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Ole Thybo Thomsen - One of the best experts on this subject based on the ideXlab platform.
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fracture behaviour at tri material junctions of crack Stoppers in sandwich structures
Composite Structures, 2015Co-Authors: W. Wang, Georgios Martakos, J M Dulieubarton, Jens Henrik Andreasen, Ole Thybo ThomsenAbstract:Abstract Inspired by a previously published peel Stopper design for foam cored composite sandwich structures, three novel markedly lighter peel Stoppers were evaluated with respect to their ability to deflect and arrest propagating face debond cracks. Of the three novel peel Stopper configurations, C1, C2 and C3, C1 was similar to the previous design, whereas C2 and C3 were modified with layers of glass fibre fabric extending from the peel Stopper tip into the face sheet (C2) or into the face sheet/core interface (C3). The previous peel Stopper was validated under mode II dominated conditions, but the novel designs were investigated under mode I dominated crack propagation conditions, which are of higher practical relevance. Both quasi-static and fatigue loading scenarios were investigated. The mechanisms controlling crack propagation at the internal peel Stopper tip were studied using thermoelastic stress analysis (TSA) and finite element (FE) analysis. The TSA has revealed significant new information about the local stress fields in the vicinity of the tri-material junction (peel Stopper tip) as well as the fracture process zone. Configuration C1 was unable to deflect debond cracks consistently, albeit it did so in most cases, whereas it was incapable of achieving crack arrest. C2 and C3 both performed better in that they consistently demonstrated the ability to deflect propagating cracks, whereas only C2 could arrest the cracks consistently as well. Detailed fracture mechanics analyses confirmed and explained the experimental observations.
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fracture behaviour at tri material junctions of crack Stoppers in sandwich structures
Composite Structures, 2015Co-Authors: W. Wang, Georgios Martakos, J M Dulieubarton, Jens Henrik Andreasen, Ole Thybo ThomsenAbstract:Abstract Inspired by a previously published peel Stopper design for foam cored composite sandwich structures, three novel markedly lighter peel Stoppers were evaluated with respect to their ability to deflect and arrest propagating face debond cracks. Of the three novel peel Stopper configurations, C1, C2 and C3, C1 was similar to the previous design, whereas C2 and C3 were modified with layers of glass fibre fabric extending from the peel Stopper tip into the face sheet (C2) or into the face sheet/core interface (C3). The previous peel Stopper was validated under mode II dominated conditions, but the novel designs were investigated under mode I dominated crack propagation conditions, which are of higher practical relevance. Both quasi-static and fatigue loading scenarios were investigated. The mechanisms controlling crack propagation at the internal peel Stopper tip were studied using thermoelastic stress analysis (TSA) and finite element (FE) analysis. The TSA has revealed significant new information about the local stress fields in the vicinity of the tri-material junction (peel Stopper tip) as well as the fracture process zone. Configuration C1 was unable to deflect debond cracks consistently, albeit it did so in most cases, whereas it was incapable of achieving crack arrest. C2 and C3 both performed better in that they consistently demonstrated the ability to deflect propagating cracks, whereas only C2 could arrest the cracks consistently as well. Detailed fracture mechanics analyses confirmed and explained the experimental observations.
M Cohen A Stuart - One of the best experts on this subject based on the ideXlab platform.
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rheology of a reversible supramolecular polymer studied by comparison of the effects of temperature and chain Stoppers
Journal of Chemical Physics, 2007Co-Authors: Wout Knoben, Nicolaas A. M. Besseling, M Cohen A StuartAbstract:The rheology of a reversible supramolecular polymer is studied by comparing the effects of an increase in temperature and the addition of chain Stoppers. The dependence of the zero-shear viscosity and the terminal relaxation time on temperature is exponential, and the activation energy for viscous flow can be calculated. Above a critical Stopper fraction, power laws describe the Stopper dependence of the viscosity and relaxation time. A simple model for the effect of the addition of chain Stoppers on the average degree of polymerization adequately describes the results. A comparison of flow curves at several temperatures and Stopper fractions reveals considerable differences between solutions with the same zero-shear viscosity. These are mainly associated with differences in the terminal relaxation time. A mechanism of shear-induced alignment and subsequent elongation of chains is proposed, with which the experimental results are consistent.
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chain Stoppers in reversible supramolecular polymer solutions studied by static and dynamic light scattering and osmometry
Macromolecules, 2006Co-Authors: Wout Knoben, Nicolaas A. M. Besseling, M Cohen A StuartAbstract:The effect of the addition of chain Stoppers to solutions of hydrogen-bonded reversible supramolecular polymers was studied by vapor pressure osmometry and static and dynamic light scattering. Vapor pressure osmometry showed that within the range of concentrations studied the average degree of polymerization is independent of the overall monomer concentration and roughly inversely proportional to the mole fraction of chain Stoppers, in agreement with theoretical predictions. The correlation length as measured by static light scattering has a maximum at the overlap concentration in solutions without chain Stoppers. In the presence of a fixed fraction of chain Stoppers, the results coincide with those without chain Stoppers at low and high concentrations, but there is a plateau in the correlation length at intermediate concentrations. From the data, information about the association constant and the persistence length of the chains is obtained. The effectiveness of the chain Stopper is discussed, and the re...
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dynamics of reversible supramolecular polymers independent determination of the dependence of linear viscoelasticity on concentration and chain length by using chain Stoppers
Physical Chemistry Chemical Physics, 2005Co-Authors: Wout Knoben, Laurent Bouteiller, Nicolaas A. M. Besseling, M Cohen A StuartAbstract:The linear viscoelasticity of solutions of a hydrogen bonded reversible supramolecular polymer in the presence of a chain Stopper was studied by rheometry and by dynamic light scattering using probe particles. The use of chain Stoppers enabled the independent variation of the degree of polymerisation and the monomer concentration, and the effect of both parameters on rheology was investigated. Scaling exponents were obtained for the chain length and concentration dependence of the zero-shear viscosity and the terminal relaxation time, and these were compared to theoretical values. The results indicate that the reversible supramolecular polymer is semiflexible, and that both breaking and reptation of chains contribute to the stress relaxation. The parameters from macroscopic rheometry were compared to microscopic values obtained from probe particle diffusion. The particles probe the macroscopic viscoelastic parameters if their size is large compared to the correlation length in the system and to the (persistence) length of the polymer chains.
Wout Knoben - One of the best experts on this subject based on the ideXlab platform.
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rheology of a reversible supramolecular polymer studied by comparison of the effects of temperature and chain Stoppers
Journal of Chemical Physics, 2007Co-Authors: Wout Knoben, Nicolaas A. M. Besseling, M Cohen A StuartAbstract:The rheology of a reversible supramolecular polymer is studied by comparing the effects of an increase in temperature and the addition of chain Stoppers. The dependence of the zero-shear viscosity and the terminal relaxation time on temperature is exponential, and the activation energy for viscous flow can be calculated. Above a critical Stopper fraction, power laws describe the Stopper dependence of the viscosity and relaxation time. A simple model for the effect of the addition of chain Stoppers on the average degree of polymerization adequately describes the results. A comparison of flow curves at several temperatures and Stopper fractions reveals considerable differences between solutions with the same zero-shear viscosity. These are mainly associated with differences in the terminal relaxation time. A mechanism of shear-induced alignment and subsequent elongation of chains is proposed, with which the experimental results are consistent.
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chain Stoppers in reversible supramolecular polymer solutions studied by static and dynamic light scattering and osmometry
Macromolecules, 2006Co-Authors: Wout Knoben, Nicolaas A. M. Besseling, M Cohen A StuartAbstract:The effect of the addition of chain Stoppers to solutions of hydrogen-bonded reversible supramolecular polymers was studied by vapor pressure osmometry and static and dynamic light scattering. Vapor pressure osmometry showed that within the range of concentrations studied the average degree of polymerization is independent of the overall monomer concentration and roughly inversely proportional to the mole fraction of chain Stoppers, in agreement with theoretical predictions. The correlation length as measured by static light scattering has a maximum at the overlap concentration in solutions without chain Stoppers. In the presence of a fixed fraction of chain Stoppers, the results coincide with those without chain Stoppers at low and high concentrations, but there is a plateau in the correlation length at intermediate concentrations. From the data, information about the association constant and the persistence length of the chains is obtained. The effectiveness of the chain Stopper is discussed, and the re...
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dynamics of reversible supramolecular polymers independent determination of the dependence of linear viscoelasticity on concentration and chain length by using chain Stoppers
Physical Chemistry Chemical Physics, 2005Co-Authors: Wout Knoben, Laurent Bouteiller, Nicolaas A. M. Besseling, M Cohen A StuartAbstract:The linear viscoelasticity of solutions of a hydrogen bonded reversible supramolecular polymer in the presence of a chain Stopper was studied by rheometry and by dynamic light scattering using probe particles. The use of chain Stoppers enabled the independent variation of the degree of polymerisation and the monomer concentration, and the effect of both parameters on rheology was investigated. Scaling exponents were obtained for the chain length and concentration dependence of the zero-shear viscosity and the terminal relaxation time, and these were compared to theoretical values. The results indicate that the reversible supramolecular polymer is semiflexible, and that both breaking and reptation of chains contribute to the stress relaxation. The parameters from macroscopic rheometry were compared to microscopic values obtained from probe particle diffusion. The particles probe the macroscopic viscoelastic parameters if their size is large compared to the correlation length in the system and to the (persistence) length of the polymer chains.
M San V Romao - One of the best experts on this subject based on the ideXlab platform.
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cork Stoppers industry defining appropriate mould colonization
Microbiological Research, 2003Co-Authors: Ana Maria Da Cruz Sousa Oliveira, J Figueiredo J Marques, Silva C Pereira, Cidalia Peres, J Correia M Pires, Silvia Vitorino, M Barreto T Crespo, M San V RomaoAbstract:Aims : The main aims of this work were the study of cork slabs moulds colonization and the evaluation of the moulds diversity during cork processing steps, in different cork Stoppers factories. Simultaneously, it was envisaged to perform an evaluation of the air quality. Methods and Results : Moulds were isolated and identified from cork slabs and cork samples in four cork Stoppers factories. The identification was based on morphological characters and microscopic observation of the reproductive structures. Airborne spore dispersion was assessed using a two stage Andersen sampler. It was observed that Chrysonilia sitophila was always present on cork slabs during the maturing period, but mould diversity appeared to be associated to the different factory configurations and processing steps. Conclusions : Spatial separation of the different steps of the process, including physical separation of the maturation step, is essential to guarantee high air quality and appropriate cork slabs colonization, i.e. C. sitophila dominance. The sorting and cutting of the edges of cork slabs after boiling and before the maturing step is also recommended. Significance and Impact of the Study : This study is very important for the cork Stopper industry as it gives clear indications on how to keep high quality manufacturing standards and how to avoid occupational health problems.
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role of chrysonilia sitophila in the quality of cork Stoppers for sealing wine bottles
Journal of Industrial Microbiology & Biotechnology, 2000Co-Authors: Silva C Pereira, J Figueiredo J Marques, Antero Pires, M J Valle, Vilas L Boas, M San V RomaoAbstract:The contribution of Chrysonilia sitophila in cork Stopper manufacture was studied and a simulation of the industrial processing of cork Stoppers was performed. Stoppers cut from slabs where mold development was inhibited were compared with others cut from slabs colonized by C. sitophila alone or with several molds, in terms of physical properties and chemical taints. C. sitophila does not produce 2,4,6-trichloroanisole, guaiacol, or 1-octene-3-ol on cork slabs incubated for 66 days. Since some chlorophenol-related compounds contaminate cork slabs during the production processes, metabolic tests were performed to investigate the capability of molds to produce 2,4,6-trichloroanisole by methylation of 2,4,6-trichlorophenol. Degradation of 2,4,6-trichlorophenol by C. sitophila resulted in a very high level of degradation without production of 2,4,6-trichloroanisole. C. sitophila restricted growth of other molds on maturing slabs for at least 30 days. These results show that C. sitophila can be exploited by industrial producers of cork Stoppers since it is able to inhibit the development of other molds and it does not produce the compounds responsible for ‘cork-taint’, even in the presence of chlorophenols. Journal of Industrial Microbiology & Biotechnology (2000) 24, 256–261.
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cork taint in wine scientific knowledge and public perception a critical review
Critical Reviews in Microbiology, 2000Co-Authors: Silva C Pereira, J Figueiredo J Marques, M San V RomaoAbstract:The manufacturing process of cork Stoppers includes a stabilization period of the cork slabs, following boiling, during which mold growth completely covers the cork slabs. This process has been used traditionally for several decades; however, due to the possibility of certain molds isolated from cork to produce off flavor compounds, especially 2,4,6-trichloroanisole and 2,3,4,6-tetrachloroanisole, recently cork Stoppers are being unsoundly targeted with the accusation of inducing cork taint in wine. This article reviews the manufacturing process of cork Stoppers, the diversity of microorganisms associated with cork, and finally the diversity and origins of the compounds associated with cork taint in wine, focusing on those currently considered as more important. Some important results recently obtained by the authors are also included. The current idea of suppressing mold growth during cork Stopper manufacturing is discussed, as well as the erroneous idea of imputing, directly and exclusively, to cork the responsibility of the so-called cork taint in wine.
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mycobiota in portuguese normal and green cork throughout the manufacturing process of Stoppers
Journal of Applied Microbiology, 1997Co-Authors: P Danesh, F Velez M Caldas, J Figueiredo J Marques, M San V RomaoAbstract:The compounds responsible for the so-called ‘cork taint’ include, among others, some microbial metabolites which can be produced by the microbial population colonizing the unprocessed cork and Stoppers. This study was intended to obtain information on the mycobiota associated with Portuguese cork throughout the manufacturing process of Stoppers. Samples of barks and Stoppers of both ‘normal’ and ‘green’ cork were examined. Moulds were isolated from ‘normal’ and ‘green’ cork throughout the entire cork Stopper manufacturing process. Yeasts were rarely detected in the corks. Fungal contamination was not detected in finished Stoppers from the company under study.
J M Dulieubarton - One of the best experts on this subject based on the ideXlab platform.
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fracture behaviour at tri material junctions of crack Stoppers in sandwich structures
Composite Structures, 2015Co-Authors: W. Wang, Georgios Martakos, J M Dulieubarton, Jens Henrik Andreasen, Ole Thybo ThomsenAbstract:Abstract Inspired by a previously published peel Stopper design for foam cored composite sandwich structures, three novel markedly lighter peel Stoppers were evaluated with respect to their ability to deflect and arrest propagating face debond cracks. Of the three novel peel Stopper configurations, C1, C2 and C3, C1 was similar to the previous design, whereas C2 and C3 were modified with layers of glass fibre fabric extending from the peel Stopper tip into the face sheet (C2) or into the face sheet/core interface (C3). The previous peel Stopper was validated under mode II dominated conditions, but the novel designs were investigated under mode I dominated crack propagation conditions, which are of higher practical relevance. Both quasi-static and fatigue loading scenarios were investigated. The mechanisms controlling crack propagation at the internal peel Stopper tip were studied using thermoelastic stress analysis (TSA) and finite element (FE) analysis. The TSA has revealed significant new information about the local stress fields in the vicinity of the tri-material junction (peel Stopper tip) as well as the fracture process zone. Configuration C1 was unable to deflect debond cracks consistently, albeit it did so in most cases, whereas it was incapable of achieving crack arrest. C2 and C3 both performed better in that they consistently demonstrated the ability to deflect propagating cracks, whereas only C2 could arrest the cracks consistently as well. Detailed fracture mechanics analyses confirmed and explained the experimental observations.
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fracture behaviour at tri material junctions of crack Stoppers in sandwich structures
Composite Structures, 2015Co-Authors: W. Wang, Georgios Martakos, J M Dulieubarton, Jens Henrik Andreasen, Ole Thybo ThomsenAbstract:Abstract Inspired by a previously published peel Stopper design for foam cored composite sandwich structures, three novel markedly lighter peel Stoppers were evaluated with respect to their ability to deflect and arrest propagating face debond cracks. Of the three novel peel Stopper configurations, C1, C2 and C3, C1 was similar to the previous design, whereas C2 and C3 were modified with layers of glass fibre fabric extending from the peel Stopper tip into the face sheet (C2) or into the face sheet/core interface (C3). The previous peel Stopper was validated under mode II dominated conditions, but the novel designs were investigated under mode I dominated crack propagation conditions, which are of higher practical relevance. Both quasi-static and fatigue loading scenarios were investigated. The mechanisms controlling crack propagation at the internal peel Stopper tip were studied using thermoelastic stress analysis (TSA) and finite element (FE) analysis. The TSA has revealed significant new information about the local stress fields in the vicinity of the tri-material junction (peel Stopper tip) as well as the fracture process zone. Configuration C1 was unable to deflect debond cracks consistently, albeit it did so in most cases, whereas it was incapable of achieving crack arrest. C2 and C3 both performed better in that they consistently demonstrated the ability to deflect propagating cracks, whereas only C2 could arrest the cracks consistently as well. Detailed fracture mechanics analyses confirmed and explained the experimental observations.
