ASTM D4018-23

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D4018 − 17 D4018 − 23
Standard Test Methods for
Properties of Continuous Filament Carbon and Graphite
Fiber Tows
This standard is issued under the fixed designation D4018; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope
1.1 These test methods cover the preparation and tensile testing of resin-impregnated and consolidated test specimens made from
continuous filament carbon and graphite yarns, rovings, and tows to determine their tensile properties.
1.2 These test methods also cover the determination of the density and mass per unit length of the yarn, roving, or tow to provide
supplementary data for tensile property calculation.
1.3 These test methods include a procedure for sizing removal to provide the preferred desized fiber samples for density
measurement. This procedure may also be used to determine the weight percent sizing.
1.4 These test methods include a procedure for determining the weight percent moisture adsorption of carbon or graphite fiber.
1.5 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety and healthsafety, health, and environmental practices and determine
the applicability of regulatory limitations prior to use.
1.7 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D70 Test Method for Specific Gravity and Density of Semi-Solid Asphalt Binder (Pycnometer Method)
D1193 Specification for Reagent Water
D3800 Test Method for Density of High-Modulus Fibers
D5550 Test Method for Specific Gravity of Soil Solids by Gas Pycnometer
E4 Practices for Force Calibration and Verification of Testing Machines
These test methods are under the jurisdiction of ASTM Committee D30 on Composite Materials and are the direct responsibility of Subcommittee D30.03 on
Constituent/Precursor Properties.
Current edition approved Jan. 15, 2017Sept. 1, 2023. Published January 2017September 2023. Originally approved in 1981. Last previous edition approved in 20112017
as D4018 – 11.D4018 – 17. DOI: 10.1520/D4018-17.10.1520/D4018-23.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D4018 − 23
E83 Practice for Verification and Classification of Extensometer Systems
2.2 Other Document:
CRC Handbook of Chemistry and Physics
3. Terminology
3.1 Definitions:
3.1.1 sizing, n—a generic term for compounds which, when applied to yarn or fabric, form a more or less continuous solid film
around the yarn and individual fibers.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 desized fiber, n—fiber which has had a sizing removed from it.
3.2.2 fiber, n—continuous filament carbon or graphite yarn, roving, or tow.
3.2.3 sized fiber, n—a fiber with a sizing applied to it.
3.2.4 unsized fiber, n—fiber which has never had a sizing applied to it.
3.3 Symbols:
3.3.1 A—Unit conversion factor for tensile strength
3.3.2 B—Unit conversion factor for tensile modulus
3.3.3 E—fiber chord modulus
3.3.4 ε —Lower strain limit
l
3.3.5 ε —Upper strain limit
u
3.3.6 k —correction factor for density of sizesizing
c
3.3.7 L—specimen length
3.3.8 MUL—the mass per unit length of the sized fiber
3.3.9 MUL —the mass per unit length of the impregnated and consolidated fiber
I
3.3.10 P—maximum load
3.3.11 P —tensile load at lower strain limit
l
3.3.12 P —tensile load at upper strain limit
u
3.3.13 ρ —density of the fiber
f
3.3.14 ρ —density of the fiber with sizing
sf
3.3.15 RC—weight percent of resin (resin content)
3.3.16 W —specimen mass
CRC Press Inc., Boca Raton, Ann Arbor, London, Tokyo, 73rd Edition, 1992–1993.
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4. Summary of Test Methods
4.1 These test methods include procedures for determining the tensile strength and modulus of a resin-impregnated and
consolidated carbon fiber tow. Also included are procedures to measure the mass per unit length and density of the carbon fiber
and the resin content of the resin-impregnated and consolidated specimens.
4.2 MUL—The MUL of the fiber is determined by dividing the mass of a sample of sized fiber by its length.
4.3 Density—The density of the fiber is determined using Archimedes’ method or a pycnometer method. The recommended
specimen is desized or unsized fiber. The ideal immersion fluid is one that completely wets the specimen and provides minimum
toxicity or environmental hazard.
4.4 Resin Content—The resin content (weight percent) of the resin-impregnated and consolidated fiber is determined by comparing
the mass per unit length of the impregnated and consolidated specimen to the fiber mass per unit length.
4.5 Tensile Properties—The tensile strength and tensile chord modulus of the fiber are determined by the tensile loading to failure
of the resin-impregnated and consolidated fiber. The chord modulus is determined between defined strain limits. The purpose of
the impregnating resin is to provide the fiber, when consolidated, with sufficient mechanical strength to produce an easily handled
test specimen capable of sustaining uniform loading of the individual filaments in the specimen. The resin shall be compatible with
the fiber and any sizesizing applied to it. The strain capability of the consolidated resin shall be at least twice the strain capability
of the fiber.
5. Significance and Use
5.1 The properties determined by these test methods are of value in material specifications, qualifications, data base generation,
certification, research, and development.
5.2 These test methods are intended for the testing of fibers that have been specifically developed for use as reinforcing agents
in advanced composite structures. The test results of an impregnated and consolidated fiber should be representative of the strength
and modulus that are available in the material when used as intended. The performance of fibers in different resin systems can vary
significantly so that correlations between results using these test methods and composite testing may not always be obtained.
5.3 The reproducibility of test results is dependent upon precise control over all test conditions. Resin type, content and
distribution, curing process, filament alignment, gripping in the testing machine, and alignment in the testing machine are of special
importance.
5.4 The measured strengths of fibers are not unique quantities and test results are strongly dependent on the test methods used.
Therefore the test method described here will not necessarily give the same mean strengths or standard deviations as those obtained
from single filaments, dry fibers, composite laminas, or composite laminates.
6. Apparatus
6.1 Three sets of apparatus are required. One set is for resin impregnation of the fiber. A second set is for curing the
resin-impregnated specimens. A third set is for tensile testing the resin-impregnated and consolidated specimens. Optional
apparatus may be used for applying end tabs to the specimens and removing sizing.
6.1.1 Resin Impregnation—The goal of the resin-impregnation apparatus is to apply and uniformly impregnate resin into the fiber.
This is normally achieved by dipping the fiber into the resin and then working the wet fiber over rolls or through a die, or both.
While automated apparatuses are preferred for consistency, any apparatus which achieves uniform impregnation of 3535 % to 60 %
resin by weight and does not damage the fiber is acceptable.
6.1.2 Consolidation—An apparatus to hold the impregnated specimens under tension during consolidation is required.
6.1.3 Optional End Tabs—An apparatus to cast resin end tabs on specimens may be used. Apparatuses to apply and align other
forms of end tabs such as bonded on cardboard or metal tabs may also be used.
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6.1.4 Testing—A tensile testing machine and recorder meeting the requirements of Practices E4 at the maximum expected test load
are required. The load recording device shall be coordinated with the extensometer and strain recorder to assure that the
corresponding load and elongation of the specimen are recorded at essentially the same time. The testing machine shall also have
the following features:
6.1.4.1 Grips—Grips suitable for loading the tabbed or untabbed specimen without damaging it are required. For resin tabbed
specimens a custom grip is generally required. For untabbed or cardboard tabbed specimens pneumatic or hydraulically powered
grips are typically used. Different grip pressure settings may be required for different fibers.
6.1.4.2 Jaws—Jaws compatible with the grips and capable of holding a specimen without damaging it are required. For untabbed
specimens, flat jaws with rubber or other compliant materials bonded to the face are generally used. Sandpaper may also be placed
on the grips to reduce slippage. For cardboard tabbed specimens serrated jaws are generally used. Jaws should be inspected
regularly and cleaned or repaired as required.
6.1.4.3 Extensometer and Recorder—An extensometer and recording device in accordance with the requirements of Practice E83
Class B-2 are required. The extensometer and recorder shall be coordinated with the tensile testing machine so that the
corresponding load and elongation of the specimen are recorded at essentially the same time.
6.1.4.4 Balance, Analytical—Accuracy of 6 0.0002 g for mass per unit length, density, and resin or sizesizing content
determinations.
6.1.4.5 Balance, Laboratory—Accuracy of 6 0.1 g for measuring components of resin.
6.1.4.6 Length Measuring Devices—Devices to measure the length of impregnated and consolidated specimens and dry fiber to
6 2 mm accuracy are required.
6.1.4.7 Density Measuring Device—See Test Methods D70, D3800, or D5550.
6.1.4.8 Forced Air Oven—A forced air oven of sufficient sizesizing and temperature capabilities to cure the impregnated fiber on
the curing device. The temperature shall be controlled to 610°C.610 °C.
7. Reagents and Materials
7.1 Reagent Water—Unless otherwise indicated, references to water shall be understood to mean reagent water as defined by Type
III of Specification D1193.
7.2 Resin.
7.3 Commercial Grade Solvent, (optional) for resin dilution.
7.4 Hardener or Catalyst.
7.5 Surfactant (optional).
8. Test Specimens
8.1 Mass per Unit Length Specimen—The specimen to measure mass per unit length is a 1 m an 1 m minimum length of fiber in
the form in which it is intended to be used. Test one specimen per sample. Coil the specimen into a usable form for testing. Care
is required to not damage and lose filaments from the specimen.
8.2 Density Specimen—Density specimens may be sized, unsized, or desized material. Unsized or desized samples are preferred.
Test one specimen per sample. AAn 1 m minimum length is required for Test Method D3800. For methods in Test Methods D70
and D5550, a suitable volume to fill the container is recommended. Coil the specimen into a usable form for testing. Care is
required to not damage and lose filaments from the specimen.
8.3 Tensile Test Specimen—The tensile specimen shall be a tabbed or untabbed resin-impregnated and consolidated fiber. Tabbed
D4018 − 23
specimens shall have a 150150 mm 6 5 mm gagegauge length between the tabs. Untabbed specimens shall be of sufficient length
to allow a 150 6 5 mm gage 150 mm 6 5 mm gauge length between the grips when they are tested. Samples with 3000 filaments
or less may be tested using specimens of more than one fiber bundle to facilitate handling. Combine the bundles before resin
impregnation and count the test results as one specimen. Test a minimum of four test specimens per sample. Separate test
specimens for modulus and strength determination are permitted; however, four specimens for each test are required. Specimens
that are fuzzy, curved, not uniform in cross section, have broken filaments, resin lumps, or other observable defects should be
rejected unless they are representative of the material being tested.
9. Conditioning
9.1 Fibers that adsorb less than 0.5 % moisture by weight at 23 6 2°C23°C 6 2 °C and 90 % or greater relative humidity require
no conditioning before testing. Conduct mass per unit length, density, and tensile testing for these materials at 23 6 7°C and
5023 °C 6 7 °C and 50 % 6 20 % relative humidity unless other conditions are the variables of interest.
9.2 Fibers that adsorb more than 0.5 % moisture by weight at 23 6 2°C23 °C 6 2 °C and 90 % or greater relative humidity require
conditioning before testing. Condition fibers at 23 6 2°C and 5023 °C 6 2 °C and 50 % 6 10 % relative humidity for a minimum
of 24 h. 24 h. Conduct mass per unit length and density testing at 23 6 2°C and 5023 °C 6 2 °C and 50 % 6 10 % relative
humidity unless other conditions are the variables of interest. Conduct tensile testing at 23 6 7°C and 5023 °C 6 7 °C and 50 %
6 10 % relative humidity unless other conditions are the variables of interest.
9.3 To determine moisture adsorption, dry a minimum of five mass per unit-type specimens at 120 6 5°C for 24 h 120 °C 6 5 °C
for 24 h in a circulating air oven. Cool samples the specimens in a desiccator. Remove samples the specimens from desiccator one
at a time and immediately weigh them. Place samples the specimens in a humidity chamber and maintain at 23 6 2°C23 °C 6
2 °C and 90 % or greater relative humidity for 24 h. Remove samples 24 h. Remove the specimens from the humidity chamber
one at a time and weigh immediately.
9.4 If all specimens are conditioned for 24 h and mass per unit length and density testing are performed at 23 6 2°C and 5023 °C
6 2 °C and 50 % 6 10 % relative humidity, then no testing for moisture adsorption is required.
9.5 Moisture adsorption testing is only required once annually for a standard product.
10. Specimen Preparation
10.1 Mass per Unit Length—No preparation is required. The sample is taken from a package of material as it is intended to be
used.
10.2 Density—The preferred density specimen is a desized or unsized fiber. This eliminates any need to correct for the density of
the sizing. The sizing may be removed using solvent extraction, pyrolysis, or other means. An example method is described in
Appendix X1. An unsized sample of a sized fiber would have to be collected during the production of the fiber and is therefore
not recommended.
10.3 Tensile Test—The tensile test specimen must be impregnated with resin and consolidated before testing.
10.3.1 Resin Preparation—Any resin that meets the requirements of 4.5 may be used. The resin when combined with the fiber
shall produce a composite (reinforcement/matrix) failure. A resin generally found satisfactory is a combination of bisphenol A (or
bisphenol F) epoxy and diethyltoluene diamine in the weight ratio of 3.9:1. A solvent that lowers the viscosity of a resin mixture
or softens the sizing, or both, may be selected for use with the resin. The amount and type of solvent used will vary with the product
and apparatus used for impregnation. Prepare and store the resin in accordance with the manufacturer’s instructions.
10.3.2 Fiber Impregnation—The resin shall be maintained within a suitable viscosity or temperature range throughout the
impregnation process that assures reproducible specimen constituency and quality. An automated impregnation device is
recommended but not required. The objective of impregnation is a uniform, well-collimated strand with adequate resin,resin
content, typically 3535 % to 60 % by weight.
10.3.2.1 Wind or attach the impregnated fiber to a rack or other device to hold it under tension to avoid fiber waviness but not
to cause fiber breakage during consolidation.
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10.3.2.2 Check the consolidated impregnated fiber resin content at least daily resin content of impregnated and consolidated fiber
to ensure adequate resin pickup. Determine the mass of a known length of impregnated and consolidated fiber. Compute the resin
content using the mass per unit length of the fiber as a reference.
10.3.2.3 Tabbing—End tabs may be applied to the impregnated and consolidated specimens but are not required. End tab material
must adequately grip the specimen without slipping. Heavy paper or poster board have been used successfully as tabs. The distance
between tabs shall be 150 6 5 mm.150 mm 6 5 mm.
11. Procedure
11.1 Mass per Unit Length—Take the mass per unit length specimen from the fiber in the same form as it is intended to be used.
Test fiber with size with the size sizing on the fiber. Test one specimen per sample.
11.1.1 Using a calibrated measuring device measure a minimum of aan 1 m (62 mm) length of fiber. Hold the fiber under light
hand tension while measuring and cutting it. Coil the fiber onto a usable form taking care not to damage or lose filaments.
11.1.2 Determine the mass of the specimen using an analytical balance.
11.1.3 Retests—Reject any specimen which has an obvious flaw or deviation from the requirements of these test methods. Prepare
a new or spare specimen from the same sample and test to replace any
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