Non-linear analysis methods were adapted and incorporated in a finite element based DIAL code. These methods are necessary to evaluate the global response of a stiffened structure under combined in-plane and out-of-plane loading. These methods include the Arc Length method and target point analysis procedure. A new interface material model was implemented that can model elastic-plastic behavior of the bond adhesive. Direct application of this method is in skin/stiffener interface failure assessment. Addition of the AML (angle minus longitudinal or load) failure procedure and Hasin's failure criteria provides added capability in the failure predictions. Interactive Stiffened Panel Analysis modules were developed as interactive pre-and post-processors. Each module provides the means of performing self-initiated finite elements based analysis of primary structures such as a flat or curved stiffened panel; a corrugated flat sandwich panel; and a curved geodesic fuselage panel. This module brings finite element analysis into the design of composite structures without the requirement for the user to know much about the techniques and procedures needed to actually perform a finite element analysis from scratch. An interactive finite element code was developed to predict bolted joint strength considering material and geometrical non-linearity. The developed method conducts an ultimate strength failure analysis using a set of material degradation models. Dorris, William J. and Hairr, John W. and Huang, Jui-Tien and Ingram, J. Edward and Shah, Bharat M. Unspecified Center AIRCRAFT STRUCTURES; COMPOSITE STRUCTURES; CURVED PANELS; FAILURE ANALYSIS; FINITE ELEMENT METHOD; FUSELAGES; MODULES; STRUCTURAL DESIGN; TARGETS; ADHESIVES; BOLTED JOINTS; DEGRADATION; JOINTS (JUNCTIONS); NONLINEARITY...

The ISPAN Program (Interactive Stiffened Panel Analysis) is an interactive design tool that is intended to provide a means of performing simple and self contained preliminary analysis of aircraft primary structures made of composite materials. The program combines a series of modules with the finite element code DIAL as its backbone. Four ISPAN Modules were developed and are documented. These include: (1) flat stiffened panel; (2) curved stiffened panel; (3) flat tubular panel; and (4) curved geodesic panel. Users are instructed to input geometric and material properties, load information and types of analysis (linear, bifurcation buckling, or post-buckling) interactively. The program utilizing this information will generate finite element mesh and perform analysis. The output in the form of summary tables of stress or margins of safety, contour plots of loads or stress, and deflected shape plots may be generalized and used to evaluate specific design. Hairr, John W. and Huang, Jui-Ten and Ingram, J. Edward and Shah, Bharat M. Unspecified Center NASA-CR-4449, NAS 1.26:4449, LG92ER0036 NAS1-18888; RTOP 510-02-13-01...

To achieve acceptable performance and long-term durability at elevated temperatures (350 to 600 F) for high-speed transport systems, further improvements of the high-performance matrix materials will be necessary to achieve very long-term (60,000-120,000 service hours) retention of mechanical properties and damage tolerance. This report emphasizes isoimide modification as a complementary technique to semi-interpenetrating polymer networks (SIPN's) to achieve greater processibility, better curing dynamics, and possibly enhanced thermo-mechanical properties in composites. A key result is the demonstration of enhanced processibility of isoimide-modified linear and thermo-setting polyimide systems. Lau, Kreisler S. Y. and Landis, Abraham L. and Chow, Andrea W. and Hamlin, Richard D. Unspecified Center AIRCRAFT STRUCTURES; COMPOSITE STRUCTURES; DURABILITY; HIGH TEMPERATURE ENVIRONMENTS; MATRIX MATERIALS; POLYIMIDES; POLYMER MATRIX COMPOSITES; SERVICE LIFE; TRANSPORT AIRCRAFT; CURING; DAMAGE; LINEAR SYSTEMS; MECHANICAL PROPERTIES; THERMODYNAMICS; TOLERANCES (MECHANICS)...