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Choice of winter tyres has, from mainly being a matter of safety and economic costs for wearing of road pavements, during later years also become a matter of inhalable particles formed during pavement wear from studded tyres and their negative effects on public health. Further, the tyres' effects on environment and noise have been illustrated in several studies. The issue is also complicated by the fact that tyre choice effects on traffic safety have several components, including such diverging parameters as friction and behaviour. Finally all aspects have to be evaluated from a socioeconomic point of view for society to be able to decide which kind of distribution of tyre types that is the most profitable. This report is a summary of current knowledge in this complex research field., Valet av vinterdäck har, från att i huvudsak varit en fråga om trafiksäkerhet och slitage av vägar under senare år även kommit att handla om negativa effekter av de inandningsbara partiklar som bildas då dubbdäck sliter på vägbanan och de effekter på befolkningens hälsa som dessa partiklar har. Vidare har vägslitagets inverkan på miljön genom spridning av bl.a. tungmetaller belysts liksom däckvalets betydelse för bullerproblematiken. Frågan kompliceras ytterligare av att däckvalets betydelse för trafiksäkerheten har många beståndsdelar inkluderande såväl tekniska parametrar, t.ex. friktion, som beteendevetenskapliga aspekter. I slutändan måste alla dessa aspekter vägas samman samhälls-ekonomiskt för att den för samhället mest lönsamma däckanvändningen skall kunna uppnås. Denna rapport belyser kunskapsläget inom detta komplexa problemområde.

This thesis deals with theoretical investigations of the electronic structure of conjugated carbon based materials. Novel materials like the C60 fullerene and the carbon nanotubes, but also the more well known, but closely related, graphite phase of carbon were studied. In addition, low dimensional structures like conjugated polymers and DNA, containing other atoms besides carbon, were investigated. The recently discovered fullerene phase of carbon, especially the C60 molecule has obtained a lot of attention among researchers. It has been observed that C60 under certain conditions can form linear polymeric chains, as well as two-dimensional polymeric structures. In the work presented in this thesis, Hückel model parameters have been developed for describing the intermolecular bonds within single bonded C60 polymers. These parameters were used in simulations to establish a simple rule explaining the phase diagram of the observed single bonded C6o polymer structures, namely that each electron added to a C60 monomer stimulates the creation of one single bond to a neighbouring C60 anion. A similar study on graphite was also performed, yielding Hückel parameters which describe the complicated bonding structure surrounding an atomic vacancy in the graphite. From calculations on large graphitic sheets containing several vacancies, insight was gained of the electronic properties associated with such defects, leading to a better understanding of Scanning Tunnelling Microscopy images of defected graphite. In one-dimensional materials, disorder is known to have an immense effect on electron localisation, seriously affecting the transport properties of these materials. Conjugated polymers and carbon nanotubes are not perfectly one-dimensional, but are often referred to as quasi one-dimensional. In this thesis, work is presented that deal with electron localisation in disordered quasi one-dimensional materials, studied at the Hückel level. To do this, a new method was developed

This thesis deals with electronic structure calculations in large carbon based materials, Especially graphite like structures have been studied. For this the tight binding method together with more sophisticated quantum chemical methods has been utilised. The first part of this thesis provides a background to the theoretical models used in the papers. In paper one, single bonded fulleride polymers of all dimensions have been studied as a function of charge state. In paper two, the effect of vacancies in graphite is modelled within the tight binding formulation. In paper three, electron localization in quasi-one dimensional systems in the presence of disorder are investigated.

It is known that when irradiating a graphite surface with ions the predominant source of defects are vacancies, Vacancies are also formed in a growing graphite sheer and cannot be filled. The theoretical work that has been carried out so far on the properties of these defects has only involved quite small model systems. Calculations on graphite, or closely related carbon phases like nanotubes, with randomly distributed vacancies require very large systems allowing only the simplest model to be used. We have used the Huckel method to model vacancies, both ordinary and hydrogenated, by fitting the Huckel energy levels to those resulting from a valence effective Namiltonian calculation. The three atoms neighboring a vacancy are treated as pseudo-pi orbitals and our calculations suggest that they together contribute with one extra electron to the system. Using this model optical and electronic properties of a graphite sheet as a function of vacancy density have been calculated.

A general method for obtaining transfer matrices in quasi-one-dimensional systems is presented. We used the method to study Anderson localization in trans-polyacetylene, polyparaphenylene, polyparaphenylene vinylene, and polythiophene. The electron localization length for the polymers as a function of disorder was calculated from the Lyapunov exponents. The polymers are shown to exhibit different sensitivity to disorder, which could be explained in terms of different dimensionality of the polymeric systems. We also give an explanation to the recently observed differences between electron and hole intrachain mobilities in alkoxy derivatives of polyparaphenylene-vinylene, as being a result of the electron-donating nature of the alkoxy substituents.

Rolling resistance has become one of the key parameters that the vehicle industry is focussing on in their efforts to make vehicles more energy-efficient. Rolling resistance is generally measured in steady-state on a test drum which results in a higher rolling resistance compared to flat track measurements for the same test settings due to the curvature of the drum which deforms the tyre more. Therefore, the drum steady-staterolling resistance is commonly converted with Clark’s formula, as suggested in the rolling resistance measurement standards. The accuracy of Clark’s formula has been questioned by Freudenmann et al who suggest an adjusted formula for steady-state measurements. The aim of this work is to compare drum and flat track measurements performed at the same inflation pressure and tyre temperature instead of at steadystate and investigate whether Clark’s or Freudenmann’s formula can be used to convert the drum measurement to a corresponding flat track level. Non-steady-state measurements have been performed on both test drum and flat track. As expected, Freudenmann’s formula is not good for the conversion at nonsteady-state settings, since it was empirically developed for steady-state. Clark’s formula works better for conversion of measurements performed at the same tyre temperature and inflation pressure compared to steady-state conversions reported in literature. However, the dependency of rolling resistance on temperature is not the same in the drum and flat track measurements, causing a difference between the results which increases as the tyre temperature decreases. Further research is needed to improve Clark’s formula by including the effects of tyre temperature, QC 20240516

A rolling resistance model has been created and parametrised with the purpose of modelling tyre rolling resistance within complete vehicle dynamics simulations. The rolling resistance model is based on a combination of the Masing and Zener model to simulate the Payne effect and the viscoelastic properties of rubber. The parametrised model is able to recreate the relationship between the rolling resistance and the tyre deformation well and it has a low computational power requirement. Today the model is limited to simulation of free-rolling tyres on a flat surface, but it can be extended to also include the effects of changes in operating conditions such as wheel angles or road surface., QC 20220530