Experimental Characterization and Numerical Modeling of the Porosity Formation Mechanisms in Thermoplastic Laminates at High Temperature

Subjecting thermoplastic-based laminates to high thermal energy, such as a flame, leads to the gradual deterioration of the matrix, involving solid-state changes and significant fluctuations in thermomechanical properties. Despite these changes and the presence of substantial temperature gradients, the laminates can still bear mechanical loads, even after the matrix has melted. When temperatures exceed the melting point, the primary mechanism of matrix thermal decomposition involves the formation of voids. While these voids weaken the material from a mechanical perspective, they also act as thermal insulators, protecting the matrix on the side facing away from the heat source. To accurately describe the evolution of thermomechanical properties whereas one face of the laminates is exposed to a flame, it is crucial to understand the kinetics of void formation. Experimental investigations revealed that porosity content and swelling are strongly dependent on the time and temperature of thermal exposure. A mesoscopic Finite Element model was thus developed, representing porosities at a structural level. The formation of voids and the associated swelling were simulated using a probabilistic approach, guiding the progressive transformation of elements into voids based on their thermal state.