Manufacturing technologies
Digital twin, CAE design, Steel structures, Life extension/retrofit

Advanced life extension technology based on digital twins for steel structures: Highly accurate prediction of cyclic
elastoplastic deformation and fatigue damage process against earthquake and traffic loads
Department of Civil Engineering, Graduate School of Engineering
Associate Professor Seiichiro Tsutsumi
https://researchmap.jp/tsutsumi?lang=en

Abstract
It is said that nearly 80% of the damage that occurs to machines,
devices, and structures of all sizes around us is caused by “fatigue”
that occurs as a result of repeated force and deformation. Therefore, it is important to establish a method that can accurately evaluate and predict the fatigue process of structures made of various
materials to prevent fatigue damage and related accidents. This isan extremely important issue for conducting social activities andincreasing international competitiveness in various industrial fields.
Fatigue damage process has been discussed in terms of the fatigue crack initiation process and the subsequent growth process,and many predictive models have been proposed that span multiple theoretical systems, such as plasticity theory and fracture mechanics. We have developed a numerical simulation (digital twin)
technology that can predict the deformation and stress states ofstructures with high precision and efficiency. Also, the method canevaluate fatigue cracks from initiation to propagation and rupture.

Fig 1 Digital Twin of Bridge pier (Cyclic elasto-plasticity FEM simulation)

Manufacturing technologies▍ Background & Results
By utilizing the digital twin/numerical simulation technology that
we are developing that targets deformation and fatigue failure phenomena in structures, we will be able to, for example, streamline
the treatment of various types of existing infrastructure steel structures that are aging rapidly. We are working to solve many socialissues, such as formulating new repair and reinforcement plans,
proposing new structures/materials that can reduce maintenancecosts, and developing new life extension technologies for steelstructures.

▍ Significance of the research and Future perspective
Many cases of fatigue damage originating from welds have beenreported in various weld structures, and the development of various
life extension techniques and remaining life diagnosis techniquesnecessary for their evaluation is progressing. The main causes ofthis fatigue damage are: a) high stress occurs due to the alignmentof the weld and the structural discontinuity, and the presence of
weld excess and sometimes defects; b) damage to the base metal due to welding heat input. Depending on the welding process
conditions, such as weld metal dilution and subsequent coolingrate, resulting in non-uniform material structure/shape/strength
distribution and residual stresses/residual deformations, and c) thecomplex stresses/strains experienced in weld structures, which ismulti-axial/non-proportional/fluctuation history, so there are limits
to experimental investigation. In other words, in order to improve
the fatigue performance evaluation method and life extension
technology for weld structures that depend on welding conditions,
it is necessary to develop and implement numerical simulation
technology that can appropriately take into account the influencing
factors a) to c) above. Deployment of these digital twin technology
to mechanical design is vitally important, and we are conducting
research with the aim of developing technology with high engineering impact that is essential to solving these problems.

Fig 2 Max. strain distribution measured by DIC (Low-cycle fatigue test of weld joint)

P a t e n t
Tsutsumi, Seiichiro et al. Effects of weld geometry and HAZ property on low-cycle fatigue behavior of welded joint. International Journal of Fatigue. 2022,159, 106683. doi: 10.1016/j.ijfatigue.2021.106683
Fincato, Riccardo; Tsutsumi, Seiichiro. Numerical implementation of the multiplicative hyperelastic-based extended subloading surface plasticity model.
Tr e a t i s e
Computer Methods in Applied Mechanics and Engineering. 2022, 401, 115612. doi: 10.1016/j.cma.2022.115612
Fincato, Riccardo; Yonezawa, Takayuki; Tsutsumi, Seiichiro. Numerical modeling of cyclic softening/hardening behavior of carbon steels from low- to highcycle fatigue regime. Archives of Civil and Mechanical Engineering. 2023, 23, 164. doi: 10.1007/s43452-023-00698-4
URL
K e y w o r d cyclic plasticity, material model, FEM, fatigue, crack initiation/propagation