Composite materials are increasingly used in the aviation industry for various aircraft components due to their lightweight and mechanical performances. However, these materials are susceptible to degradation due to environmental factors such as hot–wet environments and freeze–thaw cycles, which can compromise their performance and safety over time. This study develops an innovative Fiber Bragg Grating (FBG) sensor system capable of not only measuring but also decoupling the simultaneous effects of temperature, humidity and strain. Unlike existing FBG systems, our approach integrates a novel theoretical framework and sensor configuration that accurately isolates these parameters in an epoxy resin material. The system incorporates three FBG sensors: one for temperature, one for temperature and humidity and a third one for all three factors. A theoretical framework based on linear strain superposition and constitutive laws was developed to isolate the individual contributions of each factor. Experimental validation in controlled hygrothermal conditions demonstrated the system’s ability to accurately detect and decouple these effects, enabling the monitoring of moisture absorption and composite degradation over time. The proposed system provides a reliable, lightweight and efficient solution for the long-term monitoring of composite structures in extreme conditions. Additionally, it enhances predictive maintenance by improving the accuracy of Health and Usage Monitoring Systems (HUMSs) and provides a method to correct data inconsistencies in already installed sensors, further extending their operational value.

Composite materials have experienced a significant increase in demand over the past five decades. This growing usage has led to a considerable production of waste, particularly from prepreg scraps, which can account for up to 35% of the purchased material. This paper explores the recycling of prepreg scraps by cutting them into smaller patches and reassembling them into new sheets. The study follows a dual approach: mechanical testing on two different types of samples is presented, along with numerical modeling strategies designed to capture not only the mechanical behavior of the new recycled material but also the failure modes of the samples. The experimental results demonstrate the feasibility of the proposed technique, with samples made from prepreg scraps retaining 85%, 57%, and 78% of the original flexural modulus, strength, and interlaminar strength, respectively. The numerical models not only fit closely to the experimental data but also successfully predict the failure modes of the new material under the two different loading conditions. The primary highlights of this work lie in (i) its innovative approach to recycling prepreg scraps, which is capable of successfully recovering material otherwise sent to landfill; (ii) an ordinated and easy-to-automate recovery process; and (iii) in the modeling strategies of the new material. The study eventually proposes the development of an “equivalent lamina” made of scrap material that can be used in standard lamination processes to manufacture components with load-bearing capabilities.

Composite materials are increasingly used in the aviation industry for various aircraft components due to their lightweight and mechanical performances. However, these materials are susceptible to degradation due to environmental factors such as hot-wet environments and freeze-thaw cycles, which can compromise their performance and safety over time. This study develops an innovative Fiber Bragg Grating (FBG) sensor system designed to simultaneously measure and decouple the effects of temperature, humidity and strain on composite materials, particularly in aerospace applications. The system incorporates three FBG sensors: one for temperature, one for temperature and humidity and a third one for all the three factors. A theoretical framework based on linear strain superposition and constitutive laws was developed to isolate the individual contributions of each factor. Experimental validation in controlled hygrothermal conditions demonstrated the system's ability to accurately detect and decouple these effects, enabling the monitoring of moisture absorption and composite degradation over time. Since SHM/HUMS systems based on optical fibers are widely used for monitoring aerospace structures, to provide real-time data for improving maintenance strategies, the proposed system offers a reliable and efficient solution for long-term structural health monitoring, enhancing predictive maintenance, optimizing operational life and ensuring safety in composite components exposed to extreme environmental conditions in aerospace applications.