5 to 400 kNTJ-125
Direct Compression Fixture
Flat, parallel platens. On a sandwich coupon the platens must stay parallel as load rises, or one facing takes the load before the other.
SpecificationsTesting standard
ASTM C364/C364M
Standard Test Method for Edgewise Compressive Strength of Sandwich Constructions
Written and technically reviewed by Dak System Inc. engineeringLast reviewed
ASTM C364 measures the compressive properties of structural sandwich construction loaded in the plane of the facings. Cores with continuous bonding surfaces such as balsa and foam are covered, as are discontinuous ones such as honeycomb.
At a glance
- Test type
- Compression — the specimen is squeezed
- Published by
- ASTM
- Edition
- C364/C364M-16(2024)
- Material
- Composites & sandwich structures
- Runs on
- Series 7200 and Series 9000
What the test does
A sandwich coupon is cut to size, its loaded ends prepared flat, parallel and square to the facings, and its facing thickness and width measured. It is stood centrally between flat parallel platens and compressed at a constant rate in the plane of its facings until it fails. The maximum force is recorded and divided by the cross-sectional area of the facings, and the way the coupon gave way is classified as facing compression, facing wrinkling, core shear or end crushing.
What it measures, and why it matters
How much in-plane compression a sandwich panel carries before it fails — the load case of a panel acting as a column, a bulkhead or the compression face of a beam. The distinction from flatwise compression is not a detail: ASTM C365 crushes the panel through its thickness and measures the core, whereas this loads along the facings and is dominated by them. Which of the four failure modes occurred decides what the number means, and only facing compression and facing wrinkling describe the panel's edgewise capacity at all.
Edgewise, not flatwise
Load runs along the facings rather than through the thickness. That is a different test from crushing the core, and a different failure.
- Direction
- In the plane of the facingsFlatwise compression through the thickness is ASTM C365 — a different property of the same panel.
- Cores in scope
- Continuous surfaces such as balsa and foam, and discontinuous ones such as honeycomb
- Units
- SI and inch-pound, used independentlyNot exact equivalents. A report mixes them at its peril.
- Loaded ends
- Flat, parallel and squareAn out-of-square end crushes locally before the panel does, and the result is an end-preparation figure.
- Failure modes
- Facing compression, facing wrinkling, core shear or end crushingOnly the first two describe the panel's edgewise capacity.
- Record which mode occurred, on every coupon
- Dak
A sandwich panel has several ways to fail edgewise and they are not interchangeable. Facing wrinkling is a stability event governed by the core's support; facing compression is a strength event. Reporting a load without the mode leaves the reader unable to tell which.
Test speed
- Rate
- A constant crosshead rate as specified
- Reported
- Ultimate edgewise compressive strength, and modulus where measured
- Ends
- Prepared square and, where the method requires, supported
- Check platen parallelism before a series
- DakA platen a fraction of a degree out loads one facing first, and a sandwich panel is unforgiving about that.
Calculations
Ultimate edgewise compressive strength—
Maximum force divided by the cross-sectional area of the facings
- area
- the facing area, not the whole panel section
The core carries very little in-plane load. Dividing by the full panel section understates the facing stress badly, and which basis was used has to be stated.
Facing wrinkling—
A local buckling of a facing on its elastic foundation, the core
It depends on core stiffness as much as on facing strength, which is why the same facings on a softer core fail lower.
How the test runs
- 01Cut coupons to the dimensions the method specifies.
- 02Prepare the loaded ends flat, parallel and square to the facings.
- 03Measure the facing thickness and the coupon width.
- 04Condition the coupons as required.
- 05Check the platens are parallel.
- 06Stand the coupon centrally between the platens.
- 07Fit an extensometer where a modulus is to be reported.
- 08Load at the specified constant rate to failure.
- 09Record the maximum force.
- 10Classify the failure: facing compression, facing wrinkling, core shear or end crushing.
- 11Calculate the strength on the facing area and report the mode and the area basis with it.
The fixture this method needs
What the report has to contain
- Reference to ASTM C364/C364M and the edition
- Facing and core materials, core density and cell size or grade
- Panel and coupon dimensions, and facing thickness
- How the loaded ends were prepared
- Conditioning and test rate
- Maximum force and the calculated strength
- The area basis used for the calculation
- Failure mode for every coupon
- Modulus where measured, and how strain was taken
- Which unit system was used
What the machine must be capable of
Moderate compressive force, commonly a few kilonewtons to tens of kilonewtons, through flat platens that stay parallel as load rises. Parallelism is the requirement that repays checking before a series: a platen a fraction of a degree out loads one facing before the other, and a sandwich panel is unforgiving about that. Where a modulus is reported an extensometer is needed, because machine compliance and bedding-in at the ends are a large share of crosshead travel on a short compression coupon.
What goes wrong in practice
Reporting a load without the failure mode, which hides whether the panel failed by facing strength, by wrinkling — a stability event that depends on core stiffness as much as on the facings — or by something that is not an edgewise property at all. Calculating the strength on the whole panel section rather than the facing area, which understates the facing stress badly on a thick, light core. Poorly squared ends. And mixing SI and inch-pound values, which the dual designation exists to warn against. Taking a modulus from crosshead travel belongs on the list too: on a coupon this short, machine compliance and the coupon bedding down onto the platens are a large fraction of the movement, so the figure describes the load train as much as the panel.
ASTM C364 or ASTM C365
| C364 — edgewise | C365 — flatwise | |
|---|---|---|
| Load direction | In the plane of the facings | Through the thickness |
| Measures | Facing-dominated capacity | Core compressive strength |
| Governs | In-plane buckling and crushing of a panel | Local crushing under a fitting or a foot |
| Substitutable | No | No |
Two orthogonal properties of the same panel, and a design usually needs both — one describes what happens when the panel is loaded as a column, the other what happens when something presses on its face.
Questions we are asked about this test
What is ASTM C364?
It is the ASTM test for the edgewise compressive strength of structural sandwich construction — compression in the plane of the facings rather than through the thickness. It covers cores with continuous bonding surfaces such as balsa and foam, and discontinuous ones such as honeycomb. The current designation is ASTM C364/C364M-16(2024).
How is edgewise different from flatwise compression?
They load the panel along different axes and measure different things. Edgewise runs the load along the facings, so the answer is dominated by the facings and by how well the core stabilises them. Flatwise, which is ASTM C365, crushes the panel through its thickness and measures the core. A design usually needs both, and neither substitutes for the other.
Why does the failure mode matter so much?
Because a sandwich panel has several ways to fail edgewise and only some of them describe its capacity. Facing compression is a strength event. Facing wrinkling is a stability event — a local buckle of the facing on the elastic foundation of the core — so the same facings on a softer core fail at a lower load. Core shear and end crushing are neither. A load reported without the mode leaves the reader unable to tell which was measured.
Should the strength be calculated on the facing area or the whole section?
On the facing area, because the core carries very little in-plane load. Dividing the failure force by the full panel section spreads it over material that was not resisting it and understates the facing stress badly. Whichever basis is used has to be stated, since the two differ by a large factor on a thick, light core.
Why does end preparation matter?
Because an out-of-square end crushes locally before the panel reaches its real capacity, and the recorded number then describes the end preparation rather than the sandwich. The loaded ends have to be flat, parallel and square to the facings — on a panel with stiff facings and a soft core, a small error concentrates the whole load into one corner of one facing.
Is a modulus available from this test?
Where strain is measured, yes, but it needs an extensometer rather than crosshead travel. Machine compliance and any bedding-in at the loaded ends are a large share of the movement on a short compression coupon, so a modulus from the crosshead reports the load train as much as the panel.
What does the dual designation mean?
That the standard is written in both SI and inch-pound units, and the two are to be regarded separately and used independently rather than converted. The values in each system are not exact equivalents, so a report should state which was used and must not mix them.
Running ASTM C364/C364M 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 | Moderate — a sandwich coupon commonly fails between a few kilonewtons and tens of kilonewtons | 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 over the working range | Verified to ASTM E4, and to ISO 7500-1 Class 0.5 |
| Gripping | Flat parallel compression platens, with the loaded ends of the coupon prepared square | Our compression anvils, built to the specimen |
| Environment | 23 ± 2 °C standard laboratory atmosphere | 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.