This study proposes a structural strain test method for investigating the buckling pressure of a composite shell in a high hydrostatic pressure water environment and the effects of different initial defects.

A high hydrostatic pressure test is conducted on a composite shell, and the strain of the structure is measured under 15 MPa hydrostatic pressure using the deep-water 3D-DIC (digital image correlation) method based on a high pressure shield. The results are compared to numerical simulations to confirm the feasibility of the 3D-DIC test system in a high hydrostatic pressure environment and verify the accuracy of the numerical method. Based on the numerical simulation method, research is then conducted on the buckling behavior of the composite shell.

The average error between the experimental results and numerical simulation results is found to be 7.2%. In addition, the ultimate load capacity of the composite shell is found to be in an almost quadratic function relationship to the size of the added geometric defects in different modes, and the average gradient of change in the ultimate load capacity is 1.48-2.12 MPa/mm in the first order mode and 1-4.32 MPa/mm in the third order mode.

3D-DIC test technology allows for the accurate strain measurement of composite shells in high hydrostatic pressure environments. Moreover, in such an environment, geometric defects largely affect the ultimate load capacity of the composite shell, while third-order modes are affected to a greater extent than first-order modes.