Open Access

ARTICLE

Fatigue Life Prediction Using Finite Element Hot-Spot and Notch Approaches: Strain-Based FAT Curves Proposal for Ti6Al4V Joints

Pasqualino Corigliano^*, Giulia Palomba

Department of Engineering, University of Messina, Contrada di Dio, Sant’Agata, Messina, 98166, Italy

* Corresponding Author: Pasqualino Corigliano. Email:

(This article belongs to the Special Issue: Advances in Fatigue Life Prediction and Reliability Assessment)

Computer Modeling in Engineering & Sciences 2025, 144(2), 1935-1955. https://doi.org/10.32604/cmes.2025.067094

Received 25 April 2025; Accepted 05 August 2025; Issue published 31 August 2025

Abstract

Experimental tests are essential for evaluating S-N curves and assessing the fatigue life of welded joints. However, in the case of complex geometries, experimental tests often cannot provide the necessary stress-strain data for specific materials and welded joints. Therefore, finite element (FE) analyses are frequently utilized to assess fatigue behavior in complex geometries and address the discontinuities induced by welding processes. In this study, the fatigue properties of titanium welded joints, produced using an innovative laser source and welded without the use of filler materials, were analyzed through numerical methods. Two different FE methods were applied to T-specimens fabricated from Ti6Al4V sheets: the hot-spot stress and notch-stress approach. The FE fatigue life predictions were validated using experimental fatigue test results. The Hot-Spot Stress method yielded a fatigue limit slightly below 100 MPa, demonstrating a consistent slope in the S-N response. Conversely, the Notch Stress method, using a 1 mm fictitious notch radius, indicated a higher fatigue strength corresponding to a range between 225 and 250 MPa, providing a more conservative and localized fatigue estimate. Fatigue resistance in welded joints of steel and aluminum is commonly assessed using specific fatigue classes called “Fatigue Strength Classes (FAT) curves” and their associated S-N curves as recommended by the International Institute of Welding (IIW). However, no such FAT class assignments currently exist for titanium alloys. To address this gap, strain-based FAT curves were proposed by normalizing steel FAT curves using titanium’s elastic properties. This strain-based framework enables direct comparison across materials and provides a foundation for fatigue evaluation of titanium weldments. The author proposed a procedure to normalize steel FAT curves considering the different elastic material properties, enabling a comparison with Ti6Al4V data in terms of hot spot strain or notch strain. This approach facilitates the development of a universal framework for strain-based fatigue evaluation across different materials.

---

Keywords

---