This paper presents a novel technology that reliably contributes to the structural integrity of newly built metal infrastructure. The technology is the nanostructured metallic multilayer (NMM) treatment, which has recently been proven in laboratory testing to increase the fatigue strength of a butt-welded joint (double V-notch) from FAT class 80 to beyond FAT class 190 [1]. This paper demonstrates, for the first time, how this novel technology is applied in-situ on a real bridge, provides insights into the processing of the NMM in-situ, discusses the quality of the deposited nanomultilayer, and quantifies the increased fatigue strength and improvement of structural integrity.

Recent research findings demonstrate that the NMM treatment of weld seams considerably enhances the fatigue strength of weld seams and extends the lifespan of the welded joint multiple times [2].

Within the study described herein, the technology is transitioned into practical application. A deposition apparatus is developed and undergoes initial tests to apply the NMM treatment on welds of a bridge in the port of Hamburg. In a comprehensive study, the ideal configuration of the deposition container, as well as the size and position of electrodes, is determined through numerical simulation of the electroplating process of the nanomultilayer consisting of copper and nickel layers. The numerical simulation allows modeling of the thickness and deposition rate of individual layers.

The deposition apparatus is fabricated by 3D printing plastics. Given the pH level of the electrolyte solution used, it is essential to use an acid-resistant material for printing. The structure has a modular design, allowing the apparatus to adapt to different surface geometries. 

In initial experiments, the deposition prototype is tested by applying the metallic nanomultilayer on flat sheets. The deposited multilayers are analyzed using X-ray diffraction (XRD) and electron microscopy, providing insights into the residual stress state and layer structure of the nanolaminate. The findings pave the way for the efficient application of the NMM treatment on fatigue-critical welded joints of the steel infrastructure and potentially ensure readiness and structural integrity of the steel infrastructure.

References

1.     Brunow, J., Spalek, N., Mohammadi, F., Rutner, M. A novel post-weld treatment using nanostructured metallic multilayer for superior fatigue strength. Scientific reports 13, 22215; 10.1038/s41598-023-49192-0 (2023).

2.     Rutner, M., Spalek, N., Falah, M., Lalkovski, N. Verknüpfung von Nano mit Makro – Chancen für den Stahlbau. Stahlbau 93, 584–596; 10.1002/stab.202400048 (2024).