Flatwise Compressive Properties of Sandwich Cores: Standard Test Method For

 

 

Designation: C365/C365M − 16

Standard Test Method for

Flatwise Compressive Properties of Sandwich Cores1 This standard is issued under the fixed designation C365/C365M; the number immediately following the designation indicates the year of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript epsilon (´) indicates an editorial change since the last revision or reapproval. This standard has been approved for use by agencies of the U.S. Department of Defense.

1. Sco Scope pe

C271/C271M  Test C271/C271M  Test Met Method hod for Den Density sity of San Sandwi dwich ch Cor Coree Materials D883   Terminology Relating to Plastics D883 D3878   Terminology for Composite Materials D3878 D5229/D5229M T D5229/D5229M  Test est Method for Moisture Absorption Properties and Equilib Equilibrium rium Conditioning Conditioning of Polym Polymer er Matrix Composite Materials D7336/D7336M Test D7336/D7336M  Test Method for Static Energy Absorption Properties of Honeycomb Sandwich Core Materials E4   Practices for Force Verification of Testing Machines E4 E6 Terminology E6  Terminology Relating to Methods of Mechanical Testing E122 Practice E122  Practice for Calculating Sample Size to Estimate, With Specified Precision, the Average for a Characteristic of a Lot or Process E177   Practice for Use of the Terms Precision and Bias in E177 ASTM Test Methods E456 Terminology E456  Terminology Relating to Quality and Statistics

1.1 This test method covers the determination determination of compressive strength and modulus of sandwich cores. These properties are usu usually ally det determ ermine ined d for des design ign pur purpos poses es in a dir directi ection on normal to the plane of facings as the core would be placed in a structural sandwich construction. The test procedures pertain to compression in this direction in particular, but also can be applied with possible minor variations to determining compressive properties in other directions. Permissible core material forms include those with continuous bonding surfaces (such as balsa wood and foams) as well as those with discontinuous bonding surfaces (such as honeycomb). 1.2 Thi Thiss test method method doe doess not cover the det determ ermina ination tion of  compre com pressi ssive ve cor coree cru crush sh pro proper perties ties.. Ref Referen erence ce Test Met Method hod D7336/D7336M for D7336/D7336M  for determination of static energy absorption properties of honeycomb sandwich core materials. 1.3 The values stated in either SI units or inch-pound inch-pound units are to be regarded separately as standard. The values stated in each system may not be exa exact ct equ equiva ivalent lents; s; the theref refore ore,, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard. 1.3.1 1.3 .1 Wi Withi thin n the text the inch-poun inch-pound d uni units ts are shown in brackets.

3. Terminology 3.1   Definitions— Terminology Terminology  D3878  D3878 defines  defines terms relating to high-modulus fibers and their composites, as well as terms relating to sandwich constructions. Terminology D883 Terminology  D883 defines  defines terms ter ms rel relatin ating g to pla plastic stics. s. Term ermino inolog logy y   E6   defines defines ter terms ms relating to mechanical testing. Terminology E456 Terminology  E456 and  and Practice E177   defin definee ter terms ms re relat latin ing g to sta statis tisti tics. cs. In th thee ev even entt of a conflict between terms, Terminology  D3878  D3878 shall  shall have precedence over the other terminologies.

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 ciated ted wi with th it itss us use. e. It is th thee responsibility of the user of this standard to establish appro priate safety and health practices and determine the applicability of regulatory limitations prior to use.

3.2   Symbols: 3.2.1   A— cross-sectional cross-sectional area of a test specimen 3.2.2   CV— coef c oefffic icien ientt of va vari riati ation on st stati atisti sticc of a sa samp mple le population for a given property (in percent)

2. Referenc Referenced ed Documents Documents

3.2.3   E  z fc  — flatwise flatwise compressive modulus

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2.1   ASTM Standards:

3.2.4   F  z fcu  — ultimate ultimate flatwis flatwisee compr compressive essive streng strength th 3.2.5   F  z fc 0.02 — flatwise flatwise compressive strength at 2 % LVDT/  compressometer deflection

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Thiss tes Thi testt met method hod is und under er the jur jurisd isdict iction ion of ASTM Com Commit mittee tee   D30   on Composite Materials and is the direct responsibility of Subcommittee D30.09 Subcommittee  D30.09  on Sandwich Construction. Curren Cur rentt edi editio tion n app approv roved ed May 15, 201 2016. 6. Pub Publis lished hed Jun Junee 201 2016. 6. Ori Origin ginall ally y approved in 1955. Last previous edition approved in 2011 as C365/C365M – 11A. DOI: 10.1520/C0365_C0365M-16. 2 For referenced ASTM standards, visit the ASTM website, www.astm.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

3.2.6   Pmax  — maximum maximum force carried by test specimen before failure 3.2.7   P0.02 — force f orce carried by test specimen at 2 % LVDT/  compressometer deflection 3.2.8   S n–1 — standard standard deviation statistic of a sample popula-

the ASTM website.

tion for a given property

Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States

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C365/C365M − 16

thickness of a test specimen 3.2.9   t— thickness

6.2  System Alignment— Non-uniform Non-uniform loading over the surface of the test specimen may cause premature failure. Nonunifo un iform rm loa loadin ding g may res result ult fr from om no nonn-un unifo iform rm sp speci ecimen men thickness, failure to locate the specimen concentrically in the fixture, or system or fixture misalignment.

3.2.10   x 1 — test test result for an individual specimen from the sample population for a given property 3.2.11   x¯—  mean or average (estimate of mean) of a sample ¯— mean population for a given property 3.2.12   δ — LVDT LVDT or compressometer deflection

6.3   Geometry— Specific Specific geometric factors that affect sandwich flatwise compressive strength include core cell geometry, core co re th thick ickne ness ss,, an and d sp spec ecim imen en sh shap apee (s (squ quar aree or cir circu cula lar) r).. Flatwisee compr Flatwis compressive essive strength and modul modulus us measur measurements ements are

3.2.13   σ z fc0.02 — flatwise flatwise compressive stress at 2 % LVDT/  compressometer deflection

particularly sensitive to thickn particularly thickness ess variations over the crosssectional area of the specimen, which can cause local loading eccen ec centri tricit cities ies,, as we well ll as to toee re regi gion onss in th thee fo forc rcee ve vers rsus us displacement curves due to specimen seating.

4. Summ Summary ary of Test Test Method 4.1 This test method consists consists of subjecting subjecting a sandwich core to a uni uniaxi axial al com compre pressi ssive ve for force ce nor normal mal to the plane of the facings as the core would be placed in a structural sandwich constr con struct uction ion.. The for force ce is tra transm nsmitte itted d to the san sandwi dwich ch cor coree using loading platens attached to the testing machine.

6.4   Environment— Results Results are affected by the environmental conditions under which specimens are conditioned, as well as the conditions conditions under which the tests are condu conducted. cted. Specimens tested in various environments can exhibit significant differences enc es in bot both h str streng ength th beh behavi avior or and fail failure ure mod mode. e. Cri Critica ticall environmen envir onments ts must be assess assessed ed indep independen endently tly for each core materiall tested. materia

5. Sign Significan ificance ce and Use 5.1 Flatwis Flatwisee compressive compressive strength and modulus are fundamental mechanical properties of sandwich cores that are used in de desig signi ning ng san sandw dwich ich pa panel nels. s. De Defo form rmati ation on dat dataa can be obtained, and from a complete force versus deformation curve, it is possible to compute the compressive stress at any applied

7. Appar Apparatus atus 7.1  Micrometers and Calipers— A micrometer with a 4 to

force (such asstrength compressive at proportional force or compressive at thestress maximum force) andlimit to compute the effective modulus of the core.

7 mm interface [0.16 to 0.28 in.] a flat anvil shall benominal used to diameter measureball-interface the specimenorthickness. A ball interface is recommended for thickness measurements of stabilized specimens (in accordance with 8.3 with  8.3)) when at least one facing plane surface is irregular (e.g. the bag-side of  a th thin in fa facin cing g lam lamin inat atee th that at is ne neith ither er sm smoo ooth th no norr flat flat). ). A microme micr ometer ter or cali caliper per with a flat anv anvil il int interf erface ace is rec recomommended mende d for thickn thickness ess measur measurements ements of stabili stabilized zed specim specimens ens when wh en bo both th fa faci cing ng pl plan anee su surf rface acess ar aree sm smoo ooth th (e (e.g .g.. to tool oled ed surfaces). A micrometer or caliper with a flat anvil interface shall be used for measuring length and width (or diameter), as well as the specimen thickness when the facing plane surfaces are not stabilized (e.g. bare). The use of alternative measurement devices is permitted if specified (or agreed to) by the test requestor reque stor and repor reported ted by the testing labora laboratory tory.. The accuracy of the instrument(s) shall be suitable for reading to within 1 % of the sample length and width (or diameter) and thickness. For typical specimen geometries, an instrument with an accuracy of    60.0 .012 12 mm [60. 0.00 0005 05 in in.] .] is ad adeq equa uate te fo forr th thic ickn kness ess measur mea sureme ement, nt, whe wherea reass an ins instru trumen mentt with an accu accurac racy y of  60.25 mm [60.010 in.] is adequate for length and width (or diameter) measurement.

5.2 This test method provides provides a standard method method of obtaining the flatwise compressive strength and modulus for sandwich core struc structural tural desig design n prop properties, erties, material specifi specification cations, s, research resear ch and development development applic applications, ations, and qualit quality y assura assurance. nce. 5.3 In order to prevent local crushing crushing of some honeycomb cores, it is often desirable to stabilize the facing plane surfaces with a suitable material, such as a thin layer of resin or thin facings. Flatwise compressive strength data may be generated using either stabilized specimens (reported as stabilized compression pressi on streng strength) th) or nonnon-stabiliz stabilized ed specime specimens ns (repo (reported rted as bare compression strength). It is customary aerospace industry practice to determine compression modulus only when using stabilized specimens. 5.4 Factor Factorss that influen influence ce the flatwis flatwisee compressive compressive strength and sha shall ll the theref refore ore be rep report orted ed inc includ ludee the fol follow lowing ing:: cor coree material, methods of material fabrication, core geometry (cell size), core density, specimen geometry, specimen preparation, specimen spec imen con conditi ditioni oning, ng, env environ ironment ment of test testing ing,, spe specime cimen n alignment, loading procedure, and speed of testing.

7.2   Loading Loading Platen Platens—  s— Force Force sha shall ll be int introd roduce uced d int into o the specimen using one fixed flat platen and one spherical seat (self-aligni (selfaligning) ng) platen. The platens shall be well-a well-aligned ligned and shall not apply eccentric forces. A satisfactory type of apparatus is shown in Figs. in  Figs. 1 and 2. 2. The platen surfaces shall extend beyond bey ond the test specimen specimen per periph iphery ery.. If the platens platens are not sufficiently hardened, or simply to protect the platen surfaces, a ha hard rden ened ed pl plat atee (w (wit ith h pa para ralle llell su surf rface aces) s) ca can n be in inse sert rted ed

6. Interfere Interferences nces 6.1  Material and Specimen Preparation— Poor Poor material fabrication practices and damage induced by improper specimen machining are known causes of high data scatter in composites and sandwich structures in general. A specific material factor that af affec fects ts san sandwi dwich ch cor cores es is var variab iabilit ility y in cor coree den densit sity y. Important aspects of sandwich core specimen preparation that contribute to data scatter include the existence of joints, voids or other core discontinuities, out-of-plane curvature, and surface roughness.

between each end of the fixture and the corresponding platen. 7.3   Testing Machine— The The testing machine shall be in accordance corda nce with Practic Practices es   E4   and sha shall ll sat satisf isfy y the fol follow lowing ing requirements: 2

 

 

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FIG. 1 Platen Platen,, Transducer Transducer,, and Rod Setup

 

FIG. 2 CloseClose-up up of Specime Specimen n Betwee Between n Loadin Loading g Platen Platens s

to large errors in measurement of strain.

7.3.1   Testing Machine Configuration— The The testing machine shall have both an essentially stationary head and a movable head. 7.3.2   Drive Mechanism— The The testing machine drive mechanism ni sm sh shall all be cap capab able le of imp impar artin ting g to th thee mo mova vabl blee he head ad a contro con trolled lled vel veloci ocity ty wit with h res respec pectt to the sta station tionary ary hea head. d. The velo ve loci city ty of th thee mo mova vabl blee he head ad sh shal alll be ca capa pabl blee of be bein ing g regulated in accordance with  11.5  11.5.. 7.3.3   Force Force Indic Indicator—  ator— The testing machine loadload-sensin sensing g device dev ice sha shall ll be cap capabl ablee of ind indicat icating ing the tot total al for force ce bei being ng carried by the test specimen. This device shall be essentially free from inertia lag at the specified rate of testing and shall indicate the force with an accuracy over the force range(s) of  interest of within 61 % of the indicated value.

7.5   Conditioning Conditioning Chamber— When condi conditionin tioning g material materialss at non non-lab -labora oratory tory env enviro ironme nments, nts, a temp temperat erature ure/vap /vapor or-lev -level el controlled environmental conditioning chamber is required that shall sha ll be cap capabl ablee of mai mainta ntainin ining g the req requir uired ed temp tempera eratur turee to within   63°C [65°F] and the required relative humidity level to within 63 %. Chamb Chamber er conditions shall be monito monitored red either on an aut automa omated ted continuo continuous us basis or on a man manual ual basis at regular intervals. 7.6   Environmenta Environmentall Test Cham Chamber—  ber— An envir environmen onmental tal test chamber is required for test environments other than ambient testing laboratory conditions. This chamber shall be capable of  main ma intai taini ning ng th thee ga gage ge se secti ction on of th thee tes testt sp speci ecime men n at th thee required test environment during the mechanical test.

7.4   Crosshe Thee tes testin ting g ma ma-Crosshead ad Displa Displacement cement Indic Indicator—  ator— Th chine shall be capable of monitoring and recording the crosshead displacement (stroke) with a precision of at least 61 %. If ma mach chin inee co comp mplia lianc ncee is si sign gnifi ifican cant, t, it is ac accep ceptab table le to measure the displacement of the movable head using an LVDT, compressome compr essometer, ter, or similar device with   61 % pre precisi cision on on displacement. displac ement. A trans transducer ducer and rod setup, setup, shown in Figs. in  Figs. 1 and 2, has been found to work satisfactorily. In the example shown, a small hole is drilled in the center of the core specimen and in

8. Sampling and Test Test Specimens 8.1   Sampling— Test Test at least five specimens per test condition unless valid results can be gained through the use of fewer spec sp ecim imen ens, s, as in th thee cas casee of a de desig signe ned d ex expe peri rime ment nt.. Fo Forr statistically statisti cally significant data, consu consult lt the proce procedures dures outlined in Practice E122 Practice  E122.. Report the method of sampling. 8.2   Geometry— Test Test specimens shall have a square or circular cross-section not exceeding 10 000 mm 2 [16.0 in.2], and

the bottom bot tom loadin loa ding g pla platen, ten,it and a tra transd nsduce ucerr rod is ins insert erted ed through the hole, such that contacts the upper loading platen.

shall be equ shall equal al in thic thickne kness ss to the sandwich sandwich cor coree thi thickn ckness. ess. Minimum specimen cross-sectional areas for various types of  core materials are as follows:

NOTE   1—Bonded 1—Bonded resistance strain gages are not usually consi considered dered satisfact satisf actory ory for mea measur suring ing str strain ain in thi thiss app applic licatio ation n bec becaus ausee of the their ir stiffness stif fness.. The reinfo reinforcing rcing effect effect of bondi bonding ng gages to some cores can lead

NOTE  2—The specimen’s cross-sectional area is defined in the facing

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C365/C365M − 16 9. Cali Calibrati bration on

plane, in regard to the orientation that the core would be placed in a structural sandwich construction. For example, for a honeycomb core the cros cr osss-se secti ction onal al ar area ea is de defin fined ed in th thee pl plan anee of th thee cel cells ls,, wh whic ich h is perpendicular to the orientation of the cell walls.

9.1 The accuracy accuracy of all mea measur suring ing equipment equipment shall hav havee certified calibrations that are current at the time of use of the equipment.

8.2.1   Contin Continuou uouss Bon Bondin ding g Sur Surfac faces es (fo (forr exa exampl mple, e, Bal Balsa sa Wood, Foams)— The The minimum minimum fac facing ing area of the specimen specimen shall be 625 mm2 [1.0 in.2].

10. Condi Conditioni tioning ng 10.1 The recommended recommended pre-test condition condition is ef effectiv fectivee moisture equilibrium at a specific relative humidity as established by Test Method D5229/D5229M Method  D5229/D5229M;; however, if the test requestor

8.2.2   Disc Discont ontinuo inuous us Cell Cellular ular Bond Bonding ing Surf Surfaces aces (for  example, Honeycomb)— The The required facing area of the specimen is dependent the cell size,facing to ensure minimum number of cells areupon tested. Minimum areasaare recommended in Table in  Table 1 for 1  for the more common cell sizes. These are intended to provide approximately 60 cells minimum in the test specime spe cimen. n. The largest largest fac facing ing area list listed ed in the tab table le (56 (5625 25 mm2 [9.0 in.2]) is a practical maximum for this test method. Cores with cell sizes larger than 9 mm [0.375 in.] may require a smaller number of cells to be tested in the specimen.

does not explicitly specify a pre-test conditioning environment, no con condit dition ioning ing is req requir uired ed and the tes testt spe specime cimens ns may be tested as prepared. 10.2 The pre-test pre-test specimen conditioning conditioning process, process, to includ includee specified environmental exposure levels and resulting moisture content, shall be reported with the test data. NOTE 5—The term moisture, as used in Test Method D5229/D5229M Method  D5229/D5229M,, includes not only the vapor of a liquid and its condensate, but the liquid itself in large quantities, as for immersion.

8.3   Specimen Preparation and Machining— Prepare Prepare the test specimens so that the loaded surfaces will be parallel to each other oth er and perpendic perpendicular ular to the sid sides es of the spe specime cimen. n. Take precautions when cutting specimens from large sheets of core to avoid notches, undercuts, and rough or uneven surfaces due to inappropriate machining methods. Obtain final dimensions by water-lubricated precision sawing, milling, or grinding. The

10.3 If no explic explicit it condi conditionin tioning g process is perfo performed, rmed, the specimen conditioning process shall be reported as “unconditioned” and the moisture content as “unknown.” 11. Proced Procedure ure 11.1  Parameters to be Specified Before Test:

use of di use diamo amond nd to tool olin ing g ha hass be been en fo foun und d to be extr extrem emely ely effec ef fective tive for man many y mat materia eriall sys system tems. s. Reco Record rd and rep report ort the specimen specime n cutting preparation method.

11.1.1 The specimen sampling method, specimen geometry, and condi conditionin tioning g travele travelers rs (if requi required). red). 11.1.2 11 .1.2 The properties properties and data reporting reporting form format at desire desired. d.

NOTE 3—In order to prevent local crushing of some honeycomb cores, it is often desirable to reinforce the facing plane surfaces with a suitable material. In such instances, the facing plane surfaces may be dipped in a thin layer of resin, or thin facings may be bonded to the facing plane surfaces of the core. When either of these stabilization techniques is used, the test shall be reported as a stabilized compression test, and the method, configuration, and process of stabilization utilized shall be reported. When honeycomb core facing plane surfaces are not stabilized, the test shall be reported as a bare compression test. It is customary aerospace industry practice to determine compression modulus only when using stabilized specimens. NOTE 4—Testing of core materials with typical manufacturing thickness tolerances (60.08 to   60.13 mm [60.003 to   60.005 in.]) may produce variant flatwise compressive modulus values, as this tolerance is too large

NOTE   6—Determ 6—Determine ine specifi specificc mater material ial prope property rty,, accura accuracy cy,, and data reporting requirements prior to test for proper selection of instrumentation and data recording equipment. Estimate the specimen strength to aid in transd tra nsduce ucerr sel select ection ion,, cali calibra bration tion of equ equipm ipment ent,, and det determ ermina ination tion of  equipment settings.

11.1.3 11 .1.3 The environmental environmental condit conditionin ioning g test parameters. 11.2   General Instructions: 11.2.1 Report any deviations from this test method, whether intentional intenti onal or inadve inadvertent. rtent. 11.2.2 11 .2.2 If core den density sity is to be rep report orted, ed, then obt obtain ain these sampless from the same sheet of core being tested. sample tested. Density may be evaluated in accordance with Test Method  C271/C271M  C271/C271M.. 11.2.3 11 .2.3 Follo Followin wing g fina finall spe specim cimen en mach machinin ining, g, but bef before ore conditi con ditioni oning ng and test testing ing,, mea measur suree the spe specime cimen n len length gth and width wid th (or dia diamete meter) r) and thi thickn ckness ess.. The accu accurac racy y of thes thesee measurements shall be within 1.0 % of the dimension. Measure the specimen length and width (or diameter) with an accuracy of   6250 µm [60.01 0.010 0 in.]. Measure the specime specimen n thickn thickness ess with wi th an acc accur uracy acy of   61 3 µ m [60.0 0.0005 005 in. in.]. ]. Reco Record rd the dimensions to three significant figures in units of millimetres [inches].

to preclu preclude de specim specimen en seatin seating g ef effects fects within the specifi specified ed displ displaceme acement nt range. Such effects are often characterized by the presence of toe regions in the force versus displacement data (see Anne (see Annex x A1 A1). ). To minimize the toe region and provide Hookean (linear) behavior in the specified displacement range, it is recommended that the core be produced or machined with a facing area thickness tolerance equal to   60.05 % of the nominal core thickness (for example, 60.013 mm [60.0005 in.] for 1.0 inch thick core).

8.4   Labeling— Label Label the test specimens so that they will be distinct from each other and traceable back to the sheet of  origin, and will neither influence the test nor be affected by it.

11.3 11 .3 Condi Condition tion the specimens as requi required. red. Store the specimens in the conditioned environment until test time, if the test environmen envir onmentt is dif differen ferentt than the condi conditionin tioning g enviro environment. nment. TABLE 1 Recommended Minimum Specimen Cross-Sectional Area Minimum Minimu m Cell Size

Maximum Cell Size

Minimum Cross-Sectional

(mm [in.]) ... 3.0 [0.125] 6.0 [0.250]

(mm [in.]) 3.0 [0.125] 6.0 [0.250] 9.0 [0.375]

Area (mm [in. ]) 625 [1.0] 2500 [4.0] 5625 [9.0]

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11.4 Followin 11.4 Following g fina finall spe specime cimen n con condit dition ioning ing,, but bef before ore testing, re-measure the specimen length and width (or diam-

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eter) and thickness as in   11.2.3. 11.2.3. 11.5   Speed of Testing esting—  — Set S et th thee sp spee eed d of testin testing g so as to produce failure within 3 to 6 min. If the ultimate strength of the material cannot be reasonably estimated, initial trials should be 4

 

 

C365/C365M − 16

conducted using standard speeds until the ultimate strength of  the material and the compliance of the system are known, and speed of testing can be adjusted. The suggested standard head displacement rate is 0.50 mm/min [0.020 in./min].

12. Validation 12.1 Values for ultimate prop properties erties shall not be calculated for any specimen that breaks at some obvious flaw, unless such flaw con constit stitute utess a var variab iable le bei being ng stu studie died. d. Rete Retests sts sha shall ll be performed for any specimen on which values are not calculated.

11.6  Test Environment— If If possible, test the specime specimen n under the same fluid exposure level used for conditioning. conditioning. However, However, cases such as elevate elevated d temperature testing of a moist specimen place unrealistic requirements on the capabilities of common testing machine environmental environmental chambers. chambers. In such cases, the mechanic mech anical al test environm environment ent may need to be mod modifie ified, d, for exampl exa mple, e, by tes testing ting at elev elevated ated temperatu temperature re wit with h no flui fluid d exposure control, but with a specified limit on time to failure from withdrawal from the conditioning chamber. Record any modifications to the test environment.

12.2 A signifi significant cant fraction fraction of failures in a sample population population occu oc curr rrin ing g alo along ng on onee co corn rner er or on onee ed edge ge sh shall all be ca caus usee to re-examine the means of force introduction re-examine introduction into the specimen. Factor Fac torss con consid sidere ered d sho should uld inc includ ludee the lo loadi ading ng pla platen ten alignment, specimen surface characteristics, and uneven machining of specimen surfaces and edges. 13. Calc Calculat ulation ion

NOTE 7—When testing a conditioned specimen at elevated temperature with wit h no flui fluid d exp exposu osure re con contro trol, l, the per percen centag tagee mo moist isture ure los losss of the spec sp ecim imen en pr prio iorr to te test st co comp mple letio tion n ma may y be es esti tima mated ted by pl plac acin ing g a conditioned traveler coupon of known weight within the test chamber at the same time the specimen is placed in the chamber. The traveler coupon should be configured to mimic the specimen, such that moisture evaporation is comparable to that of the test specimen. Upon completion of the test, the traveler coupon is removed from the chamber, weighed, and the percentage weight calculated and reported.

13.1   Ultimate Stren Calcu culat latee the ult ultima imate te flat flatwis wisee Strength—  gth— Cal compressive strength using Eq using  Eq 1  and report the results to three significant figures. F  fcu  A  /  A  z 5 P max 

 

(1 )

where: F  z fcu = ultimate flatwise flatwise compressive compressive strength, strength, MPa [psi], ultimate mate fo force rce prior prior to failur failure, e, N [lbf], [lbf], and Pmax    = ulti

11.7   Specimen Installation— Mark a rectangle or circle (de-

2

pen pendin ding g upo upon nto the specime cimen’ n’ss specimen crosscro ss-sec section tional al sha shape) pe)platens. on the lower platen helpspe center the between the Place the specimen on the lower platen, accommodating the LVDT or compressometer as necessary.

2

  = cross-sectional cross-sectional area, mm [in. ]. 13.2   2 % Deflect Deflection ion Str Stress—  ess— If 2 % deflection is achieved prior to stopping the test, calculate the flatwise compressive stress at 2 % deflection using   Eq 2   and report the results to three significant figures.

 A

NOTE   8—Take care to align specimens well between the platens, in order to distribute the applied force as uniformly as possible over the entire loading surface. This will help to ensure that the specimen edges are loaded uniformly. Non-uniform loading often results in failures that are confined to one corner or one edge of the specimen.

0.02 σ fc 5  z

P 0.02 /  A

 

(2 )

where:  fc0.02

σ z

= flatwise compres compressive sive stress stress at 2 % deflection, deflection, MPa [psi], applied d force corre correspond sponding ing to   δ0.02, N [lbf], P0.02   = applie recorded ded deflecti deflection on value such that   δ / t  is closest to δ0.02   = recor t  is 0.02, and t    = meas measur ured ed thick thickne ness ss of cor coree specim specimen en prio priorr to loading, mm [in.].

11.8   Pre-loading— Move Move the actuator or crosshead such that the loa loadin ding g pla platen ten con contac tacts ts the LVDT VDT/com /compre presso ssomet meter er and specimen, and apply a standard initial load of 45 N [10 lbf]. Zero and balance the LVDT or compressometer. 11.9   Loading— Apply Apply a compressive force to the specimen at the specified rate while recording data. Load the specimen until fail until failure ure,, or unt until il the meas measure ured d LVDT VDT/co /compr mpress essome ometer ter deflection equals 2 % of the initial core thickness.

13.3   Compressive Calculat ulatee the flat flatwise wise com com-Compressive Modu Modulus—  lus— Calc pressive chord modulus using   Eq 3  and report the results to three thr ee sig signifi nifican cantt figu figures res.. The defl deflect ection ion valu values es sele selected cted are intended to represent the lower half of the core’s stress-strain curve. cur ve. For core mate materia rials ls whi which ch fal falll bel bellow low   δ / t  0.00 006, 6, a t   = 0. deflection range of 25 to 50 % of ultimate is recommended. However, for some other materials, another range may be more appropriate. Other definitions of chord modulus may be evaluated and rep report orted ed at the user’s user’s dis discre cretion tion.. If suc such h dat dataa are genera gen erated ted and rep report orted, ed, rep report ort als also o the defi definit nition ionss use used, d, the defle de flect ctio ion n ra rang ngee us used ed,, an and d th thee re resu sults lts to th thre reee si sign gnifi ifican cantt figures.

11.10   Data Recording— Record Record force versus head displacement and force versus LVDT/compressometer deflection data contin con tinuou uously sly,, or at fre freque quent nt reg regula ularr int interv ervals; als; for this test method, a sampling rate of 2 to 3 data recordings per second, and a target minimum of 100 data points per test are recommended. If a compliance change or initial failures are noted, record the force, displacement, and mode of damage at such points. Record the maximum force, the failure force, the head displacement and the LVDT/compressometer deflection at, or as near as possible to, the moment of failure. Also record the force and head displacement at 2 % deflection, if that deflection level is achieved prior to failure.

NOTE  9—To account for seating effects related to specimen thickness variance, toe: comp variance, compensati ensation on may be made in accord accordance ance with Annex A1,

11.11   Failure Modes— Uniform Uniform compressive failure of the sandwich core is the only acceptable failure mode. Compressive failures confined to one corner or edge of the specimen shall be considered invalid.

unless it is shown that the toe region of the curve is not due to the take-up unless of sla slack, ck, seating seating of the specimen specimen,, or other artifact, artifact, but rat rather her is an authentic material response.  E  fc ~~ δ 0.003 2 δ 0.001! · A !  z 5 ~~ P 0.003 2 P 0.001! · t ! / ~~

5

 

(3 )

 

 

C365/C365M − 16

where:  E  z fc P0.003   P0.001   δ0.003   δ0.001

 

14.1.7 Meth 14.1.7 Method od of pre prepar paring ing the test spe specim cimen, en, inc includ luding ing specimen specim en labelin labeling g scheme and method method,, specim specimen en geomet geometry ry,, sampling method, and specimen cutting method. 14.1.8 14.1. 8 For honeycomb honeycomb core specimens, method of stabilizing the specimen (if performed), including material(s), processing cycle, specimen geometry after stabilization, and so forth. 14.1.9 14.1. 9 Results of any nond nondestruc estructive tive evaluation tests. 14.1.10 Calibration dates and methods methods for all measurements and test equipment.

= core core flatw flatwise ise com compre pressi ssive ve cho chord rd mod modulu ulus, s, MPa [psi], = applie applied d force force corres correspond ponding ing to   δ0.003, N [lbf], = applie applied d force force corres correspond ponding ing to   δ0.001, N [lbf], = recor recorded ded deflect deflection ion value such that   δ / t  t  is is closest to 0.003, and = recor recorded ded deflect deflection ion value such that   δ / t  is closest to t  is 0.001.

13.4   Statistics— For For each series of tests calculate the average value, standard deviation, and coefficient of variation (in percent) percen t) for ultimate flatwis flatwisee compr compressive essive strength and modulus:

S ( D

14.1.11 14.1. 11 Details of loading platens and appara apparatus, tus, including including dimensions and material(s) used. 14.1.1 14. 1.12 2 Type of test machine, machine, alig alignme nment nt res result ults, s, and data acquisition sampling rate and equipment type. 14.1 14 .1.1 .13 3 Typ Type, e, ra rang nge, e, an and d se sens nsit itiv ivit ity y of LVD VDT T or compre com presso ssomet meter er,, or any oth other er ins instru trumen ments ts use used d to mea measur suree loading loadin g platen deflecti deflection. on. 14.1.14 14.1. 14 Measur Measured ed length and width (or diameter) and thicknesss for each spe nes specime cimen n (pr (prior ior to and after con condit dition ioning ing,, if  appropriate). 14.1.15 14.1. 15 Weight of specimen. 14.1.16 14.1. 16 Condit Conditionin ioning g param parameters eters and resul results. ts. 14.1.1 14. 1.17 7 Rela Relative tive hum humidi idity ty and temp temperat erature ure of the test testing ing laboratory. 14.1.1 14. 1.18 8 Env Enviro ironme nment nt of the test mach machine ine env enviro ironme nmenta ntall

n

 x  H5

Œ S ( n

S n

2

1

i

5

1

i

5

1

 x i  / n

 

(4 )

D

 x 2i 2 nx  H 2  / ~ n 2 1 !

CV 5 100 3 S n 1 /  x  H 2

   

(5 ) (6 )

where:  x¯  ¯    = sample mean (aver (average), age), S n-1   = sample standard standard deviati deviation, on, CV    = sample coef coeffficient of of variation, variation, %, n    = number beredofor specime spe cimens, ns, and rty.. = num measured measur derived derive d prope property  x  i

chamber (if used) and soak time at environment. 14.1.19 14.1. 19 Numbe Numberr of specime specimens ns tested. 14.1.20 14.1. 20 Speed of testing. testing. 14.1.21 14.1. 21 Indiv Individual idual ultimate flatwise compressive compressive streng strengths ths and ave averag ragee val value, ue, stan standar dard d dev deviati iation, on, and coe coeffficie icient nt of  variation (in percent) for the population. 14.1.22 14.1. 22 Indiv Individual idual ultimate flatwise compressive compressive modul modulus us values and average value, standard deviation, and coefficient of  variation (in percent) for the population. 14.1.23 14.1. 23 Force versus crosshead crosshead displacement displacement data for each specimen so evaluated. 14.1.24 14.1. 24 Force versu versuss recor recorded ded LVDT/co VDT/compress mpressometer ometer deflection data for each specimen so evaluated. 14.1.25 14.1. 25 Failur Failuree mode, location of failure, and percentage percentage of  failure area of core for each specimen.

14. Repor Reportt 14.1 Report the following following information, information, or refere references nces pointing to other documentation containing this information, to the maximu max imum m ext extent ent app applica licable ble (re (repor portin ting g of item itemss bey beyond ond the control of a given testing laboratory, such as might occur with material details or panel fabrication parameters, shall be the responsibili respo nsibility ty of the reque requestor) stor):: 14.1.1 14.1. 1 The revision revision level or date of issue of this test method. 14.1.2 14.1. 2 The name(s) of the test operator(s). operator(s). 14.1.3 14.1. 3 Any variations variations to this test method, anomalies anomalies noticed during testing, or equipment problems occurring during testing. 14.1.4 14.1. 4 Ident Identification ification of all the materials constituent constituent to the sandwich cored), specimen tested stabilization materials if uti utilize lized), includ inc luding ing for(including each:: mat each materia eriall spe specific cificatio ation, n, material type, manufacturer’s material designation, manufacturer’s batch or lot number, source (if not from manufacturer), date of certification, and expiration of certification. 14.1.5 14.1. 5 Descri Description ption of the fabri fabrication cation steps used to prepare the sandw sandwich ich core including: including: fabri fabrication cation start date, fabrication end en d da date, te, pr proc oces esss sp speci ecific ficati ation on,, an and d a de desc scri ript ptio ion n of th thee equipment used. 14.1.6 14. 1.6 If req reques uested ted,, cor coree den density sity test meth method, od, spe specime cimen n sampling samp ling met method hod and geo geomet metries ries,, tes testt par parame ameters ters,, and test results.

15. Pre Precisi cision on and Bias 15.1   Precision— The The data required for the development of a precision statement is not available for this test method. 15.2   Bias— Bias Bias cannot be determined for this method as no acceptable refer acceptable reference ence standa standards rds exist. 16. Keyw Keywords ords 16.1 compressive modulus; compressive strength; core; flatwise compression; sandwich

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C365/C365M − 16 ANNEX (Mandatory Information) A1. TOE COMPENSA COMPENSATION

A1.1 In a typical force force versus displacement displacement curve (see Fig. (see  Fig. A1.1), A1.1 ), th ther eree is a to toee re regi gion on,, AC, th that at do does es no nott re repr pres esen entt a property of the material. It is an artifact caused by a take-up of  slack alignment or seating of the specimen. In order to obtainand correct compressive modulus values, this artifact must be compensated for to give the corrected zero point on the displacement axis. A1.2 For cor A1.2 coree mate materia rials ls exh exhibi ibiting ting a reg region ion of Hoo Hookea kean n (linear) behavior (see  Fig. A1.1), A1.1), a continuation of the linear (CD)) re (CD regi gion on of th thee cu curv rvee ma may y be co cons nstru tructe cted d th thro roug ugh h th thee zero-fo zero -force rce axi axis. s. Thi Thiss int inters ersecti ection on (B) is the cor correc rected ted zer zero o displacement point (δ  = 0.000) from which all displacements must be measured. A1.3 For core mod A1.3 modulu uluss meas measure uremen ment, t, it is pre prefer ferabl ablee tha thatt   the toe region fall below   δ0.001.

FIG. A1.1 Core Materia Materiall with Hookea Hookean n Region

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C365/C365M − 16 ASTM International position on respecting the validi validity ty of any patent rights assert asserted ed in connec connection tion with any item mentio mentioned  ned  International takes no positi in this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the risk  of infringement of such rights, are entirely their own responsibility. This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years and  if not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standards  and should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of the  responsible respon sible technical technical committee, which you may attend. If you feel that your comments have not receiv received ed a fair hearing you should  make your views known to the ASTM Committee on Standards, at the address shown below. This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the above  address or at 610address 610-832832-9585 9585 (pho (phone), ne), 610610-832832-9555 9555 (fax (fax), ), or serv service@ ice@astm astm.org .org (e-m (e-mail) ail);; or thro through ugh the ASTM webs website  ite  (www.astm. (www .astm.org). org). Permission Permission rights to photocopy the standa standard rd may also be secure secured d from the Copyri Copyright ght Clearance Center, Center, 222  Rosewood Drive, Danvers, MA 01923, Tel: (978) 646-2600; http://www.copyright.com/ 

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