| The tube-to-tubesheet joints in the shell-tube heat exchangers are usually made by expanding the tube into the tubesheet. Tube rolling is the most popular form of expansion. However, uniform pressure expansion has been often assumed in the studies of the joint strength. The joint strength is influenced by many factors such as the method of attachment, material properties, geometry and dimensions. To simplify the analysis, researchers have assumed zero initial radial clearance and elastic-perfectly-plastic material in the study of the joint strength.; In this thesis, finite element analysis is conducted on axisymmetric, plane stress and plane strain models to investigate the effect of initial radial clearance and tube strain hardening on the residual contact pressure between the tube and tubesheet hole after expanding the tube by applying uniform pressure. Results show that the radial clearance has a negative effect on the joint strength. The effect becomes more significant with increasing the level of tube strain hardening. A practical equation to calculate the reduction factor due to the initial radial clearance and tube strain hardening, which could be used with the closed-form solution of the residual contact pressure available in the literature, is proposed. Other equations for calculating the tube's inner and outer surfaces radial deformation, which are used to calculate the tube wall reduction and tube thinning, are also proposed. The results obtained from the finite element analysis are compared with the experimentally measured results, which were conducted on roller-expanded tubes into a nine holes square block. Because of the low level of tube strain hardening, experimental results show that the joint strength seems to be unaffected by the initial radial clearance. |
