ASTM D7250/D7250M-20
(Practice)Standard Practice for Determining Sandwich Beam Flexural and Shear Stiffness
Standard Practice for Determining Sandwich Beam Flexural and Shear Stiffness
SIGNIFICANCE AND USE
5.1 Flexure tests on flat sandwich constructions may be conducted to determine the sandwich flexural stiffness, the core shear strength and shear modulus, or the facing’s compressive and tensile strengths. Tests to evaluate core shear strength may also be used to evaluate core-to-facing bonds.
5.2 This practice provides a standard method of determining sandwich flexural and shear stiffness and core shear modulus using calculations involving measured deflections of sandwich flexure specimens. Tests can be conducted on short specimens and on long specimens (or on one specimen loaded in two ways), and the flexural stiffness, shear rigidity, and core shear modulus can be determined by simultaneous solution of the complete deflection equations for each span or each loading. If the facing modulus values are known, a short span beam can be tested and the calculated bending deflection subtracted from the beam's total deflection. This gives the shear deflection from which the transverse shear modulus can be determined.
Note 1: Core shear strength and shear modulus are best determined in accordance with Test Method C273, provided bare core material is available.
Note 2: For cores with high shear modulus, the shear deflection will be quite small and ordinary errors in deflection measurements will cause considerable variations in the calculated shear modulus.
Note 3: To ensure that simple sandwich beam theory is valid, a good rule of thumb for a four-point bending test is the span length divided by the sandwich thickness should be greater than 20 (L1/d > 20) with the ratio of facing thickness to core thickness less than 0.1 (t/c
SCOPE
1.1 This practice covers determination of the flexural and transverse shear stiffness properties of flat sandwich constructions subjected to flexure in such a manner that the applied moments produce curvature of the sandwich facing planes. 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). The calculation methods in this practice are limited to sandwich beams exhibiting linear force-deflection response. This practice uses test results obtained from Test Methods C393/C393M or D7249/D7249M, or both.
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, 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.
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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: D7250/D7250M − 20
Standard Practice for
1
Determining Sandwich Beam Flexural and Shear Stiffness
This standard is issued under the fixed designation D7250/D7250M; 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 2. Referenced Documents
2
2.1 ASTM Standards:
1.1 This practice covers determination of the flexural and
C273 Test Method for Shear Properties of Sandwich Core
transverse shear stiffness properties of flat sandwich construc-
Materials
tions subjected to flexure in such a manner that the applied
C393/C393M Test Method for Core Shear Properties of
moments produce curvature of the sandwich facing planes.
Sandwich Constructions by Beam Flexure
Permissible core material forms include those with continuous
D883 Terminology Relating to Plastics
bonding surfaces (such as balsa wood and foams) as well as
D3878 Terminology for Composite Materials
those with discontinuous bonding surfaces (such as honey-
D7249/D7249M Test Method for Facesheet Properties of
comb). The calculation methods in this practice are limited to
Sandwich Constructions by Long Beam Flexure
sandwich beams exhibiting linear force-deflection response.
E6 Terminology Relating to Methods of Mechanical Testing
This practice uses test results obtained from Test Methods
E122 Practice for Calculating Sample Size to Estimate,With
C393/C393M or D7249/D7249M, or both.
Specified Precision, the Average for a Characteristic of a
Lot or Process
1.2 Units—The values stated in either SI units or inch-
E177 Practice for Use of the Terms Precision and Bias in
pound units are to be regarded separately as standard. The
ASTM Test Methods
values stated in each system are not necessarily exact equiva-
E456 Terminology Relating to Quality and Statistics
lents; therefore, to ensure conformance with the standard, each
system shall be used independently of the other, and values
3. Terminology
from the two systems shall not be combined.
3.1 Definitions—Terminology D3878 defines terms relating
1.2.1 Within the text, the inch-pound units are shown in
to high-modulus fibers and their composites, as well as terms
brackets.
relating to sandwich constructions. Terminology D883 defines
1.3 This standard does not purport to address all of the
terms relating to plastics. Terminology E6 defines terms
safety concerns, if any, associated with its use. It is the
relating to mechanical testing. Terminology E456 and Practice
responsibility of the user of this standard to establish appro-
E177 define terms relating to statistics. In the event of a
priate safety, health, and environmental practices and deter-
conflict between terms, Terminology D3878 shall have prece-
mine the applicability of regulatory limitations prior to use.
dence over the other terminologies.
1.4 This international standard was developed in accor-
3.2 Symbols:
dance with internationally recognized principles on standard-
b = sandwich width, mm [in.]
ization established in the Decision on Principles for the
c = core thickness, mm [in.]
Development of International Standards, Guides and Recom-
d = sandwich thickness, mm [in.]
2 2
mendations issued by the World Trade Organization Technical
D = flexural stiffness, N-mm [lb-in. ]
Barriers to Trade (TBT) Committee.
∆ = beam mid-span deflection, mm [in.]
G = core shear modulus, MPa [psi]
S = support span length, mm [in.]
L = load span length, mm [in.] (L = 0.0 for 3-point mid-span
loading configuration)
n = number of specimens
1
This practice is under the jurisdiction ofASTM Committee D30 on Composite
Materials and is the direct responsibility of Subcommittee D30.09 on Sandwich
2
Construction. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved July 1, 2020. Published August 2020. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 2006. Last previous edition approved in 2016 as D7250/D7250M – 16. Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/D7250_D7250M-20. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
1
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D7250/D7250M − 20
P = total applied force, N [lb] independently for each specific combination of core material,
t = facing thickness, mm [in.] facing material, and core-to-facing interfacial adhesive (if
U = transverse sh
...
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: D7250/D7250M − 16 D7250/D7250M − 20
Standard Practice for
1
Determining Sandwich Beam Flexural and Shear Stiffness
This standard is issued under the fixed designation D7250/D7250M; 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 practice covers determination of the flexural and transverse shear stiffness properties of flat sandwich constructions
subjected to flexure in such a manner that the applied moments produce curvature of the sandwich facing planes. 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). The calculation methods in this practice are limited to sandwich beams exhibiting linear
force-deflection response. This practice uses test results obtained from Test Methods C393/C393M and/oror D7249/D7249M., or
both.
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 mayare not benecessarily exact equivalents; therefore, to ensure conformance with the standard, each system shall
be used independently of the other. Combiningother, and values from the two systems may result in non-conformance with the
standard.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
2.1 ASTM Standards:
C273 Test Method for Shear Properties of Sandwich Core Materials
C393/C393M Test Method for Core Shear Properties of Sandwich Constructions by Beam Flexure
D883 Terminology Relating to Plastics
D3878 Terminology for Composite Materials
D7249/D7249M Test Method for Facesheet 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
3. Terminology
3.1 Definitions—Terminology D3878 defines terms relating to high-modulus fibers and their composites, as well as terms
relating to 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 terminologies.
1
This practice 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, 2016July 1, 2020. Published April 2016August 2020. Originally approved in 2006. Last previous edition approved in 20122016 as
D7250/D7250M – 06D7250/D7250M – 16.(2012). DOI: 10.1520/D7250_D7250M-16.10.1520/D7250_D7250M-20.
2
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
1
---------------------- Page: 1 ----------------------
D7250/D7250M − 20
3.2 Symbols:
b = sandwich width, mm [in.]
c = core thickness, mm [in.]
d = sandwich thickness, mm [in.]
2 2
D = flexural stiffness, N-mm [lb-in. ]
Δ = beam mid-span deflection, mm [in.]
G = core shear modulus, MPa [psi]
S = support span length, mm [in.]
L = load span length,
...
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