Axial mechanical experiments of unbonded flexible pipes.

Axial structural damping behavior induced by internal friction and viscoelastic properties of polymeric layers may have an inevitable influence on the global analysis of flexible pipes. In order to characterize this phenomenon and axial mechanical responses, a full-scale axial tensile experiment on a complex flexible pipe is conducted at room temperature, in which oscillation forces at different frequencies are applied on the sample. The parameters to be identified are axial strains which are measured by three kinds of instrumentations: linear variable differential transformer, strain gauge and camera united particle-tracking technology. The corresponding plots of axial force versus axial elongation exhibit obvious nonlinear hysteretic relationship. Consequently, the loss factor related to the axial structural damping behavior is found, which increases as the oscillation loading frequency grows. The axial strains from the three measurement systems in the mechanical experiment indicate good agreement, as well as the values of the equivalent axial stiffness. The damping generated by polymeric layers is relatively smaller than that caused by friction forces. Therefore, it can be concluded that friction forces maybe dominate the axial structural damping, especially on the conditions of high frequency. [ABSTRACT FROM AUTHOR]