복합재 정수압 성형용 SUS316L 용접 멤브레인의 적용 가능성 평가

초록

The fabrication of large-area membranes with sufficient structural integrity, deformation stability, and pressure-tightness is essential for hydrostatic forming of composite structures. In this study, the feasibility of a laser butt-welded SUS316L membrane was evaluated through weld morphology analysis, micro-Vickers hardness measurements, uniaxial tensile tests, biaxial hydraulic bulge tests, and a scaled unit pressurization test. Morphological observations confirmed sound welds with full penetration and no internal porosity. The hardness in the heat-affected zone increased from approximately 180 to 200 HV, indicating localized microstructural changes induced by the welding thermal cycle. In tensile tests, the welded specimens showed a yield strength comparable to that of the base metal, whereas the tensile strength decreased from 572.0 to 546.5 MPa and the elongation decreased from 62.06% to 28.78%. In biaxial hydraulic bulge tests, the welded specimens exhibited burst pressures of 23.14–24.47 MPa, comparable to those of the base metal, 24.32–24.36 MPa, but showed lower major strain and earlier fracture. No leakage or membrane fracture was observed up to 6.5 bar in the scaled unit test. These results demonstrate that the laser butt-welded SUS316L membrane is a feasible candidate for hydrostatic forming of composite structures, provided that local thickness reduction in the weld region is minimized to improve deformation stability and fracture resistance.

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