Size-effect in Very High Cycle Fatigue: A review

•Size-effect strongly affects the VHCF of materials.•A general rule for size-effect in VHCF could not be found in this research.•Size-effect depends on the material, manufacturing process and material cleanliness.•The ODA/FGA size must be taken into account when components are designed.•Tests on specimens with large risk-volumes are recommended. It is well-known that fatigue failures in VHCF originate from defects present within the risk-volume. Moreover, experimental results have shown that the larger the specimen size and the risk-volume, the shorter is the VHCF life. This is known as size-effect and is generally due to the statistical increment of the defect size with the material volume. In the paper, size-effect in VHCF is critically revised. The experimental results obtained by testing specimens with different sizes are analyzed and the methodologies proposed to model size-effect are discussed, with the aim of guiding the future research on size-effect in VHCF.