MEASUREMENT OF STRAIN AND AXIAL CONTRACTION OF AN FRP TUBE UNDER LARGE ROTATION

Large strain measurement and axial contraction of a fiber-reinforced p lastic (FRP) tube under biaxial loading were investigated theoreticall y and experimentally. The equation for calculating strains from strain gage measurements for the case of large deformation and large rotatio n was derived based on the analysis of kinematics of deformation. Axia l contraction of a tube could be predicted as a function of stresses, a twist angle and an initial elastic modulus of the axial direction. T o demonstrate applicability of the equations, the tests of a cross-ply carbon/epoxy composite tube were conducted under uniaxial and tension /torsion biaxial loading up to failure. The signal of a linear variabl e differential transformer (LVDT) and angular displacement transducer (ADT) of a testing machine could be adopted in strain measurement of t he biaxial test for fairly large deformation. The prediction of axial contraction of a CFRP tube agreed well with the LVDT result of the tes ting machine.