Fiber Bragg Grating Sensors Subjected to Mechanical and Hygrothermal Load

In recent decades, the aviation industry has embraced the use of composite materials in various aircraft components. However, these materials face challenges in extreme environmental conditions during the operational life of aircraft. One prominent issue contributing to safety concerns is the potential failure of composite components due to the degradation of their mechanical properties caused by moisture absorption. Numerous aviation accidents have been linked to this phenomenon, underscoring the critical need for robust monitoring systems to ensure the continued performance and structural integrity of composite structures. To address this challenge, this research analyzes the effect of hygrothermal load on Fiber Bragg Grating (FBG) sensors. We present a new mathematical formulation that takes into account the contributions of mechanical strain, thermal expansion, and hygroscopic swelling to the normalized Bragg wavelength variation. This formulation, developed by differentiating the Bragg equation and applying compatibility equations through the rules of mixtures, allows for accurate measurement by accounting for humidity-induced deformations and avoiding measurement errors related to moisture absorption.