Atsumichi Kushibe

Capability of superplastic forming in the seismic device using Zn–22Al eutectoid alloy

Abstract For the purpose of the improvement and mass-producing of a superplastic damping device, the mechanical properties in the extruded samples and the capability of superplastic forming were investigated. The mechanical properties after superplastic forging satisfied the performance needed to utilize in practice.

Reduction of Artifact of Metallic Implant in Magnetic Resonance Imaging by Coating of Diamagnetic Material

Metallic implants composed of paramagnetic materials, such as stainless steel (SUS), Ti, Co-Cr-Mo alloy, etc., are widely used as artificial hip joints or aneurysm clips. When the metallic implant is placed in a uniform magnetic field of a magnetic resonance scanner, a magnetic disturbance is created due to its magnetization. This magnetic disturbance distorts the image of the metallic implant and body tissues in the magnetic resonance imaging (MRI). In order to overcome this problem, a method of coating the metallic implant with diamagnetic material has been proposed as the magnetic disturbance created by the metallic implant can be removed by the cancellation of the respective magnetizations of the paramagnetic and diamagnetic materials. But the optimal thickness of the diamagnetic coating has been obtained only for a sphere model by mathematical modeling. In this paper, the effects of a straight cylindrical hip joint model and an aneurysm clip model on the magnetic disturbance are investigated by using the magnetic field analysis of the finite element method (FEM). First, the magnetic disturbances generated by the two models made of paramagnetic material are calculated and compared with measured results. Moreover, the associations of susceptibilities chipar and chidia of the paramagnetic and diamagnetic materials and the optimal thicknesses of the diamagnetic coating when the magnetic disturbances can be reduced for the two models are shown.

Internal Friction of Fe-Mn-Si-Based Shape Memory Alloys Containing Nb and C and Their Application as a Seismic Damping Material

The damping behavior of an Fe-28Mn-6Si-5Cr-0.5NbC (mass%) shape memory alloy was measured by low cycle fatigue tests during tension-compression loadings. A remarkable damping capacity was observed above the strain amplitude of 0.1%, and the specific damping capacity (SDC) parameter reached saturation at ~ 80% above 0.4%. The reversible motion of the γ/ε interfaces is considered to dominate the cyclic deformation behavior, while the work hardening during tension-compression loading is negligible. These characteristics are favorable for seismic damping devices that protect civil structures from earthquakes.

Application to Seismic Dampers in High-Strain-Rate Superplastic Zn-Al Alloy

High strain rate superplasticity has been realised at room temperature for the first time with a ultra fine grained Zn-22wt%Al alloy. Zn-Al alloys have some advantages over low-yieldpoint steels in their low work-hardening rate and high ductility. In addition, Zn-Al alloys are environment-conscious because of no harmful metal like Pb. However, when Zn-Al alloys are subjected to plastic deformation, the strain is localised and local fracture can take place because of their low work-hardening property. In this study, a seismic damper was designed with a Ultra fine grained Zn-Al alloy. As a result, an ecological and high performance seismic damper, the so-called “maintenance-free seismic damper”, has been successfully developed.

Reduction of artifact of metallic implant in magnetic resonance imaging by combining paramagnetic and diamagnetic materials

The method of coating the metallic implant made of paramagnetic materials with diamagnetic materials has been proposed to reduce the magnetic disturbance of metallic implants which causes artifact in magnetic resonance imaging. The optimal thicknesses of the diamagnetic coatings have been obtained for a straight cylindrical hip joint and an aneurysm clip by using the magnetic field analysis of the finite element method (FEM). Whereas in the manufacturing, with respect to the mechanical force of the diamagnetic material, etc., the new structure of dual-material model with diamagnetic material inside and paramagnetic material outside is considered better. In this paper, first the effectiveness of the structure of the dual-material model with actual diamagnetic material inside and paramagnetic material outside is investigated by using the FEM. Then optimal thicknesses of paramagnetic coating of two models are obtained. Finally the effectiveness of the dual-material model is verified by the experiment.

Application of High-Strain-Rate Superplastic Zn-Al Alloy to Seismic Dampers and its Optimised Shape Design

As a new damping material, the authors first developed a Zn-22wt.%-Al eutectoid alloy with ultra-fine grains exhibiting superplasticity at room temperature by means of thermomechanical controlling processes (TMCPs). The Zn-Al alloy has a few advantages such as low work-hardening rate and high ductility over a conventional seismic damping material, for instance, a low-yield-point steel. In addition, Zn-Al alloys are environment-conscious because of no harmful metal like Pb. However, when Zn-Al alloys are subjected to plastic deformation, since its work hardening is small, plastic deformation proceeds locally so that required absorption energy cannot be sufficiently obtained, and local fracture and local deformation instability can take place easily, which is the intrinsic characteristic of superplastic materials. Therefore we attempted to develop a shear panel type, a brace type damper for tall buildings and a bending type damper for Japanese wooden houses using FEM analysis in order to minimize localized strain and local deformation and to determine the optimum shape for this Zn-Al superplastic seismic damper. As a result, an ecological and high-energy absorption seismic dampers, so-called “maintenance-free seismic damper,” was successfully developed.

Post-Mechanical Properties of Superplastically-Forged Zn-22wt%Al Alloy

Recently, the superplastic damping device, which has been using Zn-22wt%Al alloys with an ultra-fine grain size, has been put into practical use for a high-rise building. For the purpose of the improvement and mass-production of a superplastic damping device, the investigation about the superplastic forming and the characterization after the forging was carried out. As the results of FVM analysis, it was verified that the high effective stress and strain occurred at the corner and in the interior of the formed samples, respectively. However, the microstructure and mechanical properties after the forging were almost equivalent to those before the forging.

FULL-SCALE SHAKING TABLE TESTS OF TRADITIONAL WOODEN FRAME

In order to evaluate the dynamic characteristics (natural period, equivalent viscous damping ratio, etc.) of traditional wooden frames, full-scale shaking table tests were performed. In these tests, the following types of specimens were included; 1) frame with hanging wall, 2) frame used non-slipping-out wedge, 3) frame installed Zn-Al dampers.Zn-Al damper and Non-slipping-out wedge were developed by the authors. As a result, horizontal displacement became from 27 to 37% smaller and equivalent viscous damping ratio became from 57 to 162% larger by using Zn-Al damper.Finally, seismic response analyses were conducted. Based on the static loading test, the hysteresis model of the joint part was made for analysis.

Structural Materials. Influence of Welding Heat on Low Yield Strength Steel.

The yield stress of the low yield strength steel (LY100) that is used well as a hysteresis dumper is reduced by coarsing grain in the heat treatment process of steel plate production. Therefore, the yield stress rises, when the steel plates are built up by welding to a member. The test specimen that welded 2 sheets of steel plates by butt welding was prepared, in order to investigate the influence of the welding heat input and the cause on the mechanical properties of the steel plate. Gathering the test pieces according to the distance from the weld line, the tension test, chemical composition analysis, optical microscope and micro Vickers hardness test were performed. Also, the change of the yield stress by means of heat treatment become hot after welding was examined. As a result, it is guessed the cause that the heat input record and the cooling under residual stress refine the grain size at the temperature rise part of vicinity of the weld line. And, the grain is coarsened once again by heat treatment for one hour at 850°C after the welding assembly. Therefore it is possible that the yield stress that have rised at the time of the welding assembly is made lower equal to that of the base material.