ASTM D4896-01(2016)
(Guide)Standard Guide for Use of Adhesive-Bonded Single Lap-Joint Specimen Test Results
Standard Guide for Use of Adhesive-Bonded Single Lap-Joint Specimen Test Results
SIGNIFICANCE AND USE
4.1 Single-lap specimens are economical, practical, and easy to make. They are the most widely used specimens for development, evaluation, and comparative studies involving adhesives and bonded products, including manufacturing quality control.
4.2 Special specimens and test methods have been developed that yield accurate estimates of the true shear strength of adhesives. These methods eliminate or minimize many of the deficiencies of the thin-adherend single-lap specimens, but are more difficult to make and test. (See Test Methods D3983, D4027, D4562, and E229.)
4.3 The misuse of strength values obtained from such Test Methods or Practices as D906, D1002, D1144, D1151, D1183, D1780, D2294, D2295, D2339, D3163, D3164, D3165, D3434, D3528, D3632, and D5868, as allowable design-stress values for structural joints could lead to product failure, property damage, and human injury.
SCOPE
1.1 This guide is directed toward the safe and appropriate use of strength values obtained from test methods using single-lap adhesive joint specimens.
1.2 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.
1.3 The discussion focuses on shear strength as measured with small thin-adherend, single-lap specimens. Many factors, however, apply to shear modulus, tensile strength, and tensile modulus measured by small laboratory specimens in general. This discussion is limited to single-lap specimens and shear strength only for simplification.
General Information
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Standards Content (Sample)
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: D4896 − 01 (Reapproved 2016)
Standard Guide for
Use of Adhesive-Bonded Single Lap-Joint Specimen Test
Results
This standard is issued under the fixed designation D4896; 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.
INTRODUCTION
The true strength of an adhesive is a material property independent of the joint geometry, adherend
properties,andload,andisagoodstartingpointfordetermininganallowabledesignstress.Allowable
stresses in shear and tension are needed to design safe, efficient, adhesively bonded joints and
structures. The true shear strength, however, cannot be easily determined using single-lap specimens.
Many factors affect the apparent shear strength of an adhesive when measured with a small
laboratoryspecimen,andinparticular,withasingle-lapspecimen.Forexample,thefailureofatypical
single-lap specimen, is usually controlled by the tensile stress in the adhesive, and not by the shear
stress. The factors that control the tensile stress in lap-joint specimen, and thus, the apparent shear
strength are the size and shape of the specimen, the properties of the adherends, the presence of
internal stresses or flaws, and the changes that take place in the specimen due to adhesive cure and the
environment.Similarlythesefactorsaffecttheapparenttensilestrengthofanadhesiveinbutt-jointtest
specimens.
Due to the effects of these factors, the apparent shear strength obtained through measurements on
small laboratory specimens may vary widely from the true shear- or tensile-strength values needed to
determine allowable shear and tension design stresses.
Theobjectivesofthisguideare:todevelopanappreciationofthefactorsthatinfluencestrengthand
other stress measurements that are made with small laboratory test specimens; to foster the acceptable
uses of the widely used thin-adherend single-lap-joint test; and, specifically, to prevent misuse of the
test results.
1. Scope 2. Referenced Documents
1.1 This guide is directed toward the safe and appropriate 2.1 ASTM Standards:
use of strength values obtained from test methods using D896 Practice for Resistance of Adhesive Bonds to Chemi-
single-lap adhesive joint specimens. cal Reagents
D906 Test Method for Strength Properties of Adhesives in
1.2 The values stated in inch-pound units are to be regarded
Plywood Type Construction in Shear by Tension Loading
as standard. The values given in parentheses are mathematical
D907 Terminology of Adhesives
conversions to SI units that are provided for information only
D1002 Test Method for Apparent Shear Strength of Single-
and are not considered standard.
Lap-Joint Adhesively Bonded Metal Specimens by Ten-
1.3 The discussion focuses on shear strength as measured
sion Loading (Metal-to-Metal)
with small thin-adherend, single-lap specimens. Many factors,
D1144 Practice for Determining Strength Development of
however, apply to shear modulus, tensile strength, and tensile
Adhesive Bonds
modulus measured by small laboratory specimens in general.
D1151 Practice for Effect of Moisture and Temperature on
This discussion is limited to single-lap specimens and shear
Adhesive Bonds
strength only for simplification.
D1183 Practices for Resistance of Adhesives to Cyclic
ThisguideisunderthejurisdictionofASTMCommitteeD14onAdhesivesand
is the direct responsibility of Subcommittee D14.80 on Metal Bonding Adhesives. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved May 1, 2016. Published May 2016. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
ɛ1
approved in 1989. Last previous edition approved in 2008 as D4896 – 01 (2008) . Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/D4896-01R16. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D4896 − 01 (2016)
Laboratory Aging Conditions 3.4 strain—the unit change due to force, in the size or shape
D1780 Practice for Conducting Creep Tests of Metal-to- of a body referred to its original size or shape. Strain is a
Metal Adhesives nondimensional quantity, but is frequently expressed in inches
D2294 Test Method for Creep Properties of Adhesives in per inch, centimeters per centimeter, etc. (Refer to Terminol-
Shear by Tension Loading (Metal-to-Metal) ogy E6 for specific notes.)
D2295 Test Method for Strength Properties of Adhesives in 3.4.1 linear (tensile or compressive) strain—the change per
Shear by Tension Loading at Elevated Temperatures unit length due to force in an original linear dimension.
(Metal-to-Metal) 3.4.2 shear strain—thetangentoftheangularchange,dueto
D2339 Test Method for Strength Properties of Adhesives in force, between two lines originally perpendicular to each other
Two-Ply Wood Construction in Shear by Tension Loading through a point in a body.
D2919 Test Method for Determining Durability ofAdhesive
3.5 stress—the intensity at a point in a body of the internal
Joints Stressed in Shear by Tension Loading
forcesorcomponentsofforcethatactonagivenplanethrough
D3163 Test Method for Determining Strength ofAdhesively
the point. Stress is expressed as force per unit of area
Bonded Rigid Plastic Lap-Shear Joints in Shear by Ten-
(pounds-force per square inch, newtons per square millimetre,
sion Loading
etc.).
D3164 Test Method for Strength Properties of Adhesively
NOTE 1—As used in tension, compression, or shear tests prescribed in
Bonded Plastic Lap-Shear Sandwich Joints in Shear by
product specifications, stress is calculated on the basis of the original
Tension Loading
dimensions of the cross section of the specimen.
D3165 Test Method for Strength Properties of Adhesives in
3.5.1 normal stress—the stress component perpendicular to
Shear by Tension Loading of Single-Lap-Joint Laminated
the plane on which the forces act. Normal stress may be either:
Assemblies
3.5.1.1 compressive stress—normal stress due to forces
D3166 Test Method for Fatigue Properties of Adhesives in
directed toward the plane on which they act, or
Shear by Tension Loading (Metal/Metal)
3.5.1.2 tensile stress—normal stress due to forces directed
D3434 Test Method for Multiple-Cycle Accelerated Aging
away from the plane on which they act.
Test (Automatic Boil Test) for Exterior Wet Use Wood
3.5.1.2.1 Discussion—In single-lap specimen testing, the
Adhesives
plane on which the forces act is the bondline. Tensile stress is
D3528 Test Method for Strength Properties of Double Lap
sometimes used interchangeably, although incorrectly, with
Shear Adhesive Joints by Tension Loading
peel or cleavage stress. Peel and cleavage involve complex
D3632 Test Method for Accelerated Aging of Adhesive
tensile, compressive, and shear stress distributions, not just
Joints by the Oxygen-Pressure Method
tensile stress.
D3983 Test Method for Measuring Strength and Shear
3.5.2 shear stress—the stress component tangential to the
Modulus of Nonrigid Adhesives by the Thick-Adherend
plane on which the forces act.
Tensile-Lap Specimen
D4027 Test Method for Measuring Shear Properties of
3.6 Definitions of Terms Specific to This Standard:
Structural Adhesives by the Modified-Rail Test
3.6.1 allowable design stress—a stress to which a material
D4562 Test Method for Shear Strength of Adhesives Using can be subjected under service conditions with low probability
Pin-and-Collar Specimen
of mechanical failure within the design lifetime.
D5868 Test Method for Lap Shear Adhesion for Fiber 3.6.1.1 Discussion—Allowable design stress is obtained
Reinforced Plastic (FRP) Bonding
usually by multiplying the true shear strength of the material
E6 Terminology Relating to Methods of Mechanical Testing (or close approximation thereof) by various adjustment factors
E229 Test Method for Shear Strength and Shear Modulus of
for manufacturing quality control, load and environmental
Structural Adhesives (Withdrawn 2003) effects, and safety.
3.6.2 apparent shear strength—(in testing a single-lap
3. Terminology
specimen) the nominal shear stress at failure without regard for
3.1 Definitions: the effects of geometric and material effects on the nominal
shear stress. Often called the lap-shear or tensile-shear
3.1.1 The following terms are defined in accordance with
Terminologies D907 and E6. strength.
3.2 creep—the time-dependent increase in strain in a solid
3.6.3 average stress—(in adhesive testing) the stress calcu-
resulting from force.
lated by simple elastic theory as the load applied to the joint
dividedbythebondareawithouttakingintoaccounttheeffects
3.3 shear strength—the maximum shear stress which a
on the stress produced by geometric discontinuities such as
material is capable of sustaining. Shear strength is calculated
holes, fillets, grooves, inclusions, etc.
from the maximum load during a shear or torsion test and is
3.6.3.1 Discussion—The average shear and tensile stresses
based on the original dimensions of the cross section of the
are denoted by τ and σ respectively. (See 5.3.1.) (Average
specimen. (See apparent and true shear strength). avg avg
stress is the same as the preferred but less common term,
nominal stress, as defined in Terminology E6.)
3.6.4 cleavage stress—(in adhesive testing) a term used to
The last approved version of this historical standard is referenced on
www.astm.org. describe the complex distribution of normal and shear stresses
D4896 − 01 (2016)
present in an adhesive when a prying force is applied at one thickness to overlap length ratio of less than 1:5 is a reasonable
end of a joint between two rigid adherends. approximation of a thin adherend for epoxy-steel joints (1 and
2).
3.6.5 peel stress—(in adhesive testing) a term used to
3.6.11 true shear strength—the maximum uniform shear
describe the complex distribution of normal and shear stresses
stress which a material is capable of sustaining in the absence
present in an adhesive when a flexible adherend is stripped
of all normal stresses.
from a rigid adherend or another flexible adherend.
3.6.6 single-lap specimen—(in adhesive testing) a specimen
4. Significance and Use
made by bonding the overlapped edges of two sheets or strips
4.1 Single-lap specimens are economical, practical, and
of material, or by grooving a laminated assembly, as shown in
easy to make. They are the most widely used specimens for
Test Methods D2339 and D3165. In testing, a single-lap
development, evaluation, and comparative studies involving
specimen is usually loaded in tension at the ends.
adhesives and bonded products, including manufacturing qual-
NOTE 2—In the past this specimen has been referred to commonly as
ity control.
the tensile-shear- or the lap-shear-specimen. These names imply that this
4.2 Special specimens and test methods have been devel-
is a shear dominated joint, and that the measured strength is the shear
strength of the adhesive. This is not true for most uses of such specimens. oped that yield accurate estimates of the true shear strength of
(An exception would be where the adhesive being evaluated is so low in
adhesives. These methods eliminate or minimize many of the
strength as not to induce any bending in the adherends.) It is recom-
deficiencies of the thin-adherend single-lap specimens, but are
mended that, henceforth, this specimen be referred to as a single-lap
more difficult to make and test. (See Test Methods D3983,
specimen.
D4027, D4562, and E229.)
3.6.7 stress concentration—a localized area of higher than
4.3 The misuse of strength values obtained from such Test
average stress near a geometric discontinuity in a joint or
Methods or Practices as D906, D1002, D1144, D1151, D1183,
member (such as a notch, hole, void, or crack); or near a
D1780, D2294, D2295, D2339, D3163, D3164, D3165,
material discontinuity (such as a bonded joint or weld) when
D3434, D3528, D3632, and D5868, as allowable design-stress
the joint or member is under load.
values for structural joints could lead to product failure,
3.6.7.1 Discussion—In adhesive testing, the most common
property damage, and human injury.
and important discontinuities are the ends of the bonded
adherends and the interfaces between the adhesive and adher-
5. Considerations for the Analysis of Small Single-Lap
ends.
Specimen Test Results
3.6.8 stress concentration factor—the ratio of the stress at a
5.1 The true shear strength of an adhesive can be deter-
point in a stress concentration to the average stress.
mined only if normal stresses are entirely absent. These
3.6.9 thick adherend—(in adhesive testing) an adherend
conditions can be approached under special conditions, but not
used in a single-lap specimen that does not bend significantly in single-lap specimens made with the thin adherends normally
when a load is applied, resulting in relatively lower tension/
used in manufacturing and in most standard test specimens. In
normal stress at the ends of the overlap; and, more uniform most cases the tensile stress in the adhesive controls joint
normal and shear stress distributions in the adhesive compared
failure. As a consequence the single-lap specimen strength is
to a joint made with thin adherends and placed under the same unrelated to, and an unreliable measure of, the true shear
load.
strength of an adhesive (1 and 2).
3.6.9.1 Discussion—A thick adherend for a typical epoxy
5.2 Changes in adhesive volume during cure, the size of the
adhesive and steel joint is at least 0.25 in. (6.36 mm) thick
joint, the modulus of the adherends, and temperature or
when the overlap is 0.50 in. (12.7 mm), based on finite element
moisture shifts after cure, all affect the magnitude of the
analysis and mechanical tests (1 and 2). Objective criteria for
stresses imposed on an adhesive in service. The thermal
determining whether or not an adherend is thick are given in
conductivity and permeability of the adherends affect the
Test Method D3983.
extentofthermalormoisturesofteningandtherateofchemical
degradationoftheadhesiveinservice.Therefore,inadditionto
3.6.10 thin adherend—(in adhesive testing) an adherend
the problems stated in 5.1, the average stress at failure of small
used in a single-lap specimen that bends significantly, causing
single-lap specimens after a given exposure is an unreliable
significant tension/normal stresses in the adhesive at the ends
measure o
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