Static and Dynamic Parameters of Railway Tracks Retrofitted With Under Sleeper Pads

The paper presents results of the laboratory tests made for the prototype resilient under sleeper pads in the Warsaw University of Technology laboratory unit. These pads are dedicated to reduce vibrations transmitted to the vicinity of the railroad and to improve the resistance of the railroad structure. The laboratory testing program was carried out for elastomeric materials (polyurethane and rubber based) due to the PN-EN 16730 standard. The obtained values of the key parameters were used in order to determine the insertion loss vibration level by applying analytical method. The paper presents the influence of selected parameters i.e. static and dynamic moduli on the reduction of vibration and structure-borne sound level.

Heat Built Up During Dynamic Mechanical Analysis (DMA) Testing of Rubber Specimens

The viscoelastic properties of rubbers play an important role in dynamic applications and are commonly measured and quantified by means of Dynamic Mechanical Analysis (DMA) tests. The rubber properties including the static and dynamic moduli are a function of temperature; and an increase in the temperature leads to a decrease in both moduli of the rubber. Due to the heat generation inside the rubber during the DMA test and the possible change of the rubber properties it is important to quantify the amount of temperature rise in the rubber specimen during the test. In this study, a Finite Element Analysis (FEA) model is used to predict the heat generation and temperature rise during the rubber DMA tests. This model is used to identify the best shape of the specimen to achieve the minimum increase in temperature during the test. The double sandwich shear test and the cyclic compression tests are considered in this study because these two tests are mostly used in industry to predict the rubber viscoelastic properties.

DYNAMIC PROPERTIES AND TIRE PERFORMANCES OF COMPOSITES FILLED WITH CARBON NANOTUBES

ABSTRACT Carbon nanotubes (CNTs) have been widely studied in rubber goods and tire compounds to improve, for example, antistatic and thermal conductivity performances. CNTs were applied in passenger tire tread compounds to improve comprehensive tire performances, especially wet traction. High frequency dynamic properties of CNT-filled compounds were revealed for the first time. There was good correlation between compound dynamic properties and vehicle tire test results. The influence of CNTs on tire performances and their mechanisms was investigated and explained by the dynamic properties and master curve analysis in the frequency domain. Substituting 50 phr carbon black N234 by 20 phr CNTs could maintain hardness but increased static and dynamic moduli, which was beneficial for the tire handling, with 0.25 point improvement in the subjective testing. For the CNT-filled compounds, 1.5% traction improvement on a dry road and 6.5% traction improvement on a wet road can be explained successfully by the increased hysteresis loss (tan δ) and decreased storage modulus (G′) at high frequency domain (104–108 Hz). It is implied by Williams–Landel–Ferry law calculation that a strong interaction between CNTs and rubber resulted in higher temperature dependence; however, the trade-off was a 7% higher tire rolling resistance coefficient and 33% worse wear resistance for the CNT tires. CNT-filled compounds were demonstrated to have superior handling and traction performances suitable for racing and sports car tires.

The influence of selected static and dynamic parameters of resilient mats on vibration reduction of railway tracks

The paper presents laboratory methods of testing the prototype resilient mats, used in rail track systems in order to reduce vibrations transmitted to the vicinity of the railroad and to improve the resistance of the railroad structure. The laboratory testing program was carried out for elastomeric materials (polyurethane based). The key parameters being investigated in the Warsaw University of Technology laboratory unit were used in order to determine the insertion loss vibration level by applying analytical method. The paper presents the influence of selected parameters i.e. static and dynamic moduli on the reduction of vibration and structure-borne sound level – i.e. the value of insertion loss parameters.

Predicting the Dynamic Characteristics of Vibration-isolating Rubbers Based on Natural and Synthetic Rubbers

The principal vibration-isolating characteristics of rubbers based on natural rubber and a combination of synthetic isoprene and butadiene rubbers were determined. The static and dynamic moduli, the hysteresis losses, and the logarithmic decrement were measured on an Yerzley mechanical oscillograph (manufactured by the US company Tavdi) in accordance with ASTM D-945. The changes in these characteristics were measured in the process of heat ageing. To convert the data to room temperature, the Arrhenius equation was used. The main changes in the static modulus occur in the first three years, and the main changes in the dynamic modulus in the first five years. Their ratio and the natural frequencies are different for various rubbers and for different storage and service times. The resonance zones are also different. It is concluded that, when predicting the useful life of the vibration isolator, it is necessary to assess all the dynamic and static parameters for each individual case.