Page 295 - Mechanics Analysis Composite Materials

280 Mechanics and ana/ysis of composite materials

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Fig. 6.12. Failure modes of a unidirectional glass epoxy composite under longitudinal compression.

It should be emphasized that the test shown in Fig. 6.12 can be misleading because
transverse deformation of the ply is not restricted in this test, while it is normally
restricted in actual laminated composite structural elements. Indeed, the long
cylinder with material structure [Oy ,] being tested under compression yields material
strength 0: = 300 MPa, while the same cylinder with material structure [Oy,/9O0]
gives 0; = 505 MPa (Katarzhnov, 1982). Thus, if we change one longitudinal ply
for a circumferential ply that practically does not work in compression along the
cylinder axis but restricts its circumferential deformation, we increase material
strength in compression by 68.3%. Correspondingly, the failure mode becomes
quite different (see Fig. 6.13).

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Fig. 6.13. Failure mode of a glassepoxy tubular specimen with 10 longitudinal plies and one outside
circumferential ply: (a) inside view; (b) outside view.