Almost all structures in service are exposed to loads with variable amplitudes, often termed as spectrum loading; many in-service failures occur because this type of loading is not considered properly. Despite of this fact, only a minority of all publications in the fatigue domain are related to variable amplitude loading, the majority concentrates on constant amplitude loading. Especially for applications in different industrial sectors such as automotive, railway, aircraft, maritime, plant and civil engineering, as well as renewable energies various facets of spectrum loading have to be considered in design and a solid background be provided for reliable and economic design and safe operation of structures. 

A series of conferences on Material and Component Performance under Variable Amplitude Loading (VAL) has been initiated on this specific topic starting in 2002 in Tours, France, followed in 2009 in Darmstadt, Germany, and then in 2015 in Prague, Czech Republic, bringing together worldwide experts from science and industry. The fourth of this series (VAL4) was originally scheduled to take place in Darmstadt, Germany, from 30 March to 1 April 2020 in order to address the following topics: load assumptions, modelling of fatigue damage and crack growth, design and analysis methods and tools, reliability concepts, advanced materials and manufacturing, testing, effects on lifetime, numerical assessment and verification. However, VAL4 unfortunately had to be cancelled at short notice because of Covid-19.

In this FFEMS Virtual Special Issue “Variable Amplitude Loading – Fracture Mechanics and Cumulative Damage Modelling” a selected set of extended papers of contributions to VAL4 is presented. Another set of the contributions has been published in parallel in the Virtual Special Issue “Variable Amplitude Loading – Load Assumptions and Structural Durability” of the International Journal of Fatigue (IJF).

The present FFEMS Virtual Special Issue focuses on fracture mechanics and cumulative damage modelling, damage detection and inspection intervals using frequency domain concepts, elastic-plastic deformation and thermal load effects. In IJF loads and load assumptions, vibrations and power spectral densities, new materials and proof of durability are main topics. In both Special Issues applications to components and structures are also considered. Thus the two Special Issues are aiming at providing an overview on the actual state of the art.

We would like to express our thanks to all authors of VAL4 and particularly to the authors and reviewers for their contributions and their efforts for the present VSI. Sincere thanks also go to FFEMS editorial team who helped and supported us during the full process.

Paul Heuler, DVM, Audi AG (retired), Germany

Georgios Savaidis, Aristotle University of Thessaloniki, Greece

James C. Newman, Jr., Mississippi State University, USA