Experimental study and analysis on residual strength of ice strengthening structure in heavy icebreakers

Objective A heavy icebreaker may experience a certain degree of permanent deformation in its ice strengthening structure after encountering over-designed ice loads. It is necessary to assess the residual strength of the ice strengthening structure after permanent deformation to ensure navigation safety.

Methods The ice strengthening structure at the midship side of a heavy icebreaker is selected for a model test. A plate frame model is constructed using EH500 steel. High strength gypsum powder is used as the main raw material to make the non-refrigerated breakable model ice through mixing and pouring. First, the weak and strong members of the plate frame model are dynamically impacted by the free-fall of the model ice, causing permanent deformation in the test plate frame. Then, a quasi-static bearing test is conducted by loading on the weak members of the permanently deformed plate frame model until plastic collapse occurs, and the residual strength is measured. Finally, the entire dynamic impact test process is simulated using numerical methods to determine the permanent deformation of the specimen. The residual strength of the ice strengthening structure is obtained through the explicit dynamic nonlinear analysis and compared with the experimental results.

Results The experimental and numerical simulation results indicate that under the impact of free-falling model ice at the same height, the maximum permanent deformation of the plate frame specimen is significantly greater when the impact acts on the weak member compared to the strong member, with the experimental and simulated values increasing by 31.49% and 33.11%, respectively. Simultaneously, the residual strength of the ice strengthening structure is reduced when the impact acts on the weak member compared to the strong member, with the experimental and simulated values decreasing by 7.24% and 3.28%, respectively. Furthermore, under both strong and weak member conditions, the error between the experimental values and numerical solutions for the residual strength of the ice strengthening structure is less than 20%, validating the rationality and reliability of the proposed analytical method.

Conclusions The research results reveal the effects of permanent deformation on the residual strength of the strong and weak members of the ice strengthening structure of heavy icebreakers, as well as the failure modes at the limit state. These findings can provide a reference for the structural design and strength assessment of heavy icebreakers.