ASTM C1341
Flexural Test on Fiber Reinforced Ceramic Composites 

ASTM C1341 Bend Fixture – Universal Grip Data Sheet (PDF)

ASTM C1341 is the standard test method for flexural properties of continuous fiber-reinforced advanced ceramic composites (CFCCs), such as SiC/SiC and C/SiC with 1D, 2D or 3D fiber architectures. A rectangular bar is bent on two supports until it fails, and the test gives flexural strength, the stress–strain curve and the flexural modulus at room or elevated temperature. Unlike monolithic ceramics (tested to ASTM C1161), CFCCs fail gradually, so the full load–deflection curve matters, not just the peak load.

Test Geometries

• Geometry I – three-point: one load at mid-span between two supports

• Geometry IIA – four-point quarter-point: two loads, load span = ½ of the support span

• Geometry IIB – four-point third-point: two loads, load span = ⅓ of the support span

Four-point bending is generally preferred because a larger length of the bar sees the maximum moment, with no shear in the load span.

Specimen and Setup

• Rectangular bars cut or formed from plates; measure width and thickness at the centre of every bar

• Support span large compared with thickness (typically a span-to-depth ratio of about 16:1 or more) so that failure is in flexure, not interlaminar shear

• Rollers or articulating supports that can rotate and tilt slightly, to avoid twisting and contact stresses on brittle material

• Constant crosshead rate chosen to give the strain rate required by the standard

• Furnace and high-temperature fixture for elevated-temperature tests

Universal Grip recommends a bend fixture with articulating supports for ceramic composites.

Flexural Strength Formulas

• Three-point: σ = 3PL / (2bd²)

• Four-point quarter-point: σ = 3PL / (4bd²)

• Four-point third-point: σ = PL / (bd²)

P = load, L = support span, b = specimen width, d = specimen thickness. Flexural modulus is calculated from the initial linear part of the stress–strain curve.

Worked Example

A CFCC bar 10 mm wide and 2.5 mm thick is tested in four-point quarter-point bending on a 40 mm support span (span-to-depth ratio 16:1). The peak load is 400 N.

σ = 3 × 400 × 40 / (4 × 10 × 2.5²) = 48,000 / 250 = 192 MPa.

Check the failure mode as well: a tension or compression failure in the outer fibres is valid; a shear (delamination) failure at mid-thickness means the span-to-depth ratio was too small and the result is not a valid flexural strength.

Similar Specifications

• ASTM C1161 – flexural strength of advanced (monolithic) ceramics

• ASTM D790 – three-point flexural properties of plastics

• ASTM D6272 – four-point flexural properties of plastics

• ASTM C1275 – tensile behaviour of CFCCs

ASTM C1341 FAQ

What materials does ASTM C1341 cover?

Continuous fiber-reinforced advanced ceramic composites with 1D, 2D and 3D fiber architectures, tested at ambient or elevated temperature.

Which loading geometry should I use?

Four-point bending (quarter-point or third-point) is generally preferred; three-point bending is allowed but concentrates the maximum stress under the centre load.

Why is span-to-depth ratio important?

CFCCs have low interlaminar shear strength. A long span relative to thickness makes the bar fail in bending rather than by delamination.

Can C1341 be run at high temperature?

Yes, using a furnace and high-temperature bend fixture. Confirm the specimen sizes, spans and rates against your copy of ASTM C1341.