ASTM D6416/D6416M-16e1
(Test Method)Standard Test Method for Two-Dimensional Flexural Properties of Simply Supported Sandwich Composite Plates Subjected to a Distributed Load
Standard Test Method for Two-Dimensional Flexural Properties of Simply Supported Sandwich Composite Plates Subjected to a Distributed Load
SIGNIFICANCE AND USE
5.1 This test method simulates the hydrostatic loading conditions which are often present in actual sandwich structures, such as marine hulls. This test method can be used to compare the two-dimensional flexural stiffness of a sandwich composite made with different combinations of materials or with different fabrication processes. Since it is based on distributed loading rather than concentrated loading, it may also provide more realistic information on the failure mechanisms of sandwich structures loaded in a similar manner. Test data should be useful for design and engineering, material specification, quality assurance, and process development. In addition, data from this test method would be useful in refining predictive mathematical models or computer code for use as structural design tools. Properties that may be obtained from this test method include:
5.1.1 Panel surface deflection at load,
5.1.2 Panel face-sheet strain at load,
5.1.3 Panel bending stiffness,
5.1.4 Panel shear stiffness,
5.1.5 Panel strength, and
5.1.6 Panel failure modes.
SCOPE
1.1 This test method determines the two-dimensional flexural properties of sandwich composite plates subjected to a distributed load. The test fixture uses a relatively large square panel sample which is simply supported all around and has the distributed load provided by a water-filled bladder. This type of loading differs from the procedure of Test Method C393, where concentrated loads induce one-dimensional, simple bending in beam specimens.
1.2 This test method is applicable to composite structures of the sandwich type which involve a relatively thick layer of core material bonded on both faces with an adhesive to thin-face sheets composed of a denser, higher-modulus material, typically, a polymer matrix reinforced with high-modulus fibers.
1.3 The values stated in either SI units or inch-pound units are to be regarded separately as standard. Within the text the inch-pound units are shown in brackets. The values stated in each system are not exact equivalents; therefore, each system must be used independently of the other. Combining values from the two systems may result in nonconformance with the standard.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
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Buy Standard
Standards Content (Sample)
This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
´1
Designation: D6416/D6416M − 16
Standard Test Method for
Two-Dimensional Flexural Properties of Simply Supported
Sandwich Composite Plates Subjected to a Distributed
Load
This standard is issued under the fixed designation D6416/D6416M; 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.
ε NOTE—Editorial corrections were made to the adjunct information in April 2021.
1. Scope mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
1.1 This test method determines the two-dimensional flex-
ural properties of sandwich composite plates subjected to a
2. Referenced Documents
distributed load. The test fixture uses a relatively large square
panel sample which is simply supported all around and has the 2.1 ASTM Standards:
C365/C365M Test Method for Flatwise Compressive Prop-
distributedloadprovidedbyawater-filledbladder.Thistypeof
erties of Sandwich Cores
loadingdiffersfromtheprocedureofTestMethodC393,where
C393 Test Method for Core Shear Properties of Sandwich
concentrated loads induce one-dimensional, simple bending in
Constructions by Beam Flexure
beam specimens.
D792 Test Methods for Density and Specific Gravity (Rela-
1.2 This test method is applicable to composite structures of
tive Density) of Plastics by Displacement
thesandwichtypewhichinvolvearelativelythicklayerofcore
D2584 Test Method for Ignition Loss of Cured Reinforced
material bonded on both faces with an adhesive to thin-face
Resins
sheets composed of a denser, higher-modulus material,
D2734 TestMethodsforVoidContentofReinforcedPlastics
typically, a polymer matrix reinforced with high-modulus
D3171 Test Methods for Constituent Content of Composite
fibers.
Materials
1.3 The values stated in either SI units or inch-pound units
D3878 Terminology for Composite Materials
are to be regarded separately as standard. Within the text the
E4 Practices for Force Verification of Testing Machines
inch-pound units are shown in brackets. The values stated in
E6 Terminology Relating to Methods of Mechanical Testing
each system are not exact equivalents; therefore, each system
E251 Test Methods for Performance Characteristics of Me-
must be used independently of the other. Combining values
tallic Bonded Resistance Strain Gages
from the two systems may result in nonconformance with the
E1237 Guide for Installing Bonded Resistance Strain Gages
standard.
2.2 ASTM Adjunct:
1.4 This standard does not purport to address all of the
Sandwich Plate Test Fixture and Hydromat Pressure Blad-
safety concerns, if any, associated with its use. It is the
der, ASTM D6416/D6416M
responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter-
3. Terminology
mine the applicability of regulatory limitations prior to use.
3.1 Terminology D3878 defines terms relating to high-
1.5 This international standard was developed in accor-
modulus fibers and their composites, as well as terms relating
dance with internationally recognized principles on standard-
to sandwich constructions. Terminology E6 defines terms
ization established in the Decision on Principles for the
relating to mechanical testing. In the event of a conflict
Development of International Standards, Guides and Recom-
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
This test method is under the jurisdiction of ASTM Committee D30 on contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Composite Materials and is the direct responsibility of Subcommittee D30.09 on Standards volume information, refer to the standard’s Document Summary page on
Sandwich Construction. the ASTM website.
Current edition approved April 1, 2016. Published April 2016. Originally Detailed drawings for the fabrication of the 500–mm test fixture and pressure
approved in 1999. Last previous edition approved in 2012 as D6416/ bladder shown in Fig. 3 and Fig. 4 are available from ASTM Headquarters,
D6416M – 01(2012). DOI: 10.1520/D6416_D6416M-16E01. www.astm.org. Order Adjunct No. ADJD6416-E-PDF.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
´1
D6416/D6416M − 16
between terms, Terminology D3878 shall have precedence 3.3.14 ω = experimentally determined deflection at center
e
over the other terminology standards. of test panel.
3.2 Definitions of Terms Specific to This Standard:
4. Summary of Test Method
3.2.1 bending stiffness, n—the sandwich property which
4.1 Asquaretestpanelissimplysupportedonallfouredges
resists bending deflections.
and uniformly loaded over a portion of its surface by a
3.2.2 core, n—a centrally located layer of a sandwich
water-filled bladder. Pressure on the panel is increased by
construction, usually low density, which separates and stabi-
moving the platens of the test frame. The test measures the
lizes the facings and transmits shear between the facings and
two-dimensional flexural response of a sandwich composite
provides most of the shear rigidity of the construction.
plate in terms of deflections and strains when subjected to a
3.2.3 face sheet, n—the outermost layer or composite com-
well-defined distributed load.
ponent of a sandwich construction, generally thin and of high
4.2 Panel deflection at load is monitored by a centrally
density, which resists most of the edgewise loads and flatwise
positioned LVDT which contacts the tension-side surface.
bending moments: synonymous with face, skin, and facing.
4.3 Load is monitored by both a crosshead-mounted load
3.2.4 footprint, n—the enclosed area of the face sheet
cell, in series with the test fixture, and a pressure transducer in
surface of a sandwich panel in contact with the pressure
the pressure bladder itself. Since the pressure bladder is also at
bladder during loading.
all times in series with the load cell and test fixture, the
3.2.5 hydromat, n—a pressure bladder with a square perim-
effective contact area of the pressure field is continuously
eter fabricated from two square pieces of industrial belting
monitored as the load/pressure quotient.
which are superposed and clamped at the edges with through-
4.4 Strain can be monitored with strategically placed strain
bolted, mild steel bar stock.
gage rosettes bonded to the tension-side face-sheet surface. A
3.2.6 isotropicmaterial,n—amaterialhavingessentiallythe
typical arrangement has four rosettes equally spaced along one
same properties in any direction.
of the axes of symmetry of the plate.
3.2.7 orthotropic material, n—a material in which a prop-
erty of interest, at a given point, possesses three mutually
5. Significance and Use
perpendicular planes of symmetry, which taken together define
5.1 This test method simulates the hydrostatic loading
the principal material coordinate system.
conditions which are often present in actual sandwich
3.2.8 pressure bladder, n—a durable, yet pliable closed
structures, such as marine hulls. This test method can be used
container filled with water, or other incompressible fluid,
to compare the two-dimensional flexural stiffness of a sand-
capable of conforming to the contour of a normally loaded test
wich composite made with different combinations of materials
panel when compressed against its face sheet surface by a test
or with different fabrication processes. Since it is based on
machine.
distributed loading rather than concentrated loading, it may
also provide more realistic information on the failure mecha-
3.2.9 shear stiffness, n—thesandwichpropertywhichresists
nisms of sandwich structures loaded in a similar manner. Test
shear distortions: synonymous with shear rigidity.
data should be useful for design and engineering, material
3.2.10 test panel, n—asquarecouponofsandwichconstruc-
specification, quality assurance, and process development. In
tion fabricated for two-dimensional flexural testing: synony-
addition, data from this test method would be useful in refining
mous with sandwich panel, sandwich composite plate, sand-
predictive mathematical models or computer code for use as
wich composite panel, and panel test specimen.
structural design tools. Properties that may be obtained from
3.3 Symbols:
this test method include:
3.3.1 a = support span of the test fixture or the length and
5.1.1 Panel surface deflection at load,
width of the test panel structure between supports.
5.1.2 Panel face-sheet strain at load,
3.3.2 A = effective contact area of the pressure bladder
5.1.3 Panel bending stiffness,
eff
when compressed against the test panel.
5.1.4 Panel shear stiffness,
3.3.3 B = test panel bending stiffness.
5.1.5 Panel strength, and
3.3.4 c = core thickness.
5.1.6 Panel failure modes.
3.3.5 ε = normal face sheet strain, x component.
x
6. Interferences
3.3.6 ε = normal face sheet strain, y component.
y
3.3.7 f = face sheet thickness.
6.1 Material and Specimen Preparation—Poormaterialfab-
3.3.8 F = total normal force applied to a test panel as
m rication practices, lack of control of fiber alignment, and
measured by the test machine load cell.
damage induced by improper coupon machining are known
3.3.9 h = average overall thickness of the test panel.
causes of high material data scatter in composites in general.
3.3.10 N = the number of included terms of the series.
Specific material factors that affect sandwich composites in-
3.3.11 P = experimentally measured bladder pressure.
clude variability in core density and degree of cure of resin in
m
3.3.12 φ = width of the unloaded border area of a test panel both face sheet matrix material and core bonding adhesive.
betweentheedgesupportsandtheeffectivefootprintboundary.
Important aspects of sandwich panel specimen preparation that
3.3.13 S = test panel shear stiffness. contribute to data scatter are incomplete wetout of face sheet
´1
D6416/D6416M − 16
fabric, incomplete or nonuniform core bonding of face sheets, extent that the edges of the sandwich specimen are compressed
the non-squareness of adjacent panel edges, the misalignment from the reactive line loads generated by the upper and lower
of core and face sheet elements, the existence of joints or other panel support structure. This direct rigid-body addition affects
core and face sheet discontinuities, out-of-plane curvature, and any LVDTpositioned to contact the tension-side panel surface.
surface roughness. To minimize the error, the edges of soft-core panels should be
reinforced in accordance with 8.3.2.
6.2 Test Fixture Characteristics—Configurationofthepanel
edge-constraint structure can have a significant effect on test
7. Apparatus
results. Correct interpretation of test data depends on the
7.1 Procedures A, B, and C—Aschematic diagram illustrat-
fixture supporting the test panel in such a manner that the
ingthekeycomponentsofthetestmethodapparatusappearsin
boundary conditions consistent with simple support can be
Fig. 1.
assumed to apply. Panel edge support journals must be copla-
7.1.1 Testing Machine—The testing machine shall be in
nar and perpendicular to the loading axis. Given the fixture
conformance with Practices E4 and shall satisfy the following
itself has sufficient rigidity, erroneous conclusions about panel
requirements:
strength and stiffness might be drawn if insufficient torque has
7.1.1.1 Testing Machine Heads—The testing machine shall
been applied to the fasteners securing the lower panel edge
have both an essentially stationary head and a movable head.
support frame. In general, panels with more flexural rigidity
7.1.1.2 Drive Mechanism—The testing machine drive
and shear rigidity require more bolt torque to approach simple
mechanism shall be capable of imparting to the movable head
support.
a controlled velocity with respect to the stationary head. The
6.3 Pressure Bladder Characteristics—When a pressure
velocity of the movable head shall be capable of being
bladderisusedtointroducenormalloadtoaplate,theresponse
regulated in accordance with 11.3.
of the plate is dependent on the resulting pressure distribution.
7.1.1.3 Load Indicator—The testing machine load-sensing
The true function of the pressure bladder is to convert the
device shall be capable of indicating the total load being
absolute load applied by the test machine into a pressure field
carried by the test specimen. This device shall be essentially
that can be specified by a relatively simple mathematical
free from inertia-lag at the specified rate of testing and shall
model. With the hydromat-style bladder, two simplifying
indicate the load with an accuracy over the load range(s) of
assumptions are permitted: (1) the shape of the contact area is
interest of within 61 % of the indicated value. The load
a readily definable geometric shape (or combination of shapes)
range(s) of interest may be fairly low for bending and shear
and (2) the pressure is constant within the boundaries of the
modulus evaluation or much higher for strength evaluation, or
contact area. The pressure distribution is then characterized
both, as required.
merely by the magnitude of the pressure and the size of the
footprint. Obviously, the size and shape of the pressure bladder
have a significant effect on test results in terms of the observed
strains and deflections. Some errors in data interpretation are
possible insofar as the actual pressure distribution differs from
the simple mathematical model used in calculations.
NOTE1—Theerrorinthehydromatmodelhasmainlytodowithdetails
of the footprint shape, since the effective contact area can be calculated at
any time by dividing the absolute applied load by the bladder pressure.A
secondary error arises from the non-zero bending stiffness of the fiber-
reinforcedindustrialbeltingfabricthatresultsinanarrowbandofvarying
pressure at the very edge of the footprint. Calibration tests using a steel
plate equipped with strain gages are recommended for each bladder unit
to verify that the errors in the pressure distribution model are negligible
(see Section 9).
6.4 Tolerances—Test panels need to meet the dimensional
and squareness tolerances specified in 8.2 to ensure proper
edge support and constraint.
6.5 SystemAlignment—Errorscanresultifthepanelsupport
structure is not centered with respect to the actuator of the test
machine, or if the plane defined by the panel edge-bearing
surfaces is not perpendicular to the loading axis
...
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
´1
Designation: D6416/D6416M − 16
Standard Test Method for
Two-Dimensional Flexural Properties of Simply Supported
Sandwich Composite Plates Subjected to a Distributed
Load
This standard is issued under the fixed designation D6416/D6416M; 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.
ε NOTE—Editorial corrections were made to the adjunct information in April 2021.
1. Scope mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
1.1 This test method determines the two-dimensional flex-
ural properties of sandwich composite plates subjected to a
2. Referenced Documents
distributed load. The test fixture uses a relatively large square
2.1 ASTM Standards:
panel sample which is simply supported all around and has the
C365/C365M Test Method for Flatwise Compressive Prop-
distributed load provided by a water-filled bladder. This type of
erties of Sandwich Cores
loading differs from the procedure of Test Method C393, where
C393 Test Method for Core Shear Properties of Sandwich
concentrated loads induce one-dimensional, simple bending in
Constructions by Beam Flexure
beam specimens.
D792 Test Methods for Density and Specific Gravity (Rela-
1.2 This test method is applicable to composite structures of
tive Density) of Plastics by Displacement
the sandwich type which involve a relatively thick layer of core
D2584 Test Method for Ignition Loss of Cured Reinforced
material bonded on both faces with an adhesive to thin-face
Resins
sheets composed of a denser, higher-modulus material,
D2734 Test Methods for Void Content of Reinforced Plastics
typically, a polymer matrix reinforced with high-modulus
D3171 Test Methods for Constituent Content of Composite
fibers.
Materials
1.3 The values stated in either SI units or inch-pound units
D3878 Terminology for Composite Materials
are to be regarded separately as standard. Within the text the
E4 Practices for Force Verification of Testing Machines
inch-pound units are shown in brackets. The values stated in
E6 Terminology Relating to Methods of Mechanical Testing
each system are not exact equivalents; therefore, each system
E251 Test Methods for Performance Characteristics of Me-
must be used independently of the other. Combining values
tallic Bonded Resistance Strain Gages
from the two systems may result in nonconformance with the
E1237 Guide for Installing Bonded Resistance Strain Gages
standard.
2.2 ASTM Adjunct:
1.4 This standard does not purport to address all of the
Sandwich Plate Test Fixture and Hydromat Pressure Blad-
safety concerns, if any, associated with its use. It is the
der, ASTM D6416/D6416M
responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter-
3. Terminology
mine the applicability of regulatory limitations prior to use.
3.1 Terminology D3878 defines terms relating to high-
1.5 This international standard was developed in accor-
modulus fibers and their composites, as well as terms relating
dance with internationally recognized principles on standard-
to sandwich constructions. Terminology E6 defines terms
ization established in the Decision on Principles for the
relating to mechanical testing. In the event of a conflict
Development of International Standards, Guides and Recom-
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
This test method is under the jurisdiction of ASTM Committee D30 on contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Composite Materials and is the direct responsibility of Subcommittee D30.09 on Standards volume information, refer to the standard’s Document Summary page on
Sandwich Construction. the ASTM website.
Current edition approved April 1, 2016. Published April 2016. Originally Detailed drawings for the fabrication of the 500–mm test fixture and pressure
approved in 1999. Last previous edition approved in 2012 as D6416/ bladder shown in Fig. 3 and Fig. 4 are available from ASTM Headquarters,
D6416M – 01(2012). DOI: 10.1520/D6416_D6416M-16E01. www.astm.org. Order Adjunct No. ADJD6416-E-PDF.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
´1
D6416/D6416M − 16
between terms, Terminology D3878 shall have precedence 3.3.14 ω = experimentally determined deflection at center
e
over the other terminology standards. of test panel.
3.2 Definitions of Terms Specific to This Standard:
4. Summary of Test Method
3.2.1 bending stiffness, n—the sandwich property which
4.1 A square test panel is simply supported on all four edges
resists bending deflections.
and uniformly loaded over a portion of its surface by a
3.2.2 core, n—a centrally located layer of a sandwich
water-filled bladder. Pressure on the panel is increased by
construction, usually low density, which separates and stabi-
moving the platens of the test frame. The test measures the
lizes the facings and transmits shear between the facings and
two-dimensional flexural response of a sandwich composite
provides most of the shear rigidity of the construction.
plate in terms of deflections and strains when subjected to a
3.2.3 face sheet, n—the outermost layer or composite com-
well-defined distributed load.
ponent of a sandwich construction, generally thin and of high
4.2 Panel deflection at load is monitored by a centrally
density, which resists most of the edgewise loads and flatwise
positioned LVDT which contacts the tension-side surface.
bending moments: synonymous with face, skin, and facing.
4.3 Load is monitored by both a crosshead-mounted load
3.2.4 footprint, n—the enclosed area of the face sheet
cell, in series with the test fixture, and a pressure transducer in
surface of a sandwich panel in contact with the pressure
the pressure bladder itself. Since the pressure bladder is also at
bladder during loading.
all times in series with the load cell and test fixture, the
3.2.5 hydromat, n—a pressure bladder with a square perim-
effective contact area of the pressure field is continuously
eter fabricated from two square pieces of industrial belting
monitored as the load/pressure quotient.
which are superposed and clamped at the edges with through-
4.4 Strain can be monitored with strategically placed strain
bolted, mild steel bar stock.
gage rosettes bonded to the tension-side face-sheet surface. A
3.2.6 isotropic material, n—a material having essentially the
typical arrangement has four rosettes equally spaced along one
same properties in any direction.
of the axes of symmetry of the plate.
3.2.7 orthotropic material, n—a material in which a prop-
erty of interest, at a given point, possesses three mutually
5. Significance and Use
perpendicular planes of symmetry, which taken together define
5.1 This test method simulates the hydrostatic loading
the principal material coordinate system.
conditions which are often present in actual sandwich
3.2.8 pressure bladder, n—a durable, yet pliable closed
structures, such as marine hulls. This test method can be used
container filled with water, or other incompressible fluid,
to compare the two-dimensional flexural stiffness of a sand-
capable of conforming to the contour of a normally loaded test
wich composite made with different combinations of materials
panel when compressed against its face sheet surface by a test
or with different fabrication processes. Since it is based on
machine.
distributed loading rather than concentrated loading, it may
also provide more realistic information on the failure mecha-
3.2.9 shear stiffness, n—the sandwich property which resists
nisms of sandwich structures loaded in a similar manner. Test
shear distortions: synonymous with shear rigidity.
data should be useful for design and engineering, material
3.2.10 test panel, n—a square coupon of sandwich construc-
specification, quality assurance, and process development. In
tion fabricated for two-dimensional flexural testing: synony-
addition, data from this test method would be useful in refining
mous with sandwich panel, sandwich composite plate, sand-
predictive mathematical models or computer code for use as
wich composite panel, and panel test specimen.
structural design tools. Properties that may be obtained from
3.3 Symbols:
this test method include:
3.3.1 a = support span of the test fixture or the length and
5.1.1 Panel surface deflection at load,
width of the test panel structure between supports.
5.1.2 Panel face-sheet strain at load,
3.3.2 A = effective contact area of the pressure bladder
5.1.3 Panel bending stiffness,
eff
when compressed against the test panel.
5.1.4 Panel shear stiffness,
3.3.3 B = test panel bending stiffness.
5.1.5 Panel strength, and
3.3.4 c = core thickness. 5.1.6 Panel failure modes.
3.3.5 ε = normal face sheet strain, x component.
x
6. Interferences
3.3.6 ε = normal face sheet strain, y component.
y
3.3.7 f = face sheet thickness.
6.1 Material and Specimen Preparation—Poor material fab-
3.3.8 F = total normal force applied to a test panel as
m rication practices, lack of control of fiber alignment, and
measured by the test machine load cell.
damage induced by improper coupon machining are known
3.3.9 h = average overall thickness of the test panel.
causes of high material data scatter in composites in general.
3.3.10 N = the number of included terms of the series.
Specific material factors that affect sandwich composites in-
3.3.11 P = experimentally measured bladder pressure.
clude variability in core density and degree of cure of resin in
m
3.3.12 φ = width of the unloaded border area of a test panel
both face sheet matrix material and core bonding adhesive.
between the edge supports and the effective footprint boundary. Important aspects of sandwich panel specimen preparation that
3.3.13 S = test panel shear stiffness. contribute to data scatter are incomplete wetout of face sheet
´1
D6416/D6416M − 16
fabric, incomplete or nonuniform core bonding of face sheets, extent that the edges of the sandwich specimen are compressed
the non-squareness of adjacent panel edges, the misalignment from the reactive line loads generated by the upper and lower
of core and face sheet elements, the existence of joints or other panel support structure. This direct rigid-body addition affects
core and face sheet discontinuities, out-of-plane curvature, and any LVDT positioned to contact the tension-side panel surface.
surface roughness. To minimize the error, the edges of soft-core panels should be
reinforced in accordance with 8.3.2.
6.2 Test Fixture Characteristics—Configuration of the panel
edge-constraint structure can have a significant effect on test
7. Apparatus
results. Correct interpretation of test data depends on the
7.1 Procedures A, B, and C—A schematic diagram illustrat-
fixture supporting the test panel in such a manner that the
ing the key components of the test method apparatus appears in
boundary conditions consistent with simple support can be
Fig. 1.
assumed to apply. Panel edge support journals must be copla-
7.1.1 Testing Machine—The testing machine shall be in
nar and perpendicular to the loading axis. Given the fixture
conformance with Practices E4 and shall satisfy the following
itself has sufficient rigidity, erroneous conclusions about panel
requirements:
strength and stiffness might be drawn if insufficient torque has
7.1.1.1 Testing Machine Heads—The testing machine shall
been applied to the fasteners securing the lower panel edge
have both an essentially stationary head and a movable head.
support frame. In general, panels with more flexural rigidity
7.1.1.2 Drive Mechanism—The testing machine drive
and shear rigidity require more bolt torque to approach simple
mechanism shall be capable of imparting to the movable head
support.
a controlled velocity with respect to the stationary head. The
6.3 Pressure Bladder Characteristics—When a pressure
velocity of the movable head shall be capable of being
bladder is used to introduce normal load to a plate, the response
regulated in accordance with 11.3.
of the plate is dependent on the resulting pressure distribution.
7.1.1.3 Load Indicator—The testing machine load-sensing
The true function of the pressure bladder is to convert the
device shall be capable of indicating the total load being
absolute load applied by the test machine into a pressure field
carried by the test specimen. This device shall be essentially
that can be specified by a relatively simple mathematical
free from inertia-lag at the specified rate of testing and shall
model. With the hydromat-style bladder, two simplifying
indicate the load with an accuracy over the load range(s) of
assumptions are permitted: (1) the shape of the contact area is
interest of within 61 % of the indicated value. The load
a readily definable geometric shape (or combination of shapes)
range(s) of interest may be fairly low for bending and shear
and (2) the pressure is constant within the boundaries of the
modulus evaluation or much higher for strength evaluation, or
contact area. The pressure distribution is then characterized
both, as required.
merely by the magnitude of the pressure and the size of the
footprint. Obviously, the size and shape of the pressure bladder
have a significant effect on test results in terms of the observed
strains and deflections. Some errors in data interpretation are
possible insofar as the actual pressure distribution differs from
the simple mathematical model used in calculations.
NOTE 1—The error in the hydromat model has mainly to do with details
of the footprint shape, since the effective contact area can be calculated at
any time by dividing the absolute applied load by the bladder pressure. A
secondary error arises from the non-zero bending stiffness of the fiber-
reinforced industrial belting fabric that results in a narrow band of varying
pressure at the very edge of the footprint. Calibration tests using a steel
plate equipped with strain gages are recommended for each bladder unit
to verify that the errors in the pressure distribution model are negligible
(see Section 9).
6.4 Tolerances—Test panels need to meet the dimensional
and squareness tolerances specified in 8.2 to ensure proper
edge support and constraint.
6.5 System Alignment—Errors can result if the panel support
structure is not centered with respect to the actuator of the test
machine, or if the plane defined by the panel edge-bearing
surfaces is not perpendicu
...
This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
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Designation: D6416/D6416M − 16 D6416/D6416M − 16
Standard Test Method for
Two-Dimensional Flexural Properties of Simply Supported
Sandwich Composite Plates Subjected to a Distributed
Load
This standard is issued under the fixed designation D6416/D6416M; 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.
ε NOTE—Editorial corrections were made to the adjunct information in April 2021.
1. Scope
1.1 This test method determines the two-dimensional flexural properties of sandwich composite plates subjected to a distributed
load. The test fixture uses a relatively large square panel sample which is simply supported all around and has the distributed load
provided by a water-filled bladder. This type of loading differs from the procedure of Test Method C393, where concentrated loads
induce one-dimensional, simple bending in beam specimens.
1.2 This test method is applicable to composite structures of the sandwich type which involve a relatively thick layer of core
material bonded on both faces with an adhesive to thin-face sheets composed of a denser, higher-modulus material, typically, a
polymer matrix reinforced with high-modulus fibers.
1.3 The values stated in either SI units or inch-pound units are to be regarded separately as standard. Within the text the
inch-pound units are shown in brackets. The values stated in each system are not exact equivalents; therefore, each system must
be used independently of the other. Combining values from the two systems may result in nonconformance with the standard.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.5 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
C365/C365M Test Method for Flatwise Compressive Properties of Sandwich Cores
C393 Test Method for Core Shear Properties of Sandwich Constructions by Beam Flexure
D792 Test Methods for Density and Specific Gravity (Relative Density) of Plastics by Displacement
D2584 Test Method for Ignition Loss of Cured Reinforced Resins
This test method is under the jurisdiction of ASTM Committee D30 on Composite Materials and is the direct responsibility of Subcommittee D30.09 on Sandwich
Construction.
Current edition approved April 1, 2016. Published April 2016. Originally approved in 1999. Last previous edition approved in 2012 as D6416D6416/D6416M – 01/
D6416M – 01 (2012).(2012). DOI: 10.1520/D6416_D6416M-16.10.1520/D6416_D6416M-16E01.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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D6416/D6416M − 16
D2734 Test Methods for Void Content of Reinforced Plastics
D3171 Test Methods for Constituent Content of Composite Materials
D3878 Terminology for Composite Materials
E4 Practices for Force Verification of Testing Machines
E6 Terminology Relating to Methods of Mechanical Testing
E251 Test Methods for Performance Characteristics of Metallic Bonded Resistance Strain Gages
E1237 Guide for Installing Bonded Resistance Strain Gages
2.2 ASTM Adjunct:
Sandwich Plate Test Fixture and Hydromat Pressure Bladder, ASTM D6416/D6416M
3. Terminology
3.1 Terminology D3878 defines terms relating to high-modulus fibers and their composites, as well as terms relating to sandwich
constructions. Terminology E6 defines terms relating to mechanical testing. In the event of a conflict between terms, Terminology
D3878 shall have precedence over the other terminology standards.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 bending stiffness, n—the sandwich property which resists bending deflections.
3.2.2 core, n—a centrally located layer of a sandwich construction, usually low density, which separates and stabilizes the facings
and transmits shear between the facings and provides most of the shear rigidity of the construction.
3.2.3 face sheet, n—the outermost layer or composite component of a sandwich construction, generally thin and of high density,
which resists most of the edgewise loads and flatwise bending moments: synonymous with face, skin, and facing.
3.2.4 footprint, n—the enclosed area of the face sheet surface of a sandwich panel in contact with the pressure bladder during
loading.
3.2.5 hydromat, n—a pressure bladder with a square perimeter fabricated from two square pieces of industrial belting which are
superposed and clamped at the edges with through-bolted, mild steel bar stock.
3.2.6 isotropic material, n—a material having essentially the same properties in any direction.
3.2.7 orthotropic material, n—a material in which a property of interest, at a given point, possesses three mutually perpendicular
planes of symmetry, which taken together define the principal material coordinate system.
3.2.8 pressure bladder, n—a durable, yet pliable closed container filled with water, or other incompressible fluid, capable of
conforming to the contour of a normally loaded test panel when compressed against its face sheet surface by a test machine.
3.2.9 shear stiffness, n—the sandwich property which resists shear distortions: synonymous with shear rigidity.
3.2.10 test panel, n—a square coupon of sandwich construction fabricated for two-dimensional flexural testing: synonymous with
sandwich panel, sandwich composite plate, sandwich composite panel, and panel test specimen.
3.3 Symbols:
3.3.1 a = support span of the test fixture or the length and width of the test panel structure between supports.
3.3.2 A = effective contact area of the pressure bladder when compressed against the test panel.
eff
3.3.3 B = test panel bending stiffness.
3.3.4 c = core thickness.
Detailed drawings for the fabrication of the 500–mm test fixture and pressure bladder shown in Fig. 3 and Fig. 4 are available from ASTM Headquarters. Headquarters,
www.astm.org. Order Adjunct No. ADJD6416ADJD6416-E-PDF.
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D6416/D6416M − 16
3.3.5 ε = normal face sheet strain, x component.
x
3.3.6 ε = normal face sheet strain, y component.
y
3.3.7 f = face sheet thickness.
3.3.8 F = total normal force applied to a test panel as measured by the test machine load cell.
m
3.3.9 h = average overall thickness of the test panel.
3.3.10 N = the number of included terms of the series.
3.3.11 P = experimentally measured bladder pressure.
m
3.3.12 φ = width of the unloaded border area of a test panel between the edge supports and the effective footprint boundary.
3.3.13 S = test panel shear stiffness.
3.3.14 ω = experimentally determined deflection at center of test panel.
e
4. Summary of Test Method
4.1 A square test panel is simply supported on all four edges and uniformly loaded over a portion of its surface by a water-filled
bladder. Pressure on the panel is increased by moving the platens of the test frame. The test measures the two-dimensional flexural
response of a sandwich composite plate in terms of deflections and strains when subjected to a well-defined distributed load.
4.2 Panel deflection at load is monitored by a centrally positioned LVDT which contacts the tension-side surface.
4.3 Load is monitored by both a crosshead-mounted load cell, in series with the test fixture, and a pressure transducer in the
pressure bladder itself. Since the pressure bladder is also at all times in series with the load cell and test fixture, the effective contact
area of the pressure field is continuously monitored as the load/pressure quotient.
4.4 Strain can be monitored with strategically placed strain gage rosettes bonded to the tension-side face-sheet surface. A typical
arrangement has four rosettes equally spaced along one of the axes of symmetry of the plate.
5. Significance and Use
5.1 This test method simulates the hydrostatic loading conditions which are often present in actual sandwich structures, such as
marine hulls. This test method can be used to compare the two-dimensional flexural stiffness of a sandwich composite made with
different combinations of materials or with different fabrication processes. Since it is based on distributed loading rather than
concentrated loading, it may also provide more realistic information on the failure mechanisms of sandwich structures loaded in
a similar manner. Test data should be useful for design and engineering, material specification, quality assurance, and process
development. In addition, data from this test method would be useful in refining predictive mathematical models or computer code
for use as structural design tools. Properties that may be obtained from this test method include:
5.1.1 Panel surface deflection at load,
5.1.2 Panel face-sheet strain at load,
5.1.3 Panel bending stiffness,
5.1.4 Panel shear stiffness,
5.1.5 Panel strength, and
5.1.6 Panel failure modes.
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D6416/D6416M − 16
6. Interferences
6.1 Material and Specimen Preparation—Poor material fabrication practices, lack of control of fiber alignment, and damage
induced by improper coupon machining are known causes of high material data scatter in composites in general. Specific material
factors that affect sandwich composites include variability in core density and degree of cure of resin in both face sheet matrix
material and core bonding adhesive. Important aspects of sandwich panel specimen preparation that contribute to data scatter are
incomplete wetout of face sheet fabric, incomplete or nonuniform core bonding of face sheets, the non-squareness of adjacent panel
edges, the misalignment of core and face sheet elements, the existence of joints or other core and face sheet discontinuities,
out-of-plane curvature, and surface roughness.
6.2 Test Fixture Characteristics—Configuration of the panel edge-constraint structure can have a significant effect on test results.
Correct interpretation of test data depends on the fixture supporting the test panel in such a manner that the boundary conditions
consistent with simple support can be assumed to apply. Panel edge support journals must be coplanar and perpendicular to the
loading axis. Given the fixture itself has sufficient rigidity, erroneous conclusions about panel strength and stiffness might be drawn
if insufficient torque has been applied to the fasteners securing the lower panel edge support frame. In general, panels with more
flexural rigidity and shear rigidity require more bolt torque to approach simple support.
6.3 Pressure Bladder Characteristics—When a pressure bladder is used to introduce normal load to a plate, the response of the
plate is dependent on the resulting pressure distribution. The true function of the pressure bladder is to convert the absolute load
applied by the test machine into a pressure field that can be specified by a relatively simple mathematical model. With the
hydromat-style bladder, two simplifying assumptions are permitted: (1) the shape of the contact area is a readily definable
geometric shape (or combination of shapes) and (2) the pressure is constant within the boundaries of the contact area. The pressure
distribution is then characterized merely by the magnitude of the pressure and the size of the footprint. Obviously, the size and
shape of the pressure bladder have a significant effect on test results in terms of the observed strains and deflections. Some errors
in data interpretation are possible insofar as the actual pressure distribution differs from the simple mathematical model used in
calculations.
NOTE 1—The error in the hydromat model has mainly to do with details of the footprint shape, since the effective contact area can be calculated at any
time by dividing the absolute applied load by the bladder pressure. A secondary error arises from the non-zero bending stiffness of the fiber-reinforced
industrial belting fabric that results in a narrow band of varying pressure at the very edge of the footprint. Calibration tests using a steel plate equipped
with strain gages are recommended for each bladder unit to verify that the errors in the pressure distribution model are negligible (see Section 9).
6.4 Tolerances—Test panels need to meet the dimensional and squareness tolerances specified in 8.2 to ensure proper edge support
and constraint.
6.5 System Alignment—Errors can result if the panel support structure is not centered with respect to the actuator of the test
machine, or if the plane defined by the panel edge-bearing surfaces is not perpendicular to the loading axis of the test machine.
Errors can also result if the pressure bladder is not centered properly with respect to fixture and actuator or if the edges of the
bladder clamping bars are not parallel to the panel edge-support journals.
6.6 Other System Characteristics—When attempting to measure panel surface deflection, an error results which is an artifact of
the test. It arises as normal load is applied, to the extent that the edges of the sandwich specimen are compressed from the reactive
line loads generated by the upper and lower panel support structure. This direct rigid-body addition affects any LVDT positioned
to contact the tension-side panel surface. To minimize the error, the edges of soft-core panels should be reinforced in accordance
with 8.3.2.
7. Apparatus
7.1 Procedures A, B, and C—A schematic diagram illustrating the key components of the test method apparatus appears in Fig.
1.
7.1.1 Testing Machine—The testing machine shall be in conformance with Practices E4 and shall satisfy the following
requirements:
7.1.1.1 Testing Machine Heads—The testing machine shall have both an essentially stationary
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