Composite lamina compressive properties using the Wyoming combined loading compression test method

The determination of lamina compressive strength and modulus using the Wyoming Combined Loading Compression (CLC) test method was investigated. In this test method an untabbed [90/0]_ns cross-ply test coupon is tested in uniaxial compression using the CLC test fixture. The longitudinal modulus and strength of the 0°-plies are determined by applying a back-out factor, calculated using Classical Lamination Theory, to the measured longitudinal laminate modulus and strength.; A parametric study revealed that specimen quality, load train alignment, and fixture dimensional tolerances have a large impact on the measured compressive properties. Thus, a significant amount of time was dedicated to developing specimen fabrication and testing procedures to minimize variations in the measured compressive properties.; A comparative study of the CLC and IITRI test fixtures showed that the CLC test fixture is superior to the IITRI fixture in many ways. Although the compressive properties measured using these two fixtures are often statistically equivalent, the CLC test fixture is easier to use, less expensive to fabricate, and much less massive than the IITRI fixture.; In a second portion of the comparative study, the 0°-ply compressive strength obtained using [90/0]_ns cross-ply test specimens was compared to the 0°-ply compressive strength obtained using quasi-isotropic test specimens. This revealed that the 0°-ply compressive strength was independent of the laminate orientation. This “backed-out” 0°-ply compressive strength is then by definition the “design value” for the strength of the composite material in compression.; The present study showed that valid “design values” for the compressive strength of laminated composite materials can be obtained using the CLC test method. This was verified by testing two classes of structural components in compression, filament-wound cylinders, and honeycomb sandwich beams. The compressive strength of the 0°-plies at failure in the honeycomb sandwich beams was nearly identical to the lamina compressive strength measured using the CLC test method. High quality filament-wound cylinders were not successfully fabricated, therefore the lamina compressive strength measured in these components did not compare well with values measured using the CLC test method.