Multifunctional Biochar-Reinforced Polymer Matrix Composites: Experimental And Numerical Investigation.

The foundation of this study lies in the intriguing engineering practice of material multifunctionality. The control of multiple characteristics of a material allows its use in fields in which several properties are essential to ensure up-to mark performances. To analyse the objective of multifunctionality, in this case declined in the EM behaviour associated with the mechanical one, an experimental campaign of test was developed alongside a numerical investigation. The experimental study is divided into several step, from the production of materials to their mechanical and EM characterization. The tested materials are thermosetting polymer matrix composites reinforced with fillers that belong to two different families: organic (BC) and hybrid (Fe@BC). The choice to use composite materials is motivated by the possibility of easily modelling their characteristics and exploiting the considerable advantages they offer, especially in contexts that require advanced characteristics, such as the aerospace sector. During this phase, materials were produced with various weight loading levels to evaluate the influence of the filler loading and determine the optimal value. An exhaustive mechanical characterization of the materials was performed analysing several aspects including general properties, adhesiveness, hardness, and tribological behaviour together with an analysis of fracture surfaces. EM properties were evaluated investigating both real and complex parameters of permittivity and permeability. Additionally, fillers morphological and compositional characterizations were conducted through EDX analysis, Raman spectroscopy, and FE-SEM micrographs. The mechanical characteristics of the tested composites yielded highly promising results. Notably, materials with hybrid fillers excelled in adhesion tests under normal and shear stress, showing a 176% and 676% improvement, respectively. After the experimental stage, the numerical investigation was run for microscale modelling of the polymer matrix composite reinforced with filler. The primary objective was to create a model reflecting experimental mechanical data, aiming to simulate a bulk material and allow low computational cost of FEA. The first step involved the realization of a model for filler dispersion within the polymer matrix. A random algorithm in MATLAB was developed to simulate the particles behaviour based on stereological parameters. Furthermore, to address particle compenetration issues arising from the random approach, a selective reduction of particle radii was applied using a master-slave approach. In the second stage a CAD model of the filler and matrix was automated using VBA. Afterwards, finite element analysis (FEA) was conducted, starting with modelling phase contact and simulating a basic tensile test on a microscopic level. To limit computational costs, the assumption of infinitely rigid fillers was adopted, justified by the filler stiffness higher than the matrix. This assumption proved accurate as the model replicated the elastic modulus properly. In the analysed case, with 5 wt. % hybrid filler loading, the elastic modulus obtained was identical to experimental data, with a margin of error below 1%.