The low-temperature fatigue crack propagation rate of 925A steel, as a rudder steel for polar special ships, has a crucial impact on the evaluation of the fatigue strength of polar ships. The purpose of this article is to study the fatigue crack propagation rate of 925A steel under different low-temperature conditions from room temperature (RT) to −60 °C. The material was subjected to fatigue crack propagation tests and stress intensity factor tests. The experimental tests were conducted according to the Chinese Standard of GB/T6398-2017. The results show that as the temperature decreases, the lifespan of 925A increases. Within a certain stress intensity factor, as the temperature decreases, the fatigue crack propagation rate decreases. At −60 °C, it exhibits ductile fracture; within normal polar temperatures, it can be determined that 925A meets the requirements for low-temperature fatigue crack propagation rates in polar regions. However, in some extreme polar temperatures below −60 °C, preventing brittle failure becomes a key focus of fatigue design. Finally, the fatigue crack propagation behavior at the microscale of 925A steel at low temperatures was described using fracture morphology. The experimental data can provide reference for the design of polar ships to further resist low-temperature fatigue and cold brittle fracture.

The anisotropic mechanical properties of selective laser melting (SLM)-processed Ti-6Al-4V (TC4) alloy hinder its deployment in polar marine equipment. This study systematically probes the relationships between laser scanning strategies (unidirectional vs. 67°-rotated scanning between layers), notch orientation (governing loading direction), and cryogenic impact energy of SLM-TC4. Charpy impact tests from −60 °C to 20 °C were performed on V-notched specimens fabricated with distinct scanning strategies and notch orientations (top/side surfaces). The analysis of impact energy data and macro/micro-fractography demonstrates that impact energy declines markedly with decreasing temperature, showing a 25–35% reduction at −60 °C versus 20 °C while exhibiting enhanced data consistency under cryogenic conditions. Notably, specimens fabricated with 67°-rotated scanning between layers achieve higher impact toughness than unidirectionally scanned equivalents. Moreover, for identical scanning strategies, side-notched specimens consistently outperform top-notched specimens, evidencing superior interfacial bonding strength between deposited layers relative to bonding within individual layers. Within individual layers, toughness normal to the laser scan path exceeds that parallel to the path. However, controlling ductile-to-brittle transition behavior and precluding brittle failure are imperative for SLM-TC4 components in polar cryogenic service. This work delivers essential quantitative benchmarks and experimental validation for optimizing SLM processing in critical polar vessel components.

For underwater vehicles navigating in Arctic Sea ice-covered waters, fatigue damage is a crucial issue. Many scholars have conducted low-temperature fatigue analysis on low-temperature materials and substrate platforms for ships, and the results show that low temperature is beneficial for improving the mechanical properties of materials. However, they have mainly focused on low-temperature performance experiments and simulation analysis of standard components of materials, and there are very few fatigue life experimental studies on underwater vehicle mechanical structures. This paper conducts experimental investigations on a scaled model of an underwater vehicle rudder mechanism in a polar environment laboratory. Using a comparative analysis method involving simulations and experiments, the low-temperature fatigue test data of the scaled underwater vehicle rudder mechanism are analyzed, and the quantified analysis between fatigue and different low-temperature loading cycles, as well as the influence of icing on the fatigue life, is explored. It is indicated that the Arctic environment can decrease the fatigue life of the underwater vehicle rudder mechanism by deteriorating its material properties. The paper builds the foundation for the fatigue life of an underwater vehicle rudder mechanism in Arctic low-temperature environments.

This study investigates the sealing performance of marine vent valves in low-temperature environments (−30 °C to −40 °C) via thermo-mechanical coupling analysis. Polytetrafluoroethylene (PTFE) was selected as the sealing material for its excellent cryogenic toughness, corrosion resistance, and cost-effectiveness. The total minimum specific sealing pressure ($q_{total}$) of PTFE, corrected for marine vibrations (15–60 Hz), was 3.702 MPa. Using ANSYS Workbench 2022, finite element simulations of a DN200 globe valve showed that low temperatures caused non-uniform thermal contraction, reducing the gasket-poppet contact width (2.5 mm to 1.75 mm) and maximum specific pressure (16.967 MPa to 13.352 MPa), leading to leakage risks. Optimizing the stem preload to 36,000 N restored effective sealing: the maximum specific pressure rebounded to 16.601 MPa, with no pressure below 3.702 MPa. This research provides a method for evaluating low-temperature sealing performance and supports safe vessel operation in cold waters.

Selective laser melting (SLM) fabricated Ti6Al4V (TC4) has broad application potential, though its mechanical behavior is highly sensitive to processing conditions. However, the coupled response of Young’s modulus, Poisson’s ratio, and impact toughness to SLM process parameters remains insufficiently understood. In this study, laser ultrasonic testing (LUT), Charpy impact testing, fractographic observation, and defect statistical analysis were combined to systematically investigate the effects of laser power, scan speed, and hatch spacing on the mechanical behavior of SLM-fabricated TC4 samples. The results show that the three properties exhibit a similar non-monotonic dependence on process parameters, with an overall parabola-formed trend. The optimized process parameters for Young’s modulus, Poisson’s ratio, and impact toughness were identified as laser powers of 315, 348, and 336 W, scan speeds of 1230, 1277, and 1193 mm/s, and hatch spacings of 77, 82, and 87 μm respectively. The data fitting indicated that impact toughness is the most affected by changes in both laser power, scan speed, and hatch spacing. It was followed by Young’s modulus. And Poisson’s ratio received the least impact. The combined defect, fracture, and microstructural analysis further reveal that both excessively low and excessively high volumetric energy density increase porosity and defect size, as well as reduce the β phase volume fraction and area weighted mean value of the transformed-phase plates’ width, thereby degrading mechanical performance. These results establish a process–defect/microstructure–property relationship for SLM TC4 and provide useful guidance for the optimization of mechanical performance in additively manufactured titanium alloy components.

For underwater vehicles navigating in Arctic Sea ice-covered waters, fatigue damage is a crucial issue. Many scholars have conducted low-temperature fatigue analysis on low-temperature ma-terials and substrate platforms for ships, and the results show that low-temperature is beneficial for improving the mechanical properties of materials. However, they mainly focus on low-temperature performance experiments and simulation analysis of standard components of materials, and there are very few fatigue life experimental studies on underwater vehicle me-chanical structures. This paper conducts experimental investigations on a scaled model of an underwater vehicle rudder mechanism in a polar environment laboratory. Using a comparative analysis method involving simulations and experiments, the low-temperature fatigue test data of the scaled underwater vehicle rudder mechanism are analyzed, and the quantified analysis be-tween fatigue and different low-temperature loading cycles, as well as the influence of icing on the fatigue life, is explored. It is indicated that the arctic environment can decrease the fatigue life of the underwater vehicle rudder mechanism by deteriorating its material properties. The paper builds the foundation for the fatigue life of an underwater vehicle rudder mechanism in arctic low-temperature environments.