Luminance change method for strain and matrix cracking monitoring of glass/epoxy composites with EL backlight

Authors have proposed a new damage monitoring system that employs luminance of EL backlight for transparent composites such as glass/epoxy composites. For the transparent composites, damage is usually easily found by visually. In the case of the sealed structures or huge structures, however, the visual inspections are difficult to perform. The previous paper adopts a system using change of luminance of transmitted light for damage monitoring of fabric glass/epoxy composites. When the composite structures are damaged, the damage reduces the luminance of the transmitted light emitted from the backside. The study adopts an electro luminescent device (EL) as the backlight similarly. In the present study, the previously proposed method is newly applied to glass/epoxy composites fabricated from unidirectional prepreg sheet to confirm availability of the method to monitor matrix cracking. Specimens are made from unidirectional plies and cross-ply laminates. Tensile tests are conducted using the specimens fabricated with measuring the luminance change of the EL backlight. In the elastic deformation region, the luminance of the transmitted light changes with the applied strain. After the creation of the matrix cracks, the luminance decreases with the increase of the loading. As a result, the method is confirmed to be available to monitor the matrix cracking for glass/epoxy laminates fabricated from unidirectional prepreg.