Testing standard
Standard Test Method for Shear Properties of Composite Materials by the V-Notched Beam Method
Written and technically reviewed by Dak System Inc. engineeringLast reviewed
ASTM D5379 is the V-notched beam — Iosipescu — shear test for composites. A coupon with a 90° notch in each edge is clamped between two fixture halves, one fixed and one sliding, so the material between the notch roots is loaded almost entirely in shear. It gives shear strength and, where instrumented, a shear stress-strain curve and chord modulus.
A flat rectangular coupon, with a 90° V-notch cut into each long edge at mid-length, is clamped between the halves of a shear fixture. One half is fixed; the other slides on low-friction bearings, driven downwards through a compression platen. The halves apply opposing forces either side of the notched section, so the material between the notch roots is loaded almost entirely in shear rather than in bending. Loading continues to failure, or to 5 % engineering shear strain if the coupon has not failed by then.
The method yields shear strength and, where strain is instrumented, a shear stress-strain curve and a shear chord modulus taken across a defined strain interval. Depending on how the coupon is cut from the laminate, the same fixture gives in-plane or interlaminar shear.
These properties govern matrix-dominated behaviour: load transfer around bolted and bonded joints, the shear web of a spar, the buckling of a stiffened panel. Shear modulus feeds laminate analysis and finite-element models directly, where an assumed value is a common source of error. The data are meant to be quantitative enough for design allowables — provided failure occurs in the notch section.
F_su = P_max / (w × h)
The area is between the NOTCH ROOTS, not the full coupon width. Using the outside width is a straightforward way to under-report shear strength by a large factor.
G = Δτ / Δγ across a defined strain interval
Engineering shear strain from ±45° gauges is the sum of the two readings, which catches people out — a single gauge gives half the strain and twice the modulus.
The fixture body seats each half of the coupon against the loading direction and prevents rotation or out-of-plane movement — alignment is a property of the fixture here, which is what makes successive results comparable. The V-notch tooling itself is made to the method's geometry.
Specifications
The load is introduced through a compression platen onto the sliding half, so the frame is doing a straightforward compression job while the fixture converts it into shear.
SpecificationsThe sheared area is small — 11.4 mm by the coupon thickness, typically 2.5 to 4 mm — so failure loads are low. A glass/epoxy laminate failing near 60 MPa breaks around 1.7 to 2.7 kN; a carbon/epoxy at 100 to 110 MPa around 3 to 5 kN. A 10 kN load cell covers nearly all of this work, and V-notched beam fixtures on the market are rated to roughly 50 kN, so the fixture is rarely the limit.
The standard rate is constant head displacement at 2 mm/min [0.05 in/min]; laboratory practice runs between about 0.5 and 2 mm/min, chosen so the coupon fails within a few minutes. Force is verified to the general ASTM practice for testing-machine verification.
Strain instrumentation is not optional in the way the absence of an extensometer might suggest: nothing is clipped to the coupon, but bonded strain gauges are mandatory whenever modulus is reported.
The fixture does the real work. Its halves run on cross-roller or linear bearings, which must be free enough that drive force is not consumed in friction, and the coupon must sit so the applied load line passes through the notch roots — most fixtures carry an alignment pin for this. Loading arrives through a compression platen, so the frame needs a compression path and good axial alignment. Fixtures of this type are commonly rated for chamber work from roughly −70 °C to +250 °C, though the method publishes no temperature envelope.
Misalignment spoils more data than anything else. A coupon seated slightly off the load line has bending superimposed on the shear, and the recorded strength means nothing — worse, the curve still looks plausible. The alignment pin exists for this reason.
Crushing is next. Where the laminate is soft through-thickness, damage starts where the fixture bears on the coupon before the notch section reaches its shear strength; the tell is crushing damage at the notch root, under the fixture's bearing faces, instead of a clean shear fracture running root to root.
Third, ±45° angle-ply laminates are a known weak case: they tend to split along the free edges before the notch section fails, giving a low number from the wrong location. This is the case the V-notched rail method was developed to handle.
Fourth, gauge problems: a rosette that debonds part-way, or sits outside the notched section, returns a modulus that is wrong rather than obviously missing.
| ASTM D5379 V-notch | ASTM D2344 short beam | Rail shear | |
|---|---|---|---|
| Stress state | Nearly pure shear at the notch section | Complex, under a nose | Nearly pure over a larger area |
| Gives modulus | Yes, with gauges | No | Yes |
| In-plane and interlaminar | Both, by cutting orientation | Interlaminar proxy only | In-plane |
| Cost per coupon | Moderate — notches must be machined | Very low | High — large coupons |
D2344 is the fast screen and D5379 is the measurement. Short-beam strength detects that something changed; the V-notch test says what the shear properties actually are, and gives a modulus a laminate model can use.
It is the ASTM V-notched beam method — commonly called the Iosipescu test — for shear properties of composites. A coupon with a 90° notch in each edge is clamped between two fixture halves, one fixed and one sliding, so that the material between the notch roots is loaded almost entirely in shear rather than in bending.
To force the shear. Without them a beam loaded this way would fail in bending; the notches reduce the section at mid-length so that shear stress reaches its limit first, and their geometry is what makes the stress state across that section close to pure shear. The notch roots are therefore the specimen, not a detail of it.
Either — it depends entirely on how the coupon is cut from the laminate. The same fixture and the same procedure give different properties depending on orientation, which is why the cutting orientation belongs on the report. A result quoted as shear strength without saying which is ambiguous.
The distance between the notch roots multiplied by the coupon thickness — not the full outside width. Using the outside width is an easy mistake and it under-reports shear strength by a large factor, since the notches remove a substantial part of the section.
With strain gauges bonded at ±45° across the notch section. Engineering shear strain is the sum of the two readings, which catches people out — a single gauge gives half the strain and therefore twice the modulus. Two gauges and their sum is the correct arrangement.
When you need the property rather than a signal. Short-beam strength is fast and cheap and tells you that something has changed in the resin or the interfaces. The V-notch test costs more — notches must be machined and gauges bonded — and gives shear strength and a shear modulus that a laminate model can actually use.
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 | The sheared section is 11.4 mm wide by the coupon thickness, typically 2.5–4 mm, so a glass/epoxy laminate at 60 MPa fails near 1.7–2.7 kN and a carbon/epoxy at 100–110 MPa near 3–5 kN. A 10 kN load cell suits nearly all of this work; commercial V-notched beam fixtures are rated to around 50 kN, so the fixture is rarely the limit. | 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 |
| Gripping | Iosipescu V-notched beam fixture — fixed and sliding halves on low-friction cross-roller or linear bearings, driven through a compression platen | Our shear fixtures, built to the specimen |
| Environment | Conditioned as the material specification requires, with D5229/D5229M equilibrium conditioning where a moisture state is called for; the fixtures are rated for chamber work from about -70 °C to +250 °C | 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.
