Papers by Author: Atsushi Moriai

Abstract: Ultrasonic impact treatment (UIT) is a remarkable post-weld treatment, which reduce not only in external stress concentration, but also in residual stress in a welded joints. Internal and surface stresses were investigated on UIT treated welded joints by neutron and X-ray diffraction method. This paper discuses the effect of internal and surface residual stress and surface stress concentration after UIT on fatigue resistance by the comparison of fatigue experiments to predictions calculated with the results of the experimental investigations.

Abstract: The Engineering Materials Diffractometer “TAKUMI” is designed and has been constructed at Materials & Life Science Facility (MLF) of Japan Proton Accelerator Research Complex (J-PARC) to conduct various kinds of studies on materials science and engineering and to promote industrial applications, related with strain measurements. The commissioning of TAKUMI has been started from September 2008, and several user programs have been done. In the commissioning, a resolution Δd/d at high resolution mode (with incident beam collimation) of less than 0.2% was achieved in a diffraction experiment using 2 mm diameter thick annealed piano wire. The d-range measured by TAKUMI with single pulse frame, i.e. standard operation, was confirmed to be 0.05 nm to 0.27 nm, showing that the optimum range for materials research is covered by this machine. TAKUMI adopted an event mode data recording method. It was found that the recording method is very useful to manipulate data as we like, for instance, detector range, time of flight binning width and time resolved data, even after the experiment has been finished.

Abstract: The Engineering Materials Diffractometer Application Kit called EMAKi has been developed to control the Engineering Materials Diffractometer, TAKUMI, and treat data obtained by it. It is expected that TAKUMI will be widely used by not only academic users but also industrial users. We have designed EMAKi to be user-friendly interface for novice users by graphical user interface (GUI). In addition, adopting Python programming language for its development has enabled advanced users to control the diffractometer flexibly and treat the data easily. During instrumentation commissioning and running user programs, the software has demonstrated useful.

Abstract: Tensile deformation behaviors of three austenitic stainless steels, JIS-SUS310S, 304 and 301L, were studied by static tensile tests and in situ neutron diffraction. In the mechanical properties obtained by the static tensile tests, the 304 and 301L steels showed better balance of tensile strength and uniform elongation than the 310S one because of TRIP effect. The angular dispersion neutron diffractions with a wavelength of 0.16 or 0.182 nm were performed during stepwise tensile testing by using a neutron diffractometer for residual stress analysis (RESA) at the Japan Atomic Energy Agency. The lattice plane strain, stress-induced martensite volume fraction, dislocation density and so on were estimated by the profile analysis as a function of applied stress. The change in lattice plane spacing for austenite indicated four deformation stages. In the comparison of lattice plane strain among the tested steels, a phase stress caused by the stress-induced martensite seems to overlap the intergranular stress of austenite phase. Judging from the results of profile analysis, the strain partitioning of austenite phase in metastable austenitic steels became larger with increasing of the volume fraction of stress-induced martensite during tensile deformation.

Abstract: The construction of The Engineering Materials Diffractometer, TAKUMI of J-PARC has been finished on March 2009, and the commissioning has been started from September 2008 being parallel with the final stage of the construction. In the commissioning, after checking the validity and the stability of the detectors and the data acquisition system, powder diffraction data of an austenitic steel alloy with 10 mm diameter without beam collimation (high intensity mode) was measured, and the resolution Δd/d of 0.4% was confirmed, as designed. Further commissioning was done also with 2 mm diameter of annealed piano wire with combination of beam collimation (high resolution mode), and the resolution Δd/d of less than 0.2% was confirmed to be achieved. TAKUMI adopted an event mode data recording method. It was found that the recording method is very useful to manipulate data as we like, for instance, detector range, time of flight binning width and time resolved data, even the experiment has been finished.

Abstract: Dislocation density and crystallite size of steel wires with various carbon concentrations and drawing strains were determined by profile analyses for neutron diffraction profiles. The density is found to increase while the size decreases with increasing of carbon concentration and/or drawing strain. Both of the Bailey-Hirsch relation and Hall-Petch relation hold for the present results to suggest that these two are not independent., i.e., indicating an identical strengthening mechanism from a different point of view.

Abstract: Neutron diffraction technique was employed to measure stress distribution in an interior region of a SUS304 rotating mechanical component with a fringe after solution treatment and after subsequently conducted stress-relief annealing. A coupon with 3x3x3 mm was prepared by spark cutting to determine stress-free spacing d0. The elastic strain was determined by using the measured (111) spacing d and d0 by (d - d0)/d0. Then the obtained strains were input into the general Hooke’s law to calculate stresses. The residual hoop stress near the surface is compressive which is lowered in the inner part. The residual stresses near the center of the component are hydrostatic tensile stresses. These residual stresses were not relaxed by the annealing treatment recommended in a handbook. Hence, more appropriate stress relief treatment has to be developed. In case of a cast specimen, coarse grains with a strong texture made it difficult to determine residual stresses precisely.

Abstract: The microstructural change with drawing and subsequent annealing for a patented pearlite steel was investigated by means of neutron diffraction. The dissolution of cementite plates with drawing and re-precipitation of spherical cementite particles with annealing after sever drawing were observed. In situ neutron diffraction during tensile loading was performed and it is revealed that the strengthening mechanism of the specimen without cementite differs from that for a ferrite-cementite steel where the load transfer is a main mechanism. The possible strengthening mechanism for the heavily drawn specimen is proposed.

Abstract: An engineering diffractometer designed to solve many problems in materials science and engineering including investigations of stresses and crystallographic structures within engineering components is now being developed at J-PARC project. This instrument views a decoupled-poisoned liquid H2 moderator providing neutrons with good symmetrical diffraction profiles in the acceptable wavelength range. The primary flight path and the secondary flight path are 40 m and 2.0 m, respectively, for 90 degree scattering detector banks. A curved supermirror neutron guide will be installed to avoid intensity loss due to the long flight path and to reduce backgrounds from fast neutrons and gamma rays. Therefore, stress measurements with sufficient accuracies in many engineering studies are quite promising. The optimization of this instrument has been performed with a Monte Carlo simulation, and an appropriate resolution of less than 0.2 % in
d/d has been confirmed. A prototyped radial collimator to define a gauge width of 1 mm has been designed and manufactured. From performance tests conducted at the neutron diffractometer for residual stress analysis RESA in JRR-3 of Japan Atomic Energy Agency, the normal distribution with a full width at half maximum of 1 mm was obtained in a good agreement with the simulation.

Abstract: In this study, we proposed the high-versatility stress measurement method using neutron diffraction which can determine the residual stress states by measuring the lattice strains in two or three orthogonal directions even if the measured diffraction families were different in all three directions. In addition, we also proposed the stress measurement method without using the stress-free lattice spacing d0 which was measured using the powder sample or annealed sample. To verify this method, the residual stress distributions in a shrink-fit ring and plug specimen of aluminum alloy A7075 with texture were measured. The profile of the measured stress distributions almost agreed with the simulated stress distributions in the assumption of the plane stress condition. Our method which can determine the tri-axial stress states using observed lattice strains in two orthogonal directions was secondly applied to evaluate the stress states of A7075, high tensile strength steel HT1000, and Ni-base alloy NCF600 loaded in-situ. Measured stresses almost agreed with theoretical value with 10 MPa to 60 MPa error. On the other hand, the residual stress states of NCF600 were measured under the uni-axial loading condition by the stress measurement method without using the measured d0. Estimated lattice constant a was almost agreed with the lattice constant of its annealed sample, and changes in stress states evaluated using the proposed method coincided with the theoretical value.