Fatigue in hybrid composites processed by RTM: influence of hybrid interface in delamination modes I and II

Author(s)

Francisco Maciel Monticeli

• Document type: Doctoral Thesis
• Press: Guaratinguetá. 2021-10-05.
• Institution: Universidade Estadual Paulista (Unesp). Faculdade de Engenharia. Guaratinguetá
• Defense date: 2021-09-13
• Advisor: Maria Odila Hilário Cioffi; Herman Jacobus Cornelis Voorwald

Abstract

Developments in the aeronautical industry have led to the search for materials that meet the mechanical requirements for structural application, aimed at obtaining more efficient structures. Many composites satisfy these requirements, but advanced composites pose challenges, mainly due to the safety coefficient and the empirical and phenomenological models used for mechanical analysis and prediction. Currently, there is a need for novel design approaches to overcome the low interlaminar resistance. The adoption of a carbon/glass fiber hybrid composite is a viable solution, reducing the manufacturing costs and environmental impacts, while allowing an increase in the properties due to synergy between the two reinforcements. The application of hybrid laminates reduces the elastic modulus, due to the contribution of each reinforcement. Also, the absence of interlaminar crack propagation has been observed for laminated composites with more than one type of reinforcement. The aim of this research was to characterize the interlaminar damage progression in hybrid composites (continuous carbon/glass fiber) and develop a crack propagation model, considering the physical fracture mechanisms when more than one type of reinforcement is used. The hybrid laminate showed greater resistance to delamination in modes I and II under quasi-static and cyclic loading compared to non-hybrid laminates. This behavior was confirmed by applying the energy balance method based on physical evidence, in which the high degree of roughness of the hybrid interface was related to greater fracture toughness. The hybrid composite has a rougher surface due to a microscopic change in the crack direction at the carbon fiber/epoxy and glass fiber/epoxy interfaces. Silane coupling agents influence the interaction at the carbon/epoxy/glass interface, enhancing the toughness behavior. The proposed model for the fatigue delamination growth rate of a hybrid composite was developed based on the fiber bridging phenomenon. A more realistic prediction model was obtained by considering the microfracture pattern measurement. The microscopic patterns formed during delamination growth reflect the growth rate at the macroscopic level under cyclic loading. Lastly, the application of the intercalated carbon fiber/glass stacking sequence in a hybrid laminate is a viable approach to increasing the delamination resistance, since the hybrid interface requires more energy for damage propagation, resulting in a longer life under fatigue loading (AU)

• FAPESP's process: 17/10606-4 - Fatigue in hybrid composites processed via RTM: hybrid interface influence in delamination modes I and II
• Grantee: Francisco Maciel Monticeli
• Support Opportunities: Scholarships in Brazil - Doctorate