ASTM D7956/D7956M-14
(Practice)Standard Practice for Compressive Testing of Thin Damaged Laminates Using a Sandwich Long Beam Fixture Specimen
Standard Practice for Compressive Testing of Thin Damaged Laminates Using a Sandwich Long Beam Fixture Specimen
SIGNIFICANCE AND USE
5.1 This practice provides a standard method of testing damaged composite laminates which are too thin to be tested using typical anti-buckling fixtures, such as those used in Test Method D7137/D7137M. The laminate is first impacted or indented in order to produce a damage state representative of actual monolithic solid laminate structure. Impacting or static indentation is not performed on an assembled sandwich panel, as the damage state is altered by energy absorption in the core and by support of the core during the impact or indentation event. After damaging, the laminate is bonded onto the core with the impacted or indentation side of the laminate against the core, and with a localized un-bonded area encompassing the damage site. Fig. 1 illustrates the adhesive removal to avoid the damaged area and the assembly of the sandwich specimen with the impacted damaged laminate flipped over from the impacting or indentation orientation. The final assembled sandwich specimen is then tested using a long beam flexure setup with the damaged laminate being on the compression side. The sandwich panel configuration is used as a form of anti-buckling support for the thin damaged laminate.
5.2 Susceptibility to damage from concentrated out-of-plane forces is one of the major design concerns of many structures made of advanced composite laminates. Knowledge of the damage resistance and damage tolerance properties of a laminated composite plate is useful for product development and material selection.
5.3 The residual strength data obtained using this test method is used in research and development activities as well as for design allowables; however the results are specific to the geometry and physical conditions tested and are generally not scalable to other configurations.
5.4 The properties obtained using this test method can provide guidance in regard to the anticipated damage tolerance capability of composite structures of similar material, thickness, stacking sequ...
SCOPE
1.1 This practice covers an approach for compressive testing thin damaged multidirectional polymer matrix composite laminates reinforced by high-modulus fibers using a sandwich long beam flexure specimen. It provides a test configuration in which the core does not constrain any protruding back side damage. It is limited to testing of monolithic solid laminates which are too thin to be tested using typical anti-buckling fixtures. It does not cover compressive testing of damaged sandwich panel facings. The composite material forms are limited to continuous-fiber or discontinuous-fiber (tape or fabric, or both) reinforced composites in which the laminate is balanced and symmetric with respect to the test direction
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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Standards Content (Sample)
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Designation: D7956/D7956M − 14
StandardPractice for
Compressive Testing of Thin Damaged Laminates Using a
Sandwich Long Beam Fixture Specimen
This standard is issued under the fixed designation D7956/D7956M; 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 D3410 Test Method for Compressive Properties of Polymer
Matrix Composite Materials with Unsupported Gage Sec-
1.1 This practice covers an approach for compressive test-
tion by Shear Loading
ing thin damaged multidirectional polymer matrix composite
D6264/D6264M Test Method for Measuring the Damage
laminates reinforced by high-modulus fibers using a sandwich
Resistance of a Fiber-Reinforced Polymer-Matrix Com-
long beam flexure specimen. It provides a test configuration in
posite to a Concentrated Quasi-Static Indentation Force
which the core does not constrain any protruding back side
D7136/D7136M Test Method for Measuring the Damage
damage. It is limited to testing of monolithic solid laminates
Resistance of a Fiber-Reinforced Polymer Matrix Com-
which are too thin to be tested using typical anti-buckling
posite to a Drop-Weight Impact Event
fixtures. It does not cover compressive testing of damaged
D7137/D7137M Test Method for Compressive Residual
sandwich panel facings. The composite material forms are
StrengthPropertiesofDamagedPolymerMatrixCompos-
limited to continuous-fiber or discontinuous-fiber (tape or
ite Plates
fabric, or both) reinforced composites in which the laminate is
D7249/D7249M Test Method for Facing Properties of Sand-
balanced and symmetric with respect to the test direction
wich Constructions by Long Beam Flexure
1.2 The values stated in either SI units or inch-pound units
E6 Terminology Relating to Methods of Mechanical Testing
are to be regarded separately as standard. The values stated in
E122 Practice for Calculating Sample Size to Estimate,With
each system may not be exact equivalents; therefore, each
Specified Precision, the Average for a Characteristic of a
system shall be used independently of the other. Combining
Lot or Process
values from the two systems may result in non-conformance
E177 Practice for Use of the Terms Precision and Bias in
with the standard.
ASTM Test Methods
1.2.1 Within the text the inch-pound units are shown in
E456 Terminology Relating to Quality and Statistics
brackets.
E1309 Guide for Identification of Fiber-Reinforced
1.3 This standard does not purport to address all of the Polymer-Matrix Composite Materials in Databases
safety concerns, if any, associated with its use. It is the
E1434 Guide for Recording Mechanical Test Data of Fiber-
responsibility of the user of this standard to establish appro- Reinforced Composite Materials in Databases
priate safety and health practices and determine the applica-
3. Terminology
bility of regulatory limitations prior to use.
3.1 Definitions—Terminology D3878 defines terms relating
2. Referenced Documents to high-modulus fibers and their composites. Terminology
2 C274 defines terms relating to structural sandwich construc-
2.1 ASTM Standards:
tions. Terminology D883 defines terms relating to plastics.
C274 Terminology of Structural Sandwich Constructions
Terminology E6 defines terms relating to mechanical testing.
D883 Terminology Relating to Plastics
Terminology E456 and Practice E177 define terms relating to
D3878 Terminology for Composite Materials
statistics.Intheeventofaconflictbetweenterms,Terminology
D3878 shall have precedence over the other terminologies.
4. Summary of Practice
This test method is under the jurisdiction of ASTM Committee D30 on
Composite Materials and is the direct responsibility of Subcommittee D30.09 on
4.1 This practice consists of fabricating a composite
Sandwich Construction.
laminate, damaging the laminate using either Test Method
Current edition approved Aug. 1, 2014. Published September 2014. DOI:
10.1520/D7956_D7956M-14.
D6264/D6264M or Test Method D7136/D7136M, bonding the
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
impacted or indented side of the laminate onto core and a back
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
side facing to form a sandwich panel, and testing the damaged
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. laminate in compression using Test Method D7249/D7249M.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7956/D7956M − 14
5. Significance and Use 5.3 The residual strength data obtained using this test
method is used in research and development activities as well
5.1 This practice provides a standard method of testing
as for design allowables; however the results are specific to the
damaged composite laminates which are too thin to be tested
geometry and physical conditions tested and are generally not
using typical anti-buckling fixtures, such as those used in Test
scalable to other configurations.
Method D7137/D7137M. The laminate is first impacted or
indented in order to produce a damage state representative of
5.4 The properties obtained using this test method can
actual monolithic solid laminate structure. Impacting or static
provide guidance in regard to the anticipated damage tolerance
indentation is not performed on an assembled sandwich panel,
capability of composite structures of similar material,
as the damage state is altered by energy absorption in the core
thickness,stackingsequence,andsoforth.However,itmustbe
and by support of the core during the impact or indentation
understood that the damage tolerance of a composite structure
event. After damaging, the laminate is bonded onto the core
is highly dependent upon several factors including geometry,
with the impacted or indentation side of the laminate against
stiffness, support conditions, and so forth. Significant differ-
the core, and with a localized un-bonded area encompassing
ences in the relationships between the existent damage state
thedamagesite.Fig.1illustratestheadhesiveremovaltoavoid
and the residual compressive strength can result due to
the damaged area and the assembly of the sandwich specimen
differences in these parameters. For example, residual strength
with the impacted damaged laminate flipped over from the
and stiffness properties obtained using this test method would
impacting or indentation orientation. The final assembled
more likely reflect the damage tolerance characteristics of an
sandwich specimen is then tested using a long beam flexure
un-stiffened monolithic skin or web than that of a skin attached
setup with the damaged laminate being on the compression
to substructure which resists out-of-plane deformation.
side. The sandwich panel configuration is used as a form of
anti-buckling support for the thin damaged laminate.
5.5 The reporting section requires items that tend to influ-
ence residual compressive strength to be reported; these
5.2 Susceptibilitytodamagefromconcentratedout-of-plane
include the following: material, methods of material
forces is one of the major design concerns of many structures
fabrication, accuracy of lay-up orientation, laminate stacking
made of advanced composite laminates. Knowledge of the
sequence and overall thickness, specimen geometry, specimen
damage resistance and damage tolerance properties of a
laminated composite plate is useful for product development preparation, specimen conditioning, environment of testing,
and material selection. void content, volume percent reinforcement, type, size and
FIG. 1 Sandwich Specimen Assembly
D7956/D7956M − 14
location of damage (including method of non-destructive 7. Sampling and Test Specimens
inspection (NDI)), fixture geometry, time at temperature, and
7.1 Sampling—Test at least five specimens per test condi-
speed of testing.
tion unless valid results can be gained through the use of fewer
5.6 Properties that result from the residual strength assess-
specimens, as in the case of a designed experiment. For
ment include the following: compressive residual strength statistically significant data, consult the procedures outlined in
CAI
F .
Practice E122. Report the method of sampling.
7.2 Specimen and Fixture Geometry—The test requestor
6. Interferences
shall specify all specimen dimensions and materials along with
6.1 The response of a damaged specimen is dependent upon
the loading fixture dimensions. Refer to Test Method D7249/
many factors, such as laminate thickness, ply thickness, stack-
D7249Mforsandwichbeamspecimensizingrequirementsand
ing sequence, environment, damage type, damage geometry,
guidelines.
damage location, and loading/support conditions.
7.2.1 Specimen—The test specimens shall be rectangular in
Consequently, comparisons cannot be made between materials
cross section. The width of the specimen shall be at least three
unless identical test configurations, test conditions, and lami-
(3) times the width of the damage (as determined by NDI).
nate configurations are used. Therefore, all details of the test
configurationshallbereportedintheresults.Specificstructural NOTE 1—The recommended specimen width is five (5) times the
damage width, however this may not be practical in all cases.Also, it may
configurations and boundary conditions must be considered
not be possible to accurately predict the damage sizes prior to fabrication
when applying the data generated using this test method to
of the test specimens. As impact or indentation damage diameters are
design applications.
often on the order of 25 mm [1.0 inch], a typical specimen width is
127 mm [5.0 inch]. Specimen width should be minimized to avoid
6.2 Material Orthotropy—The degree of laminate orthot-
excessive anti-clastic bending.
ropy strongly affects the failure mo
...
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