101,451 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
No full textExternally 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
MODELING NEW APPROACHES IN EDUCATION: PROCESSES AND TOOLKITS
No full textThe increasing complexity of markets and social contexts need highly educated professionals to face contemporary challenges. They involve different scale of problems and stakeholders and push academies to restructure their traditional educational offer, redefining their boundaries towards the external ecosystem in search for more sustainable, social and economic paradigms, opening up novel knowledge synergies. In recent years, there has been a growing interest in the potential of design approaches and knowledge to transform businesses and generate innovation. The triadic relationship creativity-innovation-design is still forming and requires a broader and deeper understanding as well as clearly defined metrics.
This book is a result of a Pan-European Tempus project – IDEA, led by the Innovation Center ACT Shenkar and supported by the European Commission 2012-2016. The project researched the topics of design-driven innovation as well as industry-academy collaboration as two essential drivers for innovation in the twenty-first century. It brings together an array of 26 experts including design researchers and educators, industrial companies, scientists and engineers from all disciplines, as well as technology transfer companies and public institutions that promote policy in the industrial and educational sectors. The authors of the different chapters took upon themselves the task of advancing a cross-sector and Pan-European discussion on the evolution of design and the way it feeds new ideas that turn into new products and services that can transform the world. It also explores the added value brought by interdisciplinary design-driven research and education for the development of a social environment that fosters innovation and creativity in Israel, in Europe and worldwide
Durability of fabric-reinforced cementitious matrix (FRCM) composites: A review
No full textStrengthening and rehabilitation of masonry and concrete structures by means of externally bonded fabric-reinforced cementitious matrix (FRCM) (also referred to as textile reinforced mortar (TRM) composites was proposed as an alternative to the use of fiber-reinforced polymer (FRP) composites due to their good mechanical properties and compatibility with the substrate. However, quite limited studies are available in the literature regarding the long-term behavior of FRCM composites with respect to different environmental conditions. This paper presents a thorough review of the available researches on the long-term behavior of FRCM composites. Namely, (i) test set-ups employed to study the FRCM durability, (ii) conditioning environments adopted, and (iii) long-term performance of FRCM and its component materials (mortar and fiber textile) subjected to direct tensile and bond tests, are presented and discussed. Based on the available results, some open issues that need to be covered in future studies are pointed out
Experimental and numerical analysis of CFRP-concrete joint bond behavior after exposure to wet-dry cycles
No full textFiber-reinforced polymer (FRP) composites have been largely used for strengthening and retrofitting reinforced concrete members in the last few decades. However, limited information is available regarding their performance after prolonged exposure to different environmental conditions. In this paper, the effect of wet-dry cycles on the bond behavior of carbon FRP-concrete joints tested using a single-lap direct shear test set-up is investigated. Specimens were exposed to 50 wet-dry cycles, each comprised of 6 h of immersion in water at 25 °C followed by 18 h of drying at 50 °C. The digital image correlation technique was used to obtain the displacement field of the composite and determine the cohesive material law and fracture energy of the FRP-concrete interface. A finite element model was then used to reproduce the load response and reinforcement strain profile observed experimentally. The results show that wet-dry cycles affect the FRP-concrete bond properties and change the failure mode from a cohesive debonding within the concrete substrate to an adhesive debonding within the interface
Analytical solution of the full-range behavior of adhesively bonded FRP-steel joints made with toughened adhesives
No full textFiber-reinforced polymer (FRP) composites represent an effective solution to strengthen and retrofit existing steel members. Namely, bonded or unbonded carbon FRP (CFRP) plates have been employed to improve the strength, fatigue behavior, and durability of steel bridges. In bonded solutions, the effectiveness of the CFRP reinforcement strongly depends on the adhesive employed to bond the plate, as failure usually occurs due to debonding. Within this framework, the use of toughened adhesives is particularly attractive since they may improve the load carrying capacity of the CFRP-steel interface, also providing a certain ductility. Debonding in CFRP-steel joints was previously studied using a cohesive approach. However, solutions able to describe the full-range behavior of joints with toughened adhesives and finite bonded length are not available in the literature. In this paper, a trapezoidal (trilinear) cohesive material law (CML) is employed to model the bond behavior of pultruded carbon FRP-steel joints made with a rubber-toughened epoxy adhesive, which showed cohesive debonding within the adhesive layer. The analytical solution provided is employed to study the experimental response of nine CFRP-steel joints tested using a single-lap direct shear set-up. Comparisons of analytical and experimental results of joints with three different bonded lengths confirm the effectiveness of the solution proposed
Letter, [Author unclear] to Paulina T. Merritt
No full textHandwritten letter to Paulina Merritt from an unknown author, October 1, 1876.
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