- Author
-
Wegner, P. M.
|
Adams, D. F.
- Title
- Verification of the Combined Load Compression (CLC) Test Method. Final Report.
- Coporate
- University of Wyoming, Laramine
- Sponsor
- Federal Aviation Administration, Washington, DC
- Report
-
DOT/FAA/AR-00/26
August 2000
261 p.
- Distribution
- AVAILABLE FROM National Technical Information Service (NTIS), Technology Administration, U.S. Department of Commerce, Springfield, VA 22161. Telephone: 1-800-553-6847 or 703-605-6000; Fax: 703-605-6900; Rush Service (Telephone Orders Only) 800-553-6847; Website: http://www.ntis.gov For more information contact: Federal Aviation Administration William J.Hughes Technical Center's full text reports page: http://www.actlibrary.tc.faa.gov (in Adobe Acrobat portble document format 'PDF')
- Keywords
-
compressing
|
test methods
|
composite materials
- Identifiers
- testing fixtures; specimen fabrication; testing machine set and test procedures
- Abstract
- A review of the current compression testing literature reveals that presently there is a great deal of confusion in the composites industry surrounding the measurement of the compressive properties of fibrous composite materials. Different compression test methods often do not produce comparable compressive properties, and values generated by different testing laboratories using the same test method often disagree. These problems with current compression testing methods led the authors to design and evaluate the Combined Loading Compression (CLC) Test Method developed at the University of Wyoming. In this test method, the Oo-ply compressive strength of a fibrous composite material is obtained by testing an untabbed, [90/O]ns cross-ply specimen in the CLC test fixture. A parametric study revealed that specimen quality, load train alignment, and fixture dimensional tolerances all have a large effect on the measured compressive properties. Thus, a significant portion of the present study was dedicated to developing specimen fabrication and testing procedures that will minimize variations in the measured compressive properties due to these parameters. A comparative study of the CLC and ASTM D 3410 (1995) Method B which uses the wedge loading arrangement developed at the Illinois Institute of Technology Research Institute (IITRI) was conducted. Results of the study suggested that the CLC test fixture is preferable to the IITRI test fixture from a practical standpoint. Although the compressive properties measured using these two fixtures are statistically similar, the CLC test fixture is easier to use, less expensive to fabricate, and less massive than the IITRI test fixture, making it easier to install and, as a result, less likely to induce testing errors. Furthermore, because of its simpler design, the CLC test fixture is considerably less prone to machining errors. In a second portion of the comparative study, the Oo-ply compressive strength obtained from [90/O]ns cross-ply test specimens was compared to the Oo-ply compressive strength obtained with quasi-isotropic test specimens. The Oo-ply compressive strength for each material was "backed out" from the measured laminate compressive strength using classical lamination theory. This comparison revealed that the Oo-ply compressive strength was independent of the laminate orientation. This "backed out" Oo-ply compressive strength is then by definition the "design strength" of the composite material in compression. The present study showed that valid "design values" for the compressive strength of laminated fibrous composite materials can be obtained by testing cross-ply laminates in the CLC test fixture. There are many benefits that result from this test method. First, the CLC test fixture is smaller and less massive than the IITRI test fixture. This is an important factor when testing at conditions other than ambient as the time required to come to thermal equilibrium is proportional to the mass of the test fixture. Second, the CLC test fixture has relatively few moving parts and most of the surfaces of the fixture are at right angles to each other. For this reason the CLC test fixture is less expensive to fabricate than the IITRI test fixture. Third, the CLC test fixture is easier to use than the IITRI test fixture, because the specimen/wedge grip assembly often gets wedged into the cavities of the ITTRI test fixture housings. this problem does not occur with the CLC test fixture. there are also benefits to using a test specimen fabricated from a cross-ply laminate. Because the axial strength of the cross-ply laminate is lower than the axial strength of a unidirectional composite having the same number of plies, the cross-ply specimen can be tested without end tabs. this significantly reduces the time and expense involved in specimen fabrication.