A New Analytical Approach for Wire Wound Frames Used to Carry the Loads of Pressure Vessel Closures

Abstract

Wirewinding technique is usually applied to increase strength to weight ratio, to improve the fatigue life and prevent rapid failure of structures with high sensitivity. Most of the relations, which are presented for wirewinding analysis, are specially introduced for wirewound pressure vessels. The purpose of this paper is to present a new approach for stress analyzing in wire layers of wirewound frames, which are subjected to tensile forces and used to carry the load from the closures of pressure vessels too. The required wirewinding force will be obtained based on constant effective stress in all layers at maximum applied force. In this work, after reviewing the theoretical background of wirewinding, a new approach called “constant effective stress theoryâ€‌ is presented. In comparison with previous published works, in this paper, the problem has been specially defined for a rectangular frame, the wire mantles have been considered as discrete elements, and Von Mises yield criterion is applied on the model at maximum applied force. The logical steps of this approach are done in four steps. First, the critical points of the wires are obtained. The maximum stress is defined according to Von Mises criterion. Then, tensile stress is obtained in all layers at working condition. In third step, tensile stress is calculated at nonworking condition, and finally, the required wirewinding force is obtained for all layers. The results are compared with Harkegard's theory and have been validated by finite element method. They show that the value of the required tensile stress during wirewinding will be reduced considerably. In addition, by assuming a final small gap at maximum applied force between frame members, yoke, and column, this stress would be reduced more. Furthermore, there is a very good agreement between the results of new approach and finite element method.