Influence of matrix resin mechanical properties on mechanochromic fluorescent damage probe response

A non-destructive inspection (NDI) technique that integrates mechanochromic fluorescent probe molecules into aerospace matrix resins was investigated. This experiment was focused on determining the effect of the matrix resin mechanical properties on the activity of the fluorescent probe molecule. In the first step of this experiment, samples of epoxy (diglycidyl ether of bisphenol A (DGEBA)-diethylenetriamine (DETA)) functionalized with fluorescent probe molecules were fabricated. To change the mechanical properties of the epoxy samples, diglycidyl ether (polypropylene glycol) (DGE(PPG)) was added to the samples incrementally from 0-100 weight percent (wt%). To determine the effect of mechanical deformation on the probe in cured DGEBA/DGE(PPG)-DETA, fluorescence spectra were taken before and after incremental compression of the functionalized epoxy samples. The fluorescence testing revealed that the fluorescence activation increases with increasing compressive strain, strain energy, and stress, with a linear relation between fluorescence activation and strain. Furthermore, the fluorescence testing revealed that the fluorescence activation decreased as the modulus of the sample decreased, with the exception of the neat DGEBA-DETA sample. The fluorescence testing also revealed that, without exception, the fluorescence activation decreased as the glass transition temperature decreased and as the wt% DGE(PPG) increased, with no fluorescence activation for 40 wt% DGE(PPG) and above. Copyright 2013 by Aurora Flight Sciences.