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Title: Tensile and fatigue strength properties of Kevlar 29 aramid/epoxy unidirectional composites

Abstract

Static and fatigue tensile strength properties of filament wound undirectional Kevlar 29/epoxy, typical of filament wound material used in flywheel rotors, were studied. Machining techniques were developed to minimize fiber fuzzing on edges. The static modulus, normalized to 70% fiber volume fraction is 8.87 x 10/sup 6/ psi. The major Poisson's ratio is 0.37. The static composite tensile strength, normalized to 70% fiber volume fraction is 200 x 10/sup 3/ psi, corresponding to a fiber stress at failure of 286 x 10/sup 3/ psi, which is good for materials having a very high fiber volume fraction. The S-N curve for R = 0.7 was found to be quite flat. Although the techniques used in this program had previously been employed successfully to study the fatigue behavior of Kevlar 29/epoxy and Kevlar 49/epoxy unidirectional materials, we were unable to overcome the persistent problem of cohesive material failure in the tab regions. The apparent reason for this is the very low interlaminar shear strength of the filament wound material. 16 figures.

Authors:
Publication Date:
Research Org.:
Lawrence Livermore National Lab., CA (USA); General Electric Co., Philadelphia, PA (USA). Valley Forge Space Center
OSTI Identifier:
5742716
Report Number(s):
UCRL-15404
ON: DE82006777
DOE Contract Number:
W-7405-ENG-48
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; COMPOSITE MATERIALS; TENSILE PROPERTIES; ARAMIDS; EPOXIDES; FAILURES; FATIGUE; FILAMENTS; POISSON RATIO; MATERIALS; MECHANICAL PROPERTIES; ORGANIC COMPOUNDS; ORGANIC OXYGEN COMPOUNDS; PETROCHEMICALS; PETROLEUM PRODUCTS; PLASTICS; SYNTHETIC MATERIALS; 360303* - Composite Materials- Mechanical Properties- (-1987)

Citation Formats

Zweben, C. Tensile and fatigue strength properties of Kevlar 29 aramid/epoxy unidirectional composites. United States: N. p., 1981. Web.
Zweben, C. Tensile and fatigue strength properties of Kevlar 29 aramid/epoxy unidirectional composites. United States.
Zweben, C. 1981. "Tensile and fatigue strength properties of Kevlar 29 aramid/epoxy unidirectional composites". United States. doi:.
@article{osti_5742716,
title = {Tensile and fatigue strength properties of Kevlar 29 aramid/epoxy unidirectional composites},
author = {Zweben, C.},
abstractNote = {Static and fatigue tensile strength properties of filament wound undirectional Kevlar 29/epoxy, typical of filament wound material used in flywheel rotors, were studied. Machining techniques were developed to minimize fiber fuzzing on edges. The static modulus, normalized to 70% fiber volume fraction is 8.87 x 10/sup 6/ psi. The major Poisson's ratio is 0.37. The static composite tensile strength, normalized to 70% fiber volume fraction is 200 x 10/sup 3/ psi, corresponding to a fiber stress at failure of 286 x 10/sup 3/ psi, which is good for materials having a very high fiber volume fraction. The S-N curve for R = 0.7 was found to be quite flat. Although the techniques used in this program had previously been employed successfully to study the fatigue behavior of Kevlar 29/epoxy and Kevlar 49/epoxy unidirectional materials, we were unable to overcome the persistent problem of cohesive material failure in the tab regions. The apparent reason for this is the very low interlaminar shear strength of the filament wound material. 16 figures.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = 1981,
month = 7
}

Technical Report:
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  • 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 versusmore » 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.« less
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  • The effects of strain rates from 0.00008 to 0.4/sec on tensile strengths and moduli of 6061 aluminum-46.5 vol% boron at temperatures up to 1000 deg F, of unidirectional and cross-ply epoxy-50 vol% boron composites at temperatures up to 500 deg F and of crossply epoxy --80 vol% graphite composites at temperatures up to 250 deg F were measured. Longitudinal properties were reduced moderately at high temperatures and were only slightly higher at high strain rates than at low strain rates. Transverse properties decreased rapidly with temperature and were either unaffected by high strain rates, particularly at low temperatures, or weremore » substantially increased, especially at high temperatures, in both aluminum- and epoxy-based systems. (auth)« less