Papers by Author: Manabu Enoki

Abstract: A possibility to reduce core loss in non-oriented (NO) electrical steel by applying magnetic coating has been investigated. This technique involves electroless plating of magnetic coating onto the surface of electrical steel. The material system was NiCoP coatings with different thicknesses (1, 5, and 10 􀁐m) deposited onto the surface of commercially available Fe-3%Si NO electrical steel. Characterization of deposited NiCoP coating was carried out using X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive X-ray (EDX) spectrometer. The deposited Ni-Co-P coatings were amorphous/nanocrystalline and composed of 56-59% Ni, 32-35% Co and 8-10% P by mass. Effect of coatings on core loss of the electrical steel was determined using a single sheet test. A core loss reduction was achieved with the NiCoP coating with a thickness of 1 􀁐m magnetized at a magnetic flux density of 0.3T.

Abstract: In this study, a new wireless smart sensor for fatigue damage detection of a single steel bar is proposed. A modified stress intensity factor is used to introduce a master curve of fatigue crack growth. Acoustic Emission signals are also measured and incorporated in the procedure for the structural health monitoring.

Abstract: AE method is a well-known technique for in-situ monitoring of damage behavior by attached piezoelectric transducer. However, this conventional detection of AE signals has certain limitations. In recent years, numerous efforts have addressed the substitution of laser-based techniques for ultrasonic nondestructive evaluation in place of conventional piezoelectric transducers. Especially, a laser interferometer can be used to measure a displacement or velocity at materials surface using Doppler-shift. However, there are few reports referring to the detection of AE signals in the practical materials and testing because of the difficulty of experiments. We developed the AE measurement system with laser interferometer to apply this technique to microcrack evaluation and reported the quantitative AE analysis in various materials. This paper demonstrates AE results from thermal spray coatings at elevated temperature.

Abstract: Self-oscillating gel is designed by copolymerizing the catalyst for the Belousov-Zhabotinsky (BZ) reaction with thermosensitive polymer. The cylindrical-shaped specimens of NIPAAm-co-(Ru(bpy)3 gel were prepared by copolymerizing (Ru(bpy)3) monomer as catalyst with NIPAAm as thermosensitive polymer. Swelling behavior during self-oscillating of gel by BZ reaction was observed using CCD camera and the force due to this reaction was evaluated using semiconductor gauge. Self-oscillating swelling-deswelling behavior in samples with different swelling ratio was evaluated by this apparatus, and mechanical parameters such as Young’s modulus, stress amplitude and oscillating period were quantitatively estimated.

Abstract: Poly-N-isopropylacrylamide (PNIPA) gel is a typical thermo responsive gel which undergoes a large volume change from the low-temperature swollen phase to the high-temperature shrunken phase. In this study, the mechanical behavior of PNIPA gels was investigated by the experiment and simulation. The cylindrical shaped specimens of PNIPA gel were prepared and tensioned at various temperature. Swelling ratio at equilibrium state was calculated by diameter of swelling gels. Young modulus was obtained from stress-strain curve plotted using tensile load measured by semiconductor gauge. Also swelling and deswelling behavior of thermo sensitive gel were simulated by using finite element method. Polymer-solvent interaction parameter, χ was used as a function of temperature. Calculated swelling ratio at equilibrium was compared with experimental result and theoretical swelling curve. Furthermore, change of volume fraction and stress distribution in swelling process were evaluated.

Abstract: A new sensing method called “smart stress memory patch”, which could estimate the maximum stress, the stress amplitude and the fatigue cyclic number simultaneously using Kaiser effect of Acoustic Emission (AE) and crack length of this patch, was developed. In this study, the crack growth characteristics of this patch was evaluated. Pure copper was used for this patch because its good corrosion resistance, stable crack propagation and so on. Two kinds of samples which were rolled and electrodeposited copper were prepared to investigate the effect of microstructure on crack growth behavior. Fatigue test was performed under constant stress amplitude to evaluate the crack growth behavior using the relationship between stress intensity factor range and crack propagation rate. The scattering in fatigue crack growth was also investigated to obtain the relationship between crack length and the fatigue cyclic number including two-sided 95% confidence interval. The effect of thickness and grain size on the scattering was discussed. Finally, good crack growth behavior was obtained and the fatigue cyclic number could be estimated by this patch.

Abstract: In order to study the texture effects on the anelastic recovery behavior of magnesium alloy, basal plane textured AZ31B alloy was compressed parallel and vertical to the extrusion direction. AE measurement was applied to characterize the deformation and the anelastic recovery behaviors. A model for the correlation between applied strain and the cumulative AE counts in detwinning was proposed. The effects of loading direction to the deformation and twinning behavior were discussed.

Abstract: Self-oscillating gel is designed by copolymerizing the catalyst for the Belousov- Zhabotinsky (BZ) reaction with thermosensitive polymer. The cylindrical-shaped specimens of NIPAAm-co-(Ru(bpy)3 gel were prepared by copolymerizing (Ru(bpy)3) monomer as catalyst with NIPAAm as thermosensitive polymer. Tensile tests were performed with cross-head speed of 10 )m/s in pure water at 20°C. Stress-strain curves were plotted using tensile load measured by semiconductor gauge and strains calculated from observation of the gel. Fracture strain and Young’s modulus were obtained from these curves. Also Poisson’s ratio was estimated from the ratio of strains in longitudinal and radial directions.

Abstract: In recent years, a thermal barrier coating technology becomes more important because it is required to develop materials which avoid high-temperature oxidation and corrosion. In order to ensure reliability of coating, it is necessary to understand microfracture criterion in terms of stress distribution and fracture morphology. The objective of this study is to clarify the damage generation process by comparing Acoustic Emission
AE) generation behavior and thermal stress simulation result based on heat history measurement. Al2O3 as the top coat (TC) and NiCrAlY as the bond coat (BC) were sprayed to SUS304 disc or plate as a base material. AE in cooling process were detected by laser heterodyne interferometer after spraying finished. Two-dimensional axisymmetric mesh for samples was made and transient heat conductivity was analyzed for various boundary conditions. Then, using the obtained heat history, transient heat stress was analyzed and the distribution of stress elements was calculated. The fracture process of ceramic coating was evaluated from these experiments and analyses.