1、Designation: C 158 02 (Reapproved 2007)Standard Test Methods forStrength of Glass by Flexure (Determination of Modulus ofRupture)1This standard is issued under the fixed designation C 158; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revi
2、sion, the 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.This standard has been approved for use by agencies of the Department of Defense.1. Scope1.1 These test methods
3、 cover the determination of themodulus of rupture in bending of glass and glass-ceramics.1.2 These test methods are applicable to annealed andprestressed glasses and glass-ceramics available in variedforms. Alternative test methods are described; the test methodused shall be determined by the purpos
4、e of the test andgeometric characteristics of specimens representative of thematerial.1.2.1 Test Method A is a test for modulus of rupture of flatglass.1.2.2 Test Method B is a comparative test for modulus ofrupture of glass and glass-ceramics.1.3 The test methods appear in the following order:Secti
5、onsTest Method ATest Method B6 to 910 to 151.4 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 regulato
6、ry limitations prior to use. Specific hazardstatements are given in Section 10 and A1.5, A2.3.3, A2.4.3and A2.5.3.2. Referenced Documents2.1 ASTM Standards:2C 148 Test Methods for Polariscopic Examination of GlassContainersE4 Practices for Force Verification of Testing MachinesSI10-02 IEEE/ASTM SI 1
7、0 American National Standardfor Use of the International System of Units (SI): TheModern Metric System3. Terminology3.1 Definitions:3.1.1 glass-ceramicssolid materials, predominantly crys-talline in nature, formed by the controlled crystallization ofglasses.3.1.2 modulus of rupture in bendingthe val
8、ue of maxi-mum tensile or compressive stress (whichever causes failure)in the extreme fiber of a beam loaded to failure in bendingcomputed from the flexure formula:Sb5McI(1)where:M = maximum bending moment, computed from themaximum load and the original moment arm,c = initial distance from the neutr
9、al axis to the extremefiber where failure occurs, andI = initial moment of inertia of the cross section about theneutral axis.3.1.3 prestressedmaterial in which a significant and con-trolled degree of compressive stress has been deliberatelyproduced in the surfaces.3.1.4 standard laboratory atmosphe
10、rean atmosphere hav-ing a temperature of 23 6 2C and a relative humidity of 40 610 %.3.2 Definitions of Terms Specific to This Standard:3.2.1 abradeddescribes a test specimen that has at least aportion of the area of maximum surface tensile stress subjectedto an operationally defined procedure for m
11、echanical abrasion.The severity and uniformity of abrasion should be sufficient toensure origin of failure substantially in the region of maximumstress.3.2.2 annealed glassdescribes a specimen that shall nothave a temper or degree of residual stress resulting from priorthermal treatment in excess of
12、 the following limits whenmeasured polarimetrically (see Annex A1):1These test methods are under the jurisdiction of ASTM Committee C14 onGlass and Glass Products and are the direct responsibility of Subcommittee C14.04on Physical and Mechanical Properties.Current edition approved April 1, 2007. Pub
13、lished May 2007. Originallyapproved in 1940. Last previous edition approved in 2002 as C 158 02.2For 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 Docume
14、nt Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.2.2.1 Specimens of rectangular section shall not have atensile stress at the midplane of more than 1.38-MPa (200-psi)nor more than 2.76-MPa (400-psi
15、) compression at the surface.3.2.2.2 Specimens in rod form may be examined by viewingthrough a diameter at least four diameters from an end. Theapparent central axial tension shall not exceed 0.92 MPa (133psi). Surface compression, if measured on sections cut from therods, shall not exceed 2.76 MPa
16、(400 psi) when viewed axially.4. Significance and Use4.1 For the purpose of this test, glasses and glass-ceramicsare considered brittle (perfectly elastic) and to have theproperty that fracture normally occurs at the surface of the testspecimen from the principal tensile stress. The modulus ofruptur
17、e is considered a valid measure of the tensile strengthsubject to the considerations discussed below.4.2 It is recognized that the modulus of rupture for a groupof test specimens is influenced by variables associated with thetest procedure. These include the rate of stressing, test envi-ronment, and
18、 the area of the specimen subjected to stress. Suchfactors are specified in the test procedure or required to bestated in the report.4.3 It is also recognized that the variables having thegreatest effect on the modulus of rupture value for a group oftest specimens are the condition of the surfaces a
19、nd glassquality near the surfaces in regard to the number and severityof stress-concentrating discontinuities or flaws, and the degreeof prestress existing in the specimens. Each of these canrepresent an inherent part of the strength characteristic beingdetermined or can be a random interfering fact
20、or in themeasurement.4.4 Test Method A is designed to include the condition ofthe surface of the specimen as a factor in the measuredstrength. It is, therefore, desirable to subject a fixed andsignificant area of the surface to the maximum tensile stress.Since the number and severity of surface flaw
21、s in glass areprimarily determined by manufacturing and handling pro-cesses, this test method is limited to products from whichspecimens of suitable size can be obtained with minimaldependence of measured strength upon specimen preparationtechniques. This test method is therefore designated as a tes
22、tfor modulus of rupture of flat glass.4.5 Test Method B describes a general procedure for test,applicable to specimens of rectangular or elliptical crosssection. This test method is based on the assumption that acomparative measurement of strength on groups of specimensis of significance for many pu
23、rposes, such as determining theeffect of environment or stress duration, or the effectiveness ofvaried prestressing techniques or strengths characteristic ofglass-ceramics of differing composition or heat treatment. Inthis test method the surfaces of the specimens are not assumedto be characteristic
24、 of a product or material, but are consideredto be determined by the procedures used to prepare thespecimens. Though the stated procedure permits a wide varia-tion in both specimen size and test geometry, it is necessary touse identical test conditions and equivalent procedures forspecimen preparati
25、on to obtain comparable strength values.The use of a controlled abrasion of the specimen as a finalnormalizing procedure is recommended for such comparativetests.4.6 A comparative abraded strength, determined as sug-gested in Test Method B, is not to be considered as a minimumvalue characteristic of
26、 the material tested nor as directly relatedto a maximum attainable strength value through test ofspecimens with identical flaws. The operationally definedabrasion procedure undoubtedly produces flaws of differingseverity when applied to varied materials, and the measuredcomparative strengths descri
27、be the relative ability to withstandexternally induced stress as affected by the specific abrasionprocedure.5. Apparatus5.1 Testing MachineThe loading mechanism shall besufficiently adjustable to give the required uniform rate ofincrease of stress. The load-measuring system shall be essen-tially fre
28、e of inertial lag at the loading rates used and shall beequipped with means for retaining indication of the maximumload applied to the specimen. The accuracy of the testingmachine shall conform to the requirements of Practice E4.5.2 Bearing EdgesCylindrical bearing edges of approxi-mately 3-mm (18-i
29、n.) radius shall be used for the support of thetest specimen and the application of the load. The bearingedges shall be of steel and sufficiently hardened to preventexcessive deformation under load. Two-point loading testsshall be performed with the loading member pivoted about acentral transverse a
30、xis to ensure equal distribution of loadbetween the two bearing edges. For the testing of specimens ofrectangular section, both loading bearing edges and one sup-port bearing edge also shall be provided laterally to compen-sate for irregularities of the test specimen. Fig. 1 shows asuitable arrangem
31、ent using pinned bearing edges. In test ofspecimens of a circular or elliptical section, the fixed cylindri-cal support edges may have a curvature of approximately 76mm (3 in.) in the plane of the bearing edge to stabilize thealignment of the specimens. Such support edges are shown inFig. 2.TEST MET
32、HOD ATEST FOR MODULUS OFRUPTURE OF FLAT GLASS6. Test Specimens6.1 Preparation of SpecimensTest specimens shall be cutfrom the sheet stock with a diamond or a cutting wheel. Bothlongitudinal cuts shall be on the same original surface and noneof the original edge of the sheet shall be used as a longit
33、udinalside of the specimen. End cuts may be on either surface. Thedirection of cutting of half of the total number of specimensshall be perpendicular to the direction of cutting of theremainder. Specimens that must be cut from sheet stock priorto the use of a prestressing treatment shall have the co
34、rners ofthe longitudinal edges rounded to minimize damage to theedges in the prestressing process. All operations shall beperformed with the direction of grind or polish parallel to thelongitudinal axis. The radius of the corner shall not exceed 1.6mm (116 in.).C 158 02 (2007)26.2 Size of SpecimensT
35、he specimens shall be approxi-mately 250 mm (10 in.) in length and 38.1 6 3.2 mm (112 618 in.) in width. The variation in width or thickness shall notexceed 5 % from one end to the other.6.3 Number of SpecimensAt least 30 specimens shall beused for one test and shall preferably be taken from several
36、sheets, or regions of a single sheet.6.4 Examination of SpecimensAny specimen may berejected prior to test for observable defects considered likely toaffect the modulus of rupture. To be considered representativeof annealed glass the specimens must meet the requirement of3.2.2. At least 30 % of the
37、specimens shall be examined forresidual stress. If any of these fail to meet the requirement, theremainder of the specimens shall be examined and thoseexceeding the stated limit shall be rejected.6.5 Float GlassThe surface of float glass in contact withtin has been found to be lower in strength (7)
38、as compared tothe “air” surface. For comparative tests, therefore, surfaceorientation should be kept constant.7. Procedure7.1 Space the supporting edges of the test fixture 200 mm(8.00 in.) apart and centrally position the loading edges with aseparation of 100 mm (4.00 in.). Break specimens having c
39、utedges with the cutter marks on the face under compression.Carefully place each specimen in the test fixture to minimizepossible damage and to ensure alignment of specimen in thefixture. The permissible maximum fiber stress due to initialload on the specimen shall not exceed 25 % of the meanmodulus
40、 of rupture. Load the specimen at a constant rate tofailure. For annealed glass the rate of loading shall correspondto a rate of increase of maximum stress of 1.1 6 0.2 MPa/s(10 000 6 2000 psi/min). Test prestressed glasses with theincrease of maximum stress per minute between 80 and 120 %of the mod
41、ulus of rupture. The first six specimens of the groupmay be tested at a loading rate based on an estimate of themodulus of rupture and the average value for these specimensused to correct this estimate. If range of width and thicknessvariation in the specimens is less than 5 %, the mean valuesmay be
42、 used to represent all specimens for the purpose ofcalculation of rate of loading.7.2 Determine the thickness and width of each specimen to61 %. To avoid damage from gaging in the critical area, takemeasurements prior to testing near each end with a separationequal to the support span, and average t
43、he values. Measure-ments following test shall be in the uniformly stressed regionof the specimen.7.3 Determine the location of point of failure and note it asedge or face origin. Plastic or other tape of low elastic modulusmay be used on the compressive surface to contain thefragmentation and allow
44、observation of point of failure forFIG. 1 Pinned Bearing EdgesFIG. 2 Fixed Cylindrical Support EdgesC 158 02 (2007)3highly prestressed specimens. Report all values, althoughsegregation of edge break values is permitted.8. Calculation8.1 Calculate the modulus of rupture, initial maximum fiberstress,
45、and rate of increase of stress as follows:8.1.1 Modulus of rupture:S 53 Labd2(2)8.1.2 Maximum stress due to initial load if present:S053 L0abd2(3)8.1.3 Rate of increase of maximum stress:R 53abd23DLDt(4)R 5 S 2S0twhere:S = modulus of rupture, MPa (psi),S0= maximum fiber stress due to initial load if
46、present, MPa (psi),R = rate of increase of maximum fiber stress, MPa/s(psi/min),L = breaking load including initial load, N (lbf),L0= initial load, N (lbf),a = moment arm or distance between adjacent sup-port and loading edges, mm (in.),b = width of specimen, mm (in.),d = thickness of specimen, mm (
47、in.),t = time from start of continuous loading to rupture,s (min), andDL/Dt = rate of increase of load, N/s (lbf/min).9. Report9.1 Report the following:9.1.1 Test method used,9.1.2 Identification of the glass tested, including any specialtreatment (for specimens derived from manufacturing pro-cesses
48、 that are asymmetric in nature; for example, the floatprocess, the side of the sheet placed in tension during test shallbe identified, if possible),9.1.3 Classification as annealed or prestressed glass,9.1.4 Test environment if other than standard laboratoryatmosphere,9.1.5 Rate of increase of maxim
49、um stress,9.1.6 Value of modulus of rupture for each specimen anddesignation of point of failure as edge or face, and9.1.7 Average value of the modulus of rupture for the groupand the standard deviation estimate of the mean. Separatevalues may be determined for edge and face origins.NOTE 1See Annex A3 for conversion from inch-pound units andother non-SI units to SI units.TEST METHOD BCOMPARATIVE TEST FORMODULUS OF RUPTURE OF GLASS AND GLASS-CERAMICS10. Hazards10.1 Care should be exercised in all handling of specimensto avoid the introduction of random and sever
