Fatigue Crack Growth vs. Chip and Cut Wear of NR and NR/SBR Blend-Based Rubber Compounds

Tyre tread directly comes in contact with various road surfaces ranging from very smooth roads up to riding on rough road surfaces (e.g. gravel roads, roots, stalks) and is prone to damage due to cut from sharp asperities during service. As tyre experiences millions of fatigue cycles in its service life, these cuts propagate continuously and lead to varied fracture processes from simple abrasion, crack growth up to catastrophic failure. In this paper firstly the complete fatigue crack growth (FCG) characteristics of rubbers from the endurance limit up to the ultimate strength and, finally, compared the data with a fast laboratory testing method determining the Chip and Cut (CC) behaviour. The study is focussed on investigation of pure natural rubber (NR) and natural rubber/styrene butadiene rubber (NR/SBR) blends, based on industrial compound formulations used for tyre tread applications. These rubbers have well-established FCG characteristics in field performance of tyre treads, with NR exhibiting the higher FCG resistance at high region of tearing energies, whereas the advantage of SBR over NR can be realized in terms of the higher fatigue threshold for SBR occurring in the low range of tearing energies. The same trend was found from the FCG analyses consisting of the complete Paris-Erdogan curve from endurance limit up to ultimate strength as well as CC behaviour determined with a laboratory Instrumented Chip and Cut Analyser (ICCA) which operates under realistic practice-like conditions and quantifies the CC behaviour using a physical parameter.