Viscoelastic properties of Kevlar-29 fabric tape strength member

Kevlar®-29 strength members find wide application in tow lines, mooring lines, oil rig pendants and underwater sensor systems. In this paper, the dynamic mechanical properties of Kevlar-29 fabric tape strength member are characterized by semi-empirical means. A series of transient and harmonic tests were conducted for a typical configuration taking into account of time scales and operating conditions of practical interest. Constitutive relations based on three-parameter and five-parameter spring-dashpot discrete models were used for extracting the properties from transient tests. The parameter values obtained through transient tests were transformed to complex modulus in the frequency domain. Comparison in the frequency domain was made between the results obtained through transient tests and harmonic tests. Effects of preload and stress rates were studied. It is observed that storage modulus increases and loss factor decreases with increase in preload. At very low frequencies, analysis of the transient tests using discrete models shows lower storage modulus values compared to harmonic tests and hence does not provide reliable estimation. At higher frequencies, i.e., above 8 Hz, five-parameter discrete model based on transient tests can adequately estimate both the storage modulus and loss modulus. The transient tests indicate a rise in the loss factor at mid frequencies whereas the harmonic tests give almost flat response. Also the modulus of Kevlar fabric tape increases with increase in stress rate. Nonlinear behaviour is noticed throughout the tensile deformation response.