In recent years, the cos α method attracts engineers as a new method of X-ray stress measurement using whole Debye-Scherrer rings recorded on two-dimensional detectors. The principle of the cos α method was first proposed by Taira, Tanaka, and Yamasaki for in-plane biaxial stress analysis, and later extended by Sasaki et al to the triaxial state of stresses. The method proposed by Sasaki et al utilizes several Debye-Scherrer rings taken at different incident angles of X-rays to determine traxial stresses. In the present paper, the cos α method was applied to measure triaxial residual stresses of uni-directionally machined surfaces of a carbon steel made by grinding, milling and planing. The recommended procedure for experimental measurement of out-of-plane shear stresses was proposed, together with a new method for determination of the normal stress perpendicular to the specimen surface. The incident angle of X-rays for stress determination is recommended to be larger than 35° and the normal incidence is for out-of-plane shear stresses. Out-of-plane shear stresses along the cutting direction which were characteristic of uni-directionally machined surfaces were increased according to the degree of cutting severity in the order of grinding, milling and planing. In-plane normal stresses were compressive, and the amount of compression was larger in the direction perpendicular to the cutting direction. Based on the stress values measured under different incident angles, the in-plane normal residual stress was suggested to increase near the surface. Out-of-plane normal stress determined by the new method was small compression.
This paper introduces the evaluation of rolling contact fatigue (RCF) under insufficient lubrication condition for carbonitrided bearing steel, JIS SUJ2. The progression of RCF was evaluated based on equivalent stress, retained austenite and the degree of martensite grain orientation which were characterized by three parameters: σeq, γR and S/S0, respectively. We calculated σeq using a tri-axial residual stress obtained by the Sasaki-Hirose method. The S/S0 was defined as the variation of peak intensities for the central angle of the X-ray diffraction ring. In order to confirm quantitativity of γR, two types of X-ray devices ware used. These parameters were compared with specimens subjected to standard heat treatment of SUJ2. As a result, the following knowledge was obtained. Carbonitride caused larger residual stresses and delayed the beginning of increasing of S/S0. In addition, the peeling area ratio at the number of cycles of 106 was smaller as compared with standard heat treatment specimen. Furthermore the γR remained until the end of the test. These results were due to the effect of nitrogen dissolved in steel.
Stress/strains in silicon-based devices play important roles in controlling the performance and the reliability, therefore it is recently very important to grasp stress/strain states in these devices. In this study, stress/strain components in (111) single crystal silicon wafers were determined by polarized micro-Raman spectroscopy. The polarized micro-Raman spectroscope equips with the devices for independently controlling the polarization direction of irradiation and scattering lights and achieves the sub-micro spatial resolution. The silicon belongs to the Oh point group with A1g, Eg and F2g vibration mode, but the measured active Raman line is the only triply-degenerate single peak with F2g mode. First, the polarization condition to decompose the triply-degenerate Raman line into three independent Raman peaks was determined by the theoretical and experimental polarization analysis of backscattered Raman spectrum for (001), (110) and (111) single crystal Si wafers. Based on the determined polarization condition, Raman shift change in (111) single crystal Si wafers under equi-biaxial stress condition was measured. The relationships between Raman shift change and applied strain were linear function, and the obtained values were good agreement with theoretical values. Therefore, three independent Raman peaks were able to be detected by polarized micro-Raman spectroscopy. Finally, the stress components around indentation-induced crack in (111) single crystal Si wafer were measured by polarized micro-Raman spectroscopy. The measured stresses around a crack tip asymptotically approached the values dominated by the stress intensity factor calculated from the empirical equations proposed by Newman and Raju. Therefore, the applicability of polarized micro-Raman spectroscopy to the measurement of stresses/strains components in (111) single crystal Si was confirmed.
Austenitic stainless steel was plastically deformed under uniaxial tension, and its plastic strain measured was 2.8%. The micro-residual stress were measured by the cos2 X method using hard synchrotron X-ray with about 70 keV. The 2θ-cos2 X diagrams for the 4 0 0 and 6 2 0 lattice planes, which belonged to a soft lattice plane, showed an upward warp. In contrast, the 2θ-cos2 X diagrams for the 4 4 0 and 3 3 1 lattice planes, which belonged to a hard lattice plane, showed a downward warp. This is caused by the micro-residual strains such as intergranular strains. To investigate detail of the micro-residual stress by plastic deformation, the distributions of the residual strains were measured in omni-azimuth angles. As a result, the micro-residual strains for a soft lattice plane balanced with that for a hard lattice plane.
The S-phases (γN-phases) of JIS standard SUS304 steel were prepared via direct current plasma nitriding (DCPN) and active screen plasma nitriding (ASPN). Furthermore, diamond-like carbon (DLC) films were prepared on these S-phases via plasma chemical vapor deposition (PCVD). The nitride layers included the γ’Fe4N phase. The X-ray stress constant K for the nitride layers was evaluated using γN (200) + γ’Fe4N (200) diffraction with CrKα characteristic X-rays. The γN (200) + γ’Fe4N (200) diffraction angles 2θ of the DCPN and ASPN powders were 73.49° and 72.98°, respectively. The X-ray stress constants, E / (1 + ν), of the γN (200) + γ’Fe4N (200) phase that was nitrided using DCPN and ASPN were 202 and 153 GPa, respectively, and the K values of the same were -2365 and -1809 MPa/deg, respectively. The X-ray residual stresses of these S-phases were approximately -5.3 and -2.6 GPa, respectively. However, Raman microprobe spectroscopy was used for residual stress measurements of the DLC films that were deposited on these S-phases. The Raman spectra of the DLC films were classified into the disorder peak D’at 1150 cm-1, the D peak, and the graphite peak G. The residual stresses in the DLC films on these S-phases, as estimated from the Raman shift of the G peak for DCPN and ASPN, were -3.2 and -3.0 GPa, respectively. The hardness of the DLC films was determined using the nanoindentation method, and the films were found to exhibit high levels pf hardness. The increase in compressive residual stresses in the DLC films could have caused the decrease in contact areas and the indentation depth of the indenter, which may have increased the value of Young’s modulus and hardness of the DLC films.
Hydrogen-entry properties of torsional prestrained ferritic-pearlitic low-carbon JIS-S10C, JIS-S25C and JIS-S45C steels were investigated. A round bar specimen was prestrained by torsion test and then charged with hydrogen by cathodic charging or immersion charging. The torsion test enabled to introduce a large plastic deformation to the specimen without necking, which led to much higher level of hydrogen content, CH, than tensile test. CH was increased with an increase in torsional prestrain at the specimen outer surface, εpre,s. In the prestrain range, εpre,s < 30%, there was little influence of pearlite on CH. By contrast, when εpre,s > 40%, there was a marked influence of pearlite on CH in JIS-S10C and JIS-S25C, whereas, CH in JIS-S45C was lower than that of JIS-S25C despite the fact that fraction of pearlite in JIS-S45C was much higher than that in JIS-S25C. It was presumed that such a complex hydrogen-entry property was determined by the competition between (I) the increase in dislocation density near the boundaries between ferrite and pearlite and (II) the inhibition against the increase in dislocation density by a stress redistribution in pearlite grains. The torsional strain at final rapture was the largest in JIS-S10C, which accordingly conduced to the largest hydrogen content in the broken specimen. The series of experimental results manifested that the torsion test enables the investigation of strength properties as well as the hydrogen-entry properties for BCC steels under an extremely large hydrogen content (∼30 mass ppm).
Information of confining ability of rock is important for the geological disposal of radioactive wastes. To maintain or improve the confining ability of rocks, it is important to seal pores and cracks. Usually, pores and cracks in rock are sealed over geological time scales. If sealing of pores and cracks in rock can be accelerated and completed by precipitation of minerals, the method would be effective for use during radioactive waste disposal. In this study, we investigated the precipitation of minerals onto the rock surface, to consider whether sealing of pores and cracks in rock can be accelerated. As rock samples, we used Berea sandstone and Toki granite in this study. It was shown that precipitation occurred clearly on the surface of rock specimens kept in calcium hydroxide solution for 1 month if the concentration was high. Specifically, if the concentration of calcium hydroxide solution was higher than 589 mg/l, the precipitation occurred obviously. After keeping rock specimens in calcium hydroxide solution, the weight of the rock samples increased and the concentration of calcium ion decreased by the precipitation. It is considered that the calcium ion in water was used for the precipitation on rock surfaces. Since the precipitation has been recognized for rock specimens, it is concluded that the sealing of pores and cracks in rocks by the mineral precipitation is possible.
It has been reported that the mechanical properties of concrete would be severely damaged due to the thermal stress and the high vapor pressure when the concrete is subjected to a high temperature environment over 500 °C especially in the cases of the high strength concrete. However, in the cases of the normal strength concrete subjected to the heating up to 300 °C could be generally used after the fire damage, although the durability of such concrete members has not been clarified enough. In this study, the chloride-induced corrosion of steel in concrete subjected to the heating up to 300 °C was investigated. As a result, it was clarified that when the heating temperature exceeded 100 °C, the increase of the porosity of the heated concrete resulted in the decrease of the compressive strength and that the Cl- penetration into concrete accelerated by the heating over 150 °C resulted in the promotion of the chloride-induced steel corrosion in the heated concrete due to not only the increase of the porosity but also the decrease of the Cl- fixing ability of the concrete.
Collagen sheets with melanin added or Maillard cross-linking were prepared as models to simulate various human skin types and age groups. The treated collagen sheets were used to study effects of ultraviolet light on the human skin. Extracts were obtained from collagen sheets after ultraviolet light irradiation and analyzed. The results revealed that ultraviolet light irradiation of up to 25 hours mainly formed cross-linkages in collagen sheets with melanin added at 9% or lower, irradiation for 200 hours mainly cleaved collagen molecule chains. In contrast, ultraviolet light was found to promote cross-linkage formation in collagen molecule chains in the collagen sheet with melanin added at 50%, but hardly cleaved the molecule chains even for long durations of ultraviolet light irradiation. Moreover, ultraviolet light irradiation did not cleave the molecule chains but maintained cross-linkage in collagen sheets that were cross-linked by Maillard processes with glyoxal solutions of 0.1 mM or higher. However, exposure to ultraviolet light irradiation for as long as 200 hours cleaved collagen molecule chains. These results demonstrate that collagen sheets that simulate various human skin types could be useful for studying human skin damage caused by ultraviolet light.