Induction hardened axles have been used since the start of the Shinkansen (Japanese Bullet train) service in 1964. Axles are subjected to cyclic loading, and induction hardened axles are used under cyclic compressive stress conditions because of the large compressive stress state caused by induction hardening along the axle surface. Japanese Railways regularly inspect its axles, and if any crack larger than 0.15mm in depth is found, the axle is taken out of service. The compressive stress is around -500MPa, and magnetic particle inspection is conducted at intervals of 2.2×10^8 and 4.4×10^8 rotation. The issue of whether or not a crack more than 0.15mm in depth will propagate under cyclic large compressive stress conditions is of great importance from the viewpoint of railroad safety. From the above mentioned background, an experiment of fatigue crack extension under a cyclic large compressive stress condition was conducted. The result shows that the crack did extend in the range of around 3.6〜5.2×10^8 cycles under the condition of -500〜0MPa cycle. An elastic perfectly-plastic stress analysis was also conducted, and shows 89MPa tensile stress origination at the crack tip when unloading. This can explain such a crack extension. Whereas, the analysis of -560〜-440MPa cycle for actual maximum stress in the field shows compressive when unloading.

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This study demonstrates near-side slits much deeper the depth of penetration can be sized using eddy current signals. The key idea is to superpose eddy current distributions and locally realize a unique eddy current distribution that does not decay exponentially and has an abrupt phase change in depth direction. Eddy current testing using an eddy current testing probe designed on the basis of this idea is carried out with an exciting frequency of 100kHz to gather signals due to 10-20mm deep near-side slits fabricated in an austenitic stainless steel plate with a thickness of 25mm. The measured signals show clear differences although all the slits are much deeper than the depth of penetration. Subsequent numerical simulations are conducted to size the slits from the measured signals. The algorithm utilized models a slit as a rectangular region having a constant width and uniform conductivity inside, and evaluates its depth, conductivity, and left and right edge locations using parameter-free genetic algorithm. The simulations evaluate slits with a depth of 12, 15, and 20mm as 12.0, 15.4, and 16.8mm, respectively.

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A novel six-axis force estimation method for arbitrary shape wheels by using strain gauges applied on wheels was proposed. The proposed method firstly estimates distributed contact loads from the tire bead to the wheel rimflange. Secondly, six-axis force is calculated through numerical integration of estimated contact loads. The distributed contact loads were expanded into a series of basical distributed loads to overcome underdetermination of the problem. A numerical experiment for an ordinary tubeless radial tire and a steel wheel with 12 strain gauges was performed. Six-axis force estimation with ±5% measurement error of strain gauges resulted in ±10% estimation error, which is the same accuracy as that of semi-empirically optimized conventional methods.

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A multi-Gaussian beam (MGB) model without the paraxial approximation has been proposed in order to calculate off-axis wave fields from an ultrasonic transducer as well as on-axis wave fields. Using this MGB model, we can model three dimensional (3-D) elastic wave fields radiated from an array transducer to a solid with an efficient computational time. In this paper, brief formulations of the MGB model are described first and then the accuracy of the MGB model is checked in comparison with results of the Rayleigh-Sommerfeld numerical integral model. As applications of the MGB model, we investigate performances of both linear and matrix phased array transducers using the MGB model. Also the 3-D wave fields from the matrix phased array transducer in solid are visualized.

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A numerical simulation based on FEM is undertaken in order to clarify the influence of the axial impact velocity V_0 on the crushing behaviour of cylindrical tubes subjected to an axial impact. In general, the initial peak load P_1 for a tube of a strain rate sensitive material is higher than that of a stain rate insensitive material. It is found that the initial peak load P_1 for a strain rate sensitive material can be predicted from that for a strain rate insensitive material by taking into account of the modified yield stress σ'_Y and the plastic hardening coefficient E'_h. Here, σ'_Y and E'_h can be calculated using the strain rate ε|_1 at the apex of a wrinkle when P_1 generates. Also, the strain rate ε|_1 is a function of a ratio of V_0 and tube radius R, and based on numerical results, an approximate technique for evaluating ε|_1, and σ_1 is proposed and checked the effectiveness of the approximation.

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In this study, the bending rigidity of a honeycomb which consists of right hexagon cells was investigated. It is found that the bending deformation of honeycomb can not be evaluated by using the equivalent elastic constants obtained from the in-plane deformation, because the moments occuring on the oblique cell wall are different for the in-plane deformation and the bending deformation. Based on the fact that the oblique wall of the honeycomb is twisted under a condition that the rotation angle in both junctions is zero in bending deformation, a theoretical analysis of the bending rigidity of a honeycomb was proposed, and the validity of the present analysis was shown by using the numerical results of the finite element method.

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In this paper, effects of a loading direction and an existence of partially-complete cells on the mechanical properties of lattice structure are discussed based on theoretical and numerical stress analysis, FEM. By comparing the relative mechanical properties (initial stiffness E^* and plastic collapse strength σ^*_<pl>) per unit relative density, it has been shown that the BCCZH lattice structure is the bending-dominated structure, and the mechanical properties of BCCZH are similar to those of BCC structure. Also, the f_2BCC structure is more stable and offers a superior mechanical response than the other lattice structures. Moreover, the effect of partially-complete cells on mechanical properties is discussed, and using an approximate solution, the parameters E^* and σ^*_<pl>, for structures with partially-complete cells can be estimated from those for complete lattice structures.

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In this study, the deformation of a McKibben type actuator is analyzed by taking various energy consumptions into account. The obtained equations simulate the deformation of the actuator well either for pressurization or for decompression. Also it is shown that suitably decreasing the number of threads and the cross-section area of thread is effective in raising the maximum contraction rate. However, in theses cases, the minus factor, such as reduction of the maximum contraction rate due to the increase in initial length and the swelling of rubber from the gaps between threads, should be considered. Moreover, it is shown that using thread having 3-circle sections, instead of rectangle section, and using pattern 2, instead of pattern 1, are effective techniques for improving the maximum contraction rate.

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In this study, the strength of T-joint and Y-joint is analyzed based on numerical results of FEM. It is found that the joint strengths are proportional to a λ-th power of thickness T of chord tube for various joints with a fixed branch-to-chord diameter ratio d/D. The index λ changes with d/D, and in the range of d/D=0.1〜0.91, it is λ&cong;1.93〜1.55, with small value corresponding to large d/D. A compressive axial force in chord will reduce the joint strength, and it is also found that the strength-reduction ratios for Y-joint are the almost same as those for T-joint having the same T and d/D. Also, the joint strengths are influenced by span-length of the chord. The joint strengths decrease as span-length increases. However, the influence is small for small d/D.

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The fracture behavior of a crack in an adhesive joint is important to investigate the integrity of adhesive structures. It is well known that the fracture toughness of a crack in an adhesive joint using ductile adhesive depends on the bond thickness. However, the mechanism of the dependence has not yet been elucidated. In the present study, we measured the fracture toughness of adhesive joints consisted of aluminum and rubber modified epoxy resin under mode I loading. The distributions of strain around a crack tip were measured using a micro-video-scope and the digital image correlation method (DICM). The measured distributions of strains were compared with that estimated using the finite element method (FEM) in conjunction with Gurson's model. The fracture toughness of adhesive joints used in this study decreased with the decrease of the bond thickness. According to the measurement and analyses, it is estimated that the stress and damage around a crack tip in a thinner adhesive layer were more increased by the higher constraint effect of adherends.

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In this paper, concrete formulation of the superposition principle is given for the elastic Tz-stress, which is known as an elastic parameter that describes out-of-plane crack tip constraint effect. Then, the validity of the formulation is shown for 3D elastic crack problems, such as a problem of quarter-elliptical corner crack in finite thickness plate and a problem of surface crack inside a hollow cylinder. By our formulation together with the existing Tz-stress solutions under simple loading conditions will enable easy computation of Tz-stress under complex non-uniform stress distribution.

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Hydrogen pressure at blister initiation of a peroxide-crosslinked EPDM composite (NFT) was successfully estimated in terms of fracture mechanics in the previous study. In that estimation, threshold tearing energy of a static crack T_<s,th> in air room temperature was employed as the resistance of the blister initiation. In this study, static crack growth tests of a sulfur-crosslinked EPDM composite (NF) were conducted using single edge crack specimens in air and in 0.7MPa hydrogen gas at room temperature; then the influence of the type of vulcanizing agents (peroxide and sulfur) and hydrogen exposure on static crack growth properties and threshold tearing energy was investigated. From the observation of static crack growth by optical and secondary electron microscopes, NF had a rougher fracture surface than NFT; consequently, the static crack rate of NF was slower than that of NFT at the same tearing energy. The T_<s,th> value of NF was also about three times higher than that of NFT. Hydrogen did not influence the tendency of the da/dt-T curves and T_<s,th> values of NF and NFT.

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On the occasion of coming of aging society, the roads and the welfare facilities with universal design become very important. However, it is still the case that wheelchair user often fells uncomfortable when passing the slopes and the steps. Therefore it is important to clarify the vibration occurring in the wheelchair and the human body in such occasions. So we examined the comfort evaluation of wheelchair users. As basic study, we performed the experiment that the wheelchair passed the step of various heights in driving at constant speed. The vibrations of the wheelchair were measured by the strain gages which were mounted at the support frame of front wheel and rear wheel. And the vibrations of the human body were measured by the accelerometers which were attached to head and upper torso. Furthermore, we measured the movement of the center of gravity of human body in driving the wheelchair.

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A new head-neck finite element model was developed. The skull base and vertebral model were created from the CT images of a typical Japanese male. The models of intervertebral discs, ligaments and muscles were also created based on the human anatomy. The material properties were taken from the published data. Furthermore, a 2D strains measurement method was proposed to evaluate the intervertebral strain due to the vertebral coupled motion of translation and rotation, and it was applied to the cervical vertebral motion data obtained from the past rear impact tests using human volunteers. Then, the head-neck model was used in a simulation reconstructing this test, and the intervertebral strains were also calculated by the same method. The model response shows good agreement with the volunteer response, indicates that the head-neck model is suitable for minor neck injury analysis and it is possible to analyze the intervertebral strain by this new head-neck model.

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Shape Memory Polymer (SMP) and Shape Memory Alloy (SMA) are known as shape memory materials that mechanical properties change with temperature. Shape-Memory Composite material (SMC) was configured with SMP and SMA. In this study, SMC is produced for applying the properties of those two materials. The purpose of this study is to get design manuals for SMC controlled by heating or coiling. Therefore, the effects of temperature by heating or cooling to SMC were clarified experimentally. We defined elongation coefficient L from tension test and deflection coefficient D from three point bending test to present the mechanical properties of SMC. L and D correspond to Young's modulus of liner elastic body. As a result, the elongation coefficient L of SMP became smaller when temperature exceeded the glass transition zone. On the other hand, L of SMA became larger when temperature exceeded the phase transformation temperature. In addition, D_c of SMC was similar to D_p of a pair of SMP. However, D_c was smaller by 20 to 30 percent than D_p. Also, when temperature exceeded the phase transformation temperature, D_c of SMC became bigger than D_p of SMP.

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Stress distributions in stepped-lap adhesive joints of dissimilar adherends subjected to bending moments are analyzed using a three-dimensional finite-element method (FEM). For establishing an optimum design method of the joints, the effects of some factors are examined. As the results, it is found that the maximum value of the maximum principal stress σ_1 occurs at the butted edge of the adherend's interfaces with higher Young's modulus. The maximum value of σ_1 decreases as Young's modulus ratio between two adherends and the adhesive thickness decrease while it decreases as the number of steps increases. In addition, the joint strength is predicted using the obtained interface stress distributions. For verification of the FEM calculations, experiments were carried out to measure the strains at the interfaces and the joint strengths. Fairly good agreements were found between the numerical and the experimental results. The joint strength of dissimilar adherends was found to be smaller than that of similar adherends.

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A fatigue failure of bolted joint frequently leads to serious accidents of machines and structures. It is well known that the fatigue failure is likely to occur around the first thread root of bolt adjacent to nut loaded surface and the run-out of bolt thread. That is because high stress amplitudes are generated there due to alternating external forces. Accordingly, it is significantly important to evaluate the stress amplitudes along the thread root in order to elucidate the fatigue failure mechanism of bolted joints. In this study, stress amplitude distributions along the thread helix including the thread run-out are analyzed by three-dimensional finite element analysis, where the numerical models of bolted joints are constructed so as to accurately take account of the effect of thread helical geometry, using the modeling scheme proposed in the previous paper. The analytical objectives are bolted joints with axi-symmetric geometry except for the helical-shaped threaded portions, and they are subjected to axi-symmetric external forces. It has been substantiated, based on the stress amplitude distributions along the thread helix, that the fatigue failures are likely to originate from the first bolt thread, as in the case of the maximum stress, and the run-out of threads. It has also been shown that a bolt with reduced shank is effective to lower the stress amplitude, by comparing the numerical results to those for normal bolts.

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Tire coming-off accidents of large vehicles frequently cause fatal disasters that threaten the safety of civic life. Most accidents were attributed to the fatigue failure of wheel bolts that tighten the rear wheels of large vehicles. Since 2003, a number of guidelines to enhance the joint safety have been issued from the Government and other allied societies and associations. However, a considerable number of accidents are still occurring. In order to achieve a drastic reduction of the accidents, the tightening characteristics of wheel bolts need to be elucidated in greater detail. In this paper, the preload scatter of wheel bolts is comprehensively studied by experiments and FEM. Using a single set of wheel bolted joint, it is shown that a large scatter in bolt preload generates due to its specific geometry. In the next place, simulating the actual tightening operation, eight bolts are successively tightened and the bolt preload scatter among them is quantitatively evaluated. The effect of elastic interaction, which occurs in the tightening process of multiple bolts, is studied by experiments and also analyzed by three-dimensional FEM. Since the scatter of friction coefficient in related threaded fasteners is found to be the primary case for the bolt preload scatter, an improved configuration is proposed by FEM for two kinds of nut loaded surfaces, such as between inner nut and inner wheel and between outer nut and outer wheel.

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In order to clarify the fatigue properties and the fracture mechanism of stainless cast steel SCS1 used as the turbine runner of hydraulic power generation for 40 years over, two types fatigue tests were carried out with a bending machine and a tension-compression machine. The results are summarized as follows: The S-N curve of aged SCS1 used in this study has wide variation and the fatigue strength by using a tension-compression machine was lower than that by using a bending machine. In order to examine the reason for that, fracture surfaces were observed by SEM. Accordingly, fatigue crack initiates at two types origin; slip and casting defects. The fatigue strength whose fracture origin was casting defects was significantly lower than that whose fracture origin was slip. So, it is clear that casting defects strongly affect the fatigue properties of aged SCS1. Furthermore, according to the estimation of fatigue life, it is clear that it is possible to evaluate the fatigue life of aged SCS1 used in this study by using the casting defect size (area)^<1/2> and the stress intensity factor K_<max> calculated by defect size.

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The fatigue behavior of prestrained type 304 stainless steel was studied. Rotating bending fatigue tests have been conducted in laboratory air and in 3%NaCl solution using specimens subjected to the tensile-prestrains of 15%, 30% and 60%. A particular attention was paid to the stress-induced martensite transformation during stress cycling. The fatigue strength of the prestrained specimens increased with increasing prestrain in both environments, but decreased significantly in 3%NaCl solution compared with in laboratory air. The strain-induced martensite transformation occurred in the prestrained specimens, and martensite phase increased with increasing prestrain and with stress cycling at the fatigue limit stress in the 30% and 60% prestrained specimens. The coaxing effect took place remarkably in the unprestrained specimen, but decreased with increasing prestrain. The increase in fatigue strength of the prestrained specimens in laboratory air and the coaxing effect were attributed to both work hardening and the strain-induced martensite transformation, where the contributions of the former and the latter decreased and increased with increasing prestrain, respectively. Since corrosion pits were present at the crack initiation site in the large prestrained specimens, the decrease in fatigue strength in 3%NaCl solution was due to larger environmental susceptibility of martensite phase.

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Fatigue properties in high cycle and very high cycle fatigue regime of high speed tool steel (0.7C-0.1W-3Mo-2V) were investigated through the experimental results obtained from a cantilever-type rotary bending fatigue test in air at room temperature using hourglass shaped specimens. Two kinds of specimen were processed by grinder and cutting tool, which led to different surface compressive residual stress. Both specimens showed clear duplex S-N curve, composed of three types of failure mode depending on the stress amplitude, such as, a surface inclusion-induced failure mode (S-mode), a subsurface inclusion-induced failure mode without (I-mode) and with granular bright facet (GBF) area in the vicinity of inclusion (IG-mode). The transition of the failure mode from S-mode to I-mode and from I-mode to IG-mode was occurred at high stress amplitude level by the large compressive residual stress on the surface layer. A map of the appearance of failure modes relating the stress amplitude with the residual stress was proposed and showed a good agreement with the experimental results. The dispersion of fatigue life in the both specimens was explained by the consideration of an inclusion size at crack origin. S-N curve depended on the inclusion size was provided with the estimation of crack growth rate from the S-N data.

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Safety is one of the most important issues in hydrogen economy. Earthquake sometimes gives damages to steel structures and machineries. The components which had not been seriously damaged would still be used after the earthquake. The residual fatigue strength of those components, however, might have been decreased. The objective of this work is to clarify the effect of relatively small number of overloads and hydrogen on the residual fatigue strength of a notched component. As a result of the experiment, it was made clear that the formation of small crack and the tensile residual stress introduced by overloads caused substantial decrease of residual fatigue limit. The test results showed that the crack depth formed by overloads was about four times deeper in hydrogen charged material. The acceleration of low cycle fatigue crack growth by overloads played a major role. The reduction of ΔK_<th> also occurred. It gave secondary contribution for the reduction of residual fatigue limit.

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In order to clarify the loading-frequency effect on the fatigue crack growth behavior of a low carbon steel JIS S10C in hydrogen gas environment, fully reversed bending fatigue tests were carried out. The main obtained results are as follows. Loading-frequency effect on FCG reveals complex behavior; that is, not only acceleration but also deceleration even in the same range of low loading-frequency. Slight acceleration appears in the low growth rate range where the ductile fracture mode is predominant. Deceleration appears due to the transition behavior from quasi-cleavage fracture mode with a higher growth rate to ductile one with a lower growth rate. This shows that lowering the load-frequency does not necessarily lead dangerous fatigue crack growth.

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Copper electroplating stress measurement method uses the grain growth in copper foil. This method can detect the maximum shearing stress by measuring the grown grain density. However, it's necessary to judge the sign of biaxial stress ratio (=σ_2/σ_1) beforehand in order to detect the principal stress. In this report, it pays attention to the grain growth direction to judge the sign of biaxial stress ratio, since it can be expected that the grain growth direction differs with the sign of biaxial stress ratio. The grain growth direction is investigated by the image processing software after carrying out the cyclic loading test under the various biaxial stress ratios which include positive and negative values. It's clear that the maximum values of relative frequency of grain growth direction occur periodically when biaxial stress ratio is negative. On the other hand, such periodicity is not observed when biaxial stress ratio is positive. Moreover, the grain growth rate is also different in the sign of biaxial stress ratio. These results can be explained by considering the direction of maximum shearing stress.

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Impact tensile properties of T6-aged 6061 and 7075 aluminum alloys affected by atmospheric hydrogen were investigated. In order to introduce hydrogen from the atmosphere, the alloys were pre-deformed by a slow strain rate testing (SSRT) in a humid air atmosphere with a relative humidity of 90%. For the pre-deformed specimens, the impact tensile tests were performed using split Hopkinson pressure bar (SHPB) method at an average strain rate of 5.0×10^2s^<-1>. Hydrogen concentration after the pre-deformation by SSRT was measured with a thermal desorption analysis. As a set of the experiments, it was shown that the ductility in the impact test decreased when the T6-aged 7075 alloys were hydrogen charged. The hydrogen embrittlement sensitivity of the T6-aged 6061 alloys was lower than that of the T6-aged 7075 alloys. The decrease of the ductility due to hydrogen charging of the T6-aged 7075 alloys was closely related to the increase in the ratio of the intergranular fracture near the specimen surface.

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Cavitation erosion often occurs in fluid machinery and piping systems of industrial plants. The erosion damage causes a reduction of performance, noise and a leak accident of fluid machine. In this study, cavitation erosion tests were carried out for cast iron FC250 and stainless steel SUS304 under the condition of the stationary specimen test method using the vibratory apparatus specified by ASTM G32-03. Test results are compared to our previous paper of S15C and discussed in terms of the maximum depth of erosion, the erosion rate and the eroded shape of test specimen after long exposure. It was found that the erosion rate decreases and the maximum depth increases with erosion time with a power of about 0.5 after long exposure regardless of the kind iron and steel.

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