Catastrophic damage in materials, whether it be in an aerospace, mechanical, or consumer application, often occurs suddenly and without warning, resulting in loss of mechanical properties, complete functionality, or even loss of life. Thus, the ability to observe and quantify the amount of damage sustained by a material before ultimate failure is quite desirable in these applications. We have completed the synthesis, characterization, and validation of multiple mechanophores, which are compounds possessing mechanically sensitive chemical moieties that act as sensors for applied stress or strain. We have developed both cyclobutane-based mechanophores, in the form of crosslinked cinnamate polymers, and cyclooctane-based mechanophores, by the dimerization of anthracene moieties with UV light. For the mechanophores studied, when damage is applied and cracks are formed, there is spontaneous bond cleavage in the cycloalkane rings, resulting in an observable fluorescent signal via the recovery of the monomeric structure. We have successfully incorporated these mechanophores into pure epoxy matrices and glass fiber-reinforced composites. Because the fluorescence is generated along propagating cracks, the exact position of cracks can be detected or the amount of cyclic applied damage from fatigue testing can be observed. The utilization of the anthracene chemistry features a number of advantages compared to the cyclobutane chemistry, including an increase in quantum fluorescence yield, a shift to longer emission wavelengths for naked eye detection, damage detection deep within the matrix, and the possibility for early damage precursor detection. Overall, the application of self-sensing mechanophores into polymer matrix composites has been successful.

Damage precursor detection in polymer matrix composites

249th National Meeting (2015)

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