ASTM C480/C480M-16(2024)

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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.4 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.

General Information

• Status: Published
• Publication Date: 30-Apr-2024
• ICS: 83.120 - Reinforced plastics
• Technical Committee: D30 - Composite Materials
• Drafting Committee: D30.09 - Sandwich Construction

Overview

ASTM C480/C480M-16(2024): Standard Test Method for Flexure Creep of Sandwich Constructions establishes procedures to determine the creep characteristics and creep rate of flat sandwich constructions loaded in flexure. Creep is defined as the time-dependent deflection under a constant load beyond the initial deformation. This standard supports the evaluation and comparison of sandwich composites, focusing on their structural behavior under sustained loads over time.

Sandwich constructions, often used in aerospace, automotive, marine, and construction industries, rely on the combination of strong facings and lightweight cores. Assessing flexure creep is essential for quality control, specification acceptance, and product development, helping manufacturers and engineers ensure long-term performance and reliability.

Key Topics

• Creep Rate Measurement: The standard describes the determination of creep rates by subjecting sandwich beams to constant force and recording deflection versus time. These data enable the calculation and analysis of material performance under long-term loading.
• Applicability to Different Core Materials: Permissible core materials include continuous (e.g., balsa wood, foams) and discontinuous (e.g., honeycomb) bonding surfaces, making the method versatile for various composite panels.
• Influencing Factors: Factors influencing creep behavior and to be reported include:
  • Facing material and stacking sequence
  • Core material, geometry (cell size), density, and thickness
  • Adhesive type and thickness
  • Fabrication method
  • Specimen preparation and geometry
  • Conditioning environment (temperature, humidity)
  • Test environment and procedure
• Standardization and Reporting: The method provides detailed guidance on specimen preparation, testing apparatus (three-point or four-point flexure), alignment, calibration, and reporting requirements to promote consistency and comparability of results.
• Flexural Failure Modes: The test distinguishes between failure in the facings, core, or core-to-facing bond, depending on specimen geometry and setup, ensuring relevant data for a range of design scenarios.

Applications

• Quality Control: Routine testing of sandwich panel creep properties for manufacturing assurance and product consistency.
• Acceptance Testing: Verifying panels meet customer or regulatory requirements before installation in critical applications.
• Research and Development: Comparing creep performance of new materials, adhesives, or core constructions in product innovation and optimization.
• Adhesive Evaluation: Assessing the long-term performance of core-to-facing adhesives under static loads, crucial for structural integrity.
• Environmental Simulation: Conducting tests at desired temperatures and humidities to simulate service conditions for aerospace, automotive, or infrastructure applications.

Manufacturers, material suppliers, engineers, and quality assurance professionals benefit from this standardized approach to flexure creep evaluation, enabling informed decisions regarding sandwich construction materials.

Related Standards

This test method references several other relevant ASTM standards for composite and sandwich construction testing:

• ASTM C393/C393M - Test Method for Core Shear Properties of Sandwich Constructions by Beam Flexure
• ASTM D7249/D7249M - Test Method for Facesheet Properties of Sandwich Constructions by Long Beam Flexure
• ASTM D5229/D5229M - Test Method for Moisture Absorption Properties and Equilibrium Conditioning of Polymer Matrix Composite Materials
• ASTM D3878 - Terminology for Composite Materials
• ASTM D883 - Terminology Relating to Plastics
• ASTM E6, E122, E177, E456 - Terminology and practices relating to mechanical testing, quality, and statistics

Implementing ASTM C480/C480M-16(2024) ensures the reliable assessment of sandwich panel creep, supports compliance, and improves structural designs across multiple industries.

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.
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 [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 − 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 diffe
...