StudyingDecreased Methods ofStress ConcentrationaroundHoles and Openings of Plate and Shell Structures Body

ABSTRACT: Phenomenon of stress concentration and creating it in shells is one of the scientifically and practically critical issues in structural and mechanical engineering. Submarines, vessels, wings and fuselages of airplanes, missiles and rockets, steam boilers and pressure tanks, pipes fittings in pipelines of fluids like gas, steam, water and wastewater are all examples of this phenomenon application in industry. Generally, creating an opening in a cylindrical shell or junction of two shells or even in plates, results in turbulence in stress field and creates stress concentration. The stress may be increased up to many times more than the stress created in body of shell structure (sometimes more than a hundred times) which is important from the standpoint of analysis and design. In this research, while reviewing previous studies and classifying the problems, we present the ruling equation in mixed form by partial derivative in fourth order; then, we present numerical solving approach with finite difference model as well as numerical solving approach with finite element model (with Ansys software). Then, we investigate trends of coefficient changes of stress concentration in plates and shells for different openings diameters and coefficient of curvatures (a dimensionless coefficient containing shell size including radius, thickness, and material as well as opening size and stress concentration depends on it) in single-hole or more mode and different types of openings such as circular, oval, square and rectangular influenced by different loadings to identify the effects of hole and opening on stress concentration phenomenon and its coefficient changes in plates and the shells. In addition, decrease of stress concentration is an important problem in theoretical, industrial, and applicable dimensions. Then, we offer some economical and practical solutions based on analysis and experimental tests. In these structures, one can decrease stress concentration using provisions like change of material, thickness (uniform and step form), using shell of different thickness (according to changes of stress diagram), using an amplification ring or loop around the opening and also inside of it. In this research, we investigate the effects of these parameters and show the results in diagrams and tables. Considering different methods for decrease of stress concentration (regarding limitations of laboratory and economic parameters), we introduce the optimum method for decreasing stress concentration of each shell with every type of openings or holes.