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Title: Hygrothermal expansion of Kevlar 49/epoxy and S2-glass/epoxy composites

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 a 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. Relationmore » 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
Authors:
;
Publication Date:
OSTI Identifier:
6802126
Report Number(s):
UCRL-15517
ON: DE83006567
DOE Contract Number:
W-7405-ENG-48
Resource Type:
Technical Report
Research Org:
Washington Univ., St. Louis, MO (USA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; COMPOSITE MATERIALS; SWELLING; REINFORCED PLASTICS; ARAMIDS; CRACKS; DESORPTION; DIFFUSION; EPOXIDES; FAILURES; FINITE ELEMENT METHOD; GLASS; MOISTURE; STABILITY; STRESS ANALYSIS; THERMAL EXPANSION; EXPANSION; MATERIALS; NUMERICAL SOLUTION; ORGANIC COMPOUNDS; ORGANIC OXYGEN COMPOUNDS; PETROCHEMICALS; PETROLEUM PRODUCTS; PLASTICS; REINFORCED MATERIALS; SYNTHETIC MATERIALS 360305* -- Composite Materials-- Corrosion, Erosion, & Degradation-- (-1987)