ASTM_D_7998_-_15.pdf

Designation:D799815Standard Test Method forMeasuring the Effect of Temperature on the CohesiveStrength Development of Adhesives using Lap Shear Bondsunder Tensile Loading1This standard is issued under the fixed designation D7998;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 parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This test method concerns bonding and testing of woodadhesives and related adhesives using small scale tensilelap-shear samples in a manner that emphasizes transientcohesive strength as a function of bonding time and tempera-ture.1.2 Use of thin adherends enables bondlines to be rapidlyheated to elevated temperatures and maintained at thosetemperatures for a range of times at a controlled pressurebefore testing.1.3 Optional rapid forced air cooling of bonds after pressingand immediately before testing enables the effect of testingtemperature on transient strength to be evaluated.1.4 Bond overlap distance is specified to ensure that failureoccurs in the bondline rather than in unbonded portions ofadherend strips,and also to minimize the effect of shear stressnon-uniformity along the overlap during tensile testing.1.5 Standard wood or alternative non-standard materialsmust be of specified high quality and uniformity of structureand dimension to minimize variability of bonding and maxi-mize stress transfer into the bonds during testing.1.6 The effect of wood variability and type,or of theproperties of alternative non-wood materials,on bond strengthdevelopment may be explored using the method.1.7 Optional hermetic sealing of bond overlaps during theirheated pressing enables the effect of moisture on bonding to beevaluated.1.8 Thermal damage,either of pre-formed bonds or byprolonging bond forming times,may be evaluated as a functionof time and elevated temperature using this test method.1.9 The values stated in SI units are to be regarded asstandard.No other units of measurement are included in thisstandard.1.10 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.Some specifichazards statements are given in Section 10 on Hazards.2.Referenced Documents2.1 ASTM Standards:2D907 Terminology of Adhesives3.Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 adherend strip,none of two adherend pieces thatconstitute a test specimen.3.2 adhesive spread rate,nthe mass of adhesive appliedper unit surface area of the overlap region of the adherend.3.3 contact heating,nthe transfer of heat energy to the testspecimen by the application of precisely temperature-controlled heads pressing on the test specimens surfaces withcontrolled force.3.4 forced air cooling,nthe rapid cooling of the overlapregion of a test specimen after bonding at elevated temperatureby the controlled application of air jets onto both external facesof the overlap portion of the specimen.3.5 test specimen,nthe lap shear sample made up of anadhesive between two pieces of adherend.3.6 thermal damage,nthe decrease in measured bondstrength due to exposure to a specified elevated temperature fora specified time.3.7 transient bond strength,nthe strength of a partiallyformed test specimen bond(sometimes referred to as“greenstrength”)upon being tested.1This test method is under the jurisdiction of ASTM Committee D14 onAdhesives and is the direct responsibility of Subcommittee D14.30 on WoodAdhesives.Current edition approved Sept.15,2015.Published November 2015.DOI:10.1520/D7998-15.2For referenced ASTM standards,visit 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.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 4.Significance and Use4.1 The test method enables strength values for wood andother materials bonded with an adhesive under a range ofcontrolled bonding temperature,time,and pressure conditionsto be evaluated.Bond formation and subsequent testing isaffected in a coordinated fashion,and this enables transientstrength values of sets of similar bond types to be exploredwith diverse parameters as independent variables.Principalamong these variables is the temperature at which bonds areformed and the time that selected temperatures are maintainedprior to testing.The use of controlled methods of adhesiveapplication,the rapid attainment of stable bond formationconditions,and the rapid transition to the bond testing modeenables snapshots of bond strength to be attained as bondsprogress from limited