MFTt1CDS, OF TEST 'FOIE IFTFIMIiNING STRFNGTI I
PROPERTIES OF CCRF MATLRIAF- TOR SAND WICI1
CONSTRUCTION, AT NORMAL-TFMIPFIR,ATIJRL S
Revised
October
1948 ,
This Report is One of a Serie s
Issued In Cooperation with th e
AIR FORCE-NAVY-CIVIL SU13CUMMITT E
on
AIRCRAFT DESIGN CRITERIA
Under the Supervision of th e
AIRCRAFT CUMM1TTF F
of the
MUNITIONS BOARD
No. 155 5
UNITED _ STATES DEPARTMENT OF AGRICULTUR E
FOWEST SERVIC E
FOREST'RODUCTS LABORATOR Y
Madison 5, Wisconsi n
In Cooperation with the University of Wisconsin
Table of Contents
Page
Introduction
1
Compression flatwise
5
Compression edgewise
7
Tension flatwise 8
:Shear test for the determination of the modulus of rigidity
9
Torsion pendulum shear test for the determination of th e
modulus of rigidity in any plane
11
Shear strength and stress-strain curves of core materiels 13
The determination of moisture content and specific gravity 15
Report No . 1555, revised
r:
F-I-7-r-'7"77717
METHOti' 0 TEST FOR DETERMINING STRENGTH PROPERT OF CORE MATERIAL FOR SANDWICH CONSTRUCTION A T
NORMALTEMPERATURES!
3; ' ' Sandwi' : ~ ori5'rQ03'&rl-nay be defined as a
materials, consisiOdi- of a comparatively lightweight
faces of which ark bonded relatively thin facings o f a denser and stronger
-material . Method. of testing core materials here outlined are based o n
experience obtain**
nga large number of specimens and have prove n
satisfactory .
The core matt
e.
at are us e
several categories, " _ . natural,
&Aped
-tV 1 le
.raiaban,
n
' .Test I , Tit
WO. of 't
c
_
R w•~ i . . .wpic
-perties O
eert i
tai*, ._
ch construction fall int o
such as balsa ; synthetic
ate, f sr p ee , ~ esins,• Ir ; hard
ness ]I ~
''
and
the
r~'. .
_
,'
~e core
'
'"
~ . es
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~
t.
, ually pe _` J
materials, however, do not ha
F strength axes, so that it may be nece .=oary tot (
ri .
detail in order to provide complete informatio
!
In me instances, parallel or perpendicular to th
arellel or perpendicular to the machin e ematri
riptive eno
identify the 'direction in which th e
In these t-e
cedures erms
-s.
"flatwise
e sandwich and "edgewise direction"
used to describe directions of loa d
e, to directions that ar e
e core material in the sandwich i s
-rials the test • -o.. edures would have to
ion
e a complet e
si p
This progress report is one of a series prepared and distributed by th e
Forest Products Laboratory under U . S . Navy, Bureau of Aeronautics No .
NBA-PO-NAer 00619, Amendment No, 1, and U . S . Air Force No . USAF-PO-(33--038)48-L1E . Results here reported are preliminary and may be revise d
as additional data become available .
Report No . 1555, revised .
-1-
General information is included on gluing procedures that have bee n
found satisfactory, as well as descriptions of fabrication methods and jig s
that may be helpful to the user of this report in preparation of specimens ,
Scone
2, These methods cover procedure for determining the following strengt h
properties of core materials :
(a) Compression :
j .) In the flatwise direction (perpendicular to the plan e
of the sandwich) ,
(2) In the edgewise direction (parallel to the plane o f
the sandwich) .
.'4b) Tension :
(1) In the flatwise direction (perpendicular to the
of the sandwich) .
plane
(c) Shear :
( 1) Shear test for the determination of the modulus o f
rigidity associated with shearing strains in plane s
., parallel to the faces of the plate .
j
~ . .
E
4(2) Torsion pendulum shear test for the determination o f
-s
he modulus of rigidity in any plane .
~ .. ,
1_
. . (3) Shear strength in the flatwise plane (parallel to th e
plane of-the sandwich) .
.
st Specimen
47
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_ _
_.
3 . (a) Selection of test specimens .--The number of test specimens t o
be chosen for test and the method of their selection depend on the purpos e
of the particular tests under consideration, so that no general rule can b e
given to cover all cases . However, with the exception of the plate shea r
test, no less than five specimens of a type shall be tested . A minimum o f
two specimens shall be tested for the determination of the modulus o f
rigidity by the plate shear method unless the results of the two tests do no t
agree, then mox'e tests shall be required . Any natural skin the core materia l
may have from the manufacturing process shall be removed before the specimen s
are tested . If desired, supplemental tests may be made on specimens that d o
not have the natural skin removed, but when this is done, the records of th e
test shall indicate this clearly .
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Report Noa 1555, revised .
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Note : Surfacing techniques for use in preparing balsa, cellula r
cellulose acetate, cellular hard rubber, and paper, glass-fabric, and cotton fabric honeycomb cores are described in Forest Products Laboratory Report No .
157)4, "Fabrication of Lightweight Sandwich Panels of the Aircraft Type . "
(b) Control of moisture content and temperatures--The strength-proper ties of some core materials may depend on the moisture content and tempera ture at time of test . When this is the case, all core material for tes t
shall be preferably conditioned to approximately constant weight and b e
tested in a room of controlled temperature and humidity . In any event, wher e
moisture content or temperature differences may affect results of tests, th e
tests shall be conducted so that the conditions will be uniform throughou t
the thickness, and so that changes will not occur during test . A temperatur e
of 75° F . and a relative humidity of 6L1 percent or a temperature of 75° F.
and a relative humidity of 50 percent are recommended .
(c) Adhesive processes and alining jigs for use in specime n
fabrication .--The adhesive process to be used in bonding the core specimen s
to test fixtures will depend on the mechanical and chemical properties of th e
core materials . For cores low in strength, room-temperature-settin g
resorcinol-resin adhesives can be used . If the solvents in these adhesive s
affect the core material, they may be replaced by room-temperature-settin g
urea-resin adhesives or intermediate-temperature-setting phenol-resin adhe sives, A medium spread of adhesive should be applied to both the core an d
the fixture surface, and an open-assembly period of 5 to 10 minutes b e
allowed, followed
assembly and pressing. Maximum allowable pressure (15
by
p .s.i. has been found
satisfactory for a number of core materials) that wil l
not damage the core should be applied and allowed to remain on the specime n
f,hours at room temperature . If the intermediate-temperatureT-resin adhesives are used, a glue-line temperature of 180° F .
,0 mi rr es should result in sufficient curing of the joint . When the
~ures4 re of metal, application of a heat-curing priming adhesive to th e
Otal andd its curing are required prior to the bonding of the core to th e
primed metal .
.
For high-strength and all honeycomb-type cores, special hot-settin g
adhesives, of the type formulated . for bonding to metal, shall be used fo r
.bonding the
aat4rials to the n4#a,l fixtures . Manufacturers' direction s
shall ba fold J the use ofth i adhesive s4 Maximum allowable pressur e
: ..• Wit .dddinage to tie cc:el material
lae used (15 p.s .i . has been use d
*&th honeycomb cores,'and te high A5~with end-grain balsa) .
S'ifficient time should be allowed for the heat to penetrate any alining ji g
a .1 fixtures to insure proper curing of the adhesive .
NN metal fixtures shall be cleaned to remove any surface contamination prio At bonding to the core material . A recommended procedure fo r
aluminum istfirst to remove as much contamination as possible by wiping wit h
an acetone-soaked cloth and then to immerse it for 10 minutes at 140° t o
160° F . in a solution of 10 parts by weight of concentrated sulphuric acid ,
one part by weight of sodium dichromate, and 30 parts by weight of water ,
and then to wash it in hot water and air dry . Steel plates have been cleane d
by abrading with No . 1/2 emery cloth and washing off the particles with ho t
water and steam, and then quickly air drying .
Report No . 1555, revised
-3-
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i in the tension. test, can b
Aluminum cubes,
ed by sanding off
adhdalve and core ma
and resurfacing to a uniform thickness on a mill ingr
nine . In sot>
tances, adhesives have been removed through the us e
ffi4"s-4f hot molten salts . The cubes shall not be reused whe n
, 5400 inch of thickness has been removed during reuse . Stee l
g
es c*
reused by scraping off as much adhesive and core material a s
possibley0by applying heat if necessary, and then sanding off th e
remainder;
emery cloth .
Slinement of specimen and fixtures is an important factor i f
accurate test results are to be obtained, it is recommended that an alinemen t
jig be used in the fabrication of test specimens . Alinement jigs that hav e
been used satisfactorily in the preparation of tension and shear specimens ar e
shown in figures 1 and 2 . The tension specimen jig will permit preparation
of as many as 25 test specimens on a single core sample . Specimens are
fabricated in this jig by placing the cubes, with adhesive spread on thei r
upper surface, in the lower alining holes ; laying the core material, wit h
adhesive on both surfaces, on the cubes ; insertion of upper alining bars o n
top of the jig ; and then placing cubes, with adhesive on the lower surface ,
in the upper holes of the jig . The assembly is then pressed under prope r
conditions . Following the curing of the specimens, the jig is taken apar t
and the specimen assembly removed . Individual specimens are cut from th e
group with the use of a bandsaw .
The shear-specimen jig shown in figure 2 has a ;lumber of adjustment s
to permit its use with several thicknesses and lengths of plates . In assembl y
the lower plate is positioned with the loading end against the movable end o f
the jig and with the adhesive-spread surface up ; the core, spread on bot h
faces with adhesive, is placed on top of the plate ; hinges are inserted a t
the ends of the core ; and then the top plate is placed with the adhesive spread surface down and loading end against the fixed end of the jig on to p
of the core, The movable end of the jig is then tightened until the distanc e
lalmnm the upper gtwps is equal to the length of the plate . In a properly
-tsadfORGI jig, the d ig
between the middle stops will be equal to th e
jMqIPk of the . ._
1 ckness of the two hinges, and the core will be
'
y posi
tween the plates . The specimen is then pressed and cure d
IIle
' I' amen removed from the jig .
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4 . The reps -of Bch test shall inotude a Complete description o f
'b rterial, incl
g its origin and kind ..-;-.T type of test and any detail s
wing to the
ication of the specimelRe
7ti bo given . When specimens
OPMN40zceived arly .,VOial conditioning prior='to test, this shall be stated .
=4'' he "
zhall be given, as well as any othe r
facto
*'might ha m '!t,#W
'its of the tests . These shal l
inter• glues,-4
m*00 tures, 'end predbures used in fabricating specimens ,
directioj_o f, 4 for other orientation data, and type of extensometer used .
A comple eesc
ion of type of trailure shall be included in the report .
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Compression
Flatwis e
Scope
5. This method shall be used to test the core material in compressio n
in the direction perpendicular to the plane of the sheet of the finishe d
sandwich .
Test Specimen
6. The test specimen shall be 2 inches square by 5 to 8 inches i n
height . The cut edges shall be smooth and free of burs . The width, depth ,
and thickness shall be measured to the nearest 0 .001 inch . If the availabl e
thickness of core material is less than 5 inches, a group of identical tes t
pieces having all surface irregularities removed shall be stacked on e .on to p
of the other without bonding to a height not less than 5 inches . If stress strain data are desired, the minimum practical height of individual tes t
piece will be 1/2 inch .
Loaded Surfaces Paralle l
7. Care shall be taken to prepare the test specimens so that th e
loaded faces (2- by 2-inch) will be parallel to one another and perpendicula r
to the edges of the specimen . Where additional support of the bearing sur faces is necessary, the ends of the specimen shall be cast in a suitable mold ing material (plaster of Paris or cast resin) so that the ends will be flus h
with the exterior surface of the cast base as shown in figure 3 .
Loading Procedur e
8. The load shall be applied to the specimen "through a spherical load ing block, preferably of the suspended, self-alining type . The load shall b e
applied with a continuous movement of the movable head of 0 .003 inch per inc h
of height of specimen per minute, with a permissible variation of ± 25 percent .
Stress-strain Curve s
9. (a) Data for stress-strain curves may be taken to determine th e
modulus of elasticity, proportional limit, and yield strength at 0 .2 percen t
offset . Increments of load shall be so chosen that approximately 12 reading s
of load and deformation are taken to the proportional limit . Deformation s
shall be read to at least the nearest 0 .0001 inch by means of a compres someter having a gage length not exceeding two-thirds of the height of th e
specimen, or two-thirds the height of the test piece in a built-up specimen .
The compressometer shall measure the strain over the central portion of th e
thickness of the specimen, or the central portion of the middle test piece i n
a built-up specimen, and, if of the lever type, shall have adequate suppor t
Report No . 1555, revised
-5-
e
n, spherics rig block, a -s a
uremen? . Also shown is the
total deformation in th e
ding a specime n
ing strain tha t
extensometer . The
orms to th e
f strain gag e
e 4 gives constrain
material, but the weight o f
ge tends t o
strain measurements on weak
ials . I wa s
e gage suspended on 7/8 inch l o
brads,
ch
the specimen, significantly affec e
cellulose acetate of about 6 pounds per c
obtain4d in this manner was 80 percen t
obta
th a ~,.9rted in figure 5 ' in which the
d by
ies focused on a specific poin t
1~
~~'beh rand. sat
0 .017-inch-diameter needles that
penetrate t 0pecimen to a dept ;Ai
,; Electric-type strain gages ar e
usually not considered satisfactory because
heir stiitfness .
Note : The use of dial gages for measuring head travel is not s o
accurate as, nor exactly comparable to, the use of strain gages mounted o n
the specimen, but is permissible for preliminary evaluation of core material .
Definition of Ultimat e
10. Ultimate stress shall be the maximum stress attained on the speci men or the stress on the specimen at 2 percent strain, whichever occurs first .
If the ultimate stress occurs below 2 percent strain, the strain at ultimat e
shall be reported (note) .
Note : It has been necessary to define failure because some core mate rials continue to yield almost indefinitely, with the load increasing wit h
the yield .
Moisture Content and Specific Gravit y
11. The moisture content and specific gravity of each specimen shal l
be determined as outlined in section 42 .
Report No . 1555, revised
-6-
CompressionEd
gewis e
Scope
12. This method shall be used to test the core material in compression in the dip @~ tion parallel to the plane of the sheet of the finishe d
sandwich .
Test Specimen
13. The test specimen shall be 2 inches wide by 2 inches high by 1/ 2
inch in thickness measured perpendicular to the plane of the sandwich (note) .
The cut edges shall be smooth and free of burs . The width, height, and thick ness shall be measured to the nearest 0 .001 inch .
Note : If a specimen 1/2 inch in thickness cannot be obtained, a
specimen 1 inch wide by 4 inches in height by the thickness of the materia l
shall be obtained and tested with lateral support in a jig as shown i n
figure 6 .
End Surfaces Parallel
14. Care shall be taken to prepare the test specimen so that the en d
surfaces will be parallel and be perpendicular to the faces of the specimen .
Loading Procedure
15. The load shall be applied to the specimen through a spherica l
loading block, preferably of the suspended self-alining type . The load shall
be applied with a continuous movement of the movable head of the testin g
machine of 0 .003 inch per inch of height of specimen with a permissible varia tion of ± 25 percent .
Stress-strain Curve s
16. (a) Data for stress-strain curves shall be taken to determin e
the modulus of elasticity, proportional limit, and yield strength at 0 .2 per cent offset . Increments in load shall be so chosen that approximately 1 2
readings of load and deformation are taken to proportional limit . Deformations shall be measured to the nearest 0 .0001 inch by means of a compres someter having a gage length not exceeding two-thirds of the height of th e
specimen . The compressometer shall measure the strain over the central por tion of the height of the specimen . The apparatus for test and the limit s
thereon shall he the sane as specified for the compression flatwise test i n
section 9 .
Report No, 1555, revised
-7-
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fatim
open shwa
e- c
in
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n def le c
ftra]L
re
eached, the height of the spec s ',
:e wlU r suit tn some mai Oer other than in
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Definition of U _ 'e'
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e.sls_
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17 . Intimate stave'
the
Am or- Ulm stress on the s _
at
, ; ,t
. e7r occurs first .
a:f tile ui t- Mate s
occ O bel.oW 2 • p
t stg:dddl,
strain at ultimat e
'll be reported .
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sou
in sectio n
19 . This method of test shall be used to determine the tensil e
strength of the core material in the direction normal to the plane of th e
sandwich .
all be a 1-inch square section of the core mate ess as will be used in the finished panel . One(17ST aluminum alloy is recommended for use wit h
rd-maple cubes, bonded to the-side-grain surfac e
Yiia having tensile strengths to 350 pounds pe r
Sri 12qt1 ~cie
ater- i 1 . One hole ,
the hol e
The
~ t
"Ca 'Ire
s shall be
ubes the
illed into the side gr a
m the face opposite th e
bonding face, and equidistant (
etween the adjacen t
sides . The specimen shall .be as s
holes in the two cube s
ented at 90° to each other ,
apposite sides of the core mat
and the sides of the two cubes b e
maximum offset tolerance ,
The dimensions of t
hall be measured to th e
nearest 0 .001 inch . The completed specimen and
ngs that apr. y the load
are shown in figure 7 . With cellular-type cor e
als havin, ell open ss of 3/8 inch, the s
increased
-1 sh
e t~
f woo3
''core I
t cqata
B
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Loading Procedure
21 . The specimen shall be loaded to failure in the fitting as show n
in figure 8 . The fittings for applying load to the specimen shall be made a s
shown in figure 9 . The load shall be applied to the specimen by continuou s
motion of the movable head of the testing machine, The rate of . head travel
shall be 0 .035 inch per minute with a permissible variation of ± 25 percent .
Test Data
22. This specimen will fail in tension in the core material or at the
glue lines, whichever is weakest . The stress at failure shall be obtained by
dividing the ultimate load by the cross-sectional area . If the failure is i n
or partially in the glue bond between core and test fixture, the test shall
be considered unsatisfactory .
Moisture Content and Specific Gravit y
23. The moisture contest and specific gravity of each specimen shal l
be determined as specified iii section 42 .
Shear , Test for the Determination of the Modulus of Rigidity ?
Scope
24. This method of test shall be used to determine the modulus o f
rigidity associated with shearing strains in the plate o f, the plate or
planes parallel thereto (notes 1 and 2) .
Note 1 : The modulus of rigidity as determined by this test method i s
the same in
directions if the material is isotropic . If not, it is the
modulus associated with the shear distortion in the planes parallel to th e
faces of the plate .
all
Note 2 : This method of test can be used instead of the method de scribed in sections 30 to 34, inclusive, for determining the modulus o f
rigidity in any of the planes of elastic symmetry by suitably cutting th e
material and edge gluing the strips obtained to provide a plate whose face s
are parallel to the plane for which the modulus of rigidity is desired .
?Further description and discussion of this method of test may be obtaine d
from Forest Products Laboratory Report No . 1301, June 1942 . 'This testing
procedure is described in and is a part of ASTM Specification D805-47 ,
" Methods of Testing Plywood, Veneer, and Other Wood and Wood-bas e
Materials . "
Report No . 1555, revised
-9-
ngth othe
ess .
ength and wid
kness equal to th e
shall be not less
s shall be measured
nearest 0 .01 inch .
igief1001
,
e.
.le inivature ;
ia1b . If sp,eelens have Initial curvature, it I'LL tn 'OBI/00hif
IMrace thI *Ices of the plate to remove the
-r '
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r.
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ti aaa,ftti,
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n 5hit*ik.
.Ardlp."rlc'
riff,* 6 011 ‘ef.;
ski;
ITtAo
1--I.sr
.1k.aFe,
1010ildbilk.be drawn .iwl.
Ilopikk4eq.,ijao shall be 9Mporte d
ly o" ,site corers, nd shall
ite coxters as shOwn i e 10 .
of tiVir-eirwhwoli
sions may be mad
ter not to excee d
at the corners .
be applied le head of th e
of
,per
Igta
otherwisebr ipaipom fit INS
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F5
Deformations shall be measured t o
Fie defter
a yoke ex
oint
di
the tjl0j,
4IM
1100b, 110APOPIOP4ilAim .4itom
IFft'srilPlItEr-hnetrate
the '
Ptuts
be measure at the quarter p4lnt s
"late .
ably
e chosen, care shall be
41f
at be cruse of load and
to av
ation
corn
elastic limit ,
ngs of load
at le
sha
,ma'•vature ,
be o fined. Successive
st
end prefer
sets or
° from the previous se t
pendicular to the plan e
1 be averaged to obtain
'dity.
edalc
form
M two'
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Calculation s
1~Ahe modulus of rigidity shall be calculated from the averaged dat a
the formula :
l
~+"#
where
;' G _ 3U2 P
.. .
W
+,
2L3
= modulus of ,igidity, in pounds per square inc h
P = load applied to each corner, in pound s
L = thickness of the plate, in inche s
W = deflection of the plate at a point along the diagonal with
reference to the center, in inches, an d
U = distance from the center of the plate to the point wher e
the deflection is measured, in inches .
Generally, values of P/W are taken from the slopes of the load-deflectio n
curves, which give averaged values . It'can be noted from the test set-u p
shown in figure 10 that P is one-half the load indicated by the testin g
machine and W is one-half the deflection indicated by the dial . However, th e
ratios of the two sets of readings are identical .
Moisture Content and Specific Gravit y
29. The moisture content and specific gravity shall be determined fo r
each specimen as specified in section 42 .
Torsion Pendulum Shear Test for the Determination
of the Modulus of Rigidity in any Plan e
Scope
30. This method of test, though not so accurate as the method of tes t
described in sections 24 to 28, may be used for preliminary evaluations or
where for any reason that method is not feasible . The modulus of rigidity
associated with shear distortion in any specified plane in an anisotropi c
material can be obtained by having the length-width plane of the specime n
under test parallel to the specified plane .
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Z imen shall be at least four times the thickness . The length of the
cimen shall be at least 20 times the width . The other dimensions of the
The test specimen shall be a long rectangular strip . The widt h
ppeeimen shall be such that the period of oscillation of the system (whe n
oscillated as specified in the following section) shall be approximately 2
seconds or more . The width and thickness of the specimen shall be measure d
to the nearest 0 .001 inch, and the clear length between clamps to the neares t
0 .01 inch,
.
Test Equipmen t
32. The specimen shall be suspended vertically and be rigidly clampe d
at the upper end . A bob shall be clamped to the free end perpendicular t o
the wide plane of the specimen with the center of gravity of the bob at th e
centerline of the thickness of the specimen . This bob shall be a round tub e
or cylinder and may be of steel, alloy, or plastic . The bob must be hel d
rigidly in the clamp so that there is no play in the clamp when the specime n
is oscillating . The bob may be from 1 to 3 feet long and from 0 .1 to 3
pounds in weight . The weight of the specimen shall be negligible when compared to the weight of the bob . The weight of the bob shall not exert a
damaging tensile force on the specimen . A suitable test set-up is shown i n
figure 11 .
Test Procedur e
33. When making the test, oscillating of the system is started b y
twisting the specimen with the bob and then relying it so that the bob
rotates about an axis through the center of the specimen . Care shall b e
taken to avoid any kind of vibration other than torsion . The time require d
for 5 or 10 complete oscillations shall be obtained with a stop watch . This
procedure shall be repeated several times, and the results be averaged to
obtain the period of vibration . This shall be repeated several times o n
each of two or more specimens, preferably of different lengths .
Calculations
34. The moduli for the specimens shall be calculated individually ,
and the results be averaged . The following approximate formula shall b e
used to calculate the modulus of rigidity :
G =
2
2 1 Lb' :4 .44 11
5 .331' w d L
.Tr;
gt2 ab 3
_a)
(3
~
_
~
,
where a = width of specimen, in inche s
b = thickness of specimen, in inche s
G = modulus of rigidity in the a-L plane, in pounds per square inc h
w = weight of bob, in pound s
Report No . 1555, revised
-12 -
' 1I
II
d = length of bob, in inche s
11.
length of specimen between clamps, in inches
164( r.,-2* '.1ZEMOR-Ije
acceleration of gravity
38
inches p
.
)
nd2
;-'_1 ;
period of oscillation, in seconds (time from IV en d
swing to the other and back again), and
As
,.1 ,, ,, :. mi,. 3,
_
errs-fig. =
?
4en a/b is greater, han 2 . 5 .
irn }
k
moisture content and specific gravity shall be determined for ,
as sified in section 42 .
.r•
. , r r,.
.011
iiiii .
The
strength obtained in this test
. ure is the s trengt
to the ngth-width plane of the specimen in G test jig and can b e
illa-tiny core material by varying the specimen orieptation . The modulus
qty obtained is that associated with the strains in a plane normal ta p ii!
rtes ~f t
est jig
parallel to the direction o.f the appli forces .
:~`i
--
ecimen shall be 2'inches wile and 12 times the thickess shall be approximately 1/2 inch . The thick e nearest 0 .01 inch, and the length and width t o
test specimen shall be rigidly supported by mean s
to the faces and ends as shown in figure 12 . The
may be varied in accordance with'the strength of th e
dimensions shall be such that the line of action o f
compressive force shall pass through the diagonall y
of the sand 'ch as shown in figure 12 .
the e
the rigid plates i n
1 block or universal join ; I
ss the width of the specimen . The
n of the movable head of th e
of application of 0 .005 inch per inch of lengt h
nute, wptil a permis ble variation of +- 25 percent .
tea_ ,.~ ~.= 1 ~
~' = l
W
r
I%
lo4Gl-de±
atioi cures may be toak n
etermi'r'
,
of
M erap.l
'abet 0 .2 pent offset yield s
nts of
d sh
be tak
in approximately l
adings of load.
gait formation belay : tit
oho
Omit . !-_
ormationsitiaAare,e
r d to
4►
Al* *moot 0 .000
an opts
x sstem, dial gaga.
'® ter s u ata. tatana .
she
up using a died;I ,
s,
:;
oxg a,agg 4miSionso .
Calculation s
40 .
i
t
T1 qiljmiflr
ing forx) . ~.
with the
ds~ be
11 t
.dir. . - i t
Ps __
ps -
y
7i-04,1
. i,:fv-t .Agktmg'
shear std
P
.
&
.
inches,
r:
in inches . ,seL„re
width of
The maximum shear strength
i t
' Q Jai
1
1
y
stowff
.
r :fit
.a
. '.
i
,;' .,- ; t
a .}'i
4-is=1 4c';is'
r-
:f 1
I
r
'+'
is,
-of a aerse, obtained by t. $
*fR~hen P
equals the maximum load . It
ure A -maximum '
Ike ~+ d lla.st if
load is due to a der 'bond be'EEveen _°the ewe- alga few pia!tee, the test shal l
be considered unsatisfactory . However, ecru, Est bed ki.
,
effectiveness of the bona by observing th,cation of th
+ .
.
shear failure in the core occurs- aver a
tively short.
gth of the- nac
specimen and a subsequent failure, ~.
, .nterpretea.`Iftb being in t
bond but really is adjacent to it, ocitodIK )Sbqhtvile remaining length of t h
specimen .
~• 1. :
, -01
,r .
The shear strains shall be cor ed as the angular movement of one
plate of the test jig with respect tc'
other about an axis located on th e
inside face of one plate, perpendicu7
Mlle..-thickness plane and ,
# refore is :
t
*he's
.'r
stx uiin'•aipl*aka_
. . .r ,
,',_
s
. .~ .µ. Gr
. .J
41 '
'_%slurs roa i-mSi me ,q'f one plate wi . respect to 3u [1 4
*
1k - tie, . :.gin _ I l es, -eftdiA; . ..
= thickness of core or distance between plates, in inches .
Report . No . 155, revised
-14 -
r1
- 4-4441401
i
i
S+
The modulus of rigidity shall be obtained by computing the slope o f
the initial straight line portion of the stress-strain curve .
Moisture Content and Specific Gravit y
41. The moisture content and specific gravity shall be determined fo r
each specimen as specified in section 42 .
TheDetermination of Moisture Content
and Specific Gravit y
42. (a) The strength properties of some core materials are dependen t
on moisture content . When this is the case, the moisture content at time o f
test must be determined . In any case, it will be necessary to remove al l
moisture from the coupon before weighing to determine the specific gravity .
Because the volume of the core taterials is usually changed or the specime n
otherwise damaged by test, separate coupons for this determination shall b e
prepared from the same material as is used in preparing the specimen . Thes e
coupons shall be kept with the specimen until time of test . Immediatel y
after test the coupon shall be weighed and measured . The thickness of th e
sample shall be measured to the nearest 0 .001 inch, and the length and widt h
to at least the nearest 0 .01 inch . The sample shall be dried in an oven a t
100° C . until approximately constant weight is attained . After drying, the
sample shall be weighed immediately . The weight of the sample shall be deter mined to an accuracy of not less than 0 .2 percent .
(b) The moisture content 'shall be calculated as follows :
M= W-F x100
F
where M = moisture content, in percen t
W = initial weight, an d
F = final weight, when oven-dr y
(note) :
( ) The apparent specific gravity shall be computed as follow s
Apparent specific gravity = F x 0 .061
L x w x t
where F = final weight, when oven-dry, in grams
L = length of coupon, in inche s
t = thickness of coupon, in inches, an d
w = width of coupon, in inches .
Note : The specific gravity as determined above is based on volume a t
test and weight when oven-dry .
Report No . 1555, revised
-15-
Figure 3 .--Compression test of honeycomb-type sandwich core material showing metho d
of providing additional end support at the bearing surface through the use of a
plaster-of-Paris cast base . A Marten's mirror type of compressometer is attache d
to the specimen for obtaining deformation readings .
z M 7$957 F
Figure 4- .--Test-set-up Yon C pie 3.on 1Latwis e
a contest of core mate ar for sa dw
struction . . emera1 layers of calk serial
are stacked together to miniOize the effects
of end restraint .
Figure 5 .--Test set-up for compression flatwise test of core material showing us e
of Filar microscopes to measure deformations .
Z M 71127 F
Figure 6 .--Lateral-support J4 of a type suitable for use in making,• .
compression-edgewise teats on materials less than 1/2 inch in '
,
thickness .
1
z'X 78958 r
_
•r
I
Figure 8 .--Test set-up for tension f1atw1$e
.test of core material for sandwich=typ e
cons#ructios , showtng specimen a
.fitting
for . eipplyipg+ . load. .
.
PULL APPLIED
AT THIS ENO
ASSEMBLED V/E W
SHOW/NG /DENT/GAG SECTIONS
?El,/Se?
. A/ARWM /94D
2 14 77014 F
SPEC/MEN HOLDER
U.S. DEPARTMENT OF AGR/CULTUR E
FOREST SERVICE
FOREST PRODUCTS LABORATOR Y
MAO/SON., WISCONSIN
SCALE : FULL SIZE
DRN BY : A,E .W.
DATE : AUG
. 1;1945
CHkD BY:
TR 'D BY:
NUMBER
APPD BY:
/,$'HEFTS
T/6
Figure 9 .--Details of construction of the fittings for tension'flatwis e
test of core material for sandwich-type construction .
..
. .
_
n .
_
.1
-,
.
-
-
-figure 11 .--Torsion pendulum test for the determination of th e
' modulus of rigidity for core materials for sandwich construction .
Z M68cflF
Figure 12 . --Shear test for sandwich material .