Designation:D5656−10
Standard Test Method for
Thick-Adherend Metal Lap-Shear Joints for Determination of the Stress-Strain Behavior of Adhesives in Shear by Tension Loading1
This standard is issued under thefixed designation D5656;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
1.1This test method covers the preparation and testing of thick-adherend lap-shear samples for the determination of the stress-strain behavior of adhesives.
1.2This test method covers data reduction and analysis of stress-strain curves obtained using thick-adherend lap-shear samples.
1.3The values stated in SI units are to be regarded as the standard.The inch-pound units in parentheses are for informa-tion only.
1.4This 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 appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.Specific precau-tionary statements are given in7.3.
2.Referenced Documents
2.1ASTM Standards:2
D907Terminology of Adhesives
D2651Guide for Preparation of Metal Surfaces for Adhesive Bonding
D4896Guide for Use of Adhesive-Bonded Single Lap-Joint Specimen Test Results
E4Practices for Force Verification of Testing Machines
3.Terminology
3.1Definitions:
3.1.1Many terms in this test method are defined in Termi-nology D907.
3.2Definitions of Terms Specific to This Standard:
3.2.1knee,n—inflection point on a load-deflection curve; the point at which plastic yielding of the adhesive begins to dominate the deformation response of the load-deflection curve.
3.2.2panel,n—two plates of a rigid material having the same dimensions that are adhesively bonded together on one face such that the thickness of the panel is approximately twice the thickness of each individual plate.
4.Summary of Test Method
4.1This test method consists of testing thick-adherend lap-shear samples whereby a tensile load is applied to the sample but the adhesive is placed in shear.Unlike Guide D4896,the adherends used in this standard test method are thick and rigid,peel forces are minimized and the shear stress-strain properties of the adhesive are obtained.Refer-enced data presents afinite element analysis of the thick-adherent metal lap shear specimen and calculates the effect of varying the adherent and adhesive stiffness.3User of this standard is cautioned that since the stress is not totally uniform across the over-lap of the specimen,factors such as adhesive stiffness,adherent stiffness and location of shear strain mea-surement along the length of the bond can affect the experi-mentally obtained load-displacement curve.3,4
N OTE1—The peel forces generated during testing are a function of the bending deformation in the adherends.Greater adherend stiffness results in less bending and smaller peel forces.
5.Significance and Use
5.1This test method can be used to determine the stress-strain properties of an adhesive in shear and to establish the proportional-limit of the stress-stain relationship.This data may be useful for the design and analysis of adhesively bonded joints.
1This test method is under the jurisdiction of ASTM Committee D14on Adhesives and is the direct responsibility of Subcommittee D14.80on Metal Bonding Adhesives
Current edition approved Oct.1,2010.Published October2010.Originally
approved in1995.Last previous edition approved in2004as D5656-04´1.DOI: 10.1520/D5656-10.
2For referenced ASTM standards,visit the ASTM website,,or contact ASTM Customer Service at For Annual Book of ASTM Standards volume information,refer to the standard’s Document Summary page on the ASTM website.
3Kassapoglou,C.and Adelmann,John C.,“KGR-1Thick Adherend Specimen Evaluation for the Determination of Adhesive Mechanical Properties,”23rd International SAMPE Conference,Oct.21–24,1991.
4Krieger,R.B.,Jr.,“Stiffness Characteristics of Structural Adhesives for Stress Analysis in Hostile Environment,”American Cyanamid Co.,Havre de Grace,MD, 1975.
Copyright©ASTM International,100Barr Harbor Drive,PO Box C700,West Conshohocken,PA19428-2959.United States
5.2This test method is not intended to determine adhesion characteristics of an adhesive to a particular substrate;rather this test method is intended to characterize the adhesive shear stress-strain properties that may be relevant for design consid-erations.
5.3This test method has been developed and applied using bonded aluminum adherends.At this time no assumptions regarding the validity of this test method with non-aluminum adherends can be made.
6.Apparatus
6.1Testing machine conforming to the requirements of Practices E4.Select the testing machine so that the breaking load of the specimens falls between15and85%of the full-scale capacity.Ensure that the machine is capable of maintaining a rate of loading of2455N(550lbf)/min,or,if the rate is dependent on cross-head motion,set the machine to approach this rate of loading.Use a suitable pair of self-aligning grips to hold the specimen.Ensure that the grips and attachments are so constructed that they will move into alignment with the test specimen as soon as the load is applied, so that the long axis of the test specimen will coincide with the
direction of the applied pull through the center line of the grip assembly.
editorial hand
N OTE2—The cross-head speed setting required to approach the specified loading rate is dependent on the modulus of the adherends and the adhesive being evaluated.
6.2Use two three-point displacement sensors,linear vari-able differential transformers(extensometers),with the capa-bility of measuring displacements in the adhesive bond overlap area and a sensitivity sufficient to measure displacements with an accuracy of1part/1000.
7.Sample Preparation
7.1Suitably prepare the bonding surfaces of two229by 229-mm(9by9-in.)by9.560.05-mm(0.37560.002-in.) rigid adherends,such as2024-T3aluminum,for the adhesive being used.For aluminum,solvent degreasing and acid etch-ing,such as Method G of Guide D2651,are recommended for removing the oxide coating from the aluminum surfaces to be bonded.
7.2Apply the adhesive in a uniform layer to one face of one of the adherend plates.In the case of paste adhesives and unsupportedfilm adhesives,metal wires or shims may be used to control the bondline thickness.In this case,take care to ensure that the shims are outside of the lap area or are located in the trim region around the panel perimeter so that they do not affect the test results.Place the other adherend plate on top of the adhesive-coated plate in accordance with Fig.1.To achieve the desired ad
hesive thickness,apply sufficient pres-sure to cause the adhesive toflow between the plates such that the plates are in contact with the shims if they are being used. Cure the adhesive in accordance with the manufacturer’s recommended practices for the adhesive being tested.
N OTE3—The use of glass beads in the adhesive to control the bondline thickness is not recommended,since their use will have an effect on the calculated values of modulus,strain,and strength.
7.3After cure,saw-cut25.4-mm(1.0-in.)wide test samples from the bonded panel,or if machined edges are preferred saw-cut the samples to27.5-mm widths and machine the saw cut edges to a sample width of25.4mm(1.0in.).Use an end mill to machine notches through the glue line in accordance with Fig.2.Drill holes for inserting support pins and steel bushings for testing in accordance with Fig.2.(Warning—Exercise caution during machining of the notches to minimize the buildup of stresses and thermal degradation of the adhesive in this region.)End milling or saw cutting has been found to carry metal from the metal plates and decrease the adhesive bondline thickness in a narrow region along the cut edge.Hand sanding using progressivelyfiner grit sandpaper on aflat sanding block has been found to eliminate this edge effect.The use of240,320,400followed by600grit sandpaper to sand the cut edges,which determine the specimen width,has been effective in removing the metal spread into the a
dhesive bondline edge.
7.4Using a vernier caliper or other suitable measuring device,measure the width of the overlap area to the nearest 0.03mm(0.001in.)for each test sample.
7.5Using an optical comparator or other suitable measuring device,measure the overlap length to the nearest0.03mm (0.001in.)for each test sample.
7.6Using an optical comparator or other suitable measuring device,measure the adhesive thickness in the overlap region to the nearest0.003mm(0.0001in.)for each test sample.Due to metal surface roughness start and end the measurement of bond thickness at the average of metal peak to valley distance. 8.Calibration of Extensometers
8.1Connect the extensometers to an amplifier with two signal inputs and one signal output,which is the average of the two input signals.Connect the amplifier output to a
strip-chart
FIG.1Bonded Adherend
Plates
recorder that will be used during testing.Allow sufficient time for the amplifier to warm up to minimize signal drift.8.2Using a micrometer gage or similar device,adjust the amplifier gain such that 0.0254mm (0.001in.)of extensometer displacement is equal to 50.8mm (2.0in.)of chart travel.8.3Repeat the procedure for the remaining extensometer.9.Conditioning
9.1The accuracy of the results of strength tests of adhesive bonds depends on the conditions under which the bonding process is carried out.Unless otherwise agreed upon between the manufacturer and the purchaser,use the bonding conditions prescribed by the manufacturer of the adhesive.In order to ensure that complete information is available to the individual conducting the tests,obtain numerical values and other specific
information from the manufacturer of the adhesive for each of the following variables:
9.2Procedure for preparation of surfaces prior to applica-tion of the adhesive,the cleaning and drying of adherend surfaces,and special surface treatments,such as sanding,that are not specifically limited by the pertinent test method,9.2.1Complete mixing directions for the adhesive,
9.2.2Conditions for application of the adhesive,including the rate of spread or thickness of film,number of coats to be applied,whether to be applied to one or both surfaces,and the conditions of drying where more than one coat is required,9.2.3Assembly conditions before application of pressure,including the room temperature,relative humidity,and length of
time,
N OTE 1—Asymmetry obviates “left-right”covention.Ship terms retain identity of test site when specimen is rotated or inverted.
FIG.2Thick Adherend Lap Shear Test
Specimen
9.2.4Curing conditions,including the amount of pressure to be applied,the length of time under pressure,method of applying pressure(pressure bag,press platens,etc.),heat-up rate,and the temperature of the assembly when under pressure. Ensure that it is stated whether this temperature is that of the bondline or of the atmosphere at which the assembly is to be maintained,
9.2.5Conditioning procedure before testing,unless a stan-dard procedure is specified,including the length of time, temperature,and relative humidity.
9.3A range may be prescribed for any variable by the manufacturer of the adhesive if it can be assumed by the test operator that any arbitrarily chosen value within such a range or any combination of such values for several variables will be acceptable to both the manufacturer and the purchaser of the adhesive.
10.Procedure
10.1Connect two extensometers to the signal amplifier and the averaged signal output from the amplifier to the strip-chart recorder.Allow sufficient time for the amplifier to warm up to minimize signal drift.
10.2Set the chart range such that the expected output signals during testing from the extensometer is between15and 85%of full scale.
10.3Using a solid bar of adherend material machined to the same overall dimensions and geometry as the test sample, attach one of the extensometers to each edge of the bar,in accordance with Fig.3.
10.4Mount the bar in the test machine by placing a steel bushing though each of the drilled holes of the solid bar and inserting steel pins through the bushings and clevises attached to the test machine.A
djust the cross-head position of the test machine to zero,the initial load on the specimen.Load the bar to4017N(900lbf)at a rate of2455N/min(550lbf/min). Repeat the loading six times and record the load versus displacement for each loading.
10.5For each of the six loadings extrapolate the load-displacement curve to4464N(1000lbf)and record the displacement at this load.Average the results of the six tests to obtain the metal load-displacement values.For2024-T3alu-minum,0.00057mm/1000N(0.00010in./1000lbf)has been found to be a reasonable value for metal deformation at22°C (72°F).
10.6Using an adhesively bonded test sample,mount the extensometers on each edge of the sample such that the adhesive bondline is centered between the contact points of each extensometer and each extensometer is centered between the machined notches in the test specimen,in accordance with Fig.4.Ensure that the single point on the extensometer is on the leg of the coupon that will be raised during testing.
10.7Mount the test specimen in the test machine by placing
a steel bushing through each of the drilled holes of the test sample and inserting steel pins through each bushing and clevis attached to the test machine.Adjust the cross-head position of the test machin
e to zero,the initial load on the specimen.Load the test sample to failure at a rate of2455N/min(550lbf/min).
10.8Test a minimum of three replicate samples.
11.Calculation(See Fig.5)
11.1Draw a tangent line to the initial,linearly rising portion of the load-displacement curve and label the line as“A.”
Label FIG.3Extensometer Positioning for Metal Deformation
Determination
the point at which the load-displacement curve diverges from the tangent as “LL”(linear limit).The calculated stress and strain at LL are d LL and g LL ,respectively (refer to 11.8and 11.9).
11.2Draw a tangent line to the horizontal or yielded portion of the load-displacement curve and label the line as “B.”11.3Draw a line through the load-displacement curve,which bisects the angle between the two tangents and label this line “C.”Label the point on load displacement curve as “KN”(knee).If digital data is utilized (see Fig.6)do not use the calculated slope of the two tangent lines “A”and “B”to determine the bisector of line “D,”instead use an equal chart distance from the intersection point “e”to define points “f”and “g”on lines “A”and “B”respectively.Use the same chart distance from point “f”and “g”to determine point “h.”Calculate a linear equation for a line through points “e”and “h”and label this line “C.”The point of intersection between line
“C”and the calculated shear stress-strain data defines the point “KN”(knee).For FM73adhesive at 72°F the corrected shear strain at the knee (see 11.12)determined by tangent line slopes “KNs”has been shown to be roughly 6%were the knee determined by using equal chart distances to determine the knee “KN”is 3%.An example calculation using digital data is shown in Appendix X1.
11.4Label the point at which the load drops as a result of adhesive failure as “UL”(ultimate load).
11.5Calculate the corrected shear strain (g i )for at least two points along Line A by subtracting the corrected displacement of the adherend (d m )obtained from testing of the solid bar,from the displacement measured on the test sample (d a )at several loads along Line A and dividing by the thickness (t )of the adhesive
layer.
FIG.4Extensometer Positioning for Thick-Adherent Lap-Shear
Specimen
FIG.5Load-Displacement
Curve
FIG.6Shear Stress-Strain Curve for Digital
Data

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