Dynamic small angle x-ray scattering study of stressed Kevlar 49 epoxy composites

Conference · Tue Jan 01 04:00:00 EST 1985

OSTI ID:5678762

Lee, J S; Fellers, J F; Tang, M Y; Lin, J S

The highly crosslinked epoxy resins gave rise to isotropic scattering patterns and applying tensile stresses resulted in very little scattering changes. The dynamic scattering studies on the epoxy resins indicate the failure process as a catastrophic dynamic process with fractures initiating from surface or internal flaws. The crack propagates across the whole sample in a very short time to complete failure. The Kevlar fibers are microporous giving rise to equatorially elongated anisotropic scattering patterns. These microvoids can be partially filled by liquid epoxy. Based on comparisons of the volume fraction of the microvoids obtained by SAXS absolute intensity measurements and by the density measurements, two sizes of microvoids are present in the Kevlar 49 fibers - one in the range of 10 to 20 nm and the other much larger. Applying tensile stresses results in an increase in the scattering intensities and in the volume fraction of smaller microvoids. The average radius of gyration of these microvoids remained constant, and hence the number of these smaller microvoids must have increased in order to account for increased scattering intensities. It is thus concluded that the failure of Kevlar 49 fibers is accompanied by the increase in number of smaller microvoids and the enlargement of the larger microvoids along the fiber axis direction. The reinforced epoxy composites of low volume fraction unidirectional Kevlar 49 fiber gave rise to anisotropic scattering patterns perpendicular to the fiber axis direction, and it is believed this scattering is due to voids within the fibers and voids entrapped along the fiber matrix interface during processing. The dynamic scattering studies on the composites indicate the failure as a catastrophic dynamic process, fracture initiating in the epoxy matrix and the fibers not being able to carry the load, thus failing catastrophically as well. The failure is thus instantaneous once incipient failure occurs.

• Research Organization: Tennessee Univ., Knoxville (USA). Dept. of Materials Science and Engineering; Oak Ridge National Lab., TN (USA)
• DOE Contract Number: AC05-84OR21400
• OSTI ID: 5678762
• Report Number(s): CONF-8504143-1; ON: DE85011408
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360303* -- Composite Materials-- Mechanical Properties-- (-1987)
ARAMIDS
CHEMICAL REACTIONS
COHERENT SCATTERING
COMPOSITE MATERIALS
CROSS-LINKING
DIFFRACTION
EPOXIDES
FIBERS
MATERIALS
MECHANICAL PROPERTIES
ORGANIC COMPOUNDS
ORGANIC OXYGEN COMPOUNDS
ORGANIC POLYMERS
PETROCHEMICALS
PETROLEUM PRODUCTS
PLASTICS
POLYMERIZATION
POLYMERS
RESINS
SCATTERING
SMALL ANGLE SCATTERING
STRESSES
SYNTHETIC MATERIALS
TENSILE PROPERTIES
X-RAY DIFFRACTION