Standard Practice Unnotched Compression Testing of Polymer Matrix Composite Laminates
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, Fxunc,
5.1.2 Ultimate compressive strain,
5.1.3 Compressive (linear or chord) modulus of elasticity, Ec, 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 (± θ 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 (e.g., 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, e.g., 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:
220.127.116.11 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
18.104.22.168 Longer and wider gage section imposing less constraint on in-plane transverse displacement.
5.2.2 Disadvantages of this practice include:
22.214.171.124 Longer and wider specimen, thus consuming more material than other standards noted above
1.1 This practice provides instructions for using the Test Method D6484 open hole compression test fixture to determine unnotched compressive strength of multi-directional laminates. The composite material forms are limited to continuous-fiber reinforced polymer matrix composites in which the laminate is both symmetric and balanced with respect to the test direction. The range of acceptable test laminates and thicknesses are described in 8.2.1.
1.2 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard.
1.2.1 Within the text the inch-pound units are shown in brackets.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health and environmental practices and determine the applicability of regulatory limitations prior to use.
1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
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