exposure environment. The parameters studied were the tensile properties of epoxy resin and CFRP coupons and the fracture energy of the CFRP-concrete interface, which was computed from the CFRP strain measured in the single-lap direct-shear tests using the digital image correlation (DIC) method. Results indicate that both the mechanical properties of the epoxy resin and the CFRP-concrete interface fracture energy were slightly affected by the exposure conditions
Stochastic Calibration of a Cyclic Cohesive Zone Model Through Monte Carlo Analysis
No full textFatigue induced crack propagation is still an open issue, relevant to many engineering applications. Cyclic loading produces damage accumulation at a localized region which results first in the formation of micro-cracks and finally leads to the creation of macro-cracks. The modeling of fatigue induced crack propagation can be done according to different approaches, such as the Paris law, where the rate of crack growth is dependent on fracture mechanics parameters, e.g., the stress intensity factor or the strain energy release rate. Other approaches are the empirical methods, typically S-N approach and the micromechanical models describing the accumulation of damage based on material microstructure changes. Another approach involves the definition of phenomenological models where the fatigue crack growth is described by adopting cohesive zone laws. In this paper a damage-based irreversible cyclic cohesive zone model is adopted, where damage healing is considered during the fatigue damage evolution. The model presents different parameters, some of which are characterized by a large variability, do not possess a precise physical meaning and then they are not amenable to direct measurement. In this context, this paper aims to provide a robust procedure for the calibration of these model parameters, based on a Monte Carlo stochastic approach. Indications regarding the minimum number of experimental measurements are also provided, to support the planning of tests setups for laboratory investigations. Finally, the definition of a well posed inverse problem allows an efficient identification of all the sought model parameters reducing then the experimental costs
Experimental and analytical investigation of PBO FRCM-concrete bond behavior using direct and indirect shear test set-ups
Full text linkExternally bonded reinforcement (EBR) represents an effective solution to strengthen existing reinforced concrete (RC) members. EBR comprising fiber-reinforced cementitious matrix (FRCM) has been increasingly adopted due to some advantages with respect to the more diffused fiber-reinforced polymer (FRP). Externally bonded FRCM often reported debonding failure at the matrix-fiber interface. In the literature, the matrix-fiber bond behavior was studied using mostly single- and double-lap direct shear (DS) tests. An alternative is represented by modified beam (MB) test set-ups. In this paper, a MB test set-up is adopted to study the effect of flexural deflection on the bond behavior of a polyparaphenylene benzobisoxazole (PBO) FRCM composite bonded to a concrete substrate. Two different MB test layouts are investigated and the results obtained are analyzed and compared with those of corresponding DS tests with the same PBO FRCM. Then, an analytical model able to describe the results of both DS and MB tests accounting for the presence of stresses normal to the matrix-fiber interface is proposed. The experimental results and analysis presented in this paper help to clarify the influence of the test set-up on the bond behavior of FRCM composites, which represents a key parameter for the design of FRCM EBR
Analytical solution of the bond behavior of FRCM composites using a rigid-softening cohesive material law
No full textThe study of the bond behavior of fiber-reinforced composite materials applied to cohesive substrates is a fundamental topic to correctly understand the composite-substrate stress-transfer mechanism. Bond tests of fiber reinforced cementitious matrix (FRCM) composites comprising one layer of fiber textile generally showed failure due to debonding of the textile at the matrix-fiber interface. This failure mode was described considering a fracture mechanics pure Mode-II loading condition, which provided a bond differential equation that was solved once a certain shape of the interface cohesive material law was assumed. In this paper, a rigid-softening cohesive material law, which considers the possible presence of friction stress contributions at the debonding interface, is adopted to provide the analytical solution of the matrix-fiber interface full-range behavior in FRCM composites. The solution obtained is employed to reproduce the load responses of a PBO FRCM composite subjected to a recently-developed pull-out test and validate the analytical approach
FATIGUE CRACK SIZE PROBABILITY-DISTRIBUTION VIA A FILTER TECHNIQUE
No full textFatigue crack propagation in a probabilistic framewor
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Variations on the Author
Full text link“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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
- …
