ASTM D6772/D6772M-22

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Designation: D6772/D6772M − 16 D6772/D6772M − 22
Standard Test Method for
Dimensional Stability of Sandwich Core Materials
This standard is issued under the fixed designation D6772/D6772M; 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 sandwich core dimensional stability in the two plan dimensions.
1.2 Units—The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in
each system are not necessarily exact equivalents; therefore, to ensure conformance with the standard, each system shall be used
independently of the other, and values from the two systems shall not be combined.
1.2.1 Within the text, the inch-pound units are shown in brackets.
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 safety, health, and healthenvironmental 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.
2. Referenced Documents
2.1 ASTM Standards:
C271/C271M Test Method for Density of Sandwich Core Materials
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
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
3. Terminology
3.1 Definitions—Terminology D3878 defines terms relating to high-modulus fibers and their composites, as well as terms relating
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, 2016May 1, 2022. Published April 2016May 2022. Originally approved in 2002. Last previous edition approved in 20152016 as
D6772 – 15.D6772/D6772M – 16. DOI: 10.1520/D6772_D6772M-16.10.1520/D6772_D6772M-22.
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
D6772/D6772M − 22
to sandwich constructions. Terminology D883 defines terms relating to plastics. 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
terminologies.
3.2 Symbols:
3.2.1 CV—coefficient of variation statistic of a sample population for a given property (in percent)
3.2.2 L — initial (pre-test) measured dimension
i
3.2.3 L —post-heating measured dimension
f
3.2.4 S —standard deviation statistic of a sample population for a given property
n-1
3.2.5 x —test result for an individual specimen from the sample population for a given property
I
3.2.6 x¯—mean or average (estimate of mean) of a sample population for a given property
4. Summary of Test Method
4.1 This test method consists of placing a small piece of sandwich core material in an elevated temperature environment for a
specified period of time. After cooling, the dimensional changes in the planar dimensions are measured and compared to the initial
measurements taken prior to thermal exposure, both immediately after heating and after re-conditioning. A typical honeycomb core
specimen is shown in Fig. 1.
FIG. 1 Dimensional Stability Specimen
5. Significance and Use
5.1 Sandwich panel cores may change planar dimensions when heated. This phenomenon can be associated with the effects of
heating upon the core material itself, as well as changes in core moisture content resulting from the heating cycle. It is prudent
to know if this may be problematic with regard to the intended final part dimensions.
5.2 This test method provides a standard method of characterizing the dimensional stability of sandwich core materials for design
properties, material specifications, research and development applications, and quality assurance.
5.3 Factors that influence dimensional stability of sandwich core materials and shall therefore be reported include the following:
core material, methods of material fabrication, core geometry, core thickness, core thickness uniformity, cell wall thickness,
specimen geometry, specimen preparation, heating and cooling environments (including temperatures and humidity levels), and
specimen conditioning (both prior to and after heating).
6. Interferences
6.1 Material and Specimen Preparation—Poor material fabrication practices and damage induced by improper specimen
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machining are known causes of high data scatter for sandwich cores. Important aspects of sandwich core specimen preparation that
contribute to data scatter include the existence of joints, voids or other core discontinuities, out-of-plane curvature, and surface
roughness.
6.2 Core Geometry—Core-specific geometric factors that affect dimensional stability include core cell size, uniformity of core cell
geometry, core cell wall thickness, core cell wall thickness uniformity, core thickness, and core thickness uniformity.
6.3 Environment—Results are affected by the environmental conditions (including both temperatures and humidity levels) under
which specimens are pre-conditioned, the elevated temperature exposure environment, the re-conditioning environment after
heating, as well as the conditions under which the planar dimensional measurements are taken. Specimens tested in various
environments can exhibit differences in dimensional stability.
7. Apparatus
7.1 Micrometers and Calipers—A micrometer having a flat anvil interface, or a caliper of suitable size, shall be used. The accuracy
of the instrument(s) shall be suitable for reading to within 0.5 % of the sample length, width and thickness. For typical specimen
geometries, an instrument with an accuracy of 60.025 mm [60.001 in.] is desirable for thickness measurement, whereas an
instrument with an accuracy of 60.25 mm [60.01 in.] is desirable for length and width measurement.
7.2 Balance or Weighing Scale—An analytical balance or weighing scale is required that is capable of measuring the mass of the
core material accurately to 60.5 %.
7.3 Oven—An air-circulating oven is required that shall be capable of maintaining the required temperature to within 63 °C [65
°F].
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,
such 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 Test Specimens:
8.2.1 Core Thickness—Standard test specimens shall utilize 13 mm [0.50 in.] thick core. When assessing dimensional stability
characteristics of core used in specific sandwich constructions, it is recommended to test the actual core thickness used in the end
application. Tests conducted using non-standard core thicknesses must be designated as such, with the core thickness reported with
any test results.
8.2.2 Core Planar Geometry—Core test specimens shall be approximately 450 mm [18 in.] by 900 mm [36 in.] in the planar
dimensions. For honeycomb cores, the planar dimension cross section is defined to be in the facing plane (in regard to the
orientation that the core would be placed in a structural sandwich construction) and is perpendicular to the orientation of the cell
walls. For honeycomb cores, the 450-mm [18-in.]450 mm [18 in.] dimension is the core’s ribbon or L direction. Other dimensions
can be used, but must be reported. Smaller specimens may be used if oven size is limited.
8.2.3 Core Preparation and Machining—Prepare the core material samples so that the facing plane surfaces are parallel to each
other and perpendicular to the sides of the core. Take precautions when cutting specimens from large sheets of core material to
avoid notches, undercuts, rough or uneven surfaces due to inappropriate machining methods. Record and report the core material
specimen cutting preparation method.
8.2.4 If core material density is to be reported, samples used to determine density shall be obtained from the same sheet of core
being tested. Density may be evaluated in accordance with Test Method C271/C271M.
8.3 Labeling—Label the test specimens so that they will be distinct from each other and traceable back to the sheet of origin, and
will neither influence the test nor be affected by it.
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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.
10. Conditioning
10.1 Pre-test environmental conditioning requirements shall be specified by the test requestor. The recommended pre-test
condition is effective moisture equilibrium at a specific relative humidity as established by Test Method D5229/D5229M; however,
if the test requestor does not explicitly specify a pre-test conditioning environment, no conditioning is required and the test
specimens may be tested as prepared.
10.2 The pre-test specimen cond
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