Modeling Hydraulically Expanded Tube-to-Tubesheet Joint Based on General Stress-Strain Curves of Tube and Tubesheet Materials

The strength of tube-to-tubesheet joints is crucial for the joint integrity and reliability of the tubular heat exchangers. The joint strength measured by residual contact pressure is affected by several design parameters, such as the yield strength and strain hardening of the tube and tubesheet materials, initial radial clearance between the tube and tubesheet hole, and the magnitude of the expansion. It is very important to determine the expansion pressure and the residual contact pressure in designing and manufacturing tube-to-tubesheet joints by the hydraulic expansion process. In this paper, a general strain-hardening material model and analytic expressions for calculating the expansion pressure and the residual contact pressure, considering the effect of the initial clearance and the material strain hardening, have been derived. The results predicted by the present model have been compared with the results predicted by elastic perfectly plastic model, linear strain-hardening model, and the nonlinear finite element analysis results. The comparison results show that the present analytic expressions can model the effects of strain-hardening of the materials and the clearance well. The models, such as elastic-perfect model, linear strain-hardening model, and power strain-hardening model, are the special cases of the present model. The parameters needed in the present model are determined by curve fitting of the actual tensile stress-strain data of tube and tubesheet materials, respectively.