The welding process, which accounts for about 60% of the shipbuilding process, inevitably involves weld deformation. Considering this, productivity can be significantly increased if weld deformation can be predicted during the design phase, taking into account the fabrication order. However, the conventional welding deformation prediction method using thermo-elasto-plastic analysis requires a long analysis time, and the welding deformation prediction method using equivalent load analysis has a disadvantage in that the welding residual stress cannot be considered. In this study, an inherent strain chart using a solid-spring model with two-dimensional constraints is proposed to predict the equivalent strain. In addition, the welding deformation prediction method proposed in this study, the equivalent strain method (ESM), was compared with the ship block experimental results (EXP), elasto-plastic analysis (EPA) results, and equivalent load analysis (ELM) results. Through this comparison, it was found that the application of the equivalent strain method made it possible to quickly and accurately predict weld deformation in consideration of the residual stress of the curved double-bottom block used in the shipyard.

In this study, the mechanical performance of melamine-urea-formaldehyde (MUF) resin plywood composed of an orthotropic material, which is used as a structural material in liquefied natural gas (LNG) cargo containment systems (CCSs), is evaluated. With a decrease in temperature, the plywood changes from ductile to brittle under compressive loads; thus, it may fail to distribute the compressive loads caused by sloshing impact as well as lose its stiffness, which helps maintain the shape of the structure. However, only a few studies investigated the mechanical characteristics of MUF resin plywood under compressive loads caused by sloshing impact as well as the crack propagation and change in material features with decreasing temperatures. Therefore, the present study investigated the mechanical performance of MUF plywoods of different thicknesses under different temperatures and grain orientation parameters. The results indicate the mechanical properties of MUF plywood for compression with decreasing temperatures. Furthermore, based on thermomechanical analysis, this study shows that the critical temperature at which the plywood material tends to transition from ductile to brittle behavior is − 110 °C. This finding will help in the design of MUF plywood-based LNG CCSs considering its low-temperature brittleness.

Plywood is a laminated wood material where alternating layers are perpendicular to each other. It is used in a liquefied natural gas (LNG) carrier for an insulation system because it has excellent durability, a light weight, and high stiffness. An LNG cargo containment system (LNG CCS) is subjected to loads from gravity, sloshing impact, hydrostatic pressure, and thermal expansion. Shear forces are applied to an LNG CCS locally by these loads. For these reasons, the materials in an LNG CCS must have good mechanical performance. This study evaluated the shear behavior of plywood. This evaluation was conducted from room temperature (25 °C) to cryogenic temperature (-163 °C), which is the actual operating environment of an LNG storage tank. Based on the plywood used in an LNG storage tank, a shear test was conducted on specimens with thicknesses of 9 mm and 12 mm. Analyses were performed on how the temperature and thickness of the plywood affected the shear strength. Regardless of the thickness, the strength increased as the temperature decreased. The 9 mm thick plywood had greater strength than the 12 mm thick specimen, and this tendency became clearer as the temperature decreased.

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