D790 – 10.pdf

Designation: D790 – 10

Standard Test Methods for

Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials 1 This standard is issued under the fixed designation D790; the number immediately following the designation indicates the year of original origin al adoption or, in the case of revis revision, ion, the year of last revision. revision. A number in paren parenthese thesess indicates the year of last reappr reapproval. oval. 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. Sco Scope* pe* 1.1 These test methods cover the determination determination of flexural flexural properties prope rties of unrei unreinforc nforced ed and reinf reinforced orced plastics, includ including ing high-modulus composites and electrical insulating materials in the form of rectangular bars molded directly or cut from sheets, plates, plat es, or mol molded ded shapes. shapes. The These se tes testt meth methods ods are gen genera erally lly applica app licable ble to bot both h rig rigid id and semi semirig rigid id mat materia erials. ls. How Howeve ever, r, flexural strength cannot be determined for those materials that do not break or that do not fail in the outer surface of the test specimen within the 5.0 % strain limit of these test methods. These test methods utilize a three-point loading system applied to a sim simply ply sup suppor ported ted bea beam. m. A fou fourr-poi point nt loa loadin ding g sys system tem method can be found in Test Method D6272 D6272.. 1.1.1 Procedure A, designed principally for materials that break at comparatively small deflections. 1.1.2 Procedure B, designed particularly for those materials that undergo large deflections during testing. 1.1.3 Proced Procedure ure A shall be used used for measur measurement ement of flexur flexural al properties, prope rties, particularly particularly flexur flexural al modul modulus, us, unless the materia materiall specification states otherwise. Procedure B may be used for measurement of flexural strength only. Tangent modulus data obta ob tain ined ed by Pr Proc oced edur uree A ten tends ds to ex exhi hibi bitt lo lowe werr sta stand ndar ard d deviations than comparable data obtained by means of Procedure B. 1.2 Compa Comparative rative tests may be run in accordance accordance with either procedure, provided that the procedure is found satisfactory for the material being tested. 1.3 The values values stated in SI uni units ts are to be reg regard arded ed as the standard. The values provided in parentheses are for information only. 1.4 This standar standard d doe doess not purport purport to add addre ress ss all of the safet sa fetyy co conc ncer erns ns,, if an anyy, as asso socia ciate ted d wit with h its us use. e. It is th thee responsibility of the user of this standard to establish appro` , , , ` ` , ` ` ` , , ` , ` ` ` , , , , , , ` ` ` , ` , ` ` , , ` , , ` , ` , , ` -

1

These test methods are under the jurisdiction of ASTM Committee D20 on Plastics and are the direct responsibility of Subcommittee D20.10 Subcommittee D20.10 on Mechanical Properties. Curren Cur rentt edi editio tion n app approv roved ed Apr April il 1, 201 2010. 0. Pub Publis lished hed Apr April il 201 2010. 0. Ori Origin ginall ally y approved in 1970. Last previous edition approved in 2007 as D790 – 07 1. DOI: 10.1520/D0790-10. ´

priate safety and health practices and determine the applicability of regulatory limitations prior to use. NOTE 1—These test methods are not technically equivalent to ISO to ISO 178. 178.

2. Referenc Referenced ed Documents 2.1 ASTM Standards: 2 D618 Practice for Conditioning Plastics for Testing D638 Test Method for Tensile Properties of Plastics D883 Terminology Relating to Plastics D4000 Classification System for Specifying Plastic Materials D4101 Specification for Polypropylene Injection and Extrusion Materi Materials als D5947 Test Test Meth Methods ods for Phy Physica sicall Dim Dimens ension ionss of Sol Solid id Plastics Specimens D6272 Test Method for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials by Four-Point Bending E4 Practices for Force Verification of Testing Machines E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method 2.2 ISO Standard: Standard:3 ISO 178 Plastics—Determination of Flexural Properties 3. Terminology 3.1 Definitions—Defini —Definitions tions of terms applying applying to these test methods appear in Terminology D883 and Annex A1 of Test Method D638 Method D638.. 4. Summ Summary ary of Test Test Method 4.1 A bar of rectangular rectangular cross section section rests on two supp supports orts and is loaded by means of a loading nose midway between the supports. A support span-to-depth ratio of 16:1 shall be used unless unl ess the there re is rea reason son to sus suspec pectt tha thatt a lar larger ger span-tospan-to-dep depth th 2

For refere referenced nced ASTM stand standards, ards, visit the ASTM webs website, ite, www www.ast .astm.org m.org,, or contact ASTM Customer Service at [email protected]. For Annual Book of ASTM Standards volume information, refer to the standard’s Document Summary page on the ASTM website. 3 Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http://www.ansi.org.

*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. Copyright ASTM International Provided by IHS under license with ASTM No reproduction or networking permitted without license from IHS

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D790 – 10 ratio may be required, as may be the case for certain laminated materials (see Section 7 Section 7 and and Note Note 7 for guidance). 4.2 The specimen specimen is defl deflecte ected d unt until il rup ruptur turee occ occurs urs in the outer surface of the test specimen or until a maximum strain (see 12.7 (see 12.7)) of 5.0 % is reached, whichever occurs first. 4.3 Proce Procedure dure A employ employss a strain rate of 0.01 mm/mm/min (0.01 in./in./min) and is the preferred procedure for this test metho met hod, d, wh while ile Pr Proc oced edur uree B em empl ploy oyss a str strain ain ra rate te of 0. 0.10 10 mm/mm/min (0.10 in./in./min). 5. Sign Significan ificance ce and Use 5.1 Flexu Flexural ral properties properties as determ determined ined by these test method methodss are esp especia ecially lly use useful ful for qua quality lity con contro troll and spe specific cificatio ation n purposes. 5.2 5. 2 Ma Mate teri rial alss th that at do no nott fa fail il by th thee ma maxi ximu mum m st stra rain in allowed under these test methods (3-point bend) may be more suited to a 4-point bend test. The basic difference between the two test methods is in the location of the maximum bending moment and maximum axial fiber stresses. The maximum axial fiber stresses occur on a line under the loading nose in 3-point bending and over the area between the loading noses in 4-point bending. 5.3 Flexur Flexural al pro proper perties ties may var vary y wit with h spe specim cimen en dep depth, th, temperature, atmospheric conditions, and the difference in rate of straining as specified in Procedures A and B (see also Note 7). 5.4 Bef Before ore pro procee ceedin ding g wit with h the these se test met method hods, s, ref refere erence nce should sho uld be mad madee to the ASTM ASTM spe specific cificatio ation n of the material material being bein g test tested. ed. Any test spe specim cimen en pre prepar paratio ation, n, con condit dition ioning ing,, dimens dim ension ions, s, or test testing ing par paramet ameters ers,, or com combin binatio ation n the thereo reof, f, covered in the ASTM material specification shall take precedence over those mentioned in these test methods. Table 1 in Classification System D4000 System D4000 lists the ASTM material specifications that currently exist for plastics. 6. Appar Apparatus atus 6.1 Testing proper perly ly cali calibra brated ted test testing ing maTesting Machine— A pro chine that can be operated at constant rates of crosshead motion over the range indicated, and in which the error in the load measuring system shall not exceed 61 % of the maximum load expected expecte d to be measured. It shall be equip equipped ped with a deflecti deflection on measuring device. The stiffness of the testing machine shall be TABLE 1 Flexur Flexural al Strength Material

ABS DAP thermoset Cast acrylic GR polyester GR polycarbonate SM C

Mean, 103 psi

9. 99 1 4 .3 1 6 .3 1 9 .5 2 1 .0 2 6. 0

A

Values Expressed in Units of % of 103 psi V rA

V RB

r C

R D

1 .5 9 6 .5 8 1 .6 7 1 .4 3 5 .1 6 4. 76

6..05 6 6. 58 11.3 2. 14 6 .0 5 7 .1 9 7.

4..44 4 1 8 .6 4 .7 3 4 .0 5 1 4. 6 1 3. 5 13

17 1 7. 2 1 8. 6 3 2. 0 6 .0 8 1 7 .1 2 0 .4 20

V r = within-laboratory coefficient of variation for the indicated material. It is obtained by first pooling the within obtained within-labor -laboratory atory standard deviations deviations of the test results from all of the participating laboratories: Sr laboratories: Sr = [[(s [[(s 1)2 + (s ( s 2)2 . . . + ( s n)2]/n] 1/2 then then V V r = (S r divided by the overall average for the material) 3 100. B V r = between-laboratory reproducibility, expressed as the coefficient of variation: S tion: S R = {S r 2 + S L2 }1/2 where where S S L is the standard deviation of laboratory means. Then: V Then: V R = (S ( S R divided by the overall average for the material) 3 100. C r = = withi within-labo n-laboratory ratory critical interval between two test results = 2.8 3 V r . D R = between-laboratory critical interval between two test results = 2.8 3 V R . R

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such that the total elastic deformation of the system does not exceed 1 % of the total deflection of the test specimen during testing test ing,, or app approp ropriat riatee cor correc rectio tions ns sha shall ll be mad made. e. The loa load d indicating mechanism shall be essentially free from inertial lag at the cross crosshead head rate used. The accuracy of the testing machine machine shall be verified in accordance with Practices E4 E4.. 6.2 Loading —Thee loa loadin ding g nos nosee and Loading Noses and Supports—Th supports shall have cylindrical surfaces. The default radii of the loading nose and supports shall be 5.0 6 0.1 mm (0.197 6 0.004 0.0 04 in.) unless oth otherw erwise ise spe specifie cified d in an ASTM mate material rial specification or as agreed upon between the interested parties. When the use of an ASTM material specification, or an agreed upon up on mo modi dific ficati ation on,, re resu sults lts in a ch chan ange ge to th thee ra radi diii of th thee loading nose and supports, the results shall be clearly identified as being obtained from a modified version of this test method and shall include the specification (when available) from which the modification was specified, for example, Test Method D790 in accordance with Specification D4101 Specification D4101.. 6.2.1 Other Radii for Loading Noses and Supports —When other than default loading noses and supports are used, in order to avoid excessive indentation, or failure due to stress concentration directly under the loading nose, they must comply with the following requirements: requirements: they shall have a minimu minimum m radiu radiuss of 3.2 mm (1 ⁄ 8 in.) for all specimens. For specimens 3.2 mm or greater in depth, the radius of the supports may be up to 1.6 times the specimen depth. They shall be this large if significant indenta ind entatio tion n or com compre pressi ssive ve fai failur luree occ occurs urs.. The arc of the loading loadin g nose in contac contactt with the specime specimen n shall be suf suffficientl iciently y large to prevent contact of the specimen with the sides of the nose. The maximum radius of the loading nose shall be no more than four times the specimen depth. 6.3 Micrometers— Suitable micrometers for measuring the width wid th and thicknes thicknesss of the tes testt spe specim cimen en to an inc increm rement ental al discriminatio discri mination n of at least 0.02 0.025 5 mm (0.00 (0.001 1 in.) shoul should d be used. All width and thickness measurements of rigid and semirigid plastics may be measured with a hand micrometer with ratchet. A suitable instrument for measuring the thickness of nonrigid test spe specim cimens ens sha shall ll hav have: e: a con contact tact mea measur suring ing pre pressu ssure re of 25 6 2.5 kPa (3.6 6 0.36 psi), a movable circular contact foot 6.35 6 0.025 mm (0.250 6 0.001 in.) in diameter and a lower fixed anvil large enough to extend beyond the contact foot in all directions and being parallel to the contact foot within 0.005 mm (0.002 in.) over the entire foot area. Flatness of foot and anvil shall conform to the portion of the Calibration section of Test Methods D5947 Methods D5947.. ` , , ` , ` , , ` , , ` ` , ` , ` ` ` , , , , , , ` ` ` , ` , , ` ` ` , ` ` , , , ` -

7. Test Specimens 7.1 The sp 7.1 speci ecime mens ns may be cu cutt fr from om sh sheet eets, s, pl plate ates, s, or mold mo lded ed sh shap apes es,, or ma may y be mo mold lded ed to th thee de desir sired ed fin finish ished ed dimensions. The actual dimensions used in Section 4.2 4.2,, Calculation, shall be measured in accordance with Test Methods D5947.. D5947 NOTE 2—Any necessary polishing of specimens shall be done only in the lengthwise direction of the specimen.

7.2 Sheet Materials (Except Laminated Thermosetting Materials and Certain Materials Used for Electrical Insulation, Including Vu Vulcanized lcanized Fiber and Glass Bonded Mica) : 2Licensee=RMIT University/5935953001 Not for Resale, 05/23/2013 10:14:22 MDT

D790 – 10 7.2.1 Materials 1.6 mm (1 ⁄ 16 16 in.) or Greater in Thickness— Forr fla Fo flatw twis isee te tests sts,, th thee de dept pth h of th thee sp spec ecim imen en sh shall all be th thee thickness of the material. For edgewise tests, the width of the specimen shall be the thickness of the sheet, and the depth shall not exceed the width (see Notes 3 and 4). 4 ). For all tests, the support span shall be 16 (tolerance 6 1) times the depth of the beam be am.. Sp Speci ecime men n wi widt dth h sh shall all no nott ex exce ceed ed on onee fo four urth th of th thee support span for specimens greater than 3.2 mm ( 1 ⁄ 8 in.) in depth. Specimens Specimens 3.2 mm or less in depth shall be 12.7 mm ( 1 ⁄ 2 in.) in width. The specimen shall be long enough to allow for overhanging on each end of at least 10 % of the support span, but in no case less than 6.4 mm ( 1 ⁄ 4 in.) on each end. Overhang shall sha ll be suf suffficie icient nt to pre preven ventt the spe specim cimen en fro from m slip slippin ping g through the supports. NOTE 3—Whenever possible, the original surface of the sheet shall be unaltered. However, where testing machine limitations make it impossible to follow the above criterion on the unaltered sheet, one or both surfaces shall be machined to provide the desired dimensions, and the location of the specimens with reference to the total depth shall be noted. The value obtained obtain ed on specim specimens ens with machin machined ed surf surfaces aces may dif differ fer from those obtained on specimens with original surfaces. Consequently, any specifications for flexural properties on thicker sheets must state whether the original surfaces are to be retained or not. When only one surface was machined, it must be stated whether the machined surface was on the tension or compression side of the beam. ` , , , ` ` , ` ` ` , , ` , ` ` ` , , , , , , ` ` ` , ` , ` ` , , ` , , ` , ` , , ` -

NOTE 4—Edgewise tests are not applicable for sheets that are so thin that specimens meeting these requirements requirements cannot be cut. If specim specimen en depth exceeds the width, buckling may occur.

7.2.2 Materials Less than 1.6 mm ( 1 ⁄ 16 16 in.) in Thickness — The specimen shall be 50.8 mm (2 in.) long by 12.7 mm ( 1 ⁄ 2 in.) wide, tested flatwise on a 25.4-mm (1-in.) support span. NOTE 5—Use 5—Use of the formulas formulas for sim simple ple beams cited in the these se tes testt methodss for calculati method calculating ng res result ultss pre presum sumes es tha thatt bea beam m wid width th is sma small ll in comparison with the support span. Therefore, the formulas do not apply rigorously to these dimensions. NOTE 6—Where machine sensitivity is such that specimens of these dimens dim ension ionss can cannot not be mea measur sured, ed, wid wider er spe specim cimens ens or sho shorte rterr sup suppor portt spans, or both, may be used, provided the support span-to-depth ratio is at least 14 to 1. All dimensions dimensions must be stated in the repor reportt (see also Note also Note 5) 5).

7.3 Lam Lamina inated ted The Thermo rmosett setting ing Mat Materia erials ls and She Sheet et and Platee Mat Plat Materia erials ls Use Used d for Elec Electric trical al Ins Insula ulatio tion, n, Inc Includ luding ing paper-base -base Vulcan ulcanized ized Fiber and Glass Glass-Bond -Bonded ed Mica—For paper and an d fa fabr bricic-ba base se gr grad ades es ov over er 25 25.4 .4 mm (1 in in.) .) in no nomi mina nall thickness, the specimens shall be machined on both surfaces to a dep depth th of 25. 25.4 4 mm. For glass-bas glass-basee and nyl nylonon-bas basee gra grades des,, specimens over 12.7 mm ( 1 ⁄ 2 in.) in nominal depth shall be machined on both surfaces to a depth of 12.7 mm. The support span-to-depth ratio shall be chosen such that failures occur in the outer fibers of the specimens specimens,, due only to the bending bending moment (see Note (see Note 7). 7). Therefore, a ratio larger than 16:1 may be necessary (32:1 or 40:1 are recommended). When laminated materials exhibit low compressive strength perpendicular to the laminations, they shall be loaded with a large radius loading nose (up to four times the specimen depth to prevent premature damage to the outer fibers. 7.4 Molding Materials (Thermoplastics and Thermosets) — The recommended specimen for molding materials is 127 by 12.7 by 3.2 mm (5 by 1 ⁄ 2 by 1 ⁄ 8 in.) tested flatwise on a support span, resulting in a support span-to-depth ratio of 16 (tolerance Copyright ASTM International Provided by IHS under license with ASTM No reproduction or networking permitted without license from IHS

Thicker spe specim cimens ens sho should uld be avo avoided ided if the they y exh exhibi ibitt 61). Thicker significant shrink marks or bubbles when molded. 7.5 High-Strength Reinforced Composites, Including Highly Orthotropic Laminates—The span-to-depth ratio shall be chosen such that failur failuree occurs in the outer fibers of the specimens and an d is du duee on only ly to th thee be bend ndin ing g mo mome ment nt (s (see ee Note Note 7). A span-to-depth ratio larger than 16:1 may be necessary (32:1 or 40:1 are recommended). For some highly anisotropic composites,, she ites shear ar def deform ormatio ation n can sig signifi nifican cantly tly infl influen uence ce mod modulu uluss measurements, even at span-to-depth ratios as high as 40:1. Hence, Hen ce, for the these se mat materia erials, ls, an inc increa rease se in the spa span-t n-to-d o-dept epth h ratio to 60:1 is recommended to eliminate shear effects when modulu mod uluss dat dataa are required required,, it sho should uld also be not noted ed tha thatt the flexural modulus of highly anisotropic laminates is a strong functio fun ction n of ply ply-st -stack acking ing seq sequen uence ce and will not nec necessa essaril rily y correlate with tensile modulus, which is not stacking-sequence dependent. NOTE 7—As a general rule, support span-to-depth ratios of 16:1 are satisfactory when the ratio of the tensile strength to shear strength is less than 8 to 1, but the support span-to-depth ratio must be increased for composite laminates having relatively low shear strength in the plane of the laminate and relatively high tensile strength parallel to the support span.

8. Numbe Numberr of Test Specimens Specimens 8.1 Test at least five specimens for each sample sample in the case of isotropic materials or molded specimens. 8.2 For each sample of anisotropic anisotropic material in sheet form, test at least five specimens for each of the following conditions. Recommended conditions are flatwise and edgewise tests on specimens cut in lengthwise and crosswise directions of the sheet. For the purposes of this test, “lengthwise” designates the principal axis of anisotropy and shall be interpreted to mean the direction of the sheet known to be stronger in flexure. “Crosswise” indicates the sheet direction known to be the weaker in flexure and shall be at 90° to the lengthwise direction. 9. Condi Condition tioning ing 9.1 Conditioning—Cond —Condition ition the test specimens in accor accor-dance with Procedure dance Procedure A of Pra Practic cticee D618 unless other otherwise wise specified specifi ed by contr contract act or the relevant ASTM material specification. Conditioning time is specified as a minimum. Temperature tu re an and d hu humi midi dity ty to toler leran ances ces sh shall all be in acc accor orda danc ncee wi with th Section Sec tion 7 of Pra Practic cticee D618 unless unless specifi specified ed dif different ferently ly by contract or material specification. 9.2 Test Conditions—Conduct the tests at the same temperaturee and hum tur humidi idity ty use used d for con conditi ditioni oning ng wit with h tole toleran rances ces in accordance with Section 7 of Practice D618 D618 unless otherwise specified specifi ed by contr contract act or the relevant ASTM material specification. 10. Procedur Proceduree 10.1 Procedure A: 10.1.1 10. 1.1 Use an unt unteste ested d spe specime cimen n for each mea measur suremen ement. t. Measure the width and depth of the specimen to the nearest 0.03 0.0 3 mm (0.001 (0.001 in. in.)) at the center center of the sup suppor portt spa span. n. For specimens less than 2.54 mm (0.100 in.) in depth, measure the depth to the nearest 0.003 mm (0.0005 in.). These measurements shall be made in accordance with Test Methods D5947 D5947.. 3Licensee=RMIT University/5935953001 Not for Resale, 05/23/2013 10:14:22 MDT

D790 – 10 10.1.2 Determine the support span to be used as described in Section 7 and and se sett th thee su supp ppor ortt sp span an to wi with thin in 1 % of th thee determined value. 10.1.3 10.1. 3 For flexural fixtures that have continuously continuously adjustable spans, measure the span accurately to the nearest 0.1 mm (0.004 in.) for spans less than 63 mm (2.5 in.) and to the nearest 0.3 mm (0.012 in.) for spans greater than or equal to 63 mm (2.5 in.). Use the actual measured span for all calcula calculations. tions. For flexural fixtures that have fixed machined span positions, verify the span distance distance the same as for adjustab adjustable le spa spans ns at each machined position. This distance becomes the span for that position and is used for calculations applicable to all subsequent que nt tes tests ts con conduc ducted ted at tha thatt pos positio ition. n. See Annex Annex A2 for information on the determination of and setting of the span. 10.1.4 10.1. 4 Calcula Calculate te the rate of crossh crosshead ead motion as follows follows and set the machine for the rate of crosshead motion as calculated by Eq 1: R 5 ZL 2 /6d

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where: crosshead d motion, motion, mm (in.)/min (in.)/min,, R = rate of crosshea suppor portt span, span, mm (in. (in.), ), L = sup depth th of bea beam, m, mm (in. (in.), ), and and d = dep straining ng of the outer fiber, fiber, mm/mm/min mm/mm/min (in./ (in./ Z = rate of straini in./min). Z shall shall be equal to 0.01. In no case shall the actual crosshead rate differ from that calculated using Eq 1, by more than 6 10 %. 10.1.5 10.1. 5 Align the loading loading nose and supports supports so that the axes of the cylindrical surfaces are parallel and the loading nose is midway between the supports. The parallelism of the apparatus may be checked by means of a plate with parallel grooves into which whi ch the load loading ing nose and supports supports will fit whe when n pro proper perly ly aligned (see A2.3 (see A2.3). ). Center the specimen on the supports, with the long axis of the specimen perpendicular to the loading nose and supports. 10.1 10 .1.6 .6 Apply Apply th thee lo load ad to th thee sp spec ecime imen n at th thee sp spec ecifie ified d crossh cro sshead ead rat rate, e, and tak takee sim simulta ultaneo neous us loa load-d d-defle eflectio ction n dat data. a. Measur Mea suree defl deflecti ection on eith either er by a gag gagee und under er the specimen specimen in contact with it at the center of the support span, the gage being mounted mou nted stationar stationary y rel relativ ativee to the spe specim cimen en sup suppor ports, ts, or by measurement of the motion of the loading nose relative to the supports. Load-deflection curves may be plotted to determine the flexural strength, chord or secant modulus or the tangent modulus of elasticity, and the total work as measured by the area under the load-deflection curve. Perform the necessary toe compensation compen sation (see Annex Annex A1 A1)) to co corr rrec ectt fo forr se seat atin ing g an and d indentation of the specimen and deflections in the machine. 10.1.7 10.1. 7 Termina erminate te the test when the maximum strain in the outer surface of the test specimen has reached 0.05 mm/mm (in./i (in ./in. n.)) or at br break eak if br brea eak k oc occu curs rs pr prio iorr to re reach achin ing g th thee maximum maximu m strain (Notes 8 (Notes 8 and 9) 9 ). The deflection at which this strain stra in will occur may be cal calcula culated ted by lett letting ing r equal equal 0.05 mm/mm (in./in.) in Eq 2: D 5 rL 2 /6d

where: midspan an deflection, deflection, mm (in.), (in.), D = midsp strain,, mm/mm (in./in (in./in.), .), r = strain

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suppor portt span, span, mm (in.), (in.), and and L = sup depth of of beam, beam, mm mm (in.). (in.). d = depth NOTE 8—For some materials that do not yield or break within the 5 % strain limit when tested by Proce Procedure dure A, the increa increased sed strain rate allow allowed ed by Procedure B (see 10.2 (see 10.2)) may induce the specimen to yield or break, or both, within the required 5 % strain limit. NOTE 9—Beyond 5 % strain, this test method is not applicable. Some other mechanical property might be more relevant to characterize materials that neither yield nor break by either Procedure A or Procedure B within wit hin the 5 % str strain ain lim limit it (fo (forr exa exampl mple, e, Test Met Method hod D638 may be considered).

10.2 Procedure B: 10.2.1 10.2. 1 Use an unteste untested d specimen for each measurement. measurement. 10.2.2 10.2. 2 Test conditions conditions shall be identical to those described described in 10.1 in 10.1,, except that the rate of straining of the outer surface of the test specimen shall be 0.10 mm/mm (in./in.)/min. 10.2.3 10.2. 3 If no break has occurred occurred in the specimen specimen by the time the maximum strain in the outer surface of the test specimen has rea reache ched d 0.0 0.05 5 mm/ mm/mm mm (in (in./in ./in.), .), dis discon contin tinue ue the tes testt (se (seee Note 9) 9 ). 11. Retests 11.1 Values for properties 11.1 properties at ruptu rupture re shall not be calculated for any specimen that breaks at some obvious, fortuitous flaw, unless such flaws constitute a variable being studied. Retests shal sh alll be mad madee fo forr an any y sp speci ecime men n on wh which ich values values ar aree no nott calculated. 12. Calc Calculat ulation ion 12.1 Toe compensa 12.1 compensation tion shall shall be made in acco accorda rdance nce with Annex A1 unless it can be shown that the toe region of the curv cu rvee is no nott du duee to th thee ta take ke-u -up p of sl slac ack, k, se seat atin ing g of th thee specimen, or other artifact, but rather is an authentic material response. 12.2 Flexur —When en a hom homoge ogeneo neous us elas elastic tic Flexural al Str Stress ess (s f )—Wh material is tested in flexure as a simple beam supported at two points and loaded at the midpoint, the maximum stress in the outer surface of the test specimen occurs at the midpoint. This stress may be calculated for any point on the load-deflection curve by means of the following equation (see Notes 10-12 10-12)): s f 5 3 PL /2bd 2

where: the outer fibers fibers at midpoint, midpoint, MPa (psi), (psi), s = stress in the load d at a given point point on the load-defl load-deflecti ection on curve, curve, N P = loa (lbf), suppor portt span, span, mm (in.) (in.),, L = sup width th of beam beam tested, tested, mm (in.), (in.), and and b = wid depth th of beam beam tested tested,, mm (in.). (in.). d = dep NOTE 10—Eq 3 applies strictly strictly to mater materials ials for which stress is linearly proportional to strain up to the point of rupture and for which the strains aree sm ar small all.. Si Sinc ncee th this is is no nott al alwa ways ys th thee cas case, e, a sl slig ight ht er erro rorr wi will ll be introduced introd uced if Eq 3 is used to calculate stress for materials materials that are not true Hookean materials. The equation is valid for obtaining comparison data and for specification purposes, but only up to a maximum fiber strain of 5 % in the outer surface of the test specimen for specimens tested by the procedures described herein. NOTE 11—When 11—When testin testing g highl highly y ortho orthotropic tropic laminates, the maxim maximum um --`,,,``,```,,`,```,,,,,,```,`,-`-`,,`,,`,`,,`---


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D790 – 10 stress may not always occur in the outer surface of the test specimen.4 Lamina Lam inated ted bea beam m the theory ory mus mustt be app applied lied to det determ ermine ine the max maximu imum m tensile stress at failure. If Eq 3 is used to calculate stress, it will yield an apparent appare nt streng strength th based on homog homogeneous eneous beam theor theory. y. This appar apparent ent streng str ength th is hig highly hly dep depend endent ent on the ply ply-st -stack acking ing seq sequen uence ce of hig highly hly orthotropic laminates. NOTE 12—The preceding calculation is not valid if the specimen slips excessively between the supports.

12.3 Flexura Flexurall Str Stress ess for Bea Beams ms Teste ested d at Lar Large ge Sup Suppor port t Spans ( s f )—If support span-to-depth ratios greater than 16 to 1 ar aree us used ed su such ch th that at de defle flecti ction onss in ex exce cess ss of 10 % of th thee supp su ppor ortt sp span an oc occu curr, th thee str stres esss in th thee ou outer ter su surf rface ace of th thee specimen for a simple beam can be reasonably approximated with the following equation (see Note 13): 13): s f 5 ~3PL /2bd 2!@1 1 6~ D / L! 2 2 4~d / L!~ D / L!#

(4)

where: are the same as for Eq 3, and s f , P, L, b, and d are defle flecti ction on of th thee cen center terlin linee of th thee speci specime men n at th thee D = de middle of the support span, mm (in.). NOTE 13—When large support span-to-depth ratios are used, significant end for forces ces are developed developed at the sup suppor portt nos noses es whi which ch wil willl af affec fectt the moment in a simple supported beam. Eq 4 includes additional terms that are an approximate correction factor for the influence of these end forces in large support span-to-depth ratio beams where relatively large deflections exist.

12.4 Flexu —Maxim ximum um flex flexura urall str stress ess Flexural ral Str Streng ength th (s fM )—Ma sustained by the test specimen (see Note (see Note 11) 11) during a bending test. It is calculated according to Eq 3 or Eq 4. Some materials that do not break at strains of up to 5 % may give a load deflection curve that shows a point at which the load does not increase with an increase in strain, that is, a yield point (Fig. ( Fig. 1, 1, Curve B), Y. The flexural strength may be calculated for these materials by letting P (in Eq 3 or Eq 4) equal this point, Y. 12.5 Flexural Offset Yield Strength—Offset yield strength is the stress at which the stress-strain curve deviates by a given strain (offset) from the tangent to the initial straight line portion of the stress-strain curve. The value of the offset must be given whenever this property is calculated. NOTE 14—This value may differ from flexural strength defined in 12.4 in 12.4.. Both methods of calculation are described in the annex to Test Method D638.. D638

12.6 Flexu —Flexur xural al str stress ess at Flexura rall St Strres esss at Br Brea eakk (s fB )—Fle break of the test specimen during a bending test. It is calculated according to Eq 3 or Eq 4. Some materials may give a load deflection curve that shows a break point, B, without a yield poin po intt (Fi Fig. g. 1, Curv Curvee a) in wh whic ich h ca case se s fB = s fM . Other materials may give a yield deflection curve with both a yield and a break point, B (Fig. 1, 1, Curve b). The flexural stress at break may be calculated for these materials by letting P (in Eq 3 or Eq 4) equal this point, B. 12.7 Str —The he str stress ess in th thee ou outer ter Stres esss at a Gi Given ven St Stra rain in—T surface of a test specimen at a given strain may be calculated in accordance with Eq 3 or Eq 4 by letting P equal the load read 4

For a discussion of these effects, see Zweben, C., Smith, W. S., and Wardle, M. W., “T “Test est Metho Methods ds for Fiber Tensile Tensile Strength, Composite Flexural Modulus and Compositee Mater Materials: ials: Testin esting g and Properties Prope rties of Fabri Fabric-Rei c-Reinforce nforced d Lamin Laminates ates,, “ Composit Design (Fifth Conference), ASTM STP 674 , 1979, pp. 228–262.


` , , ` , ` , , ` , , ` ` , ` , ` ` ` , , , , , , ` ` ` , ` , , ` ` ` , ` ` , , , ` -

NOTE—Curv —Curvee a: Specim Specimen en that breaks breaks before before yielding. yielding. Curve b: Specim Specimen en that yields yields and then breaks breaks before before the 5 % strain strain limit. Curve c: Speci Specimen men that neither neither yields yields nor nor breaks before before the the 5 % strain limit. FIG.. 1 Typi FIG ypical cal Curv Curves es of Flexu Flexural ral Stre Stress ss (ßf ) Versus Flexural Strain (´f )

from the load-deflection curve at the deflection corresponding to the desired strain (for highly orthotropic laminates, see Note 11). 11 ). 12.8 Flexural Strain, ´ f —Nominal fractional change in the length of an element of the outer surface of the test specimen at mid midsp span an,, wh wher eree th thee ma maxi ximu mum m str strain ain oc occu curs rs.. It ma may y be calculated for any deflection using Eq 5: ´ f 5 6 Dd / L2

(5)

where: in the outer outer surface, surface, mm/mm mm/mm (in./in.), (in./in.), ´ f = strain in maximu imum m deflectio deflection n of the cen center ter of the beam, beam, mm D = max (in.), suppor portt span, span, mm (in.) (in.),, and L = sup depth, th, mm (in (in.). .). d = dep 12.9 Modulus of Elasticity: 12.9.1 Tangent Modulus of Elasticity —The tangent modulus of elasticity, often called the “modulus of elasticity,” is the ratio, within the elastic limit, of stress to corresponding strain. It is calc calcula ulated ted by dra drawin wing g a tan tangen gentt to the steepest steepest ini initial tial straight-line portion of the load-deflection curve and using Eq 6 (for highly anisotropic composites, see Note 15). 15). E B 5 L3m /4bd 3

where: modulus of elasticity elasticity in bendi bending, ng, MPa (psi), (psi), E B = modulus = sup suppor portt span span,, mm mm (in. (in.), ), L


(6)

D790 – 10 b d m

= width width of of beam beam tested tested,, mm (in (in.), .), = dep depth th of of beam beam teste tested, d, mm (in (in.), .), and and = slope of the the tangent tangent to the initial initial straightstraight-line line portion portion of the load-deflection curve, N/mm (lbf/in.) of deflection.

NOTE 15—Shear deflections can seriously reduce the apparent modulus of highly anisotropic anisotropic comp composites osites when they are tested at low span-todepth ratios ratios..4 Fo Forr th this is re reas ason on,, a sp span an-t -too-de dept pth h ra rati tio o of 60 to 1 is recommended for flexural modulus determinations on these composites. Flexur Fle xural al str streng ength th sho should uld be det determ ermine ined d on a sep separa arate te set of rep replica licate te specimens at a lower span-to-depth ratio that induces tensile failure in the outer fibers of the beam along its lower face. Since the flexural modulus of hig highly hly ani anisot sotrop ropic ic lam lamina inates tes is a crit critica icall fun functio ction n of ply ply-st -stack acking ing sequence, it will not necessarily correlate with tensile modulus, which is not stacking-sequence dependent.

12.9.2 Secant Modulus— The secant modulus is the ratio of stress stre ss to cor corres respon pondin ding g str strain ain at any selected selected poi point nt on the stress-strain curve, that is, the slope of the straight line that joins the origin and a selected point on the actual stress-strain curve. It shall be expressed in megap megapascals ascals (pounds (pounds per squar squaree inch). The selected point is chosen at a prespecified stress or strain in accordance with the appropriate material specification or by customer contract. It is calculated in accordance with Eq 6 by let lettin ting g m equa equall th thee slo slope pe of the se secan cantt to th thee lo load ad-deflection curve. The chosen stress or strain point used for the determination of the secant shall be reported. 12.9.3 Chord —Thee cho chord rd mod modulu uluss may be Chord Modul Modulus us (E f )—Th calcula calc ulated ted fro from m two dis discre crete te poi points nts on the load deflection deflection curve. The selected points are to be chosen at two prespecified stress stre ss or str strain ain poi points nts in acco accorda rdance nce with the app approp ropriat riatee material mate rial spe specific cificatio ation n or by cus custom tomer er con contrac tract. t. The cho chosen sen stress or strain points used for the determination of the chord modulus modul us shall be reported. Calculate the chord modulus, modulus, E f using the following equation: E f 5 ~s f 2 2 s f 1! / ~´ f 2 2 ´ f 1!

(7)

where:

s f 2 and s f 1 are the flexural stresses, calculated from Eq 3 or Eq 4 an and d me meas asur ured ed at th thee pr pred edefi efine ned d po poin ints ts on th thee lo load ad deflection curve, and ´ f 2 and ´ f 1 are the flexural strain values, calculated from Eq 5 and measured at the predetermined points on the load deflection curve. TABLE 2 Flexur Flexural al Modulus Material

ABS DAP thermoset Cast acrylic GR polyester GR polycarbonate SMC

Mean, 103 psi

338 4 85 8 10 8 16 1 7 90 1 9 50

A

Values Expressed in units of % of 103 psi V rA

V RB

r C

R D

4 .7 9 2 .8 9 1 3 .7 3. 49 5 .5 2 1 0 .9

7..69 7 7 .1 8 1 6. 1 4 .2 0 5. 52 1 3 .8 13

13 1 3. 6 8 .1 5 3 8 .8 9. 91 1 5. 6 3 0 .8 30

21 2 1 .8 2 0 .4 4 5. 4 11.9 1 5 .6 3 9 .1 39

V r = within-laboratory coefficient of variation for the indicated material. It is obtained by first pooling the within obtained within-labor -laboratory atory standard deviations deviations of the test results result s from all of the partic participatin ipating g labora laboratories tories:: Sr Sr = = [[(s [[(s 1)2 + ( s 2 )2 . . . + (s ( s n )2]/ n n] 1/2 then then V V r = (S r divided by the overall average for the material) 3 100. B V r = between-laboratory reproducibility, expressed as the coefficient of variation: S tion: S R = {S r 2 + S L2}1/2 where where S S L is the standard deviation of laboratory means. Then: V Then: V R = (S R divided by the overall average for the material) 3 100. C r = = within within-labor -laboratory atory critical interval between two test results = 2.8 3 V r . D R = between-laboratory critical interval between two test results = 2.8 3 V R . R


12.10 Arithmet Forr ea each ch se seri ries es of te test sts, s, th thee Arithmetic ic Mean— Fo arithmetic mean of all values obtained shall be calculated to three significant figures and reported as the “average value” for the particular property in question. 12.11 Standard —Thee sta standa ndard rd dev deviati iation on (es (estitiStandard Deviat Deviation ion—Th mated) shall be calculated as follows and be reported to two significant figures: ¯ 2! / ~n 2 1 ! s 5 =~ ( X 2 2 nX

(8)

where: estimated d standar standard d deviatio deviation, n, s = estimate single observ observation, ation, X = value of single numberr of obser observation vations, s, and and n = numbe ¯ arithmetic tic mean of the set of obser observation vations. s. X = arithme 13. Repo Report rt 13.1 Repor Reportt the follow following ing information: information: 13.1.1 Complete identification of the material tested, includincluding type, source, manufacturer’s code number, form, principal dimens dim ension ions, s, and pre previo vious us his histor tory y (fo (forr lam lamina inated ted mate materia rials, ls, ply-stacking sequence shall be reported), 13.1.2 13. 1.2 Dir Directi ection on of cut cuttin ting g and loa loadin ding g spe specim cimens ens,, whe when n appropriate, 13.1.3 13.1. 3 Condit Conditioning ioning procedure, procedure, 13.1.4 13.1. 4 Depth and width of specimen, specimen, 13.1.5 13.1. 5 Proced Procedure ure used (A or B), 13.1.6 13.1. 6 Suppo Support rt span length, 13.1.7 13.1. 7 Suppo Support rt span-to-depth span-to-depth ratio if dif different ferent than 16:1, 13.1.8 13. 1.8 Radi Radius us of sup suppor ports ts and loa loadin ding g nos noses, es, if dif differ ferent ent than 5 mm. When support and/or loading nose radii other than 5 mm are used, the results shall be identified as being generated by a modified version of this test method and the referring specification referenced as to the geometry used. 13.1.9 13.1. 9 Rate of crosshead motion, motion, 13.1.1 13. 1.10 0 Flex Flexura urall str strain ain at any giv given en str stress, ess, ave averag ragee val value ue and standa standard rd deviat deviation, ion, 13.1.11 13.1. 11 If a specim specimen en is rejecte rejected, d, reason(s) for rejection, rejection, 13.1.1 13. 1.12 2 Tangen Tangent, t, sec secant ant,, or cho chord rd mod modulu uluss in ben bendin ding, g, average value, standard deviation, and the strain level(s) used if secant or chord modulus, 13.1.1 13. 1.13 3 Flex Flexura urall str streng ength th (if des desired ired), ), ave averag ragee val value, ue, and standard deviation, 13.1.14 13.1. 14 Stress at any given given strain up to and including including 5 % (if desired), with strain used, average value, and standard deviation, 13.1.15 13.1. 15 Flexur Flexural al stress at break (if desired), desired), average value, and standa standard rd deviat deviation, ion, 13.1.16 13.1. 16 Type of behav behavior ior,, wheth whether er yielding or ruptu rupture, re, or both, bot h, or oth other er obs observ ervatio ations, ns, occ occurr urring ing with within in the 5 % str strain ain limit, and 13.1.17 13.1. 17 Date of specific version of test used.

` , , ` , ` , , ` , , ` ` , ` , ` ` ` , , , , , , ` ` ` , ` , , ` ` ` , ` ` , , , ` -

14. Pre Precisi cision on and Bias 14.1 Tab Table less 1 an and d 2 are are ba base sed d on a ro roun undd-ro robi bin n te test st conducted in 1984, in accordance with Practice E691 E691,, involving six materials tested by six laboratories using Procedure A. For each mat materia erial, l, all the specimens specimens were pre prepar pared ed at one 6Licensee=RMIT University/5935953001 Not for Resale, 05/23/2013 10:14:22 MDT

D790 – 10 source. Each “test result” was the average of five individual determinations. Each laboratory obtained two test results for each material. NOTE 16—Caution: The follow following ing explan explanations ations of r and R (14.214.2.3) are intended only to present a meaningful way of considering the 14.2.3) approximate precision of these test methods. The data given in Tables 2 and 3 should not be applied rigorously to the acceptance or rejection of materials, as those data are specific to the round robin and may not be representative of other lots, conditions, materials, or laboratories. Users of these test methods should apply the principles outlined in Practice E691 Practice E691 to to generate data specific to their laboratory and materials, or between specific laboratories labora tories.. The princi principles ples of 14.2-14.2.3 14.2-14.2.3 would then be valid for such data.

14.2 Concept of “r” and “R” in Tables 1 and 2—If 2—If S S r and S R have been calculated from a large enough body of data, and for test results that were averages from testing five specimens for each test result, then: 14.2.1 Repeatability— Two test results obtained within one laboratory shall be judged not equivalent if they differ by more

than the r value for that material. r is the interval representing the critical difference between two test results for the same mater ma teria ial, l, ob obtai taine ned d by th thee sa same me op oper erat ator or us usin ing g th thee sam samee equipment on the same day in the same laboratory. 14.2.2 Reproducibility— Two test results obtained by differentt labor feren laboratories atories shall be judged not equivalent if they differ differ by more than the R value for that material. R is the interval representing the critical difference between two test results for the same material, obtained by different operators using different equipment in different laboratories. 14.2.3 14. 2.3 The jud judgme gments nts in 14.2.1 14.2.1 and 14. 14.2.2 2.2 will will ha have ve an approximately 95 % (0.95) probability of being correct. 14.3 Bias—No statement may be made about the bias of these test methods, as there is no standard reference material or reference test method that is applicable. 15. Keyw Keywords ords 15.1 flexur flexural al prop properties; erties; plastics; stiffness; stiffness; streng strength th

ANNEXES (Mandatory Information) A1. TOE COMPENSA COMPENSATION

A1.1 In a typical typical stress-s stress-strain train curve curve (see (see Fig. Fig. A1.1) A1.1) there is a toe region, AC, that does not represent a property of the mater mat erial ial.. It is an ar artif tifac actt cau cause sed d by a tak takeu eup p of sla slack ck an and d ` , , , ` ` , ` ` ` , , ` , ` ` ` , , , , , , ` ` ` , ` , ` ` , , ` , , ` , ` , , ` -

alignment or seating of the specimen. In order to obtain correct values of such parameters as modulus, strain, and offset yield poin po int, t, th this is ar artif tifac actt mu must st be co comp mpen ensa sated ted fo forr to gi give ve th thee corrected zero point on the strain or extension axis. A1.2 In the ca A1.2 case se of a ma mate teri rial al ex exhi hibi biti ting ng a re regi gion on of Hookean (linear) behavior (see Fig. A1.1), A1.1), a continuation of the linear (CD) region of the curve is constructed through the zero-stress zerostress axis. This inters intersection ection (B) is the cor correc rected ted zer zeroostra st rain in po poin intt fr from om wh which ich al alll ex exten tensi sion onss or st stra rain inss mu must st be measured, including the yield offset (BE), if applicable. The elastic modulus can be determined by dividing the stress at any point along the Line C CD D (or its extension) by the strain at the same point (measured from Point B, defined as zero-strain). A1.3 In the case of a mat A1.3 mater erial ial that that do does es not exhib exhibit it any linear region (see Fig (see Fig.. A1. A1.2 2), the same kind of toe correction of the zero-strain point can be made by constructing a tangent to the maximum slope at the inflection Point H . This is extend extended ed to intersect the strain axis at Point B , the corrected zero-strain point. Using Point B as zero strain, the stress at any point (G ) on the curve can be divided by the strain at that point to obtain a secant modulus (slope of Line B G ). For those materials with no linear region, any attempt to use the tangent through the inflection point as a basis for determination of an offset yield point may result in unacceptable error. 8

8

8

8

8

NOTE—Some chart recorders plot the mirror image of this graph. FIG.. A1.1 FIG A1.1 Mat Materi erial al with with Hook Hookean ean Regio Region n



8

D790 – 10

NOTE—Some chart recorders plot the mirror image of this graph. FIG. A1.2 Material with No Hookean Region

A2. MEASURING AND SETTING SPAN SPAN

A2.1 For flexura A2.1 flexurall fixt fixture uress tha thatt hav havee adj adjust ustabl ablee spa spans, ns, it is import imp ortant ant tha thatt the spa span n bet between ween the sup suppor ports ts is mai maintai ntained ned constant or the actual measured span is used in the calculation of stress, modulus, and strain, and the loading nose or noses are positioned and aligned properly with respect to the supports. Some simple steps as follows can improve the repeatability of your results when using these adjustable span fixtures.

FIG. A2.1 Markings on Fixed Specim Specimen en Suppo Supports rts

A2.2 A2. 2 Mea Measur suremen ementt of Span: Span: A2.2.1 This technique A2.2.1 technique is needed to ensur ensuree that the correc correctt span sp an,, no nott an es estim timate ated d sp span an,, is us used ed in th thee cal calcu culat latio ion n of results. A2.2.2 A2.2. 2 Scribe a permanent permanent line or mark at the exact center of the support where the specimen makes complete contact. The type of mark depends on whether the supports are fixed or rotatable rotatab le (see (see Figs. Figs. A2.1 and A2.2). A2.2 ). A2.2 A2 .2.3 .3 Us Usin ing g a ve vern rnier ier ca calip liper er wi with th po poin inte ted d tip tipss th that at is readable to at least 0.1 mm (0.004 in.), measure the distance between the supports, and use this measurement of span in the calculations. ` , , , ` ` , ` ` ` , , ` , ` ` ` , , , , , , ` ` ` , ` , ` ` , , ` , , ` , ` , , ` -


FIG. A2.2 Marking Markings s on Rotat Rotatable able Specimen Suppo Supports rts

A2.3 Se Sett ttin ing g th thee Sp Span an an and d Al Alig ignm nmen entt of Lo Load adin ing g Nose(s)—To ensure a consistent day-to-day setup of the span and ensure the alignment and proper positioning of the loading nose no se,, si simp mple le jig jigss sh shou ould ld be man manuf ufact actur ured ed fo forr eac each h of th thee standard setups used. An example of a jig found to be useful is shown in Fig. A2.3. A2.3.


D790 – 10

FIG. A2.3 Fixture Used to Set Loading Nose and Support Spacing and Alignment

APPENDIX (Nonmandatory Information) X1. DEVELOPME DEVELOPMENT NT OF A FLEXURAL MACHINE MACHINE COMPLIANCE CORRECTION

X1.1 Introduction

X1.3.5 Steel bar, bar, with smooth smoothed ed surfaces and a calculat calculated ed flexural stiffness of more than 100 times greater than the test material. The length should be at least 13 mm greater than the supp su ppor ortt sp span an.. Th Thee wi widt dth h sh shal alll mat match ch th thee wi widt dth h of th thee tes testt specimen and the thickness shall be that required to achieve or exceed the targ target et stif stiffness fness..

X1.1.1 Unive X1.1.1 Universal rsal Testing Testing instru instrument ment drive systems always exhibit a certain level of compliance that is characterized by a variance varian ce betwee between n the repor reported ted crosshead displacement displacement and the displacement displac ement actually imparted to the specimen. This variance is a function of load frame stiffness, drive system wind-up, load cell compliance and fixture compliance. To accurately measure the flexural modulus of a material, this compliance should be measured and empirically subtracted from test data. Flexural modulus results without the corrections are lower than if the correction is applied. The greater the stiffness of the material the more influence the system compliance has on results. X1.1.2 X1.1. 2 It is not necess necessary ary to make the machine compliance compliance correction when a deflectometer/extensometer is used to measure the actual deflection occurring in the specimen as it is deflected.

X1.4 Safety Precautions Precautions X1.4.1 The universal universal testing machine should should stop the machine crosshead movement when the load reaches 90 % of load cell capacity, to prevent damage to the load cell. X1.4 X1 .4.2 .2 The co comp mplia lianc ncee cur curve ve de deter termin minati ation on sh shou ould ld be made at a speed no higher than 2 mm/min. Because the load builds up rapidly since the steel bar does not deflect, it is quite easy to exceed the load cell capacity. X1.5 Proced Procedure ure

X1.2 Terminology

NOTE X1.1—A new compliance correction curve should be established each time there is a chang changee made to the setup of the test machi machine, ne, such as, load cell changed or reinstallation of the flexure fixture on the machine. If the test machine is dedicated to flexural testing, and there are no changes to the setup, it is not necessary to re-calculate the compliance curve. NOTE X1.2—On those machines with computer software that automatically make this compliance correction; refer to the software manual to determine how this correction should be made.

X1.2.1 Compliance—The displac displacement ement dif differen ference ce between test mac machin hinee dri drive ve sys system tem dis displac placeme ement nt valu values es and actu actual al specimen displacement X1.2.2 Compliance Correction—An ana analyt lytical ical meth method od of modifying test instrument displacement values to eliminate the amount amo unt of tha thatt meas measure uremen mentt attr attribu ibuted ted to tes testt ins instru trumen mentt compliance.

X1.5.1 The procedure procedure to determ determine ine compliance follows: follows: X1.5.1.1 X1.5.1 .1 Config Configure ure the test system to match the actual test configuration. X1.5.1 X1. 5.1.2 .2 Plac Placee the steel bar in the test fixt fixture ure,, dup duplica licatin ting g the position of a specimen during actual testing. X1.5.1.3 X1.5.1 .3 Set the crosshead crosshead speed to 2 mm/min. or less and startt the cro star crossh sshead ead mov moving ing in the test dir directi ection on rec record ording ing crosshead displacement and the corresponding load values.

X1.3 Appar Apparatus atus X1.3.1 Unive X1.3.1 Universal rsal Testing Testing machine X1.3.2 X1.3. 2 Load cell cell X1.3.3 Flexure fixture including loading nose and specimen supports X1.3.4 X1.3. 4 Compu Computer ter Software Software to make corrections corrections to the displacements --`,,,``,```,,`,```,,,,,,```,`,-`-`,,`,,`,`,,`---



D790 – 10 X1.5.1.4 Incre X1.5.1.4 Increase ase load to a point exceeding exceeding the highest highest load expecte exp ected d dur during ing spe specime cimen n tes testing ting.. Sto Stop p the cro crossh sshead ead and return to the pre-test location. X1.5.1.5 X1.5. 1.5 The recorded load-deflection load-deflection curve, starting when the loading loading nose contacts contacts the steel bar to the time that the highest load expected is defined as test system compliance. X1.5 X1 .5.2 .2 Proced Procedur uree to ap appl ply y co comp mplia lianc ncee co corr rrect ectio ion n is as follows: X1.5.2.1 X1.5. 2.1 Run the flexural flexural test method on the material at the crosshead required for the measurement. X1.5.2.2 X1.5. 2.2 It is prefe preferable rable that computer computer software be used to make the displacement corrections, but if it is not available compliance corrections can be made manually in the following manner. Determine the range of displacement (D) on the load versus ver sus dis displa placeme cement nt cur curve ve for the mate materia rial, l, ove overr whi which ch the modulus is to be calculated. For Young’s Modulus that would steepest region of the curve below the proportional limit. For Secant and Chord Modulii that would be at specified level of strain stra in or spe specifi cified ed lev levels els of str strain, ain, res respec pective tively ly.. Dra Draw w two verticall lines up from the displ vertica displacement acement axis for the two chosen displacements (D1, D2) to the load versus displacement curve for the material. In some cases one of these points maybe at zero dis displa placeme cement nt afte afterr the toe com compen pensat sation ion cor correc rectio tion n is made. Draw two horizontal lines from these points on the load displacement curve to the Load (P) axis. Determine the loads (L1, L2). X1.5.2.3 X1.5. 2.3 Using the Compli Compliance ance Correction load displa displacecement curve for the steel bar, mark off L1 and L2 on the Load (P) axis. From these two points draw horizontal lines across till they contact the load versus displacement curve for the steel

bar. From these two points on the load deflection curve draw two vertical lines downwards to the displacement axis. These two points on the displacement axis determine the corrections (c1, c2) that need to be made to the displacements measurements for the test material. X1.5.2 X1. 5.2.4 .4 Sub Subtrac tractt the cor correc rection tionss (c1 (c1,, c2) fro from m the mea mea-sured displacements (D1, D2), so that a true measures of test specimen deflection (D1-c1, D2-c2) are obtained.

FIG. X1. 1 E xa xample of M od odulus Curve for a M at ate ri rial

FIG. X1.2 Compliance Curv e for Steel Bar

X1.6 Calculations X1.6.1 Calcula Calculation tion of Chord Modulus X1.6.1.1 X1.6.1 .1 Calculat Calculatee the stresses stresses (sf1, sf2) for load points L1 and L2 from Fig. X1.1 using X1.1 using the equation in 12.2 3. 3. X1.6.1.2 X1.6. 1.2 Calculat Calculatee the strains (´f1, ´f2) for displacements D1-c1 and D2-c2 from Fig. X1.3 using X1.3 using the equation in 12.8 in 12.8 Eq. Eq. 5. X1.6.1 X1. 6.1.3 .3 Calc Calcula ulate te the flex flexura urall cho chord rd mod modulu uluss in acc accor or-dance with 12.9.3 with 12.9.3 Eq. 7. X1.6.2 X1.6. 2 Calcula Calculation tion of Secant Modulus X1.6.2 X1. 6.2.1 .1 Calc Calcula ulatio tion n of the Sec Secant ant Mod Modulu uluss at any str strain ain along alo ng th thee cu curv rvee wo woul uld d be th thee sa same me as co cond nduc uctin ting g a ch chor ord d modulus measurement, except that s f1 = 0, L1= 0, and D1-c1 = 0. X1.6.3 Calculation of Young’s Young’s Modulus X1.6.3.1 X1.6. 3.1 Determi Determine ne the steepest slope “m” along the curve, below the proportional limit, using the selected loads L1 and L2 from Fig. X1.1 and the displacements D1-c1 and D2-c2 from Fig. from Fig. X1.3. X1.3. X1.6.3.2 Calculate the Young’s Young’s modulus in accordance with 12.9.1 Eq. 12.9.1 Eq. 6.

--`,,,``,```,,`,```,,,,,,```,`,-`-`,,`,,`,`,,`---


10 Licensee=RMIT University/5935953001 Not for Resale, 05/23/2013 10:14:22 MDT

D790 – 10

FIG. X1.3 Example of the Material Curve Corrected for the Compliance Corrected Displacement or Strain

SUMMARY OF CHANGES Committ Comm ittee ee D20 D20 ha hass id iden enti tified fied th thee lo loca catio tion n of sel select ected ed ch chan ange gess to th this is st stan anda dard rd sin since ce th thee las lastt is issu suee 1 (D790 (D79 0 - 07 ) that may impact the use of this standard. (April 1, 2010) ´

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