17 Jul Doctoral thesis on high-volume manufacturing of advanced composite parts.
On June 14, 2024, Ivan Ruiz Cozar defended his PhD thesis entitled “Development of constitutive models for the accurate simulation of advanced polymer-based composites under complex loading states” at the University of Girona. His research was supervised by Dr. Pere Maimí Vert and Dr.Emilio V. González Juan from University of Girona, and Dr. Fermin E. Otero Gruer from the Polytechnic University of Catalonia.
In his thesis, Ivan Ruiz Cozar developed a new constitutive model to predict the plastic deformation and fracture of fibre-reinforced polymers (FRPs) under quasi-static conditions. He proposed a new plastic yield function and a new non-associative flow rule to properly define the evolution of the plastic strains. The proposed model was developed under the continuum damage mechanics and the thermodynamics of irreversible process framework. The damage evolution laws were defined to account for the failure mechanisms on both longitudinal and transverse directions. The model predicts various failure mechanisms in FRPs including fibre breakage, fibre pull-out, fibre kinking, and matrix cracking.
Extensive numerical-experimental comparisons were conducted to demonstrate the predictive capabilities of the proposed constitutive models to forecast the mechanical behaviour of FRPs. Additionally, guidelines for calibrating the model input parameters were provided. Moreover, a new methodology to experimentally measuring the transverse Poisson’s ratio was also proposed. This method was applied to measure the elastic transverse Poisson’s ration, but also to measure it in the plastic region, of a carbon fibre thermoplastic polymer-based composite material.
The constitutive model was extended to account for the viscous effects due to high loading rates. The generalized Maxwell model was employed to predict the viscoelastic response under dynamic loading conditions. An overstress model was used to account for the viscoplastic strains of CFRPs. In addition, a new viscodamage model was proposed to account for the onset of damage as well as its propagation under different loading rates. A numerical-experimental comparison of off-axis compressive tests at different loading rates was also carried out to demonstrate the ability of the viscous constitutive model to predict the mechanical response of CFRP laminates. The comparison of the dynamic tests showed good agreement in the viscoelastic, viscoplastic, and viscodamage regions.
This thesis was supported by the predoctoral Grant 2019FI_B_01117 from the Catalan government and conducted within the framework of VITAL project. The work also received funding from the Clean Sky 2 Joint Undertaking (JU) under grant agreements No. 864723 (TREAL) and No. 886519 (BEDYN). The JU receives support from the European Union’s Horizon 2020 research and innovation programme and the Clean Sky 2 JU members other than the Union.
