In the application of sandwich composite materials in ship structures, to ensure the structural strength characteristics, bolt connections are usually used between the sandwich composite structure and steel main hull. However, due to local stress concentration around the holes and the boundary effects at the connection locations, the bolt connection position is often becomes the most critical area of the structure, necessitating strength and fatigue assessments.

For a full-scale steel-sandwich composite panel structure, the strength characteristics of the plate frame under a 0.1 MPa uniform load are studied using experimental and finite element methods. The accuracy of the finite element method is then verified by comparing its results with those from the experimental method. Subsequently, based on the finite element method, fatigue tests for two equivalent bolted joints are designed through structural stress equivalence, and the fatigue life of the steel-sandwich composite structure is evaluated and verified.

It is determined that the fatigue life of the panel structure under the design load meets the design requirement of 5 million cycles.

Regarding the fatigue problem of large bolted connections, equivalent joints can be designed for fatigue testing, and load equivalence can be achieved through structural stress equivalence.

To study the mechanical behavior of aluminum alloy sheets for ships under low-speed impact load, horizontal low-speed impact dynamic response tests are conducted on 5059-H116 aluminum alloy plates.

Based on the impact tests, the damage and dynamic response of test plates under different impact speeds and masses are compared. Based on a mixed hardening plastic model, a low-speed impact numerical model is established to numerically simulate the failure process under different impact velocities. The finite element method is used to analyze the influence of specimen size, impact position and impact head shape on critical failure energy, and a modified empirical formula for critical failure energy is proposed.

The results indicate that with the increase in impact velocity, the critical failure energy of the test plate increases correspondingly, but the increase is very small. Under the same impact energy, different impact masses have no effect on the critical failure energy of aluminum alloy sheets. The sensitivity of critical failure energy on the aspect ratio of the test plate is very small. The critical failure energy of blunt impact test plates with the same cross-sectional area can be considered equivalent.

The results of this study can provide references for research on the low-speed impact mechanical behavior and load-bearing capacity of aluminum alloy sheets.