Validation of a frustrated total internal reflection test bench for tire footprint pressure measurement

The development and industrialization of a compact tire footprint pressure distribution test bench is the focus of this work. The test bench work principle is the total internal frustration of light (FTIR) that illuminates a glass sheet from the sides. It allows to obtain a correlation between the brightness of a photographic image of the footprint and the normal pressure applied. In order for the measurements to be independent of the tire compound and the environmental conditions such as ambient light and tire compound, a suitable interface material has to be interposed between the test specimen and the glass surface. The response of the tested materials, i.e. their characteristic pressure - brightness curve, along with their homogeneity, have been measured with purposely designed calibration procedures. Special care has been taken in defining the material deal properties for the application. The selection process led to the selection of a suitable polymeric film. Validation towards the large-scale implementation of the system has been carried out by comparing the results obtained with a well established piezo-resistive sensor, with the aim of evaluating the system’s accuracy and repeatability. The results obtained are very promising: the FTIR system is able to provide pressure distribution measurements with a level of accuracy similar to that the standard piezo-resistive pressure measurement system, but with about forty times the spatial resolution and at a much lower economic costs, both considering initial investment and maintenance. Validation of a frustrated total internal reflection test bench for tire footprint pressure measurement.