PSI - Issue 40

I.G. Emel’yanov et al. / Procedia Structural Integrity 40 (2022) 124–128 I. G. Emel’yanov / StructuralIntegrity Procedia 00 (2022) 000 – 000

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Taking into account the experimental data given in Zubchenko (2003), "stress-strain" diagrams ( , ) f T    for a given steel can be approximated by bilinear broken lines with points of the yield point Y  , Y  and ultimate strength ult  , ult  for different temperatures. Influence of a hydrogen-containing medium on the mechanical parameters of the muffle. When assessing the strength of the muffle, it is necessary to take into account the experimental fact that the strength properties of the metal change during hydrogenation. During operation of a structural element, the relationship between stress σ , deformation ε , hydrogen concentration c, element temperature T and operation time t can be represented as ( , , , ) f T c t    . The problem of hydrogen diffusion and determination of the distribution of hydrogen concentration as a function of time for a shell of revolution was considered in Emelyanov and Mironov (2018). Taking into account the small thickness of the shell, let us assume that the hydrogen concentration is the same throughout the thickness. Consequently, the mechanical properties of the shell material, as it is saturated with hydrogen, will change in proportion to the parameter – the hydrogenation time t. Let us use the experimental data for steels, which show that with an increase in the hydrogen concentration, the resistance limit decreases by approximately 20%, Galaktionova (1959). Since the tensile curves for the original steel specimen are approximated by a bilinear broken line, when calculating the operation of the muffle, the values ult  must be reduced by 20%. Structural limit state criterion. The criterion for the strength of structures is usually the condition when the intensity of shear stresses in the shell S reaches the fracture stresses of the sample material 3 ult  , where ult  is the ultimate strength at rupture of the sample material. For our case, we will accept the criterion that the destruction of the structure during operation will occur when, at the most loaded point of the muffle shell, the shear deformation intensity H reaches the fracture deformation for the sample ult  . Therefore, this will be the limiting state for the muffle design. 4. EXAMPLE OF DETERMINING THE LIMIT STATE FOR MUFFLE DESIGN The muffle design is loaded with an internal excess p = 0.037 MPa and a muffle weight of 1100 kg. The calculation was carried out for various temperature regimes of the muffle from T = 20 ° C to T = 800° C. The table shows the values of the intensity of shear stresses and shear strains S and H for the most loaded point of the muffle - the point on the inner surface of the cover close to the connection with the cylindrical shell

Table 1. The values of the intensity of tangential stresses S and shear strains H for the most loaded point of the muffle, depending on the operating temperature T . Temperature S,MPa H 20°С 142 0.00068 300°С 120 0.0014 400°С 92 0.0021 500°С 77 0.0124 600°С 77 0.0142

It should be added that at a temperature of T = 20 ° C all elements of the muffle work in the elastic domain. At a temperature of T = 300 ° C, plastic deformation appears at the most loaded point of the muffle, and 7 approximations are required to achieve an accuracy of  =0.01, Emelyanov and Mironov (2012). At a temperature of T = 400 ° C, 14 approximations are required, at T = 500 ° C and T = 600 ° C, 32 approximations are required. A numerical solution at T = 800 ° С cannot be obtained. From a computational point of view, this can be explained by the fact that during the iterative procedure of linearization of the problem, the intensity of shear deformations H exceeds the fracture deformation for the sample ult  .And it is not possible to provide the specified accuracy of calculations. From the point of view of materials science, this can be explained by the fact that after T = 600 ° C the material begins to creep, and the muffle structure cannot resist the given load. Therefore, the mechanical properties of steel at temperatures above 500 ° C have not been studied , Zubchenko (2003), and it is not recommended to