Effects of cyclic hydrostatic pressure on the water absorption of polymer matrix solid buoyancy material

From the perspective of service, the effects of cyclic hydrostatic pressure on the water absorption of polymer-matrix solid buoyancy material (PSBM) are critical for the submarine safety. However, the underlying mechanism has not been fully clarified to date. This work is focused on the performance aging and underlying mechanisms of PSBM under cyclic hydrostatic pressure. To comprehensively exhibit the actual service, a drying process was incorporated after each cycle during the hydrostatic pressure tests. The results show that the water absorption of PSBM increases with the number of uses, and long-term stress relaxation induces continuous internal stress redistribution, which exacerbates local stress concentration and ultimately triggers the initiation of microcracks. Stress relaxation is attributed to such performance degradation. Moreover, a model correlating the number of cycles to water absorption behavior was established, which enables the prediction of PSBM water absorption behavior during cyclic service. These findings are beneficial for improving the safety of submersibles and provide significant insights for the design of buoyancy materials in engineering applications.