In the process of material innovation, multi-phase and composite materials have been developed to achieve high performance and reliability. Residual stresses inevitably introduced into materials often play a key role in performance and reliability. To measure residual stresses in crystalline materials, the X-ray diffraction method has been used as one of the most powerful nondestructive tools, and so has been the neutron diffraction method as a complimentary tool. Both X-ray and neutron methods are based on crystal diffraction. Diffractions from crystals are separately recorded depending on the crystalline structure, and the mean stress in each diffracting phase, called phase stress, is calculated from the peak shift of each separated diffraction profile. The macrostress is determined from phase stresses using the rule of mixture. The deviation of each phase stress from the macrostress is named microstress. In the present article, the fundamentals of measurements of phase stresses and the determination of macrostress and microstress are described. Micromechanics are briefly presented as a basis for theoretical analysis of phase stresses in composites. Applications of the X-ray and neutron methods to the measurement of residual macrostress and microstress in various multi-phase materials, metal-based, ceramic-based, polymer-based composites are reviewed, together with future perspective of the methods.
Residual stresses of a plate of aluminum alloy were measured using a double exposure method (DEM) with synchrotron X-rays of 30 keV. However, the DEM has not be applied in the range of high-energy synchrotron X-rays. In this study, the stress measurements of a shrink-fitted ring using the DEM with synchrotron monochromatic X-rays beyond about 70 keV were performed. A CdTe pixel detector and a CCD camera were used as a detector. The shrinkfitted specimen of SUS304 was quasi-coarse grains of 43 micro-meters, and the diffraction rings were spotty. Despite quasi-coarse grains, it was possible to measure the stresses of the shrink-fitted specimen using the DEM. As a result, the DEM is excellent method to measures the stress for coarse grained materials. In addition, it is better to make the length between the detection positions longer to improve precision of the DEM. On the other hand, it was ineffective to increase the positions of detection.
Recrystallization process of an aluminum (Al) single crystal was observed in situ using synchrotron X-rays. Al single-crystalline samples were deformed in tension along a <111> direction to a strain of 8%, and were subsequently annealed at 753 K. The changes in the shape and intensity of diffraction spots were analyzed using a two-dimensional detector. A diffraction spot from the deformation matrix had three peaks which reflected a sub-grained microstructure of the sample. The in situ observation during annealing unveiled the appearance of diffraction spots from a recrystallized grain at 330.8 s. As the diffraction spots from the recrystallized grain became larger, the diffraction spots from the deformation matrix gradually disappeared. The application of the X-ray topography method revealed the crystal orientation variation in a recrystallized grain in order of 0.001 degree.
Aluminum laminate films have been widely used for packing materials of lithium ion battery and other electronic devices, and the emboss process is commonly used for shaping films for packages. Thermal stress cycling due to on-off switching of devices may result in thermal fatigue of aluminum layer of laminated films. In the present paper, the X-ray diffraction method is applied to detect the progress of deformation and fatigue damage of aluminum layer in laminate films subjected to tensile deformation and fatigue. The full-width at half maximum (FWHM) was increased with tensile strain. Fatigue loading increased FWHM, and also induced ratcheting extension, which was identified as an indicator of fatigue damage progress. The relation between FWHM and ratcheting strain is nearly identical to that obtained in tensile deformation. The residual stress as received was compression due to mismatch of thermal expansion between aluminum and plastic layers. The compressive residual stress increased with fatigue ratcheting extension as well as with tensile deformation, and the amount of increase of compressive residual stress with film extension is nearly identical between two deformation modes. The increase of compressive residual stress was caused by deformation mismatch between aluminum and plastic layers during extension of films. The contraction of films may introduce tensile residual stress in aluminum layer. The tensile residual stress in the aluminum layer was measured at emboss corners of laminate films.
The extruded profiles of 6000-series aluminium alloys have a textured surface structure, different from those having the inner cube and Goss and surface (110) orientations. This structure difference possibly contributes to the decrease in mechanical properties. Although the mechanism of degradation has been discussed for the size, morphology, and density of precipitates, texture and share band, it is necessary to reconsider it from the viewpoint of residual stress distribution. In this study, we first determine the optimal method to evaluate the residual stress in a textured structure of extruded aluminium profiles. The cosα method with 3-axis oscillation successfully yielded highly precise residual stress values even in extruded aluminium alloys. The regions of preferred orientation corresponded well with the major changes in residual stress as a function of depth from the surface. The boundary of the (110) and (100) textures matched well to the first local maximum in the von Mises stress for both alloys. The grain-growth region of A6005C corresponded to the region between the first and second local maxima of von Mises stress.
In general, metal products have a characteristic surface layer called a work-affected layer, formed by polishing at the time of manufacture. This layer has many differences in mechanical properties such as crystal state and residual stress depending on the processing conditions. Regarding this, if the crystal and residual stress states of the work-affected layer, formed during manufacturing was able to be clearly evaluated, it may be possible to clarify the manufacturing history from its characteristics. In other words, the evaluation of the work-affected layer can add new information to archaeological research as an appraisal method for metal products. X-ray measurement, which can be evaluated non-destructively, is very effective as a means of examining the state of the work-affected layer of metal. Therefore, in this study, we investigated the possibility of confirming the crystal state and evaluating the residual stress using the X-ray diffraction method for three types of copper-based casting old coins with different elemental compositions. As a result, the Debye rings obtained by X-ray diffraction were diverse, such as uniform continuous rings and discontinuous rings with light spots, depending on the specimens. That is, it was found that the crystal state of the surface layer of old coins has fine crystals, texture, coarse crystals, etc., depending on the elemental composition. In addition, compressive residual stress of about -140 to -370 MPa exists in all specimens. It was confirmed that this value differs depending on the measurement diffraction plane and the measurement direction, and that a clear difference occurs due to the difference in the elemental composition.
A uniaxial creep test method using an ultra-miniature creep (Ultra-MC) specimen with a size equivalent to that of a small punch creep (SPC) specimen was developed in this study. It was confirmed that the devised Ultra-MC specimen had the self-alignment function and geometry optimized by FEM analysis. In addition, by comparing the creep test results of the Ultra-MC specimen with the standard specimen (ϕ6), the applicability of Ultra-MC testing method was confirmed. The creep rupture time of the Ultra-MC specimen was found to be good agreement with that of the standard specimen, and the deviation of the creep rupture time was small. On the other hand, the creep deformation of the Ultra-MC specimen was larger than that of the standard specimen. By FEM analysis, this was found to be due to the creep deformation in the shoulder portion of the Ultra-MC specimen. So, a modification procedure for adjusting the creep property of the Ultra-MC specimen to that of the standard specimen was proposed.
Anti-freezing agents are commonly used in cold-weather concreting, in which the ambient temperature is generally maintained at +5 °C or more for 24 h after casting in the mold. Consequently, the freezing inhibition effect and strength development of cementitious materials exposed to a low temperature (below the freezing point) immediately after mixing with an anti-freezing agent, remain unclear. In this study, several physicochemical reviews were performed to clarify this relationship between the strength development and hydrate formation behavior at the freezing point immediately after mixing, resulting from the addition of different amounts of anti-freezing agents to cement paste. Lithium nitrite and calcium nitrite were used as the anti-freezing agents. The freeze temperature of the cement paste with lithium nitrite was lower than that of the cement paste with calcium nitrite when cured at -10 °C immediately after mixing. An increase in the amount of lithium nitrite prevented the freezing of cement paste and promoted the hydration reaction even below the freezing point, thereby contributing to strength development.
Chemical alterations of bentonite are critical factors for the ultra-long-term stabilization of barriers and backfill in radioactive waste disposal. The chemical alterations may deteriorate the properties of bentonite-based materials. However, experimental studies on the effects of chemical alterations on the swelling characteristics and permeability of bentonite-based materials have not been investigated extensively. In this study, the effects of chemical factors on the swelling properties and permeability of bentonite-based materials were clarified based on one-dimensional swelling pressure, hydraulic conductivity, X-ray powder diffraction patterns, and element mapping images. From the analytical and experimental results, a small amount of K+, Fe3+, and Mg2+ can significantly deteriorate the swelling characteristic and permeability of bentonite-based materials in geological disposal (i.e., cause a decrease in swelling pressure and an increase in hydraulic conductivity). Therefore, we conclude that it is necessary to pay close attention to the existence of these cations.
Dakekanba is the most popular broad leaf tree in Hokkaido. This study proposed the wood for manufacturing baseball bat. In order to compare the dakekanba wood with the others manufactured historically; sugar maple, aodamo, yellow birch, and white ash, full baseball bats with the same dimension were prepared from these woods. The performance of bat was studied by the impact test with fast pitched ball. The flexural vibration was measured by means of strain gauge. Results of the modal analysis showed that the first natural frequency was around 35 Hz and the second, 233 Hz, which were almost equal among these woods. The amplitudes of these modes increased with increasing the speed of pitched ball. As a result, the maple bat was the hardest in deflection and slowest in damping, and aodamo was the softest in deflection and the fastest in damping. It was concluded that these properties of dakekanba bat were close to those of yellow birch and white ash, which have served as intermediate between maple and aodamo.