Vibration Control Materials Group

2021.01.22 Update

The goal of the vibration control materials group is to reveal the microstructural mechanisms underlying various phenomena such as the vibration, fatigue, plasticity, and phase transition of metals. We aim to contribute toward developing solutions of various social problems by developing new materials based on a fundamental understanding of material properties. In the current 4th NIMS mid-term project, we elucidate deformation mechanisms in order to achieve an ultra-long fatigue life for steels used in seismic dampers, which are employed to protect structures from earthquakes. We attempted to develop and clarifying the process of casting materials, to improve the structural properties of titanium alloys, and to reveal the mechanisms governing fatigue cracks in metals, with regard to plasticity and dislocations.

Specialized Research Field

1. Development of novel, seismic damping austenitic steels and welding techniques

A seismic damper protects structures from earthquakes by converting the seismic energy into heat.
In the 3rd NIMS mid-term project, a novel seismic damping steel, Fe-15Mn-10Cr-8Ni-4Si (wt.%), was developed; this steel was installed in a skyscraper in 2014. In the current 4th NIMS mid-term project, we are developing the second-generation of seismic damping steels featuring improved weldability and corrosion resistance, in addition to being cheaper. In 2018, a welded seismic damper was installed, which was manufactured via a new welding technology using a long plate steel with the continuous casting method.

2. Development of casting materials

Casting is a technique of manufacturing objects by pouring hot metal into a mold. Although this approach is advantageous when creating complex shapes, the material properties of the finished product are generally inferior to those of wrought materials. Furthermore, castability is another important aspect that needs to be considered, and material development can be limited owing to polarization and casting defects. Therefore, we focus on using optimal compositions and process parameters; we are working towards developing new casting materials and addressing the existing problems in casting, based on the design guidelines for wrought and rolled materials, which feature excellent characteristics.

3. Composition and structure control and improving characteristics of titanium alloys

Titanium alloys exhibit different phases and deformation mechanisms depending on their chemical composition and microstructures; these factors have an impact on mechanical properties such as strength, ductility, and fatigue characteristics. We are working on developing titanium alloys with excellent mechanical properties in terms of strength and reliability, making them suitable for application in construction; this is achieved through techniques such as composition control based on alloy design and microstructural control based on heat treatments. In recent years, we have paid attention to the segregation in materials, which is the local heterogeneity of alloy elements, to improve their mechanical properties.

4. Crack-plastic deformation–dislocation relationship for metal fatigue

Fatigue is a major cause of damage in machines and structures; consequently, adopting appropriate measures to address this is essential to ensure the safety and reliability of these machines and structures. Fatigue fracture can be observed macroscopically as the formation and propagation of cracks caused by repeated loading; however, it is actually caused by repeated plastic deformation, that is, microscopic dislocation. Therefore, it is necessary to study such strongly related phenomenon in a comprehensive manner, in order to elucidate the fatigue mechanism. We perform fractography, crystallographic analyses, and multi-scale investigations on the fatigue mechanism through in situ observations of the fracture behavior of materials by using a digital microscope, TEM, and synchrotron radiation.

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Vibration Control Materials Group
1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, JAPAN
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