The silica fiber reinforced silica and boron nitride-based composites （SiO2f/SiO2-BN） were prepared firstly via the sol-gel method and then the urea route, and the effects of oxidation treatment on the component, st...The silica fiber reinforced silica and boron nitride-based composites （SiO2f/SiO2-BN） were prepared firstly via the sol-gel method and then the urea route, and the effects of oxidation treatment on the component, structure, mechanical and dielectric properties of the composites were investigated. The results show that the oxidation treatment at 450 ℃ will not impair the structure of boron nitride, and carbon is the main impurity with the excessive urea. The density of SiO2f/SiO2-BN composites is 1.81 g/cm3, and the flexural strength and elastic modulus are 113.9 MPa and 36.5 GPa, respectively. After oxidation treatment, the density varies to 1.80 g/cm3, and the flexural strength and elastic modulus are decreased to 58.9 MPa and 9.4 GPa, respectively. The mechanical properties of the composites are severely damaged, but they still exhibit a good toughness. The composites show excellent dielectric properties with the dielectric constant and loss tangent being 3.22 and 0.003 9, respectively, which indicates that the oxidation treatment is ineffective to improve the dielectric properties of SiOzf/SiO2-BN composites.展开更多
On the basis of elastic-plastic damage model of cement consolidated soil,the authors took organic contents into reasonable damage variable evolution equation in order to seek relation between the organic contents and ...On the basis of elastic-plastic damage model of cement consolidated soil,the authors took organic contents into reasonable damage variable evolution equation in order to seek relation between the organic contents and parameters in the equation,and established the elastic-plastic damage model of cement consolidated soil considering organic contents.The results show that the parameters change correspondingly with difference of the organic contents.The higher the organic contents are,the less the valves of the parameters such as elastic modulus(E),material parameters(K,n) and damage evolution parameter(ε) become,but the larger strain damage threshold value(εd) of the sample is.Meanwhile,the calculation results obtained from established model are compared with the test data in the condition of common indoors test,which is testified with reliability.展开更多
Under repeated train-induced loads, cement and emulsified asphalt mortar(CA mortar) as a viscoelastic material has a time-dependent deformation, part of which is irreversible. This could lead to debonding between the ...Under repeated train-induced loads, cement and emulsified asphalt mortar(CA mortar) as a viscoelastic material has a time-dependent deformation, part of which is irreversible. This could lead to debonding between the mortar layer and the track slab. Based on the theory of viscoelasticity and the analytical method of the time hardening law(THL), the viscoelastic deformation behavior of CA mortar was studied. Using ABAQUS, we established a solid model of China railway track system(CRTS) Ⅰ prefabricated slab track, with CA mortar at different initial Young’s moduli under cyclic loading corresponding to the influence of actual train loads. The results reveal that the fitted parameters of the THL for CA mortar are suitable for describing its viscoelastic deformation. As the initial Young’s modulus increases, the strain difference before and after cyclic loading gradually decreases, and the displacement difference increases from 0.2 mm to 0.6 mm. The deformation mainly occurs at the end of a mortar layer with longitudinal distribution of about 2.5 times the fasteners’ spacing. It follows that the viscoelastic performance of CA mortar is one of the most important reasons that cause debonding underneath the track slab. Therefore, we suggest that the adverse effects of viscoelastic behavior of CA mortar should be considered when researching such deformation and damage.展开更多
基金Projects(50902150,90916019) supported by the National Natural Science Foundation of ChinaProject (9140C8203040905) supported by the State Key Laboratory Foundation of ChinaProject(S100103) supported by the Graduate Innovation Foundation of National University of Defense Technology,China
文摘The silica fiber reinforced silica and boron nitride-based composites （SiO2f/SiO2-BN） were prepared firstly via the sol-gel method and then the urea route, and the effects of oxidation treatment on the component, structure, mechanical and dielectric properties of the composites were investigated. The results show that the oxidation treatment at 450 ℃ will not impair the structure of boron nitride, and carbon is the main impurity with the excessive urea. The density of SiO2f/SiO2-BN composites is 1.81 g/cm3, and the flexural strength and elastic modulus are 113.9 MPa and 36.5 GPa, respectively. After oxidation treatment, the density varies to 1.80 g/cm3, and the flexural strength and elastic modulus are decreased to 58.9 MPa and 9.4 GPa, respectively. The mechanical properties of the composites are severely damaged, but they still exhibit a good toughness. The composites show excellent dielectric properties with the dielectric constant and loss tangent being 3.22 and 0.003 9, respectively, which indicates that the oxidation treatment is ineffective to improve the dielectric properties of SiOzf/SiO2-BN composites.
基金Supported by Projects of National Natural Science Foundation of China(Nos.40372122, 40672180)Education Reform and Development Fund of Jilin University (No.498020200029)
文摘On the basis of elastic-plastic damage model of cement consolidated soil,the authors took organic contents into reasonable damage variable evolution equation in order to seek relation between the organic contents and parameters in the equation,and established the elastic-plastic damage model of cement consolidated soil considering organic contents.The results show that the parameters change correspondingly with difference of the organic contents.The higher the organic contents are,the less the valves of the parameters such as elastic modulus(E),material parameters(K,n) and damage evolution parameter(ε) become,but the larger strain damage threshold value(εd) of the sample is.Meanwhile,the calculation results obtained from established model are compared with the test data in the condition of common indoors test,which is testified with reliability.
基金Project supported by the National Natural Science Foundation of China(No.51578472)。
文摘Under repeated train-induced loads, cement and emulsified asphalt mortar(CA mortar) as a viscoelastic material has a time-dependent deformation, part of which is irreversible. This could lead to debonding between the mortar layer and the track slab. Based on the theory of viscoelasticity and the analytical method of the time hardening law(THL), the viscoelastic deformation behavior of CA mortar was studied. Using ABAQUS, we established a solid model of China railway track system(CRTS) Ⅰ prefabricated slab track, with CA mortar at different initial Young’s moduli under cyclic loading corresponding to the influence of actual train loads. The results reveal that the fitted parameters of the THL for CA mortar are suitable for describing its viscoelastic deformation. As the initial Young’s modulus increases, the strain difference before and after cyclic loading gradually decreases, and the displacement difference increases from 0.2 mm to 0.6 mm. The deformation mainly occurs at the end of a mortar layer with longitudinal distribution of about 2.5 times the fasteners’ spacing. It follows that the viscoelastic performance of CA mortar is one of the most important reasons that cause debonding underneath the track slab. Therefore, we suggest that the adverse effects of viscoelastic behavior of CA mortar should be considered when researching such deformation and damage.
