A visco-hyperelastic analysis scheme based on a full Eulerian formulation is proposed for dynamics of pressuresensitive adhesives (PSAs). PSAs are usually based on an elastomer, which has rubber elasticity and viscosity. Young's modulus of PSAs is notably low compared with other solid materials. Thus extremely large deformation of PSAs can be observed. The numerical scheme is based on a full Eulerian finite element method, which allows arbitrarily large deformations and new free surfaces to be created in a natural manner in the spatially fixed mesh. The 3D PLIC-VOF method is used to capture the material interfaces with high accuracy. The constitutive relation of PSAs is described with Simo's viscoelastic model. In this model, rubber elasticity is modeled as Mooney-Rivlin materials as a function of the left Cauchy-Green deformation tensor. To validate the proposed approach, a steel ball impact on acrylic PSAs is simulated and computational results are almost identical with experimental results.

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In this study, the thread deformation mechanism and relation between thread deformation and anti-loosening effect for nut with circumference slits are studied by the experiment and using FEM. The slit nut is adequately compressed before use. Two methods for compressive pre-strain are compared. It is found that cylinder compression method provides thread with rotational deformation than plate compression method. The rotational deformation has an important role as slowing the increase of the resistance torque with the amount of compression. Therefore, cylinder compression method is superior for processing control. The effects of the slit geometries, which is defined by the location h, the inner diameter d and the width w are investigated based on the experiment and the numerical analysis. It is found that h and d has large effect on thread deformation and w has little effect on that.

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Plane bending fatigue tests were conducted using DLC (Diamond-like Carbon) coated magnesium alloy, AZ61, with two different kinds of film elastic moduli in order to investigate the effect of film rigidity on the fatigue behavior. From the experimental results, it was found that the DLC coating was effective to improve the fatigue strength when the film had larger elastic modulus and rigidity. Cracks and delamination of the film were observed near the crack initiation sites and they were prominent when the film elastic modulus was larger. By the DLC coating, the stress near the boundary between the base material and the DLC film was redistributed in a specimen and then the stress was relaxed at the base material and concentrated at the DLC film. The stress relaxation at the base material and the stress concentration at the DLC film near the boundary were evaluated by the FEM (Finite Element Method) analysis. From the stress analysis, it was quantitatively confirmed that the stress relaxation and the stress concentration were larger when the film elastic modulus was larger. It is considered that the DLC coating could improve the fatigue strength by the restraint of slip deformation in the base material by a film. The stress concentration at the DLC film could cause cracks and delamination after the film fracture but it would not give the negative effect on the fatigue strength.

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In this paper, fatigue strength behavior of ultraviolet irradiated high-modulus type poly-p-phenylene benzobisoxazole (PBO) fiber was investigated in monofilament tests. The tensile tests of a monofilament were carried out at a gauge length of 12.5 mm and deformation rate of 0.5 mm/min. The fatigue tests of a monofilament were carried out to determine the S-N property at a frequency of 10 Hz with three stress ratios of 0.1, 0.5 and 0.7. Irradiation time was set to 100 h, while radiance was arranged to become 8 W/m². It was found that the tensile strength of 100 h-irradiated PBO fiber was represented by a two-parameter Weibull distribution. The tensile strength of 100 h-irradiated PBO fiber was lower than that of non-irradiated fiber. And, the fatigue strength of 100 h-irradiated PBO fiber was lower than that of non-irradiated fiber over all fatigue lives. The relationship between the maximum stress and fatigue life was independent of the stress ratio. In addition, it was found by SEM observation that 100 h-irradiated PBO fiber had split vertically in the surface to a depth of about 0.5μm, but non-irradiated fiber had not the split. Moreover, it was found by EDX analysis that the amount of carbon and oxygen at the surface layer of PBO fiber increased by irradiating UV ray. Thus, reduction in fatigue strength of the PBO fiber by UV irradiation was caused by a degradation of the fiber surface by autoxidation

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In this paper, effect of strain rate on the tensile strength of high-modulus type poly-p-phenylene benzobisoxazole (PBO) fiber was investigated in monofilament tests. Tensile tests were carried out at a gauge length of 12.5 mm. The strain rate ranged from 6.7×10^-4 to 3.2×10^-1 s^-1. It was found that the tensile strength removed size effect in diameter direction of PBO fiber was represented by a two parameter Weibull distribution under all strain rate conditions. The mean tensile strength at high strain rate range from 4.0×10^-2 to 3.2×10^-1 s^-1 was about 8 % higher than that at low strain rate range from 6.7×10^-4 to 1.3×10^-2 s^-1. In addition, it was found by SEM observation that there were distinct differences between fracture surface image of specimen at high strain rate range and at low strain rate range, i.e., the crack length in fiber direction at high strain rate range was much shorter than that at low strain rate range. However the crack grew along boundaries of microfibrils at the low strain rate range, the crack grew not only along the boundaries but also in the microfibrils at the high strain rate range. Therefore, the increase in tensile strength at the high strain rate range was caused by the difference in the path of crack propagation.

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In the present study, the effects of weld metal and test temperature on the fatigue behavior in type 444 stainless steel welds were investigated. Two weld metals with different chemical compositions, NbL1 and NbL2, had been used for the MIG butt welding of type 444. NbL2 with Al and Ti showed finer grains in the weld microstructure than NbL1. The hardness of weld and base metals increased by the aging at 500°C due to 475°C embrittlement. At both ambient temperature and 500°C, the tensile strengths of weld metals were higher than that of base metal. Fully reversed axial fatigue tests have been performed using as-welded specimens with the excessive convexities, smooth specimens of welds and base metal at ambient temperature and 500°C in laboratory air. In the smooth specimens of welds, the excessive convexity at the weld metal was removed in order to focus on the microstructural effect. In the as-welded specimen with the excessive convexity, the fatigue strength at ambient temperature decreased compared with the base metal, which could be attributed to the stress concentration at the toe of the weld. By removing the excessive convexity, the fatigue strengths of NbL1 and NbL2 welds were improved, while still lower than that of base metal. Weld defects were responsible for the lower strengths of welds. On the other hand, both welds exhibited higher fatigue strength than base metal at 500°C. The softening of material at 500°C had eliminated the detrimental effect of weld defects on fatigue crack initiation.

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In order to ensure the safety of carbon fiber reinforced tanks for 35 and 70 MPa fuel cell vehicles, it is necessary to clarify the fatigue crack growth behavior of A6061-T6 aluminum alloy for the tank liner. In this study, the fatigue crack growth tests were carried out under the conditions of test frequencies f = 0.001-10 Hz in 90 MPa (≒70 MPa×125 %) hydrogen gas, 90 MPa nitrogen gas, air and deionized water at room temperature. The fatigue crack growth rates in hydrogen and nitrogen gas at f = 1-10 Hz were lower than those in air and deionized water. However, the fatigue crack growth rates in hydrogen and nitrogen gas at f = 0.001-0.1 Hz were nearly the same as those in air and deionized water. It was found from those results that the fatigue crack growth rate was not accelerated in 90 MPa hydrogen gas. The results of fatigue crack growth tests in this study were applied to the failure analysis of 35 MPa hydrogen tanks. In JARI (Japan Automotive Research Institute), using 35 MPa hydrogen tanks, the pressure cycling tests were conducted at -40, 25 and 85°C by water or PEPF (Perfluoroalkylpolyether) under 125 % filling pressure. The tanks fractured by LBB (Leak Before Break). Increasing in the test temperature increased in the number of cycles to LBB failure. Such a behavior was predicted by the fatigue crack growth properties of A6061-T6 obtained in this study.

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CFRP laminated structures are applied to many aerospace structures. Although the CFRP laminates have high specific strength and specific stiffness, an impact load easily creates damage of the CFRP laminates such as delamination cracking, matrix cracking and fiber breakages. The damages of the laminated CFRP are usually difficult to be detected by visual inspections. This requires a damage monitoring system for large laminated CFRP structures. Many researchers have already proposed self-sensing monitoring system using electrical resistance changes of the laminated CFRP. The method, however, requires a lot of electrodes. In the present study, Time Domain Reflectometry method is adopted using the reinforcement carbon fibers as sensors. The new self-sensing TDR method uses an electrical pulse signal and observes the reflected signal. The method is applied to a long CFRP strip plate specimen of 2 m length and an ideal damage of mechanical notch is detected from the reflected pulse signal. Effect of the orthotropic conductance of CFRP plate is experimentally investigated here using multiple electrodes. As a result, the effect of the orthotropic conductance is shown to be negligible.

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On the basis of shock wave theory one of the author derived that the micro-crack nucleation is caused by the jump of the velocity along the intersected crossing line between two different stationary discontinuity bands characterized by vanishing velocity of an acceleration wave. In the previous paper, to consider dependence of the progress of ductile fracture of crystal solids on crystal orientations, the algorithm of acoustic tensors derived from the proposed model was built into finite element crystal plasticity model (FEPM) and the progress of ductile fracture in FCC bi-crystal was analyzed. In particular, the role of the crystal orientation and the grain boundary in the trigger of the transcrystalline fracture or intercrystalline fracture was examined. In this paper, the role of the crystal orientation and the grain-boundary triple junction in the trigger of the ductile fracture is studied and then the correlation between the progress of the ductile fracture and the amount of the jog caused by intersected cross slides of the dislocation slips is examined from the viewpoint of deformation controlled and/or diffusion controlled processes.

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To prevent stress corrosion cracking (SCC) initiation at the inner surface of the butt-welding region of a small-diameter pipe, a residual stress improvement method has been developed. In this method, the butt-welding region is heated up to 325 degrees centigrade in air. After heating, a water quenching process is applied to the inner surface of the butt-welding region. During a water quenching process, a large thermal stress is generated by the temperature difference between inner and outer surfaces. When a thermal stress exceeds the yield stress of piping material, a tensile yield is generated at the inner surface of the butt-welding region. Because a tensile yield changes into a compressive residual stress, a compressive residual stress can be introduced at the inner surface of the butt-welding region after application of this method. In this study, residual stresses at the inner surface of the butt-welding region were measured. The measured residual stresses proved this method effectively reduces residual stresses and prevents SCC initiation.

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Cavitation often occurs in inducer pumps of space rockets. Silver plated coating on the inducer liner faces the damage of cavitation. In this study, we carried out cavitation erosion tests using silver plated coatings with different thermodynamic parameter at a constant cavitation number. Then we carried out cavitation erosion tests using some liquid with the same thermodynamic parameter and cavitation number as liquid oxygen condition. Thermodynamic parameter ∑ proposed by Brennen was used as a thermodynamic parameter. The fluids used for the cavitation erosion tests were water, ethanol and hexane. We discussed the relation between thermodynamic parameter and mass loss rate, and th e relation between acoustic impedance and mass loss rate.

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In order to consider ability of absorbing impact energy in functionally graded materials (FGM), longitudinal impact problem of a FGM bar was analyzed mathematically by using Laplace transformation and numerically inverse transformation. The FGM bar was subjected to step impact load at one end, and was fixed at the other end. The longitudinal elastic modulus in the FGM bar was assumed to be proportional to the square of its density. As the numerical results, in the FGM bar having increasing longitudinal modulus from the impact end to the fixed end, the larger compressive stress and even large tensile stress occurred near the fixed end compared with the ones in uniform bar. The FGM bar was clarified to have ability of high impact energy absorption by collapse and/or fracture. In the FGM bar having decreasing modulus from the impact end, the compressive stress was approximately the same as the one in the uniform bar, and the history of the stress varied smoothly. The impact energy absorption in the bar was predicted to be damping.

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During the plastic deformation, the influence of voids on macroscopic mechanical behaviors is an important consideration, because ductile fracture occurs through the growth and the coalescence of voids. However, in order to analyze the model with distributed voids by finite element method directory, a large number of elements and nodes are required. Mesoscopic model which describes the effect of such voids by internal state variables is needed. In this paper, perforated sheets with randomly distributed holes are regarded as a two-dimensional ideal model of real ductile materials containing voids. The increase in stress around holes was approximated by the net stress tensor which incorporates the damage tensor obtained by the voronoi tessellation and the shape of each hole. Substituting the net stress into Gurson's yield function, an anisotropic Gurson's yield function and its constitutive relation are derived. Moreover, in order to evaluate the proposed mesoscopic model, the comparison was made between the mesoscopic and the usual FE analyses of sheets with randomly distributed holes. As a result, it is found that the proposed mesoscopic model well describes the macroscopic deformation of perforated sheets. The influence of the element size is also examined.

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Creep properties of strontium doped lanthanum manganite (LSM) were studied in SOFC operating conditions, i.e. in the temperature range of 800°C to 1050°C and in air and argon gas environment. Although the difference of atmosphere did not affect creep properties, temperature and applied stress dependence of steady-state creep rate changed around 900°C. Considering previous reports, it was concluded that dominant creep mechanism of LSM in the temperature range of 950°C to 1300 °C was diffusion creep and the dominant creep mechanism changed at the temperature lower than 900°C. This indicated that dominant creep mechanism was grain boundary sliding creep. Because grain boundary sliding creep showed higher stress dependence and lower temperature dependence than diffusion creep, creep deformation during SOFC operation will be larger than expectations based on diffusion creep.

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Bending fatigue life tests with notched plane specimens up to 10⁷ cycles in 3-70 MPa hydrogen gas and fatigue crack growth tests with CT specimens in 0.7-90 MPa hydrogen gas were carried out for SCM435 low alloy steel. The fatigue crack growth rate depended on the hydrogen gas pressure and test frequency. The fatigue crack growth rate was 34 times higher than that in air at the maximum. The equation for fatigue life estimation was derived from these results and provided good fit to the experimental data of bending fatigue life tests of sharp notched and pre-cracked specimens at low-cycle fatigue range. It was deduced that this equation would be actually useful for the fatigue life estimation of various high-pressure hydrogen systems such as storage cylinder and piping which can not avoid the defects on the surface of an inner side. In addition, fatigue life tests showed that fatigue limit was the same as that in air. Non-propagating cracks were observed at the notch root of non fractured specimens at 10⁷ cycles both in air and 70 MPa hydrogen. It was deduced that fatigue crack closure was probably a key factor for the fatigue limit in hydrogen gas and air. Hardness affected fatigue limit in hydrogen gas and air, whereas chemical components of S, Mo and V in materials did not affect fatigue life in hydrogen gas in this study.

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To evaluate the effects of cold working ratio, stress intensity factor and water chemistry on an IGSCC susceptibility of non-sensitized austenitic stainless steel, constant displacement DCB specimens were applied to SCC tests in simulated BWR and PWR primary water for the three types of austenitic stainless steels, Types 316L, 347 and 321. IGSCC was observed on the test specimens in simulated BWR and PWR primary water. The observed IGSCC was categorized into the following two types. The one is that the IGSCC observed on the same plane of the pre-fatigue crack plane, and the other is that the IGSCC observed on a plane perpendicular to the pre-fatigue crack plane. The later IGSCC fractured plane is parallel to the rolling plane of a cold rolled material. Two types of IGSCC fractured planes were changed according to the combination of the testing conditions (cold working ratio, stress intensity factor and simulated water). It seems to suggest that the most susceptible plane due to fabrication process of materials might play a significant role of IGSCC for non-sensitized cold worked austenitic stainless steels, especially, in simulated PWR primary water. Based upon evaluating on the reference crack growth rate (R-CGR) of the test specimens, the R-CGR seems to be mainly affected by cold working ratio. In case of simulated PWR primary water, it seems that the effect of metallurgical aspects dominates IGSCC susceptibility.

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The development of the friction welded joint between Zircaloy-2 (Zry-2) and Type 316L stainless steel (SUS316L) has been carried out for the fabrication of irradiation capsules with the fuel irradiation test in Japan Materials Testing Reactor (JMTR). As the fabrication test of the Zry-2/SUS316L friction welded joint, the welding condition was determined from the results of total loss and tensile strength. Especially, the joint efficiency of the joint was more than 95% from the tensile tests at R.T. when the friction time was more than 3s. The joint interface was characterized by metallographic observation, elemental analysis and micro-hardness test. It was found that heat-affected zones at the joint interface were different between the center and outside positions, but the thickness of reaction layer was about 5μm. The tensile strength of the joint was equal to that of base Zry-2 metals at 300°C. From the results of these tests, it was obvious that the Zry-2/SUS316L friction welded joints were promised to use for the structural material of irradiation capsules for fuel irradiation tests.

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A conformable wedge for ultrasonic phased array transducer has been developed for the inspection of power generation components with various surface geometries. This low-cost wedge uses a standard linear phased array coupled to the pipe-work surface via a low-loss rubber-based tissue mimicking material impregnated with oil. This material has a longer usable life than hydrogel tissue mimicking material. After comparison testing between the conformable wedge and conventional rigid wedge technology was performed in terms of velocity and attenuation of longitudinal waves at temperatures from 0 to 60°C, the influence was investigated of deformation of conformable wedge on the velocity. The test reveals the conformable wedge is expected to be useful from practical point of view.

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Various toughened-material systems to reinforce interlaminar strength of CFRP have been proposed on the basis of the results of coupon tests. In this paper, an applicability of toughened-material systems to structural model such as curved beam subject to static bending was examined. Two kinds of CFRP with different toughened-material system were selected, and both microscopic observation and numerical FEM simulation using VCCT were performed for test results. A difference between coupon and structural model tests was found for the case of the curved beam with artificial anomaly, and the cause was considered due to the difference of delamination pass between coupon and curved beam tests. From a view point of numerical simulation for predicting the strength behavior of the curved beam, an adoption of different fracture toughness from that by coupon test was necessary.

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