In-situ visualization of hydrostatic-dependent mechanical deformation evolution for underwater acoustic coating using customized X-ray imaging technology

Abstract

Acoustic absorption in underwater coatings decreases with increasing hydrostatic pressure due to pressure-induced morphological changes in embedded air cavities. However, limited experimental characterization and imprecise modeling of cavity deformation under high pressure have hindered both theoretical progress and mechanistic understanding. Here, we use X-ray computed tomography (CT) to measure cavity deformation in situ, establishing a multiscale framework to analyze structural changes over 0–10 MPa. In situ measurements and improved imaging techniques allow accurate tracking of microstructural changes under triaxial stress, revealing patterns of cavity evolution and petal-like deformations caused by edge effects. By combining experiments and simulations, we demonstrate that cavity volume contraction follows a nonlinear power-law dependence on hydrostatic pressure and explain stress-concentration mechanisms at cavity-matrix interfaces. Impedance-tube experiments and numerical modeling show that CT-informed models that account for edge effects outperform simplified models. This work offers technological support and new analytical methods for designing pressure-resistant, low-frequency broadband underwater acoustic coatings.