ASTM D6641 Test Fixture - Compression Testing for Polymer Matrix Composite Laminates
Standard Test Method for Compressive Properties of Polymer Matrix Composite Materials Using a Combined Loading Compression (CLC) Test Fixture
ASTM D6641 provides a method for evaluating the compressive strength and stiffness parameters of polymer matrix composite materials using a combined loading compression (CLC) or equivalent test fixture. Combined Loading Compression (CLC) uses a combination of end and shear loading; shear stresses are decreased, and clamping pressures can be generated using bolted clamps.
Dimensions of ASTM D6641 Specimens
Test specimens can be tabbed or untabbed (process A) (Procedure B). When put in the fixture, a typical ASTM D 6641 test specimen (drawings below indicate typical specimen measurements in the ASTM D 6641 Standard) has a 140 mm length, 12 mm width, and an unsupported gauge length of 12 mm. According to ASTM D 6641 testing requirements, gauge lengths ranging from 12 mm to 25 mm are permissible parameters.
The specimen ends must be perpendicular to the specimen's longitudinal axis and parallel to one another within 0.03 mm for Procedures A and B.
Tabs normally have square ends and are 1.6 mm [0.06 in.] thick, though this can be modified as needed.
The specimen's faces could be lightly lapped to smooth out any minor surface defects and imperfections, resulting in flatter surfaces for a more uniform fixture grip.
The 13 mm gauge length allows for the insertion of a strain gauge device on the opposite surface.
Preparation of Combined Loading Compression Test Fixture Specimens
- The specimen preparation device is fitted with guide pins.
- The specimen preparation device is loaded with the CLC test fixture.
- Insert an alignment bar into the gauge length of the fixture to adjust the gauge length.
- Place the specimen into the fixture, such that it sits on top of the guiding pins.
- Insert the alignment bar into the CLC test fixture's gauge length.
- Using an Allen wrench, tighten the fixture. According to ASTM D 6641, the torques of all eight 6mm diameter screws should be 2.5 to 3 Nm.
- Remove the alignment bars from the test fixture.
ASTM D6641 Combined Loading Compression Testing
The samples’ long side should be parallel to the direction to be tested.
After that the sample has been ready, insert the sample into the ASTM D 6641 test fixture.
Place the ASTM D 6641 test fixture between 2 compression plates in the testing machine.
Load the specimen in compression to failure at a nominal rate of 1.3 mm/min, while recording strain data, force and displacement.
For valid test results, the final failure of the test specimen must occur within the gauge section.
Calculations:
- Laminate Compressive Strength
- Laminate Compressive Modulus (Chord Modulus)
- Compressive Poisson’s Ratio by Chord Method is the compressive properties that can be calculated.
Recommended Equipment for ASTM D 6641 Testing
Compression Platens for CLC Testing
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