Prediction of elasto-plastic behavior of pressurized composite reinforced metal tube by means of Acoustic Emission measurements and theoretical investigation

摘要

This paper gives a theoretical background and provides results of laboratory measurements for the nonlinear mechanical behavior of the composite overwrapped metal cylinder, subjected to pressure load. The chamber structure consisting of metal tube and fiber reinforced composite shell is analyzed by means of elasto-plastic study, and validated by Acoustic Emission (AE) measurements. The full-scale compound cylinder was checked against internal working pressure of 75 MPa. It was generally found that, at high loads, the composite reinforcement provides a strong support for the metal tube when the steel material approaches plastic deformation. In case of plastic flow within the steel, the bigger percentage of the external load is safely transferred to the composite fibers having much higher elastic limit, which prevents deformations of the metal tube from being too large. This phenomenon has been clearly visualized by AE signals, appearing in the frequency range between 330 and 420 kHz. The significant increase of AE hits was noted at the load pressure of 45 MPa, when some substantial friction and deformation processes within the composite structure could be observed. A new normalized stress factor was proposed to describe the mechanism of the internal load distribution between the composite reinforcement and steel cylinder. It was calculated that this composite-to-metal stress ratio, ns, starts from about 26% - when the steel tube works in its elastic range, and grows to 70% at full load of 75 MPa. It makes the usage of the composite reinforcement significantly more efficient at higher working pressure. Both the developed analytical model for elasto-plastic behavior of the composite reinforced metal structures, and the applied AE technique allowed to propose the optimal design parameters for the chamber under study, and increase its performance-to-weight ratio.