Michiaki Kobayashi

Ultrasonic nondestructive material evaluation method and study on texture and cross slip effects under simple and pure shear states

Abstract Ultrasonic wave velocities propagating in a plastically deformed medium are known to depend upon its microstructural material properties. Therefore, the authors have proposed the theoretical modeling of an ultrasonic nondestructive method to evaluate plastically deformed states. In the present paper, we verify the proposed theoretical modeling of an ultrasonic nondestructive method and examine its accuracy by comparing the experimental results with the simulated subsequent yield surfaces, the longitudinal and transverse wave velocities under combined stress states of an aluminum alloy using internal state variables of an anisotropic distortional yield model which were determined to achieve a good fit for the experimental results of the longitudinal and transverse wave velocity changes under uniaxial tension test. As a special case, the velocity changes of longitudinal wave under pure shear state subjected to the combinations of tension and compression are also studied, it shows a different result compared with that of longitudinal wave velocity under torsional tests of thin thickness cylinders, i.e., simple shear state. The effects on ultrasonic wave velocity changes due to texture and cross slip under simple and pure shear states are studied via a finite element polycrystal model (FEPM).

Ultrasonic nondestructive evaluation of microstructural changes of solid materials under plastic deformation—Part I. Theory

Abstract In general, finite plastic deformation is accompanied by microstructural material property changes such as texture change and growth of localized slip bands. However, it is very difficult to evaluate these microstructural material property changes nondestructively by means of the usual methods used to date. The ultrasonic nondestructive evaluation method proposed by the author has been successfully applied to the evaluation of plastically deformed state. The purpose of the present paper is to formulate precisely a generalized acoustoelastic theory for plastically deformed solids with finite plastic deformation and, moreover, to provide a method of nondestructive evaluation of the plastically deformed state, i.e. yield surface, texture change and the occurrence of the instability associated with the microslip band.

Ultrasonic nondestructive evaluation of microstructural changes of solid materials under plastic deformation—Part II. Experiment and simulation

Abstract The microstructure of materials introduced by rolling, drawing, heat treatment or other methods of material processing relates to the macroscopic mechanical properties of the materials, such as the strength and anisotropy. The velocity and attenuation of the ultrasonic waves propagating in the materials are known to be dependent upon such microstructural material properties. The author has proposed a theoretical modeling of an ultrasonic nondestructive method to evaluate the microstructural property changes of materials in Part I of this work. In the present paper, annealed effects on plastically deformed states of an aluminium alloy were studied using the proposed ultrasonic nondestructive evaluation method and it was found that close agreement between the simulated results and experimental data was possible.

Transmission Imaging and Strain Mapping in the Vicinity of Internal Crack Tip Using Synchrotron White X-Ray

A transmission imaging and a strain mapping in the vicinity of a crack tip in steel were investigated using a high energy white X-ray obtained from BL28B2 beam line at SPring-8 in Japan. Low-alloy and high-tensile steel was used as a specimen prepared in the G-type geometry with a rectangular sectional part of 5mm thickness for a four-point bending. A fatigue crack was introduced into the notch root on the tension side of the specimen by a pulsating bending load. The imaging of the crack in the specimen under the bending load was carried out by using the CCD camera that can detect indirectly the X-ray transmitted through the specimen. To measure the internal strain in the vicinity of the crack tip, the synchrotron white X-ray beam, which had a height of 80m and a width of 300m, was incident on the specimen with the Bragg angle  of 5 degrees using the energy dispersive X-ray diffraction technique. As the results, the transmitted image of the crack showed that the crack in the specimen was propagated deeper than that on the surface. The map of the internal strain near the crack tip could be obtained using the white X-ray with energy ranging from 50keV to 150keV. It became clear by the numerical simulation that the FWHM of diffracted X-ray profile measured near the crack tip was increased due to the steep change in the strain distribution. It was confirmed that the synchrotron white X-ray was useful for the imaging of the internal crack and the strain mapping near it.

Strain Measurement in the Depth of the Order of Millimeter Using High Energy White X-Rays

The strain in the bulk of material was evaluated using high energy white X-rays from a synchrotron radiation source of SPring-8 in Japan. An austenitic stainless steel (JIS-SUS304L) was used for a specimen. The specimen of 5 mm thickness was subjected to the bending. The internal strain of it could be measured using white X-rays which range of energy from 60 keV to 125 keV. The measurement of the internal strain with a high accuracy was accomplished using the strain data from several lattice planes of γ-Fe simultaneously. Furthermore, the measurement error of strain could be decreased by using the diffracted beam with high energy, high peak count and the similar profile with the Gaussian distribution. The results showed that the high energy white X-rays is effective for the internal strain measurement in the depth of the order of millimeter.

Ultrasonic Nondestructive Evaluation of Micro Slip Band and Plastic Anisotropy Growth

The purpose of the present paper is to evaluate microstructural changes of the aluminum alloy induced by plastic deformation by using the proposed ultrasonic nondestructive evaluation method.

Evaluation of Ductile Damage Progress of Aluminum Single Crystal with Prior Activity of Single Slip System under Tensile Loading by Using Synchrotron White X-Ray

A ductile damage progress of an aluminum single crystal with the prior activity of the single slip system under tensile loading was verified by a profile analysis using white X-ray obtained in BL28B2 beam line of SPring-8. In this study, the aluminum single crystal of the purity 6N was used as a specimen prepared in I-type geometry for tensile test. A notch was introduced into one side of the center of a parallel part of the specimen by the wire electric discharge machining. White X-ray beam, which has 50 μm in both height and width, was incident into the specimen on the Bragg angle θ of 3 degrees using energy dispersive X-ray diffraction technique. The specimen was deformed by elongation in the direction of 45°to [11 and [11 crystal orientations, respectively, and a diffraction profile of the white X-ray from Al220 plane was analyzed. In profile analysis, an instrumental function was defined in consideration both of a divergence by a slit and a response function peculiar to the energy dispersive method. The Gauss component of integral breadth related to non-uniform strain and the Cauchy component of integral breadth related to crystallite size were determined by eliminating the broadening by the instrumental function from the diffraction profile of white X-ray. As a result, the characteristics of ductile damage progress near the notch of the aluminum single crystal were inspected from the distribution of both non-uniform strain and dislocation density.

Study on Ductile Damage Progress of Aluminum Single Crystal Using Synchrotron White X-Ray

A ductile damage progress of FCC single crystal was verified by a profile analysis using white X-ray obtained in BL28B2 beam line of SPring-8. In this study, an aluminum single crystal of the purity 6N was used as a specimen prepared in I-type geometry for tensile test. A notch was introduced into one side of the center of a parallel part of the specimen by the wire electric discharge machining. White X-ray, which has 100 microns in height and 200 microns in width, was incident into the specimen on the Bragg angle θ of 3 degrees using energy dispersive X-ray diffraction technique. The specimen was deformed by elongation along crystal orientation [001], and a diffraction profile of the white X-ray which penetrated it was analyzed. In profile analysis, an instrumental function was defined in consideration both of a divergence by a slit and a response function peculiar to the energy dispersive method. The Gauss component of integral breadth related to non-uniform strain and the Cauchy component of integral breadth related to crystallite size were determined by eliminating the broadening by the instrumental function from the diffraction profile of white X-ray. As a result, the direction of progress and the characteristics of ductile damage near the notch of the aluminum single crystal were clarified from the Gauss component and the Cauchy component of integral width of the single diffraction profile.

Measurement of Internal Strain in Materials Using High Energy White X-Ray at SPring-8

This paper presents a basic research on a measurement of strain in the bulk of materials by using high energy white X-ray from a synchrotron radiation source of SPring-8 in Japan. A high-tensile strength steel (JIS-SHY685) was used as a specimen loaded with bending. Strain distribution in it was evaluated by the energy dispersive method using diffracted X-ray transmitted through the specimen. As a result, the internal strain of high-tensile steel of 5, 10 and 15 mm thickness could be evaluated using white X-ray which range of energy from 50 keV to 150 keV. The measurement with a high degree of accuracy was accomplished using α-Fe321 diffraction in this material. The results showed that the internal strain measurement in the depth of the order of millimeter using the high energy white X-ray is practicable at SPring-8.

In Situ Measurement of Lattice Spacing of Ternary Ni-Ti-Nb Alloys during Hydrogen Absorption

Microscopic deformation of each crystal of duplex phases of Ni-Ti-Nb alloy due to hydrogen absorption was investigated by X-ray diffraction technique. Ni30Ti30Nb40 which is hydrogen permeation alloy and consists of the primary phase, NbTi, and the eutectic phases, NiTi + NbTi, was used as a specimen. The change of lattice spacing of the specimen during hydrogen absorption was measured by Cu-Kα characteristic X-ray. As a result, the lattice spacing of crystal of NbTi phase increased extremely, while that of NiTi phase increased slightly. It was pointed out that the NbTi phase is responsible for hydrogen absorption in the Ni-Ti-Nb alloy. When hydrogen gas was released from the specimen at high temperature, both lattice spacing returned nearly to those of them before hydrogen absorption, and the specimen kept its original shape. Therefore, it was confirmed that the volume expansion of crystal of the Ni-Ti-Nb alloy due to hydrogen absorption was elastic deformation.