ASTM_D_6746_-_15.pdf

Designation:D674615Standard Test Method forDetermination of Green Strength and Stress Relaxation ofRaw Rubber or Unvulcanized Compounds1This standard is issued under the fixed designation D6746;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 covers methods to evaluate a charac-teristic of raw rubber or unvulcanized rubber compounds thatis designated as green strength.This special strength propertyfor uncured rubbers is an important processing performanceattribute in rubber product manufacturing.1.2 The values stated in SI units are to be regarded asstandard.No other units of measurement are included in thisstandard.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.Referenced Documents2.1 ASTM Standards:2D412 Test Methods for Vulcanized Rubber and Thermoplas-tic ElastomersTensionD1349 Practice for RubberStandard Conditions for Test-ingD3182 Practice for RubberMaterials,Equipment,and Pro-cedures for Mixing Standard Compounds and PreparingStandard Vulcanized SheetsD4483 Practice for Evaluating Precision for Test MethodStandards in the Rubber and Carbon Black ManufacturingIndustries3.Terminology3.1 Definitions:3.1.1 green strength,na characteristic property of a raw orunvulcanized rubber compound that indicates resistance todeformation when stress is applied.3.1.1.1 DiscussionThe word“green,”applied to rubber,isa synonym for uncured or unvulcanized rubber.3.1.2 tensile green modulus,nratio of stress to strain of araw or unvulcanized rubber compound that indicates resistanceto tensile deformation or strain.3.1.3 tensile green strength,nyield stress of a raw orunvulcanized rubber compound that indicates loss of resistanceto tensile deformation or stress.4.Summary of Test Method4.1 This test method is divided into two parts.Part Aconsists of measurement of tensile stress and tensile moduluswhile a test specimen of raw or unvulcanized compoundedrubber is subjected to a constant rate of crosshead separation.Part B consists of subjecting a test specimen of raw orunvulcanized compounded rubber to a 100%strain conditionand measuring tensile stress after an interval while maintainingthe strained condition.4.2 Part A of this test method consists of measuring thetensile stress-strain characteristics of a dumbbell or otherrecommended test piece of raw or unvulcanized compoundedrubber are determined on a tensile testing machine capable ofmaintaining a constant rate of separation of the moving jaws.4.3 In evaluating tensile green strength,several types ofstress-strain behavior may be observed,depending on therubber and the composition of the unvulcanized compound.(See Section 5.)Fig.1 indicates three typical stress-straincurves.Type 1 has a yield point and exhibits increasing stressbeyond the yield point,culminating in rupture at a higher stressand elongation compared to the initial yield stress.Type 2 alsohas a yield point,but beyond this point follows a decreasingstress behavior as the maximum rupture elongation is attained.Type 3 has a stress-strain curve that is similar to cured rubbers,with no elongation beyond the point of rupture at maximum(yield)stress.4.4 Part B of this test method consists of a dumbbell or otherrecommended test specimen being placed in the grips of atensile machine capable of a constant rate of grip separation,pausing the grip separation when an initial strain condition of1This test method is under the jurisdiction of ASTM Committee D11 on Rubberand is the direct responsibility of Subcommittee D11.12 on Processability Tests.Current edition approved Nov.1,2015.Published December 2015.Originallyapproved in 2002.Last previous edition approved in 2010 as D6746 10.DOI:10.1520/D6746-15.2For 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 FIG.1 Typical Tensile Stress-Strain CurvesD6746 152 100%is reached,and reporting the tensile stress after aspecific time interval or the time for a given percentage ofstress decay.5.Significance and Use5.1 The stress-strain properties of unvulcanized rubber(ei-ther in a compound or in the raw state)are important to certainprocessing operations in the rubber industry.These unvulca-nized rubber properties are frequently referred to as“greenstrength.”5.2 Green strength is determined primaril