The Experts below are selected from a list of 267 Experts worldwide ranked by ideXlab platform
Nikhil A. Koratkar - One of the best experts on this subject based on the ideXlab platform.
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heterogeneity in epoxy nanocomposites initiates Crazing significant improvements in fatigue resistance and toughening
Small, 2009Co-Authors: Wei Zhang, Iti Srivastava, Catalin R. Picu, Nikhil A. KoratkarAbstract:Crazing is a failure mode of bulk polymers and occurs under predominant uniaxial tensile load when the bulk eventually forms denser ligaments (or fibrils) while preserving its continuity. [1‐2] The bridging of cracks by such fibrils is an importantmechanismforenergydissipationandtougheningin thermoplastic polymers. However, craze phenomena are not observed [3‐5] in thermosetting polymers such as epoxies due to the high crosslinking density of the epoxy chains, which limits molecular mobility and inhibits craze fibril formation. Such thermosetting epoxies typically display a brittle failure. [6‐7] We demonstrate here that thermosetting epoxies reinforced with amido-amine-functionalized multiwalled carbon nanotubes (A-MWNTs) exhibit Crazing. We show order of magnitude reduction in fatigue crack growth rates as a result of the Crazing. The fracture toughness and ductility of the brittle epoxy is also significantly enhanced by the Crazing. Importantly these enhancements in fatigue resistance and toughness are achieved without any softening of the material. In fact, the Young’s modulus of the nanocomposite is � 30% greater and the average hardness of the nanocomposite is � 45% higher than the baseline (pristine) epoxy. We show that this effect is related to heterogeneous curing of the epoxy, which results in localized pockets of uncrosslinked epoxy that are trapped (or frozen) at the nanotube‐matrix interfaces. Under mechanical loading, these localized regions of high molecular mobility can evolve (or coalesce) to generate conditions that are favorable for Crazing. Recently, in a very interesting study, [8] Crazing has been reported for a poly(lactide
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Heterogeneity in Epoxy Nanocomposites Initiates Crazing: Significant Improvements in Fatigue Resistance and Toughening
Small, 2009Co-Authors: Wei Zhang, Iti Srivastava, Yue-feng Zhu, Catalin R. Picu, Nikhil A. KoratkarAbstract:A study was conducted to demonstrate significant improvement in fatigue resistance, toughening, and homogeneity in epoxy nanocomposite initiated Crazing. It was demonstrated that the fracture toughness and ductility of the brittle epoxy were significantlty enhanced by Crazing. It was observed that these enhancements in fatigue resistance and toughness were achieved without any softening of the material. It was shown that the effect was related to heterogeneous curing of the epoxy, which resulted in localized uncrosslinked epoxy that were trapped at the nanotube-matrix interfaces. It was demonstrated that these localized regions of high molecular mobility was evolved to generate conditions that were favorable for Crazing under mechanical loading. Fatigue crack propagation tests showing crack propagation rate in comparison with stress intensity factor amplitude were performed.
Wei Zhang - One of the best experts on this subject based on the ideXlab platform.
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heterogeneity in epoxy nanocomposites initiates Crazing significant improvements in fatigue resistance and toughening
Small, 2009Co-Authors: Wei Zhang, Iti Srivastava, Catalin R. Picu, Nikhil A. KoratkarAbstract:Crazing is a failure mode of bulk polymers and occurs under predominant uniaxial tensile load when the bulk eventually forms denser ligaments (or fibrils) while preserving its continuity. [1‐2] The bridging of cracks by such fibrils is an importantmechanismforenergydissipationandtougheningin thermoplastic polymers. However, craze phenomena are not observed [3‐5] in thermosetting polymers such as epoxies due to the high crosslinking density of the epoxy chains, which limits molecular mobility and inhibits craze fibril formation. Such thermosetting epoxies typically display a brittle failure. [6‐7] We demonstrate here that thermosetting epoxies reinforced with amido-amine-functionalized multiwalled carbon nanotubes (A-MWNTs) exhibit Crazing. We show order of magnitude reduction in fatigue crack growth rates as a result of the Crazing. The fracture toughness and ductility of the brittle epoxy is also significantly enhanced by the Crazing. Importantly these enhancements in fatigue resistance and toughness are achieved without any softening of the material. In fact, the Young’s modulus of the nanocomposite is � 30% greater and the average hardness of the nanocomposite is � 45% higher than the baseline (pristine) epoxy. We show that this effect is related to heterogeneous curing of the epoxy, which results in localized pockets of uncrosslinked epoxy that are trapped (or frozen) at the nanotube‐matrix interfaces. Under mechanical loading, these localized regions of high molecular mobility can evolve (or coalesce) to generate conditions that are favorable for Crazing. Recently, in a very interesting study, [8] Crazing has been reported for a poly(lactide
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Heterogeneity in Epoxy Nanocomposites Initiates Crazing: Significant Improvements in Fatigue Resistance and Toughening
Small, 2009Co-Authors: Wei Zhang, Iti Srivastava, Yue-feng Zhu, Catalin R. Picu, Nikhil A. KoratkarAbstract:A study was conducted to demonstrate significant improvement in fatigue resistance, toughening, and homogeneity in epoxy nanocomposite initiated Crazing. It was demonstrated that the fracture toughness and ductility of the brittle epoxy were significantlty enhanced by Crazing. It was observed that these enhancements in fatigue resistance and toughness were achieved without any softening of the material. It was shown that the effect was related to heterogeneous curing of the epoxy, which resulted in localized uncrosslinked epoxy that were trapped at the nanotube-matrix interfaces. It was demonstrated that these localized regions of high molecular mobility was evolved to generate conditions that were favorable for Crazing under mechanical loading. Fatigue crack propagation tests showing crack propagation rate in comparison with stress intensity factor amplitude were performed.
Iti Srivastava - One of the best experts on this subject based on the ideXlab platform.
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heterogeneity in epoxy nanocomposites initiates Crazing significant improvements in fatigue resistance and toughening
Small, 2009Co-Authors: Wei Zhang, Iti Srivastava, Catalin R. Picu, Nikhil A. KoratkarAbstract:Crazing is a failure mode of bulk polymers and occurs under predominant uniaxial tensile load when the bulk eventually forms denser ligaments (or fibrils) while preserving its continuity. [1‐2] The bridging of cracks by such fibrils is an importantmechanismforenergydissipationandtougheningin thermoplastic polymers. However, craze phenomena are not observed [3‐5] in thermosetting polymers such as epoxies due to the high crosslinking density of the epoxy chains, which limits molecular mobility and inhibits craze fibril formation. Such thermosetting epoxies typically display a brittle failure. [6‐7] We demonstrate here that thermosetting epoxies reinforced with amido-amine-functionalized multiwalled carbon nanotubes (A-MWNTs) exhibit Crazing. We show order of magnitude reduction in fatigue crack growth rates as a result of the Crazing. The fracture toughness and ductility of the brittle epoxy is also significantly enhanced by the Crazing. Importantly these enhancements in fatigue resistance and toughness are achieved without any softening of the material. In fact, the Young’s modulus of the nanocomposite is � 30% greater and the average hardness of the nanocomposite is � 45% higher than the baseline (pristine) epoxy. We show that this effect is related to heterogeneous curing of the epoxy, which results in localized pockets of uncrosslinked epoxy that are trapped (or frozen) at the nanotube‐matrix interfaces. Under mechanical loading, these localized regions of high molecular mobility can evolve (or coalesce) to generate conditions that are favorable for Crazing. Recently, in a very interesting study, [8] Crazing has been reported for a poly(lactide
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Heterogeneity in Epoxy Nanocomposites Initiates Crazing: Significant Improvements in Fatigue Resistance and Toughening
Small, 2009Co-Authors: Wei Zhang, Iti Srivastava, Yue-feng Zhu, Catalin R. Picu, Nikhil A. KoratkarAbstract:A study was conducted to demonstrate significant improvement in fatigue resistance, toughening, and homogeneity in epoxy nanocomposite initiated Crazing. It was demonstrated that the fracture toughness and ductility of the brittle epoxy were significantlty enhanced by Crazing. It was observed that these enhancements in fatigue resistance and toughness were achieved without any softening of the material. It was shown that the effect was related to heterogeneous curing of the epoxy, which resulted in localized uncrosslinked epoxy that were trapped at the nanotube-matrix interfaces. It was demonstrated that these localized regions of high molecular mobility was evolved to generate conditions that were favorable for Crazing under mechanical loading. Fatigue crack propagation tests showing crack propagation rate in comparison with stress intensity factor amplitude were performed.
Catalin R. Picu - One of the best experts on this subject based on the ideXlab platform.
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heterogeneity in epoxy nanocomposites initiates Crazing significant improvements in fatigue resistance and toughening
Small, 2009Co-Authors: Wei Zhang, Iti Srivastava, Catalin R. Picu, Nikhil A. KoratkarAbstract:Crazing is a failure mode of bulk polymers and occurs under predominant uniaxial tensile load when the bulk eventually forms denser ligaments (or fibrils) while preserving its continuity. [1‐2] The bridging of cracks by such fibrils is an importantmechanismforenergydissipationandtougheningin thermoplastic polymers. However, craze phenomena are not observed [3‐5] in thermosetting polymers such as epoxies due to the high crosslinking density of the epoxy chains, which limits molecular mobility and inhibits craze fibril formation. Such thermosetting epoxies typically display a brittle failure. [6‐7] We demonstrate here that thermosetting epoxies reinforced with amido-amine-functionalized multiwalled carbon nanotubes (A-MWNTs) exhibit Crazing. We show order of magnitude reduction in fatigue crack growth rates as a result of the Crazing. The fracture toughness and ductility of the brittle epoxy is also significantly enhanced by the Crazing. Importantly these enhancements in fatigue resistance and toughness are achieved without any softening of the material. In fact, the Young’s modulus of the nanocomposite is � 30% greater and the average hardness of the nanocomposite is � 45% higher than the baseline (pristine) epoxy. We show that this effect is related to heterogeneous curing of the epoxy, which results in localized pockets of uncrosslinked epoxy that are trapped (or frozen) at the nanotube‐matrix interfaces. Under mechanical loading, these localized regions of high molecular mobility can evolve (or coalesce) to generate conditions that are favorable for Crazing. Recently, in a very interesting study, [8] Crazing has been reported for a poly(lactide
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Heterogeneity in Epoxy Nanocomposites Initiates Crazing: Significant Improvements in Fatigue Resistance and Toughening
Small, 2009Co-Authors: Wei Zhang, Iti Srivastava, Yue-feng Zhu, Catalin R. Picu, Nikhil A. KoratkarAbstract:A study was conducted to demonstrate significant improvement in fatigue resistance, toughening, and homogeneity in epoxy nanocomposite initiated Crazing. It was demonstrated that the fracture toughness and ductility of the brittle epoxy were significantlty enhanced by Crazing. It was observed that these enhancements in fatigue resistance and toughness were achieved without any softening of the material. It was shown that the effect was related to heterogeneous curing of the epoxy, which resulted in localized uncrosslinked epoxy that were trapped at the nanotube-matrix interfaces. It was demonstrated that these localized regions of high molecular mobility was evolved to generate conditions that were favorable for Crazing under mechanical loading. Fatigue crack propagation tests showing crack propagation rate in comparison with stress intensity factor amplitude were performed.
A L Volynskii - One of the best experts on this subject based on the ideXlab platform.
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green environmental Crazing of polymers in oil in water emulsions with high water content
Polymer, 2020Co-Authors: O V Arzhakova, Yu A Kopnov, A I Nazarov, A A Dolgova, A L VolynskiiAbstract:Abstract This work addresses "green" environmental Crazing of polymers in biphase oil-in-water (O/W) emulsions with high water content (above 95 vol %), which can serve as an ecologically safe alternative to pure organic solvents (hydrocarbons and aliphatic alcohols as oils) with respect to their effect on the mechanical behavior of polymers and stress-induced development of porosity via environmental Crazing. This approach is shown to be universal for both modes of environmental Crazing as intercrystallite Crazing for semicrystalline (high-density polyethylene, polytetrafluoroethylene) and classical Crazing for amorphous glassy polymers (PET). The mechanism behind the action of the O/W emulsions on polymers is discussed. The applied advantages of the use of the O/W emulsions with high water content for the preparation of mesoporous and nanocomposite polymer materials are highlighted.
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biaxial tensile drawing of poly ethylene terephthalate via environmental Crazing as a method for creating a porous structure
Polymer, 2018Co-Authors: Yu A Yarysheva, O V Arzhakova, L M Yarysheva, A L VolynskiiAbstract:Abstract Crazing of poly(ethylene terephthalate) thin film has been studied upon its successive biaxial drawing in adsorption-active liquid media in two mutually perpendicular directions. During both primary and secondary drawing, crazes propagate in the direction perpendicular to the drawing axes, thereby leading to the formation of crazes oriented orthogonally relative to each other in the polymer. The secondary drawing occurs at values of elastic modulus, stress, and tensile strain that corresponds to the onset of orientation-induced strengthening decreased due to a lower fraction of undeformed polymer available for Crazing. It has been shown that, as compared with the uniaxial drawing, the biaxial deformation of polymers via the Crazing mechanism leads to a higher porosity. After the removal of a liquid medium, deformed polymers partly retain their open porosity and remain to be permeable to water vapor, with the vapor permeability being higher for biaxially deformed polymers. Thus, the biaxial Crazing is a promising method for the creation of breathful and porous membrane materials, as well as nanocomposites based on them.
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the structural evolution of high density polyethylene during Crazing in liquid medium
European Polymer Journal, 2015Co-Authors: Alena Yu Yarysheva, A L Volynskii, E G Rukhlya, L M Yarysheva, D V Bagrov, N F BakeevAbstract:Abstract Atomic force microscopy (AFM) was employed to study structural transformations occurring in high-density polyethylene (HDPE) during deformation in a liquid medium by Crazing mechanism. Processing of the obtained images yielded the parameters of HDPE structure at different tensile strains. It was shown that Crazing causes the development of a fibrillar–porous structure in the interlamellar space, the fragmentation of lamellae, and the displacement of lamella fragments relative to each other. Moreover, the deformation is accompanied by the separation of lamellae and the long period increases in the proportion to the tensile strain. The scheme of HDPE deformation upon Crazing in liquid medium was constructed based on the AFM images.
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Crazing of polymers in the presence of hyperbranched poly ethoxysiloxane
Polymer Science Series A, 2007Co-Authors: E S Trofimchuk, A L Volynskii, N I Nikonorova, E A Nesterova, A S Eliseev, E V Semenova, I B Meshkov, V V Kazakova, A M Muzafarov, N F BakeevAbstract:The Crazing of various polymers (PET, isotactic PP, and HDPE) in the presence of branched poly(ethoxysiloxane) and its low-molecular-mass analog—tetraethoxysilane—has been studied. The hyperbranched poly(ethoxysiloxane) is shown to be an effective adsorptionally active medium for Crazing of various solid polymers and development of nanoporous structures with a volume porosity of up to 60%. Depending on the nature of polymers, two mechanisms of Crazing (either classical or delocalized Crazing) can take place. The reactions of hydrolysis (basic and acidic) within the pores leading to formation of solid silica have been performed. Electron microscopic observations provide evidence that the transformation of a viscous adsorptionally active liquid into a solid compound directly within the volume of a polymer matrix leads to the stabilization of a highly dispersed polymer structure that arises in the course of Crazing.
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Nanocomposites on the Basis of Crazed Polymers
Russian Journal of General Chemistry, 2002Co-Authors: A L Volynskii, E S Trofimchuk, N I Nikonorova, N F BakeevAbstract:Analysis of published data on the mechanism of structural rearrangements in solid polymers on their Crazing in liquid media is presented. The experimental evidence characterize Crazing not only as a kind of spontaneous polymer dispersion under joint action of a mechanical stress and an active liquid medium, but also as the method of colloidal dispersion of low-molecular substances in a polymer. In the process of Crazing, active liquid fills the porous structure of crazes, thereby transporting various low-molecular substances to the polymer volume. Crazing is believed to open the ways for preparing various nanocomposites on the basis of a wide variety of glassy and crystalline polymers, on the one hand, and target additives on the basis of practically any low-molecular substances, on the other.