Non-destructive assessment of strain and mechanical fatigue in neat and glass fibre-reinforced epoxy via NIR spectroscopy

In this study, changes in the near-infrared (NIR) spectrum in neat epoxy and glass fibre-reinforced plastic under tensile stress and cyclic fatigue loading are investigated. Specimens were fabricated using resin transfer moulding. During mechanical testing, NIR spectra were collected at regular intervals, enabling monitoring of characteristic absorption bands. Results demonstrate that both material systems show measurable and reproducible shifts in the wavenumber of the absorbed light in specific NIR bands as a function of applied mechanical load. These shifts closely track the progression of damage accumulation, particularly in the context of mechanical fatigue. Overall, the findings underscore the potential of NIR spectroscopy as a powerful, non-destructive, in-situ monitoring tool for assessing the integrity and damage evolution of fibre-reinforced plastic under mechanical stress. This approach provides valuable insights for the development of advanced structural damage monitoring systems and contributes to improving the safety and reliability of composite materials in engineering applications. • In situ NIR spectroscopy enables non-destructive monitoring of fatigue damage. • Assessment of the peak shift to measure damage and strain in neat epoxy and GFRP. • Fractographic analysis of failure mechanisms and stiffness degradation in GFRP.