Standard Test Method for Edgewise Compressive Strength of Sandwich Constructions - PDF

ASTM C364 Compression Platens – Universal Grip Data Sheet (PDF)

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ASTM C364/C364M measures the edgewise compressive strength of structural sandwich panels: a short specimen is loaded parallel to the facings until the panel fails. The result is reported as the stress developed in the facings, which makes it a direct check of how much in-plane load a panel can carry before the skins wrinkle, dimple or crush. It applies to cores with continuous bonding surfaces (foam, balsa) and to honeycomb cores.

Why Run an Edgewise Compression Test?

• Panel design allowables for floors, bulkheads, decks and walls loaded in-plane

• Comparing facing materials, layups, core types and adhesives

• Material specifications and quality assurance of production panels

• Research on facing wrinkling and intracell dimpling

Typical Applications

• Aircraft floor panels and bulkheads

• Composite marine decks and hulls

• Cargo container and truck body walls

• Rail interior panels

• Satellite and UAV structural panels

ASTM C364 Specimen Requirements

• Specimen is a full sandwich: both facings bonded to the core, cut with clean, square and parallel loaded ends

• Width: at least 50 mm (2 in) and at least twice the total sandwich thickness

• Unsupported height: no more than 8 times the total thickness, so the panel fails in the facings rather than by overall column buckling

• Measure width, total thickness and each facing thickness before testing

• Test at least 5 specimens per condition; condition at 23 °C and 50% RH or per D5229 for environmental work

Confirm exact limits against your copy of the current C364/C364M edition.

Fixture and Equipment

• Universal testing machine with compression platens and a load cell sized to the panel (10–250 kN is typical)

• Edgewise compression fixture with end clamps that grip the top and bottom edges so the loaded ends do not brush or crush

• Side supports (knife edges or simple supports) along the vertical edges to stop the specimen from buckling sideways

• Optional strain gauges on both facings to check load sharing and bending

• Environmental chamber (-80 to +280 °C) for hot/wet or cold testing

Test Procedure

• Square the specimen in the end clamps and center it under the crosshead

• Fit the side supports without preloading the specimen

• Load in compression at about 0.50 mm/min (0.020 in/min), so failure occurs in 3–6 minutes

• Record load and crosshead displacement (and strains, if used) to failure

• Note the failure mode and location; failures at the clamped ends are not valid

Calculations

Facing stress σ = Pmax ÷ [w × (t1 + t2)]

For equal facings this becomes σ = Pmax ÷ (2 × t × w), where Pmax is the maximum load, w is the specimen width and t is the thickness of one facing. The core carries very little of the edgewise load, so only the facing area is used.

Example: a 75 mm wide panel with two 0.5 mm aluminum facings fails at 18,000 N. σ = 18,000 ÷ (2 × 0.5 × 75) = 240 MPa.

Failure Modes

• Facing wrinkling (local buckling of a skin into or away from the core)

• Intracell dimpling of the facing over honeycomb cells

• Facing compression failure

• Core shear crimping

• Facing-to-core debonding

• End crushing (invalid; improve end clamping or potting)

Related Standards

• ASTM C393 – flexural properties of sandwich beams

• ASTM C297 – flatwise tensile strength (bond quality)

• ASTM C273 – core shear properties

• ASTM C365 – flatwise compressive properties of cores

• ASTM D7249 – facing properties by long-beam flexure

ASTM C364 FAQ

What does ASTM C364 measure?

Edgewise compressive strength of a sandwich panel, reported as the stress developed in the facings at maximum load when the panel is loaded parallel to its skins.

How big is a C364 specimen?

Width at least 50 mm (2 in) and at least twice the total thickness; unsupported height no more than 8 times the total thickness, to avoid overall column buckling.

What test speed does ASTM C364 use?

About 0.50 mm/min (0.020 in/min), adjusted so the specimen fails within 3–6 minutes.

How is facing stress calculated?

σ = Pmax ÷ [w × (t1 + t2)], or Pmax ÷ (2 × t × w) for equal facings. Only the facing area is used, because the core carries little edgewise load.