含气孔体积缺陷薄壁奥氏体不锈钢贮箱极限载荷研究

Limit Load Analysis of Thin-Walled Austenitic Stainless Steel Tanks with Volumetric Pore Defects

摘要

薄壁304奥氏体不锈钢贮箱是低成本火箭研究的关键部件之一，常用于贮存液氢、液氧等低温推进剂，工作时需承受低温及内压的影响，其制造通常采用焊接工艺，该过程极易引入气孔缺陷，显著降低贮箱的承载性能并诱发结构失稳．为此，针对含气孔体积缺陷的 304 奥氏体不锈钢贮箱开展极限载荷的数值模拟研究．对冷轧 10%和 20%的 304 奥氏体不锈钢母材及激光焊接接头进行微观组织观察，结果表明，母材因冷轧产生孪晶与微孔洞，冷轧 20%的母材晶粒细化更显著，焊缝呈现枝晶组织并存在 δ 铁素体与微孔洞，使得其强度弱于母材．通过-180 ℃低温拉伸试验获取焊接接头的真应力-真应变曲线，为后续模拟提供必要的材料参数．基于贮箱的实际结构建立含气孔体积缺陷的有限元模型，系统分析单个球形气孔位置、尺寸以及长条气孔长度对贮箱极限载荷的影响，并采用非线性拟合方法构建气孔参数(位置、尺寸及长度)与极限载荷之间的定量关系模型．研究结果表明：已知材料屈服强度时，可通过关系模型预测任意气孔参数(位置、尺寸及长度)下贮箱的极限载荷；当单个球形气孔位于壁厚中心时，极限载荷最大，随其向两侧表面偏移而逐渐减小；气孔直径增大会导致极限载荷下降，当直径达壁厚 90%时，极限载荷降至无缺陷状态的 60%；长条气孔对贮箱极限载荷的削弱作用显著大于单个球形气孔；长条气孔长度增加会使极限载荷持续下降并最终稳定在无缺陷状态的 50%．研究结果可为含气孔体积缺陷低温贮箱的结构安全评估与工艺优化提供有效参考．

Abstract

Thin-walled 304 austenitic stainless steel tanks are key components of inexpensive launch vehicles. These vessels typically store cryogenic propellants such as liquid hydrogen and oxygen and endure low-temperature conditions and internal pressure during operation. However，common welding processes used in their fabrication are susceptible to the formation of porosity defects. These defects significantly reduce tank load-bearing capacity and can induce structural instability. Therefore，a numerical simulation study was conducted on the limit load of 304 austenitic stainless steel tanks containing volumetric pore defects. The microstructures of 10% and 20% cold-rolled 304 austenitic stainless steel base metal and the corresponding laser-welded joints were first characterized. The results indicated that the base metal contained cold-rolling-induced twins and micro-voids. The 20% cold-rolled base metal showed more significant grain refinement. The corresponding weld zones exhibited a dendritic microstructure characterized by δ ferrite and micro-pores，resulting in reduced tensile strength relative to the base metal. Cryogenic tensile test was conducted at −180 ℃ to obtain the true stress-strain curves of the welded joints，providing necessary material parameters for subsequent simulations. Finite element models incorporating volumetric pore defects were established based on the actual tank structure. The effects of defect positioning，spherical-pore size，and elongated pore length on the tank limit load were systematically analyzed. A nonlinear fitting method was employed to construct a quantitative predictive model relating the pore parameters(location，size，and length)to the limit load. The results showed that given the material yield strength，the limit load for any combination of pore parameters(location，size，and length)could be accurately predicted using this relational model. The maximum limit load was observed when a single spherical pore was positioned at the mid-plane of the wall thickness，with the load-bearing capacity decreasing gradually as the defect shifted toward the internal or external surface. An increase in pore diameter caused a corresponding decrease in the limit load. When the pore diameter reached 90% of the wall thickness，the limit load dropped to 60% of the defect-free capacity. Compared with single spherical pores，elongated pores induced a significantly greater reduction in the limit load. As the elongated pore length increased，the limit load decreased continuously before eventually stabilizing at 50% of the defect-free state. These findings provide valuable insights for the structural-safety assessment and process optimization of cryogenic propellant tanks containing volumetric pore defects.

关键词

304 奥氏体不锈钢贮箱 / 极限载荷 / 焊接气孔 / 气孔体积缺陷

Key words

304 austenitic stainless steel tank / limit load / welding porosity / volumetric pore defect

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基金资助

国家自然科学基金资助项目(U2541269)