ASTM D8511/D8511M-23

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: D8511/D8511M − 23
Standard Guide for
Design and Analysis of Local Buckling and Crippling Test
Specimens
This standard is issued under the fixed designation D8511/D8511M; 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 mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
1.1 This guide covers designing local buckling and crip-
pling test specimens to obtain empirical strength data for
2. Referenced Documents
one-edge-free and no-edge-free cross section configurations
2.1 ASTM Standards:
using solid laminate composite material construction. This
D883 Terminology Relating to Plastics
guide also discusses data analysis procedures for these test
D3878 Terminology for Composite Materials
specimens. Test procedures for local buckling and crippling
D8510/D8510M
specimens are covered in Test Method D8510/D8510M. This
guide is intended to be used by persons requesting these test
3. Terminology
types.
3.1 Definitions:
1.2 Local buckling and crippling tests require careful speci- 3.1.1 Terminology D3878 defines terms relating to high-
men design, instrumentation, data measurement and data
modulus fibers and their composites. Terminology D883 de-
analysis. Test requestors designing these specimen need to be fines terms relating to plastics. In the event of a conflict
familiar with Test Method D8510/D8510M, CMH-17 Volume
between terms, Terminology D3878 shall have precedence.
3 Chapter 9 (1) , and the stress analysis methods that will use
NOTE 1—If the term represents a physical quantity, its analytical
the resulting local buckling and crippling design data.
dimensions are stated immediately following the term (or letter symbol) in
fundamental dimension form, using the following ASTM standard sym-
1.3 Units—The values stated in either SI units or inch-
bology for fundamental dimensions, shown within square brackets: [M]
pound units are to be regarded separately as standard. The
for mass, [L] for length, [T] for time, [θ] for thermodynamic temperature,
values stated in each system are not necessarily exact equiva-
and [nd] for non-dimensional quantities. Use of these symbols is restricted
lents; therefore, to ensure conformance with the standard, each to analytical dimensions when used with square brackets, as the symbols
may have other definitions when used without the brackets.
system shall be used independently of the other, and values
from the two systems shall not be combined.
3.2 Definitions of Terms Specific to This Standard:
cc -2
1.3.1 Within the text the inch-pound units are shown in 3.2.1 crippling force, P [MLT ], n—the applied compres-
brackets. sive force at or above the local buckling force at which
specimen failure occurs.
1.4 This standard does not purport to address all of the
cc -1 -2
3.2.2 crippling stress, F [ML T ], n—the average stress
safety concerns, if any, associated with its use. It is the
in the test specimen cross-section at failure.
responsibility of the user of this standard to establish appro-
lcr -2
priate safety, health, and environmental practices and deter-
3.2.3 local buckling force, P [MLT ], n—the applied
mine the applicability of regulatory limitations prior to use.
compressive force at which buckling initiates.
lcr -1 -2
1.5 This international standard was developed in accor-
3.2.4 local buckling stress, F [ML T ], n—the average
dance with internationally recognized principles on standard-
stress in the test specimen cross-section at which buckling of a
ization established in the Decision on Principles for the
compression element within the cross-section initiates.
Development of International Standards, Guides and Recom-
3.2.5 slenderness ratio, L’/ρ [nd], n—the ratio of the speci-
men length adjusted for end boundary condition effects divided
by the minimum radius of gyration of the specimen cross-
This guide is under the jurisdiction of ASTM Committee D30 on Composite
section.
Materials and is the direct responsibility of Subcommittee D30.05 on Structural Test
Methods.
Current edition approved Sept. 1, 2023. Published September 2023. DOI: For referenced ASTM standards, visit the ASTM website, www.astm.org, or
10.1520/D8511_D8511M-23. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
The boldface numbers in parentheses refer to a list of references at the end of Standards volume information, refer to the standard’s Document Summary page on
this standard. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D8511/D8511M − 23
3.2.6 width to thickness ratio, b/t [nd], n—the ratio of the be familiar with the stress analysis methods that will use the
width of the buckling critical section of the specimen cross- resulting local buckling and crippling design data. The follow-
section to the specimen thickness. ing references discuss these methods and associated test data
3.2.6.1 Discussion—The width to thickness ratio may be for metallic and composite structures:
either a nominal value determined from nominal thickness or 4.1.1 CMH-17, Volume 3 Chapter 9 (1),
an actual value determined from measured thickness. 4.1.2 Esp, Chapter 17 (2),
4.1.3 Peery, Chapter 14 (3),
3.3 Symbols:
2 2
4.1.4 Peery and Azar, Chapter 11 (4),
3.3.1 A—cross-sectional area, mm [in. ].
4.1.5 Niu, Chapter 10 (5), and
3.3.2 b—width of buckling critical segment of specimen
4.1.6 Ziemian (6).
cross-section, relative to laminate centerline, mm [in.].
3.3.3 c—specimen end boundary condition factor (= 1.0 for 5. Background
both ends pinned; = 4 for both ends fully fixed).
5.1 When beams or stiffened panels are loaded in
lcr
3.3.4 F —local buckling stress, MPa [psi].
compression, force is shared between skin and stiffener cross
cc
section elements in proportion to their respective stiffnesses.
3.3.5 F —crippling stress, MPa [psi].
After initial buckling of an element of the cross section, the
3.3.6 L1—specimen length between end potting or fixture
effective tangent stiffness of the buckled element is reduced
inner surfaces, mm [in.].
sharply; the unbuckled elements will carry additional force as
3.3.7 L2—total specimen length, mm [in.].
the overall structural force is increased.
3.3.8 L’ —specimen length adjusted for end boundary
5.2 Prior to any buckling, an axially loaded stiffener or
condition (= L/√c), mm [in.].
structural member will have a uniformly distributed compres-
3.3.9 P—total compressive force applied to specimen, N
sive stress as shown in Fig. 1(a). At some force one or more flat
[lbf].
elements of the section begin to buckle, with additional force
lcr
carried by unbuckled portions (for example, corners, Fig. 1(b)).
3.3.10 P —applied compressive force at which buckling
Metallic structures can exhibit local yielding in the buckled
initiates, N [lbf].
cross-section prior to reaching maximum force (“crippling”
cc
3.3.11 P —maximum applied compressive force, N [lbf].
failure). In composite structure sections the onset of local
3.3.12 ρ—minimum cross-section radius of gyration.
failure occurring anywhere in the cross-section typically results
3.3.13 t—specimen thickness (nominal or actual, as
in complete section failure. The failure onset can occur in
specified), mm [in.]. compression in the unbuckled areas or in bending in the
buckled areas. In some cases ultimate failure may be preceded
3.3.14 w—overall width of buckling critical segment of
by delaminations induced by the post-buckled deformations.
specimen cross-section, mm [in.].
This ultimate failure mode is also referred to as “crippling” (or
4. Summary of Guide sometimes as “post-buckling failure”) even though the failure
mechanisms are different from those of metallic structure.
4.1 This guide provides information for designing test
Similar to metals, composite crippling failure stress can be
specimens to determine the local instability (buckling) force in
significantly higher than the initial local buckling stress.
one or more cross-section segments and the maximum post-
buckled force sustained by a composite specimen. The test 5.3 The analysis of sections or stiffened panels loaded in the
involves applying an axial compressive force to an unsup- post-buckling range becomes a geometrically nonlinear prob-
ported specimen until local buckling and subsequent cata- lem and, therefore, "conventional" plate buckling linear analy-
strophic failure (“crippling”) occurs. Users of this guide should sis cannot be used to estimate the crippling strength of
FIG. 1 Typical Stiffener Stress Distribution Prior and After Local
Buckling
D8511/D8511M − 23
composite plates. The analysis of laminated plates is further postbuckling range are shown in CMH-17 (1). Typical load-
complicated by high interlaminar stresses in the corners or at displacement curves of no-edge-free and one-edge-free tests
the free edge of the plate may trigger a premature failure.
are shown in CMH-17 (1).
Non-linear finite element methods have been used to predict
6.1.3 General factors that influence the mechanical response
the strength of post-buckled stiffened panels, but typically
of composite laminates and should therefore be reported
require some degree of test data for analysis calibration and
include the following: material, methods of material prepara-
validation. Empirical crippling curves are therefore typically
tion and lay-up, specimen stacking sequence, specimen
used for laminated composite stiffener design.
preparation, specimen conditioning, environment of testing,
5.4 Classical local buckling and crippling stress analysis of
specimen alignment and gripping, speed of testing, time held at
plate segment structural members is based on dividing the test temperature, void content, and volume percent reinforce-
section into individual plate elements having various boundary
ment.
conditions (for example, free edges and no free edges, as
6.1.4 Test Method D8510/D8510M does not provide an
shown in Figs. 2-4).
explicit specimen geometry or data reduction methodology
beyond calculation of local buckling and crippling stresses.
6. Test Specimen Design
The discussions below provide guidance on designing speci-
6.1 General:
men geometry to produce the required design data. The
6.1.1 Compressive loading of composite column type speci-
following three test procedures are covered in the test standard,
mens may exhibit one of four modes: (1) a compression
Fig. 5.
material strength failure, (2) an overall column flexural,
6.1.4.1 Procedure A – One Edge Free (OEF)—The test
torsional, and or flexural-torsional instability, (3) a local
specimen consists of a straight, constant cross-section, sym-
instability followed by a continued post-buckled force carrying
metric L-section with potted ends. Both segments of the
capability which eventually results in a material strength
L-section are intended to buckle at the same applied force.
failure, or (4) a combination of local and overall instability
When one leg buckles inward and the other leg buckles
followed by post-buckling failure. The first two modes are
outward, the instability mode is a combined flexural-torsional
outside the scope of Test Method D8510/D8510M. The latter
buckling mode which produces lower bound OEF results
two modes are categorized as crippling failure and is the
(7, 8). In rare cases both legs buckle the same direction, either
purpose of this guide and Test Method D8510/D8510M. Note
inwards or outwards and the torsional mode is not present.
that a combined local and global instability in a test specimen
6.1.4.2 Procedure B – No Edge Free (NEF)—The test
is not a desired response as it can produce conservative
specimen consists of a straight, constant cross-section, sym-
crippling results.
metric C-section with potted ends. The center “web” segment
6.1.2 The standard generic configurations for this testing,
of the C-channel is intended to buckle while the edge segments
Fig. 5, provide data for the two types of cross-section seg-
are intended to remain unbuckled up to the specimen failure
ments: one-edge-free and no-edge-free. Typical no-edge-free
and one-edge-free tests in progress with the specimens in the force.
FIG. 2 Plate Buckling (a) 4 Edges Supported (No Edge Free Condition) (b) 3 Edges Supported (One Edge Free Condition)
D8511/D8511M − 23
FIG. 3 Example One-Edge-Free Elements in Structural Stiffener Shapes
FIG. 4 Example No-Edge-Free Elements in Structural Stiffener Shapes
FIG. 5 Specimen Types
6.1.4.3 Procedure C – No Edge Free (NEF)—The test local buckling and crippling are provided in CMH-17 (1), and
specimen consists of a flat laminate specimen that is supported Fig. 6. Data is also sometimes plotted in normalized forms,
on the unloaded edges by V-groove fixture restraints and such as Fcc/Fcu vs b/t, or nondimensional form based on
loaded with a clamping fixture on each end. laminate stiffness parameters, as discussed in CMH-17 (1).
6.1.5 The initial local buckling behavior of composite plates
6.2 One-Edge Free (OEF) Specimen Design:
can be predicted fairly reliably with analytical or finite element
6.2.1 At least five types of specimens have been previously
methods; refer to (1) or (2). However, since local buckling
used for OEF crippling tests (Fig. 7):
stresses are obtained from the same test specimens used to
6.2.1.1 Flat plates with V-groove fixture on one edge,
generate crippling stresses, these empirical buckling results are
6.2.1.2 Symmetric L-angle sections (with two “legs” being
often also used to generate design curves.
OEF),
6.1.6 Tests have been conducted over the decades by a
6.2.1.3 Cruciform (“+”) sections (with four “legs” being
number of companies and research organizations using rela-
OEF),
tively narrow plates, with one supported and one free unloaded
6.2.1.4 Z-shaped sections (with two flanges being OEF),
edges ("one-edge-free", OEF) or with two supported unloaded
and
edges ("no-edge-free", NEF).
6.2.1.5 C-channel sections (with two flanges being OEF).
6.1.7 As discussed in 5.3, the post-buckling behavior of
composite plates is derived from empirical test data. This data 6.2.2 Some of the empirical OEF test data shown in
cc
is often graphed on a log-log plot as F vs b/t, similar to what CMH-17 comes from flat plate tests. However, these speci-
cc
is done for metal section F data. Example data plots for both mens have a tendency to slip out of the fixture V-groove on the
D8511/D8511M − 23
lcr cc
FIG. 6 Typical Composite Laminate F and F Curves vs b/t Ratio
symmetric L-angle sections, and this is the only test configu-
ration included in Test Method D8510/D8510M.
6.2.2.1 As stated in 6.1.4.1, buckling of a symmetric
L-angle specimen involves either a local flexural or flexural-
torsional instability mode.
6.2.3 As shown in Fig. 6, OEF data is typically obtained for
width-to-thickness (b/t) ratios between 8 and 40. With a b/t less
than ~ 8, depending on the material and layup, buckling does
not occur before ultimate compressive failure (as shown by
lcr cc
convergence of the F and F lines in the plot. Most stiffener
geometries do not have b/t ratios above 20, so test data may not
be needed for design purposes above that value.
6.2.4 The number of tests to conduct at different b/t values
is a function of the intended stiffener design space, which
includes the ranges of thicknesses, laminate layups, and b/t
values. The test matrix should consider at least the minimum
and maximum thickness values along with at least two or three
layups (covering the range of axial stiffnesses) over the b/t
range anticipated for structural design. Also, tests at different
FIG. 7 Historical Crippling Specimen Cross-Sections
environmental conditions may be necessary. Since there can be
a large number of unique configurations tested and the speci-
one unloaded edge after buckling. Also, this test configuration
mens relatively expensive, typically only small numbers of
does not adequately represent the unbuckled corners of actual
replicates (3-5) are tested. In general the laminate layup and
stiffener sections (results can be too conservative). Cruciform
thickness should be constant throughout the specimen.
sections a
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