Measurement of strain and axial contraction of an FRP tube under large rotation

Abstract

Large strain measurement and axial contraction of a fiber-reinforced plastic (FRP) tube under biaxial loading were investigated theoretically and experimentally. The equation for calculating strains from strain gage measurements for the case of large deformation and large rotation was derived based on the analysis of kinematics of deformation. Axial contraction of a tube could be predicted as a function of stresses, a twist angle and an initial elastic modulus of the axial direction. To 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 variable differential transformer (LVDT) and angular displacement transducer (ADT) of a testing machine could be adopted in strain measurement of the biaxial test for fairly large deformation. The prediction of axial contraction of a CFRP tube agreed well with the LVDT result of the testing machine.