In order to investigate the effect of laser peening treatment on high cycle fatigue properties, rotating bending fatigue tests were carried out for laser peened gas-carburized SCM420H steel. In this study, two types of pulse laser oscillators such as conventional high power laser equipment and hand-held compact laser equipment were prepared to generate different residual stress distributions in specimens and the effectiveness of the hand-held laser oscillator was verified as a laser peening equipment. Fatigue test results showed that laser peening with the hand-held laser oscillator improved fatigue strength to the same extent as that with the high power laser oscillator. Since fatigue strength was correlated with hardness distribution and residual stress distribution, the fatigue limit was predicted using both distributions. The attenuation behavior of the residual stress was predicted from the hardness and used to estimate the fatigue limit. Although the hand-held laser peening imparted compressive residual stress only near the material surface, the fatigue limit was significantly improved. Furthermore, no fatigue failure occurred inside the specimens despite the application of stresses exceeding the local fatigue limit. This suggests that there is an unknown factor in the hand-held laser peening that suppresses fatigue crack initiation.

In this paper, fatigue tests using SENT specimens with different thicknesses were carried out to evaluate the effect of plate thickness on the DIC measurements and fatigue crack propagation properties. The fatigue crack propagation rate da/dN of the thin specimen was slower than that of the thicker specimens. The crack opening/closure behaviors at the arbitrary crack location were evaluated by the crack opening displacement measured by the DIC. The crack opening load P_op was higher with thinner specimens, especially with shorter crack lengths. da/dN was correlated with effective stress intensity factor range ΔK_eff based on the P_op at the fatigue crack tip, but the error increased with thinner plate thicknesses and longer crack lengths. The strain range at the fatigue crack tip measured by DIC showed a good correlation with da/dN, irrespective of the plate thickness and crack length.

Extremely low-cycle fatigue tests were conducted on the Fe-15Mn-10Cr-8Ni-4Si bidirectional-TRIP (B-TRIP) steel, up to an axial total strain amplitude of 10%. The fatigue life was about five times longer than that of SUS316 in the range of total strain amplitude of 4% or more. The improved fatigue life of the Fe-15Mn-10Cr-8Ni-4Si was attributed to the reversible bidirectional γ↔ε transformation during fatigue deformation that might mitigate the fatigue damage. On the other hand, the fatigue life tended to decrease with increasing strain rate when the strain rate was varied from 0.1 to 2.5%/s with the total strain amplitude of 10%. The fractography revealed that the fracture surface varied significantly with strain rate. At low strain rates, the crystallographic fracture surface characterized by facets and secondary cracks were observed, whereas these features were not observed at high strain rates. EBSD measurements on the postmortem microstructure showed that frequent ε-martensite formation occurred at low strain rates, whereas martensitic transformation was suppressed at high strain rates. The change in the specimen surface temperature was evaluated in terms of the Gibbs free energy difference between γ-austenite and ε-martensite ΔG^γ→ε, and the effect of strain rate on the extremely low-cycle fatigue was discussed from the viewpoint of the deformation mechanism as follows. At low strain rate, ΔG^γ→ε ≲ 0 (negative close-to-zero ΔG^γ→ε), the condition for B-TRIP to work effectively, is maintained over the entire life span. At high strain rate, the deformation mechanism changes to one in which γ-austenite is dominant due to the increase in ΔG^γ→ε caused by self-heating; the fatigue damage mitigation mechanism by B-TRIP is less likely to occur at high strain rates, resulting in a reduction in life.

Small cracks propagate at the glass surface due to the combined effects of water vapor and applied load. This phenomenon is known as glass fatigue. In this study, four-point bending fatigue tests under static and cyclic loading conditions were conducted for the soda-lime glass plate specimens with the initial crack and indentation pit induced by Vickers diamond indentation. Fatigue cracks were observed by the in-situ crack observation system using optical microscopy in order to obtain the relationship between crack growth rate, da/dt, and maximum stress intensity factor, K_max, during fatigue tests. The da/dt decreased and then increased with the K_max value. In addition, photoelasticity was applied to measure the residual stress distribution generated on the surface of the glass. The results showed that the da/dt at the early stage varied with indentation load due to the residual stress, whereas the effect of the indentation load on the da/dt was not observed in the region without residual stress.

Recently, multiple fatigue life extension techniques have been proposed utilizing crack closure, while no detailed mechanisms have been discussed for them. On the other hand, the authors have proposed the assessment method on crack initiation and propagation life based on an elasto-plastic model, and that would work for better assessment with detailed mechanisms of them. In this paper, fatigue crack growth tests were carried out using SENT specimens corroded at the crack length of 3mm by 35% HNO₃, and shape measurements for fractured specimens were conducted after the tests. The results show that crack growth rates are retarded due to corrosion products between crack faces (Wedge effect). Furthermore, corrosion products distribute on the crack faces with 20 to 50µm thickness, which suggests correlations between the thickness of corrosion products and the level of life extension effect.

In this study, SCM440 steel specimens with different surface morphology and hardness were prepared by shot peening and fine particle peening, followed by induction hardening and tempering at different temperatures. Rotating bending fatigue tests were performed for these specimens, and the combined effects of the surface dent formed by peening and residual stress on the fatigue limit of the induction hardened steels were quantitatively investigated. It was found that the fatigue limit of the induction hardened steel tended to decrease with an increase in the size of the particles used in the peening. The parameter of surface morphology that showed a good correlation with the fatigue limit of the induction hardened steel was the waviness parameter, but not the roughness parameter. Furthermore, a fatigue limit estimation for induction hardened steels with different surface morphology was described. The improvement in the fatigue limit of steels with surface dents due to compressive residual stress was more significant as the hardness decreased, and the maximum fatigue limit improved by compressive residual stresses increased as the size of surface dents decreased.

Two types of tensile specimens of short-glass-fiber reinforced PPS (polyphenylene sulfide) (SGFRP) were cut from the surface layer of injection molded plates. They were 0° specimens with fibers predominantly oriented in the loading direction and 90° specimens with fibers perpendicular to the loading direction. During loading and unloading, the change of the matrix phase stress in SGFRP measured by the synchrotron X-ray method showed a good agreement to the value computed by micromechanics considering fiber orientation distribution. The matrix phase stress in the loading direction at tensile fracture of 0° and 90° specimens were about the same, although the tensile strength of the former is much higher than the latter. The matrix phase stress of SGFRP at fracture was nearly half of the fracture stress of PPS specimens without reinforcement. The reduction of fracture stress of PPS matrix comes from the stress concentration due to fibers. The fatigue life of smooth specimens of SGFRP was also controlled by the matrix stress increased by an amount of stress concentration factor. When the fatigue life is correlated to the matrix equivalent stress, S-N diagrams of 0° and 90° specimens including PPS specimens showed an almost identical relationship. The same factor of stress concentration applicable to tensile and to fatigue fracture may provide a physical basis for good correlation between the fatigue strength and the tensile strength of SGFRP.

Spring steels subjected to torsional cyclic loading may fail even in the very high cycle region. In order to improve the very high cycle torsional fatigue strength of spring steels, it is necessary to clarify the governing factors of the very high cycle torsional fatigue strength. In this study, ultrasonic torsional fatigue tests were conducted for spring steel to investigate the fatigue crack initiation and growth processes with periodical observations of specimen surface using an optical microscope and with an observation of a cross section of a shear-mode fatigue crack. The results revealed that most of the shear-mode fatigue cracks originated in the early stage of the fatigue life at axially elongated MnS inclusions, the crack growth rates of the shear-mode fatigue cracks at surface were smaller than 10^-10 m/cycles, and most of the fatigue life was consumed for the shear-mode fatigue crack growth.

Compression-compression fatigue tests were conducted using Ti-6Al-4V lattice structures, which were additively manufactured by electron beam melting (EBM) method. The specimens with two different sizes were used to investigate the effect of lattice sizes on the fatigue properties. Fatigue cracks mainly initiated in the horizontal pillars during fatigue tests, which indicated that the initiated cracks were parallel to the compression loading direction. Strain measurement on the horizontal pillars revealed that tension stress occurred in the horizontal pillars under compression of lattice structure. Buckling of the vertical pillars under compression was suppressed by the horizontal pillars, which induced tension stress in the horizontal pillars and fatigue crack initiation parallel to the loading direction. That fatigue crack initiation mechanism was irrespective of the lattice sizes and applied load levels. However, fatigue strength was lower in the smaller samples. When the lattice size gets smaller, Euler buckling load becomes lower because of the decrease of area moment of inertia, which results in the lower fatigue strength of smaller lattice structure.

For the purpose of evaluating the reactivity of coal gasification slag sand (CGS), a cement paste was prepared by partially replacing alite (C₃S) with CGS, and the reaction rate of C₃S and CGS was evaluated by XRD/Rietveld analysis. As a result, the use of CGS improved the hydration degree of C₃S and the tendency of CH consumption during long-term aging. The CGS hydration degree was calculated by setting the sintering temperature of the hydrated sample to 1000 - 1100 ℃ according to the quality of the CGS, and calculating only the minerals along the crystal product during CGS sintering. It was confirmed that the results of Mid-FTIR also suggested that the use of CGS produced C-S-H with a longer chain length than the hydration product of simple C₃S.

The endurance limit of polycrystalline pure iron is high. To understand its mechanism, tensile strength (σ_B), cyclic yield stress (σ_yc), and fatigue limit (σ_w) were evaluated for both single-crystalline and polycrystalline pure iron. The endurance ratio (σ_w/σ_B) of rotary bending test and axial loading using polycrystalline specimens ranged from 0.58–0.68. Moreover, the σ_w/σ_B of axial loading using a single-crystalline specimen indicated a high value of 1.06. Even without considering the strain rate dependence, the σ_w/σ_B of pure iron was higher than that of general-purpose steels such as low-carbon steel, general structural steel, stainless steel, and martensitic steel. Contrary to these results, σ_w/σ_yc of single-crystalline and polycrystalline pure iron showed the same value (0.881) as that of general-purpose steels. Thus, σ_yc would be more correlated with σ_w than σ_B. Furthermore, attempts were made to quantify the effect of strain rate, residual stresses, and work-hardened layers on fatigue limit. Consequently, the change in the endurance ratio (0.58–0.68) was quantitatively explained by the strain rate, residual stress, and work-hardened layer.

A new quartz crystal microbalance (QCM) composite material was developed by applying an aqueous dip-coating process to the ship-in-bottle-type zeolite powder which included cobalt-phthalocyanine (CoPc) molecules. A coat layer was not made only with zeolite and CoPc-zeolite (faujasite) powders. But it can be obtained by an aqueous slurry of 75wt% CoPc-zeolite mixed with γ-Al₂O₃, without heat-treatment at high temperature. Over the inner surface of the hydrophilic faujasite, which was suitable for a water system slurry process, the good toluene adsorption characteristic was given with by letting faujasite-type zeolite contain CoPc. We achieved the manufacture of the QCM sensor by all inorganic slurry coating technology and confirmed that it showed detectability of the adsorption gas. In this study, we made use of an aqueous molding technique of the ship-in-bottle-type zeolite and provided new knowledge about the materials development concerning sensor-functionalization using CoPc-zeolite.

Polyamide (PA) is an engineering polymer the main chain is composed of repeating units of amide bonds (-NHCO-). In this study, we performed tensile simulations on four types of amorphous polyamides (PA6, PA11, PA10T, and PAMXD10) using the all-atom molecular dynamics simulation based on the AMBER force field. The monomers of PA6 and PA11 have 6 and 11 CH₂ straight nodes connected with amide bonds, while those of PA10T and PAMXD10 have aromatic rings with 10 CH₂ + amide bonds. PA10T shows the highest stress increase and PA11 does two-thirds of PA10T, while PA6 and PAMXD10 don’t show stress increase. Thus, the aromatic ring doesn’t directly contribute to the stress increase. We defined the straight segment ratio (SSR), which represents the ratio against the perfect straight chain (SSR=1 is the maximum length while SSR=0 is a circular shape). The SSR is 0.72 and 0.57 for PA10T and PA11, respectively, while that is 0.11 and 0.26 for PAMXD10 and PA6 in the initial equilibrium in this simulation. Investigation on the change in the radius of gyration, SSR, and the distribution of the start-to-end vector of each chain against periodic cell revealed that the PA10T and PA11 are composed of radial bundles of long straight chains, octuple (PA10T) and quadruple (PA11) against cell length, and elongate in the tensile direction and shrink in the lateral direction (Poisson contraction). On the other hand, the start-to-end chain length of PAMXD10 and PA6 is close to the cell length (curly chains), so they deform as fluid under tension without stress increase. We also investigated the change in the bond stretch and bending angle in each node and revealed that the C-H and C=O bonds are elongated while the backbone C-C bonds are not. The decrease in bending angles for these -H and =O nodes also suggests that the forces between these -H and =O atoms is the key interaction for stress increase, contrary to the direct entanglements of backbone chains in coarse-grained MD.

We have developed a novel transparent hygroscopic film using 4A zeolite with primary particle size of 50 nm, which is shorter than the wavelength of visible light, as a hygroscopic agent. Although zeolite is an excellent moisture absorber in the low humidity range, their moisture absorption capacity is about 20% of the zeolite weight, and this capacity decreases further when surface modification is applied to improve dispersion and transparency. Increasing the amount of zeolite additives is a possible way to increase the moisture absorption capacity of the film, however high concentrations of nano-sized fillers cause difficulties in kneading with the resin. Therefore, in this study, the addition of nano-sized zeolite and another inorganic particle with a large moisture absorption capacity to LLDPE was attempted for use as a hygroscopic agent. Among the many inorganic hygroscopic agents, the combination of burnt alum and zeolite was found to be effective in this study. It was found that by using a small amount of burnt alum in combination with nano-sized zeolite, it was possible to increase the moisture absorption capacity while maintaining the transparency of the hygroscopic film.