Nickel nanocrystalline thin films with various grain sizes were produced by electrodeposition using sulfamate solution with different brightener contents at two bath temperatures. The distribution of the grain size of deposited films was determined by Fourier profile analysis of X-ray diffraction (XRD) and transmission electron microscopy (TEM). The grain size determined by Fourier analysis of 111-222 diffraction pairs gave smaller sizes than that of 200-400 diffraction pairs for thin films with 200 texture, while the reverse is true for films with random orientation. The distribution of grain sizes determined by TEM followed log-normal distribution. The variance was smaller for smaller sizes for both cases of XRD and TEM. The mean grain size determined by XRD of 111-222 pair agreed with that determined by TEM for sizes lower than 30 nm, while it was smaller for larger sizes. The size determined by Scherrer`s method using 111 diffraction was close to that determined by Fourier analysis of 111-222 pair, and agreed with that determined by TEM for sizes lower than 30 nm. The grain size decreased with increasing content of brightener at lower temperature of the solution bath. The yield stress of films increased with decreasing grain size, nearly following the Hall-Petch relation down to the grain size of 20 nm.
Plastic forming for magnesium alloy requires warm working. However, warm working causes micro-structure change or strength decreasing to mechanical characteristics grant material by work hardened, or grain refinement. To study warm working conditions, it is important to find out β phase (β-Mg17Al12) transition of magnesium alloy and crystal grain growth in heating process. In this report, rolled AZ61 magnesium alloy crystalline structure changing in heating process were in-situ measured by synchrotron radiation. As results, crystal grain growth of α-magnesium, and β-Mg17Al12 solution was not found under holding temperature 400℃ till 50 seconds. Furthermore, temperature rising rate 2℃/sec or over is necessary at time.
Diffraction method is very useful to evaluate the stress/strain of crystalline material. Especially, the X-ray method has been widely used for measurement of the stress in engineering components. However, when the very small measurement area is required, accuracy of determination by the X-ray method may be insufficient. On the other hand, spatial resolution of EBSD method becomes a nanometer order. In the present study, in-situ measurement of the stress/strain distribution near notch in 3%Si iron was carried out by EBSD method. Obtained results were compared with the results analyzed by the finite element method. The strain near notch could be measured within the scatter of ±500 micro strain. Ten point average value of the strain was almost identical to the macro strain distribution calculated by FEM. For the stress distribution in the elastic region, hundred point average value was coincident with the calculated result. For the plastic deformation, change of the angle of crystal rotation corresponds to the displacement of the specimen surface. Kernel averages misorientation increased with the plastic deformation.
In this study, the effects of work-hardening and pre-existing stress in the machined surface layer of low-carbon austenitic stainless steel on the welding-induced residual stress were experimentally investigated through the use of weld specimens with three different surface layers; as-cutout, mechanically-polished and electrolytically-polished. The high tensile and compressive stresses exist in the work-hardened surface layer of the as-cutout and mechanically-polished specimens, respectively. Meanwhile, no stress and work-hardened surface layer exist in the electrolytically-polished specimen. TIG bead-on-plate welding under the same welding heat input conditions was performed to introduce the residual stress into these specimens. Using these welded specimens, the distributions of welding-induced residual stress were measured by the X-ray diffraction method. Similarly, the distributions of hardness in welds were estimated by the Vickers hardness test. And then, these distributions were compared with one another. Based on the results, the residual stress in the weld metal (WM) is completely unaffected by the machined surface layer because the work-hardened surface layer disappears through the processes of melting and solidification during welding. The local maximum longitudinal tensile residual stress in the heat affected zone (HAZ) depends on the work-hardening but not on the existing stress, regardless of whether tensile or compressive, in the machined surface layer before welding. At the base metal far from WM and HAZ, the residual stress is formed by the addition of the welding-induced residual stress to the pre-existing stress in the machined surface layer before welding. The features of the welding-induced residual stress in low-carbon austenitic stainless steel with the machined surface layer and their influential factors were thus clarified.
The circumferential residual stress on the inner surface of a round pipe was measured by using the dual-axis inclining method. The dual-axis inclining method is an X-ray stress measurement technique using the iso-inclination method jointly with the side-inclination method. It is not possible to apply the conventional X-ray stress measurement method based upon the sin2ψ method to such measurement even if the irradiated area is at the neighborhood of the open-end of the hole. The dual-axis inclining method was described, and the analysis was made of the relation between the position of the irradiated area, the diameter of hole and the scannable angle range. On the assumption that the ψ angle should be scanned up to 30 deg for the stress measurement, the result of the analysis shows that the distance between the irradiated area and the open-end of the hole should be less than a quarter of the hole diameter. The experiment was conducted for a round pipe of carbon steel. It was found that even when the intensity of background decreased only on the lower side of diffraction peak due to the shielding by the side wall of the pipe, the circumferential stress can be evaluated by directly applying the parabola peak method or the 2/3-value breadth method to the collapsed diffraction profiles without processing the background.
We have developed a novel residual stress measurement instrument based on the X-ray diffraction technique. An image plate was used as the detector to sample the full diffraction ring. The image plate and the scanning unit were built into the one system. Compared with the traditional X-ray stress measurement systems, the physical size and weight of the instrument were significantly reduced. The instrument also has the capability to measure the distance from the specimen to the image plate. This capability contributes to improve the accuracy and simplicity of the stress measurement. The developed instrument was focused on measuring a ferrite sample and the acquired diffraction ring was analyzed using the cosα method. In the present work, we evaluated the accuracy of the measurement data from the instrument using a ferrite powder compared with strain gauge results obtained from four-point bending measurements.
In this study, X-ray stress measurements of ferritic steel based on Fourier analysis are conducted. Taira et al. developed the cosα method for X-ray stress measurements using a two-dimensional X-ray detector. Miyazaki et al. reported that the cosα method can be described more concisely by developing the Fourier series (the Fourier analysis method). The Fourier analysis method is expected to yield the stress measurement with an imperfect Debye-Scherrer ring and there is a possibility that the materials evaluation is different compared with the conventional method, that is, the sin2ψ method. In the Fourier analysis method, the strain measured by X-rays is developed as a Fourier series, and all the plane-stress components can be calculated from the Fourier series. In this study, the normal stress calculation was confirmed. In addition, the Fourier-analysis and cosα methods were used for X-ray stress measurements during a four-point bending test on a S45C test piece, and the effectiveness of the Fourier analysis method was confirmed. It was found that the experimental results from the Fourier analysis and cosα methods were nearly identical. In addition, the measurement accuracies of both the methods were equivalent.
GBFS (granulated blast furnace slag) has a hydraulic property in natural environment by its hydration reaction. In this study, in order to investigate the progress of hardening and self-restoration characteristics of GBFS under different conditions such as plain water, seawater and Ca(OH)2 solution, the change in the unconfined compressive strength and the percentage of hydration reaction of GBFS were observed. It can be seen from test results, the strength of GBFS cured in seawater and Ca(OH)2 solution increases in the early stage due to the rapid hydration reaction which occurs earlier in comparison with the plain water. In addition, in the same level of hydration reaction, the restoration of strength depends on the condition of curing water. Furthermore, based on the relation between the strength and the hydration reaction of GBFS which was taken from the test embankment constructed 11 years ago, it is clarified that the strength of GBFS under long term curing in natural condition also increases with the hydration reaction.
An expansive additive containing lime(CaO), ye’elimite(3CaO・3Al2O3・CaSO4) and Anhydrite(CaSO4) was treated with high-temperature carbonation, and the effects of the treatment temperature and time on weathering resistance of the treated expansive additive were examined. After carbonation treatment between 400℃ and 800℃, the weathering was suppressed. Among the compounds constituting the expansive additive, the lime actively reacted with CO2 under high-temperature environment, the film of calcium carbonate was formed on the surface of the free lime. While the ye’elimite and anhydrite showed slow reaction with CO2. The hydration activity of calcium carbonate is smaller than that of lime, the reaction between the moisture and the expansive additive was suppressed, which seemed to have contributed to weathering resistance. From the viewpoints of expansion performance and improvement of weathering resistance, it can be considered preferable to apply carbonation treatment to the expansive additives between 500℃ and 600℃ for a short time.
The present study investigates the effect of different thicknesses of steel and fiber reinforced polymer (FRP) cover plates on the mechanical behavior of bearing-type multi-row bolted connections for FRP composite structures. Connections with a double-lap configuration up to four rows of bolts subjected to tensile loads have been studied numerically. These numerical data are examined in detail to understand the effects of cover plate stiffness on load distributions among rows of bolts. The study also considers the influence of geometric parameters on the load distributions. For validation of the connection model, numerical results are compared with experimental results available in literature. The results show that the load distribution in bearing-type multi-row bolted connections is significantly affected by the cover plate stiffness. A connection with higher cover plate stiffness tends to show lower efficiency. For a connection with steel cover plates, to increase number of bolt rows more than three does not lead to a higher capacity of a connection. The results also indicate that effect of geometric parameters on the load distribution is not significant with change of cover plate stiffness.
From our previous findings, the recycling of ceramic waste aggregate (CWA) in mortar has been proved an ecological means plus an excellent outcome against chloride ingress. The CWAs were electric porcelain insulator wastes supplied from an electric power company, which were crushed and ground to fine aggregate sizes. In this study, to further develop the CWA mortar as an eco-efficient, ground granulated blast-furnace slag (GGBS) was incorporated. The GGBS was utilized as a supplementary cementitious material (SCM) at three different replacement levels of 15, 30, and 45% by weight of cement. The time dependency of the GGBS on enhancing chloride resistance in the CWA mortars was experimentally assessed by using an electron probe microanalysis (EPMA). The tests were carried out on mortar samples after immersion in 5.0% NaCl solution for 24, 48, and 96 weeks. Another set of the mortar samples was exposed to a laboratory ambient condition for 24, 48, and 96 weeks and then followed with a carbonation test. The resistance to the chloride ingress of the CWA mortar becomes more effective in proportion to the replacement level of the GGBS. Meanwhile, the carbonation depth of the CWA mortar increases with increasing the GGBS. The relationship between the apparent chloride diffusion coefficient and the GGBS replacement level was shown along with the immersion time.