High-cycle and very-high-cycle fatigue of additively manufactured metallic materials


Youshi Hong
Professor, Institute of Mechanics, Chinese Academy of Sciences
Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China
 
Abstract
Additive manufacturing (AM) has become a promising technology to produce complex engineering components with high efficiency and relatively low cost. As an echo of manufacturing process, AM parts inevitably contain intrinsic features such as large amounts of surface and internal defects, fine microstructure with inhomogeneity and anisotropy, and remarkable residual stresses. In engineering practice, the performance of high-cycle fatigue (HCF) and very-high-cycle fatigue (VHCF) for AM parts is much concerned because key engineering components require a long service life under cyclic loading, and the behavior of HCF and VHCF for AM parts is different from that of conventionally made counterparts. Among the mentioned features of AM parts, the influence of defects on fatigue behavior is the most vital issue to be investigated.
The topic of this presentation is on the HCF and VHCF behavior of additively manufactured metallic materials especially titanium alloys and aluminum alloys produced by commonly used selective laser melting or laser powder bed fusion. The presentation will focus on how to reduce the defect content by controlling AM processing parameters and post treatments, how to explain the size effect on fatigue performance caused by defects, and how to understand HCF and VHCF mechanisms at different stress ratios of AM parts.
 

Fatigue Life Prediction of Additively Manufactured Metals:
A Hybrid Critical Plane-Fracture Mechanics Approach
 
Ali Fatemi
Ring Companies Professor and Department Chair
Department of Mechanical Engineering, The University of Memphis, Memphis, TN, USA
 
13th International Fatigue Congress (Fatigue 2022+1)
Hiroshima-Japan, November 6th to 10th, 2023
 
ABSTRACT
Although there has been much research and knowledge gained on additive manufacturing (AM) in recent years, its application to safety-critical components prone to fatigue failure remains very limited.  This is partly due to the challenges at the current stage of the technology such as defects, surface roughness, and residual stresses.  However, another major contributing factor is due to the wide variation in performance resulting from the wide range of the many AM process control parameters and post-process treatments.  This contrasts with conventional materials and processes, where such variations in performance are typically much smaller and more predictable.  To facilitate better fatigue performance predictability in AM metals, despite the wide variability, a computational framework is proposed where variations such as in microstructure, defects, and residual stresses can be explicitly accounted for with a physics-based approach.  This approach combines the successful concept of critical plane based on small crack growth often used for multiaxial fatigue crack initiation, with the fracture mechanics-based crack growth analyses.  This talk will present an overview of the proposed approach and demonstrates its application to data generated from Ti-6Al-4V and 17-4 PH stainless steel specimens made by laser-based powder bed fusion (LB-PBF) and with different surface and post-treatment conditions.  Different loading conditions including constant as well as variable amplitude axial, torsion, and combined axial-torsion loadings will be considered.
 
BRIEF BIOGRAPHY OF ALI FATEMI
Dr. Fatemi is currently the Ring Companies Endowed Professor and Chair of the Department of Mechanical Engineering at the University of Memphis. Prior to joining the University of Memphis in August 2017, he was a Distinguished University Professor at the University of Toledo in Ohio. Fatemi's primary research interests and publications involve fatigue and fracture of engineering materials including metals, polymers and elastomers, and composites. He has published over 250 refereed papers dealing with fatigue and fracture with more than 18,000 citations. He is also a co-author of the 2nd edition of Metal Fatigue in Engineering published by Wiley. Dr. Fatemi has directed sponsored research projects from many companies, foundations, and government agencies. He is a Fellow of the American Society of Mechanical Engineers (ASME), a member of the American Academy of Mechanics, and a member of ASTM Committee E-8 on Fatigue and Fracture.  He is on the editorial board of the International Journal of Fatigue, Theoretical and Applied Fracture Mechanic, and Fatigue and Fracture of Engineering Materials and Structures.