ASTM D7337/D7337M-12(2019)

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: D7337/D7337M − 12 (Reapproved 2019)
Standard Test 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 D5229/D5229M Test Method for MoistureAbsorption Prop-
erties and Equilibrium Conditioning of Polymer Matrix
1.1 This test method outlines requirements for tensile creep
Composite Materials
rupture testing of fiber reinforced polymer matrix (FRP)
D7205/D7205M Test Method for Tensile Properties of Fiber
composite bars commonly used as tensile elements in
Reinforced Polymer Matrix Composite Bars
reinforced, prestressed, or post-tensioned concrete.
E4 Practices for Force Verification of Testing Machines
1.2 Data obtained from this test method are used in design
E6 Terminology Relating to Methods of Mechanical Testing
of FRPreinforcements under sustained loading. The procedure
E456 Terminology Relating to Quality and Statistics
for calculating the one-million hour creep-rupture capacity is
E1012 Practice for Verification of Testing Frame and Speci-
provided in Annex A1.
men Alignment Under Tensile and Compressive Axial
1.3 The values stated in either SI units or inch-pound units Force Application
are to be regarded separately as standard. Within the text, the
inch-pound units are shown in brackets. The values stated in 3. Terminology
each system are not exact equivalents; therefore, each system
3.1 Terminology in D3878 defines terms relating to high-
must be used independently of the other. Combining values
modulus fibers and their composites. Terminology in D883
from the two systems may result in nonconformance with the
defines terms relating to plastics. Terminology in E6 defines
standard.
terms relating to mechanical testing. Terminology in E456
1.4 This standard does not purport to address all of the
defines terms relating to statistics and the selection of sample
safety concerns, if any, associated with its use. It is the
sizes. In the event of a conflict between terms, Terminology in
responsibility of the user of this standard to establish appro-
D3878 shall have precedence over the other terminology
priate safety, health, and environmental practices and deter-
standards.
mine the applicability of regulatory limitations prior to use.
3.2 Definitions of Terms Specific to This Standard:
1.5 This international standard was developed in accor-
3.2.1 anchor, n—a protective device placed on each end of
dance with internationally recognized principles on standard-
a bar, between the bar and the grips of the tensile testing
ization established in the Decision on Principles for the
apparatus, to prevent grip-induced damage. Usually used on
Development of International Standards, Guides and Recom-
bars with irregular surfaces, as opposed to flat strips where
mendations issued by the World Trade Organization Technical
bonded tabs are more typical.
Barriers to Trade (TBT) Committee.
3.2.2 anchoring section, n—the end parts of the specimen
2. Referenced Documents
where an anchor is fitted to transmit the forces from the testing
apparatus to the test section.
2.1 ASTM Standards:
D883 Terminology Relating to Plastics
3.2.3 bar, n—a linear element, often with surface undula-
D3878 Terminology for Composite Materials
tions or a coating of particles that promote mechanical inter-
lock with concrete.
This test method is under the jurisdiction of ASTM Committee D30 on
3.2.4 creep, n—time-dependent deformation (or strain) un-
Composite Materials and is the direct responsibility of Subcommittee D30.10 on
der sustained force (or stress).
Composites for Civil Structures.
Current edition approved Feb. 1, 2019. Published February 2019. Originally
3.2.5 creep rupture, n—material failure caused by sustained
approved in 2007. Last previous edition approved in 2012 as D7337/D7337M – 12.
force (or stress) over time.
DOI: 10.1520/D7337_D7337M-12R19.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
3.2.6 creep rupture capacity, n—the force at which failure
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
occurs after a specified period of time from initiation of a
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. sustainedforce.Thepredictedforcecausingfailureat1million
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7337/D7337M − 12 (2019)
hours is referred to as the million-hour creep rupture capacity. tained stress, creep rupture of FRP bars may take place below
This capacity is determined by the method described in the the static tensile strength. Therefore, the creep rupture strength
Annex. is an important factor when determining acceptable stress
levelsinFRPbarsusedasreinforcementortendonsinconcrete
3.2.7 creep rupture strength, n—the stress causing failure
members designed to resist sustained loads. Creep rupture
after a specified period of time from initiation of a sustained
strength varies according to the type of FRP bars used.
force.
5.2 This test method measures the creep rupture time of
3.2.8 creep rupture time, n—the lapsed time between the
FRP bars under a given set of controlled environmental
start of a sustained force and failure of the test specimen.
conditions and force ratios.
3.2.9 failure, n—rupture of the bar under test into two
5.3 This test method is intended to determine the creep
separate pieces.
rupture data for material specifications, research and
3.2.10 force ratio, n—the ratio of a constant sustained force
development, quality assurance, and structural design and
applied to a specimen to its tensile capacity as determined
analysis. The primary test result is the million-hour creep
according to Test Method D7205/D7205M.
rupture capacity of the specimen.
3.2.11 grid, n—a two-dimensional (planar) or three-
5.4 Creep properties of reinforced, post-tensioned, or pre-
dimensional (spatial) rigid array of interconnected FRP bars
stressed concrete structures are important to be considered in
that form a contiguous lattice that can be used to reinforce
design. For FRP bars used as reinforcing bars or tendons, the
concrete. The lattice can be manufactured with integrally
creep rupture shall be measured according to the method given
connected bars or constructed of mechanically connected
herein.
individual bars. The grid bar elements have transverse dimen-
sions typically greater than 3 mm [0.12 in.].
6. Interferences
3.2.12 nominal cross-sectional area, n—a measure of cross-
6.1 Gripping—The method of gripping has been known to
sectional area of a bar, determined over at least one represen-
cause premature creep rupture in bars. Anchors, if used, shall
tative length, used to calculate stress.
be designed in such a way that the creep rupture capacity can
3.2.13 representative length, n—the minimum length of a
be achieved without excessive slip throughout the length of the
bar that contains a repeating geometric pattern that, placed
anchor during the test.
end-to-end, reproduces the geometric pattern of a continuous
6.2 System Alignment—Excessive bending may cause pre-
bar (usually used in reference to bars having surface undula-
mature failure. Every effort shall be made to eliminate bending
tions for enhancing interlock with concrete).
from the test system. Bending may occur due to misalignment
3.2.14 surface undulation, n—variation in the area,
of the bar within anchors or grips or associated fixturing, or
orientation, or shape of cross-section of a bar along its length,
from the specimen itself if improperly installed in the grips or
intended to enhance mechanical interlock between a bar and
if it is out-of-tolerance due to poor specimen preparation. See
concrete, made by any of a number of processes such as, for
Practice E1012 for verification of specimen alignment under
example, indentation, addition of extra materials, and twisting.
tensile loading.
3.2.15 test section, n—the portion of a specimen between
6.3 Measurement of Cross-Sectional Area—The nominal
the anchoring sections of the test specimen.
cross-sectional area of the bar is measured by immersing a
3.3 Symbols:
prescribed length of the specimen in water to determine its
a , b = empirical constants
1 1 buoyant weight. Bar configurations that trap air during immer-
A = nominal or standard cross-sectional area of a bar, see
sion (aside from minor porosity) cannot be assessed using this
Test Method D7205/D7205M
method.This method may not be appropriate for bars that have
F = stress carried by specimen at rupture
r
large variations in cross-sectional area along the length of the
P = force carried by specimen at rupture
r bar.
t = time, hours
6.4 Test Conditions—Creep rupture is highly dependent
Y = creep rupture trend line
c
upon environmental conditions such as, for example,
temperature, humidity, and chemical agents. Every effort shall
4. Summary of Test Method
be made to test FRP bars for creep rupture under tightly
4.1 This test method consists of measuring the time to
controlledandmonitoredconditions(seeSections7,10,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
5. Significance and Use 7.1 The testing apparatus shall be capable of applying and
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
variable is the size or type of FRP bars, magnitude of applied 7.2 Test Apparatus—Use a testing apparatus with a force
force, and duration of force application. Unlike steel reinforc- capacity in excess of the tensile capacity of the specimen and
ing bars or prestressing tendons subjected to significant sus- calibrated according to Practices E4.
D7337/D7337M − 12 (2019)
7.3 Anchors—Anchors, if used, shall be in accordance with 9. Test Matrix
Test Method D7205/D7205M.
9.1 The quasi-static tensile strength of the bars as deter-
7.4 Temperature Control—The temperature of the test envi-
mined by Test Method D7205/D7205M is used as a basis for
ronment shall be maintained at the specified temperature selecting the applied tensile forces for creep rupture tests. At
62°C [64 °F] during the test period. If no temperature is
each given force ratio—for example, 80 %, 70 %, 60 % of the
specified, maintain the temperature at 23 °C [73 °F].
tensile strength—the applied force must be maintained con-
stant until failure occurs while the time elapsed to rupture of
7.5 Environmental Test Chamber—An environmental test
each test specimen is recorded.
chamber may be required for test environments other than
NOTE 1—The selection of force ratios is dependent on the fiber
ambient testing laboratory conditions. For environments where
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
with less resistance to creep rupture (for example, glass FRP composite)
ing environmental conditions such as fluid exposure or relative
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 five 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-
ap
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