Technology development and structural mechanics of composites built of spread tow thin-ply technology

Tese de mestrado integrado. Engenharia Mecânica. Faculdade de Engenharia. Universidade do Porto. 201

Structural Batteries: A Review

Structural power composites stand out as a possible solution to the demands of the modern transportation system of more efficient and eco-friendly vehicles. Recent studies demonstrated the possibility to realize these components endowing high-performance composites with electrochemical properties. The aim of this paper is to present a systematic review of the recent developments on this more and more sensitive topic. Two main technologies will be covered here: (1) the integration of commercially available lithium-ion batteries in composite structures, and (2) the fabrication of carbon fiber-based multifunctional materials. The latter will be deeply analyzed, describing how the fibers and the polymeric matrices can be synergistically combined with ionic salts and cathodic materials to manufacture monolithic structural batteries. The main challenges faced by these emerging research fields are also addressed. Among them, the maximum allowable curing cycle for the embedded configuration and the realization that highly conductive structural electrolytes for the monolithic solution are noteworthy. This work also shows an overview of the multiphysics material models developed for these studies and provides a clue for a possible alternative configuration based on solid-state electrolytes

Effect of tailored fiber deposition in 3D printed composites: application of an anisotropic phase field model

Continuous Fiber 3D printing is a relatively new technology which can allow for tailored reinforcement of critical regions in structural components, i.e., stress concentrations, following principal stress lines. The influence the fiber deposition path has on the mechanical and failure behavior of such components is assessed using an anisotropic phase field model. A comparison with experimental results for notched unidirectional composite plates, available in the literature, demonstrates the ability of the method to produce satisfactory predictions for unidirectional reinforcement paths. The analysis is then extended to Open-Hole and Double Edge-Notched tension coupons of both unidirectional and variable stiffness reinforcement patterns. It is observed that the strength obtained for the components made with a reinforcement pattern that follows the principal stress lines is markedly higher than that for the equivalent unidirectionally reinforced ones. It is highlighted that the improvement in strength deriving from the tailored fiber deposition cannot be deduced solely by the analysis of the stress concentration factor but an analysis taking damage into account is necessary. In addition, the effect of the reinforcement strategy on the size effect was also explored, highlighting how the tailored fiber path leads to an increase in the failure load attainable by the specimens for all the dimensions analyzed

Modeling fracture of multidirectional thin-ply laminates using an anisotropic phase field formulation at the macro-scale

An equivalent single layer approach to model fracture events of multidirectional balanced thin-ply laminates via the use of the Phase Field method is explored. The inherent anisotropic nature of a multidirectional laminate is taken into account through the use of a structural tensor, defined from scaled directional vectors, which can account for the variation in fracture toughness of the laminates in varying directions. The scaling constants are defined using the lay-up of the laminate and the intra-laminar fracture toughness of the lamina, minimizing the number of input parameters required while also alleviating the structural tensor of a pure numerical and geometric meaning. They have a significant effect in the solution, and are here related to materials properties, not only providing a new perspective on their definition but also allowing the reduction of the number of numerical parameters used to calibrate the anisotropic PF model. The numerical implementation of the proposed formulation is performed using a simple and robust thermal analogy in Abaqus by exploiting the use of an anisotropic conductivity matrix that plays the role of the structural tensor in the anisotropic phase field formulation, which reduces the complexity of the simulations. Experimental results, based on open-hole tension and double edge-notched tension, are reproduced via simulation validating the model for size effects and for the response to off-axis loading. Successful prediction of notch size effects in multidirectional composite laminates is achieved by means of an equivalent single layer approach, incl. the off-axis open-hole tension strengths of a directional thin-ply laminate. All numerical strength predictions were well within acceptable errors of the respective experimental values