1、Designation:D 2951 00Standard Test Method forResistance of Types III and IV Polyethylene Plastics toThermal Stress-Cracking1This standard is issued under the fixed designation D 2951;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,th
2、e year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon(e)indicates an editorial change since the last revision or reapproval.1.Scope*1.1 This test method covers determination of the suscepti-bility of Types III and IV polyethylene plastics(as defin
3、ed inthe table on Classification of Polyethylene Plastics Moldingand Extrusion Materials According to Type,in SpecificationD 1248)to thermal stress-cracking.NOTE1It has also been found useful in testing specimens fromfabricated items such as pipe or conduit.1.2 The values stated in SI units are to b
4、e regarded as thestandard,except in cases where materials,products,or equip-ment are available only in inch-pound units.The values inparentheses are given for information only.1.3 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibili
5、ty 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.Specific precau-tionary statements are given in Note 7.NOTE2There is no similar or equivalent ISO standard.2.Referenced Documents2.1 ASTM Stan
6、dards:A 276 Specification for Stainless Steel Bars and Shapes2D 618 Practice for Conditioning Plastics and ElectricalInsulating Materials for Testing3D 883 Terminology Relating to Plastics3D 1248 Specification for Polyethylene Plastics Molding andExtrusion Materials3D 4703 Practice for Compression M
7、olding ThermoplasticMaterials into Test Specimens,Plaques,or Sheets4E 145 Specification for Gravity-Convection and Forced-Ventilation Ovens53.Terminology3.1 Definitions:3.1.1 For definitions of terms see Terminology D 883.4.Summary of Test Method4.1 Strips of material 127 by 6.4 by 1.3 mm(5.0 by 0.2
8、5 by0.050 in.)are cut from a molded test sheet.The strips arehelically wrapped and fastened to a 6.4-mm(0.25-in.)diametermetal rod.The assembly is then placed in the specified testenvironment.The specimens are examined at the end ofspecified time intervals and the cumulative number of thosewhich hav
9、e failed is recorded for each time interval.5.Significance and Use5.1 Resistance to thermal stress-cracking is a property thatis of importance in material used for jacketing and insulation ofwire and cable.5.2 As a general correlation between test results and fieldperformance has been recognized,thi
10、s test may be consideredsuitable for specification acceptance.6,75.3 Some polyethylenes embrittle or crack if they areexposed to elevated temperatures.This embrittlement mayresult in severe cracking,especially if the polymers are stressedduring exposure.The phenomena causing thermal-stress crack-ing
11、 are not clearly understood.It is evident that either increas-ing the density or decreasing the molecular weight has adetrimental effect on the resistance to thermal-stress cracking.5.4 This is a pass or fail test,not intended for arrangingvarious Type III and IV polyethylene plastics in a series.6.
12、Apparatus6.1 Blanking Die,with a rectangular opening,127 by 6.4mm(5.0 by 0.25 in.).The cutting edges shall be sharp and freeof nicks so that clean cuts are made.86.2 Leather Punch,Drill or Equivalent,capable of produc-ing clean holes approximately 1.6 mm(116in.)in diameter.1This test method is under
13、 the jurisdiction ofASTM Committee D20 on Plasticsand is the direct responsibility of Subcommittee D20.15 on Thermoplastic Materi-als.Current edition approved July 10,2000.Published September 2000.Originallypublished as D 2951 71.Last current edition D 2951 95.2Annual Book of ASTM Standards,Vol 01.0
14、3.3Annual Book of ASTM Standards,Vol 08.01.4Annual Book of ASTM Standards,Vol 08.03.5Annual Book of ASTM Standards,Vol 14.04.6Heiss,J.H.,and Lanza,V.L.,Wire and Wire Products,Vol 33,pp 118287(1958).7Heiss,J.H.,Lanza,V.L.,and Martin,W.M.,Wire and Wire Products,pp592593,pp 626627,May 1959.ASTM Round R
15、obin,RR:D201000.8Round-robin data for this test method may be obtained from ASTM Headquar-ters.Request RR:D20-1008.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959,United States.6.3 Speci
16、men MandrelsStainless steel or brass rods,6.406 0.05 mm(0.25 6 0.002 in.)in diameter by 165 mm(6.5 in.)long with three pairs of 1.6-mm(116-in.)diameter holes spaced34.9 mm(1.375 in.)apart(center-to-center)and each pairseparated from adjacent pairs by 12.7 mm(0.50 in.).The holesin the mandrel must be parallel.See Fig.1.NOTE3Type 316 stainless steel,Specification A 276 is satisfactory.6.4 Machine Screws,stainless steel or brass,size 0-80,0.50in.long(or approximately 1.4-mm diameter,0.3-mm pitch,12
