Research on Two-Step Hydro-Bulge Forming of Ellipsoidal Shell with Larger Axis Length Ratio

The two-step hydro-bulge forming technique was proposed to manufacture the ellipsoidal shell with the length ratio of the long axis to the short axis larger than 1.4. A central tube was introduced into the first step of the hydro-bulge forming process to constrain the over growth of the short axis during bulging,and then the central tube was replaced with two polar plates in the second step of the hydro-bulge forming process to manufacture an integral ellipsoidal shell. It is shown that the central tube restricts the growth of the short axis and simultaneously reduces the shrunk tendency of the long axis. The wrinkling occurs due to the latitudinal compressive stress at the equator at the early stage of hydro-bulge forming. However,with the increase of internal pressure,the compressive stress areas gradually decrease and finally the tensile latitudinal stress occupies approximately the whole shell,thus the wrinkles are eliminated. A sound ellipsoidal shell with the axis length ratio of 1.8 is obtained after two-step hydro bulging.

Stress Analysis of Ellipsoidal Shell with Inner Guide Structure

In order to overcome stress concentration and increase fatigue life of ellipsoidal shells with inner guide structure,the stress analysis for strength check is very important. Owing to the main sectional profile with ellipsoidal shape,the stress distribution for perfect ellipsoidal shell is firstly conducted based on the theoretical calculation and strain gauges measurement. The experiment results show that the stresses increase gradually from pole region to equatorial plane,but still within elastic range. Secondly,strain gauge measurement for ellipsoidal shells with inner guide structure is conducted. The results show that stresses are concentrated at the vicinity of bottom plate and beyond elastic range,so the structural redesign is needed. Finally based on the analysis mentioned above,a redesigned structure with local thickening is proposed. Experimental research shows that the stress varies more even after structural redesign and within allowable range. Numerical simulation shows that both the deformation and fatigue life after redesign are acceptable.

Full Discretization Scheme for the Dynamics of Elliptic Membrane Shell Model

In this study,the dynamics of elliptic membrane shell model has been proposed and discussed numerically for the first time.Firstly,we show that the solution of this model exists and is unique.Secondly,we consider spatial and time discretizations of the time-dependent elliptic membrane shell by finite element method and Newmark scheme,respectively.Then,the corresponding existence,uniqueness,stability,convergence and a priori error estimate are given.Finally,we present numerical results involving a portion of an ellipsoidal shell and a portion of a spherical shell to verify the efficiency and convergence of the numerical scheme.