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Title: Aging and quality assurance of Kevlar 49-epoxy composites

Abstract

The aging of Kevlar 49-epoxy composites under the service environment conditions expected by ESA will be insignificant to the best of our knowledge at this time. However, certain precautions in materials acceptance criteria and composite fabrication should be followed.

Authors:
Publication Date:
Research Org.:
Lawrence Livermore National Lab., CA (USA)
OSTI Identifier:
6592748
Report Number(s):
UCID-19026
DOE Contract Number:
W-7405-ENG-48
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; COMPOSITE MATERIALS; AGING; QUALITY ASSURANCE; EPOXIDES; FIBERS; POLYMERS; MATERIALS; ORGANIC COMPOUNDS; ORGANIC OXYGEN COMPOUNDS 360300* -- Composite Materials-- (-1987)

Citation Formats

Morgan, R.J.. Aging and quality assurance of Kevlar 49-epoxy composites. United States: N. p., 1981. Web.
Morgan, R.J.. Aging and quality assurance of Kevlar 49-epoxy composites. United States.
Morgan, R.J.. 1981. "Aging and quality assurance of Kevlar 49-epoxy composites". United States. doi:.
@article{osti_6592748,
title = {Aging and quality assurance of Kevlar 49-epoxy composites},
author = {Morgan, R.J.},
abstractNote = {The aging of Kevlar 49-epoxy composites under the service environment conditions expected by ESA will be insignificant to the best of our knowledge at this time. However, certain precautions in materials acceptance criteria and composite fabrication should be followed.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = 1981,
month = 5
}

Technical Report:
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  • Ply failure occurred during preconditioning at 75/sup 0/C of (0/90)/sub 2S/ S2-glass/epoxy and Kevlar 49/epoxy laminates. Wet specimens showed different thermal expansion beavior near and above the glass transition temperature. Various available theories can be used to predict the thermal expansion coefficients. Stress analysis showed that the compressive normal stress at the interface in Kevlar 49/epoxy after cure is very small compared with those in other composites. Significant and rapid changes in the transverse coefficient of thermal expansion occurs in the T/sub g/ region. The two-phase diffusion model is a good representation of the diffusion behavior. Desorption process reveals amore » higher diffusion coefficient than absorption. S2-glass/epoxy was found to be unstable under the conditions applied, with cracking and losses during desorption. Maximum moisture contents were approx. 0.31% at 75/sup 0/C/75% RH and approx. 0.412% at 75/sup 0/C/water. The composite swelled transversely up to about 0.11 and 0.16%. Kevlar 49/epoxy was more stable than S2-glass/epoxy; max moisture contents were approx. 2.47% at 75/sup 0/C/75% RH and approx. 5.5% at 75/sup 0/C/water. The composite swelled transversely up to 1.0 and 2.23%. Results indicate that Kevlar 49 fibers swell radially. Relation between swelling strain and moisture content undergoes hysteresis during moisture cycling. Relation between swelling strain and moisture concentration is fairly linear for S2-glass/epoxy, Kevlar 49/epoxy and AS 3501/5 graphite/epoxy and only weakly depends on the material system. The equilibrium moisture content in (+-45)/sub 2S/ laminate is higher than in unidirectional lamina. The equilibrium thickness swelling strain can be predicted by laminated plate theory.« less
  • Water has been observed to be adsorbed, and possibly absorbed, by desiccated Kevlar 49 fiber to 6 percent of the fiber weight in 100 percent relative humidity. The effect of the water on the transverse flexural strength and elastic modulus of an aliphatic amine-cured epoxy, unidirectionally reinforced with saturated Kevlar 49, has been determined. Such composites are weaker than those made with fiber equilibrated to 0 percent relative humidity, and the effect persists after a 75/sup 0/C, 16-h postcure. It is suggested that glycol formation and a consequent excess of curing agent, resulting from a water-resin reaction at the fiber-matrixmore » interface, accounts for the weakening.« less
  • 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 formore » 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.« less