Search

Unstable crack propagation behavior of carbon fiber reinforced plastic (CFRP) composites has a significant impact on the safety and reliability of structures in practical applications. Herein, we reported a method to improve the stability of crack growth by coating polydopamine (PDA) and graphene oxide (GO) on the surface of carbon fabric. The Mode I and Mode II testswere performed to study the delamination and crack behaviors of pure CFRP and modified CFRP. The crack propagation behavior can be tuned from unstable to stable manner without sacrificing the crack initiation during the opening mode test. It was revealed that the crack tended to fracture through the GO sheets, leading to the tearing and peeling of GO. The PDA&GO coated layers contributed to improving the load transfer between carbon fibers and polymer matrix, reducing the crack blunting degree, minimizing the unstable crack growth, and thus dissipating more energy. (C) 2016 Elsevier Ltd. All rights reserved.

Unstable crack propagation behavior of carbon fiber reinforced plastic (CFRP) composites has a significant impact on the safety and reliability of structures in practical applications. Herein, we reported a method to improve the stability of crack growth by coating polydopamine (PDA) and graphene oxide (GO) on the surface of carbon fabric. The Mode I and Mode II testswere performed to study the delamination and crack behaviors of pure CFRP and modified CFRP. The crack propagation behavior can be tuned from unstable to stable manner without sacrificing the crack initiation during the opening mode test. It was revealed that the crack tended to fracture through the GO sheets, leading to the tearing and peeling of GO. The PDA&GO coated layers contributed to improving the load transfer between carbon fibers and polymer matrix, reducing the crack blunting degree, minimizing the unstable crack growth, and thus dissipating more energy. (C) 2016 Elsevier Ltd. All rights reserved.

Unstable crack propagation behavior of carbon fiber reinforced plastic (CFRP) composites has a significant impact on the safety and reliability of structures in practical applications. Herein, we reported a method to improve the stability of crack growth by coating polydopamine (PDA) and graphene oxide (GO) on the surface of carbon fabric. The Mode I and Mode II testswere performed to study the delamination and crack behaviors of pure CFRP and modified CFRP. The crack propagation behavior can be tuned from unstable to stable manner without sacrificing the crack initiation during the opening mode test. It was revealed that the crack tended to fracture through the GO sheets, leading to the tearing and peeling of GO. The PDA&GO coated layers contributed to improving the load transfer between carbon fibers and polymer matrix, reducing the crack blunting degree, minimizing the unstable crack growth, and thus dissipating more energy. (C) 2016 Elsevier Ltd. All rights reserved.

The fracture toughness of carbon fiber reinforced plastic laminates was investigated in term of modifying the epoxy matrix with the pristine and functionalized stacked-cup carbon nanofibers. The results showed that the highest enhancements in Mode I (13.6%) and Mode II (45.3%) fracture toughness were achieved by adding 0.5. wt% and 1.0. wt% functionalized nanofibers, respectively. The toughening mechanism was analyzed based on the morphology evaluations of the fracture surfaces. The evidence of bridging, pull-out, peeling-off and unravelling of nanofibers were clearly observed, which contributed to dissipating more energy for crack propagation, resulting in the improvement of fracture toughness. © 2015 Elsevier Ltd.

The fracture toughness of carbon fiber reinforced plastic laminates was investigated in term of modifying the epoxy matrix with the pristine and functionalized stacked-cup carbon nanofibers. The results showed that the highest enhancements in Mode I (13.6%) and Mode II (45.3%) fracture toughness were achieved by adding 0.5. wt% and 1.0. wt% functionalized nanofibers, respectively. The toughening mechanism was analyzed based on the morphology evaluations of the fracture surfaces. The evidence of bridging, pull-out, peeling-off and unravelling of nanofibers were clearly observed, which contributed to dissipating more energy for crack propagation, resulting in the improvement of fracture toughness. © 2015 Elsevier Ltd.

A thermotropic liquid crystalline polymer (TLCP), denoted as TLCP(1), was used as a processing aid for high density polyethylene (HDPE). The TLCP was a copolyester of hydroxybenzoic acid, hydroquinone and sebacic acid and was blended with HDPE to give 0.2, 0.5 and 2 wt\% TLCP(1) blends. At a temperature of 185 degrees C, when TLCP(1) is in the nematic regime, the processing window for HDPE was increased tenfold from a maximum shear rate of 100 s(-1) for pure HDPE to 1170 s(-1) for a 2 wt\% TLCP(1) blend, There were large viscosity reductions of between 85\% and 90\% compared with the pure HDPE when the blended material was used at a wall shear stress value of approximately 2.4 x 10(5) Pa. This viscosity reduction was attributed to the TLCP(I) droplets changing shape from spheres to slender fibrils under shear flows.

A thermotropic liquid crystalline polymer (TLCP), denoted as TLCP(1), was used as a processing aid for high density polyethylene (HDPE). The TLCP was a copolyester of hydroxybenzoic acid, hydroquinone and sebacic acid and was blended with HDPE to give 0.2, 0.5 and 2 wt\% TLCP(1) blends. At a temperature of 185 degrees C, when TLCP(1) is in the nematic regime, the processing window for HDPE was increased tenfold from a maximum shear rate of 100 s(-1) for pure HDPE to 1170 s(-1) for a 2 wt\% TLCP(1) blend, There were large viscosity reductions of between 85\% and 90\% compared with the pure HDPE when the blended material was used at a wall shear stress value of approximately 2.4 x 10(5) Pa. This viscosity reduction was attributed to the TLCP(I) droplets changing shape from spheres to slender fibrils under shear flows.

A thermotropic liquid crystalline polymer (TLCP), denoted as TLCP(1), was used as a processing aid for high density polyethylene (HDPE). The TLCP was a copolyester of hydroxybenzoic acid, hydroquinone and sebacic acid and was blended with HDPE to give 0.2, 0.5 and 2 wt\% TLCP(1) blends. At a temperature of 185 degrees C, when TLCP(1) is in the nematic regime, the processing window for HDPE was increased tenfold from a maximum shear rate of 100 s(-1) for pure HDPE to 1170 s(-1) for a 2 wt\% TLCP(1) blend, There were large viscosity reductions of between 85\% and 90\% compared with the pure HDPE when the blended material was used at a wall shear stress value of approximately 2.4 x 10(5) Pa. This viscosity reduction was attributed to the TLCP(I) droplets changing shape from spheres to slender fibrils under shear flows.

The rheology of a liquid crystalline copolyester of hydroxybenzoic acid, hydroqui none, and sebacic acid (HBA/HQ/SA copolyester) was studied on both a rotational and a capillary rheometer. DSC studies show that the copolyester has a crystal-mesophasic and a broad mesophasic-isotropic transition at 170 degrees C and 220 degrees C. Optical texture observations show the mesophase is characterized by line defect textures, which are characteristic of a nematic structure. At 220 degrees C, both isotropic and nematic phases coexist with the latter being the major. As temperature reaches 250 degrees C, a clear dominance of isotropic phase is observed. At this temperature, the nematic phase of irregular shapes randomly disperses within the isotropic matrix. Subsequent rheological studies were thus conducted in crystal/nematic biphase, single nematic phase, nematic/isotropic biphase, and the near single isotropic phase. Dynamic strain sweep measurements show that a linear viscoelastic region exists at all temperatures tested. The maximum strain amplitude for the linear viscoelastic region is found to be highly structure dependent; it is >100\% in the nematic phase, similar to 20\% in the biphases, and only about 5\% in the isotropic phase. The concurrence of curves obtained at different temperatures in a Cole-Cole plot of G' vs. G `' indicates similar structures in the nematic phase and biphases. Measurements of steady shear viscosity using a rotational rheometer and a roundhole capillary rheometer show that in the nematic phase the copolyester behaves as a shear thinning fluid for a wide shear rate range of 1 similar to 10,000 s(-1), in which the power law index Is about 0.6 similar to 0.8, and the viscosity is <10 Pa.s at shear rates >1 s(-1).

The rheology of a liquid crystalline copolyester of hydroxybenzoic acid, hydroqui none, and sebacic acid (HBA/HQ/SA copolyester) was studied on both a rotational and a capillary rheometer. DSC studies show that the copolyester has a crystal-mesophasic and a broad mesophasic-isotropic transition at 170 degrees C and 220 degrees C. Optical texture observations show the mesophase is characterized by line defect textures, which are characteristic of a nematic structure. At 220 degrees C, both isotropic and nematic phases coexist with the latter being the major. As temperature reaches 250 degrees C, a clear dominance of isotropic phase is observed. At this temperature, the nematic phase of irregular shapes randomly disperses within the isotropic matrix. Subsequent rheological studies were thus conducted in crystal/nematic biphase, single nematic phase, nematic/isotropic biphase, and the near single isotropic phase. Dynamic strain sweep measurements show that a linear viscoelastic region exists at all temperatures tested. The maximum strain amplitude for the linear viscoelastic region is found to be highly structure dependent; it is >100\% in the nematic phase, similar to 20\% in the biphases, and only about 5\% in the isotropic phase. The concurrence of curves obtained at different temperatures in a Cole-Cole plot of G' vs. G `' indicates similar structures in the nematic phase and biphases. Measurements of steady shear viscosity using a rotational rheometer and a roundhole capillary rheometer show that in the nematic phase the copolyester behaves as a shear thinning fluid for a wide shear rate range of 1 similar to 10,000 s(-1), in which the power law index Is about 0.6 similar to 0.8, and the viscosity is <10 Pa.s at shear rates >1 s(-1).

The rheology of a liquid crystalline copolyester of hydroxybenzoic acid, hydroqui none, and sebacic acid (HBA/HQ/SA copolyester) was studied on both a rotational and a capillary rheometer. DSC studies show that the copolyester has a crystal-mesophasic and a broad mesophasic-isotropic transition at 170 degrees C and 220 degrees C. Optical texture observations show the mesophase is characterized by line defect textures, which are characteristic of a nematic structure. At 220 degrees C, both isotropic and nematic phases coexist with the latter being the major. As temperature reaches 250 degrees C, a clear dominance of isotropic phase is observed. At this temperature, the nematic phase of irregular shapes randomly disperses within the isotropic matrix. Subsequent rheological studies were thus conducted in crystal/nematic biphase, single nematic phase, nematic/isotropic biphase, and the near single isotropic phase. Dynamic strain sweep measurements show that a linear viscoelastic region exists at all temperatures tested. The maximum strain amplitude for the linear viscoelastic region is found to be highly structure dependent; it is >100\% in the nematic phase, similar to 20\% in the biphases, and only about 5\% in the isotropic phase. The concurrence of curves obtained at different temperatures in a Cole-Cole plot of G' vs. G `' indicates similar structures in the nematic phase and biphases. Measurements of steady shear viscosity using a rotational rheometer and a roundhole capillary rheometer show that in the nematic phase the copolyester behaves as a shear thinning fluid for a wide shear rate range of 1 similar to 10,000 s(-1), in which the power law index Is about 0.6 similar to 0.8, and the viscosity is <10 Pa.s at shear rates >1 s(-1).