ASTM D2734-94(2003)
(Test Method)Standard Test Methods for Void Content of Reinforced Plastics
Standard Test Methods for Void Content of Reinforced Plastics
SIGNIFICANCE AND USE
The void content of a composite may significantly affect some of its mechanical properties. Higher void contents usually mean lower fatigue resistance, greater susceptibility to water penetration and weathering, and increased variation or scatter in strength properties. The knowledge of void content is desirable for estimation of quality of composites.
SCOPE
1.1 These test methods cover the void content of reinforced plastics or "composites." The test methods are applicable to composites for which the effects of ignition on the materials are known. Most plastics, glass, and asbestos reinforcements fall into this class. These test methods are not applicable to composites for which the effects of ignition on the plastics, the reinforcement, and any fillers are unknown. This class may include silicone resins, which do not burn off completely, reinforcements consisting of metals, organic materials, or inorganic materials which may gain or lose weight, and fillers consisting of oxides, carbonates, etc., which may gain or lose weight. Note that separate weight loss tests of individual materials will usually, but not necessarily, give the same result as when all the materials are combined.
Note 1—There is no known ISO equivalent to these test methods.
1.2 The values stated in SI units are to be regarded as the standard.
1.3 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 health practices and determine the applicability of regulatory limitations prior to use.
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Designation:D2734–94 (Reapproved 2003)
Standard Test Methods for
Void Content of Reinforced Plastics
This standard is issued under the fixed designation D2734; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the Department of Defense.
1. Scope 3. Summary of Test Methods
1.1 These test methods cover the void content of reinforced 3.1 The densities of the resin, the reinforcement, and the
plastics or “composites.” The test methods are applicable to composites are measured separately. Then the resin content is
compositesforwhichtheeffectsofignitiononthematerialsare measured and a theoretical composite density calculated. This
known. Most plastics, glass, and reinforcements fall into this iscomparedtothemeasuredcompositedensity.Thedifference
class. These test methods are not applicable to composites for in densities indicates the void content.Agood composite may
which the effects of ignition on the plastics, the reinforcement, have 1% voids or less, while a poorly made composite can
and any fillers are unknown. This class may include silicone have a much higher void content. Finite values under 1%
resins, which do not burn off completely, reinforcements should be recognized as representing a laminate density
consisting of metals, organic materials, or inorganic materials quality, but true void content level must be established by
whichmaygainorloseweight,andfillersconsistingofoxides, complementary tests or background experience, or both.
carbonates, etc., which may gain or lose weight. Note that
4. Significance and Use
separate weight loss tests of individual materials will usually,
but not necessarily, give the same result as when all the 4.1 Thevoidcontentofacompositemaysignificantlyaffect
some of its mechanical properties. Higher void contents
materials are combined.
usually mean lower fatigue resistance, greater susceptibility to
NOTE 1—There is no known ISO equivalent to these test methods.
water penetration and weathering, and increased variation or
1.2 The values stated in SI units are to be regarded as the
scatterinstrengthproperties.Theknowledgeofvoidcontentis
standard.
desirable for estimation of quality of composites.
1.3 This standard does not purport to address all of the
5. Interferences
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
5.1 The density of the resin, in these test methods, is
priate safety and health practices and determine the applica-
assumed to be the same in the composite as it is in a large cast
bility of regulatory limitations prior to use.
mass.Although there is no realistic way to avoid this assump-
tion, it is nevertheless not strictly correct. Differences in
2. Referenced Documents
curing, heat and pressure, and molecular forces from the
2.1 ASTM Standards:
reinforcement surface all change the composite resin density
D618 Practice for Conditioning Plastics for Testing
from the bulk resin density. The usual change is that bulk
D792 TestMethodsforDensityandSpecificGravity(Rela-
densityislower,makingvoidcontentseemlowerthanitreally
tive Density) of Plastics by Displacement
is.
D1505 Test Method for Density of Plastics by the Density-
5.2 For composites with high void contents, this error will
Gradient Technique
lower the true value an insignificant amount, from a true 7%
D2584 Test Method for Ignition Loss of Cured Reinforced
down to a calculated 6.7%, for example. For composites with
Resins
low and void contents, the value may be lowered from a true
0.2% to a calculated−0.1%. This would indicate an obvious
1 error, and illustrates that as the void content gets lower the
These test methods are under the jurisdiction of ASTM Committee D20 on
constant error in resin density gets progressively more impor-
Plastics and are the direct responsibility of Subcommittee D20.18 on Reinforced
Thermosetting Plastics.
tant. Note that these values are for example only, that different
Current edition approved Jan. 10, 2003. Published March 2003. Originally
resin systems can give different errors, and that it is left to the
approved in 1968. Last previous edition approved in 1994 as D2734–94.
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.
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D2734–94 (2003)
individual tester to determine the accuracy of the calculated 7.1.3.1 Densities calculated from weight and volume mea-
result in his particular measurement. surementsareacceptableifthespecimensaresmooth,uniform,
5.3 For the special case of semi-crystalline plastics, such as and of such shape that the volume can be calculated accurately
polyphenylene sulfide (PPS) and polyetheretherketone from the dimensions.
(PEEK),aninterferenceduetothelevelofcrystallinitypresent 7.1.3.2 Procedure—The volume of each specimen shall not
3 3
in the composite can cause significant variation in the mea- be less than 2 cm [0.125 in. ]. Make dimensional measure-
surement of void content by this test method. The level of ments with a micrometer at all edges (12 in all for a 6-sided
crystallinity can be affected by a variety of circumstances, rectangular block). Use the averages for each dimension to
including the molding conditions. For these polymers, the calculate the volume.
densityusedinthecalculationmustbetheactualdensityofthe 7.1.3.3 The tolerance on the accuracy of the micrometer
resin in the composite. measurements shall be 60.0013 cm [60.0005 in.]. With
maximum tolerance buildup on a small sample, this could
NOTE 2—The actual degree of crystallinity of the composite can be
result in an error in the calculated volume of 0.6%. For larger
measured by techniques such as differential scanning calorimetry (DSC)
samples, and with some measurements being in error on the
or by X-ray difraction.
plus side and some on the minus side, the error in the
6. Conditioning
calculated volume should not exceed 0.2%.
7.1.3.4 Calculate the density by dividing the weight by the
6.1 Conditioning—Condition the test specimens at 23 6
volume; express as grams per cubic centimetre.
2°C[73.4 63.6°F]and50 65%relativehumidityfornotless
7.2 Density of the Glass or Other Reinforcement—Most
than 40 h prior to test in accordance with Procedure A of
glass reinforcement is E glass, which typically has a de
...
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