PSI - Issue 60

R.P. Pandey et al. / Procedia Structural Integrity 60 (2024) 324–334 R. P. Pandey/ Structural Integrity Procedia 00 (2023) 000 – 000

330

7

same surfaces. Similarly contact has been defined between roller and pressure tube inner surface with coefficient of friction as 0.05 emulating rolling friction.

4.3. Description of roller movement during rolling process

The rollers motion has been defined independently for all the 5 roller with reference to their initial position. The rollers were moved in outward spiral motion in order to reduce the thickness of the pressure tube gradually. The locus of the movement of a typical roller during the rolling process is shown in Fig. 8 and this serves as an input to the FE analysis.

Fig. 8: Actual locus of movement of roller during the rolling process which has been used as input in FE analysis

5. Determination of residual stress and pull-out strength of the joint at different temperatures The residual stresses are developed in the joint after the rolling process due to difference in stiffness of the end-fitting and the pressure tube. It may be noted that the pressure tube undergoes a severe plastic deformation process during rolling in the rolled region. However, the deformation of the end-fitting remains in the elastic region due to large thickness. After the rollers are retrieved, the end-fitting tries to come back to the initial radial position as its diameter has been forces to increase during the rolling process. However, the pressure tube obstructs this contraction and this generates very high magnitude of residual stress in the rolled joint. The typical values of von Mises equivalent stress in the joint after the rolling process (before roller retrieval) can be seen from the contour plot as presented in Fig. 9(a) and the cut-section view in Fig. 9(b).