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Static and dynamic characteristics of an externally pressurized porous annular thrust gas bearing (PATGB), which has a thin restricted surface layer, are investigated by numerical analysis and experiment. In the analysis, it is assumed that the fluid flow obeys Darcy’s law in the porous material, restricted with Darcy’s restrictor (Darcy-Darcy model) or orifice restrictor (Darcy-Orifice model) in the surface layer. From experimental investigation, it is found that the theoretical results calculated by the Darcy-Darcy model agree with the experimental data better than those of the Darcy-Orifice model. Based on the Darcy-Darcy model, the unique relationships among the design parameters, which can provide the maximum damping ratio, were derived as functions of feeding parameter under the conditions of allowable static stiffness and the local minimum dynamic stiffness. Considering the dimensionless mass of the body supported by the bearing, an optimal design method is proposed to maximize the damping ratio at the natural frequency, while maintaining the required stiffness in the low frequency region.

AH36 marine steel processed through high heat-input welding is subjected to microstructural characterization, hydrogen permeation test, internal friction test, and slow strain rate tensile test to reveal its hydrogen diffusion and hydrogen embrittlement failure behaviors. Compared with the base metal, the coarsegrained heat-affected zone (CGHAZ) exhibits a significantly coarsened microstructure and decreased hydrogen trap density, resulting in a high hydrogen diffusion coefficient and short hydrogen permeation time. The presence of hydrogen yields a hydrogen-induced Snoek internal friction peak and promotes the movement of the Snoek-Kê-Köster internal friction peak to the lowtemperature region. In addition, B and Kê peaks, which are not found in the base metal, appear in the CGHAZ. With increasing hydrogen content, the plastic loss and brittle fracture of the AH36 marine steel become increasingly significant, and the hydrogen embrittlement sensitivity of the heat-affected zone increases compared with that of the base metal. The discontinuous yield phenomenon gradually disappears under slow strain rate tension owing to the weak pinning effect of the Cottrell atmosphere on mobile dislocations.

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