ASTM_D_3532_-_D_3532M_-_12.pdf

Designation:D3532/D3532M12Standard Test Method forGel Time of Carbon Fiber-Epoxy Prepreg1This standard is issued under the fixed designation D3532/D3532M;the number immediately following the designation indicates theyear of original adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of lastreapproval.A superscript epsilon()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 This test method covers the determination of gel time ofcarbon fiber-epoxy tape and sheet.The test method is suitablefor the measurement of gel time of resin systems having eitherhigh or low viscosity.1.2 The values stated in either SI units or inch-pound unitsare to be regarded separately as standard.The values stated ineach system may not be exact equivalents;therefore,eachsystem shall be used independently of the other.Combiningvalues from the two systems may result in non-conformancewith the standard.1.2.1 Within the text,inch-pound units are shown in brack-ets.1.3 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.Summary of Test Method2.1 A specimen of prepreg material approximately 5 mm0.25 in.square is placed between microscope cover glasseson a hot plate preheated to either of two test temperatures,120or 175C 250 or 350F.Pressure is applied to the specimenthrough the coverglass with a wood pick to form a bead of resinat the edge of the cover glass.The time from the application ofheat until the resin ceases to form strings by contact with thepick is noted and reported as the gel time.3.Significance and Use3.1 This test method can be used to obtain the gel time ofresin squeezed from prepreg tape or sheet material.This test isa useful measure for material acceptance.3.2 The gel time will vary with the test temperature.Thetemperatures specified in this test method are two of manytemperatures often used in processing epoxy prepreg material.If other test temperatures are used,this is to be clearly noted asindicated in 9.1.2.3.3 Gel time is not recommended as a measure of outline(unacceptable degree of cross-linking).Use Resin Flow TestMethod D3532,or Dynamic Viscosity Practice D4473.4.Apparatus4.1 Cutting Knife.4.2 Hot Plate,capable of maintaining temperatures of either120C 250F or 175C 350F and the means of measuringits surface temperature to an accuracy of 61C 62F.4.3 Stopwatch or Suitable Timer,capable of reading 1-sintervals up to 60 min.4.4 Microscope Coverglasses,18 to 22 mm 0.7 to 0.9 in.in diameter.4.5 Wooden Probe,small,such as a toothpick,mounted in adrafting pencil holder or fine glass rod.A low thermal capacityis needed.5.Interferences5.1 The test is a subjective measure of when a gel point isreached.The visual evidence of gel may vary betweenmaterials,reinforcements,and,in some cases,between resinmaterial batches.If the definition of gel in this method is notsufficiently standard for a given material,interested partiesshall agree on a further definition of gelation.6.Test Specimen6.1 A minimum of three specimens shall be tested for eachsample.6.2 The test specimen shall consist of prepreg material cutto approximately 6-mm 0.25-in.square.7.Conditioning7.1 Storecarbonfiber-epoxyprepregtapeatlowtemperatures,approximately 18C 0F,to prolong the use-fulness of the material.Allow the sealed packages of materialto warm to ambient temperature before the seal is opened toensure that the material does not absorb moisture from theatmosphere.1This test method is under the jurisdiction of ASTM Committee D30 onComposite Materials and is the direct responsibility of Subcommittee D30.03 onConstituent/Precursor Properties.Current edition approved May 1,2012.Published June 2012.Originallyapproved in 1976.Last previous edition approved in 2009 as D3532 99(2009).DOI:10.1520/D3532_D3532M-12.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 8.Procedure8.1 Cut the specimen of prepreg.8.2 Preheat the hot plate to either test temperature A,120 61C 250 6 2F or B,175 6 1C 350 6 2F or thetemperature that has been specified.8.3 Place a cover glass on the hot plate and allow 20 s for itto reach temperature.8.4 Place the specimen in the center of the coverglass andcover it with another coverglass.8.5 Commence timing immediately.8.6 Probe the surface of the coverglass to apply pressure tothe prepreg specimen.Use the probe to isolate a bead of resinat the edge of the specimen.Continue to probe the bead of resinand observe its tendency to form strings.Select the point atwhich strings cannot be formed by contact with a pick as thegel time.Record this time as gel time.9.Report9.1 The report shall include the followi