Modeling and simulation allow methodical variation of material properties beyond the capacity of experimental methods. The polymers are one of the most commonly used matrices of choice for composites and have found ap...Modeling and simulation allow methodical variation of material properties beyond the capacity of experimental methods. The polymers are one of the most commonly used matrices of choice for composites and have found applications in numerous fields. The stiff and fragile structure of monolithic polymers leads to the innate cracks to cause fracture and therefore the engineering applications of monolithic polymers, requiring robust damage tolerance and high fracture toughness, are not ubiquitous. In addition, when “many-parts” cling together to form polymers, a labyrinth of molecules results, which does not offer to electrons and phonons a smooth and continuous passageway. Therefore, the monolithic polymers are bad conductors of heat and electricity. However, it is well established that when polymers are embedded with suitable entities especially nano-fillers, such as metallic oxides, clays, carbon nanotubes, and other carbonaceous materials, their performance is propitiously improved. Among various additives, graphene has recently been employed as nano-filler to enhance mechanical, thermal, electrical, and functional properties of polymers. In this review, advances in the modeling and simulation of grapheme based polymer nanocomposites will be discussed in terms of graphene structure, topographical features, interfacial interactions, dispersion state, aspect ratio, weight fraction, and trade-off between variables and overall performance.展开更多
Modeling and simulation allow methodical variation of material properties beyond the capacity of experimental methods. Due to the hexagonal structure of graphene, it is considered as frame-like structure. In the frame...Modeling and simulation allow methodical variation of material properties beyond the capacity of experimental methods. Due to the hexagonal structure of graphene, it is considered as frame-like structure. In the frame, covalent C-C bonds are taken as beams joined together with carbon atoms placed at the joints. Uniaxial beam elements, defined by their cross-sectional area, material properties, and moment of inertia represent the covalent bonds. The parameters of the beam elements are determined by establishing equivalence between structural and computational mechanics. However, the bonds connecting the carbon atoms do not have physical existence as they are a compromise between attractive and repulsive forces. Also, defects at nanoscale make graphene different from frame-like structure. In addition, the topography of graphene makes it non-linear structure and even the axial loading changes to eccentric loading. Here we show that, by using basic statics principles, disparities between graphene and frame-likes structures can be highlighted.展开更多
The environmental stress cracking resistance of halloysite nanoclay-polyester nanocomposites was investigated using fracture mechanics approach. The incorporation of halloysite nanoclay was found to improve the enviro...The environmental stress cracking resistance of halloysite nanoclay-polyester nanocomposites was investigated using fracture mechanics approach. The incorporation of halloysite nanoclay was found to improve the environmental stress cracking resistance of the nano-composites. The storage modulus of nano-composites measured by dynamic mechanical analysis increased remarkably as a function of halloysite nanoclay content. At 0.7 wt% nanoclay, the Tg improved from 72°C to 76°C. The fracture toughness increased up to 33% and time to failure improved 155% with the addition of 0.7 wt% of halloysite nanoclay. The maximum microhardness was found 119% higher for the same nano-filler concentration compared to monolithic polyester. The reinforcement with 1 wt% showed lower fracture toughness due to agglomerations of nanoclay which act as flaws. The presence of agglomerates weakened the bond between nano-particles and matrix hence reduces the environmental stress cracking resistance by halloysite nanoclay reinforcement.展开更多
The topographical features of fractured tensile, flexural, K<sub>1C</sub>, and impact specimens of monolithic epoxy have been studied and correlated with mechanical properties and surface features of sampl...The topographical features of fractured tensile, flexural, K<sub>1C</sub>, and impact specimens of monolithic epoxy have been studied and correlated with mechanical properties and surface features of samples before fracture. The topographical features studied include waviness (W<sub>a</sub>), roughness average (R<sub>a</sub>), root mean square value (R<sub>q</sub>), and maximum roughness height (R<sub>max</sub> or R<sub>z</sub>). As surface notches generate triaxial state of stress, therefore, the crack propagation is precipitated resulting in catastrophic failure. Although surfaces can be examined before fracture for any deleterious topographical elements, however, fractured surfaces can reveal finer details about the topography. It is because, as discussed in this article, surfaces with specific topography produce fracture patterns of peculiar aesthetics, and if delved deeper, they can further be used to estimate about the topography of surfaces before fracture. In addition, treating the samples with surfaces of specific topography can help improve the mechanical properties of monolithic epoxy.展开更多
Influence of topographical features on mechanical properties of monolithic epoxy samples has been studied. The topographical features studied include waviness (W<sub>a</sub>), roughness average (R<sub&g...Influence of topographical features on mechanical properties of monolithic epoxy samples has been studied. The topographical features studied include waviness (W<sub>a</sub>), roughness average (R<sub>a</sub>), root mean square value (R<sub>q</sub><sub>)</sub>, and maximum roughness height (R<sub>max</sub> or R<sub>z</sub>). The Rz of as-cast monolithic epoxy samples was 13.93 μm. By treating with velvet cloth, the R<sub>z</sub> value significantly decreased to 2.28 μm. The R<sub>z</sub> value of monolithic epoxy sample treated with abrasive paper 1200P was 4.85 μm which was also lower than that of as-cast monolithic epoxy samples. However, Rz values significantly increased by treating with abrasive papers 320P and 60P and became 20.32 μm and 39.32 μm, respectively. It was interesting to note that although R<sub>a</sub>, W<sub>a</sub>, and R<sub>q</sub>, all increased by treating the monolithic epoxy samples with abrasive paper 1200P, however, R<sub>z</sub> decreased by abrasive paper 1200P. A weight loss of up to 17% was observed in monolithic epoxy samples after the treatment with the abrasive papers. Both V-shaped and U-shaped notches were produced on the surfaces of the samples. The mechanical properties were significantly degraded due to surface notches mainly because of the associated stress concentration effect. The topographical features also influenced the dynamic mechanical properties and fracture mode.展开更多
The stiff and fragile structure of thermosetting polymers, such as epoxy, accomplices the innate cracks to cause fracture and therefore the applications of monolithic epoxy are not ubiquitous. However, it is well esta...The stiff and fragile structure of thermosetting polymers, such as epoxy, accomplices the innate cracks to cause fracture and therefore the applications of monolithic epoxy are not ubiquitous. However, it is well established that when reinforced especially by nano-fillers, its ability to withstand crack propagation is propitiously improved. The crack is either deflected or bifurcated when interacting with strong nano-filler such as Multi-Layer Graphene (MLG). Due to the deflection and bifurcation of cracks, specific fracture patterns are observed. Although these fracture patterns seem aesthetically appealing, however, if delved deeper, they can further be used to estimate the influence of nano-filler on the mechanical properties. Here we show that, by a meticulous examination of topographical features of fractured patterns, various important aspects related to fillers can be approximated such as dispersion state, interfacial interactions, presence of agglomerates, and overall influence of the incorporation of filler on the mechanical properties of nanocomposites.展开更多
Triangular voltage waveform was employed to distinguish the contributions of dielectric permittivity,electric conductivity and domain switching in current-electricfield curves.At the same time,it is shown how those co...Triangular voltage waveform was employed to distinguish the contributions of dielectric permittivity,electric conductivity and domain switching in current-electricfield curves.At the same time,it is shown how those contributions can affect the shape of the electric displacement-electricfield loops(D-E loops).The effects of frequency,temperature and microstructure(point defects,grain size and texture)on the ferroelectric properties of several ferroelectric compositions is reported,including.BaTiO_(3);lead zirconate titanate(PZT);lead-free Na_(0.5)K_(0.5)NbO_(3);perovskite-like layer structured A_(2)B_(2)O_(7)with super high Curie point(T_(c));Aurivillius phase ferroelectric Bi_(3.15)Nd_(0.85)Ti_(3)O_(12);and multiferroic Bi_(0.89)La_(0.05)Tb_(0.06)FeO_(3).This systematic study provides an instructive outline in the measurement of ferroelectric properties and the analysis and interpretation of experimental data.展开更多
文摘Modeling and simulation allow methodical variation of material properties beyond the capacity of experimental methods. The polymers are one of the most commonly used matrices of choice for composites and have found applications in numerous fields. The stiff and fragile structure of monolithic polymers leads to the innate cracks to cause fracture and therefore the engineering applications of monolithic polymers, requiring robust damage tolerance and high fracture toughness, are not ubiquitous. In addition, when “many-parts” cling together to form polymers, a labyrinth of molecules results, which does not offer to electrons and phonons a smooth and continuous passageway. Therefore, the monolithic polymers are bad conductors of heat and electricity. However, it is well established that when polymers are embedded with suitable entities especially nano-fillers, such as metallic oxides, clays, carbon nanotubes, and other carbonaceous materials, their performance is propitiously improved. Among various additives, graphene has recently been employed as nano-filler to enhance mechanical, thermal, electrical, and functional properties of polymers. In this review, advances in the modeling and simulation of grapheme based polymer nanocomposites will be discussed in terms of graphene structure, topographical features, interfacial interactions, dispersion state, aspect ratio, weight fraction, and trade-off between variables and overall performance.
文摘Modeling and simulation allow methodical variation of material properties beyond the capacity of experimental methods. Due to the hexagonal structure of graphene, it is considered as frame-like structure. In the frame, covalent C-C bonds are taken as beams joined together with carbon atoms placed at the joints. Uniaxial beam elements, defined by their cross-sectional area, material properties, and moment of inertia represent the covalent bonds. The parameters of the beam elements are determined by establishing equivalence between structural and computational mechanics. However, the bonds connecting the carbon atoms do not have physical existence as they are a compromise between attractive and repulsive forces. Also, defects at nanoscale make graphene different from frame-like structure. In addition, the topography of graphene makes it non-linear structure and even the axial loading changes to eccentric loading. Here we show that, by using basic statics principles, disparities between graphene and frame-likes structures can be highlighted.
文摘The environmental stress cracking resistance of halloysite nanoclay-polyester nanocomposites was investigated using fracture mechanics approach. The incorporation of halloysite nanoclay was found to improve the environmental stress cracking resistance of the nano-composites. The storage modulus of nano-composites measured by dynamic mechanical analysis increased remarkably as a function of halloysite nanoclay content. At 0.7 wt% nanoclay, the Tg improved from 72°C to 76°C. The fracture toughness increased up to 33% and time to failure improved 155% with the addition of 0.7 wt% of halloysite nanoclay. The maximum microhardness was found 119% higher for the same nano-filler concentration compared to monolithic polyester. The reinforcement with 1 wt% showed lower fracture toughness due to agglomerations of nanoclay which act as flaws. The presence of agglomerates weakened the bond between nano-particles and matrix hence reduces the environmental stress cracking resistance by halloysite nanoclay reinforcement.
文摘The topographical features of fractured tensile, flexural, K<sub>1C</sub>, and impact specimens of monolithic epoxy have been studied and correlated with mechanical properties and surface features of samples before fracture. The topographical features studied include waviness (W<sub>a</sub>), roughness average (R<sub>a</sub>), root mean square value (R<sub>q</sub>), and maximum roughness height (R<sub>max</sub> or R<sub>z</sub>). As surface notches generate triaxial state of stress, therefore, the crack propagation is precipitated resulting in catastrophic failure. Although surfaces can be examined before fracture for any deleterious topographical elements, however, fractured surfaces can reveal finer details about the topography. It is because, as discussed in this article, surfaces with specific topography produce fracture patterns of peculiar aesthetics, and if delved deeper, they can further be used to estimate about the topography of surfaces before fracture. In addition, treating the samples with surfaces of specific topography can help improve the mechanical properties of monolithic epoxy.
文摘Influence of topographical features on mechanical properties of monolithic epoxy samples has been studied. The topographical features studied include waviness (W<sub>a</sub>), roughness average (R<sub>a</sub>), root mean square value (R<sub>q</sub><sub>)</sub>, and maximum roughness height (R<sub>max</sub> or R<sub>z</sub>). The Rz of as-cast monolithic epoxy samples was 13.93 μm. By treating with velvet cloth, the R<sub>z</sub> value significantly decreased to 2.28 μm. The R<sub>z</sub> value of monolithic epoxy sample treated with abrasive paper 1200P was 4.85 μm which was also lower than that of as-cast monolithic epoxy samples. However, Rz values significantly increased by treating with abrasive papers 320P and 60P and became 20.32 μm and 39.32 μm, respectively. It was interesting to note that although R<sub>a</sub>, W<sub>a</sub>, and R<sub>q</sub>, all increased by treating the monolithic epoxy samples with abrasive paper 1200P, however, R<sub>z</sub> decreased by abrasive paper 1200P. A weight loss of up to 17% was observed in monolithic epoxy samples after the treatment with the abrasive papers. Both V-shaped and U-shaped notches were produced on the surfaces of the samples. The mechanical properties were significantly degraded due to surface notches mainly because of the associated stress concentration effect. The topographical features also influenced the dynamic mechanical properties and fracture mode.
文摘The stiff and fragile structure of thermosetting polymers, such as epoxy, accomplices the innate cracks to cause fracture and therefore the applications of monolithic epoxy are not ubiquitous. However, it is well established that when reinforced especially by nano-fillers, its ability to withstand crack propagation is propitiously improved. The crack is either deflected or bifurcated when interacting with strong nano-filler such as Multi-Layer Graphene (MLG). Due to the deflection and bifurcation of cracks, specific fracture patterns are observed. Although these fracture patterns seem aesthetically appealing, however, if delved deeper, they can further be used to estimate the influence of nano-filler on the mechanical properties. Here we show that, by a meticulous examination of topographical features of fractured patterns, various important aspects related to fillers can be approximated such as dispersion state, interfacial interactions, presence of agglomerates, and overall influence of the incorporation of filler on the mechanical properties of nanocomposites.
基金This work was supported by the UK Royal Society International Joint Project(2009/R2)Xi'an Jiaotong University international incoming short visits(2008 and 2009).
文摘Triangular voltage waveform was employed to distinguish the contributions of dielectric permittivity,electric conductivity and domain switching in current-electricfield curves.At the same time,it is shown how those contributions can affect the shape of the electric displacement-electricfield loops(D-E loops).The effects of frequency,temperature and microstructure(point defects,grain size and texture)on the ferroelectric properties of several ferroelectric compositions is reported,including.BaTiO_(3);lead zirconate titanate(PZT);lead-free Na_(0.5)K_(0.5)NbO_(3);perovskite-like layer structured A_(2)B_(2)O_(7)with super high Curie point(T_(c));Aurivillius phase ferroelectric Bi_(3.15)Nd_(0.85)Ti_(3)O_(12);and multiferroic Bi_(0.89)La_(0.05)Tb_(0.06)FeO_(3).This systematic study provides an instructive outline in the measurement of ferroelectric properties and the analysis and interpretation of experimental data.
