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Title: Interlocked fabric and laminated fabric Kevlar 49/epoxy composites

Abstract

The mechanical behavior of a novel interlocked fabric reinforced Kevlar 49/epoxy composite has been measured and compared to those of a laminated Kevlar 49 fabric composite (which served as a reference material). Both composites were 5.0 mm thick, contained the same 50% in-plane fiber volume fraction and were fabricated in a similar manner using the same Dow DER 332 epoxy, Jeffamine T403-hardened resin system. The reference material (Material 1) was reinforced with seven plies of Dupont style 1033 Kevlar 49 fabric. A photomicrograph of a section polished parallel to one of the fiber directions is shown. The interlocked fabric was designed and woven for Sandia National Laboratories by Albany International Research Co., Dedham, MA. The main design criterion was to duplicate a sewn through-the-thickness fabric used in preliminary studies. The interlocked fabric composite (Material 2) contains roughly 4% by volume of through-the-thickness fiber reinforcement for the purpose of improving interlaminar strength. A photomicrograph of a section showing the warp-aligned binder yarns interlocking the six fabric plies together is shown. 2 refs., 8 figs.

Authors:
;
Publication Date:
Research Org.:
Sandia National Labs., Albuquerque, NM (USA)
OSTI Identifier:
6774753
Report Number(s):
SAND-88-2579C; CONF-8810151-4
ON: DE89000459
DOE Contract Number:
AC04-76DP00789
Resource Type:
Conference
Resource Relation:
Conference: JOWOG-28 meeting, Albuquerque, NM, USA, 1 Oct 1988; Other Information: Portions of this document are illegible in microfiche products
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; COMPOSITE MATERIALS; MECHANICAL PROPERTIES; EPOXIDES; REINFORCED MATERIALS; COMPARATIVE EVALUATIONS; MATERIALS TESTING; PHOTOMICROGRAPHY; MATERIALS; ORGANIC COMPOUNDS; ORGANIC OXYGEN COMPOUNDS; PHOTOGRAPHY; TESTING 360603* -- Materials-- Properties

Citation Formats

Guess, T.R., and Reedy, E.D. Jr. Interlocked fabric and laminated fabric Kevlar 49/epoxy composites. United States: N. p., 1988. Web.
Guess, T.R., & Reedy, E.D. Jr. Interlocked fabric and laminated fabric Kevlar 49/epoxy composites. United States.
Guess, T.R., and Reedy, E.D. Jr. 1988. "Interlocked fabric and laminated fabric Kevlar 49/epoxy composites". United States. doi:.
@article{osti_6774753,
title = {Interlocked fabric and laminated fabric Kevlar 49/epoxy composites},
author = {Guess, T.R. and Reedy, E.D. Jr.},
abstractNote = {The mechanical behavior of a novel interlocked fabric reinforced Kevlar 49/epoxy composite has been measured and compared to those of a laminated Kevlar 49 fabric composite (which served as a reference material). Both composites were 5.0 mm thick, contained the same 50% in-plane fiber volume fraction and were fabricated in a similar manner using the same Dow DER 332 epoxy, Jeffamine T403-hardened resin system. The reference material (Material 1) was reinforced with seven plies of Dupont style 1033 Kevlar 49 fabric. A photomicrograph of a section polished parallel to one of the fiber directions is shown. The interlocked fabric was designed and woven for Sandia National Laboratories by Albany International Research Co., Dedham, MA. The main design criterion was to duplicate a sewn through-the-thickness fabric used in preliminary studies. The interlocked fabric composite (Material 2) contains roughly 4% by volume of through-the-thickness fiber reinforcement for the purpose of improving interlaminar strength. A photomicrograph of a section showing the warp-aligned binder yarns interlocking the six fabric plies together is shown. 2 refs., 8 figs.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = 1988,
month = 1
}

Conference:
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  • Hygrothermal effects can significantly influence the failure behavior of high performance epoxy-based composites. As such, it is necessary to determine, for one, the moisture diffusion rates in the composite's principal axes so that moisture densities and distributions can be estimated for life-cycle exposures. In this study, moisture diffusion coefficients are determined for quasiisotropic Kevlar 49 181-style fabric reinforced Narmco 5208 epoxy laminates, and for the epoxy and fabric components individually. A microbalance technique is employed to continuously monitor the percentage weight gain of specimens exposed to 76 percent relative humidity at room temperature. The anisotropy of moisture diffusivity in themore » composite laminates is determined by use of a slope ratio (absorption vs time) technique and specimens of appropriate geometry. Results show that moisture diffuses in the laminate plane (6.6 x 10/sup -8/ cm/sup 2//sec) two orders of magnitude faster than through the thickness (1.9 x 10/sup -10/ cm/sup 2//sec). These values compare to a resin diffusivity of 7.1 x 10/sup -10/ cm/sup 2//sec. It is speculated that the rapid inplane diffusion is due to the preferential diffusion of moisture in the filament along its length.« less
  • Creep and recovery of thick Kevlar 49/epoxy composites were investigated in transverse compressive loading at room temperature. Cylindrical samples with void contents of 4 and 14 percent were tested along with those of unreinforced resin. The composites exhibited logarithmic creep. Creep rates were 2 times higher over the entire stress range for the high porosity composites. At a stress of 87 MPa the resin creep curve was similar to that of the composites. At higher stresses, the resin crept faster and exhibited more strain. It is proposed that axial compressive creep of the cylindrical composite specimens is governed by Poissonmore » induced strains leading to tensile loading of the reinforcing fibers. Axial initial strain and creep rate data for the composite were converted to radial data using measured values of Poisson ratio. These values of composite specimen radial creep rate were in good agreement with tensile creep data of Kevlar 49 fibers.« less
  • The fracture topographies of Kevlar 49/epoxy composite strands and multilayer composites in the form of pressure vessels are discussed in terms of the microscopic deformation and failure processes of the composites. The effect of resin ductility and fiber-matrix interfacial bond strength on mechanisms of fiber damage are considered. The failure of the Kevlar 49 fibers by a splitting process and the parameters, such as fiber fibrillation and macromolecular chain scission, that control such a process, are discussed in relation to fiber and composite performance.
  • 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 andmore » 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.« less
  • This study compares the mechanical behavior of aminated Kevlar 49 polyaramid fabric/DER 332-MPDA laminates with laminates fabricated with untreated polyaramid filaments. Interface-sensitive tests show that interface-dominated properties are increased by the amination. Peel resistance increases > 100% while +-45/sup 0/ tensile shear yield increased 30 to 40%. Examination of the transverse tensile fracture surfaces showed that the failure mode changed from an interface-dominated one to a mixture of filament splitting and matrix cracking in the aminated laminates. These results show that the mechanical properties of polyaramid/epoxy laminates may be improved by the formation of covalent bonds at the filament-matrix interface.more » It is expected that environmental resistance would also be improved.« less