Study Of Time-dependent Mechanical Behavior Of Stainless Steel Plate-fin Structure Under High Temperature

As key equipment in fourth-generation HTGR, plate-fin heat exchangers were widely used in the integration of high-temperature system due to its high specific surface area and high heat transfer efficiency. However, the safety and reliability of plate-fin heat exchangers operating under high pressure and temperature were dependent on their high-temperature mechanical behavior, which would affect the further application of the other corresponding high technology in nuclear power fields.Due to the restriction of experimental conditions and complexity of analytical calculation, study on the deflection and stress distribution and viscoelastic behavior of the plate-fin structure were limited. The simplified analysis of the elastic-plasticity and creep behavior of plate-fin structures is still in the preliminary stage. In addition, failure location and failure mechanism of plate-fin structure were not completely investigated.Based on the above issues, the main research work and conclusions are summarized as follows:(1) The creep material parameters of316L stainless steel at600℃are obtained by tensile test and creep test, creep constitutive relations and viscoelasticity constitutive model are established.(2) Based on the small deformation thin plate bending theory, analytic expression of the deformation and internal stresses are derived under thermal load. Combined with finite element numerical methods, the viscoelastic behavior of the plate-fin structure is analyzed by using2D and3D modeling. The distributions of viscoelastic deformation and stress and their influences from different loads are obtained.(3) The mechanical constitutive equations for orthogonal anisotropic plate-fin cell are derived by simulating the uniaxial tensile, pure shear and creep models. Along the y-direction the main load applied, equivalent Young’s modulus, yield stress and minimum creep rate of homogenization solid model are obtained with high precision. The results indicate that homogenization method is able to simplify the analysis of plate-fin structure high temperature mechanical behavior effectively.(4) The tensile strength and the correlations between stress and creep rate are obtained by high temperature short-time tensile test and creep tests. By analyzing the location of fracture and facture features, it indicates that the creep rate differential between two different metals will lead to the creep rupture of brazed joints.