Shin-ichi Ohya

Advanced x-ray stress analysis method for a single crystal using different diffraction plane families

Generalized formula of the x-ray stress analysis for a single crystal with unknown stress-free lattice parameter was proposed. This method enables us to evaluate the plane stress states with any combination of diffraction planes. We can choose and combine the appropriate x-ray sources and diffraction plane families, depending on the sample orientation and the apparatus, whenever diffraction condition is satisfied. The analysis of plane stress distributions in an iron single crystal was demonstrated combining with the diffraction data for Fe{211} and Fe{310} plane families.Generalized formula of the x-ray stress analysis for a single crystal with unknown stress-free lattice parameter was proposed. This method enables us to evaluate the plane stress states with any combination of diffraction planes. We can choose and combine the appropriate x-ray sources and diffraction plane families, depending on the sample orientation and the apparatus, whenever diffraction condition is satisfied. The analysis of plane stress distributions in an iron single crystal was demonstrated combining with the diffraction data for Fe{211} and Fe{310} plane families.

PREDICTIONS OF ANISOTROPY AFFECTED FATIGUE CRACK PROPAGATION PATHS IN PURE ALUMINUM SHEETS

The anisotropy affected fatigue cracks that propagate on the rolling direction as mixed mode I-II cracks in CCT-specimens of pure aluminum sheets were predicted using Finite Element Method. The crack growth paths were estimated based on the value of mode I, II, total stress intensity factor range, and the ratio of mode II and mode I energy release rate of the crack. The predictions of crack propagation paths in no-hole specimens and 6-type holed specimens with 0, 30, 45 and 60 degrees of rolling direction towards loading direction were performed and the results were coincided with experimental results.

Internal stress distribution for generating closure domains in laser-irradiated Fe–3%Si(110) steels

Internal stress distribution for generating closure domains occurring in laser-irradiated Fe–3%Si(110) steels was investigated using high-energy X-ray analysis and domain theory based on the variational principle. The measured triaxial stresses inside the specimen were compressive and the stress in the rolling direction became more dominant than stresses in the other directions. The calculations based on the variational principle of magnetic energy for closure domains showed that the measured triaxial stresses made the closure domains more stable than the basic domain without closure domains. The experimental and calculation results reveal that the laser-introduced internal stresses result in the occurrence of the closure domains.

Standard Sample Package for Calibration of X-Ray Stress Measurement

The purpose of our study is to provide standard samples for X-ray stress measurement. Typically zero adjustment is performed by a stress free sample which is a fine powder of pure metal. However, if the sample has stress (not stress-free), the stress value obtained by measurement can contain the errors caused by each stress measurement instrument. To solve this instrumental error, we have created a standard sample package. The sample package includes the following three samples. 1) Fluorescent powder to confirm the beam position and size. 2) Iron powder (particle size 6-8μm) to calibrate the zero-stress. 3) Bulk iron material which has approx. -100(MPa) of residual stress. Each sample has been laid out in a 6mm thick plate, and each sample can be selected by sliding the plate manually. By measuring the bulk material and the powder, correction and calibration of the stress measurement instrument is possible. The manufacturing process employed in this study has confirmed that the iron bulk material does not have residual stress and FWHM changes over time in the past 20 years. Therefore, the standard sample can be used semi permanently by adequate management. Correction of instrument by using this standard sample package increases the reliability of X-ray stress measurement method which will help to employ it in a wide range of practical uses.

Measurement for Actual Stress Distribution by Using X-Ray Diffraction during Rotary Bending Fatigue Test

The purpose of this investigation is to detect a damage from actual stress distribution in the surface of specimen by using X-ray diffraction technique during fatigue test. An apparatus to measure the actual stress distribution along specimen circumference was fabricated by use of a cantilever type rotary bending fatigue machine and a stress analyzer based on single exposure technique with two position sensitive proportional counters. The authors developed a method for collecting separately the diffraction profile at each position along the circumference. Actual stress distributions at the maximum tensile applied stress were dynamically measured. As a result, the shape of the distribution was keeping stable with the increase in the number of stress cycles until crack initiation. When the crack length reached greater in size than the width of irradiation area, the actual stresses at the crack position were suddenly decreased down to 0MPa, and the distribution showed a V-shape. These results show that the method adopted in this study is available for detecting both the position and the period of crack initiation.

X-Ray Study on Deformation and Fracture of Solid. Measurement of Actual Stress during Fatigue Process.

There are several investigations on the behavior of residual stress during fatigue process. It is, however, difficult to detect the crack initiation from the change in residual stress because of no significant change in residual stress through the fatigue process. The purpose of this investigation is to detect the fatigue damage from the change in actual stress measured by X-ray diffraction technique during fatigue test. In this paper, a cantilever type rotary bending test machine was developed for an X-ray stress analysis based on Single Exposure Technique. The actual stress at the maximum tensile applied stress was measured to failure during cyclic loading.The actual stress was keeping stable with increasing number of cycles until crack initiation, and this behaivior was independent of stress amplitude. After the crack initiation, it decreased suddenly with crack propagation because of stress relaxation at the crack. These results show that the change in actual stress at the maximum tensile applied stress has much higher sensitivity to detect crack initiation than one in residual stress. In-situ X-ray observation of actual stress during fatigue test is useful to detect fatigue damage.

Study on solidification of aluminum alloy weld metal (Report 3). The behavior of temperature decreasing and fraction solid increasing in solid-liquid coexisting zone.

It is the ultimate purpose of this investigation to elucidate the fundamental phenomena in cooling and solidification process and to establish reasonably the methods of estimating hot cracking sensitivity and preventing Al alloy weld from hot cracking.In this report, temperature measurement was carried out by CA thermocouple in coiling and solidification process on TIG arc spot welds of commercial Al alloy 2024 and 5083 and various analyses were performed.On the basis of the measured value, the authors made Continuous Cooling Solidification Process diagram (CCSP diagram) showing the relation among passed time from arc stop, phase change and the position of welds.By using the CCSP diagram, the authors could investigate the solidification process of the welds. With regard to fraction solid cooling rate (cooling rate in solid-liquid coexisting zone), it was found that the cooling rate at every definite fraction solid was more meaningful than one in a whole solidification time.Increasing behavior of fraction solid were very different between 2024 and 5083 Al alloy at the latter stage of solidification process in the molten pool.

Correction of X-ray diffraction profiles measured by PSPC method.

When the X-ray stress analysis is performed by using a position sensitive proportional counter (PSPC), a parabolic (curved) background line is obtained on the X-ray diffraction profile because of geometrical problem of PSPC and absorption of X-rays. Since such phenomenon is especially remarkable in the broadened profile, it is necessary to correct it to a straight background for measuring a diffraction angle or a half-value breadth with high accuracy.This paper analyzes such curvature of background line of the profile and suggests a correction method to linearize the background line.The results obtained are summarized as follows:1) The intensities at the both ends of effective length of the PSPC decreased because of the tilt incidence of X-ray beam.2) The correcting factor for the linearization of the background line was essentially the inverse of background intensity. However, because the background is apt to scatter due to the statistical property of X-rays, such factor was determined by smoothing the inverse of the scattering X-ray intensity obtained from a glass plate.3) By correcting the background line, the half-value breadth was able to be measured as a constant value wherever the starting points for determining the background line by digital calculation were positioned.4) On the other hand, the correction was not necessary on the stress measurement.

Time-resolved X-ray stress measurement by PSPC method during cyclic loading.

The X-ray stress analysis at an arbitrary stress level during cyclic loading is effective to make clear the effect of residual stress on fatigue behavior. The method of sampling the diffracted X-rays at only one applied stress level in a short time during cyclic loading is required to perform such X-ray stress measurement, because the actual stress of specimen always changes during stress measurement.This paper suggests the method of measuring the diffraction profile during cyclic loading by using an X-ray stress analyzer with a position sensitive proportional counter (PSPC) and discusses the accuracy of this X-ray stress measurement.The results obtained are summarized as follows:1) The method of time-resolved measurement of the diffraction profile by using PSPC was established. X-rays are constantly irradiated on the specimen during cyclic loading, and as soon as the applied stress reaches to a set stress level, the diffracted X-rays are sampled for a minute time, and the profile is determined by integrating the diffracted X-rays for several time-resolved samplings at this applied stress level.2) The X-ray stresses at various levels of applied stress were measured very accurately. However, when the sampling time per one cycle was very short, the error of the X-ray stress increased.3) The number of cycles needed for the stress measurement was considerably decreased by using a stress analyzer with PSPC. It was also decreased by decreasing the preset peak counts for measuring diffraction profile as well as the angles of X-ray incidence for the analysis.4) It was confirmed by the time-resolved X-ray stress measurement that the actual stress during cyclic loading was the algebraic sum of the applied stress and the residual stress.