As the structural engineering sector explores innovative materials such as Fibre Reinforced Polymer Composites (FRP), understanding their behavior under static and fatigue is critical. This thesis focuses on developing a numerical method to model the fatigue behavior of FRP composites, reducing the need for extensive experimental testing, resulting in a reduction of costs. Static and dynamic load tests were performed on Glass Fibre Reinforced Polymer (GFRP) coupons extracted from a vacuum-infused sandwich panel deck.

Based on these experimental test results, a numerical model was developed in Abaqus, integrating a VUSDFLD user subroutine to simulate stiffness degradation using a Continuum Damage Mechanics model. The model, which accounts for stress dependent stiffness degradation, was applied to coupons containing imperfections such as dimples from the manufacturing process, and without imperfections.

The research demonstrates promising results for higher load fatigue life predictions, with estimates within 10% of experimental results for both coupons with and without imperfections. However, at lower load levels, the model underestimates fatigue life by 85% for normal coupons and 30% for imperfection ones. These deviations highlight the need for further research, particularly at lower stress levels.

Despite the deviations at lower stress levels, this study presents an advancement in numerically predicting the fatigue life of FRP composites based on stiffness degradation, offering a cost-effective alternative to extensive experimental testing. The numerical model successfully integrates material degradation and manufacturing imperfections, providing valuable insights for the design and evaluation of composite structures subjected to fatigue loads. These findings also highlight the important role that imperfections play in fatigue performance. Future research should focus on optimizing the model, particularly at lower load levels, to enhance accuracy and increase its applicability. In conclusion, this study opens the door to more reliable, efficient, and improved use of FRP in structural applications, particularly in areas where fatigue behavior plays an important role.