Thermochromic Polymer Film Sensors for Detection of Incipient Thermal Damage in Carbon Fiber–Epoxy Composites

Abstract

Carbon fiber–epoxy composites have become prevalent in the aerospace industry where mechanical properties and light weight are at a premium. The significant non-destructive evaluation challenges of composites require new solutions, especially in detecting early-stage, or incipient, thermal damage. The initial stages of thermal damage are chemical rather than physical, and can cause significant reduction in mechanical properties well before physical damage becomes detectable in ultrasonic testing. Thermochromic fluorescent probe molecules have the potential to sense incipient thermal damage more accurately than traditional inspection methods. We have designed a molecule which transitions from a colorless, non-fluorescent state to a colorful, highly fluorescent state when exposed to temperature–time combinations that can cause damage in composites. Moreover, this molecule can be dispersed in a polymer film and attached to composite parts as a removable sensor. This work presents an evaluation of the sensor performance of this thermochromic film in comparison to ultrasonic C-scan as a method to detect incipient thermal damage in one of the most widely used carbon fiber–epoxy composite systems. Composite samples exposed to varying thermal exposures were used to evaluate the fluorescent thermal sensor films, and the results are compared to the results of ultrasonic imaging and short-beam shear tests for interlaminar shear strength.

Multi‐Stimuli Responsive Thiazolothiazole Viologen‐Containing Poly(2‐Isopropyl‐2‐Oxazoline) and Its Multi‐Modal Thermochromism, Photochromism, Electrochromism, and Solvatofluorochromism Applications

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signals with regenerated and reusable characters have received a great deal of attention recently for their numerous applications in high-tech fields such as sensors, [1] smart windows, [2,3] displays, [4] rewritable copy papers, [5] secret writings, [6] anti-counterfeiting, etc. [7][8][9][10] Among multistimuli responsive materials, crystalline chromic compounds such as spiropyran, [11] azobenzene, [12] diarylethenes, [13] spirooxazine, [14] and viologen, [14] with reversible hue shifts have received a significant lot of interest.

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Blood Pressure Sensors: Materials, Fabrication Methods, Performance Evaluations and Future Perspectives

“…Mechanophore- and mechanochemical-based sensors and probe molecules in the mechanochemistry research area have progressed considerably over the past years [ 448 , 449 , 450 , 451 , 452 , 453 ]. In contrast, thermo- and electrochromic have advanced differently with less attention on thermochromic fluorescence [ 454 ], thermochromic sensors [ 455 ] and electrochromic sensors [ 456 ]. Self-diagnosis and self-reporting, as well as, self-damage sensing that correlates the electrical conductivity of the CNTs or graphene flakes composite with damage severity [ 457 , 458 , 459 ], or utilizes electrical resistance tomography mapping [ 460 ] can be further improved using the unique properties of thermo- and electrochromic polymeric materials.…”