Contact pressure evaluation at the interface of a shrink-fitted connection in a nuclear reactor head

This work investigates the contact pressure at the interface of a shrink-fitted pipe-to-sphere connection representative of a pressurised water reactor vessel head. In the literature, most related studies rely on numerical approaches based on the finite element method, which enable a detailed investigation of specific configurations. In this paper, an analytical model and a surrogate model are proposed to predict the mean contact pressure over the operating domain using different approaches. These methods are computationally efficient and reveal general behavioural trends. The geometry deviates from the classical plane-ring configuration commonly treated in the shrink-fit literature, and its thermo-mechanical response under operating conditions remains poorly documented. Three complementary approaches are developed: an analytical model based on thick-walled cylinder theory extended to account for the spherical ring geometry, an axisymmetric finite element model, and a surrogate model trained on numerical data. The models are used to predict the evolution of contact pressure and interface stresses under combined temperature and internal pressure. Temperature increases raise the contact pressure due to the larger thermal expansion of the shaft, whereas internal pressure reduces it by pushing further outward the spherical ring than the external surface of the shaft, which may locally induce loss of contact. The three approaches provide consistent trends and magnitudes over the operating domain. The surrogate model accurately reproduces the finite element results and enables rapid evaluation of the contact pressure for arbitrary load cases. These findings highlight the dominant influence of thermo-mechanical loading paths and geometric effects on the behavior of large-scale spherical shrink-fit assemblies. • Internal pressure reduces contact pressure in pipe–head shrink-fits due to spherical head deformation. • Contact loss initiates at the lower edge of the interface. • Friction has limited influence on the mean contact pressure for the studied cases. • Surrogate and analytical models give consistent results and enable fast exploration of operating conditions.