In Plane Compressive Composite Failure Test Plans

Test Specimen Requirements:

• At least 3-5 specimens per test condition

• Standard Configuration Dimension: 75mm width, 200mm length, specimen height/depth equal to the sandwich stack (2 layers of CF plus divinycell foam core and another 2 layers of CF)

• Non Standard Configuration Dimension: width should not be less than 2x total thickness and not greater than 6x total thickness. In addition, the specimen length will be equal to support span length plus 50mm or 1/2x more of sandwich thickness whichever of the two offers a longer length.

Equipment Needed:

• Deflectometer: deflection of specimen measured in the center of support span

• Conditioning Chamber: maintains temperature and humidity of the material for complete control

• Environmental Chamber: similar to conditioning chamber, where temperature and humidity can be controlled and other factors can be introduced to the specimen as well to alter its physical and chemical properties

Loading Fixtures:

• Either 3 point or 4 point bend test can be used for this experiment. A 3 point bend test features one downward force, while a 4 point bend test is two downward forces onto the specimen

• The specimen will be held by two support bars at each end and below the material. The 3 point bend test is the standard procedure with a separation width of 150mm between the two support bars.

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As you can see in the image above, the test specimen is laid flat onto the two support bars shown using arrows. The head of the UTM applies a downward force onto the object while the support bars are stationary.

Testing Machine:

• Universal testing machine required, both stationary and moveable head required

• The head velocity should be able to be adjusted and controlled that is capable of producing a displacement of 6mm/min and thus create a specimen failure at 3-6min.

Procedure:

• Check if the specimen needs to be in a conditioned environment, and needed conditioning steps beforehand.

• Measure the specimen dimensions as accurate as possible. Length, width, as well as thickness with an accuracy of +/- 0.254mm should be considered. Support and loading fixture should be recorded as well.

• Place the specimen onto the loading fixture depending on which testing procedure is required. 3 point bend test and the 4 point bend test require different loading fixtures.

• Attach the deflection transducer to the fixture and specimen, ensuring that proper attachment per manufacturer instruction is followed. Ensure strain gauges are zeroed and deflection transducer is balanced.

• Apply a downward compressive force onto the center of the specimen until failure or until the deflection measured is equal to to the thickness of the test specimen.

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The green device shown in the image above is the deflectometer that can be used to measure small deflections in any direction.

Data that should be recorded:

• Force vs crosshead displacement and force vs deflection at close intervals or continuous

• Failures should be recorded, taking note of the force at failure, displacement, and mode of damage at point of failure.

• Record max force, failure force, head displacement, and deflection at moment of failure

For more info regarding this specific ASTM test standard, click the link below for more details.

ASTM C393_Standard Test Method for Shear Strength