Polymer fatigue: mechanism, mechanics and design

Most structural failures, such as those that occur in aircraft wings, rotating blades, and tires, are caused by fatigue. During cyclic loading, polymers often accumulate substantial and irreversible damage, eventually leading to failure. To address this challenge, it is necessary to enhance the fatigue resistance of polymers. Herein, to provide a guiding theoretical basis and methodological framework for the research of high-durability polymers, this review presents polymer fatigue from the perspectives of mechanisms, mechanics and design. It covers four types of polymers, namely, thermosets, thermoplastics, elastomers and hydrogels, and discusses (i) fatigue tests, damage accumulation theories and fatigue crack growth models; (ii) crack initiation and fatigue crack propagation in the four polymer classes; (iii) factors affecting polymer fatigue properties, which influence fatigue resistance, including both internal and external aspects; and (iv) anti-fatigue mechanisms and strategies across multiple length scales. Finally, we discuss recent advances, challenges and future developments. New mechanisms and mechanical theories have enhanced our understanding of the principles of fatigue resistance, while new designs have improved polymer fatigue properties. It is hoped that this review will greatly promote the development of fatigue research and provide strong support for the design and application of next-generation anti-fatigue polymers.