Ratchetting of composite pipes

Abstract

The uniaxial ratchetting characteristics of fibre glass reinforced epoxy laminate have been investigated in the present project. The specimens were subjected to cyclic axial stress with a constant mean stress of 40 MPa and a varying amplitude stress of 26.67 MPa and 53.33 MPa. Tests were also performed on 50 mm diameter, Glass fibre Reinforced Epoxy (GRE) straight pipe. The pipe was subjected to a constant internal pressure of 1.875 MPa and a cyclic axial load. The finite element model in ABAQUS has also been simulated in similar loading case. The comparisons between experiment and simulation results were observed. The effect of fibre orientation on the rate of ratchetting was also investigated at the present project. The uniaxial and biaxial ratchetting strain was observed to increase with a number of cycles but decreased the rate of ratchetting. The specimen showed no further ratchetting rate and exhibited shakedown after some strain accumulation. On the basis of experiment and simulation, it appears that ratchetting would occur in the circumferential direction for a composite pipe subjected to constant internal pressure and cyclic displacement with no ratchetting observed in axial direction. A direction in fibre orientation seemed to have effect on the rate of ratchetting. Thus, the increasing of fibre angle from the axial load axis will increase the rate of ratchetting.