Self-tighteningTJ-15
Universal Parallel Wedge Grips
Self-tightening wedges hold a flat coupon squarely. Shims or offset grips keep the load line through the bond, since the two adherends lie on different planes.
SpecificationsTesting standard
ASTM D3163 / D5868
ASTM D3163, Standard Test Method for Determining Strength of Adhesively Bonded Rigid Plastic Lap-Shear Joints in Shear by Tension Loading; ASTM D5868, Standard Test Method for Lap Shear Adhesion for Fiber Reinforced Plastic (FRP) Bonding
Written and technically reviewed by Dak System Inc. engineeringLast reviewed
ASTM D3163 and ASTM D5868 are the single-lap shear tests for bonded plastics. Both say in their own scopes that they complement ASTM D1002 and extend it — D3163 to rigid plastic adherends, D5868 to fibre-reinforced plastic bonded to itself or to metal. Two coupons bonded over a short overlap are pulled in line, and the failure load divided by the bonded area is the result.
At a glance
- Test type
- Shear
- Published by
- ASTM
- Edition
- D3163-01(2023)
- Material
- Adhesives, tapes & bonded joints
- Runs on
- Series 7200 and Series 9000
What the test does
Two flat coupons are bonded over a short overlap at one end and pulled apart in line, so the glue line is loaded mainly in shear. The peak force divided by the bonded area is the reported strength. This is the single-lap geometry that D1002 established for metal, carried over unchanged to adherends that metal-based practice cannot simply be applied to: plastics soften, and laminates fail in their own plies long before a good adhesive gives up.
What it measures, and why it matters
Comparative shear strength of a bonded joint and, just as often, the effect of a surface treatment. Both methods name the comparison of surface preparations as a principal use, which is the honest description of what a lap-shear number is for. Plastics are difficult to bond, and flame, plasma, abrasion and primer treatments are the variables that decide whether a joint works; this test is how they are ranked.
The division between the two methods is a real one, not an administrative one. D3163 explicitly excludes anisotropic materials such as reinforced plastic laminates, and it applies only at temperatures below the softening point of the adherends. D5868 exists to cover exactly what D3163 excludes: FRP, both random and fibre-oriented, bonded to itself or to metals. Choosing by adherend rather than by habit is the whole of it.
The bonded coupon
Two flat coupons, bonded at one end over a short overlap and pulled apart along their length.
- D3163 adherends
- Rigid plasticAnisotropic materials such as reinforced plastic laminates are excluded by the scope. Those go to D5868.
- D5868 adherends
- Fibre-reinforced plastic, to itself or to metalBoth random and fibre-oriented FRP are covered.
- Coupon size
- Of the order of 25 mm wide by 100 mm longPractice
- Overlap
- Commonly between 12.7 mm and 25.4 mmPracticeChosen short enough that failure occurs in the adhesive rather than in the adherend.
- Measured after bonding
- Overlap length and bond width, on every couponThe reported stress is the failure load divided by that measured area, not by a nominal one.
- Bond-line thickness
- Controlled and recorded
- Surface preparation
- Specified in full and followed exactlyOn plastics this is usually the variable under test — flame, plasma, abrasion or primer.
- Temperature limit (D3163)
- Below the softening point of the adherends
Adherend failure is the constraint that shapes the specimen. A rigid plastic coupon can yield or craze before the bond does, and an FRP coupon can delaminate in its surface ply and take the joint with it. Both are real observations; neither is an adhesive strength.
Test speed
The two methods run at different rates, which is one of the practical distinctions between them.
- D5868
- 13 mm/min (0.5 in./min)
- D3163
- Commonly 1.3 mm/min (0.05 in./min)PracticeThe crosshead equivalent used for D1002, the method D3163 complements. Published descriptions also give the rate for D3163 as a controlled shear stress of 8.3 to 9.7 MPa/min, which is the same D1002 figure in the other control mode. Take the rate from the edition in force and report which one was used.
- Recorded quantity
- Peak force at rupture
Calculations
Lap-shear strengthτ
τ = P_max / (l × w)
- P_max
- peak force at rupture, N
- l
- measured overlap length, mm
- w
- measured bond width, mm
An average over a stress distribution the test does not resolve. Shear stress in a lap joint peaks at both ends of the overlap and dips in the middle, and the two adherends lie on different planes, so the joint also rotates and adds peel at those same ends.
How the test runs
- 01Cut the coupons to size from the plastic or laminate under test.
- 02Apply the specified surface treatment to both bonding faces.
- 03Bond to the chosen overlap, controlling glue-line thickness.
- 04Cure to the adhesive's schedule.
- 05Measure the actual overlap length and bond width on each coupon.
- 06Condition in the specified atmosphere.
- 07Grip each free end, with shims or offset jaws so the load line passes through the bond.
- 08Pull at the rate the method specifies, to rupture, recording peak force.
- 09Examine both faces and classify the failure — cohesive, interfacial, or in the adherend.
- 10Divide peak force by the measured bonded area and report the failure mode with it.
Grips and fixtures for this method
TJ-144
Heavy Duty Hydraulic Grips
Hydraulic closure where a thick laminate or a strong structural bond would let a manually tightened wedge slip before the joint failed.
SpecificationsWhat the report has to contain
- Reference to ASTM D3163 or D5868, and the edition
- Adhesive identification, batch and cure schedule
- Adherend material — resin, reinforcement and lay-up for FRP
- Adherend thickness
- Surface preparation for each adherend
- Measured overlap length and bond width
- Bond-line thickness where controlled
- Conditioning and test temperature
- Rate of loading
- Lap-shear strength for each coupon
- FAILURE MODE for every coupon
- Number of coupons, mean and standard deviation
What the machine must be capable of
A tensile frame with grips that keep the load line through the bond. The bonded area on these coupons is a few hundred square millimetres, so an adhesive at a few megapascals fails in the hundreds of newtons and a strong structural bond on a stiff laminate can reach the tens of kilonewtons; a 10 to 30 kN frame covers the range comfortably. Because the two adherends lie on different planes the coupon wants to rotate as it loads, so shims or offset jaws bring the bond onto the load axis rather than adding avoidable bending to what the geometry already produces. Grip faces must hold a plastic or laminate coupon without crushing it.
The two methods run at different rates, and that is one of the practical distinctions between them: D5868 specifies a rate of 13 mm/min (0.5 in./min), while D3163 work is commonly run at 1.3 mm/min (0.05 in./min), the crosshead equivalent used for D1002. The rate is reported with the result. No extensometer is used — only force is recorded, to rupture.
What goes wrong in practice
Reading the result as a design allowable. It is not one: the stress is not uniform across the overlap, it peaks at both ends, and the average at failure moves with overlap length, adherend stiffness and bond-line thickness. Grip crushing on soft or thin-walled plastic coupons. Testing a plastic close to its softening point, outside D3163's stated range. Running an FRP joint to D3163 rather than D5868, which the scope excludes. And reporting a strength without classifying the failure — cohesive, interfacial, or in the adherend — which is the part of the result that tells you what to change.
Which lap-shear method for which adherend
| ASTM D1002 | ASTM D3163 | ASTM D5868 | ISO 4587 | |
|---|---|---|---|---|
| Adherends | Metal to metal | Rigid plastic | FRP to itself or to metal | Rigid to rigid, generally |
| Reinforced laminates | Not covered | Excluded by scope | This is its purpose | Covered generally |
| Rate | Stress-rate controlled | About 1.3 mm/min in practice | 13 mm/min | As specified |
| Result | Apparent shear strength | Shear strength, comparative | Shear strength, comparative | Tensile lap-shear strength |
All four report a load divided by a bonded area, and none of them is a design allowable. The value moves with overlap length, adherend stiffness and bond-line thickness, so it does not transfer to a joint of different proportions.
Questions we are asked about this test
What is ASTM D3163?
It is the ASTM lap-shear test for adhesively bonded rigid plastic joints, loaded in shear by tension. Two plastic coupons bonded over a short overlap are pulled apart and the peak load is divided by the bonded area. The scope states that it complements ASTM D1002 and extends that method to plastic adherends.
What is ASTM D5868?
It is the ASTM lap-shear test for fibre-reinforced plastic bonding. It covers FRP bonded to itself and to metals, in both random and fibre-oriented forms, and like D3163 it describes itself as complementing ASTM D1002. It is the method for the laminates D3163 excludes.
Which of the two do I use?
Choose by adherend. If the plastic is isotropic and rigid, D3163 applies. If it is a reinforced laminate — anisotropic, with fibre in it — D3163's scope excludes it explicitly and D5868 is the correct method. The exclusion is a real technical boundary, not paperwork: a laminate fails in its own plies in a way an unreinforced plastic does not.
Do the two methods run at the same speed?
No, and that is one of the practical differences between them. D5868 specifies 13 mm/min (0.5 in./min). D3163 work is commonly run at the slower crosshead rate of 1.3 mm/min (0.05 in./min) that corresponds to D1002 practice. Whichever is used, the rate is reported with the result.
Can I use lap-shear strength as a design allowable?
No. The stress is not uniform across the overlap — it peaks at both ends and dips in the middle — and the average at failure moves with overlap length, adherend stiffness and bond-line thickness. The figure ranks adhesives and qualifies surface treatments; it does not size a joint of different proportions.
Why is the overlap kept short?
Two reasons. Mechanically, a longer overlap makes the stress peaking at its ends more pronounced, so the average stress at failure falls even as the joint carries more total load. Practically, a long overlap on a plastic or FRP coupon puts enough load into the adherend to break it first, and an adherend failure is not a bond strength.
What does delamination of the FRP mean?
That the surface ply gave way before the adhesive did. Fibre is left on both faces and the joint has separated inside the laminate rather than at or within the glue line. It is a genuine result about that bonded assembly, and it means the adhesive is stronger than the material it was asked to hold — but it is not a measurement of adhesive strength and should not be averaged in as one.
Why does surface preparation dominate these results?
Because plastics are difficult to bond. Low surface energy, mould release, and additives that migrate to the surface all work against wetting, and flame, plasma, abrasion and primer treatments are what make a joint possible. Both methods name the comparison of surface treatments as a principal use, which is an honest description of what the number is usually reporting on.
Running ASTM D3163 / D5868 on the Series 7200 and Series 9000
Dak verifies against whichever standard the method names, and where a class applies our frames sit a class tighter than it asks.
| The method asks for | Dak supplies | |
|---|---|---|
| Capacity | A few hundred square millimetres of bond, so a flexible adhesive at a few megapascals fails in the hundreds of newtons while a strong structural bond on a stiff laminate reaches the tens of kilonewtons. A 10 to 30 kN frame covers the range comfortably. | Load cells from 1 kg to 60 ton on the Series 7200, and 0.5 to 100 kN on the Series 9000 |
| Force accuracy | unknown — no force-verification class could be confirmed for either method from a publisher record, and none is asserted here | ISO 7500-1 Class 0.5, verified to ASTM E4, DIN 51221 and BS 1610 |
| Gripping | Ordinary tensile grips with shims or offset jaws, so the load line passes through the bond rather than adding bending to what the offset geometry already produces | Our self-tightening serrated wedge grips, with V-jaws for round specimens, built to the specimen |
| Environment | D3163 applies only below the softening point of the adherends; conditioning atmosphere and test temperature are reported with the result | 3009 series chambers, −150 °C to +400 °C — temperature only |
This page describes the method as practised. The governing text is the current edition from the issuing body. Tell us what you are testing and we will answer with the machine, the fixture and a quotation.