Analysis of microcrack formation mechanism in mural cultural relics based on digital holography of large field of view and molecular dynamics simulation

Ancient mural relics in China are facing various erosive deteriorations, with surface and subsurface microcracks formed by internal and external factors being the primary origin. Therefore, the non-destructive detection, formation mechanism, and degradation trend analysis of microcracks are crucial in the restoration and preservation of ancient mural relics. To comprehend the growth process of mural cracks correctly, a digital holographic deformation detect system of large field of view (FOV) for in-situ detection of large murals was established. Combined with Gaussian 1σ criterion and histogram segmentation method, quantifiable three-dimensional distribution of microcrack structures can be obtained. According to the structure of defective mural, microscopic molecular dynamics model of the material particles and voids of the defective micro-nano layer in the mural was established to analyse the expansion mechanism and degradation mechanism of mural microcracks. Results indicate that the system can achieve three-dimensional characterization of elongated microcracks with extensive ranges. Molecular dynamics simulations reveal that temperature cycle affects stress distribution, leading to the fracture and recombination of atomic bonds. The stress reaching threshold partly triggers secondary fracture of dislocations, serving as the root cause of sub-crack formation. This suggests that the temperature of environment influence the expansion speed, trend, and direction of microcracks, consistent with the macroscopic evolution trend of pathological cracks. This study, integrating digital holography of large FOV with molecular dynamics simulation, provides a new reference for the study of the formation mechanism of ancient mural microcrack damage and the formulation of cultural heritage protection strategies.