5.1 This practice provides supplemental instructions for the use of Test Method D6484/D6484M to determine unnotched compressive strength data for material specifications, research and development, material design allowables, and quality assurance. Factors that influence compressive strengths and shall therefore be reported include the following: material, methods of material fabrication, accuracy of lay-up, laminate stacking sequence and overall thickness, specimen preparation, specimen conditioning, environment of testing, specimen alignment and gripping, speed of testing, time at temperature, void content, and volume percent reinforcement. Composite properties in the test direction that may be obtained from this test method include:

5.1.1 Unnotched compressive (UNC) strength, F_x^unc,

5.1.2 Ultimate compressive strain,

5.1.3 Compressive (linear or chord) modulus of elasticity, E^c, and

5.1.4 Poisson's ratio in compression.

5.2 This practice provides a compression test method for laminates containing fibers in multiple fiber directions, particularly those combining axial (0 degree) fibers and off-axis (± ? degree) fibers. Other compression strength test methods include SACMA SRM-1 (also known as the modified D695), D3410/D3410M, D5467/D5467M, D6641/D6641M, and D7249/D7249M. The SRM-1 test uses 12.6 mm [0.50 in.] wide specimens, which is only appropriate for unidirectional tape, cross-ply [0/90]ns tape, or small unit-cell-size fabrics (e.g. 3K-70-P). Larger cell-size fabrics (for example, spread-tow 12K fabrics) should be tested with wider specimens. The standard D3410/D3410M and D6641/D6641M test fixtures do permit the use of wider specimens, for example, 25.4 mm [1.0 in.] wide, and thus can be used to test laminates containing both axial and off-axis fibers; however their gage lengths are relatively short. Test Method D5467/D5467M is intended to obtain the compressive strength of unidirectional laminates, but is expensive due to the sandwich beam configuration. Test Method D7249/D7249M is intended to obtain the compressive strength of sandwich facesheets.

5.2.1 Advantages of this practice include:

5.2.1.1 Avoiding the use of tabs, which are typically required with the end-loaded SRM-1 specimen, which are often required with the shear loaded Test Method D3410/D3410M specimen, and sometimes required with the Test Method D6641/D6641M test specimen, in order to obtain valid failure modes, and

5.2.1.2 Longer and wider gage section imposing less constraint on in-plane transverse displacement.

5.2.2 Disadvantages of this practice include:

5.2.2.1 Longer and wider specimen, thus consuming more material than other standards noted above