In order to clarify the influences of the morphology and interfacial strength on the microstructural deformation and micro-damage evolution process, a coarse-grained molecular dynamics (MD) simulation is conducted on a mesoscopic specimen of the thermoplastic polypropylene (PP) blended with the ethylene-propylene rubber (EPR) and talc under uniaxial tension. The studied morphologies are two types. The first morphology is composed of three independent phases of PP, EPR and talc. The second morphology consists of core-shell structure of EPR and talc in PP matrix. The first morphology shows that the micro-damage initiates at the interface between PP matrix and talc particle. Then, the micro void is generated there leading to the fibrils of the PP matrix and EPR particles. The second morphology indicates that the micro-damage initiates at the interface between EPR and talc. Meanwhile, the effects of the interfacial strengths of PP-EPR and PP-talc in the first morphology, and PP-EPR and EPR-talc in the second morphology on the macroscopic mechanical properties are further investigated. It appears that the elastic modulus is larger in the first morphology than that in the core-shell structure. It is also found that the maximum stress depends more strongly on the interfacial strength of PP-EPR than the morphological types. It is indicated that the absorbed strain energy is sensitive to both the morphology and the interfacial strength of PP-EPR.

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In this study, we examine those properties of freestanding CoNiCrAlY thin film detached chemically from the coated substrate. Tensile tests are conducted using the small testing device, which was developed by us, inserted into a vacuum chamber of a scanning electron microscope (SEM). Based on SEM continuous observation during tensile loading of the thin film, the deformation and fracture mechanisms of freestanding CoNiCrAlY are discussed. It was found that CoNiCrAlY thin film has a typical brittle-ductile transition; it indicates brittle deformation and fracture at testing temperature lower than 700[K]. In the testing temperature higher than that, the CoNiCrAlY thin film elongates and is fractured with a high ductility. The reason for this transition was considered from SEM observations to be brought by mobility such as splat boundary sliding occurred during tensile loading. SEM also showed that a large inelastic deformation observed at the high-temperature is caused by the damage factors of both the micro cracking formed at splat boundary and the crack opening. Those factors leads to ductile fracture in CoNiCrAlY thin film exposed at the high temperature.

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In order to investigate the effect of loading frequency on crack growth behavior, ultrasonic fatigue and rotating bending fatigue tests were carried out for an extruded age-hardened Al alloy 7075-T6 in ambient air and in N₂ gas. Fatigue strength increased in ultrasonic fatigue due to the retardation of crack initiation and its early propagation. In ultrasonic fatigue, however, crack growth transition took place from tensile mode to shear mode when cracks grew faster than ∼3x10^-9m/cycle. As a result, macroscopic crack paths changed from nearly vertical to stress axis to oblique ∼35 degrees against the axis. Fracture mechanism involved in ultrasonic fatigue also changed from striations featured to transgranular facets characterized with microscopic voids. The relation between the applied stress, σ_a, and the crack depth at the crack growth transition, b_T, can be expressed as σ_aⁿb_T = constant. The results were discussed from the viewpoints of time dependent environmental effect and the texture of the alloy.

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Steel conveying rollers used in hot rolling mills must be changed very frequently at great cost because hot conveyed strips induce wear on the roller surface in short periods. In this study new roller is considered where a ceramics sleeve is connected with two short shafts at both ends by shrink fitting. Here, the ceramics sleeve may provide longer life and reduces the cost for the maintenance. However, care should be taken for maximum tensile stress appearing between the sleeve and shaft because the fracture toughness of ceramics is extremely lower than the values of steel. In this study FEM analysis is applied to the new structure, and the maximum tensile stress has been investigated with varying the dimensions of the structure. It is found that the maximum tensile stress appearing at the end of sleeves takes a minimum value at a certain amount of shrink fitting ratio.

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We determine the out-of-plane elastic constants C₃₃ of ultra-thin films using gigahertz coherent acoustic phonons. Acoustic phonons are generated and detected using femtosecond-laser pulses, and by measuring the resonance frequency of non-propagating acoustic phonons in thin films, C₃₃ is determined. In determining the C₃₃, film thickness and mass density are required, and we determine them by the x-ray reflectivity measurements. We apply this method to the Fe thin films of 11-52 nm thickness. When the film thickness is 11 nm, C₃₃ was larger than C₃₃ of the bulk Fe. As the film thickness increases, C₃₃ decreases, and when the film thickness is larger than 35 nm, C₃₃ was smaller than the bulk value. However, by heating the substrate, C₃₃ shows recovery towards the bulk value. There results are explained by the incohesive bonding at grain boundaries and residual stress.

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Biocompatible piezoelectric materials are becoming increasingly important for actuators and sensors in medical devices. In this study, we examined the possibility of five perovskite-type silicon oxides MgSiO₃, MnSiO₃, FeSiO₃, ZnSiO₃ and CaSiO₃, which have been found from the stable combinations of biocompatible elements in our previous studies, by employing first-principles DFT. At first, the stable cubic structure and the phonon properties were analyzed for the paraelectric non-polar phase. After the promising silicon oxides were distinguished with the phonon eigenfrequency and eigenvector in consideration of the structural phase transition, their characteristics of stable tetragonal structure were then analyzed for the ferroelectric phase. Computations indicated that MgSiO₃ has superiority on the phase transition from cubic structure to tetragonal one. Additionally, tetragonal MgSiO₃ has a large spontaneous polarization and it can exhibit a good piezoelectric response.

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Slow strain rate tensile (SSRT) tests and fatigue tests were conducted to investigate the influence of irreversible hydrogen on the quasi static SSRT strength and fatigue strength for cold drawn eutectoid steels which were cathodically hydrogen charged. Internal hydrogen states were changed as follows: (a) virgin sample, (b) the sample that contained both diffusible and irreversible hydrogen, and (c) the one that contained only irreversible hydrogen. The SSRT strength properties of only irreversible hydrogen contained sample were the same as that of virgin sample, whereas those of the sample having both diffusible and irreversible hydrogen were smaller than the others. This indicates that only the diffusible hydrogen caused hydrogen embrittlement under the quasi-static loading. Contrary to this, the fatigue strength of the sample having both diffusible and irreversible hydrogen was lower than that of virgin sample. However, the influence of irreversible hydrogen on the fatigue strength was unclear since S-N curves had a large scatter. This is due to the fact that the fatigue crack was initiated at internal inclusion. Therefore, the fatigue strength was discussed based on the stress intensity factor, ΔK_inc, calculated from stress and inclusion size. ΔK_inc giving the same N_f decreased in the order of virgin sample, irreversible hydrogen charged sample and the sample having diffusible and irreversible hydrogen, indicating irreversible hydrogen caused the fatigue strength degradation.

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In this study, a new hybrid surface modification process, fine particle peening (FPP) treatment prior to nitriding, was proposed. In order to clarify the effects of FPP treatment prior to nitriding on the fatigue strength of notched AISI 4135 steel with a stress concentration factor K_t of 2.36, fatigue tests were conducted at room temperature using a rotational bending fatigue testing machine. Hardness and residual stress distributions were measured in order to characterize the surface-modified layer. As a result, the surface hardness of the FPP-treated specimen before nitriding was higher than that of the nitrided specimen. The surface microstructures of treated specimens were characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The crystal structure of the compound layer of the FPP-treated specimen before nitriding was different to that of the nitrided specimen. The compound layer of the FPP-treated specimen was dense. This suggests that FPP treatment prior to nitriding is very effective for improvement of the fatigue strength of steel.

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The electric potential change method (EPCM) was applied to identify delamination in quasi-isotropic carbon fiber reinforced plastic (CFRP) laminate. The authors have introduced EPCM previously to detect delamination in a cross-ply CFRP laminate although it was difficult to apply to quasi-isotropic CFRP laminate because of its complicated electric anisotropy. In this study, a new concept was introduced to resolve this problem. Residual stress that developed during the curing process in CFRP laminate fabrication was utilized. This residual stress was released locally by the creation of a delamination which resulted in a local strain variation on the laminate surface. Since the electric conductivity of CFRP may change with applied strain because of its piezoresistivity a CFRP cloth was used as a strain sensor. The release of residual stress was detected as an electric potential change of the CFRP cloth by applying electric current to the laminate. The delamination location and size were estimated from electric potential changes. A finite element study was performed to investigate the applicability of the method. Two steps of finite element analysis were performed to calculate the electric potential change due to delaminations and matrix cracks, structural analyses to calculate strain variation due to release of the residual stress by the delamination and then electric field analyses to calculate electric potential change due to strain variation. The delamination location and size were estimated from electric potential changes using a response surface methodology. A numerical simulation was successful in estimating delaminations in quasi-isotropic CFRP laminate.

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A time domain simulation tool for the ultrasonic propagation in concrete is developed using the elastodynamic finite integration technique (EFIT) and the image-based modeling. The EFIT is a grid-based time domain differential technique and easily treats the different boundary conditions in the inhomogeneous material such as concrete. Here, the geometry of concrete is determined by a scanned image of concrete and the processed color bitmap image is fed into the EFIT. Although the ultrasonic wave simulation in such a complex material requires much time to calculate, we here execute the EFIT by a parallel computing technique using a shared memory computer system. In this study, formulations of the EFIT and treatment of the different boundary conditions are briefly described and examples of shear horizontal wave propagations in reinforced concrete are demonstrated. The methodology and performance of parallelization for the EFIT are also discussed.

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In recent years, magnesium alloy has been widely used because of its low weight and ease of recycling. However, because magnesium alloys provide inferior wear resistance, it is necessary to improve this property to use magnesium alloy for more machine parts. For this study, we produced a diamond like carbon (DLC) coating that has high hardness, low friction, and excellent wear resistance. With DLC coated onto a soft material such as magnesium alloy, the adhesion strength between the substrate and the coating poses an important problem. Therefore, in this study, to acquire high adhesion strength, the DLC coating process was performed using unbalanced magnetron sputtering (UBMS). A tungsten-doped inter-layer was formed on the substrate. Onto the inter-layer, nano-order DLC coatings of two kinds were laminated. Wear tests and fatigue tests were carried out. The DLC-coated magnesium alloy exhibited excellent wear friction. Furthermore, DLC coatings raised its fatigue reliability over that of the substrate alone.

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