ASTM D7250/D7250M-16
(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 facings 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 insure 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 and/or D7249/D7249M.
1.2 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.
1.2.1 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 and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: D7250/D7250M − 16
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 D3878 Terminology for Composite Materials
D7249/D7249M Test Method for Facing Properties of Sand-
1.1 This practice covers determination of the flexural and
wich Constructions by Long Beam Flexure
transverse shear stiffness properties of flat sandwich construc-
E6 Terminology Relating to Methods of Mechanical Testing
tions subjected to flexure in such a manner that the applied
E122 Practice for Calculating Sample Size to Estimate,With
moments produce curvature of the sandwich facing planes.
Specified Precision, the Average for a Characteristic of a
Permissible core material forms include those with continuous
Lot or Process
bonding surfaces (such as balsa wood and foams) as well as
E177 Practice for Use of the Terms Precision and Bias in
those with discontinuous bonding surfaces (such as honey-
ASTM Test Methods
comb). The calculation methods in this practice are limited to
E456 Terminology Relating to Quality and Statistics
sandwich beams exhibiting linear force-deflection response.
This practice uses test results obtained from Test Methods
3. Terminology
C393/C393M and/or D7249/D7249M.
3.1 Definitions—Terminology D3878 defines terms relating
1.2 The values stated in either SI units or inch-pound units
to high-modulus fibers and their composites, as well as terms
are to be regarded separately as standard. The values stated in
relating to sandwich constructions. Terminology D883 defines
each system may not be exact equivalents; therefore, each
terms relating to plastics. Terminology E6 defines terms
system shall be used independently of the other. Combining
relating to mechanical testing. Terminology E456 and Practice
values from the two systems may result in non-conformance
E177 define terms relating to statistics. In the event of a
with the standard.
conflict between terms, Terminology D3878 shall have prece-
1.2.1 Within the text the inch-pound units are shown in
dence over the other terminologies.
brackets.
3.2 Symbols: b = sandwich width, mm [in.]
1.3 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the c = core thickness, mm [in.]
responsibility of the user of this standard to establish appro-
d = sandwich thickness, mm [in.]
2 2
priate safety and health practices and determine the applica-
D = flexural stiffness, N-mm [lb-in. ]
bility of regulatory limitations prior to use.
∆ = beam mid-span deflection, mm [in.]
G = core shear modulus, MPa [psi]
2. Referenced Documents
S = support span length, mm [in.]
2
2.1 ASTM Standards:
L = load span length, mm [in.] (L = 0.0 for 3-point mid-span
C273 Test Method for Shear Properties of Sandwich Core
loading configuration)
Materials
n = number of specimens
C393/C393M Test Method for Core Shear Properties of
P = total applied force, N [lb]
Sandwich Constructions by Beam Flexure
t = facing thickness, mm [in.]
D883 Terminology Relating to Plastics
U = transverse shear rigidity, N [lb]
4. Summary of Practice
1
This practice is under the jurisdiction ofASTM Committee D30 on Composite
Materials and is the direct responsibility of Subcommittee D30.09 on Sandwich
4.1 This practice consists of calculating the flexural
Construction.
stiffness, transverse (through-thickness) shear rigidity and core
Current edition approved April 1, 2016. Published April 2016. Originally
shear modulus of a sandwich beam using deflection and/or
approved in 2006. Last previous edition approved in 2012 as D7250/
D7250M – 06(2012). DOI: 10.1520/D7250_D7250M-16.
strain data from two or more flexure tests of different loading
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
configurations conducted under Test Methods C393/C393M
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
and/or D7249/D7249M. This practice also includes equations
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. for calculating the shear rigidity and core shear modulus of a
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
1
---------------------- Page: 1 ----------------------
D7250/D7250M − 16
sandwich beam using deflection data from a single flexure test statistically significant data, consult the procedures outlined in
conducted under Test Method C393/C393M when the facing Practice E
...
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 − 06 (Reapproved 2012) D7250/D7250M − 16
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/or D7249/D7249M.
1.2 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.
1.2.1 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 and health practices and determine the applicability of regulatory
limitations prior to use.
2. Referenced Documents
2
2.1 ASTM Standards:
C273 Test Method for Shear Properties of Sandwich Core Materials
3
C274 Terminology of Structural Sandwich Constructions (Withdrawn 2016)
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 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
3
E1309 Guide for Identification of Fiber-Reinforced Polymer-Matrix Composite Materials in Databases (Withdrawn 2015)
3
E1434 Guide for Recording Mechanical Test Data of Fiber-Reinforced Composite Materials in Databases (Withdrawn 2015)
3. Terminology
3.1 Definitions—Terminology D3878 defines terms relating to high-modulus fibers and their composites.
Terminologycomposites, as C274 defineswell as 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
terminologies.
3.2 Symbols: b = sandwich width, mm [in.]
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 Feb. 1, 2012April 1, 2016. Published March 2012April 2016. Originally approved in 2006. Last previous edition approved in 2012 as
D7250/D7250M – 06(2012). DOI: 10.1520/D7250_D7250M-06R12.10.1520/D7250_D7250M-16.
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 − 16
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, mm [in.] (L = 0.0 for 3-point mid-span loading configuration)
n = number of specimens
P = total applied force,
...
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