Truck tyre rolling resistance : Experimental testing and constitutive modelling of tyres

Sammanfattning: Global warming sets a high demand to reduce the CO2 emissions of vehicles. In the European Union heavy-duty road transports account for 6 % of the total greenhouse gases and one of the main factors affecting these emissions is related to the rolling resistance of tyres. The optimal usage of tyres is an important part of solving these challenges, thereby it is important to understand the parameters affecting rolling resistance and the different compromises coupled to them. These compromises could be analysed using computational and experimental methods. To set out the groundwork necessary to minimise the energy consumption of trucks and assess the different parameters affecting tyre behaviour, the following studies have been conducted during this thesis. A framework to model and parametrise truck tyre rubber has been developed for finite element simulations. The presented parallel rheological material model utilises Mooney-Rivlin hyperelasticity, Prony series viscoelasticity, and perfectly plastic networks. A method to reduce tuneable parameters of the model, which significantly simplifies possible parameter studies, is presented. The model has been parametrised using test data from dynamic mechanical analysis of samples from a long haulage heavy truck tyre, and shows a good agreement with the test data. To test the suitability of the modelling technique for tyre simulations, the constitutive model is used in various tyre simulations using the arbitrary Lagrangian-Eulerian method. The material modelling technique is shown to work for static force-deflection as well as dynamic simulations estimating longitudinal force build-up with varying slip levels. Additionally, the modelling technique captures the uneven contact pressure in steady-state rolling, which indicates that the model could also be used in rolling resistance simulations. To study the change of ambient temperature on rolling resistance using experimental methods, a climate wind tunnel is used where the rolling resistance is quantified using a measurement drum. Tests were conducted between -30 °C and +25 °C, and a considerable ambient temperature dependency on rolling resistance was found. Moreover, temperature measurement inside a tyre shoulder is a good indicator for rolling resistance in a broad range of ambient temperatures. Finally, battery-electric long haulage truck driving range calculations are also conducted with varying rolling resistance and air density at different temperatures, showing a significant decrease of driving range with decreasing ambient temperature.