| dc.description.abstract | The tyre industry is the leading consumer of rubber materials, accounting for approximately 70% of annual natural rubber production. The inherent properties and strength of rubber makes it suitable for engineering applications. However, to have useful lifetimes, rubber needs to be reinforced with fillers such as carbon black or silica. Fillers account for approximately 30% of materials by weight used in tyre tread compounds with CB being the most widely used reinforcing filler in tyres and engineering rubber materials. Various studies have shown that CB generally enhances properties such as modulus, tensile and tear strength, crack growth and abrasion resistance. For tyre tread applications, CB also influences other properties such as rolling resistance and grip. Less understood though, is how the morphological properties of CB influence fatigue and fracture properties of the rubber composite. The aim of this thesis is to conduct a systematic study to understand how these CB morphological properties including the structure and surface area affect reinforcement in tyre tread compounds. Eight different CB fillers varying widely in their structure and surface area were examined. The wide variation of CBs allows quantitative correlations to be drawn to understand the extent the CB properties affect these parameters. The CBs had an equivalent loading of 50 parts per hundred (phr) in natural rubber. An unfilled equivalent was also included. A series of experiments including conventional static and dynamic mechanical tests, strain induced crystallisation estimations, heat build-up and energy dissipation characterisation, fatigue crack growth resistance measurements, intrinsic and critical tear strength tests were conducted. Abrasion resistance as well as cut and chip resistance experiments were also performed. The results show the controlling CB morphological property is influenced by parameters such as the applied strain level, strain rate, severity of loading and the predominant deformation type (strain-, energy- or stress- controlled) in the test or application. Increasing CB surface area generally increases heat build-up and energy dissipation while CB structure affects crystallinity due to strain amplification effects. There is a step change in crack growth resistance below certain tearing energies which is attributed to the kinetics of strain induced crystallisation. There is a flip in ranking of cut and chip damage, with high structure CB compounds preferred at low impact forces and low structure CB compounds preferred at high impact forces. Abrasion tests show the formation of smear wear causes better abrasion resistance. The formation of smear wear is a factor of both the CB structure and surface area. Overall, the results highlight the difficulty to simultaneously optimise different parameters in tyre tread design. However, this work provides the tyre design engineer greater clarity on which CB to use to obtain a desired performance. | en_US |
