ASTM D7616/D7616M-11(2023)
(Test Method)Standard Test Method for Determining Apparent Overlap Splice Shear Strength Properties of Wet Lay-Up Fiber-Reinforced Polymer Matrix Composites Used for Strengthening Civil Structures
Standard Test Method for Determining Apparent Overlap Splice Shear Strength Properties of Wet Lay-Up Fiber-Reinforced Polymer Matrix Composites Used for Strengthening Civil Structures
SIGNIFICANCE AND USE
5.1 Overlap splices are used in field applications of FRP composites when site conditions prohibit continuous access to a structural element or when the specified length of the FRP composite is such that saturation and placement of the entire length would be cumbersome. This method can be used as a quality control mechanism for ensuring that overlap splices constructed under field conditions meet or exceed the requirements established by the design engineer or FRP system manufacturer. Both the saturant mixing and fiber saturation method can be verified for wet-layup FRP systems.
5.2 Caution is recommended when interpreting apparent shear strength results obtained from this method. Single shear lap splices develop non-uniform shear stress distributions within the overlap splice region during testing. Additional guidance on the interpretation and use of results obtained from lap shear testing is found in D4896.
5.3 This test method focuses on the FRP material itself, irrespective of gripping method. Therefore, strengths resulting from failure or pullout at either grip are disregarded. The strength measurements are based solely on test specimens that fail in the gauge section (away from the grips) or at the splice.
SCOPE
1.1 This test method describes the requirements for sample preparation and tensile testing of single-lap shear splices formed with fiber-reinforced polymer (FRP) composite materials commonly used for strengthening of structures made of materials such as metals, timber, masonry, and reinforced concrete. The objective of this method is to determine the apparent shear strength of an overlap splice joint through the application of a far-field tensile force. The method applies to wet lay-up FRP material systems fabricated on site or in a laboratory setting. The FRP composite may be of either unidirectional (0°) or cross-ply (0/90 type) reinforcement. For cross-ply laminates, the construction may be achieved using multiple-layers of unidirectional fibers at either 0 or 90°, or one or more layers of stitched or woven 0/90 fabrics. The composite material forms are limited to continuous fiber or discontinuous fiber-reinforced composites in which the laminate is balanced and symmetric with respect to the test direction. The method is often used to determine the length of the overlap splice needed to ensure that a tension failure occurs in the material away from the splice rather than the splice connection itself.
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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.4 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.
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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: D7616/D7616M − 11 (Reapproved 2023)
Standard Test Method for
Determining Apparent Overlap Splice Shear Strength
Properties of Wet Lay-Up Fiber-Reinforced Polymer Matrix
Composites Used for Strengthening Civil Structures
This standard is issued under the fixed designation D7616/D7616M; 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 responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter-
1.1 This test method describes the requirements for sample
mine the applicability of regulatory limitations prior to use.
preparation and tensile testing of single-lap shear splices
1.4 This international standard was developed in accor-
formed with fiber-reinforced polymer (FRP) composite mate-
dance with internationally recognized principles on standard-
rials commonly used for strengthening of structures made of
ization established in the Decision on Principles for the
materials such as metals, timber, masonry, and reinforced
Development of International Standards, Guides and Recom-
concrete. The objective of this method is to determine the
mendations issued by the World Trade Organization Technical
apparent shear strength of an overlap splice joint through the
Barriers to Trade (TBT) Committee.
application of a far-field tensile force. The method applies to
wet lay-up FRP material systems fabricated on site or in a
2. Referenced Documents
laboratory setting. The FRP composite may be of either
2.1 ASTM Standards:
unidirectional (0°) or cross-ply (0/90 type) reinforcement. For
D883 Terminology Relating to Plastics
cross-ply laminates, the construction may be achieved using
D3039/D3039M Test Method for Tensile Properties of Poly-
multiple-layers of unidirectional fibers at either 0 or 90°, or one
mer Matrix Composite Materials
or more layers of stitched or woven 0/90 fabrics. The compos-
D3878 Terminology for Composite Materials
ite material forms are limited to continuous fiber or discon-
D4896 Guide for Use of Adhesive-Bonded Single Lap-Joint
tinuous fiber-reinforced composites in which the laminate is
Specimen Test Results
balanced and symmetric with respect to the test direction. The
D5229/D5229M Test Method for Moisture Absorption Prop-
method is often used to determine the length of the overlap
erties and Equilibrium Conditioning of Polymer Matrix
splice needed to ensure that a tension failure occurs in the
Composite Materials
material away from the splice rather than the splice connection
D5687/D5687M Guide for Preparation of Flat Composite
itself.
Panels with Processing Guidelines for Specimen Prepara-
1.2 The values stated in either SI units or inch-pound units
tion
are to be regarded separately as standard. The values stated in
D7565/D7565M Test Method for Determining Tensile Prop-
each system may not be exact equivalents; therefore, each
erties of Fiber Reinforced Polymer Matrix Composites
system shall be used independently of the other. Combining
Used for Strengthening of Civil Structures
values from the two systems may result in non-conformance
E6 Terminology Relating to Methods of Mechanical Testing
with the standard.
E122 Practice for Calculating Sample Size to Estimate, With
1.2.1 Within the text, the inch-pound units are shown in
Specified Precision, the Average for a Characteristic of a
brackets.
Lot or Process
1.3 This standard does not purport to address all of the
E177 Practice for Use of the Terms Precision and Bias in
safety concerns, if any, associated with its use. It is the
ASTM Test Methods
E456 Terminology Relating to Quality and Statistics
This test method is under the jurisdiction of ASTM Committee D30 on
Composite Materials and is the direct responsibility of Subcommittee D30.10 on
Composites for Civil Structures. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved April 1, 2023. Published April 2023. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 2011. Last previous edition approved as D7616/D7616M – 11(2017). Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/D7616_D7616M-11R23. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7616/D7616M − 11 (2023)
2.2 Other Standards: 3.3.7 L'—length of the overlap splice region
DOT/FAA/AR-01/33 Investigation of Thick Bondline Adhe-
3.3.8 n—number of specimens.
sive Joints, June 2001
3.3.9 P—force carried by test specimen.
DOT/FAA/AR-02/97 Shear Stress-Strain Data for Structural
max
3.3.10 P —maximum tensile force.
Adhesives, November 2002
3.3.11 w—coupon width.
3. Terminology
3.3.12 V*—apparent shear strength of the overlap splice per
3.1 Definitions—Terminology D3878 defines terms relating unit width for the L' under consideration.
to high-modulus fibers and their composites. Terminology
4. Summary of Test Method
D883 defines terms relating to plastics. Terminology E6 defines
terms relating to mechanical testing. Terminology E456 and 4.1 Overlap splice specimens are prepared using a wet
Practice E177 define terms relating to statistics. In the event of
lay-up procedure. Wet lay-up material may be prepared in a
a conflict between terms, Terminology D3878 shall have laboratory or field setting, as the testing objectives dictate. For
precedence over the other standards.
testing in single shear, two thin, flat strips of material having a
nominally constant cross section are joined together with a
3.2 Definitions of Terms Specific to This Standard:
specified overlap and allowed to cure. The cured specimen is
3.2.1 nominal value, n—a value, existing in name only,
mounted in the grips of a mechanical testing machine and
assigned to a measurable property for the purpose of conve-
monotonically loaded in tension while force is recorded. The
nient designation. Tolerances may be applied to a nominal
following items are reported for each specimen: ultimate force
value to define an acceptable range for the property.
at failure, failure mode, and the apparent shear strength per unit
3.2.2 screed, v—to move a flat rule along the top of a
width at failure.
saturated laminate to level the top of the laminate and
simultaneously remove excess resin.
5. Significance and Use
3.2.3 wet lay-up FRP composite, n—an FRP composite
5.1 Overlap splices are used in field applications of FRP
material fabricated by manually impregnating dry fibers with a
composites when site conditions prohibit continuous access to
matrix of polymeric resin. Semi-automated processes such as
a structural element or when the specified length of the FRP
machine-aided wetting of fabrics before placement or vacuum
composite is such that saturation and placement of the entire
aided impregnation of laminates after placement are considered
length would be cumbersome. This method can be used as a
part of wet lay-up FRP. For civil infrastructure strengthening
quality control mechanism for ensuring that overlap splices
applications, the degree of control over the volume fractions of
constructed under field conditions meet or exceed the require-
fibers, matrix, and voids as well as the overall cross-sectional
ments established by the design engineer or FRP system
geometry in wet lay-up FRP composites may be less than that
manufacturer. Both the saturant mixing and fiber saturation
for shop manufactured FRP composites on account of the
method can be verified for wet-layup FRP systems.
manual process. For strengthening applications, wet lay-up
5.2 Caution is recommended when interpreting apparent
FRP composites are typically applied to the substrate at the
shear strength results obtained from this method. Single shear
same time the dry fiber is impregnated. The impregnating resin
lap splices develop non-uniform shear stress distributions
may act as the saturant for the FRP composite as well as the
within the overlap splice region during testing. Additional
bonding agent between the composite reinforcement and the
guidance on the interpretation and use of results obtained from
substrate. Wet lay-up specimens may be fabricated in either a
lap shear testing is found in D4896.
field or a laboratory setting.
5.3 This test method focuses on the FRP material itself,
3.3 Symbols:
irrespective of gripping method. Therefore, strengths resulting
3.3.1 F*—strength of FRP laminate per unit width.
from failure or pullout at either grip are disregarded. The
3.3.2 h —laminate thickness measured outside of the over-
strength measurements are based solely on test specimens that
lap splice on the bottom (flat) laminate.
fail in the gauge section (away from the grips) or at the splice.
3.3.3 h —laminate thickness measured outside of the over-
6. Interferences
lap splice on the top (kinked) laminate.
6.1 A summary of the interferences, specifically material
3.3.4 h —laminate thickness measured within the overlap
and specimen preparation, gripping, system alignment, and
splice region.
edge effects in cross-ply laminates, are presented in D3039/
3.3.5 h' —the reference thickness of a fiber, fabric or
D3039M.
preform layer without resin, measured outside of the overlap
6.2 Additional interferences may arise from lack of control
splice.
in wet lay-up specimen preparation procedures outlined in
3.3.6 L—entire length of the overlap splice specimen in-
8.3.1. Specimen variations in resin content, ply thickness, void
cluding the portion dedicated to gripping.
content and degree of cure may contribute to variability in test
results.
6.3 Construction of single lap-splice samples using wet-lay
Available at the Federal Aviation Administration William J. Hughes Technical
Center Full-Text Technical Reports page: http://207.67.203.68/F10011. FRP will result in kinked fibers for the top laminate (see Fig.
D7616/D7616M − 11 (2023)
1). The effects of this kink on lap shear results will be overlap splice lengths. Variation in the overlap splice length as
magnified as the thickness, h and h , of the FRP increases. measured along both edges of the specimen shall be no greater
1 2
This kink may also result in laminate failure outside the region than 6 5 %.
of the bondline and the severity of the kink can impart moment
8.2.2 Specimen Width—Minimum specimen width for uni-
loading to the bonded joint.
directional wet lay-up FRP specimens shall be 25 mm [1.0 in.].
Minimum width for cross-ply specimens shall be 38 mm
6.4 Overlap splice length, L’, is identified in D4896, 5.3.2 as
[1.5 in.] for wet lay-up composites. Variation in specimen
a geometric parameter which affects apparent shear strength
width shall be no greater than 6 1 %.
properties obtained from overlap splice tests. The results
obtained using this test method are valid exclusively for the
8.3 Specimen Preparation:
overlap splice length under consideration.
8.3.1 Wet Lay-up FRP—Make field-prepared specimens in a
6.5 If a supplementary adhesive material (for example,
manner similar to the actual field installation of the material. A
thickened epoxy tack coat) is used to promote bond between
polymer release film, typically 600 mm by 600 mm [24 in. by
composite layers within the overlap splice region, it should be
24 in.] is placed on a smooth, flat horizontal surface. The
noted that variations in the bond-line thickness may result in
release film shall be at least 0.076 mm [0.003 in.] thick and
different apparent shear strength values or different failure
made of a polymer that will not adhere to the resin used to
modes. The typically observed trend is that increasing bondline
impregnate the fibers. Usually, acetate and nylon are accept-
thickness results in decreased apparent shear strength (DOT/
able. Resin is first applied to the release film. The dimensions
FAA/AR-01/33 and DOT/FAA/AR-02/97).
of each ply should be no less than 150 mm by 300 mm [6 in. by
6.6 The fiber/ply orientation within the overlap splice region 12 in.] (or longer as required by the specimen size, see Fig. 2).
has also been shown to influence the apparent shear strength or In order to facilitate the construction of the overlap splice joint
failure mode, or both, in lap shear specimens (DOT/FAA/AR- and to ensure the desired overlap splice length, L', is obtained,
02/97). the width of the bottom laminate may be slightly larger (5 mm
to 10 mm) than the width of the top laminate. Any excess
6.7 The temperature and moisture conditions experienced
material present in the bottom laminate shall be removed and
by a specimen during curing and load testing can affect the
discarded during the specimen machining process described in
apparent shear strength of an overlap splice joint. Additional
8.3.4. The dry fibers are saturated or coated with the specified
guidance is provided in D3039/D3039M, 11.4.
amount of resin and placed on the release film. This can be
7. Apparatus done using a properly calibrated saturator machine or using a
manufacturer-specified fiber to resin weight ratio. The specified
7.1 Requirements for testing machines and instrumentation
number of plies at the specified angles (0 or 90°) for the bottom
are the same as those given in D3039/D3039M, Section 7.
laminate of the single lap splice are sequentially impregnated
with resin and stacked onto the release film using the specified
8. Sampling and Test Specimens
amount of resin per ply per unit area as in the actual
8.1 Sampling—Test at least five specimens per test condi-
installation. Using the flat edge of a small hand tool or a
tion unless valid results can be gained through the use of fewer
grooved roller, air bubbles are worked out of the material. The
specimens, such as in the case of a designed experiment. For
bubbles shall be worked out in the direction of the primary
statistically significant data, the procedures outlined in Practice
fibers to ensure that no damage is caused to the fibers. At this
E122 shall be consulted. Report the method of sampling.
point the specified number of plies for the top laminate of the
NOTE 1—If specimens are to undergo environmental conditioning to
lap splice are sequentially impregnated with resin and stacked
equilibrium, and are of such type or geometry that the weight change of
onto a second piece of release film. If a supplementary
the material cannot be properly measured by weighing t
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