Conference topics & mini-symposia

Description: In the case of high-strength steels, the occurrence of locally limited, dynamic fine-grain formation is observed during high and very cycle fatigue (VHCF) loading leading to so-called fine-grained areas or optical dark areas (FGA or ODA). In contrast to fine grain formation, which is often intentionally enhanced by processes of severe plastic deformation (SPD), the FGA are undesirable and often cause premature failure of the components below the classic fatigue strength. Even in the event of early failures of highly stressed bearings, which have increasingly occurred in recent years, e.g., in wind turbines, fine grain formation is often found in the area of damage initiation, which is associated with crack networks below the bearing treads. These cracks are referred to as white etching cracks (WEC) because of the etching behaviour of the direct crack environment, which is also mentioned as white etching area (WEA), during nital etching. In the symposium, any aspects of the mechanisms leading to fine-grained areas (FGA) and/or white etching areas (WEA) during cyclic loading are discussed.

Description: Very High Cycle Fatigue (VHCF) studies are crucial in industries where components must withstand billions of load cycles without failure. VHCF research is essential for designing durable, safe, and cost-effective systems in applications. This mini-symposium will provide discussions on the industrial case studies demonstrating the impact of VHCF across sectors such as aerospace, automotive, and energy sectors, railway and transportation, microelectronics and MEMS and medical devices. By sharing practical insights from industries, the aims of the symposium are to enhance understanding of VHCF behavior and support the development of safer, longer-lasting engineering systems operating under extreme cyclic conditions.

Description:This symposium aims to explore the critical and emerging challenges in the realm of very high cycle fatigue (VHCF) for materials produced through additive manufacturing (AM) processes. AM has revolutionized the manufacturing industry, and this symposium will bring together experts, researchers, and practitioners from academia and industry to share their findings, methodologies, and insights on the VHCF behavior of AM materials. Topics of interest include, but are not limited to:

• Experimental characterization techniques for VHCF in AM components
• Computational modelling and simulation of VHCF crack initiation and propagation
• The role of microstructure, residual stress, surface texture, and volumetric defects on VHCF mechanisms
• Environmental effects (e.g., temperature, corrosion) on VHCF response
• Fatigue damage mechanisms in the VHCF regime (microstructure effects, plasticity, short crack propagation, etc.) for AM materials
• Post-processing effects (e.g., heat treatment, surface finishing, hot isostatic pressing)
• Approaches to non-destructive evaluation, qualification and certification in fatigue and fracture critical applications
• Artificial intelligence (AI) and machine learning (ML) in VHCF characterization of AM materials

Description: Despite the advances in simulation technologies from both the software and hardware viewpoints, with experienced model order reduction and machine learning techniques, the response of materials and structures to mega-cyclic loadings remains an unsolved challenge, due to the nonlinear constitutive equation (inelasticity), couplings, and many characteristic times related to the material and the loading. Many strategies have been proposed to reduce computational complexity; however, all face significant limitations.

This special session aims to revisit major advances, remaining challenges, and the opportunities offered by the most advanced simulation techniques. Particular attention will be given—without being exhaustive—to multiscale approaches, model order reduction methods, and recent developments in artificial intelligence and machine learning, especially when informed or augmented by physical principles.

Description: Fiber-reinforced polymers often lack a traditional fatigue limit and show continuous degradation up to the range beyond 10 million cycles. This phenomenon is critical for high-performance applications like in aerospace or automotive engineering. The assessment of the fatigue behavior of polymer-matrix composites beyond 10 million cycles is challenging. Major reasons are long-lasting experiments to reach very high cycles in a reasonable time by conventional testing methods. The easy idea to increase the testing frequency from 5 to 1000 Hz or even higher up to the ultrasonic regime. One major challenge is corresponding to intrinsic dissipation processes of polymers at high strain rates and the availability of testing systems to avoid thermal-related issues during fatigue testing at high frequencies. This session should bring together the latest concepts for VHCF analysis of polymer composites: All ideas from medium to high frequency methods, the needed measuring equipment to study VHCF characteristics of polymer composites and finally new findings on damage mechanisms as well as failure modes and predictive models are welcome.

Description: Ultrasonic (US) fatigue testing have rapidly advanced to meet the need for VHCF data within reasonable timeframes. Recent facilities now allow testing at ultrasonic frequencies (starting from 19 kHz) while enabling constant and variable amplitude (VA) loading as well as non-zero mean stresses, extending beyond classical R=-1 fatigue experiments. Load trains for axial and torsion loading, cyclic bending and multiaxial loading have been developed. Advanced US fatigue testing systems have integrated high-temperature furnaces, allowing studies of materials up to 1000 °C, critical for aerospace applications. Observations of crack formation at artificial defects, studies of crack paths in the scanning electron microscope, and in-situ monitoringof the progress of fatigue damage in the synchrotron are unique capabilities made possible with ultrasonic testing. Intermitted loading and innovations in cooling techniques, such as vortex tubes, are now standard to prevent unwanted heat generation during high-frequency resonance testing. Measuring techniques have been enhanced like the use of 3D scanning laser vibrometry, offering high-resolution analysis of surface deformation under ultrasonic loads or Digital Image Correlation (DIC) to cross-calibrate laser displacement measurements, increasing accuracy in measuring strain amplitudes. Analysis of specimen's acoustic properties are used to monitor the progress of fatigue damage. AI and data-driven models will be integrated into new testing frameworks to predict fatigue crack propagation and fatigue life in a much stronger manner than ever before. Future directions will also focus on combining high-frequency mechanical testing with multi-environment setups to simulate real service conditions. This VHCF10 session should bring together the world-leading community in ultrasonic fatigue testing of various engineering materials (metals, polymers, ceramics and composites) to discuss the latest developments and novel opportunities for the VHCF research.

Description: This symposium focuses on the statistical modelling of the Very High Cycle Fatigue (VHCF) response of materials. In the VHCF regime, failure mechanisms differ significantly from those observed in the high-cycle fatigue (HCF) range, with crack initiation typically occurring at internal defects rather than at the surface. This requires the adoption of statistical models for fatigue life that can capture both the role of defects and the specific crack initiation mechanisms of the VHCF domain. Closely related to this topic is the (specimen) size effect, which accounts for the increasing probability of critical defects as material volume increases. Modelling this effect is essential not only for the interpretation of experimental results, but also for the reliable design of large structures and components, whose volumes are often considerably greater than those of laboratory specimens.

This symposium aims to bring together researchers working on the statistical modelling of fatigue behaviour in the VHCF regime. Contributions addressing experimental data analysis, as well as methodologies for the design of large-volume components/specimens accounting for size effects, are welcome. Models incorporating the influence of defects, the peculiar failure modes typical of VHCF, and the duplex S-N response encompassing both HCF and VHCF regimes are especially encouraged.