Abstract
This study develops an engineering prediction model for stress relaxation of polymer composites, allowing the prediction of stress relaxation behaviour under a constant strain, over a range of temperatures. The model is based on the basic assumption that in the stress relaxation process the reversible strain is transformed to irreversible strain continuously. A strain-hardening model is proposed to incorporate nonlinear elastic behaviour, and a creep rate model is used to describe the irreversible deformation in the process. By using stress relaxation data at different temperatures, under different strains, the dependence on temperature and initial strain of the model parameters can be established. The effectiveness of the proposed model is verified and validated using three polymer composite materials. The performance of the model is compared with three commonly used stress relaxation models such as the parallel Maxwell and Prony series models. To ease the use of the proposed model in realistic structural problems, a user subroutine is developed, and the stress relaxation of a plate structure example is demonstrated.
Highlights
This study develops an engineering prediction model for stress relaxation of polymer composites, allowing the prediction of stress relaxation behaviour under a constant strain, over a range of temperatures
Stress relaxation is a common phenomenon in polymer composite materials and the rate of relaxation can be affected by time, temperature, initial strain, environment, and so on [1,2,3,4]
The linear approximation to the nonlinear elasticity can lead to modelling error in predicting the stress relaxation of polymer composites, such an error can be reduced by increasing the number of Maxwell elements in the parallel Maxwell model and the Prony series model
Summary
Stress relaxation is a common phenomenon in polymer composite materials and the rate of relaxation can be affected by time, temperature, initial strain, environment, and so on [1,2,3,4]. [22], the plastic strain rate using Orowan’s equation was adopted for the irreversible component to obtain the stress relaxation model for general crystals. The linear approximation to the nonlinear elasticity can lead to modelling error in predicting the stress relaxation of polymer composites, such an error can be reduced by increasing the number of Maxwell elements in the parallel Maxwell model and the Prony series model. The model can eliminate the need for tuning the number of Maxwell elements in existing parallel Maxwell and Prony series models to meet the required fitting accuracy To this end, a strain-hardening model is adopted, allowing for taking the nonlinear effect into the reversible strain component.
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