1、Designation: D 2734 94 (Reapproved 2003)Standard Test Methods forVoid Content of Reinforced Plastics1This standard is issued under the fixed designation D 2734; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revis
2、ion. A number in parentheses indicates the year of last reapproval. Asuperscript 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. Scope1.1 These test methods cover the void content of r
3、einforcedplastics or “composites.” The test methods are applicable tocomposites for which the effects of ignition on the materials areknown. Most plastics, glass, and reinforcements fall into thisclass. These test methods are not applicable to composites forwhich the effects of ignition on the plast
4、ics, the reinforcement,and any fillers are unknown. This class may include siliconeresins, which do not burn off completely, reinforcementsconsisting of metals, organic materials, or inorganic materialswhich may gain or lose weight, and fillers consisting of oxides,carbonates, etc., which may gain o
5、r lose weight. Note thatseparate weight loss tests of individual materials will usually,but not necessarily, give the same result as when all thematerials are combined.NOTE 1There is no known ISO equivalent to these test methods.1.2 The values stated in SI units are to be regarded as thestandard.1.3
6、 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Docu
7、ments2.1 ASTM Standards:2D 618 Practice for Conditioning Plastics for TestingD 792 Test Methods for Density and Specific Gravity (Rela-tive Density) of Plastics by DisplacementD 1505 Test Method for Density of Plastics by the Density-Gradient TechniqueD 2584 Test Method for Ignition Loss of Cured Re
8、inforcedResins3. Summary of Test Methods3.1 The densities of the resin, the reinforcement, and thecomposites are measured separately. Then the resin content ismeasured and a theoretical composite density calculated. Thisis compared to the measured composite density. The differencein densities indica
9、tes the void content. A good composite mayhave 1 % voids or less, while a poorly made composite canhave a much higher void content. Finite values under 1 %should be recognized as representing a laminate densityquality, but true void content level must be established bycomplementary tests or backgrou
10、nd experience, or both.4. Significance and Use4.1 The void content of a composite may significantly affectsome of its mechanical properties. Higher void contentsusually mean lower fatigue resistance, greater susceptibility towater penetration and weathering, and increased variation orscatter in stre
11、ngth properties. The knowledge of void content isdesirable for estimation of quality of composites.5. Interferences5.1 The density of the resin, in these test methods, isassumed to be the same in the composite as it is in a large castmass. Although there is no realistic way to avoid this assump-tion
12、, it is nevertheless not strictly correct. Differences incuring, heat and pressure, and molecular forces from thereinforcement surface all change the composite resin densityfrom the bulk resin density. The usual change is that bulkdensity is lower, making void content seem lower than it reallyis.5.2
13、 For composites with high void contents, this error willlower the true value an insignificant amount, from a true 7 %down to a calculated 6.7 %, for example. For composites withlow and void contents, the value may be lowered from a true0.2 % to a calculated 0.1 %. This would indicate an obviouserror
14、, and illustrates that as the void content gets lower theconstant error in resin density gets progressively more impor-tant. Note that these values are for example only, that differentresin systems can give different errors, and that it is left to the1These test methods are under the jurisdiction of
15、 ASTM Committee D20 onPlastics and are the direct responsibility of Subcommittee D20.18 on ReinforcedThermosetting Plastics.Current edition approved Jan. 10, 2003. Published March 2003. Originallyapproved in 1968. Last previous edition approved in 1994 as D 2734 94.2For referenced ASTM standards, vi
16、sit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-
17、2959, United States.individual tester to determine the accuracy of the calculatedresult in his particular measurement.5.3 For the special case of semi-crystalline plastics, such aspolyphenylene sulfide (PPS) and polyetheretherketone(PEEK), an interference due to the level of crystallinity presentin
18、the composite can cause significant variation in the mea-surement of void content by this test method. The level ofcrystallinity can be affected by a variety of circumstances,including the molding conditions. For these polymers, thedensity used in the calculation must be the actual density of theres
19、in in the composite.NOTE 2The actual degree of crystallinity of the composite can bemeasured by techniques such as differential scanning calorimetry (DSC)or by X-ray difraction.6. Conditioning6.1 ConditioningCondition the test specimens at 23 62C 73.4 6 3.6F and 50 6 5 % relative humidity for not le
20、ssthan 40 h prior to test in accordance with Procedure A ofPractice D 618, for those tests where conditioning is required.In cases of disagreement, the tolerances shall be 1C 1.8Fand 62 % relative humidity.6.2 Test ConditionsConduct tests in the standard labora-tory atmosphere of 23 6 2C (73.4 6 3.6
21、F) and 50 6 5%relative humidity, unless otherwise specified in the test meth-ods. In cases of disagreement, the tolerances shall be 1C(1.8F) and 62 % relative humidity.7. Procedure7.1 Density of the Resin and the CompositeThree testmethods are presented for these measurements. Measure thedensity on
22、pieces of resin that are bubble-free and that werecured under heat, time, and pressure conditions that are as closeas practicable to the conditions under which the composite wascured. Density measurements supplied by the resin manufac-turer are acceptable if they are certified for each batch.7.1.1 T
23、est Method AMeasure densities using Test Meth-ods D 792. Paragraph 1.1 of that test method requires thespecimen to have smooth edges and surfaces. For composites,this requirement may necessitate hand sanding the specimenwith 400-grit emery paper to remove fuzzy edges caused bycutting. The specimen s
24、hould be as free as possible fromgeometric irregularities which tend to trap air bubbles. Removeany bubbles by a wire, or other mechanical means. Do not usea vacuum to remove bubbles, because cut surfaces of compos-ites may be porous and exposure to a vacuum will force waterinto the pores, causing a
25、n error in the density measurement. Insome cases of extreme porosity, just immersing the compositein water, without using a vacuum, will allow an unacceptablylarge amount of water takeup by the composite. In these cases,seal the porous surfaces by coating them with a known amountof sealer of known d
26、ensity. This will require weighing thespecimen, then spraying-on or wiping-on the sealer, thenreweighing. A correction for this added material will then berequired in the calculations.7.1.2 Test Method BMeasure densities in accordance withTest Method D 1505. The comments in 7.1.1 concerning fuzzyedg
27、es and removal of bubbles apply here also.7.1.3 Test Method C:7.1.3.1 Densities calculated from weight and volume mea-surements are acceptable if the specimens are smooth, uniform,and of such shape that the volume can be calculated accuratelyfrom the dimensions.7.1.3.2 ProcedureThe volume of each sp
28、ecimen shall notbe less than 2 cm30.125 in.3. Make dimensional measure-ments with a micrometer at all edges (12 in all for a 6-sidedrectangular block). Use the averages for each dimension tocalculate the volume.7.1.3.3 The tolerance on the accuracy of the micrometermeasurements shall be 60.0013 cm 6
29、0.0005 in. Withmaximum tolerance buildup on a small sample, this couldresult in an error in the calculated volume of 0.6 %. For largersamples, and with some measurements being in error on theplus side and some on the minus side, the error in thecalculated volume should not exceed 0.2 %.7.1.3.4 Calcu
30、late the density by dividing the weight by thevolume; express as grams per cubic centimetre.7.2 Density of the Glass or Other ReinforcementMostglass reinforcement is E glass, which typically has a densitybetween 2.54 and 2.59 g/cm3; S glass density is 2.46 to 2.49g/cm3. However, if a density determi
31、nation is necessary, useTest Methods D 792. Pay particular attention to Note 11 of thattest method, which discusses removal of trapped air byexposure of the sample to a vacuum. This step can be assumedto be necessary in every determination of glass density. Use avacuum of 3 mm Hg or better. Several
32、cycles of atmosphericpressure-to-vacuum may be required before the trapped air iscompletely removed.NOTE 3It is suggested that the density of the glass supplied beverified with the glass fiber producer.7.3 Resin Content of CompositeDetermine in accordancewith Test Method D 2584. The ignition loss in
33、 that test methodis the resin content of the sample and is to be recorded as theweight percent as indicated.8. Theoretical Density8.1 CalculationUsing the values determined in 7.1, 7.2,and 7.3, calculate theoretical density of a composite as follows:T 5 100/R/D 1 r/d! (1)where:T = theoretical densit
34、y,R = resin in composite, weight %,D = density of resin,r = reinforcement in composite, weight %, andd = density of reinforcement.8.2 Examples:From 7.1:D 5 1.230 g/cm3(2)From 7.2:d 5 2.540 g/cm3(3)From 7.3:R 5 28.55 weight %, (4)r 5 71.45 weight % (5)T 5 100/28.55/1.230 1 71.45/2.540! 5 1.949 g/cm (
35、6)D 2734 94 (2003)29. Void Content9.1 Test Method A:9.1.1 Calculation:V 5 100Td2 Md!/Td(7)where:V = void content, volume %,Td= theoretical composite density, andMd= measured composite density.Note that dividing two densities gives an unlabeled ratio,which in this case is the fraction of material mis
36、sing. It isequally correct to interpret this as a weight fraction or volumefraction, but in expressing voids it is always considered to bea volume fraction.9.1.2 Example:From 8:Td5 1.949 g/cm3(8)From 7.1:Md 5 1.903 g/cm (9)V 5 100 3 1.949 2 1.903!/1.949 5 2.36 % (10)Note that four significant figure
37、s have been used in thesecalculations. This represents a level of accuracy achieved onlyby careful work with optimum samples. For many, or perhapsthe majority of, determinations, such accuracy is not attainedand only three significant figures are warranted.9.2 Test Method BUsers may find this test m
38、ethod moreconvenient when only the void content value is wanted and thetheoretical density value is of no interest:9.2.1 Calculation:V 5 100 2 MdSrdr1gdgD(11)where:V = void content, volume %,Md= measured density,r = resin, weight %,g = glass, weight %,dr= density of resin, anddg= density of glass.9.
39、2.2 ExampleUsing the same number as in 8.2 and 9.1.2but to only three significant figures:V 5 100 2 1.90S28.61.23171.42.54D5 2.4 % (12)10. Report10.1 Report the following information:10.1.1 Complete identification of the materials tested,10.1.2 Density of all specimens,10.1.3 Weight fraction of resi
40、n and reinforcement, theoreti-cal density (if calculated), and void content of all compositespecimens,10.1.4 Method of test, and10.1.5 Date of test.11. Precision and Bias11.1 This test method does not yet contain a numericalprecision and bias statement and it shall not be used as a refereemethod in
41、case of dispute. The precision and bias of this testmethod are under investigation by a task group of Subcommit-tee D20.18. Anyone wishing to participate in this may contactthe Chairman, Subcommittee D20.18,ASTM, 100 Barr HarborDrive, West Conshohocken, PA 19428.12. Keywords12.1 composites; ignition
42、 loss; plastics; reinforced plastics;void content; weight fractionsASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any
43、such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are inv
44、ited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received
45、 a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).D 2734 94 (2003)3
