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Title: Evaluation of filament-wound Kevlar-49/epoxy fatigue properties. Final report

Abstract

This study was conducted by AiResearch Manufacturing of California for LLL to investigate the long-term properties of Kevlar-49/epoxy composite in a fatigue and elevated temperature environment to provide additional information on the material properties of Kevlar-49/epoxy for use in the design of composite flywheel energy storage units. Testing showed that Kevlar-49 has the unusual property of increasing tensile modulus of elasticity under fatigue loading conditions. The change in modulus was shown to be a function of temperature, induced stress level, and number of fatigue cycles. The average modulus before cycling was 13.28 x 10/sup 6/ psi at ambient temperature versus 11.96 x 10/sup 6/ psi at 150/sup 0/F. Creep or residual strain after 100,000 cycles was 4.1 x 10/sup -4/ in/in (ambient) and 11.7 x 10/sup -4/ in/in (150/sup 0/F) at 140 ksi maximum stress level. At 190 ksi temperature did not show any effects on creep, which was measured to be approximately 28 x 10/sup -4/ in/in. The ultimate strength of 150/sup 0/F rings was 249,000 psi compared to 262,000 psi for ambient temperature.

Publication Date:
Research Org.:
AiResearch Mfg. Co., Torrance, CA (USA)
OSTI Identifier:
5220686
Report Number(s):
UCRL-15264
DOE Contract Number:
W-7405-ENG-48
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 33 ADVANCED PROPULSION SYSTEMS; ARAMIDS; TENSILE PROPERTIES; EPOXIDES; CREEP; ELASTICITY; FATIGUE; FLYWHEEL ENERGY STORAGE; RESIDUAL STRESSES; THERMAL STRESSES; ENERGY STORAGE; MECHANICAL PROPERTIES; ORGANIC COMPOUNDS; ORGANIC OXYGEN COMPOUNDS; PETROCHEMICALS; PETROLEUM PRODUCTS; PLASTICS; STORAGE; STRESSES; 360303* - Composite Materials- Mechanical Properties- (-1987); 330500 - Advanced Propulsion Systems- Flywheel Propulsion

Citation Formats

Not Available. Evaluation of filament-wound Kevlar-49/epoxy fatigue properties. Final report. United States: N. p., 1980. Web.
Not Available. Evaluation of filament-wound Kevlar-49/epoxy fatigue properties. Final report. United States.
Not Available. 1980. "Evaluation of filament-wound Kevlar-49/epoxy fatigue properties. Final report". United States. doi:.
@article{osti_5220686,
title = {Evaluation of filament-wound Kevlar-49/epoxy fatigue properties. Final report},
author = {Not Available},
abstractNote = {This study was conducted by AiResearch Manufacturing of California for LLL to investigate the long-term properties of Kevlar-49/epoxy composite in a fatigue and elevated temperature environment to provide additional information on the material properties of Kevlar-49/epoxy for use in the design of composite flywheel energy storage units. Testing showed that Kevlar-49 has the unusual property of increasing tensile modulus of elasticity under fatigue loading conditions. The change in modulus was shown to be a function of temperature, induced stress level, and number of fatigue cycles. The average modulus before cycling was 13.28 x 10/sup 6/ psi at ambient temperature versus 11.96 x 10/sup 6/ psi at 150/sup 0/F. Creep or residual strain after 100,000 cycles was 4.1 x 10/sup -4/ in/in (ambient) and 11.7 x 10/sup -4/ in/in (150/sup 0/F) at 140 ksi maximum stress level. At 190 ksi temperature did not show any effects on creep, which was measured to be approximately 28 x 10/sup -4/ in/in. The ultimate strength of 150/sup 0/F rings was 249,000 psi compared to 262,000 psi for ambient temperature.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = 1980,
month = 6
}

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  • A study of nondestructive evaluation techniques on spherical filament-wound Kevlar-epoxy test specimens has been performed, and the results are presented. The objectives of the study were (1) to determine the sensitivity of several NDE techniques for the detection of a series of flaw conditions in an enclosed geometry and (2) to determine which flaw conditions affected the mechanical strength of the composite specimens. Seventy spherical specimens were made. Ten of the specimens contained one of seven defect conditions which simulated manufacturing or handling defects. Defect conditions involving delaminations, voids, inclusions, loss of fiber, loss of matrix, reduced fiber modulus, ormore » matrix cracking were readily detectable with one or more inspection techniques. Specimens with fiber tension variation could not be distinguished from standard no-defect specimens with the inspection techniques used in this study. It was found that nominal defects introduced during the manufacturing or handling process do not significantly reduce the ultimate burst strength of the composite material in this geometry; however, impact damage was found to significantly affect burst pressure and location. Acousto-ultrasonic and acoustic emission techniques were found to be predictive of burst pressure for specimens with a normal matrix. Low-epoxy matrix specimens were found to sustain more damage for a given impact energy than specimens containing a normal matrix. 23 refs., 3 tabs.« less
  • The nondestructive evaluation of Kevlar-epoxy filament wound spherical composite pressure vessels is performed through the use of a six axis rotatorially articulated robotic manipulator. Ultrasonic pulse-echo techniques are employed to form C-scan images based upon amplitude and attenuation data gathered by a 68000 based microcomputer system. The data are imaged in planar and three dimensional forms and are further enhanced and analyzed through image processing techniques specifically developed for the analysis of complex composite structures. 25 figs.
  • The results of a study of the acoustic emission (AE) behavior of impact-damaged, spherical, composite test specimens subjected to thermal cycling and biaxial mechanical loading are presented. Seven Kevlar{reg_sign}-epoxy, filament-wound, spherical composite test specimens were subjected to different levels of impact damage. The seven specimens were a subset of a group of 77 specimens made with simulated fabrication-induced flaws. The specimens were subjected to two or three cycles of elevated temperature and then hydraulically pressurized to failure. The pressurization regime consisted of two cycles to different intermediate levels with a hold at each peak pressure level; a final pressurization tomore » failure followed. The thermal and pressurization cycles were carefully designed to stimulate AE production under defined conditions. Both impacted and nonimpacted specimens produced thermo-AE (the term given to emission stimulated by thermal loading), but impacted specimens produced significantly more. Thermo-AE was produced primarily by damaged composite material. Damaged material produced emission as a function of both rising and falling temperature, but the effect was not repeatable. More seriously damaged specimens produced very large quantities of emission. Emission recorded during the static portion of the hydraulic loading cycles varied with load, time, and degree of damage. Static load AE behavior was quantified using a newly developed concept, the event-rate moment, and various correlations with residual strength were attempted. Correlations between residual strength, long-duration events, and even-rate moments were developed with varying degrees of success.« less
  • Increased use of composite materials in enclosed geometries such as cylindrical, spherical, or conical shapes has led to the desire to transfer and further develop the most promising nondestructive evaluation (NDE) techniques used on nonenclosed geometries to enclosed geometries. Known defects were placed within spherical Kevlar-epoxy filament wound test specimens to determine the extent to which they could be detected. These defects included Teflon shim-simulated delaminations, macrosphere-simulated voids, dry-band sets, variable tension, Kevlar 29 fiber, and an alternate high void content winding pattern. Ultrasonic C-scan analysis of Kevlar-epoxy filament wound spheres was performed to determine detectability of normal winding patternsmore » and implanted flaw conditions in the composite using this technique. Ultrasonic waveform analysis was performed in both the time and frequency domains to determine the detectability and locatability of structural flaws within the composite.« less