Developing new multiscale models for the numerical simulation of Pultruded GFRP Structural Elements

Abstract

Pultruded Fibre-Reinforced Polymers (FRP) are innovative structural elements gaining popularity for various structural applications due to their unique properties, such as magnetic transparency and an excellent strength-to-weight ratio. These materials have been extensively studied through experimental and numerical methods to assess their performance as structural components. Accurately describing the micro- and macro-scale mechanical features of FRP elements necessitates complex computational models to predict their strength and investigate design parameters through numerical simulations.

This research initially reviews the state-of-the-art in numerical modelling of structural fibre-reinforced polymeric elements, particularly pultruded Glass Fibre Reinforced Polymers (GFRP). It highlights their use as load-bearing structural elements and evaluates various numerical methods, including Finite Element Method (FEM), eXtended Finite Element Method (XFEM), Virtual Crack Closure Technique (VCCT), Cohesive Zone Modelling (CZM), Multiscale Reduced Order Modelling (ROM), and Random Lattice Modelling (RLM). Each method's distinctive features, challenges, and capabilities are discussed in detail. The aim is to assess the reliability of these numerical models for simulating FRP structural elements and provide recommendations for future research by discussing 160 references from the literature.

In the next step, the experimental characterization of Pultruded GFRP materials evaluated. These composites exhibit remarkable strength, comparable or even superior to steel, and resistance to environmental effects. However, their strongly orthotropic behaviour and spatial variability in mechanical properties present challenges. Fibre orientation and distribution significantly affect the ultimate strength and stiffness of these materials. This work includes an experimental campaign on GFRP specimens in uniaxial tension and three-point bending, testing coupon specimens with fibre orientations of 0, 15, 45, and 90 degrees to characterize ultimate strength and failure modes. Detailed statistical measures of the strength values are presented, aiming to understand the variability in mechanical properties of commercially available profiles.

In addition, the stiffness parameter was considered to investigate by analytical study comparing experimental results. Despite the promising properties of pultruded GFRP, their relatively low stiffness and strength in the direction orthogonal to the fibres limit their widespread adoption in civil engineering applications. This work investigates the mechanical behaviour of pultruded GFRP beams using analytical methods, presenting experimental results from a small-scale campaign conducted by the researcher. These results validate the analytical model and compare the elastic stiffness concerning fibre orientation, providing insights into the potential and limitations of pultruded GFRP elements in structural applications.

Finally, the last step of study demonstrates the inherent limitations of traditional lattice models and propose a new model to simulate the orthotropic materials` behaviours in different conditions. This section presents an innovative approach by using irregular lattice networks to simulate the elastic behaviour of orthotropic GFRP structural elements by Voronoi Cell Lattice Modelling (VCLM), focusing on different fibre-to-matrix elasticity ratios and fibre to load orientations. The proposed method first estimates the elastic properties for various fibre orientations and verifies the model against standard deformation cases and experimental data. Additionally, it compares numerical predictions to established theories like the Tsai-Hill criterion. Through sensitivity analysis, it explores how fibre-to-matrix ratios and Young’s modulus affect macroscopic Poisson’s ratio, offering new insights into stiffness effects on anisotropic material simulations.