Bolt holes lead to peak stress due to structural discontinuities and stress concentrations

The finite element analysis of the sealed end of the cooler is based on the sealing plate, bolts, gaskets, tube sheets and partial shells, and the take-over of the sealing plate is omitted. Because the temperature difference between the sealed end of the cooler is small, it is mainly subjected to the pressure load. Therefore, the temperature difference stress is not considered in the analysis, and only the strength and sealing reliability of the structure under pressure are analyzed. Due to the symmetry of the model, a 1/4 of the sealed end section is used to establish a three-dimensional finite element model. The plane of symmetry in the yz plane is defined as a plane of symmetry, and the plane of symmetry in the xz plane is defined as a plane of symmetry. The bolts and nuts are all 10-node tetrahedral solid92 units, and the six-level precision is freely meshed. The gaskets are three-dimensional solid45 units and four-level precision scanning mesh. A pretension 179 pretensioning unit is defined on each of the meshed bolts. Then, between the nut and the sealing plate, the sealing plate and the gasket, and the tube plate and the gasket, three contact pairs are defined by the contact 170 target unit and the contact 174 contact unit, respectively, the contact between the bottom surface of the nut and the outer surface of the sealing plate, and the inner surface of the sealing plate. Contact with the gasket and contact of the outer surface of the tubesheet with the gasket.

Strength analysis (1) The VonMiser stress distribution of the tube sheet and part of the shell tube sheet and part of the shell is shown in Fig. 3. The maximum stress is at the corner angle of the side of the gasket, and the stress value is 255.649 MPa. The secondary stress and peak stress are mainly due to the geometrical abrupt changes of the structure, resulting in local stresses due to the coordination of deformation. (2) The VonMiser stress distribution of the sealing plate is shown on the contact surface. Due to the opening of the bolt holes, there is a peak stress due to structural discontinuity and stress concentration, and the nut and the bolt are coupled here, which not only generates primary compressive stress and primary bending stress, but also secondary stress which limits mutual deformation. Since the equivalent stress of each part of the main structure satisfies the strength requirement, the sealed end structure is safe in strength.

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