Abstract
Static tests under tension/compression-torsion biaxial loading were conducted using tubular FRP specimens reinforced by plain woven glass cloth. Stress-strain curves were observed with a biaxial extensometer developed by the authors. In order to take account of the large deformation which is one of the unique charactaristics of FRP, the strength and S-S curve were evaluated with the Piola-Kirchhoff stress tensor and the Green-Saint Venant strain tensor, and these results were also compared with the S-S curves based on the nominal stress and nominal strain. The effects of normal stress to shear stress ratio (i.e, combined stress ratio) on both strength and steess-strain relations were also investigated. The following results were obtained;
(1) For orthotropic materials having large deformation capability, their properties (strength and stress-strain relations) must be evaluated with Piola-Kirchhoff stress tensor and Green-Saint Venant strain tensor.
(2) The combined stress ratio has no effect on the stress-strain relation within an elastic range, but it affects not only on the stress level where the yield point appears but also on modulus decay after yielding.
