Graduation Year

2011

Document Type

Dissertation

Degree

Ph.D.

Degree Granting Department

Civil and Environmental Engineering

Major Professor

Manjriker Gunaratne

Co-Major Professor

Autar K. Kaw

Keywords

LuGre model, semi-empirical parameterization, standardization, tire-pavement interaction, tire property measurement

Abstract

Accurate characterization and evaluation of tire/pavement friction is critical in assuring runway and highway safety. Historically, Pavement Friction Measurement Devices (PFMDs) employing different measuring mechanisms have been used to evaluate tire/pavement friction. They yield significantly disparate friction coefficients under the same contact conditions. Currently, an empirically developed data harmonization method based on a reference device (Dynamic Friction Tester (DFT)) is used in an attempt to overcome the disparities between the measurements using various different PFMDs. However, this method, which has been standardized by the American Society for Testing and Materials (ASTM E1960), has been criticized for its inconsistency by researchers and runway/highway operations personnel.

The objective of this dissertation research was to develop a systematic and physically intuitive harmonization method for PFMDs that will improve the comparability of their data. As a foundation for such a harmonization, the LuGre tire model that employs physically meaningful parameters to represent the main attributes of tire/pavement friction was evaluated and validated. Measurements of tire/pavement friction by three widely used PFMDs; Locked Wheel Skid Trailer (LWST), Runway Friction Tester (RFT) and DFT, were accurately predicted using nonlinear optimization of LuGre model parameters. The LuGre model was found to be superior compared to the model used in the current ASTM E1960 standardization procedure for predicting PFMD measurements.

A sensitivity analysis was performed to identify the relative significance of the LuGre model parameters in characterizing tire/pavement friction, and to study the effects of variation of those parameters on predicted frictional behavior. A set of laboratory tire experiments was designed and performed to validate the physical significance of LuGre tire model parameters and to study how they behave under typical load, inflation pressure, excitation frequency, and amplitude conditions. An empirical method was developed to accommodate the effects of water film thickness on tire/pavement friction in the LuGre model. The results of the sensitivity analysis and the experiments to directly estimate the model parameters were used to identify and quantify appropriate modifications to the measurement mechanisms of PFMDs that can be introduced to improve the comparability of their results. Friction experiments performed after introducing such modifications to the LWST showed an average reduction of 20% in the deviations between the results of LWST and RFT measurements.

The research carried out in this dissertation is significant because it: (i) identified the deficiencies in the current method for harmonizing PFMD measurements and the underlying reasons for these deficiencies, (ii) emphasized the importance of a standardization approach that regulates the physical condition of PFMDs, in order to achieve universal comparability of tire/pavement friction measurements, (iii) validated that the LuGre tire model is a tire/pavement friction model capable of facilitating a better standardization approach, and, (iv) initialized the development of a physically meaningful harmonization procedure for PFMDs.

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