MECHANICAL PERFORMANCE OF THIN-WALLED TUBULAR COMPOSITE ELEMENTS UNDER UNIAXIAL LOADING .2. COMPRESSIVE BEHAVIOR

Filament wound thin-wall CFRP and GFRP composite tubes were tested und er uniaxial compressive loading up to failure. Elastic and strength pr operties as well as failure mechanism were evaluated as related to the wall lay-up configuration. Angle-ply lay-ups of different (+/-0)(3) o rientations were compared with tubes having the same thickness but whe re internal and external theta plies were replaced by hoop (90) layers [90, (+/- 0)(2), 90]. The three directional specimens with the hoop l ayers, showed a strength value which is between the predicted first pl y failure (FPF) strength and the ultimate laminate failure (ULF) value . Angle-pip specimens, on the other hand, failed catastrophically at F PF. Significant higher ultimate compressive strength (30-100%) of the three-directional tubes as compared with their angle-ply reference wer e evident for all the tested tube configurations. This was attributed to the transverse stabilizing effect of the hoop layers which support the angle-ply fibers and reduced the chance for transverse cracking an d local buckling. This effect was also manifested by a significant red uction of the longitudinal Poisson ratio as compared with the angle-pl y counterpart.