ASTM C480/C480M-08(2015)

Standard Test Method for Flexure Creep of Sandwich Constructions

SIGNIFICANCE AND USE
5.1 The determination of the creep rate provides information on the behavior of sandwich constructions under constant applied force. Creep is defined as deflection under constant force over a period of time beyond the initial deformation as a result of the application of the force. Deflection data obtained from this test method can be plotted against time, and a creep rate determined. By using standard specimen constructions and constant loading, the test method may also be used to evaluate creep behavior of sandwich panel core-to-facing adhesives.  
5.2 This test method provides a standard method of obtaining flexure creep of sandwich constructions for quality control, acceptance specification testing, and research and development.  
5.3 Factors that influence the sandwich construction creep response and shall therefore be reported include the following: facing material, core material, adhesive material, methods of material fabrication, facing stacking sequence and overall thickness, core geometry (cell size), core density, core thickness, adhesive thickness, specimen geometry, specimen preparation, specimen conditioning, environment of testing, specimen alignment, loading procedure, speed of testing, facing void content, adhesive void content, and facing volume percent reinforcement. Further, facing and core-to-facing strength and creep response may be different between precured/bonded and co-cured facesheets of the same material.
SCOPE
1.1 This test method covers the determination of the creep characteristics and creep rate of flat sandwich constructions loaded in flexure, at any desired temperature. 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 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 either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, 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 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 and health practices and determine the applicability of regulatory limitations prior to use.

General Information

• Status: Historical
• Publication Date: 30-Jun-2015
• ICS: 83.120 - Reinforced plastics
• Technical Committee: D30 - Composite Materials
• Drafting Committee: D30.09 - Sandwich Construction

Relations

• Replaces: ASTM C480/C480M-08 - Standard Test Method for Flexure Creep of Sandwich Constructions
• Effective Date: 01-Jul-2015
• Replaced By: ASTM C480/C480M-16 - Standard Test Method for Flexure Creep of Sandwich Constructions
• Effective Date: 01-Apr-2016
• Referred By: ASTM D4762-18 - Standard Guide for Testing Polymer Matrix Composite Materials
• Effective Date: 01-Jul-2015

Standards Content (Sample)

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
Designation: C480/C480M − 08(Reapproved 2015)
Standard Test Method for
Flexure Creep of Sandwich Constructions
This standard is issued under the fixed designation C480/C480M; the number immediately following the designation indicates the year
of original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.
A superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope E6Terminology Relating to Methods of MechanicalTesting
E122PracticeforCalculatingSampleSizetoEstimate,With
1.1 This test method covers the determination of the creep
Specified Precision, the Average for a Characteristic of a
characteristics and creep rate of flat sandwich constructions
Lot or Process
loaded in flexure, at any desired temperature. Permissible core
E177Practice for Use of the Terms Precision and Bias in
material forms include those with continuous bonding surfaces
ASTM Test Methods
(such as balsa wood and foams) as well as those with
E456Terminology Relating to Quality and Statistics
discontinuous bonding surfaces (such as honeycomb).
E1309 Guide for Identification of Fiber-Reinforced
1.2 The values stated in either SI units or inch-pound units
Polymer-Matrix Composite Materials in Databases
are to be regarded separately as standard. Within the text the
E1434Guide for Recording Mechanical Test Data of Fiber-
inch-pound units are shown in brackets. The values stated in
Reinforced Composite Materials in Databases
eitherSIunitsorinch-poundunitsaretoberegardedseparately
as standard.The values stated in each system may not be exact
3. Terminology
equivalents;therefore,eachsystemshallbeusedindependently
3.1 Definitions—Terminology D3878 defines terms relating
of the other. Combining values from the two systems may
to high-modulus fibers and their composites. Terminology
result in non-conformance with the standard.
C274 defines terms relating to structural sandwich construc-
1.3 This standard does not purport to address all of the
tions. Terminology D883 defines terms relating to plastics.
safety concerns, if any, associated with its use. It is the
Terminology E6 defines terms relating to mechanical testing.
responsibility of the user of this standard to establish appro-
Terminology E456 and Practice E177 define terms relating to
priate safety and health practices and determine the applica-
statistics.Intheeventofaconflictbetweenterms,Terminology
bility of regulatory limitations prior to use.
D3878 shall have precedence over the other terminology
documents.
2. Referenced Documents
3.2 Symbols:
2.1 ASTM Standards:
3.2.1 A—distance between pivot point and point of applied
C274Terminology of Structural Sandwich Constructions
force on the specimen
C393/C393MTest Method for Core Shear Properties of
3.2.2 b—specimen width
Sandwich Constructions by Beam Flexure
D883Terminology Relating to Plastics 3.2.3 B—distancefrompivotpointtocenterofgravityofthe
D3878Terminology for Composite Materials
loading arm
D5229/D5229MTestMethodforMoistureAbsorptionProp-
3.2.4 c—core thickness
erties and Equilibrium Conditioning of Polymer Matrix
3.2.5 CR —creep rate at time, i
I i
Composite Materials
3.2.6 d—sandwich total thickness
D7249/D7249MTestMethodforFacingPropertiesofSand-
wich Constructions by Long Beam Flexure
3.2.7 d—initial static deflection under the same load and at
the same temperature
3.2.8 D—total deflection at time, t
This specification is under the jurisdiction of ASTM Committee D30 on
3.2.9 F—applied facing stress
Composite Materials and is the direct responsibility of Subcommittee D30.09 on
f
Sandwich Construction.
3.2.10 F —applied core shear stress
s
Current edition approved July 1, 2015. Published August 2015. Originally
approved in 1961. Last previous edition approved in 2008 as C480/C480M–08.
3.2.11 M—distance between point and weight point
DOI: 10.1520/C0480_C0480M-08R15.
2 3.2.12 n—number of specimens
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
3.2.13 p—mass of loading plate and rod
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. 3.2.14 P—applied force
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C480/C480M − 08 (2015)
3.2.15 S—length of support span 7. Apparatus
3.2.16 w—mass of lever arm
7.1 Micrometers and Calipers—Amicrometer having a flat
anvil interface, or a caliper of suitable size, shall be used. The
3.2.17 W—mass of weight (including tray mass)
instruments(s) shall have an accuracy of 625 µm [60.001 in.]
for thickness measurement, and an accuracy of 6250 µm
4. Summary of Test Method
[60.010 in.] for length and width measurements.
4.1 This test method consists of subjecting a beam of
NOTE 1—The accuracies given above are based on achieving measure-
sandwich construction to a sustained force normal to the plane
ments that are within1%ofthe sample length, width and thickness.
of the sandwich, using either a 3-point or a 4-point loading
7.2 Loading Fixtures—The fixture for loading the specimen
fixture. Deflection versus time measurements are recorded.
shall be a 3-point loading configuration that conforms to either
Test Method D7249/D7249M (for a long beam test) or to Test
4.2 For long beam specimens conforming to Test Method
D7249/D7249M, the only acceptable failure modes for sand- Method C393/C393M (for a short beam test) except that a
constantforceshallbeappliedbymeansofweightsandalever
wich facesheet strength are those which are internal to one of
the facesheets. Failure of the sandwich core or the core-to- system.Fig.1showsaleverandweight-loadingapparatusthat
has been found satisfactory.
facesheetbondprecedingfailureofoneofthefacesheetsisnot
an acceptable failure mode for this specimen configuration.
7.3 Deflectometer (LVDT)—The deflection of the specimen
shall be measured in the center of the support span by a
4.3 For short-beam specimens conforming to Test Method
properly calibrated device having an accuracy of 60.025 mm
C393/C393M,theonlyacceptablefailuremodesarecoreshear
[60.001 in.] or better.
or core-to-facing bond. Failure of the sandwich facing preced-
ing failure of the core or core-to-facing bond is not an
7.4 Conditioning Chamber—When conditioning materials
acceptable failure mode for this specimen configuration.
at non-laboratory environments, a temperature/vapor-level
controlledenvironmentalconditioningchamberisrequiredthat
4.4 Careful post-test inspection of the specimen is required
shall be capable of maintaining the required temperature to
as facing failure occurring in proximity to the loading points
within 63°C [65°F] and the required relative humidity level
canbecausedbylocalthrough-thicknesscompressionorshear
to within 63 %. Chamber conditions shall be monitored either
failure of the core that precedes failure of the facing.
on an automated continuous basis or on a manual basis at
regular intervals (a minimum of once daily checks are recom-
5. Significance and Use
mended).
5.1 The determination of the creep rate provides informa-
7.5 Environmental Test Chamber—An environmental test
tion on the behavior of sandwich constructions under constant
chamber is required for test environments other than ambient
applied force. Creep is defined as deflection under constant
testing laboratory conditions.This chamber shall be capable of
force over a period of time beyond the initial deformation as a
maintaining the gage section of the test specimen at the
result of the application of the force. Deflection data obtained
required test environment during the mechanical test.
from this test method can be plotted against time, and a creep
ratedetermined.Byusingstandardspecimenconstructionsand
8. Sampling and Test Specimens
constant loading, the test method may also be used to evaluate
creep behavior of sandwich panel core-to-facing adhesives.
8.1 Sampling—Test at least five specimens per test condi-
tionunlessvalidresultscanbegainedthroughtheuseoffewer
5.2 This test method provides a standard method of obtain-
specimens, as in the case of a designed experiment. For
ingflexurecreepofsandwichconstructionsforqualitycontrol,
statistically significant data, consult the procedures outlined in
acceptance specification testing, and research and develop-
Practice E122. Report the method of sampling.
ment.
8.2 Geometry, Facing, Core:
5.3 Factors that influence the sandwich construction creep
response and shall therefore be reported include the following:
facing material, core material, adhesive material, methods of
material fabrication, facing stacking sequence and overall
thickness, core geometry (cell size), core density, core
thickness, adhesive thickness, specimen geometry, specimen
preparation, specimen conditioning, environment of testing,
specimen alignment, loading procedure, speed of testing,
facing void content, adhesive void content, and facing volume
percent reinforcement. Further, facing and core-to-facing
strength and creep response may be different between
precured/bondedandco-curedfacesheetsofthesamematerial.
6. Interferences
6.1 The interferences listed in Test Methods C393/C393M
and D7249/D7249M are also applicable to this test method. FIG. 1 Creep Test Apparatus and Loading System
C480/C480M − 08 (2015)
includes not only the vapor of a liquid and its condensate, but the liquid
8.2.1 Core or Core-to-Facing Failure Mode Desired—The
itself in large quantities, as for immersion.
testspecimenconfigurationshallbeasandwichconstructionof
a size and proportions conforming to the flexure test specimen 10.3 If no explicit conditioning process is performed, the
described in Test Method C393/C393M. The standard speci- specimen conditioning process shall be reported as “uncondi-
men configuration should be used whenever the specimen tioned” and the moisture content as “unknown”.
designequationsinSection8.2.3ofC393/C393Mindicatethat
11. Procedure
acoreofcore-to-facingbondfailuremodeisexpected.Incases
where the standard C393/C393M specimen configuration will
11.1 Parameters to Be Specified Before Test:
notproduceadesiredfailure,anon-standardspecimenshallbe
11.1.1 The specimen sampling method, specimen geometry,
designed to produce a core or bond failure mode.
and conditioning travelers (if required).
8.2.2 Facesheet Failure Mode Desired—The test specimen
11.1.2 Theloadingfixturesupportspan(andloadingspanif
configuration shall be a sandwich construction of a size and
a 4-point loading configuration is used).
proportions conforming to the flexure test specimen described
11.1.3 The force, P, to be applied to the specimen and the
in Test Method D7249/D7249M.Anon-standard 3-point load-
maximum time for the test.
ing specimen configuration shall be designed per Section 8.2.3
11.1.4 The properties and data reporting format desired.
of D7249/D7249M to achieve a facing failure mode. The
11.1.5 The environmental conditioning test parameters.
standard 4-point loading D7249/D7249M specimen configura-
11.1.6 The nominal thicknesses of the facing materials.
tion may be used if a suitable creep loading apparatus is used.
NOTE 3—Determine specific material property, accuracy, and data
8.3 Compression Side Facing—Unless otherwise specified
reportingrequirementspriortotestforproperselectionofinstrumentation
and data recording equipment. Estimate the maximum specimen deflec-
by the test requestor, the bag-side facing of a co-cured
tion to aid in transducer selection, calibration of equipment, and determi-
composite sandwich panel shall be placed as the upper,
nation of equipment settings.
compression-loaded facing during test, as facing compression
11.2 General Instructions:
strength is more sensitive to imperfections typical of bag-side
11.2.1 Reportanydeviationsfromthistestmethod,whether
surfaces (for example, intra-cell dimpling) than is facing
intentional or inadvertent.
tensionstrength.Creepresponseisexpectedtofollowthesame
11.2.2 Conditionthespecimensasrequired.Storethespeci-
trends as static strength.
mens in the conditioned environment until test time, if the test
8.4 Specimen Preparation and Machining—Specimen
environment is different than the conditioning environment.
preparation is extremely important for this test method. Take
11.2.3 Before testing, measure and record the specimen
precautionswhencuttingspecimensfromlargepanelstoavoid
length, width and thickness at three places in the test section.
notches,undercuts,roughorunevensurfaces,ordelaminations
Measure the specimen length and width with an accuracy of
due to inappropriate machining methods. Obtain final dimen-
6250 µm [60.010 in.]. Measure the specimen thickness with
sions by water-lubricated precision sawing, milling, or grind-
anaccuracyof 625µm[60.001in.].Recordthedimensionsto
ing. The use of diamond coated machining tools has been
three significant figures in units of millimeters [inches].
found to be extremely effective for many material systems.
11.3 Measure and record the length of the support and
Edges should be flat and parallel within the specified toler-
loading spans.
ances. Record and report the specimen cutting preparation
method.
11.4 The weight required to apply the specified force to the
specimen by the 3-point loading lever system shown in Fig. 1
8.5 Labeling—Label the test specimens so that they will be
may be calculated as follows:
distinct from each other and traceable back to the panel of
origin, and will neither influence the test nor be affected by it.
~P 2 p! A 2 wB
W 5 (1)
M
9. Calibration
where:
9.1 The accuracy of all measuring equipment shall have
W = mass of weight (including tray mass), N [lb],
certified calibrations that are current at the time of use of the
P = force applied to specimen, N [lb],
equipment
p = mass of loading plate and rod, N [lb],
w = mass of lever arm, N [lb],
10. Conditioning
A = distance between pivot point and point of applied force
10.1 The recommended pre-test specimen condition is ef- on the specimen, mm [in.].
fective moisture equilibrium at a specific relative humidity per B = distance from pivot point to center of gravity of the
loading arm, mm [in.], and
D5229/D5229M; however, if the test requestor does not
M = distance between pivot point and weight point, mm,
explicitly specify a pre-test conditioning environment, condi-
tioning is not required and the test specimens may be tested as
11.5 Test Environment—If possible, test the specimen under
prepared.
the same fluid exposure level used for conditioning. However,
cases such as elevated temperature testing of a moist specimen
10.2 The pre-test specimen conditioning process, to include
place unrealistic requirements
...

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.
Designation: C480/C480M − 08 C480/C480M − 08 (Reapproved 2015)
Standard Test Method for
Flexure Creep of Sandwich Constructions
This standard is issued under the fixed designation C480/C480M; 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.
1. Scope
1.1 This test method covers the determination of the creep characteristics and creep rate of flat sandwich constructions loaded
in flexure, at any desired temperature. 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 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 either SI units or inch-pound units are to be regarded separately as
standard. The values stated in each system may not be exact equivalents; therefore, 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 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 and health practices and determine the applicability of regulatory
limitations prior to use.
2. Referenced Documents
2.1 ASTM Standards:
C274 Terminology of Structural Sandwich Constructions
C393/C393M Test Method for Core Shear Properties of Sandwich Constructions by Beam Flexure
D883 Terminology Relating to Plastics
D3878 Terminology for Composite Materials
D5229/D5229M Test Method for Moisture Absorption Properties and Equilibrium Conditioning of Polymer Matrix Composite
Materials
D7249/D7249M Test Method for Facing Properties of Sandwich Constructions by Long Beam Flexure
E6 Terminology Relating to Methods of Mechanical Testing
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 ASTM Test Methods
E456 Terminology Relating to Quality and Statistics
E1309 Guide for Identification of Fiber-Reinforced Polymer-Matrix Composite Materials in Databases
E1434 Guide for Recording Mechanical Test Data of Fiber-Reinforced Composite Materials in Databases
3. Terminology
3.1 Definitions—Terminology D3878 defines terms relating to high-modulus fibers and their composites. Terminology C274
defines terms relating to structural sandwich constructions. Terminology D883 defines terms relating to plastics. Terminology E6
defines terms relating to mechanical testing. Terminology E456 and Practice E177 define terms relating to statistics. In the event
of a conflict between terms, Terminology D3878 shall have precedence over the other terminology documents.
3.2 Symbols:
3.2.1 A—distance between pivot point and point of applied force on the specimen
3.2.2 b—specimen width
This specification 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 Sept. 1, 2008July 1, 2015. Published October 2008 August 2015. Originally approved in 1961. Last previous edition approved in 20052008 as
C480 – 99C480/C480M – 08.(2005). DOI: 10.1520/C0480_C0480M-08.10.1520/C0480_C0480M-08R15.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. 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
C480/C480M − 08 (2015)
3.2.3 B—distance from pivot point to center of gravity of the loading arm
3.2.4 c—core thickness
3.2.5 CR —creep rate at time, i
I i
3.2.6 d—sandwich total thickness
3.2.7 d—initial static deflection under the same load and at the same temperature
3.2.8 D—total deflection at time, t
3.2.9 F —applied facing stress
f
3.2.10 F —applied core shear stress
s
3.2.11 M—distance between point and weight point
3.2.12 n—number of specimens
3.2.13 p—mass of loading plate and rod
3.2.14 P—applied force
3.2.15 S—length of support span
3.2.16 w—mass of lever arm
3.2.17 W—mass of weight (including tray mass)
4. Summary of Test Method
4.1 This test method consists of subjecting a beam of sandwich construction to a sustained force normal to the plane of the
sandwich, using either a 3-point or a 4-point loading fixture. Deflection versus time measurements are recorded.
4.2 For long beam specimens conforming to Test Method D7249/D7249M, the only acceptable failure modes for sandwich
facesheet strength are those which are internal to one of the facesheets. Failure of the sandwich core or the core-to-facesheet bond
preceding failure of one of the facesheets is not an acceptable failure mode for this specimen configuration.
4.3 For short-beam specimens conforming to Test Method C393/C393M, the only acceptable failure modes are core shear or
core-to-facing bond. Failure of the sandwich facing preceding failure of the core or core-to-facing bond is not an acceptable failure
mode for this specimen configuration.
4.4 Careful post-test inspection of the specimen is required as facing failure occurring in proximity to the loading points can
be caused by local through-thickness compression or shear failure of the core that precedes failure of the facing.
5. Significance and Use
5.1 The determination of the creep rate provides information on the behavior of sandwich constructions under constant applied
force. Creep is defined as deflection under constant force over a period of time beyond the initial deformation as a result of the
application of the force. Deflection data obtained from this test method can be plotted against time, and a creep rate determined.
By using standard specimen constructions and constant loading, the test method may also be used to evaluate creep behavior of
sandwich panel core-to-facing adhesives.
5.2 This test method provides a standard method of obtaining flexure creep of sandwich constructions for quality control,
acceptance specification testing, and research and development.
5.3 Factors that influence the sandwich construction creep response and shall therefore be reported include the following: facing
material, core material, adhesive material, methods of material fabrication, facing stacking sequence and overall thickness, core
geometry (cell size), core density, core thickness, adhesive thickness, specimen geometry, specimen preparation, specimen
conditioning, environment of testing, specimen alignment, loading procedure, speed of testing, facing void content, adhesive void
content, and facing volume percent reinforcement. Further, facing and core-to-facing strength and creep response may be different
between precured/bonded and co-cured facesheets of the same material.
6. Interferences
6.1 The interferences listed in Test Methods C393/C393M and D7249/D7249M are also applicable to this test method.
7. Apparatus
7.1 Micrometers and Calipers—A micrometer having a flat anvil interface, or a caliper of suitable size, shall be used. The
instruments(s) shall have an accuracy of 625 μm [60.001 in.] for thickness measurement, and an accuracy of 6250 μm [60.010
in.] for length and width measurements.
NOTE 1—The accuracies given above are based on achieving measurements that are within 1 % of the sample length, width and thickness.
C480/C480M − 08 (2015)
7.2 Loading Fixtures—The fixture for loading the specimen shall be a 3-point loading configuration that conforms to either Test
Method D7249/D7249M (for a long beam test) or to Test Method C393/C393M (for a short beam test) except that a constant force
shall be applied by means of weights and a lever system. Fig. 1 shows a lever and weight-loading apparatus that has been found
satisfactory.
7.3 Deflectometer (LVDT)—The deflection of the specimen shall be measured in the center of the support span by a properly
calibrated device having an accuracy of 60.025 mm [60.001 in.] or better.
7.4 Conditioning Chamber—When conditioning materials at non-laboratory environments, a temperature/vapor-level controlled
environmental conditioning chamber is required that shall be capable of maintaining the required temperature to within 63°C
[65°F] and the required relative humidity level to within 63 %. Chamber conditions shall be monitored either on an automated
continuous basis or on a manual basis at regular intervals (a minimum of once daily checks are recommended).
7.5 Environmental Test Chamber—An environmental test chamber is required for test environments other than ambient testing
laboratory conditions. This chamber shall be capable of maintaining the gage section of the test specimen at the required test
environment during the mechanical test.
8. Sampling and Test Specimens
8.1 Sampling—Test at least five specimens per test condition unless valid results can be gained through the use of fewer
specimens, as in the case of a designed experiment. For statistically significant data, consult the procedures outlined in Practice
E122. Report the method of sampling.
8.2 Geometry, Facing, Core:
8.2.1 Core or Core-to-Facing Failure Mode Desired—The test specimen configuration shall be a sandwich construction of a size
and proportions conforming to the flexure test specimen described in Test Method C393/C393M. The standard specimen
configuration should be used whenever the specimen design equations in Section 8.2.3 of C393/C393M indicate that a core of
core-to-facing bond failure mode is expected. In cases where the standard C393/C393M specimen configuration will not produce
a desired failure, a non-standard specimen shall be designed to produce a core or bond failure mode.
8.2.2 Facesheet Failure Mode Desired—The test specimen configuration shall be a sandwich construction of a size and
proportions conforming to the flexure test specimen described in Test Method D7249/D7249M. A non-standard 3-point loading
specimen configuration shall be designed per Section 8.2.3 of D7249/D7249M to achieve a facing failure mode. The standard
4-point loading D7249/D7249M specimen configuration may be used if a suitable creep loading apparatus is used.
8.3 Compression Side Facing—Unless otherwise specified by the test requestor, the bag-side facing of a co-cured composite
sandwich panel shall be placed as the upper, compression-loaded facing during test, as facing compression strength is more
sensitive to imperfections typical of bag-side surfaces (for example, intra-cell dimpling) than is facing tension strength. Creep
response is expected to follow the same trends as static strength.
8.4 Specimen Preparation and Machining—Specimen preparation is extremely important for this test method. Take precautions
when cutting specimens from large panels to avoid notches, undercuts, rough or uneven surfaces, or delaminations due to
inappropriate machining methods. Obtain final dimensions by water-lubricated precision sawing, milling, or grinding. The use of
diamond coated machining tools has been found to be extremely effective for many material systems. Edges should be flat and
parallel within the specified tolerances. Record and report the specimen cutting preparation method.
8.5 Labeling—Label the test specimens so that they will be distinct from each other and traceable back to the panel of origin,
and will neither influence the test nor be affected by it.
9. Calibration
9.1 The accuracy of all measuring equipment shall have certified calibrations that are current at the time of use of the equipment
FIG. 1 Creep Test Apparatus and Loading System
C480/C480M − 08 (2015)
10. Conditioning
10.1 The recommended pre-test specimen condition is effective moisture equilibrium at a specific relative humidity per
D5229/D5229M; however, if the test requestor does not explicitly specify a pre-test conditioning environment, conditioning is not
required and the test specimens may be tested as prepared.
10.2 The pre-test specimen conditioning process, to include specified environmental exposure levels and resulting moisture
content, shall be reported with the test data.
NOTE 2—The term moisture, as used in Test Method D5229/D5229M, includes not only the vapor of a liquid and its condensate, but the liquid itself
in large quantities, as for immersion.
10.3 If no explicit conditioning process is performed, the specimen conditioning process shall be reported as “unconditioned”
and the moisture content as “unknown”.
11. Procedure
11.1 Parameters to Be Specified Before Test:
11.1.1 The specimen sampling method, specimen geometry, and conditioning travelers (if required).
11.1.2 The loading fixture support span (and loading span if a 4-point loading configuration is used).
11.1.3 The force, P, to be applied to the specimen and the maximum time for the test.
11.1.4 The properties and data reporting format desired.
11.1.5 The environmental conditioning test parameters.
11.1.6 The nominal thicknesses of the facing materials.
NOTE 3—Determine specific material property, accuracy, and data reporting requirements prior to test for proper selection of instrumentation and data
recording equipment. Estimate the maximum specimen deflection to aid in transducer selection, calibration of equipment, and determination of equipment
settings.
11.2 General Instructions:
11.2.1 Report any deviations from this test method, whether intentional or inadvertent.
11.2.2 Condition the specimens as required. Store the specimens in the conditioned environment until test time, if the test
environment is different than the conditioning environment.
11.2.3 Before testing, measure and record the specimen length, width and thickness at three places in the test section. Measure
the specimen length and width with an accuracy of 6250 μm [60.010 in.]. Measure the specimen thickness with an accuracy of
625 μm [60.001 in.]. Record the dimensions to three significant figures in units of millimeters [inches].
11.3 Measure and record
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