چكيده به لاتين
The use of composite materials in the design of structures is expanding. Due to the viscoelastic behavior of the matrix, creep and stress relaxation phenomena are commonly observed in polymeric composite materials even at low temperatures. Therefore, considering the creep phenomenon in the design of composite structures is of great importance. In this study, the creep behavior of polymeric and composite materials was investigated using non-linear 3D material model within a finite element environment. The proposed constitutive model is implemented as a recursive-iterative code using material subroutine (UMAT) of the ABAQUS. Initially, an isotropic polymer material and the corresponding creep response was Investigated. Subsequently, employing a micromechanical approach and based on the concept of RVE, the creep behavior of unidirectional composites, consisting elastic fibers and viscoelastic matrix, was evaluated. At the end, utilizing the macromechanical model of Sawant, the creep response of unidirectional and multidirectional composites has been predicted at various stress and temperature levels. The accuracy of the developed constitutive model to simulate the creep response of polymeric materials was validated by existing empirical test results, showing a maximum error of 3%. In addition, the results obtained from the micromechanical analysis indicate good agreement with the experimental data. It was shown that the macromechanical approach is capable of predicting the creep behavior of composites, yielding acceptable results. As the Prony series and non-linear parameters are defined within a special range of stresses and temperatures, using these data beyond this range would result in considerable errors. In conclusion, the results show that at higher stress levels as well as elevated temperatures, the creep strain rate and the influence of nonlinear parameters on the predicted creep response increase, leading to errors as high as 6%.