Papers by Author: Kenichi Saruwatari

Abstract: In order to understand the phenomena caused by the contact stresses occurring within surface, non-destructive methods that can be related to contact conditions are necessary. The main purpose of this work is to study the relationship between magnetization location and direction, spherical Hertzian contact and changes in the magnetic field asymmetry. In the present work, we used a newly developed GaAs film sensor-equipped scanning Hall probe microscope (SHPM) and observed magnetic fields in tool steel plates before and after contact tests under 196N load, at room temperature in air. Medium carbon low alloy steels specimens (JIS S45C) were used in the experiments. Around the contact test area, changes in ‘S’ and ‘N’ poles generated by magnetization using a square magnet block were investigated.

Abstract: Fatigue failure of machine components occurs when cracks form in the stress concentration area and propagate under continued loading during component work. In order to understand the relation between the phenomena of stress concentration and crack propagation, non-destructive evaluation methods using in-situ measurements in the stress concentration areas are necessary. In the present work, a scanning Hall probe microscope (SHPM) equipped with a GaAs film sensor was developed and the three dimensional magnetic fields were observed at room temperature in air. The effect of stress on the changes in the magnetic field in steel components is reported. A steel specimen (JIS SKS93) embedded in acrylic resin were strained at different loads and the magnetic field before and after straining were observed. The obtained magnetic images clearly corresponded with the shape of the steel plate. It was possible to measure the changes in the magnetic field of the steel sample after straining under tensile loading, by neutralizing the initial magnetic field of the specimens prior to testing.

Abstract: Failure of dies and molds is caused by wear and deformation during the metal sheet forming process. Die wear takes various forms, and the contact conditions in die-parts affect the strength of the components. Non-destructive methods that can be related to contact conditions are necessary to study and understand the phenomena caused by the contact stresses. In the present work, a newly developed scanning Hall probe microscope (SHPM) equipped with a GaAs film sensor was used to observe the three-dimensional magnetic fields in tool steel plates before and after contact tests at room temperature in air. It was found that the intensity of three-dimensional magnetic fields is only slightly affected by the spherical Hertzian contact. However, all of the three-dimensional components of the magnetic fields change significantly. The extent of the changes depends not on the distribution of stress under spherical Hertzian contact but on the initial distribution of the magnetic fields.

Abstract: Cyclic stresses around welding joint-part affect the strength of mechanical components. In order to understand the fatigue phenomena caused by the cyclic stresses, non-destructive methods that can be related to number of stress cycles are necessary. In the present work, we used a newly developed scanning Hall probe microscope (SHPM) equipped with a GaAs film sensor and observed three dimensional magnetic fields of the specimen before and after four point fatigue testing at room temperature in air. Low carbon steel plates (JIS, SS400) were used in the experiments. It was found that the intensity of the magnet field in a direction perpendicular to the specimen surface was strongly affected by the fatigue testing. This result means that we can evaluate the fatigue in welding-joint area using quantitative magnetic field measurements. Furthermore, it was discovered that the key factor to evaluate the fatigue is the range between “S” and “N” (“peak-to-bottom” values) of the magnetic fields.