skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Comparison of methods for predicting fiber stresses in a cracked Kevlar/epoxy monolayer

Abstract

Shear-lag and 3-D finite element predictions for the fiber stresses in a cracked Kevlar 49/epoxy monolayer are compared. Results are given for a 5-fiber wide monolayer containing a single broken fiber. Both methods of analysis are found to predict nearly the same fiber stress distribution along the crack-tip fiber when the monolayer is fully elastic. Results for highly loaded monolayers with extensive matrix yielding are not in quite as good agreement, but even then the predicted stress distributions are within 5%. These calculations show that a shear-lag analysis is accurate even though the Kevlar 49 fiber is highly anisotropic.

Authors:
Publication Date:
Research Org.:
Sandia National Labs., Albuquerque, NM (USA)
OSTI Identifier:
6337526
Report Number(s):
SAND-84-0867C; CONF-841201-11
ON: DE84016118
DOE Contract Number:
AC04-76DP00789
Resource Type:
Conference
Resource Relation:
Conference: ASME winter annual meeting, New Orleans, LA, USA, 9 Dec 1984
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; COMPOSITE MATERIALS; FIBERS; STRESSES; ARAMIDS; EPOXIDES; LAYERS; MATERIALS; ORGANIC COMPOUNDS; ORGANIC OXYGEN COMPOUNDS; PETROCHEMICALS; PETROLEUM PRODUCTS; PLASTICS; SYNTHETIC MATERIALS; 360303* - Composite Materials- Mechanical Properties- (-1987)

Citation Formats

Reedy, E.D. Jr. Comparison of methods for predicting fiber stresses in a cracked Kevlar/epoxy monolayer. United States: N. p., 1984. Web.
Reedy, E.D. Jr. Comparison of methods for predicting fiber stresses in a cracked Kevlar/epoxy monolayer. United States.
Reedy, E.D. Jr. 1984. "Comparison of methods for predicting fiber stresses in a cracked Kevlar/epoxy monolayer". United States. doi:.
@article{osti_6337526,
title = {Comparison of methods for predicting fiber stresses in a cracked Kevlar/epoxy monolayer},
author = {Reedy, E.D. Jr.},
abstractNote = {Shear-lag and 3-D finite element predictions for the fiber stresses in a cracked Kevlar 49/epoxy monolayer are compared. Results are given for a 5-fiber wide monolayer containing a single broken fiber. Both methods of analysis are found to predict nearly the same fiber stress distribution along the crack-tip fiber when the monolayer is fully elastic. Results for highly loaded monolayers with extensive matrix yielding are not in quite as good agreement, but even then the predicted stress distributions are within 5%. These calculations show that a shear-lag analysis is accurate even though the Kevlar 49 fiber is highly anisotropic.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = 1984,
month = 1
}

Conference:
Other availability
Please see Document Availability for additional information on obtaining the full-text document. Library patrons may search WorldCat to identify libraries that hold this conference proceeding.

Save / Share:
  • Kevlar 49 fibers were surface modified by gas (ammonia, oxygen, and water vapor) plasmas etching and chlorosulfonation and subsequent reaction with some reagents (glycine, deionized water, ethylenediamine, and 1-butanol) to improve the adhesion to epoxy resin. After these treatments, the changes in fiber topography, chemical compositions of the fiber surfaces and the surface functional groups introduced to the surface of fibers were identified by SEM XPS and static SIMS. Interlaminar shear strength (ILSS) and T-peel strength between the fiber and epoxy resin were markedly improved by gas plasma and chlorosulfonation (0.1% and 0.25% ClSO{sub 3}H at 30 s). However, itmore » is clear from the similar G{sub IC} values of the treated and untreated fiber composites that the fiber/matrix interfacial bond strength is only a minor contributor to G{sub IC}. SEM was also used to study the surface topography of the fracture surfaces of composites in T-peel test.« less
  • This study compares different approaches for imaging the internal architecture of graphite/epoxy composites using backscattered ultrasound. Two cases are studied. In the first, near-surface defects in a thin graphite/epoxy plates are imaged. The same backscattered waveforms were used to produce peak-to-peak, logarithm of signal energy, as well as entropy images of different types. All of the entropy images exhibit better border delineation and defect contrast than the either peak-to-peak or logarithm of signal energy. The best results are obtained using the joint entropy of the backscattered waveforms with a reference function. Two different references are examined. The first is amore » reflection of the insonifying pulse from a stainless steel reflector. The second is an approximate optimum obtained from an iterative parametric search. The joint entropy images produced using this reference exhibit three times the contrast obtained in previous studies. These plates were later destructively analyzed to determine size and location of near-surface defects and the results found to agree with the defect location and shape as indicated by the entropy images. In the second study, images of long carbon graphite fibers (50% by weight) in polypropylene thermoplastic are obtained as a first step toward ultrasonic determination of the distributions of fiber position and orientation.« 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