1、Designation: D2734 16Standard Test Methods forVoid Content of Reinforced Plastics1This standard is issued under the fixed designation D2734; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in par
2、entheses indicates the year of last reapproval. Asuperscript 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 void content of reinforcedplasti
3、cs 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 plastics, the reinfo
4、rcement,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 or lose weight.
5、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 asstandard.1.3 This standard does
6、 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 Documents2.1 ASTM Stand
7、ards:2D618 Practice for Conditioning Plastics for TestingD792 Test Methods for Density and Specific Gravity (Rela-tive Density) of Plastics by DisplacementD1505 Test Method for Density of Plastics by the Density-Gradient TechniqueD2584 Test Method for Ignition Loss of Cured ReinforcedResins3. Summar
8、y 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 indicates the void content. A
9、 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 background experience, or both.
10、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 strength properties. The kn
11、owledge 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 thisassumption, it is nevertheless not
12、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 For composites with high
13、 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, and illustrates that as
14、 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 ASTM Committee D20 onPla
15、stics and are the direct responsibility of Subcommittee D20.18 on ReinforcedThermosetting Plastics.Current edition approved Sept. 1, 2016. Published September 2016. Originallyapproved in 1968. Last previous edition approved in 2009 as D2734 09. DOI:10.1520/D2734-16.2For 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.*A Summary of Changes section appears at the end of this standardCopyright ASTM International,
17、100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1individual 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(PEE
18、K), an interference due to the level of crystallinity presentin 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, thedens
19、ity used in the calculation must be the actual density of theresin 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 diffraction.6. Conditioning6.1 ConditioningCondition the test specimen
20、s at 23 62C (73.4 6 3.6F) and 50 6 10 % relative humidity for notless than 40 h prior to test in accordance with Procedure A ofPractice D618, for those tests where conditioning is required.In cases of disagreement, the tolerances shall be 1C (1.8F)and 62 % relative humidity.6.2 Test ConditionsConduc
21、t tests in the standard labora-tory atmosphere of 23 6 2C (73.4 6 3.6F) 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 65 % relative humidity.7. Procedure7.1 Density of the Resin and the CompositeThree tes
22、tmethods are presented for these measurements. Measure thedensity on 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 manu
23、fac-turer are acceptable if they are certified for each batch.7.1.1 Test Method AMeasure densities using Test MethodsD792. Paragraph 1.1 of that test method requires the specimento have smooth edges and surfaces. For composites, thisrequirement may necessitate hand sanding the specimen with400-grit
24、emery paper to remove fuzzy edges caused by cutting.The specimen should be as free as possible from geometricirregularities which tend to trap air bubbles. Remove anybubbles by a wire, or other mechanical means. Do not use avacuum to remove bubbles, because cut surfaces of compositesmay be porous an
25、d exposure to a vacuum will force water intothe pores, causing an error in the density measurement. In somecases of extreme porosity, just immersing the composite inwater, without using a vacuum, will allow an unacceptablylarge amount of water take-up by the composite. In these cases,seal the porous
26、 surfaces by coating them with a known amountof sealer of known density. 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
27、withTest Method D1505. The comments in 7.1.1 concerning fuzzyedges 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 accu
28、ratelyfrom the dimensions.7.1.3.2 ProcedureThe volume of each specimen shall notbe less than 2 cm3(0.125 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 o
29、n the accuracy of the micrometermeasurements shall be 60.0013 cm (60.0005 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, th
30、e error in thecalculated volume should not exceed 0.2 %.7.1.3.4 Calculate the density by dividing the weight by thevolume; express as grams per cubic centimeter.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
31、; S glass density is 2.46 to 2.49g/cm3. However, if a density determination is necessary, useTest Methods D792. 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 determ
32、ination of glass density. Use avacuum of 3 mm Hg or better. Several 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 be verifiedwith the glass fiber producer.7.3 Resin Content of Composite
33、Determine in accordancewith Test Method D2584. The ignition loss in 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 comp
34、osite as follows:Td5 100/R/D1r/d! (1)where:Td= theoretical composite density,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%,
35、(4)D2734 162r 5 71.45 weight% (5)Td5 100/28.55/1.230171.45/2.540! 5 1.949 g/cm (6)9. 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 unl
36、abeled ratio,which in this case is the fraction of material missing. 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:Md5 1.903 g/cm3(9)V 5 100 3 1.94
37、9 2 1.903!/1.949 5 2.36% (10)Note that four significant figures 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 fig
38、ures are warranted.9.2 Test Method BUsers may find this test method 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 MdSRD1rdD(11)where:V = void content, volume %,Md= measured composite density,R = resin in compo
39、site, weight %,r = reinforcement in composite, weight %,D = density of resin, andd = density of reinforcement.9.2.2 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
40、 Complete identification of the materials tested,10.1.2 Density of all specimens,10.1.3 Weight fraction of resin 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 meth
41、od does not yet contain a numericalprecision and bias statement and it shall not be used as a refereemethod in 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, Su
42、bcommittee D20.18,ASTM, 100 Barr HarborDrive, West Conshohocken, PA 19428.12. Keywords12.1 composites; ignition loss; plastics; reinforced plastics;void content; weight fractionsSUMMARY OF CHANGESCommittee D20 has identified the location of selected changes to this standard since the last issue (D27
43、34 - 09)that may impact the use of this standard. (September 1, 2016)(1) Corrected the spelling of “diffraction” in Note 2.(2) Corrected the spelling of “take-up”in 7.1.1.(3) Corrected the spelling of “centimeter” in 7.1.3.4.(4) Modified terms and variables of Eq 1 (8.1) to be consistentthroughout t
44、he document.(5) Corrected format of variable and units in Eq 9 (9.1.2).(6) Modified terms and variables of Eq 11 (9.2.1)tobeconsistent throughout the document.D2734 163ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin t
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