Using Hydrostatic Pressure to Maximize Frequency Dependent Damping Properties of Thermoplastic Polyurethane

AbstractThe frequency-dependent viscoelasticity of Chinese fir (Cunninghamia lanceolata) during moisture desorption was investigated and the applicability of the time-moisture superposition (TMS) relation on wood stiffness and damping during the moisture desorption was verified. The hygrothermal conditions for the moisture desorption were set up as six constant temperatures ranging from 30 to 80°C and three relative humidity (RH) levels at 0, 30 and 60%. Due to the elimination of water during the moisture desorption, the stiffness of the Chinese fir increased, whereas the damping decreased. With the increase in frequency, increased stiffness and decreased damping were observed. Utilizing the TMS relation, it was possible to construct master curves of wood stiffness at temperatures ranging from 30 to 80°C. The linear relationship between the shift factor and the moisture content (MC) manifested a low intermolecular cooperativity between the polymers and a narrow relaxation window. However, the TMS relation was not able to predict the wood damping properties during the moisture desorption, because wood is a multi-relaxation system. The non-proportional relationship between the free volume and MC during the moisture desorption may also explain why the TMS relation failed to construct master curves of the wood damping properties.

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Damping properties of bi-dimensional sandwich structures with multi-layered frequency-dependent visco-elastic cores

Composite Structures ◽

10.1016/j.compstruct.2016.07.056 ◽

2016 ◽

Vol 154 ◽

pp. 334-343 ◽

Cited By ~ 13

Author(s):

Ayodele Adessina ◽

Mohamed Hamdaoui ◽

Chao Xu ◽

El Mostafa Daya

Keyword(s):

Sandwich Structures ◽

Damping Properties ◽

Frequency Dependent

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The Influence of Amplitude- and Frequency-Dependent Stiffness of Rail Pads on the Random Vibration of a Vehicle-Track Coupled System

Shock and Vibration ◽

10.1155/2016/7674124 ◽

2016 ◽

Vol 2016 ◽

pp. 1-10 ◽

Cited By ~ 2

Author(s):

Kai Wei ◽

Pan Zhang ◽

Ping Wang ◽

Junhua Xiao ◽

Zhe Luo

Keyword(s):

Random Vibration ◽

Thermoplastic Polyurethane ◽

Coupled Model ◽

Ground Vibration ◽

Coupled System ◽

Element Model ◽

Static Stiffness ◽

Frequency Dependent ◽

Low Speed ◽

Secant Stiffness

The nonlinear curves between the external static loads of Thermoplastic Polyurethane Elastomer (TPE) rail pads and their compressive deformations were measured. A finite element model (FEM) for a rail-fastener system was produced to determine the nonlinear compressive deformations of TPE rail pads and their nonlinear static stiffness under the static vehicle weight and the preload of rail fastener. Next, the vertical vehicle-track coupled model was employed to investigate the influence of the amplitude- and frequency-dependent stiffness of TPE rail pads on the vehicle-track random vibration. It is found that the static stiffness of TPE rail pads ranges from 19.1 to 37.9 kN/mm, apparently different from the classical secant stiffness of 26.7 kN/mm. Additionally, compared with the nonlinear amplitude- and frequency-dependent stiffness of rail pads, the classical secant stiffness would not only severely underestimate the random vibration acceleration levels of wheel-track coupled system at frequencies of 65–150 Hz but also alter the dominant frequency-distribution of vehicle wheel and steel rail. Considering that these frequencies of 65–150 Hz are the dominant frequencies of ground vibration accelerations caused by low-speed railway, the nonlinear amplitude- and frequency-dependent stiffness of rail pads should be taken into account in prediction of environment vibrations due to low-speed railway.

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