Standard Test Method for Open-Hole Compressive Strength of Polymer Matrix Composite Laminates - PDF

ASTM D6484 Compression Fixture – Universal Grip Data Sheet (PDF)

 

ASTM D6484/D6484M is the standard test method for the open-hole compressive (OHC) strength of polymer matrix composite laminates. A long, flat laminate with a single drilled hole is held in an anti-buckling support fixture and loaded in compression until it fails at the hole. OHC strength is one of the key notched design values in aerospace composite allowables, alongside open-hole tension (ASTM D5766), because fastener holes and cutouts control the strength of real structures.

Specimen

• Width: 36 mm (1.5 in); length: 300 mm (12 in).

• Thickness: typically 3 to 5 mm, from a balanced, symmetric laminate (the reference is a quasi-isotropic [45/0/−45/90]ns layup).

• Hole: 6 mm (0.25 in) diameter at the center, drilled without delamination or heat damage, so width ÷ hole diameter = 6.

• Condition as required by the material specification, then measure width and thickness near the hole.

Fixture and Equipment

• Support fixture: two pairs of face-support plates bolted around the specimen to stop buckling, with a window that leaves the hole region unsupported. The bolts are torqued only enough to keep the plates in contact.

• Universal testing machine with enough capacity for the laminate (often 50 to 150 kN).

• Procedure A: the ends of the support fixture are clamped in hydraulic wedge grips and load is introduced into the specimen in shear.

• Procedure B: the fixture and specimen are end-loaded between flat, parallel compression platens.

• Strain measurement (optional): strain gauges or extensometers if compressive stiffness is also wanted.

Test Procedure

1. Assemble the specimen in the support fixture with the hole centered in the window and tighten the plates to the specified torque.

2. Mount the fixture in hydraulic grips (Procedure A) or between platens (Procedure B), checking alignment.

3. Load in compression at a constant crosshead speed of about 1 to 2 mm/min (0.05 in/min is typical), so failure occurs within roughly 1 to 10 minutes.

4. Record the maximum force and note the failure mode and location; a valid failure passes through the hole.

OHC Strength Calculation

OHC strength = Pmax ÷ (w × h)

Gross area is used: w is the specimen width and h the thickness, without subtracting the hole. Example: a 36 × 4.0 mm specimen (144 mm²) fails at 45,000 N. OHC strength = 45,000 ÷ 144 = 312.5 MPa (45.3 ksi).

Related Standards

• ASTM D5766 – open-hole tensile strength of composite laminates

• ASTM D6742 – filled-hole tension and compression (adds a fastener in the hole)

• ASTM D5961 – bearing response of composite laminates

• ASTM D6641 – Compression strength of composites using combined loading (non-hole test)

• ASTM D3039 – Standard tensile testing for composite laminates

ASTM D6484 FAQ

What size is the ASTM D6484 specimen?

A flat laminate 36 mm (1.5 in) wide and 300 mm (12 in) long, typically 3 to 5 mm thick, with a 6 mm (0.25 in) hole drilled at the center, giving a width-to-hole-diameter ratio of 6.

How is open-hole compressive strength calculated?

On the gross area, ignoring the hole: OHC strength = Pmax ÷ (w × h). Using gross area makes results comparable between labs and with notched design allowables.

What is the difference between Procedure A and Procedure B?

In Procedure A the support fixture is clamped in hydraulic wedge grips and load is transferred into the specimen in shear. In Procedure B the fixture and specimen are end-loaded between flat compression platens.

Why does D6484 need a support fixture?

A 300 mm long, 4 mm thick laminate would buckle long before it fails in compression. The bolted face-support plates stop buckling while leaving the area around the hole free to fail.