ASTM D6484/D6484M-99e1
(Test Method)Standard Test Method for Open-Hole Compressive Strength of Polymer Matrix Composite Laminates
Standard Test Method for Open-Hole Compressive Strength of Polymer Matrix Composite Laminates
SCOPE
1.1 This test method determines the open-hole compressive strength of multidirectional polymer matrix composite laminates reinforced by high-modulus fibers. 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. The range of acceptable test laminates and thicknesses are described in 8.2.1.
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.
1.2 The values stated in either SI units or inch-pound units are to be regarded separately as standard. Within the text the inch-pound units are shown in brackets. The values stated in each system are not exact equivalents; therefore, each system must be used independently of the other. Combining values from the two systems may result in nonconformance with the standard.
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Designation: D 6484/D 6484M – 99
Standard Test Method for
Open-Hole Compressive Strength of Polymer Matrix
Composite Laminates
This standard is issued under the fixed designation D 6484/D 6484M; 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 (e) indicates an editorial change since the last revision or reapproval.
e NOTE—The designation was editorially corrected to make it a dual designation in November 2000.
1. Scope Composites by Matrix Digestion
D 3878 Terminology of High-Modulus Reinforcing Fibers
1.1 This test method determines the open-hole compressive
and Their Composites
strength of multidirectional polymer matrix composite lami-
D 5229/D 5229M Test Method for Moisture Absorption
nates reinforced by high-modulus fibers. The composite mate-
Properties and Equilibrium Conditioning of Polymer Ma-
rial forms are limited to continuous-fiber or discontinuous-fiber
trix Composite Materials
(tape or fabric, or both) reinforced composites in which the
D 5687/D 5687M Guide for Preparation of Flat Composite
laminate is balanced and symmetric with respect to the test
Panels with Processing Guidelines for Specimen Prepara-
direction. The range of acceptable test laminates and thick-
tion
nesses are described in 8.2.1.
E 4 Practices for Force Verification of Testing Machines
1.2 This standard does not purport to address all of the
E 6 Terminology Relating to Methods of Mechanical Test-
safety concerns, if any, associated with its use. It is the
ing
responsibility of the user of this standard to establish appro-
E 83 Practice for Verification and Classification of Exten-
priate safety and health practices and determine the applica-
someters
bility of regulatory limitations prior to use.
E 122 Practice for Choice of Sample Size to Estimate a
1.3 The values stated in either SI units or inch-pound units
Measure of Quality for a Lot or Process
are to be regarded separately as standard. Within the text the
E 177 Practice for Use of the Terms Precision and Bias in
inch-pound units are shown in brackets. The values stated in
ASTM Test Methods
each system are not exact equivalents; therefore, each system
E 456 Terminology Relating to Quality and Statistics
must be used independently of the other. Combining values
E 691 Practice for Conducting an Interlaboratory Study to
from the two systems may result in nonconformance with the
Determine the Precision of a Test Method
standard.
E 1309 Guide for Identification of Composite Materials in
2. Referenced Documents Computerized Material Property Databases
E 1434 Guide for Recording Mechanical Test Data of Fiber-
2.1 ASTM Standards:
Reinforced Composite Materials in Databases
D 792 Test Methods for Density and Specific Gravity (Rela-
E 1471 Guide for Identification of Fibers, Fillers, and Core
tive Density) of Plastics by Displacement
Materials in Computerized Material Property Databases
D 883 Terminology Relating to Plastics
D 2584 Test Method for Ignition Loss of Cured Reinforced
3. Terminology
Resins
3.1 Definitions—Terminology D 3878 defines terms relating
D 2734 Test Method for Void Content of Reinforced Plas-
to high-modulus fibers and their composites. Terminology
tics
D 883 defines terms relating to plastics. Terminology E 6
D 3039/D 3039M Test Method for Tensile Properties of
defines terms relating to mechanical testing. Terminology
Polymer Matrix Composite Materials
E 456 and Practice E 177 define terms relating to statistics. In
D 3171 Test Method for Fiber Content of Resin-Matrix
the event of a conflict between terms, Terminology D 3878
shall have precedence over the other terminologies.
3.2 Definitions of Terms Specific to This Standard:
This test method is under the jurisdiction of ASTM Committee D30 on
Composite Materials and is the direct responsibility of Subcommittee D30.05 on
NOTE 1—If the term represents a physical quantity, its analytical
Structural Test Methods.
Current edition approved Dec. 10, 1999. Published March 2000.
Annual Book of ASTM Standards, Vol 08.01.
3 5
Annual Book of ASTM Standards, Vol 08.02. Annual Book of ASTM Standards, Vol 03.01.
4 6
Annual Book of ASTM Standards, Vol 15.03. Annual Book of ASTM Standards, Vol 14.02.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
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D 6484/D 6484M – 99
dimensions are stated immediately following the term (or letter symbol) in
x¯—mean or average (estimate of mean) of a sample popu-
fundamental dimension form, using the following ASTM standard sym-
lation for a given property
bology for fundamental dimensions, shown within square brackets: [M]
s—normal stress
for mass, [L] for length, [T] for time, [u] for thermodynamic temperature,
and [nd] for nondimensional quantities. Use of these symbols is restricted
4. Summary of Test Method
to analytical dimensions when used with square brackets, as the symbols
may have other definitions when used without the brackets.
4.1 A uniaxial compression test of a balanced, symmetric
laminate is performed with a centrally located hole. Edge-
3.2.1 nominal value, n—a value, existing in name only,
mounted extensometer displacement transducers are optional.
assigned to a measurable property for the purpose of conve-
Ultimate strength is calculated based on the gross cross-
nient designation. Tolerances may be applied to a nominal
sectional area, disregarding the presence of the hole. While the
value to define an acceptable range for the property.
hole causes a stress concentration and reduced net section, it is
3.2.2 principal material coordinate system, n—a coordinate
common aerospace practice to develop notched design allow-
system with axes that are normal to the planes of symmetry
able strengths based on gross section stress to account for
inherent to a material.
various stress concentrations (fastener holes, free edges, flaws,
3.2.3 Discussion—Common usage, at least for Cartesian
damage, and so forth) not explicitly modeled in the stress
axes (123, xyz, and so forth), generally assigns the coordinate
analysis.
system axes to the normal directions of planes of symmetry in
4.2 The test specimen is face-supported in a multipiece
order that the highest property value in a normal direction (for
bolted support fixture. The specimen/fixture assembly is
elastic properties, the axis of greatest stiffness) would be 1 or
clamped in hydraulic wedge grips and the load is sheared into
x, and the lowest (if applicable) would be 3 or z. Anisotropic
the support fixture and then sheared into the test specimen.
materials do not have a principal material coordinate system
4.3 The only acceptable failure mode for ultimate open-hole
due to the total lack of symmetry, while, for isotropic materials,
compressive strength is one which passes through the hole in
any coordinate system is a principal material coordinate
the test specimen.
system. In laminated composites, the principal material coor-
dinate system has meaning only with respect to an individual
5. Significance and Use
orthotropic lamina. The related term for laminated composites
5.1 This test method is designed to produce notched com-
is “reference coordinate system.”
pressive strength data for structural design allowables, material
3.2.4 reference coordinate system, n—a coordinate system
specifications, research and development, and quality assur-
for laminated composites used to define ply orientations. One
ance. Factors that influence the notched compressive strength
of the reference coordinate system axes (normally the Carte-
and should therefore be reported include the following: mate-
sian x-axis) is designated the reference axis, assigned a
rial; methods of material fabrication; accuracy of lay-up;
position, and the ply principal axis of each ply in the laminate
laminate stacking sequence and overall thickness; specimen
is referenced relative to the reference axis to define the ply
geometry; specimen preparation (especially of the hole); speci-
orientation for that ply.
men conditioning; environment of testing; specimen alignment
3.2.5 specially orthotropic, adj—a description of an ortho-
and gripping; speed of testing; void content; and volume
tropic material as viewed in its principal material coordinate
percent reinforcement. Properties that may be derived from this
system. In laminated composites, a specially orthotropic lami-
test method include open-hole (notched) compressive strength
nate is a balanced and symmetric laminate of the [0 /90 ]
i j ns
(OHC).
family as viewed from the reference coordinate system, such
that the membrane-bending coupling terms of the laminate
6. Interferences
constitutive relation are zero.
6.1 Hole Preparation—Because of the dominating presence
3.3 Symbols:
of the notch, and the lack of need to measure the material
A—cross-sectional area of a coupon
response, results from this test method are relatively insensitive
CV—coefficient of variation statistic of a sample population
to parameters that would be of concern in an unnotched
for a given property (in percent)
compressive property test. However, since the notch dominates
B —edgewise percent bending
z
the strength, consistent preparation of the hole without damage
D—hole diameter
to the laminate is important to meaningful results. Damage
h—coupon thickness
caused by hole preparation will affect strength results. Some
n—number of coupons per sample population
types of damage, such as delaminations, can blunt the stress
N—number of plies in laminate under test
concentration caused by the hole, increasing the load-carrying
ohcu
F —ultimate open hole (notched) compressive strength
x
capacity of the coupon and the calculated strength.
in the test direction
6.2 Geometry—Results are affected by the ratio of specimen
P —maximum load carried by test coupon before failure
max
width to hole diameter; this ratio should be maintained at 6,
S —standard deviation statistic of a sample population for
unless the experiment is investigating the influence of this
n–1
a given property
ratio. Results may also be affected by the ratio of hole diameter
w—coupon width
to thickness; the preferred ratio is the range from 1.5 to 3.0
x —test result for an individual coupon from the sample unless the experiment is investigating the influence of this
population for a given property ratio. Results may also be affected by the ratio of ungripped
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D 6484/D 6484M – 99
specimen length to specimen width; this ratio should be or gage capable of determining the hole diameter to 625 μm
maintained at 2.7, unless the experiment is investigating the [60.001 in.] is required.
influence of this ratio. 7.2 Support Fixture—The fixture is a face-supported com-
6.3 Support Fixture—Results are affected by the amount of pressive test fixture as shown in Fig. 1. The fixture consists of
lateral pressure applied to the test specimen by the support two short-grip/long-grip assemblies, two support plates, and
fixture. Sources of variation in this lateral pressure include stainless steel shims as required to maintain a nominally zero
fixture bolt torque, hydraulic gripping pressure, and fixture (0.00- to 0.12-mm [0.000- to 0.005-in.] tolerance) gap between
shimming choices, and should be controlled and reported as support plates and long grips. If this gap does not meet the
required in the Procedure and Report sections. minimum requirement, shim the contact area between the
6.4 Material Orthotropy—The degree of laminate orthot- support plate and the short grip with stainless steel shim stock.
ropy strongly affects the failure mode and measured OHC If the gap is too large, shim between the support plate and the
strength. Valid OHC strength results should only be reported long grip, holding the shim stock on the support plate with
when appropriate failure modes are observed, in accordance tape. Fig. 2 shows shim requirements. The fixture should be
with 11.10. checked for conformity to engineering drawings. Each short-
6.5 Thickness Scaling—Thick composite structures do not grip/long-grip assembly is line-drilled as shown in Figs. 3 and
necessarily fail at the same strengths as thin structures with the 4 and must be used as a matched set. The threading of the
same laminate orientation (that is, strength does not always support plate is optional. Standard test specimens are 36 by 300
scale properly). Thus, data gathered using this test method may mm [1.5 by 12 in.]. The fixture is hydraulically gripped on each
not translate directly into equivalent thick-structure properties. end and the compressive load is sheared by means of friction
through the fixture and into the test specimen. A cutout exists
7. Apparatus
on both faces of the fixture for a thermocouple, fastener, or
7.1 Micrometers—The micrometer(s) shall use a 4- to 5-mm extensometer, if required by the requesting organization. The
[0.16- to 0.20-in.] nominal diameter ball-interface on irregular long and short fixtures have an undercut along the corner of the
surfaces such as the bag-side of a laminate, and a flat anvil specimen grip area so that specimens are not required to be
interface on machined edges or very smooth-tooled surfaces. chamfered and to avoid damage caused by the radius. The
The accuracy of the instrument(s) shall be suitable for reading fixtures also allow a slight clearance between the fixture and
to within 1 % of the sample width and thickness. For typical the gage section of the specimen, in order to minimize grip
specimen geometries, an instrument with an accuracy of 625 failures and friction effects. This fixture does not allow
μm [60.001 in.] is desirable for thickness measurement, while specimens to be end loaded.
an instrument with an accuracy of 676 μm [60.003 in.] is 7.2.1 Support Fixture Details—The detailed drawings for
desirable for width measurement. Additionally, a micrometer manufacturing the support fixture are contained in Figs. 5-12.
FIG. 1 Support Fixture Assembly
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D 6484/D 6484M – 99
NOTE 1—
FIG. 2 Support Fixture—Shim Requirements
(a) All dimensions in inches.
(b) The long grip and short grip should be part marked with a unique test
fixture assembly identification.
An optional threaded support plate is shown in Figs. 13 and 14, (c) Tolerance except as noted is linear 60.01 in.
FIG. 3 Support Fixture—Line Drilling Details (Inch-Pound
to be used instead of the support plate shown in Figs. 11 and 12
Version)
and the nuts called out in Fig. 1. Other fixtures that meet the
requirements of this section may be used (for example, M
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