Virtual manufacturing of composite structures with embedded piezoelectric sensors

This thesis focuses on simulating the manufacturing process of composite materials with the integration of piezoelectric sensors, using virtual manufacturing. This methodology allows for the digital reproduction of production steps, enabling a preliminary analysis of the material's behavior under operating conditions and significantly reducing time and costs compared to physical testing. Composite materials, while offering high mechanical performance, are subject to structural defects that can arise during or after manufacturing. The introduction of piezoelectric sensors within the composite matrix represents a strategy for internal material monitoring, both during manufacturing and in operation. However, this integration brings additional challenges related, for example, to interaction with the mold, residual stresses, material compatibility, and non-uniform thermal distribution. The main objective of this thesis is to extend the functionality of the numerical code MUL2 Polito, developed at the "Politecnico di Torino", to simulate the electromechanical behavior of composites with integrated piezoelectric sensors. This involves integrating electromechanical physics into a multiphysics framework, with particular reference to the interaction between mechanical stresses and electric fields, using the Carrera Unified Formulation (CUF) for structural modeling, focusing on one-dimensional models. The work is divided into several phases: an introductory section analyzing composite materials and their manufacturing processes, with a focus on the aerospace sector; a review of the state of the art regarding the use of piezoelectric sensors for structural health monitoring; a theoretical and practical description of the MUL2 Polito code and the CUF; and finally, the implementation of the electromechanical model. To validate the modified code, two test cases were studied: a double-jointed beam and a multilayer beam, comparing the results with analytical solutions and data available in the literature. The behavior of a system composed of a piezoelectric material coupled to an isotropic beam was also analyzed, evaluating its performance as both an actuator and a sensor. Subsequently, the sensor capacitance was calculated in depth, both analytically and through FEM simulations. Finally, the capacitance variation in the integrated sensors was analyzed, first in an isotropic plate with variable elastic modulus and then in a ten-layer laminate composite. This last analysis took into account the changes in the laminate's mechanical properties during the manufacturing process, using reference data from the literature to validate the results.