This study looks at the feasibility of using structural optimization techniques to address the problem of designing composite fuselage frames for crashworthiness. A key feature of any optimization strategy for increasing structural crashworthiness is a progressive failure analysis. Currently, the most widely used analysis methods for progressive failure of composite structures are considered too expensive computationally for practical optimization in today's computing environment. Developing an efficient analysis method for progressive failure of composite frames is a first step in the optimization for crashworthiness. In the current work a progressive failure analysis for thin-walled open cross-section curved composite frames is developed using a Vlasov type beam theory. A curved thin-walled composite beam theory is developed and a finite element implementation of the beam theory is used for progressive failure analysis. The accuracy and limitations of this analysis method are discussed. A model for progressive failure of the composite fuselage frame is developed from an extension of the laminate progressive failure analysis of Tsai-Wu. Comparisons based on a limited amount of available experimental data are encouraging. The first major failure event is captured by the theory, and the prediction of total energy absorbed follows the trend of the experimental data. It is believed that this accuracy is sufficient for preliminary design and optimization for crashworthiness. This progressive failure analysis is then incorporated into a frame optimization for crashworthiness based on the genetic algorithm method. The optimization methodology is demonstrated analytically to obtain frame designs with substantially increased crashworthlness. Laminate stacking sequence and cross-section shape are design variables for optimization / Ph. D.

In recent years, the use of computer-aided design (CAD) systems for conceptual aircraft design has greatly increased. As a result, new and better methods for creating surface models of aircraft geometry using dimensional parameters are needed. One such method, the Rule-Based Fuselage method, was suggested by Lockheed. The Rule-Based Fuselage method allows an aircraft designer to define complex aircraft fuselage geometry by specifying the fuselage profile and individual parametric cross-sections along the fuselage. This thesis describes the Rule-Based Fuselage method and discusses the implementation of the method in an interactive, object-oriented environment. Also included in this system is the Spine and Cross-Section method for creating arbitrarily shaped aircraft components. The design and implementation of both the Rule-Based Fuselage and Spine and Cross-Section methods are described. The integration of these methods with the conceptual aircraft design code, ACSYNT, is also discussed. / Master of Science