Fluorescence stress probing enhanced crack detection and quantification in ancient Chinese murals for deterioration mechanism analysis

Ancient Chinese murals are precious cultural heritage and vulnerable to structural defects like cracking and delamination, which severely impact their preservation. To address early damage detection and deepen mechanistic insights, this study applies fluorescence stress-sensing technology using mechanochromic 1,1,2,2-tetrakis(4-nitrophenyl)ethene (TPE-4N) coatings on laboratory mock-ups. Under UV light, microcracks (tens of microns) were visualized, quantified, and monitored via photographic analysis. Environmental aging tests revealed distinct defect patterns including failure within pigment layer (cracking) and interlayer debonding (cleavage, cupping, and lifting) with crack propagation rates quantitatively analyzed. Elevated adhesive concentrations and humidity variations exacerbated defects and influenced pigment layer failure modes due to the combined effects of pigment layer strength, interlayer bonding, and stress. Furthermore, crack-propagation dynamics in most samples exhibited three characteristic phases: induction, stable development, and saturation, underscoring the necessity for fatigue monitoring in cultural relic conservation to prevent sudden failure.