ASTM C480/C480M-16(2024)

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.
Designation: C480/C480M − 16 (Reapproved 2024)
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 D5229/D5229M Test Method for Moisture Absorption Prop-
erties and Equilibrium Conditioning of Polymer Matrix
1.1 This test method covers the determination of the creep
Composite Materials
characteristics and creep rate of flat sandwich constructions
D7249/D7249M Test Method for Facesheet Properties of
loaded in flexure, at any desired temperature. Permissible core
Sandwich Constructions by Long Beam Flexure
material forms include those with continuous bonding surfaces
E6 Terminology Relating to Methods of Mechanical Testing
(such as balsa wood and foams) as well as those with
E122 Practice for Calculating Sample Size to Estimate, With
discontinuous bonding surfaces (such as honeycomb).
Specified Precision, the Average for a Characteristic of a
1.2 The values stated in either SI units or inch-pound units
Lot or Process
are to be regarded separately as standard. Within the text the
E177 Practice for Use of the Terms Precision and Bias in
inch-pound units are shown in brackets. The values stated in
ASTM Test Methods
either SI units or inch-pound units are to be regarded separately
E456 Terminology Relating to Quality and Statistics
as standard. The values stated in each system may not be exact
equivalents; therefore, each system shall be used independently
3. Terminology
of the other. Combining values from the two systems may
3.1 Definitions—Terminology D3878 defines terms relating
result in non-conformance with the standard.
to high-modulus fibers and their composites, a well as terms
1.3 This standard does not purport to address all of the
relating to sandwich constructions. Terminology D883 defines
safety concerns, if any, associated with its use. It is the
terms relating to plastics. Terminology E6 defines terms
responsibility of the user of this standard to establish appro-
relating to mechanical testing. Terminology E456 and Practice
priate safety, health, and environmental practices and deter-
E177 define terms relating to statistics. In the event of a
mine the applicability of regulatory limitations prior to use.
conflict between terms, Terminology D3878 shall have prece-
1.4 This international standard was developed in accor-
dence over the other terminology documents.
dance with internationally recognized principles on standard-
3.2 Symbols:
ization established in the Decision on Principles for the
3.2.1 A—distance between pivot point and point of applied
Development of International Standards, Guides and Recom-
force on the specimen
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
3.2.2 b—specimen width
3.2.3 B—distance from pivot point to center of gravity of the
2. Referenced Documents
loading arm
2.1 ASTM Standards:
3.2.4 c—core thickness
C393/C393M Test Method for Core Shear Properties of
3.2.5 CR —creep rate at time, i
I i
Sandwich Constructions by Beam Flexure
3.2.6 d—sandwich total thickness
D883 Terminology Relating to Plastics
D3878 Terminology for Composite Materials
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 May 1, 2024. Published May 2024. Originally
approved in 1961. Last previous edition approved in 2016 as C480/C480M – 16.
3.2.11 M—distance between point and weight point
DOI: 10.1520/C0480_C0480M-16R24.
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 service@astm.org. 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 − 16 (2024)
3.2.15 S—length of support span 7. Apparatus
3.2.16 w—mass of lever arm
7.1 Micrometers and Calipers—A micrometer 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 within 1 % of the 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
constant force shall be applied by means of weights and a lever
wich facesheet strength are those which are internal to one of
the facesheets. Failure of the sandwich core or the core-to- system. Fig. 1 shows a lever and weight-loading apparatus that
has been found satisfactory.
facesheet bond preceding failure of one of the facesheets is not
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, the only acceptable failure modes are core shear
[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
controlled environmental conditioning chamber is required that
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
can be caused by local through-thickness compression or shear
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
rate determined. By using standard specimen constructions and
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-
tion unless valid results can be gained through the use of fewer
5.2 This test method provides a standard method of obtain-
specimens, as in the case of a designed experiment. For
ing flexure creep of sandwich constructions for quality control,
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/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. FIG. 1 Creep Test Apparatus and Loading System
C480/C480M − 16 (2024)
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.
test specimen configuration shall be a sandwich construction of
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”.
design equations in Section 8.2.3 of C393/C393M indicate that
11. Procedure
a core of core-to-facing bond failure mode is expected. In cases
where the standard C393/C393M specimen configuration will
11.1 Parameters to Be Specified Before Test:
not produce a desired failure, a non-standard specimen shall be
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 The loading fixture support span (and loading span if
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. A non-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
reporting requirements prior to test for proper selection of instrumentation
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 Report any deviations from this test method, whether
surfaces (for example, intra-cell dimpling) than is facing
intentional or inadvertent.
tension strength. Creep response is expected to follow the same
11.2.2 Condition the specimens as required. Store the speci-
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
precautions when cutting specimens from large panels to avoid
length, width and thickness at three places in the test section.
notches, undercuts, rough or uneven surfaces, or delaminations
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-
an accuracy of 625 μm [60.001 in.]. Record the dimensions to
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
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