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At least 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Reliability analysis of continuous fiber composite laminates

This paper describes two methods, the maximum distortion energy (MDE) and the principle of independent action (PIA), developed for the analysis of the reliability of a single continuous composite lamina. It is shown that, for the typical laminated plate structure, the individual lamina reliabilities can be combined in order to produce the upper and the lower bounds of reliability for the laminate, similar in nature to the bounds on properties produced from variational elastic methods. These limits were derived for both the interactive and the model failure considerations. Analytical expressions were also derived for the sensitivity of the reliability limits with respect to changes in the Weibull parameters and in loading conditions.

Thomas, David J.↗
NASA NTRS1990

Scaling of fiber composite structures

Structural scaling is being investigated using graphite/epoxy Z-section stiffeners loaded in compression. Sections of various web, flange and web-to-flange corner radii dimensions are being considered. Initial local buckling loads and modes have been determined analytically, numerically and by experiment. A normalizing parameter has been developed for initial buckling data. Postbuckling behavior has been evaluated numerically and experimentally. The nature of the load redistribution following buckling is a key factor in relating the response of the various section sizes. Additional experiments and the development of scaling parameters for postbuckling and crippling are underway.

Wieland, Todd M.↗
NASA NTRS1992

Thermostructural tailoring of fiber composite structures

A significant area of interest in design of complex structures involves the study of multidisciplined problems. The coordination of several different intricate areas of study to obtain a particular design of a structure is a new and pressing area of research. In the past, each discipline would perform its task consecutively using the appropriate inputs from the other disciplines. This process usually required several time-consuming iterations to obtain a satisfactory design. The alternative pursued here is combining various participating disciplines and specified design requirements into a formal structural computer code. The main focus of this research is to develop a multidiscipline structural tailoring method for select composite structures and to demonstrate its application to specific areas. The development of an integrated computer program involves the coupling of three independent computer programs using an excutive module. This module will be the foundation for integrating a structural optimizer, a composites analyzer and a thermal analyzer. With the completion of the executive module, the first step was taken toward the evolution of multidiscipline software in the field of composite mechanics. Through the use of an array of cases involving a variety of objective functions/constraints and thermal-mechanical load conditions, it became evident that simple composite structures can be designed to a combined loads environment.

Acquaviva, Thomas H.↗
NASA NTRS1992

Intercalated graphite fiber composites as EMI shields in aerospace structures

The requirements for electromagnetic interference (EMI) shielding in aerospace structures are more complicated than those for ground structures because of their weight limitations. As a result, the best EMI shielding materials must combine low density, high strength, and high elastic modulus with high shielding ability. EMI shielding characteristics were calculated for shields formed from pristine and intercalated graphite fiber/epoxy composites and compare to preliminary experimental results for these materials and to the characteristics of shields made from aluminum. Calculations indicate that effective EMI shields could be fabricated from intercalated graphite composites which would have less than 12 percent of the mass of conventional aluminum shields, based on mechanical properties and shielding characteristics alone.

Gaier, James R.↗
NASA NTRS1996

Progressive Fracture of Fiber Composite Builtup Structures

The damage progression and fracture of builtup composite structures was evaluated by using computational simulation to examine the behavior and response of a stiffened composite (0 +/- 45/90)(sub s6) laminate panel subjected to a bending load. The damage initiation, growth, accumulation, progression, and propagation to structural collapse were simulated. An integrated computer code (CODSTRAN) was augmented for the simulation of the progressive damage and fracture of builtup composite structures under mechanical loading. Results showed that damage initiation and progression have a significant effect on the structural response. Also investigated was the influence of different types of bending load on the damage initiation, propagation, and final fracture of the builtup composite panel.

Gotsis, Pascal K.↗
NASA NTRS1997

Progressive Fracture of Fiber Composite Build-Up Structures

Damage progression and fracture of built-up composite structures is evaluated by using computational simulation. The objective is to examine the behavior and response of a stiffened composite (0/ +/- 45/90)(sub s6) laminate panel by simulating the damage initiation, growth, accumulation, progression and propagation to structural collapse. An integrated computer code, CODSTRAN, was augmented for the simulation of the progressive damage and fracture of built-up composite structures under mechanical loading. Results show that damage initiation and progression have significant effect on the structural response. Influence of the type of loading is investigated on the damage initiation, propagation and final fracture of the build-up composite panel.

Gotsis, Pascal K.↗
NASA NTRS1997

Progressive Fracture of Fiber Composite Build-Up Structures

Damage progression and fracture of built-up composite structures is evaluated by using computational simulation. The objective is to examine the behavior and response of a stiffened composite (0 +/-45/90)(sub s6) laminate panel by simulating the damage initiation, growth, accumulation, progression and propagation to structural collapse. An integrated computer code CODSTRAN was augmented for the simulation of the progressive damage and fracture of built-up composite structures under mechanical loading. Results show that damage initiation and progression to have significant effect on the structural response. Influence of the type of loading is investigated on the damage initiation, propagation and final fracture of the build-up composite panel.

Minnetyan, Levon↗
NASA NTRS2006

Testing of Carbon Fiber Composite Overwrapped Pressure Vessel Stress-Rupture Lifetime

This paper contains summaries of testing procedures and analysis of stress rupture life testing for two stress rupture test programs, one for Kevlar COPVs performed at Lawrence Livermore National Laboratory, and the other a joint study between NASA JSC White Sands Test Facility and the Jet Propulsion Laboratory. These will be discussed in detail including test setup and issues encountered during testing. Lessons learned from testing in these two programs will be discussed.

lightweight propellant tanks↗