Testing standard
ASTM D3410
Standard Test Method for Compressive Properties of Polymer Matrix Composite Materials with Unsupported Gage Section by Shear Loading
Written and technically reviewed by Dak System Inc. engineeringLast reviewed
ASTM D3410 measures the compressive strength and modulus of a polymer matrix composite. The coupon is loaded through tapered wedges that introduce force by shear along its tabs rather than by pushing on its ends, leaving a very short unsupported gauge section — typically 12.7 mm — so the specimen fails by compression rather than by buckling.
At a glance
- Test type
- Compression — the specimen is squeezed
- Published by
- ASTM
- Edition
- D3410/D3410M-16
- Material
- Composites & sandwich structures
- Runs on
- Series 7200 and Series 9000
What the test does
A flat rectangular coupon, usually with bonded end tabs, is assembled into a self-contained compression fixture. Tapered wedges grip the tabbed ends, and as the fixture is squeezed between the machine platens the wedges drive force into the coupon by friction and shear along its faces. Nothing pushes on the coupon ends themselves. Between the two grip regions the coupon is unsupported over a very short length, typically 12.7 mm. Strain gauges are bonded back to back at the centre of that gauge section, and the coupon is loaded at about 1.5 mm/min until it fails.
What it measures, and why it matters
The method gives compressive strength and compressive modulus, and — through the two strain channels — a percentage bending figure that says whether those numbers are trustworthy. Compressive properties matter because composites are markedly weaker in compression than in tension, so it is very often compression that sizes a structure. Any laminate in bending has a compressive face; buckling and crippling calculations need compressive modulus; and damage tolerance work depends on compression after impact, which in turn needs the undamaged compressive strength as its baseline. A design that used tensile allowables in compression would be unsafe by a wide margin.
Specimen and fixture
A composite coupon in compression is a column looking for an excuse to buckle. Every dimension in this method is set by that problem.
- Unsupported gauge length
- 12 to 25 mm; 12.7 mm is the common choiceShort deliberately. A longer gauge buckles before it crushes and reports the wrong failure.
- Width
- Commonly 6.4 to 25 mm depending on lay-up
- Tabs
- Usually bonded, to spread the wedge grip loadUntabbed specimens are permitted for some lay-ups; tabbing is decided by whether the grip damages the coupon.
- Load introduction
- By shear through tapered wedgesThis is the defining feature. Nothing pushes on the coupon ends, so brooming and end-crushing are avoided.
- Strain measurement
- Back-to-back, on both facesNot for redundancy. The difference between the two faces is how bending is detected, and a coupon with excessive bending is invalid.
- Flatness and parallelism
- Tightly controlledA coupon with non-parallel faces sits crooked in the wedges and bends from the first newton.
- Check percentage bending before accepting a result
- Every specimenDakIt is the one diagnostic that distinguishes a real compressive strength from a buckling load dressed up as one.
Compression testing of composites is unusually sensitive to fixturing. A result without a bending check is not a compressive strength — it is the load at which that particular coupon became unstable in that particular fixture.
Test speed
- Crosshead speed
- 1.5 mm/min nominal
- Modulus range
- Between 1000 and 3000 microstrainA defined strain window, so the chord is taken from the same place by every laboratory.
- Percentage bending limit
- Checked against the method's criterion
- Watch the two strain traces diverge
- It is the early warningDakFaces separating on the plot means the coupon is bending, and everything after that point is suspect.
Calculations
Fᶜᵘ = Pmax / A
- Pmax
- maximum force, N
- A
- cross-sectional area of the gauge section, mm²
Eᶜ = Δσ / Δε between 1000 and 3000 µε
- Δσ
- stress increment over the range, MPa
- Δε
- corresponding strain increment
Taken from the average of the two back-to-back gauges, so that any bending cancels in the modulus even where it invalidates the strength.
Bʸ = |ε₁ − ε₂| / |ε₁ + ε₂| × 200
- ε₁, ε₂
- strains on the two opposite faces
The validity check. A high value means the coupon is bending rather than compressing uniformly, and the strength is not usable.
How the test runs
- 01Machine coupons to the specified width and length, keeping faces flat and parallel.
- 02Bond tabs where the lay-up and grip arrangement require them.
- 03Measure the gauge section and record the area.
- 04Bond strain gauges back to back at the centre of the gauge section.
- 05Condition to the specification.
- 06Assemble the coupon into the shear-loading fixture, seating the wedges evenly.
- 07Place the fixture between the compression platens and check alignment.
- 08Load at 1.5 mm/min, recording force and both strain channels.
- 09Take modulus from the averaged strains between 1000 and 3000 microstrain.
- 10Compute percentage bending and check it against the criterion.
- 11Record the maximum force and classify the failure location and mode.
- 12Reject results with excessive bending or failure outside the gauge section.
What the report has to contain
- Reference to ASTM D3410 and the edition
- Material, lay-up, ply orientation and cure schedule
- Coupon dimensions and gauge cross-section
- Tab material, adhesive and geometry, or a note that none were used
- Conditioning and test temperature
- Crosshead speed
- Compressive strength and modulus for each coupon
- Percentage bending for each coupon
- Failure mode and location, classified
- Specimens rejected, with the reason
- Mean, standard deviation and coefficient of variation
What the machine must be capable of
Force measurement to ASTM E4 up to loads that can reach several tens of kilonewtons on a small section, a crosshead holding 1.5 mm/min, and at least two strain channels recorded simultaneously with force. Platens must be flat and parallel, since they load the fixture body and any tilt there is transmitted straight into the coupon. Alignment is the dominant requirement throughout: composite compression amplifies imperfection rather than correcting it, so a load path that is acceptable for tensile work may not be adequate here. Where elevated-temperature or conditioned testing is specified, the fixture has to be brought to temperature with the specimen rather than merely surrounded by hot air.
What goes wrong in practice
The central failure is accepting a buckling load as a compressive strength. It looks entirely plausible — a smooth curve and a clean maximum — and only the back-to-back strain traces reveal it, which is precisely why the bending check is mandatory rather than advisory. Beyond that, the recurring problems are coupons machined without adequate flatness and parallelism, tabs of uneven thickness that tilt the specimen in the wedges, wedges seated unevenly during assembly, and failures at the tab ends being reported rather than rejected. A subtler error is taking modulus from a single gauge, which builds any bending directly into the result instead of cancelling it.
ASTM D3410 or ASTM D6641
| ASTM D3410 | ASTM D6641 | |
|---|---|---|
| Load introduction | Shear only, through wedges | Combined — part shear through the grips, part end loading |
| Fixture | Shear-loading fixture | Combined Loading Compression (CLC) fixture |
| Tabs | Usually required | Often unnecessary for moderate-strength lay-ups |
| Practical appeal | Long-established, widely specified | Simpler specimen, quicker turnaround |
Both are valid and both are in current use. D6641's untabbed specimen is cheaper and faster, but on very high-strength unidirectional material the end loading it applies can crush the coupon ends, and the shear-only route of D3410 remains the safer choice there.
Questions we are asked about this test
What is ASTM D3410?
It is the ASTM method for the compressive properties of polymer matrix composites using shear loading. Force is introduced into the coupon by friction and shear through tapered wedges gripping its ends, rather than by pushing on the ends themselves, and the unsupported gauge section is kept very short — typically 12.7 mm — so that the specimen fails in compression rather than by buckling.
Why is the gauge section so short?
Because a thin composite coupon in compression is essentially a column, and a column fails by buckling long before it reaches its material compressive strength. Shortening the unsupported length raises the buckling load above the compressive strength, so the coupon crushes instead. Everything else in the method — the fixture, the tabs, the alignment requirements — exists to make that short gauge work.
Why are strain gauges needed on both faces?
To detect bending, not for redundancy. If the coupon is bending, one face sees more compressive strain than the other, and the difference between them quantifies it. The method sets a limit on percentage bending, and a coupon that exceeds it has not produced a valid compressive strength — it has produced the load at which that coupon became unstable in that fixture.
What is the difference between D3410 and D6641?
How the load gets in. D3410 introduces it purely by shear through wedge grips. D6641 uses a combined loading fixture that puts part of the load in by shear and part directly into the coupon ends. D6641's specimen is simpler and often needs no tabs, which makes it quicker and cheaper; D3410 avoids end loading altogether, which is safer on very high-strength unidirectional laminates where end crushing is a real risk.
Do I always need bonded tabs?
Not always. Tabs exist to spread the grip load and stop the wedges damaging the coupon, so whether they are needed depends on the lay-up strength and the grip arrangement. Softer and lower-strength laminates often test satisfactorily untabbed. The practical test is where failures occur: repeated failures at or under the grip mean the coupon needs tabbing.
What counts as a valid failure?
One inside the gauge section, by a compressive mechanism — through-thickness shear, kinking, or transverse cracking — rather than at the grips or by gross buckling. Failures at the tab ends, brooming at the coupon end, or an obviously buckled specimen are all rejected. Classifying the failure mode and location is part of the report because it is the evidence that the number is real.
Why is composite compression so much harder than tension?
Because tension is self-stabilising and compression is not. A coupon in tension straightens itself as it loads; a coupon in compression amplifies any initial crookedness, so small imperfections in specimen flatness, tab thickness or fixture alignment grow into bending. That is why compression methods specify fixtures in such detail, demand back-to-back strain measurement, and reject results on a bending criterion — none of which a tension method needs.
Running ASTM D3410 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 | High for the section — a unidirectional carbon laminate commonly fails between 20 and 60 kN | Load cells from 1 kg to 60 ton on the Series 7200, and 0.5 to 100 kN on the Series 9000 |
| Force accuracy | ASTM E4 | Verified to ASTM E4, and to ISO 7500-1 Class 0.5 |
| Strain measurement | An extensometer to ASTM E83 Class B-1 where modulus is reported, gauge length 12.7 | Certified to ASTM E83 and ISO 9513 Class 1 — non-contact video, clip-on and high-elongation |
| Gripping | Shear-loading compression fixture with wedge grips, aligned in a trapped guide | Our self-tightening serrated wedge grips, with V-jaws for round specimens, built to the specimen |
| Environment | Standard laboratory atmosphere, or conditioned and elevated-temperature where the specification requires | 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.