Issue 29

M. Scafè et alii, Frattura ed Integrità Strutturale, 29 (2014) 399-409; DOI: 10.3221/IGF-ESIS.29.35 408 Figure 9 : SEM image of A6 sample brooming failure (lateral view). Figure 10 : SEM image (detail) of A6 sample brooming failure (0° ply). C ONCLUSIONS he present paper is aimed to study the unidirectional lamina compressive strength of a carbon/epoxy composite lamina by using two cross-ply and two angle-ply composite materials. The Combined Loading Compression Test Fixture (ASTM D 6641) was employed to execute the experimental tests. The results showed that failure strengths determined by using cross-ply and angle-ply specimens and Back-out Factors are about twice to those obtained for 0° unidirectional specimens. This is due to the phenomenon of fibre micro-buckling in the UD samples at 0°, which is instead limited in the cross-ply and angle-ply samples. Furthermore the values of strengths, determined by linear lamination theory, are in agreement with those reported in the data sheet of the prepreg used to make our composite materials. In particular the maximum compressive strength was obtained for cross-ply composite with the minimum percentage of 0° plies 21.1 %, while the value specified in the data sheet is between those obtained for the two cross-ply samples. The strength coefficients of variation (CV%), associated with the materials A, B, C and D, were between 3% (B composite) and 6% (A composite). Considering the type of material examined, these are low levels of data scatter. As previously mentioned, the compressive strength values obtained for the cross-ply composites agree better with those reported in the data sheet, compared to those obtained for the angle-ply composites. Also the cross-ply lamination is simpler than the angle-ply lamination and the BF equation is considerably simplified in the first case than in the second. Then, the estimate of the 0° lamina strength obtained by linear lamination theory, seems to be better for cross-ply specimens respect to angle-ply ones. Finally this indirect analytical method, developed according to the classical lamination theory, and applied to a 0° unidirectional lamina, produced an high compressive strength associated with a low data scatter, two attractive characteristics for this kind of composite materials. R EFERENCES [1] Wegner, P. M., Adams, D. F., Verification of the Combined Load Compression (CLC) Test Method, U.S. Department of Transportation / Federal Aviation Administration, Final Report - DOT/FAA/AR-00/26 (2009). [2] ASTM D 6641 / D 6641 M – 09. – Standard Test Method for Determining the Compressive Properties of Polymer Matrix Composites Laminates Using a Combined Loading Compression (CLC) Test Fixture (2009). [3] Welsh, J.S., Adams, D. F. – Testing of angle-ply laminates to obtain unidirectional composite compression strengths, , Composites Part A 28A (1997) 387-396. [4] Adams, D. F., Carlsson, L. A., Byron Pipes, R. – Experimental Characterization of Advanced Composite Materials, Third ed., CRC Press LLC (2003). [5] http://www.compositesworld.com/articles/back-out-factors - Adams, D. F., (2014).