Measurement of Modulus Change with Temperature of Synthetic Track Materials

Pei-Hsin Kuo


The effect of the weather, season and air temperature on the condition of synthetic tracks has been a topic of considerable recent interest. No published study to date has considered the temperature effect in a systematic manner, and no scientific result to date has researched the mechanical properties and design of synthetic track materials based on the experience of the inventors. The purpose of the study was to investigate two hypotheses: 1) the correlations, within the racing speeds, between layer temperatures and hardness of the track, and 2) the responses of the elastic moduli of synthetic track materials with temperature changes. In-situ test, during training and racing at Del Mar race track, the air temperature, surface temperature, the temperature at four depths within the surface, and the Clegg Impact Value (CIV) of the synthetic race surface was measured twice daily over a 41 day period. The racing work times at six furlongs races were also acquired over the same 41 day meet period. Pearson's product moment coefficient and simple linear regression were used to identify the correlations within the parameters. In material properties test, the chamber system was developed to control the temperatures and pressures for measurement of the Young's and shear modulus of synthetic track materials by using the ultrasonic techniques. A pair of longitudinal and shear ultrasonic wave transducers were used to propagate samples with the transmission method. Before the experiment, dynamic compaction was used to compact dry samples for preparation. The six levels of temperatures and five levels of pressure were applied from 21 to 66 °C and 90 to 537 kPa, progressively. The fastest and average times have higher correlations with the temperatures at the shallower layers during morning training, but lower correlations with the hardness of track surfaces. The results of experiment by using ultrasonic measurement show that the elastic moduli stiffen with increased pressures at lower temperatures from 21 to 33 °C. When the temperatures increase above 38 °C, the elastic moduli decay regardless of high pressure. This explains the phenomenon of stiffer track surface at the morning and the softer surfaces at the afternoon based on the impact values. The results of this study highlighted the effects of melting mechanism of waves with increased temperatures on the synthetic track as an important factor that influences the track conditions and the speed of the horses. Future work should focus on the investigation of proportion and types of waxes separated from the synthetic track materials by chemical analysis and effects of moisture to the materials properties of the materials by in-situ and laboratory test.