A unit cell model is applied to study the creep damage behavior after fiber fractures in the fiber-reinforced composites at high temperature. The user subroutine CREEP has been programmed for ABAQUS. The fiber breakag...A unit cell model is applied to study the creep damage behavior after fiber fractures in the fiber-reinforced composites at high temperature. The user subroutine CREEP has been programmed for ABAQUS. The fiber breakage results in a new crack. The results show that the stress concentration factor resulted from the fiber breakage increases with the creep time. The creep damage takes place near the crack, and then grows in the matrix along a certain angle, up to the total failure. The influences of the ratio of modulus of the fiber to the matrix (Ef/Em) on the creep deformation, damage and stress distributions have been studied. With the increasing Ef/Em, the damage in the matrix increases. Analysis on the different ductility of matrix shows that the creep damage of low ductile matrix composites is higher than high ductile matrix composites.展开更多
The universal creep function derived from the kinetic equations is successful in relating the creep (ε) to the aging time (t a), coefficient of retardation time (β), and intrinsic time (t 0). The rel...The universal creep function derived from the kinetic equations is successful in relating the creep (ε) to the aging time (t a), coefficient of retardation time (β), and intrinsic time (t 0). The relation was used to treat the creep experimental data for polystyrene (PS) specimens which were aged at a given temperature and different times (short term) and tested at a certain temperature and different stress levels. Then unified master lines were constructed with the treated data and curves according to the universal equation. The master lines can be used to predict the long term creep behaviour and lifetime by extrapolating to a required ultimate strain. The verifications of results obtained with this method were shown as well.展开更多
The universal creep equation relates creep behavior (ε/ε 0) to aging time (t a), coefficient of retardation time (β), and intrinsic time (t 0). The relation was used to treat the creep experimental ...The universal creep equation relates creep behavior (ε/ε 0) to aging time (t a), coefficient of retardation time (β), and intrinsic time (t 0). The relation was used to treat the creep experimental data for pipe specimens of polypropylene block copolymer (PPC), which were aged for different days (short term) and tested under different stress levels at a certain temperature. Then unified master lines were constructed with the treated data and curves according to the universal equation. The master straight lines can be used for extrapolation to predict the long term creep behavior and lifetime of the pipe materials of PPC in the same way as plate materials.展开更多
The aim of the paper is to discover the general creep mechanisms for the short fiber reinforcement matrix composites (MMCs) under uniaxial stress states and to build a relationship between the macroscopic steady creep...The aim of the paper is to discover the general creep mechanisms for the short fiber reinforcement matrix composites (MMCs) under uniaxial stress states and to build a relationship between the macroscopic steady creep behavior and the material micro geometric parameters. The unit cell models were used to calculate the macroscopic creep behavior with different micro geometric parameters of fibers on different loading directions. The influence of the geometric parameters of the fibers and loading directions on the macroscopic creep behavior had been obtained, and described quantitatively. The matrix/fiber interface had been considered by a third layer, matrix/fiber interlayer, in the unit cells with different creep properties and thickness. Based on the numerical results of the unit cell models, a statistic model had been presented for the plane randomly-distributed-fiber MMCs. The fiber breakage had been taken into account in the statistic model for it starts experimentally early in the creep life. With the distribution of the geometric parameters of the fibers, the results of the statistic model agree well with the experiments. With the statistic model, the influence of the geometric parameters and the breakage of the fibers as well as the properties and thickness of, the interlayer on the macroscopic steady creep rate have been discussed.展开更多
文摘A unit cell model is applied to study the creep damage behavior after fiber fractures in the fiber-reinforced composites at high temperature. The user subroutine CREEP has been programmed for ABAQUS. The fiber breakage results in a new crack. The results show that the stress concentration factor resulted from the fiber breakage increases with the creep time. The creep damage takes place near the crack, and then grows in the matrix along a certain angle, up to the total failure. The influences of the ratio of modulus of the fiber to the matrix (Ef/Em) on the creep deformation, damage and stress distributions have been studied. With the increasing Ef/Em, the damage in the matrix increases. Analysis on the different ductility of matrix shows that the creep damage of low ductile matrix composites is higher than high ductile matrix composites.
文摘The universal creep function derived from the kinetic equations is successful in relating the creep (ε) to the aging time (t a), coefficient of retardation time (β), and intrinsic time (t 0). The relation was used to treat the creep experimental data for polystyrene (PS) specimens which were aged at a given temperature and different times (short term) and tested at a certain temperature and different stress levels. Then unified master lines were constructed with the treated data and curves according to the universal equation. The master lines can be used to predict the long term creep behaviour and lifetime by extrapolating to a required ultimate strain. The verifications of results obtained with this method were shown as well.
文摘The universal creep equation relates creep behavior (ε/ε 0) to aging time (t a), coefficient of retardation time (β), and intrinsic time (t 0). The relation was used to treat the creep experimental data for pipe specimens of polypropylene block copolymer (PPC), which were aged for different days (short term) and tested under different stress levels at a certain temperature. Then unified master lines were constructed with the treated data and curves according to the universal equation. The master straight lines can be used for extrapolation to predict the long term creep behavior and lifetime of the pipe materials of PPC in the same way as plate materials.
文摘The aim of the paper is to discover the general creep mechanisms for the short fiber reinforcement matrix composites (MMCs) under uniaxial stress states and to build a relationship between the macroscopic steady creep behavior and the material micro geometric parameters. The unit cell models were used to calculate the macroscopic creep behavior with different micro geometric parameters of fibers on different loading directions. The influence of the geometric parameters of the fibers and loading directions on the macroscopic creep behavior had been obtained, and described quantitatively. The matrix/fiber interface had been considered by a third layer, matrix/fiber interlayer, in the unit cells with different creep properties and thickness. Based on the numerical results of the unit cell models, a statistic model had been presented for the plane randomly-distributed-fiber MMCs. The fiber breakage had been taken into account in the statistic model for it starts experimentally early in the creep life. With the distribution of the geometric parameters of the fibers, the results of the statistic model agree well with the experiments. With the statistic model, the influence of the geometric parameters and the breakage of the fibers as well as the properties and thickness of, the interlayer on the macroscopic steady creep rate have been discussed.
