Magnetorheological (MR) fluids are categorized as smart fluids, which are made of small iron particles suspended in carrier fluids such as silicone oil. A presence of a magnetic field will instantaneously increase the viscosity of the MR fluid, also kwon as the MR effect. The application of the MR fluid for automobiles and buildings for viscous dampers has shown excellent performance for shock absorption. In order to expand practical application of the MR fluid, various evaluations of shock-absorption performance under high-loading conditions are needed. Therefore, we decided to investigate the performance on high-speed impact. As the first step, impact experiments were conducted in transparent liquids—tap water and two kinds of silicone oils with different kinematic viscosity—instead of the MR fluid, and it was investigated whether the kinematic viscosity and the speed of sound (i.e. compressibility) of each liquid affect the shock-absorption performance or not. As the result, it was found that the kinematic viscosity and the speed of sound did not affect the velocity attenuation of the projectile. Furthermore, it was found that the speed of sound affected the pressure of stress wave generated by the entry of projectile into liquid. It is considered that these results are related to the conditions of liquid around the projectile.

It is known that the dynamic behavior of polymers depends greatly on not only the strain rate but also the hydrostatic pressure, and furthermore, the volume change after plastic deformation is larger than that of the metal material. Therefore, it is necessary to clarify these material properties for high precision simulation of polymers. In this study, we developed a new constitutive equation considering the hydrostatic pressure dependence on the yield function and applying the strain rate dependence model T-M2009 for polymers, and implemented using the user subroutine function of the impact analysis code LS-DYNA. Then, tensile and compression dynamic tests were performed on polycarbonate using the Sensing Block Type High Speed Material Testing System, and material parameters of the developed constitutive equation were determined. Furthermore, verification simulation by LS-DYNA using these constituent equation and material parameters was carried out. As a result, the dynamic behavior of tensile and compression by simulation agreed well with the dynamic test results, and the validity of the constitutive equation and it's material parameters were confirmed.

Fluid-structure interaction (FSI) and wave propagation occurred in engineering structure may cause severe damages and result in a deadly accident such as explosion of pipe-lines in a plant. However, how the FSI affects the wave propagation is still not fully understood. From the previous studies, a disagreement was reported between the induced pressure value on the solid-fluid movable interface and predicted value with the classical one-dimensional theory due to the effect of two-dimensional wave propagation. To address this problem, in this paper, two-dimensional axisymmetric simulation of wave propagation across solid-fluid interface with fluid-structure interaction was conducted. The simulation was carried out using ANSYS AUTODYN with Lagrangian solver for solids and Eulerian solver for water. The results showed that the transmitted pressure is attenuated near the tube wall due to the rarefaction wave generated by the tube and fluid's expansion. The averaged pressure distribution after the transmission gradually converged to one-dimensional acoustic theory as the pressure wave propagating away from the interface. Consequently, it was indicated that a transition region for the transmitted pressure existed immediately after the solid-fluid interface to the axial direction until the point of 0.38 in ratio to the inner diameter of the tube. In this region, the transmitted peak pressure can be estimated with normal wave speed in the unconfined fluid in the sight of safety engineering.

The purpose of this study is to estimate the surface condition of road material, such as dry, wet, ice and snow, by using the ultrasonic system on the moving vehicle. As a first step, the asphalt, concrete and brick block were used as the specimen for examination and verification of the possibility of estimation by the ultrasonic with moving. The ultrasonic wave (the central frequency of 40 kHz) which propagated to the specimen in the air reflects at the material surface by the difference of an acoustic impedance and surface condition, and it is received the ultrasonic transducer. The ultrasonic system was set on the hand cart and moved 10m at the low velocity (walking speed) for measurement. Brick block specimen has bigger value for the mean of maximum amplitude, and also the dispersion of the measurement result is wider than other road material.

Transmission characteristics of the lowest-order symmetric (S0) and antisymmetric (A0) Lamb modes at contacting edges of plates are experimentally examined. The edges of two aluminum alloy plates were mated together and a compressive load was applied from both plate ends to constitute a butt-type contacting interface. Wedge transducers were used to emit and detect a single Lamb mode dominantly. For the excitation of the S0 mode, the transmission coefficient of the S0 mode increases with increasing contact pressure and slightly decreases with increasing frequency. For the excitation of the A0 mode, on the other hand, the transmission coefficient of the A0 mode shows complicated behavior with contact pressure and frequency. When the contacting edges of the plates are modeled as a linear spring-type interface which is characterized by normal and tangential stiffnesses, the transmission coefficients of the S0 and A0 modes below the cut-off frequencies are approximated by the results of thin-plate theories. Comparison of the measured transmission coefficients to the theoretical results enables the estimation of the interfacial stiffnesses of contacting edge faces. The estimated normal and tangential stiffnesses show increasing behavior with increasing contact pressure. The dependence of the measured transmission coefficients on frequency and contact pressure is well reproduced by the theoretical results based on the estimated interfacial stiffnesses.

Recently, automotive industry have paid attention to multi-material structures. Hence, joining methods for these dissimilar materials are the key to apply them into the structural parts of the vehicles in combination. Adhesive bonding can be one of the leading joining methods for the structural parts of vehicles. To apply adhesive joint to the parts of the vehicles, the characteristics such as strength and energy absorption under higher deformation rates should be known. Several tests have been proposed to evaluate the impact resistance of the joints. To evaluate the mode I fracture energy of adhesive joints, DCB(Double Cantilever Beam) tests have been standardized only under the quasi-static condition. To measure the mode I fracture energy under the impact loading condition, a falling-wedge impact test machine using DCB specimens were proposed by Xu and Dillard(2003). However, the inertial effects under dynamic condition have not considered. In this study, DCB tests under dynamic conditions were conducted using a falling-wedge testing machine and a high-speed camera. A mode I fracture energy for adhesive joint under dynamic condition is discussed.

Small scale structures can be manufactured by utilizing surface effects. In this study, a cylindrical structure is formed from a thin film on liquid surface by pulling up a thread connected at the center of the film. The film is being bent during pulling up process due to elasto-capillary, and both ends of the film eventually contacts by surrounding a small liquid volume. The actual structure formed from this proposed method is not a exact cylindrical structure, but a teardrop-shaped structure. To estimate the formed shape, a simple 2D model consisting of a circular arc, tangent lines, and contact parts was established. The central angle and the radius of the teardrop-shaped structure were successfully determined by minimizing the potential energy. As a result, it was revealed that the radius depends on bending stiffness of the film and density of the liquid, but the central angle is constant. The teardrop-shaped structure obtained from the analytical model was compared with experimental results by their areas, and it was shown to be effective.

Fracture of distal radius bone, which is vicinity of a wrist joint angle, is major disease for elderly people. After the treatment, the associated part must be fixed for a long time. As a result, soft tissues such as muscle, skin, ligaments and like around the affected part often become rigid. Such a case is referred to as contracture in which movable range of the joint is restricted. Thus, effective rehabilitation for the contracture of the wrist joint angle is required. Traction of the wrist during flexing and extending the wrist joint is proposed as efficient rehabilitation procedure. Previously, we fabricated a rehabilitation equipment capable of such rehabilitation, and dynamic motion of carpals in the wrist was observed by radiography. From the obtained results, the rehabilitation effect was evaluated with contribution ratio of the joint angles. This study compares the rehabilitation effect of the fabricated equipment with that of an occupation therapist and confirmed its availability. Furthermore, it is clarified that the evaluation of joint angle displacements is important to investigate the effect of the rehabilitation procedure.

After aluminum alloy A2017-T4 spheres with a diameter of 1.0mm struck thick pure aluminum targets, 4N, 3N and A1050, at an impact velocity of 5 km/s, ejecta size distribution were examined in detail. A two-stage light-gas gun at the Institute of Space and Astronautical Science (ISAS)/Japan Aerospace Exploration Agency (JAXA) was used for impact experiments. The size of the ejecta collected from the test chamber was measured using image analysis software. The size distribution from the pure aluminum targets was compared with that of aluminum alloy 6061-T6.

The purpose of this study is to elucidate the effect of inner fluid on compressive properties in cellular solids using SPH (Smoothed particle hydrodynamics)-FEM (Finite element method) technique. Numerical experiments were performed by SPH-FEM solver, RADIOSS. The analysis model were made with cell walls, inner fluid and the rigid walls. The cell walls were meshed using shell elements, and the inner fluids were filled with the SPH particles. Compressive simulations were performed by applying the constant velocity to the upper rigid wall. The constant velocities were 0.075, 0.75 and 7.5 m/s. Air-filled and no-air models were prepared to investigate the effect of the inner air on the compressive properties in the models. In the air-filled model, the flow load showed higher value in comparison with the no-air model. It was confirmed that the flow load was increased by increase of the inner air pressure. In this model, the influence of the applied velocity on the flow load could not be observed. The compressive numerical simulation was also carried out using the perforated models with same condition. In the perforated models, the compressive velocity dependence of the flow load was observed since the residual fluid did not have enough time to escape from the cell. It was clarified that the compressive properties of cellular solids were affected by the flow-out of the inner fluid.

For more improvement of the collision safety, it is necessary that not only collision safety evaluation and measure at the primary collision, which is the accident between the vehicles at the first collision, but also collision safety evaluation at the secondary collision, which is another accident occurred by subsequence collision. However, collision experiment and safety measure, which is considered to secondary collision, are not sufficiently carried out, since the vehicle motion after the first collision is complicated and difficult to predict, although theoretical analysis has been reported. In this study, in order to evaluate the influence factors for collided vehicle motion after collision, we carried out the collision experiment at the difference of collision position with vehicle model, and compare the experimental results at the each collision position. As the results, the difference of collision position affects vehicle rotation and moving distance.

It is generally considered that plant leaves have appropriate bending stiffness for the purpose of effective photosynthesis. However, effect of lateral veins on the bending stiffness of leaves are not obvious since lateral veins don't change cross-sectional shape of leaves in contrast of a central vein. In this study, in-plane Young's moduli parallel and perpendicular to lateral veins (E_∥ and E_⊥) of leaves of Epipremnum aureum were determined by a combination of non-destructive acoustic resonance measurements and numerical analyses using finite element method. Leaves were clamped by metal plates which have oval windows and oscillated by a speaker through the windows. The bending vibrations of the leaves were measured using a laser displacement sensor and resonant frequencies were obtained using fast Fourier transform. In-plane Young's moduli parallel and perpendicular to lateral veins were determined from measured resonance frequencies, dimensions, and mass densities using finite element analyses. The in-plane elastic anisotropies E_∥/E_⊥ obtained from all the measurement areas suggested that lateral veins increase the bending stiffness of leaf laminas of Epipremnum aureum. It was also suggested that effects of primary lateral veins on in-plane Young's moduli were larger than those of secondary lateral veins.

Impact hardness measurement based on the Split-Hopkinson Pressure Bar method is promising technique to characterize dynamic surface properties of basic and advanced materials for mechanics and electronics. Since the force to impress an indenter increases sharply with depth associating with high rate of deformation, it is fundamental requirement to identify the whole process of measurement even in the initial region with high accuracy. In the present investigation the spatial difference method instead of time difference method is newly developed taking account of wave propagation characteristics of this kind of measurement, and is applied to simulate force-depth relations. The method was found to provide reliable time-difference measurements of impact hardness test together with direct measurements in the initial small force stage of the process, and was also applied to experiments on Titanium alloys.

Prediction method of viscoelasticity of laminated resin sheet using resin having different viscous characteristics.

Analytical technique of thermoforming using predicted viscoelasticity.

In order to evaluate quantitatively the strain rate dependence of the dynamic flow stress of A1070 at very high strain rates, high strain rate and decrement strain rate tests are performed in the strain rate range from 4000/sec to 22000/sec. The reduction ratio caused by the collision between an impact bar and a decelerator is 0.586 of the strain rate before reduction. The flow stress drop obtained by the rate reduction increases with strain rate, and which was assumed to be a response to an instantaneous strain rate. An activation volume is determined from the relation of a thermal activation process and the amount of the flow stress drop obtained from the reduction tests. The activation volume decreases slightly with strain rate. High strain rate tests at high temperatures of 373 K and 473K also performed in the above strain rate range. Calculation curves predicted by thermally activated process show a good agreement with experimental results. The rate controlling mechanism of A1070 at very high strain rates can be represented by the thermal activation process.

Mechanical properties of nano-sized fiber reinforced polypropylene were investigated by using a carbon nanotube reinforced polypropylene. Dumbbell and beam shaped carbon nanotube reinforced polypropylene specimens were prepared by injection molding. Uniaxial tensile and three point bending tests were conducted to identify strength and modulus. Tensile yield stress and modulus of polypropylene were decreased by increasing carbon nanotube content. Flexural strength and the modulus were not affected by increasing carbon nanotube content. Yield stress was calculated from three point bending test results, and it was found that there was a positive correlation between the stress and tensile modulus. It was also suggested that the slope of this relationship represents the break elongation of carbon nanotube.

This paper reports experimental results of the amplification effect of shock wave by an explosion in a closed space for establishment of shock wave amplitude method related to the shock wave medical and biomedical application. In this study, a metal tube made of stainless steel (SUS304) was used as a closed space. The metal tube was placed partly under the water surface in a water-filled chamber. A shock wave was generated in the metal tube by detonating a micro-explosive (10 mg silver azide pellet) was placed about 5, 10, 15, 20 mm from the bottom of the tube. The process of underwater shock wave propagation from the tube was visualized optically by shadowgraph method and recorded by a high-speed framing camera. The pressure histories of generated shock wave were measured simultaneously by a spatiotemporal pressure sensor. The peak overpressure of induced underwater shock wave from a metal tube with a relatively large diameter was larger than that of shock wave by detonating in water open space.

In this research, the effect of strain rate on the shear strength of cryptomeria and Japanese cypress in the longitudinal direction was investigated experimentally by using double shear face specimen at room temperature. A screw gear type universal testing machine and sprit Hopkinson pressure bar (SHPB) testing machine were used for quasi-static and dynamic shear tests, respectively. It was found that there is almost no effect of strain rate on the shear strength of both wood materials at least in the rage of strain rate from 10^-3 to 10³ s^-1.

In the study, the soft actuator which generated tensile and bending deformations due to internal pressure was developed and designed on the basis of non-linear finite element analysis. The actuator shape was an eccentric cylinder added with stiffeners to generate the deformations efficiently due to air pressure. The optimal shape and distance of the eccentric stiffeners were determined from the results of the finite element analyses. Additionally, the stiffeners were also determined as the eccentric non-circular plates by removing the regions with extreme low equivalent stress from the stiffeners. The soft actuator with the stiffeners was designed according to the considerations of the stiffener shape and distance and manufactured by pouring silicone rubber into the polymer mold made with a three-dimensional printer. The characteristics of the actuator were confirmed by measuring the deformations of the manufactured actuator due to air pressure.

The Electromagnetic Flux Compression (EMFC) technique which is made from four coils, liner, primary, support and Helmholtz coils, is used to generate ultra-high magnetic field over 700 T inside a laboratory, and scientists use the ultra-high magnetic field generated with this technique to investigate electronic properties on novel materials. Scientists are focusing on the increase of generation of the magnetic field and have a plan to obtain the field over 1000 T with stability inside a laboratory. Recent advances of simulation techniques such as optimization techniques will play an important role in realizing the plan. In order to investigate effectiveness of the simulation technique for the purpose of combination with optimization technique, a two-dimensional axisymmetric electromagnetic simulation has been carried out on the EMFC technique in coupling with structural and thermal solvers. Time history of the magnetic field predicted by the axisymmetric solver shows almost the same tendency obtained by the three dimensional solver previously reported, while the diameter of the liner coil as a function of magnetic field slightly differs from an experimental result. As compared with the result previously reported, it is found that a gap of the primary coil is a major reason for the difference and that the difference is inevitable as long as the axisymmetric solver is employed. On the other hand, it is also found that calculation time of the method used in this study is drastically reduced by 1/10 or more than that of the three dimensional solver. Therefore, the simulation technique proposed in this study is considered valid.

The crash safety structure of railway vehicles is effective as one of the safety measures in the event of a collision accident. However there is no standard for crash safety in Japan. In order to ensure the crash safety, it is important to grasp the impact deformation behavior of the railway carbody in a collision accident. Therefore, we carried out Finite Element (FE) analyses of a level crossing accident with a dump-car under various conditions (collision position, collision angle and collision speed) and evaluated their results such as the contact force, the deformation energy of the rail vehicle, the deformation amount of the cabin, the maximum and mean deceleration of the passenger's area. The degree of correlation among these results was also discussed.

Injury occurs due to disruption of the interaction between human, products and environments, whose interactions are latent in vast living environments. Furthermore, from the temporal structure of the injury, injury occurs as a consequence of human behavior, protective reaction, body motion, tissue deformation and cell damage. In order to understand the spatiotemporal structure of injuries, we have conducted integrated injury biomechanics researches regarding human behavior, protective reaction, tissue deformation and cell damage.

The influence of microstructure on crack initiation behavior of Ti - 6Al - 4V was investigated with atomic force microscope (AFM) and electron backscattered diffraction (EBSD). Also, fatigue crack initiation point was identified by the replica method. Experimental results showed that the fatigue crack was generated by the basal plane activity of the hcp crystal structure. In addition, the fatigue crack occurred in α phase with high values of both the Schmid factor (SF) and the slip angle γ on the basal plane, because of the higher force perpendicular to the plane of the resolved shear stress, intrusion and extrusion grown earlier than other grains. With the increase of the number of cycle of fatigue test, fatigue crack occurred in the α phase of grains with very high basal SF and orientation change. Even in α phase with low force perpendicular to the plane of the resolved shear stress, with the increase of the number of cycle of fatigue test, intrusion and extrusion grew gradually in α phase of grains with very high basal SF and orientation change, which may lead to fatigue crack initiation. Therefore, when considering the crack initiation site, SF×sin γ was appropriate in low cycles and SF and GROD was appropriate in high cycles.

In order to elucidate the influence of microstructure on the crack non-propagation behavior, I did fatigue crack propagation test with K-decreasing process to obtain the threshold stress intensity range ΔK_th. Then, I investigated the effect of crystal grain size on its value. As a result, it was found that the value of ΔK_th is substantially constant irrespective of crystal grain size. Also, I examined fatigue crack non-propagation behavior using slip factor. Just for information, slip factor is the resolved shear stress ratio calculated considering the singular stress field at the crack tip. Slip factor is calculated for each slip system, but even if the value of the slip factor is large, it was observed that the slip system did not happen and the crack did not propagate. Then, I focused on the distance from the crack tip to the grain boundary. As a result, it was found that cracks do not propagate as long as the slip factor is large but the distance from the crack tip to the grain boundary is small. Therefore, it was found that not only the slip factor but also the influence of grain boundary should be taken into consideration when studying fatigue crack non-propagation behavior.

Fatigue crack propagation in a polycrystalline Ni-base superalloy was experimentally investigated. Special focus was put on the effect of grains crystal orientation and grain boundary on fatigue crack propagation, employing bi-crystal CT specimen extracted from a directional solidified superalloy, MGA-1400. A series of experiments revealed that transgranular crack propagation was affected by the primary and secondary crystal orientation of grains, and fundamental mechanism of Stage I cracking along slip planes could be interpreted by the experimental and analytical finding in the single crystal material. It was also found that the grain boundary in the bi-crystal specimen caused the retardation of crack propagation depending on crack propagation modes both before and after the grain boundary. In case the crack propagated in Stage I manner after the grain boundary, crack retardation became more pronounced due to the mode transition from Stage II to Stage I cracking.

Effects of crystallographic orientation and grain boundary on Stage I fatigue crack propagations were investigated in a single crystal and a bi-crystal Ni-base superalloy. Fatigue crack propagation tests at room temperature were conducted using four types of single crystal CT specimens with different combinations of primary and secondary orientations. Stage I cracks in the single crystal superalloy were mixed mode with mode I, II and III components, and the <100> primary orientation or the <110> secondary orientation resulted in higher crack propagation rate. In order to interpret the effect of crystal orientations on the Stage I cracking, crystal plasticity finite element model was developed considering the 3-D geometry of the mixed mode crack plane. Damage parameter calculated from crack tip slip field provided reasonable explanations on the preferable crack paths and growth rate of Stage I cracks. Effect of grain boundary was also investigated using a bi-crystal finite element model involving two coarse grains. Analytical results proved that slip deformation was disturbed by the grain boundaries and resultant damage parameters were strongly affected by the crystal orientation of the grain ahead of the grain boundary.

Plane bending fatigue tests and fatigue crack propagation tests were conducted at room temperature in a laboratory atmosphere to examine the effect of stress ratios on the fatigue crack initiation and propagation behavior of magnesium alloy (AZ31). Plane bending fatigue tests were performed using computer-controlled electro-dynamic fatigue testing machine under stress ratios of -1, -0.1, 0.1 and 0.5. Result of fatigue tests, fatigue strength at 10⁷ cycles of magnesium alloy tended to decrease as stress ratio increased. In addition, the specimen surface were observed by optical microscopy, and the specimen surface near crack initiation site were analyzed using the electro backscattered diffraction (EBSD) to discuss the small fatigue crack initiation mechanism. On the basis of EBSD analysis, the crack initiation and propagation mechanism was not influenced by twinning. Furthermore, a near-threshold fatigue crack propagation tests were conducted using the compact-tension C(T) specimens under several stress ratios. Threshold stress intensity range, ΔK_th, decreased and the crack propagation rate, da/dN, became high as stress ratio increased.

Bulk Metallic Glasses (BMGs) hold a noticeable attention in the scientific community. This type of material exhibits indeed very interesting properties, such as high strength, noticeable elongation at fracture and good corrosion resistance. However, it is common knowledge that BMGs show poor fatigue resistance, such as present usage of BMGs is restricted to non-structural applications. In order to grasp the complexity surrounding the fatigue loading, the present study investigates the effect of the stress ratio R (= σ_min / σ_max) up to high value of R = 0.7.

Such a high stress ratio induced some typical irregularities on the fatigue crack propagation of Zr₅₅Al₁₀Ni₅Cu₃₀ BMG. Indeed, the fracture surface displayed a very peculiar feature, which consists of peak and valley radiating from the crack initiation site. Due to its geometry, this feature is called “gutter-like” pattern. In addition, some other particularities were also observed on the tensile surface of failed specimen

The fatigue damage behavior of Zr₁₂Ti₂Cu₂₅Al₁₂ (ZT1) bulk metallic glass (BMG) was investigated based on the stress-life approach and the damage tolerance approach. The ZT1 exhibits the highest fatigue endurance limit among all monolithic BMGs, with a fatigue limit of σ_a=441 MPa under four-point-bending load, or ～0.27 of its tensile strength. The relation between the range of stress intensity factor (ΔK) and the crack-growth rate (da/dN) was also determined. ZT1 shows a fatigue threshold, ΔK_th, of 2.8 MPa√m, which appears to be related to its atomic topological structure.

Influence of load amplitude and stress ratio on crack closure behavior for fatigue crack growth was experimentally investigated by fatigue tests in air environment. Cyclic loads were applied to specimens and magnitude of load amplitude was stepwise increased under constant stress ratios. It was confirmed that the effective load amplitude on fatigue crack growth increases with increasing the load amplitude. The effective load amplitude becomes a constant value if the magnitude of load amplitude is larger. In addition, the effective load amplitude decreases with decreasing the stress ratio. Applicability of the fatigue crack growth evaluation method for fatigue crack growth under negative stress ratio is discussed on the basis of the experimental results.

Occurrence of fatigue crack cannot be prevented in industrial structures under various severe conditions. In maintenance of these structures, early detect of fatigue crack on material surface and are required. “Making of stop hole” and “tighten around crack tip” are introduced as one of emergency control of fatigue crack in sheet metal. Stress concentration around defect is reduced by making of stop hole. Bolt, nut and washer are used to tight sheet metal. "Compressive stress working" and "contribution of stiffness for bolt, nut and washer" are increased with tighten torque. However, these effects are not clarified based on fracture mechanics. In this study, stress concentration density of defect are discussed from 2D numerical simulation results. Finite element analyses are demonstrated based on the condition of fatigue crack growth of previous experimental study. Fatigue crack re-growth process are also simulated in the finite element analyses. J integral and stress intensity factor are measured from stress singular field around fatigue crack tip. Tighten effects are introduced as “additional compressive stress” and “virtual thickness change of numerical model”. The effects of stop hole making and tighten are appeared in histories of stress intensity factor. By working of higher tighten torque, stick condition is caused between the washer and the sheet metal. Washer, bolt and nut are also deformed by cyclic tensile load under stick conditions. Because sheet metal loading is decreased by the tighten, stress concentration is also decreased.

Occurrence of fatigue crack cannot be prevented in industrial structures under various severe conditions. In maintenance of these structures, early detect of fatigue crack on material surface and are required. “Making of stop hole” and “tighten around crack tip” are introduced as one of emergency control of fatigue crack in sheet metal. Stress concentration around defect is reduced by making of stop hole. Bolt, nut and washer are used to tight sheet metal. "Compressive stress working" and "contribution of stiffness for bolt, nut and washer" are increased with tighten torque. However, these effects are not clarified based on fracture mechanics. In this study, effects of emergency control for fatigue crack tip are reported based on experimental results. The specimen material SCM440 has higher yield stress, therefore some fatigue troubles are reported in the SCM440 structures. Under cyclic tensile loading, fatigue crack re-growth from stop hole are observed. Stress intensity factor is measured from the tensile loading density. Parameter about fatigue crack growth (Paris low) are estimated from approximation based on experimental data. Dependence of crack re-growth on tighten torque are also discussed. Retardation of crack re-growth are distinguished by increase of tighten torque.

In order to improve the fatigue properties of a similar butt friction stir welded joint of A2024 Aluminum alloy, two types of laser peening with femtosecond or nanosecond pulse laser equipment were applied. Fatigue tests were conducted at stress ratio R= -1, road frequency 23Hz with plane bending fatigue condition. Fatigue property was improved by both laser peening treatments and the fatigue strength at 10⁷ cycles of FSWed specimen was improved to the same level as that of the base metal for both treatments. Residual stress distribution, Vickers hardness distribution and surface roughness were measured and the relation between fatigue strength and these peening effects were investigated. As the results, it became clear that the residual stress was the most effective factor in improving the fatigue strength.

Although it is generally recognized that forgings has anisotropy in the fatigue strength, there are few reports on the relationship between the forging ratio and fatigue strength. In production, forging ratio becomes sometimes higher when the different sizes of products are taken from one ingot. It is also often in the case that the grain flow of the surface is out by machining to from the product. In this study, rotating bending fatigue tests were conducted using the specimens of four forging ratio cut out in the orthogonal direction to the grain flow. The fracture surfaces were observed with scanning electron microscope. In addition, the distributions of the size of inclusions were investigated using high-frequency ultrasonic testing. From the result of fatigue tests, it was shown that fatigue strength of the specimens of the highest forging ratio is lower than others. From the result of observation of fracture surface, the inclusions of the higher aspect ratio were included in those with higher forging ratio. From the result of high-frequency ultrasonic testing, the size of inclusions are larger as the forging ratio is higher. From the above investigation, it is concluded that lower fatigue strength of the higher forging ratio is caused by the larger size of inclusions related with the higher aspect ratio by forging.

Hot isostatic pressing (HIP) has generally considered to improve fatigue strengths of cast materials. To study the effect of HIP on the fatigue strength of Ni-based cast alloy IN100, a fatigue test was carried out on both as-cast and HIP specimens at 650 and 850°C. The test results showed that HIP increased the fatigue strength by 20 ~ 30％ at both temperatures and reduced the data scatter. For the as-cast specimens, the fatigue cracks always initiated from the inside of specimens and their fracture origins were casting defects. For the HIP specimens, however, some fatigue cracks initiated from the surface and others initiated from the inside. In most cases, their fracture origins were not casting defects but carbides of Ti and Mo. It was found that when HIP was conducted and the casting defects became small enough, the fatigue strength was dominated by the carbide size.

Spot welds are fabricated using high strength and low carbon steel sheets with three different strength levels by a resistance spot welding (RSW) procedure. The nugget sizes are changed by controlling welding process parameters. Subsequently, tensile-shear fatigue tests are conducted to investigate the effects of strength levels of steels and nugget sizes on the fatigue behavior of welds. The fatigue strengths of the welds with 4√t nugget size are nearly the same irrespective of strength levels of steels, because fatigue crack propagation life is dominant in total fatigue life. In the welds with 3√t nugget size, the steel with higher strength exhibits lower joint fatigue strength.

Hydraulic excavators and cranes are major heavy equipment with numerous one-sided welded joints. Although fillet welded joints are easily implemented and economical, the unwelded portion frequently initiates crack propagation. Because of this problem, high evaluation method is needed for the unwelded area. In this study, the fatigue properties and the fracture mechanism of the load carrying type fillet joints with one-sided welding were investigated experimentally to evaluate its fatigue damage with high accuracy based on the experimental and analysis results. As the results, there was little crack start. Almost the all lifetime is crack propagation. Cracks were initiated at multiple sites in the test piece. As the number of cycles increased, these cracks propagated and combined, and we confirmed these behaviors using FEM analysis. In addition, because analysis crack propagation parameters are important, we performed CT test, and analyzed using acquired values. We found crack propagation parameter between standard values (wes2805-1) and tested values are different.

This study discusses an effect of loading path on fatigue life for type 316 stainless steel. The testing machine for multiaxial fatigue test is equipped with three actuators. This testing machine can apply push-pull, reversed torsion and inner pressure to the specimen by controlling the three actuators. Load and pressure controlled fatigue tests at room temperature were carried out using a hollow cylinder specimen under multiaxial loading. The fatigue life N_f is determined as the cycle at which the maximum inner pressure was reduced by the oil leak due to an initiation of through crack or rupture of the specimen. Loading conditions were 5 types: they are a cyclic pull loading, a cyclic inner pressure loading, a cyclic equi-biaxial loading and two combination loadings by cyclic inner pressure and cyclic pull loading. The two combination loadings are a Square-shape loading and a L-shape loading. In the Square-shape test, axial stress σ_z and hoop stress σ_θ are applied by trapezoidal waveforms with 90° degree phase difference so that the loading path is shown by square shape in a plane stress state. In the L-shape test, axial stress σ_z and hoop stress σ_θ are applied alternately so that the shape of loading path becomes the shape of the letter “L”. Fatigue lives of the latter two combination loadings were reduced due to increase in cyclic ratchetting deformation. In addition, the cyclic deformation behavior was discussed through simple finite element analysis. The analysis results shows that the strain energy density W under the Square-shape and the L-shape tests were larger than those under the other tests.

The goal of this work is to find a suitable method based on Itoh-Sakane model to estimate fatigue life of notched specimens under multiaxial low cycle fatigue under non-proportional loading, accounting of notch sensitivity and crack initiation position. Cylindrical bars of Al6061 aluminum alloy and AISI 316L stainless steel with four values of stress concentration factors referred to the net section K_t,n 1.5, 2.5, 4.2 and 6.0 have been tested. Aluminum alloy features a lower notch sensitivity compared to steel. Cyclic curves evidenced a high additional hardening caused by non-proportional loading for steel and low additional hardening for aluminum. Low cycle fatigue test results evidenced a reduction of fatigue life for non-proportional loading both for aluminum and steel. Furthermore, the crack initiation position resulted moved from the notch tip for low values of K_t,n only in case of steel. The phenomenon has been thought to be dependent on the additional hardening. Stress concentration factor evaluated in the elastic field K_t,n has been included in the Itoh-Sakane parameter to evaluate fatigue life, returning an overestimation for high values of K_t,n Material notch sensitivity and crack initiation position have been taken into account through a new stress concentration factor to further modify the model, returning sound results.

Fretting fatigue process have many features such as early stage crack initiation at contact edge, very slow crack propagation and fatigue failure after very long life operation. In previous paper we present fretting fatigue model which was considering the wear process, and this model can explain these fretting fatigue features reasonably. But, the estimation of fretting wear process requires a large amount of labor, so this precise wear estimation method is not suitable for actual design site. In this paper we try to present simple fretting fatigue limit and life estimation method using critical distance stress theory. In this method the critical distance rc for fatigue limit estimation can be derived using fatigue limit of smooth specimen and threshold stress intensity factor range ΔK_th. And the critical distance r’_c for fatigue life estimation can be derived using tensile strength of smooth specimen and fracture toughness K_IC. And we apply this simple fatigue limit and life estimation method for the fatigue strength evaluation of fretting fatigue strength improved models such as grooving at contact edge. And finally we confirm the validity of this simple fatigue life estimation method and fretting fatigue improvement by providing groove at contact edge by fretting fatigue tests.

Stress distribution of brake disks during braking is complicated due to sliding contact and frictional heat. To investigate the effect of sliding contact on fatigue strength of low alloy steel, a new fatigue test method which enables to apply cyclic loading with sliding contact is developed. Two main results are obtained by this method. Firstly, the fatigue life with sliding contact is longer than that without sliding contact at finite life regime. Wear volume measurement results suggest that the condition with sliding contact has longer life because fatigue damaged layers are possibly worn away. Secondly, the fatigue limit with sliding contact is 36 % lower than that without sliding contact. Moreover, the fatigue tests without sliding contact have no fatigue failure at more than 10⁶ cycles, whereas the tests with sliding contact have. To discuss the fatigue limit reduction caused by sliding contact, fatigue tests applying sliding contact prior to cyclic loading are conducted. The fatigue tests after sliding contact have no fatigue failure at more than 10⁶ cycles similar to the tests without sliding contact. This result indicates that change of surface properties such as surface roughness during the fatigue tests due to sliding contact is one of the main causes of the fatigue limit reduction. Measured surface roughness actually increase with increasing of sliding time. Predicted fatigue limits by using √area parameter calculated from surface roughness correspond well to experimental fatigue limits. Therefore, it is concluded that surface roughness variation due to sliding contact much affects on fatigue strength of the tested low alloy steel.

The initiation and growth of internal fatigue crack in Ti-6Al-4V were non-destructively observed using synchrotron radiation micro-CT at the large synchrotron radiation facility SPring-8. From the observation result, the initiation life and growth rate of internal cracks were measured. Numbers of cracks were detected by repeating a combination of a fatigue test and micro-CT. The initiation lives of these cracks were widely different from each other. The crack length just after the initiation was measured, and the relationship between the crack initiation life and the size of crack origin was investigated. As a result, the initiation lives had no apparent relationship with the initial crack lengths; that is, there is a possibility that the size of crack origin, which is a facet formed at α phase, had no influence on the following growth behavior. Additionally, the crack growth behaviors had nothing to do with their initiation lives; for example, some cracks with short initiation lives didn't show apparent growth for a while after initiations. The growth rate of internal crack was less than 10^-10 m/cycle, and was significantly lower than that of surface crack. The slow growth rate of internal crack might be due to the vacuum-like environment inside the crack.

Gigacycle fatigue tests were conducted at 100Hz for three years and at 20kHz for one week on heats A and B of SUS630 stainless steels. 480°C (H900) and 580°C (H1075) aging samples were prepared. In the gigacycle fatigue tests, almost all specimens showed internal fracture in case of H900, while H1075 showed surface and internal fractures in short and long life regions, respectively. In the gigacycle fatigue properties, although the heat A revealed higher fatigue strength than the heat B, the difference was small between the H900 and H1075. The gigacycle fatigue strength of the present materials was lower than that of other high-strength steel in spite of almost equal inclusion sizes.

Using a metal plate specimen with a through hole embedded by epoxy resins, fatigue delamination behavior along the resin/metal bonded interface was observed. The metal plate is an aluminum alloy and the resins are ThreeBond 2222P and 2249G with low and high bonding strength, respectively. The interface was observed by a digital microscope and AE (Acoustic Emission) signals caused by the delamination was measured. As a result, high AE signals are counted for 2249G. Opening and sliding displacements along the interface delamination were evaluated by DIC (Digital Image Correlation) method. The experimental results obtained from DIC method are smaller than theoretical values calculated from FEM analysis for 2222P. On the other hand, the experimental results are larger than theoretical values for 2249G and thereby the stress intensity factors evaluated from measured opening and sliding displacements are larger than those evaluated from FEM model.

The short-fiber reinforced plastic made by injection molding have three-layer structure where two skin layers sandwich the core layer. The fiber direction on the skin layer of injection-molded plates is nearly along the molding flow direction (MFD), and that of the core layer is perpendicular. Three types of specimens loaded to parallel (MD), 45°(45°) and perpendicular (TD) to molding direction were fatigued. As a result, fatigue strength decreased in the order of MD, 45°, TD and the stiffness of the specimens decreased with stress cycles. Crack initiation and propagation life were estimated and the cause of the decrease in the stiffness was discussed.

The influence of plate thickness on the crack propagation behavior was studied by using center-notched specimens which were cut from injection-molded plates (IMP) of short carbon-fiber reinforced polyphenylene sulfide(PPS) at two fiber angles relative to the molding flow direction (MFD), i. e. θ=0° (MD), 90°(TD). The thickness of IMP was 1, 2 and 3mm. IMP have three layer laminated structure where the fiber orientation in the shell layer was parallel to MFD and that of the core layer was nearly perpendicular to MFD. The fraction of the shell layer decreases with decreasing plate thickness. The macroscopic crack propagation path was perpendicular to the loading axis in MD and TD, showing mode I propagation. In the relation between crack propagation rate, da/dN, and stress intensity factor, ΔK, da/dN increases with increase in thickness for MD. Conversely, da/dN decreases with increase in thickness for TD. Crack opening displacement obtained by DIC (Digital Image Correlation) method is smaller than that analyzed by FEM in 1mm IMP.

In fluid machinery operation, besides cavitation impact load, other external loads such as centrifugal force and hydraulic pressure do exist. These loads could generate not only cavitation erosion but also cracks on the machine components. To repair these damages, coating technology utilizing epoxy resin materials is often applied. However, the damage behavior of epoxy resin under a mixed condition of cavitation and external loads has not been understood comprehensively. In the present work, evaluation on the crack growth mechanism in epoxy resin specimen under both tensile load and cavitation impact was conducted. An experimental apparatus for conducting the test was specially manufactured so that a tensile load can be applied at the same time with a cavitation load to the specimen. An initial crack was firstly made in the specimen. Them, the tensile-cavitation tests were done inside a tank filled with distilled water with fixed temperature. When only cavitation was applied to the specimen, the initiated crack did not propagate while erosion damages were generated on the surface. When only tensile load was applied, the initiated crack propagated slowly. Moreover, the growth rate increased as the load was increased. However, when both tensile load and cavitation impact were applied, the crack growth rate was significantly accelerated. The crack growth rates at this condition were then quantified and compared.

We had clarified the relationship of fatigue strength reduction factors K_f of engineering plastics PBT, PEEK, PC between strain concentration factor K_ε in the region of high- and low-cycle fatigue. In this study, we have proposed new design method of calculation on the basis of the size-effect defined on the ratio of standard smooth fatigue specimen to damaged area of structures size. In order to obtain the new conceptual size-effect : S, low- and high-cycle fatigue tests carried out on 100 smooth specimens made of super engineering plastics :PEEK. As the results of those experiments and calculations, it is clarified that life-size-effect :S_life is N_f0^0.81 for large structure, N_f0^1.30 for small structure, and strength -size-effect :S_st is ⊿ε₀^0.69 for large structure, ⊿ε₀^1.53 for small structure.

To quantitatively investigate the cause of the changes in arithmetic mean roughness R_a and arithmetic mean waviness W_a of austenitic stainless steel under low-cycle fatigue loading, precise observation focusing on slip bands and grain deformations was conducted on SUS316NG. During the fatigue tests, the specimen's surface topography was regularly measured using a laser microscope. The surface topographies obtained were analyzed by frequency analysis to separate the surface relief due to persistent slip bands (PSBs) from that due to crystal grain deformation. The height caused by PSBs and that by crystal grain deformation were measured respectively. As a result, the both heights developed with the increase of usage factor (UF). The amount of increase in the heights with respect to UF increased with strain range. The trend of development of both heights was similar with the trend of R_a and W_a. A comparison between R_a and the height caused by PSBs showed that these values strongly correlated with each other. A comparison between W_a and the height caused by crystal grain deformation also showed that these values strongly correlated with each other. Consequently, the surface texture parameters R_a and W_a represent the changes in the heights of surface reliefs due to PSBs and crystal grain deformation.

Deformation and fracture of fatigue in an ultra-high strength maraging stainless steel were investigated to understand the effects of frequency on fracture mechanisms. The servo-hydraulic testing machine was used for fatigue tests at a frequency of 30Hz. After mechanical tests, the fracture surfaces were observed by scanning electron microscope (SEM). It was found that the tensile fracture surfaces show ductile characteristic of dimples although the elongation of the specimen is as low as 3%. The fatigue limit for 10⁷ cycles at 30Hz is 500MPa, which is much higher than that (407MPa) at 20kHz, because of no melting occurred during fatigue tests.