Guest Editorial of Virtual Special Issue: The Ninth International Conference on Very High Cycle Fatigue (VHCF9)

This is the authors' abstract. We don't add key points for this paper.

In service, many components and structures experience very long-life loadings either because of a low cyclic loading frequency yet a very long targeted life, for instance, mooring chains of offshore petroleum platforms, or because of high loading frequency and long life, for instance, turbine blades of turbojet engines.This means that materials and components must withstand a very large number of cyclic loadings without failure, which is beyond the classic number of cycles (around a few million) used for more than a century to define the so-called "fatigue limit."Furthermore, since the 1980s, it has been known that in the very high cycle fatigue (VHCF) regime, most of the fatigue cracks initiate in the bulk of materials whereas cracks nucleate at the surface in high cycle fatigue (HCF).Consequently, it is important for a safe design to understand the behavior of materials and structures under very low stress or strain amplitudes leading to the VHCF regime (i.e., 10 7 or even 10 9 cycles and beyond).The Ninth International Conference on Very High Cycle Fatigue (VHCF9) was successfully held in Lisbon, Portugal, from June 26 to 28, 2024.VHCF9 continues the successful series of previous events starting with VHCF1 1998 in Paris, France, followed by VHCF2 2001 in Vienna, Austria, VHCF3 2004 in Kyoto/ Kusatsu, Japan, VHCF4 2007 in Ann Arbor, USA, VHCF5 2011 in Berlin, Germany, VHCF6 2014 in Chengdu, China, VHCF7 2017 in Dresden, Germany, and VHCF8 2021 in Sapporo, Japan (online and on demand).To go further and understand the VHCF of materials and structures, the conference series will continue in Paris, France, in April 2027.VHCF9 was an interactive forum with 124 delegates from 22 countries and regions.A total of 97 oral communications and five plenary lectures were presented.All the extended abstracts were included in the conference booklet distributed to the delegates in a pdf file.This virtual special issue (VSI), with the title "The Ninth International Conference on Very High Cycle Fatigue (VHCF9)," contains a selection of papers presented at VHCF9.In this VSI,