The effects of fibre/matrix bonding, fabric density, fibre volume fraction and bundle size on microstructure, mechanical properties and failure mechanisms in carbon fibre reinforced composites （plastic and carbon mat...The effects of fibre/matrix bonding, fabric density, fibre volume fraction and bundle size on microstructure, mechanical properties and failure mechanisms in carbon fibre reinforced composites （plastic and carbon matrix） have been investigated. The microstructure of unloaded and cracked samples was studied by optical microscopy and scanning electron microscopy （SEM）, respectively whereas the mechanical behaviour was examined by 3- point bending experiments. Exclusively one type of experimental resole type phenolic resin was applied. A strong fibre/matrix bonding, which is needed for high strength of carbon fibre reinforced plastic （CFRP） materials leads to severe composite damages during the pyrolysis resulting in low strength, brittle failure and a very low utilisation of the fibres strain to failure in C/C composites. Inherent fabric parameters such as an increasing fabric density or bundle size or a reduced fibre volume fraction introduce inhomogenities to the CFRP＇s microstructure. Results are lower strength and stiffness whereas the strain to failure increases or remains unchanged. Toughness is almost not affected. In C/C composites inhomogenities due to a reduced bundle size reduce strain to failure, strength, stiffness and toughness. Vice versa a declining fibre volume fraction leads to exactly the opposite behaviour. Increasing the fabric density （weight per unit area） causes similar effects as in CFRPs.展开更多
Following the natural structure of the nacre,the material studied consists of a multitude of hexagonal tiles that are glued together in an offset manner with a ductile adhesive.This so-called“wood nacre”consists of ...Following the natural structure of the nacre,the material studied consists of a multitude of hexagonal tiles that are glued together in an offset manner with a ductile adhesive.This so-called“wood nacre”consists of macroscopic tiles of birch wood veneer with a thickness of 0.8 mm and a size of 20 or 10 mm in diameter in order to mimic the aragonite tiles and the ductile PUR-adhesive corresponds to the layers of collagen in between.E-modulus(MOE),bending strength(MOR)and impact bending strength of the samples were determined and compared with reference samples of birch laminated wood.The hierarchical layered structure of the tiles does not cause any relevant loss in stiffness.Like nacre,“wood nacre”also shows tough fracture behaviour and a high homogenization effect.However,strain hardening and high fracture toughness of the natural model could not be fully achieved.The reason for this is the insufficient ratio between the strength and stiffness of the veneer layers and the adhesive.By adjusting the size of the tiles,increasing the strength and surface roughness of the veneers,e.g.by densification,and using more ductile adhesives that can be applied in smaller layer thicknesses,it should be possible to better reproduce the natural ratios of nacre and thus achieve a significant improvement in the material properties of“wood nacre”.In addition to the mechanical properties,the high potential of the new material lies in the possibility of producing 3D shell-shaped elements for lightweight wood hybrid construction.展开更多
This study presents the first step of a research project that aims at using a three-dimensional （3D） hybridfinite-discrete element method （FDEM） to investigate the development of an excavation damaged zone（EDZ） ...This study presents the first step of a research project that aims at using a three-dimensional （3D） hybridfinite-discrete element method （FDEM） to investigate the development of an excavation damaged zone（EDZ） around tunnels in a clay shale formation known as Opalinus Clay. The 3D FDEM was first calibratedagainst standard laboratory experiments, including Brazilian disc test and uniaxial compression test. Theeffect of increasing confining pressure on the mechanical response and fracture propagation of the rockwas quantified under triaxial compression tests. Polyaxial （or true triaxial） simulations highlighted theeffect of the intermediate principal stress （s2） on fracture directions in the model： as the intermediateprincipal stress increased, fractures tended to align in the direction parallel to the plane defined by themajor and intermediate principal stresses. The peak strength was also shown to vary with changing s2. 2014 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting byElsevier B.V. All rights reserved.展开更多
文摘The effects of fibre/matrix bonding, fabric density, fibre volume fraction and bundle size on microstructure, mechanical properties and failure mechanisms in carbon fibre reinforced composites （plastic and carbon matrix） have been investigated. The microstructure of unloaded and cracked samples was studied by optical microscopy and scanning electron microscopy （SEM）, respectively whereas the mechanical behaviour was examined by 3- point bending experiments. Exclusively one type of experimental resole type phenolic resin was applied. A strong fibre/matrix bonding, which is needed for high strength of carbon fibre reinforced plastic （CFRP） materials leads to severe composite damages during the pyrolysis resulting in low strength, brittle failure and a very low utilisation of the fibres strain to failure in C/C composites. Inherent fabric parameters such as an increasing fabric density or bundle size or a reduced fibre volume fraction introduce inhomogenities to the CFRP＇s microstructure. Results are lower strength and stiffness whereas the strain to failure increases or remains unchanged. Toughness is almost not affected. In C/C composites inhomogenities due to a reduced bundle size reduce strain to failure, strength, stiffness and toughness. Vice versa a declining fibre volume fraction leads to exactly the opposite behaviour. Increasing the fabric density （weight per unit area） causes similar effects as in CFRPs.
文摘Following the natural structure of the nacre,the material studied consists of a multitude of hexagonal tiles that are glued together in an offset manner with a ductile adhesive.This so-called“wood nacre”consists of macroscopic tiles of birch wood veneer with a thickness of 0.8 mm and a size of 20 or 10 mm in diameter in order to mimic the aragonite tiles and the ductile PUR-adhesive corresponds to the layers of collagen in between.E-modulus(MOE),bending strength(MOR)and impact bending strength of the samples were determined and compared with reference samples of birch laminated wood.The hierarchical layered structure of the tiles does not cause any relevant loss in stiffness.Like nacre,“wood nacre”also shows tough fracture behaviour and a high homogenization effect.However,strain hardening and high fracture toughness of the natural model could not be fully achieved.The reason for this is the insufficient ratio between the strength and stiffness of the veneer layers and the adhesive.By adjusting the size of the tiles,increasing the strength and surface roughness of the veneers,e.g.by densification,and using more ductile adhesives that can be applied in smaller layer thicknesses,it should be possible to better reproduce the natural ratios of nacre and thus achieve a significant improvement in the material properties of“wood nacre”.In addition to the mechanical properties,the high potential of the new material lies in the possibility of producing 3D shell-shaped elements for lightweight wood hybrid construction.
文摘This study presents the first step of a research project that aims at using a three-dimensional （3D） hybridfinite-discrete element method （FDEM） to investigate the development of an excavation damaged zone（EDZ） around tunnels in a clay shale formation known as Opalinus Clay. The 3D FDEM was first calibratedagainst standard laboratory experiments, including Brazilian disc test and uniaxial compression test. Theeffect of increasing confining pressure on the mechanical response and fracture propagation of the rockwas quantified under triaxial compression tests. Polyaxial （or true triaxial） simulations highlighted theeffect of the intermediate principal stress （s2） on fracture directions in the model： as the intermediateprincipal stress increased, fractures tended to align in the direction parallel to the plane defined by themajor and intermediate principal stresses. The peak strength was also shown to vary with changing s2. 2014 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting byElsevier B.V. All rights reserved.
