A Comparison of Uniform and 3-D Tyre Contact Pressure Representations Using a Finite Element Method

Abstract

In pavement engineering a crude uniform contact pressure over a circular contact area is used to generate key strains for an analytical design method. The use of a more advanced tyre contact pressure measurement device has led to a situation where there is more information that is available to generate a more accurate uniform representation of contact pressure. This measurement device also offers the ability to measure non-uniform 3-D tyre contact pressure. That is to say the vertical, transverse and longitudinal components of pressure generated by a tyre in contact with a pavement. A comparison of the key strains generated by this improved uniform contact pressure representation and the measured 3-D contact pressure is of great interest. Of course a tyre does not display the same contact pressure for different combinations of axle loading and inflation pressure. The combination of these two factors greatly affects the nature of the contact pressure observed. A finite element mesh of a 3-layer thin pavement structure was created in CAPA-3D. This was used to model the uniform and 3-D contact pressure representations of a wide based tyre. This was done for 3 inflation pressures and 3 tyre loads. The inflation pressures were for a recommended inflation pressure and then plus and minus 200kPa. The tyre loading was for a maximum European axle loading and then greater and lower than this value. This gave a good spread of conditions that are relevant to the tyre operating conditions. The key strains at different locations in the pavement relevant to the major distresses of a pavement were assessed. The main distress mechanisms being top down cracking, asphalt cracking/rutting, traditional bottom up cracking and subgrade rutting. These gave a good spread of possible distresses that tyre contact pressure can contribute to. The results showed that there was a large effect on surface strains caused by 3-D contact pressure in comparison to uniform contact pressure for all combinations of inflation pressure and tyre loading. The difference between the two contact pressure representations diminished with depth in the pavement. Therefore, it was clear that 3-D contact pressure has an effect on the distress of a pavement surface. This means to accurately understand the deterioration of a pavement surface, 3-D contact pressure must be considered. In the case of the other distresses the uniform contact pressure generated greater strains and would give a conservative pavement design. Both methods generated greatly different key strains depending on the combination of inflation pressure and tyre loading. If a complex highly accurate analysis is required, then a fully 3-D representation in combination with finite element analysis is the best option. However, if a more routine analysis is required then the improved uniform contact pressure representation could be used with a simple modelling tool (e.g. BISAR) to get good results for a traditional analytical design.