ASTM D6641

Theory:

ASTM D6641 covers a test for polymer matrix materials using an ASTM specific compression fixture. The fixture is designed to compress the sample from the sides, prior to the test. The sides are compressed by tightening multiple torque screws which squeeze the fixture together. 

Once the sample has been mounted, it is then compressed until failure. There are several types of failure modes and it can often be difficult to discern the exact failure mode without strain gauges.  The test seeks to create a total compression failure, and any buckling failures should be discarded and remedied with better test preparation.

Geometry:

The D6641 fixture is designed to hold up to a 40 inch wide sample. The samples are long rectangular bars and extend the entire height of the fixture. Each end is designed to sit flush at the top and bottom surface of the fixture.

Solution:

Compression Platens are required in order to use this fixture. Two fixed platens are used to compress the fixture and create failure on the sample. The fixture ships with embedded jaws with serrated style faces. Also included are two .5x.5" spacer bars which help with sample set up.

A 50kN or 100kN Galdabini universal testing machine is recommended for this test. The Galdabini machines can ship as a plug & play solution with the procedure for ASTM D6641 pre-loaded onto the system. These material testing systems are flexible, easy to use, and last a long time with virtually no maintenance.

Analysis:

Compressive Strength is given when a total compressive failure is achieved. The units are usually megapascals or also ksi. There is a specific equation called the Euler buckling equation which can serve to predict the buckling stress.