Squeezing light out of crystals: Triboluminescent sensors

Currently, there are no simple sensing techniques for determining in real-time both the severity and location of structural damage in a composite caused by a dynamic impact event. Materials are known which emit light when they are fractured. This fracture-induced light emission is known as triboluminescence. A triboluminescent material embedded in, or attached on, a composite structure could act as a real-time damage sensor. The occurrence and severity of the damage is given by the intensity of the resulting triboluminescent light. Since the triboluminescent light emission is fracture-initiated, no signal would be generated by a triboluminescent sensor until damage had actually occurred. Hence no false alarms are generated by this type of sensor. An array of triboluminescent sensors may allow real-time damage location monitoring simply by determining the wavelength of the emitted light. We have developed a series of highly efficient triboluminescent materials with sufficient thermal and chemical properties to allow doping into composites. We report a series of proof-of-principle experiments with these materials which strongly support the potential of triboluminescent sensors to monitor in real-time both the magnitude and location of structural damage.