Setsuo Miura

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).

Ageing effects on the lattice strain behaviour of duplex stainless steel

The mechanical properties of duplex stainless steel (DSS) are known to display embrittlement due to ageing effects. Knowledge of the micro behaviour of aged DSS is important for understanding the mechanisms of deformation and failure, but it has proved difficult to obtain due to the complex effects created by the duplex structure. Lattice strain measurements of DSS aged under various conditions of temperature and time have been performed in order to determine the strain behaviour of individual (hkl) planes in the α- and γ-phases using white synchrotron radiation X-rays at SPring-8. It was found that the lattice strain of α-Fe(200) depends strongly on the ageing conditions and that the lattice strain behaviour in the γ-phase is more stable than that in the α-phase. These results suggest that the changes in macro mechanical properties, including yield strength and ultimate strength, which are revealed by standard tensile tests, are solely due to ageing effects in the α-phase. The results further suggest that the lattice strain of α-Fe(200) can be used as an index to evaluate 475 °C ageing effects in DSS.

Strain Measurement of Aged Duplex Stainless Steel Using SR White X-Rays

Duplex stainless steels (DSSs) have microstructures of α and γ-phases of iron and exhibit changing of their mechanical properties by aging above 300°C, so that strain behavior is expected to be complicated under stress loading. In order to estimate lattice strains and to determine their behavior, lattice strain measurements of aged DSSs have been performed using synchrotron radiation white X-rays. As a result, it was found that the lattice strain was not always correspond with applied macro strain, and the lattice strains of γ-phase showed no elongation in comparison with those of α-phase in the aged specimen. These results mean that complex strain distributions between (hkl) planes already exist in the early stage of elastic deformation, and suggest that fracturing of aged DSSs under tensile loading occurs preferentially on γ-phase rather than α-phase.

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.

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.

Evaluation of Surface Roughening in Polycrystalline Aluminum by Laser Speckle Technique and Fractal Analysis.

The speckle intensity distributions of a laser beam reflected from a surface of a polycrystalline aluminum specimen were changed due to the plastic deformation of the specimen and were measured using the image processing technique. The cross section of the laser speckle pattern on a same gray level could be expressed quantitatively by an elliptic function ; the correlation between an aspect ratio of the ellipsoidal shape and the growth of anisotropy induced by the plastic deformation, the onset of yielding and localized deformation was studied in the preceding paper. In this paper, the effects of the grain size and the rolling reduction of an aluminum specimen upon both the reflected speckle intensity distribution of the laser beam from the surface of the specimen and the optical surface image obtained by the optical microscope under the plastic deformation were studied through the fractal dimensional analysis. The results obtained are summarized as follows ; (1) The speckle intensity distribution expanded with increase of plastic strain ; the degree of the expansion was increased with the growth of the grain size of specimen, while the change of aspect ratio was very small. (2) At the initial stage of the plastic deformation, the aspect ratio of rolled specimen rapidly decreased, and the change of the aspect ratio was dependent upon the rolling reduction of the specimen. (3) The good correlation between the plastic strain and the fractal dimension of the speckle intensity distribution due to the surface roughening of the specimen was obtained.

Ultrasonic Nondestructive Evaluation of Lankford Value.

In plastic processes such as deep drawing, it is important to evaluate the anisotropy of the material, especially the Lankford value in the sheet, nondestructively. The microstructure of the materials introduced by rolling, drawing, or other materials processing relates to the mechanical properties of the materials such as the strength and anisotropy, and influences the velocity and attenuation of the ultrasonic waves propagating in the materials. Therefore, we are able to investigate the growth of the plastic anisotropy using the ultrasonic waves. In this paper, in order to establish an ultrasonic method for nondestructively evaluating the Lankford value of the material, we examined the correlation between the changes in the Lankford value and the subsequent yield surfaces numerically simulated using the parameters of the plastic anisotropy which were determined from the velocity changes in the longitudinal waves propagating in the directions of width and thickness of the aluminum alloy specimen in a uniaxial tensile test.