ASTM D7337/D7337M-07
(Test Method)Standard Test Method for Tensile Creep Rupture of Fiber Reinforced Polymer Matrix Composite Bars
Standard Test Method for Tensile Creep Rupture of Fiber Reinforced Polymer Matrix Composite Bars
SIGNIFICANCE AND USE
This method for investigating creep rupture of FRP bars is intended for use in laboratory tests in which the principal variable is the size or type of FRP bars, magnitude of applied force, and duration of force application. Unlike steel reinforcing bars or prestressing tendons subjected to significant sustained stress, creep rupture of FRP bars may take place below the static tensile strength. Therefore, the creep rupture strength is an important factor when determining acceptable stress levels in FRP bars used as reinforcement or tendons in concrete members designed to resist sustained loads. Creep rupture strength varies according to the type of FRP bars used.
This test method measures the creep rupture time of FRP bars under a given set of controlled environmental conditions and force ratios.
This test method is intended to determine the creep rupture data for material specifications, research and development, quality assurance, and structural design and analysis. The primary test result is the million-hour creep rupture capacity of the specimen.
Creep properties of reinforced, post-tensioned, or prestressed concrete structures are important to be considered in design. For FRP bars used as reinforcing bars or tendons, the creep rupture shall be measured according to the method given herein.
SCOPE
1.1 This test method outlines requirements for tensile creep rupture testing of fiber reinforced polymer matrix (FRP) composite bars commonly used as tensile elements in reinforced, prestressed, or post-tensioned concrete.
1.2 Data obtained from this test method are used in design of FRP reinforcements under sustained loading. The procedure for calculating the one-million hour creep-rupture capacity is provided in .
1.3 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.
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: D7337/D7337M − 07
StandardTest Method for
Tensile Creep Rupture of Fiber Reinforced Polymer Matrix
Composite Bars
This standard is issued under the fixed designation D7337/D7337M; 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 E456 Terminology Relating to Quality and Statistics
E1012 Practice for Verification of Testing Frame and Speci-
1.1 This test method outlines requirements for tensile creep
men Alignment Under Tensile and Compressive Axial
rupture testing of fiber reinforced polymer matrix (FRP)
Force Application
composite bars commonly used as tensile elements in
reinforced, prestressed, or post-tensioned concrete.
3. Terminology
1.2 Data obtained from this test method are used in design
3.1 Terminology in D3878 defines terms relating to high-
of FRPreinforcements under sustained loading. The procedure
modulus fibers and their composites. Terminology in D883
for calculating the one-million hour creep-rupture capacity is
defines terms relating to plastics. Terminology in E6 defines
provided in Annex A1.
terms relating to mechanical testing. Terminology in E456
defines terms relating to statistics and the selection of sample
1.3 The values stated in either SI units or inch-pound units
sizes. In the event of a conflict between terms, Terminology in
are to be regarded separately as standard. Within the text, the
D3878 shall have precedence over the other terminology
inch-pound units are shown in brackets. The values stated in
standards.
each system are not exact equivalents; therefore, each system
must be used independently of the other. Combining values
3.2 Definitions of Terms Specific to This Standard:
from the two systems may result in nonconformance with the
3.2.1 anchor, n—a protective device placed on each end of
standard.
a bar, between the bar and the grips of the tensile testing
apparatus, to prevent grip-induced damage. Usually used on
1.4 This standard does not purport to address all of the
bars with irregular surfaces, as opposed to flat strips where
safety concerns, if any, associated with its use. It is the
bonded tabs are more typical.
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
3.2.2 anchoring section, n—the end parts of the specimen
bility of regulatory limitations prior to use.
where an anchor is fitted to transmit the forces from the testing
apparatus to the test section.
2. Referenced Documents
3.2.3 bar, n—a linear element, often with surface undula-
2.1 ASTM Standards:
tions or a coating of particles that promote mechanical inter-
D883 Terminology Relating to Plastics
lock with concrete.
D3878 Terminology for Composite Materials
3.2.4 creep, n—time-dependent deformation (or strain) un-
D5229/D5229M Test Method for MoistureAbsorption Prop-
der sustained force (or stress).
erties and Equilibrium Conditioning of Polymer Matrix
3.2.5 creep rupture, n—material failure caused by sustained
Composite Materials
force (or stress) over time.
D7205/D7205M Test Method for Tensile Properties of Fiber
3.2.6 creep rupture capacity, n—the force at which failure
Reinforced Polymer Matrix Composite Bars
occurs after a specified period of time from initiation of a
E4 Practices for Force Verification of Testing Machines
sustainedforce.Thepredictedforcecausingfailureat1million
hours is referred to as the million-hour creep rupture capacity.
1 This capacity is determined by the method described in the
This test method is under the jurisdiction of ASTM Committee D30 on
Composite Materials and is the direct responsibility of Subcommittee D30.10 on Annex.
Composites for Civil Structures.
3.2.7 creep rupture strength, n—the stress causing failure
Current edition approved Aug. 1, 2007. Published September 2007. DOI:
after a specified period of time from initiation of a sustained
10.1520/D7337_D7337M-07.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
force.
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
3.2.8 creep rupture time, n—the lapsed time between the
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. start of a sustained force and failure of the test specimen.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7337/D7337M − 07
3.2.9 failure, n—rupture of the bar under test into two 5.2 This test method measures the creep rupture time of
separate pieces. FRP bars under a given set of controlled environmental
conditions and force ratios.
3.2.10 force ratio, n—the ratio of a constant sustained force
applied to a specimen to its tensile capacity as determined 5.3 This test method is intended to determine the creep
rupture data for material specifications, research and
according to Test Method D7205/D7205M.
development, quality assurance, and structural design and
3.2.11 grid, n—a two-dimensional (planar) or three-
analysis. The primary test result is the million-hour creep
dimensional (spatial) rigid array of interconnected FRP bars
rupture capacity of the specimen.
that form a contiguous lattice that can be used to reinforce
5.4 Creep properties of reinforced, post-tensioned, or pre-
concrete. The lattice can be manufactured with integrally
stressed concrete structures are important to be considered in
connected bars or constructed of mechanically connected
design. For FRP bars used as reinforcing bars or tendons, the
individual bars. The grid bar elements have transverse dimen-
creep rupture shall be measured according to the method given
sions typically greater than 3 mm [0.12 in.].
herein.
3.2.12 nominal cross-sectional area, n—a measure of cross-
sectional area of a bar, determined over at least one represen-
6. Interferences
tative length, used to calculate stress.
6.1 Gripping—The method of gripping has been known to
3.2.13 representative length, n—the minimum length of a
cause premature creep rupture in bars. Anchors, if used, shall
bar that contains a repeating geometric pattern that, placed
be designed in such a way that the creep rupture capacity can
end-to-end, reproduces the geometric pattern of a continuous
be achieved without excessive slip throughout the length of the
bar (usually used in reference to bars having surface undula-
anchor during the test.
tions for enhancing interlock with concrete).
6.2 System Alignment—Excessive bending may cause pre-
3.2.14 surface undulation, n—variation in the area,
mature failure. Every effort shall be made to eliminate bending
orientation, or shape of cross-section of a bar along its length, from the test system. Bending may occur due to misalignment
intended to enhance mechanical interlock between a bar and
of the bar within anchors or grips or associated fixturing, or
concrete, made by any of a number of processes such as, for from the specimen itself if improperly installed in the grips or
example, indentation, addition of extra materials, and twisting.
if it is out-of-tolerance due to poor specimen preparation. See
Practice E1012 for verification of specimen alignment under
3.2.15 test section, n—the portion of a specimen between
tensile loading.
the anchoring sections of the test specimen.
6.3 Measurement of Cross-Sectional Area—The nominal
3.3 Symbols:
cross-sectional area of the bar is measured by immersing a
a , b = empirical constants
1 1
prescribed length of the specimen in water to determine its
A = nominal or standard cross-sectional area of a bar, see
buoyant weight. Bar configurations that trap air during immer-
Test Method D7205/D7205M
sion (aside from minor porosity) cannot be assessed using this
F = stress carried by specimen at rupture
method.This method may not be appropriate for bars that have
r
P = force carried by specimen at rupture large variations in cross-sectional area along the length of the
r
bar.
t = time, hours
Y = creep rupture trend line 6.4 Test Conditions—Creep rupture is highly dependent
c
upon environmental conditions such as, for example,
4. Summary of Test Method temperature, humidity, and chemical agents. Every effort shall
be made to test FRP bars for creep rupture under tightly
4.1 This test method consists of measuring the time to
controlled and monitored conditions (see Sections 7, 10 and 11
rupture of a bar subjected to a constant tensile force. Multiple
for requirements).
force levels are specified by the method so that a relationship
between force and time-to-failure can be derived.
7. Apparatus
7.1 The testing apparatus shall be capable of applying and
5. Significance and Use
maintaining a force on the specimen within 61 % of the
5.1 This method for investigating creep rupture of FRPbars desired sustained force.
is intended for use in laboratory tests in which the principal
7.2 Test Apparatus—Use a testing apparatus with a force
variable is the size or type of FRP bars, magnitude of applied
capacity in excess of the tensile capacity of the specimen and
force, and duration of force application. Unlike steel reinforc-
calibrated according to Practices E4.
ing bars or prestressing tendons subjected to significant sus-
7.3 Anchors—Anchors, if used, shall be in accordance with
tained stress, creep rupture of FRP bars may take place below
Test Method D7205/D7205M.
the static tensile strength. Therefore, the creep rupture strength
is an important factor when determining acceptable stress 7.4 Temperature Control—The temperature of the test envi-
levelsinFRPbarsusedasreinforcementortendonsinconcrete ronment shall be maintained at the specified temperature 62°C
members designed to resist sustained loads. Creep rupture [64°F] during the test period. If no temperature is specified,
strength varies according to the type of FRP bars used. maintain the temperature at 23°C [73°F].
D7337/D7337M − 07
7.5 Environmental Test Chamber—An environmental test stant until failure occurs while the time elapsed to rupture of
chamber may be required for test environments other than each test specimen is recorded.
ambient testing laboratory conditions. For environments where NOTE 1—The selection of force ratios is dependent on the fiber
architecture and fiber volume fraction for the bar. Material systems with a
temperature is specified, the chamber shall be capable of
high resistance to creep rupture (for example, carbon FRPcomposite) will
maintaining the required temperature to within 62°C [64°F].
necessitate the selection of closely-spaced force ratios at stress levels
In addition, the chamber may have to be capable of maintain-
approaching 100 % of the quasi-static tensile strength. Material systems
ing environmental conditions such as fluid exposure or relative
with less resistance to creep rupture (for example, glass FRP composite)
will necessitate the selection of widely-spaced force ratios.
humidity during the test. For environments where relative
humidity is specified, the chamber shall be capable of main-
9.2 A minimum of four force ratios are required (see Fig.
taining the required humidity to within 610 %RH.
A1.1 for example). A minimum of 5 valid test results are
required for each force ratio. For the entire group of tests
8. Sampling and Test Specimens
reported, the range between the longest and shortest recorded
rupture times shall be at least three decades. Data from
8.1 Specimens shall be representative of the lot or batch
specimens that break before the applied tensile force is fully
being tested. For grid-type FRP specimens, linear test speci-
applied to the specimen shall be disregarded.
mens may be prepared by cutting away extraneous material in
such a way as not to affect the performance of the part to be
NOTE 2—It is suggested that additional specimens be tested at each
used. Leaving a minimum 2 mm [0.08 in.] projection of the
force ratio, especially for those force ratios that require long times to
cross bars is recommended. In the test section of the specimen,
rupture.
no postproduction machining, abrading, or other such process-
9.2.1 The highest force ratio shall be selected such that at
ing is permitted. Such processing may be used in the anchoring
least four specimens in this group ruptures at a time of greater
sections to promote bond of the rod to the anchoring device.
than 1 h.
8.2 During the sampling and preparation of test specimens,
NOTE 3—The highest force is specified with the aim of minimizing the
all deformation, heating, outdoor exposure to ultraviolet light,
effects of the initial loading ramp on the creep rupture time.
and other conditions possibly causing changes to the material
9.2.2 The lowest force ratio shall be selected such that at
properties of the specimen shall be avoided, unless these
least one specimen in this group ruptures at a time of greater
conditions are specified as part of the test procedure.
than 8000 h.
8.3 The length of the specimen shall be in accordance with
Test Method D7205/D7205M. NOTE 4—The lowest force is specified with the aim of limiting the
extent of extrapolation required to determine the one million hour creep
8.4 The cross-sectional area of the specimen shall be deter-
rupture capacity.
mined in accordance with either of the two methods described
9.2.3 The remaining force ratios shall be roughly equally
in Test Method D7205/D7205M: nominal area or standard
spaced in relation to the highest and lowest force ratios
area.
determined in 9.2.1 and 9.2.2, respectively.
8.5 If a specimen fails at or slips out of an anchoring
section, an additional test shall be performed on a separate
10. Conditioning
specimen taken from the same lot as the failed specimen.
10.1 The recommended pre-test condition is effective mois-
8.6 A100 mm [4 in.] long specimen of the bar shall be used
ture equilibrium at a specific relative humidity as established
to determine the average moisture content of the as-received or
byTest Method D5229/D5229M; however, if the test requestor
as-conditioned bar before the start of creep rupture testing.The
doesnotexplicitlyspecifyapre-testconditioningenvironment,
average moisture content shall be determined according to
no conditioning is required and the specimens may be tested as
Procedure D, section 3.2.2, of Test Method D5229/D5229M.
prepared.
8.7 A100 mm [4 in.] long traveler specimen of the same
10.2 The pre-test specimen conditioning process, to include
cross-section geometry and appropriate size (but without
specified environmental exposure levels and resulting moisture
anchors) shall
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