Fracture diagram for stiffened panel and computer based approach for structural life prediction

Abstract

Over the past few decades the aircraft industry has devoted considerable effort incorporating fracture control procedures in the design of their structures. One of the problems confronting aircraft designers is the modeling of the ductility effect into their fracture analysis. The first part of this dissertation presents a new analytical method for predicting the fracture of a stiffened panel containing an existing crack. Ductility of the panel is taken into account through the use of a strip yield plastic model at each crack tip. The results take the form of fracture diagrams which can be used to evaluate causes for panel failure ranging from linear elastic fracture to net section yielding. The second part of the dissertation is related to the formulation and development of the framework for a general purpose structural life prediction computer code and associated data base. The present philosophy behind this code includes its modular structure, which facilitates the ease of adding both existing crack growth models and new fracture theory as it evolves. Models for crack initiation, fatigue propagation, and catastrophic fast fracture are discussed as they are treated in the code. Finally, the data storage of known mechanics solution and materials properties for quantitative life estimates is explained.