ITRO treatment is one of surface treatments based on flame treatment, which is used liquid petroleum gas containing silane compounds, and forms silica deposits on substrates. This treatment brings high adhesion strength for aircraft coatings with only one-time treatment. ITRO treatment could be promising technology in aviation industry because that is quick, easy, clean and less costly process compared with traditional surface treatment processes such as anodizing or chemical conversion process. However, few studies have focused on ITRO treatment and the bond mechanism of ITRO treatment has not been clarified so far. In this research, the bond mechanism of ITRO treatment was investigated by using Fourier transform infrared spectroscopy. The analysis of the non-coated samples revealed that silica, absorbed water and SiOH groups exist in the silica deposits on the aluminum substrates and the spectral absorbance of them increases as the number of treating increases. The SiOH groups could be the source of hydrogen bonds and the amount of them depends on the number of treating. Furthermore, the analysis of the coated samples revealed spectral peaks of ester and ether groups in the coating materials shift to low wavenumber. This means new hydrogen bonds were formed inside the coating materials around the silica deposits formed by ITRO treatment.

In design of bolted joints, it is important to understand bolt axial tensions to avoid joint loosening. In recent years, FEM models with three dimensional threads have been applied to analyze mechanical characteristics of bolted joints. In this paper, tightening experiments, elastic FEM analyses and simplified calculations were conducted for bolted joints which consist of two hollow discs tightened by a hexagonal bolt with flange and a hexagonal nut with flange in order to obtain relationships among rotation angle θ [°], bolt axial tension F [kN] and tightening torque T [Nm]. As the results, it was shown that the relationships between the rotation angle θ [°] and bolt axial tension F [kN] obtained by FEM analyses with three dimensional thread have good agreement with the experimental results in a range of an initial tightening, which has non-linear relationship between the rotation angle θ [°] and bolt axial tension F [kN]. After tightening the nuts and bolts until rundown condition, the relationships become linear in both experiments and FEM analyses. However, the values of bolt axial tensions obtained by FEM analyses are a little higher than experimental ones at a same rotation angle. Also, stress distributions of the bolted joints are revealed.

Recently, weight reduction of vehicles has been advanced to improve the fuel efficiency. It is necessary to use not only steel but also various kinds of materials in order to reduce weight. Therefore, we need to apply methods to join different materials. So, we focused on spot welding, which is the most frequently used joining method in automobile production lines. Strength analysis of dissimilar spot welding using stainless steel and copper is conducted. We use SUS304 and C1100 as test pieces. After spot welding, we observe the cross section using an optical microscope and scanning electron microscope. Also, the temperature distribution of the cross section is calculated using finite element simulation software "ANSYS". In addition, a tensile shear test is also conducted. Heat is mainly generated not in the contact surface but in the steel. Also, as the current is increased, the heat generation increases too. As the base material softens by the heat, the deformation by electrode force also increases. Some parts of the contact surface are melted. In addition, atomic diffusion can be observed under all current. Moreover, the strength improves and stabilizes as the current is increased. The reason of heat concentration in the steel is large electrical resistance of the steel. Also, as temperature becomes higher, base materials are easy to deform because of characteristics of Young's modulus. Dissimilar spot welding of SUS304 and C1100 can be joined by melting, diffusion and deformation on the contact surface.

In recent years, it has been promoted to apply aluminum alloys to automobile structural components in order to reduce body weight and improve the fuel efficiency. On the other hand, resistance spot welding is commonly used as the method of welding of thin steel plates. Therefore, it is demanded that the dissimilar material joining used resistance spot welding at the production line of automobile. It is known that joining strength of peeling direction is increased as thickness of intermetallic compound edge part decrease for Fe-Al dissimilar material resistance spot welding. However, it is known that in spite of thickness of intermetallic compound edge part decrease, joining strength of peeling direction is not increased depending on conditions of construction of welding conditions. Therefore, it is thought that there is the factor other than thickness of intermetallic compound edge part affects cross tension strength. In this study, in order to investigate the factor affects cross tension strength, crack propagation behavior was observed and conducted Vickers hardness test at resistance spot welded area in aluminum alloy. As the result, it was indicated that the crack was progressed in the aluminum alloy of melted area. In addition, it was confirmed that there was the difference of crack propagation behavior for the aluminum alloy of melted area, depending on the shape of the electrodes. Moreover, cross tension strength was increased as the average Vickers hardness of aluminum alloy of melted area increased. Therefore, the average Vickers hardness of aluminum alloy of melted area suggested to be a factor affecting cross tension strength.

In recent years, electronic devices have remarkably achieved miniaturization and high performance with the development of MEMS. In addition, the current density in the interconnect has risen due to the increase of electric energy accompanying the development of power devices. The delamination of thin film due to thermal stress and electromigration has become a problem. One method to improve the adhesion strength of thin film on a substrate is using an adhesion layer such as Cr or Ti between the thin film and the substrate. However, this method has the disadvantages that additional materials are required and the thickness of the interconnect increases. The adhesion strength of the thin film needs to be improved itself. This study proposed a method to apply high-density current with high frequency to thin film to improve the adhesion strength of it. The Au thin film (Size: 5 mm×45 mm×150 nm) was deposited on a glass substrate by radio frequency sputtering. Then, high-density current with high frequency was applied in thin film and the adhesion strength was measured by using peel test. As a result, the adhesion strength was improved by 20% or greater by applying high-density current with high frequency. Therefore, this method is expected to be a new strength improvement method for thin film.

In order to investigate the influence of laser processing on interfacial fracture toughness of coatings, a convex edge-indent test was carried out on the specimens. The surface of the aluminum alloy plate with various curvatures were laser processed to create straight grooves, and Cr₃C₂-NiCr and WC-Co coatings were thermal sprayed on the plates. The convex edge indent test was carried out by pressing a conical diamond indenter from the surface of the convex shaped specimen at a distance from the edge. The results showed that the load lineally increased with increasing indentation depth, and delamination occurred at the maximum indentation load. The delamination loads of the Cr₃C₂-NiCr coating were larger than those of the WC-Co coating. The measured interfacial fracture toughness of the Cr₃C₂-NiCr coating also showed larger values than that of the WC-Co coating.

A model experiment was conducted using paraffin wax to clarify the residual stress generated during solidification and adhesion of molten droplets. In the experiment, molten paraffin droplets were dropped onto the center of a stainless steel substrate, and the strain generated on the substrate back surface was measured by strain gauge. The experiments were conducted with changing material of paraffin wax and substrate temperature. By comparing the experimental results, the influence of adhesion state along the interface on the strain was investigated. It was also found that wettability of paraffin wax on the substrate could affect the strain. A thermal-structural coupled analysis was conducted to quantitfy the effects of material properties of paraffin waxes, the geometry of coating and interfacial property between the substrate and the coating on the strain. According to the analytical result, it was found that the larger Young’s modulus, the larger stress-free temperature and the larger coefficient of thermal expansion lead to the larger strain. It was also shown that the strain could be diminished when substrate temperature is low or melting point of paraffin wax is high, due to decrease in adhesion area on the interface between the substrate and the coating.

There are several micromechanics tests available to study the fibre/matrix bond. The best-known are fragmentation, pull-out test and micro-bond test. This study focuses on study the constraints of micro-bond test, and the results are compared with the pull-out test, that have similar geometry, on the basis of intensity of singular stress fields. In order to study the effect of bonded length l_b on the Intensity of Singular Stress Fields (ISSF) at the dagerous point, other constraints and material combination are set to be same in the Finite Element Method (FEM) analysis. Normal stress on the interface is tension at the near intersection (Point E), while it is compression at the far intersection (Point A). This stress condition is similar to that in pull-out test, in which normal stress along the axial interface is compression at the bured end (Point A*) and tension near the intersection (Point E*). No matter how the bonded length l_b changes, the near intersection (Point E) in micro-bond test is the most dangerous point. The effect of bonded length l_b on ISSF at the near end intersection (Point E) show similar trend in micro-bond test and pull-out test. For the material combination and constraints discussed in this paper, the ISSF of the most dangerous point in micro-bond test is about 1.5 times that of pullout test.

In the earlier studies, the singular indexes at the vertex and along the side on the interface in the 3D bonded body were computed by the eigen analysis based on the FEM. It has been shown that the eigen equation has the single real root under bad pair condition. Then, the authors have proposed the proportional method for calculating the intensity of the singular stress field (ISSF) at the vertex in 3D bonded body. In this study, the ISSFs are calculated by changing the material combinations. The differences between dimensionless ISSFs for 3D bonded body and 2D bonded plate are discussed. It is shown that dimensionless ISSFs for 3D bonded body is almost controlled by Dundurs’ parameters.

Adhesive bonding is light weight, low cost and easy to manufacture, so it is used in various industrial fields. In order to ensure the reliability of adhesive bonding, an appropriate evaluation of adhesive strength is indispensable. However, since experimental evaluation has a large time and economic burden, a simple and practical delamination criterion and evaluation method are required.

The authors proposed a method for evaluation adhesive strength by Intensity of singular stress field (ISSF) and showed that bond strength can be easily evaluated. In the previous study, analysis was performed in consideration of the three-dimensional geometry of the specimen, and it was shown that the ISSF distribution at the interface end was obtained accurately. In this study, the fracture surface of the actual specimen was observed, and the mechanism by which the fracture occurred was considered from the comparison with the analysis result.

The distribution of ISSF is constant at most positions, but once it approaches the fillet, it decreases once and then increases again, returning to almost the same value as the center. It was also found that the position where the ISSF decreases becomes closer to the center as the adhesive layer becomes thicker. As a result of observing the fracture surface, the fracture origin occurred not in the corner but in the straight part of the bonded end face, which is considered to be in good agreement with the analysis result.

The singular stress field induced at the edge of the interface is determined by the shape and material combination of the interface edge. In the case of lap joints, two different singular stress fields appear depending on the bonding angle. The stress field with two singularity indices λ₁ and λ₂ can be expressed by superposing the different singular terms with λ₁ and λ₂. Therefore, in this study, the stress intensity factors of a small interfacial crack at the interface edge are separated into two components corresponding to the two singularity indices. The dimensionless factors of small interface crack can be obtained by using the result of two different crack dimensions.

Thin crystal layer with nanoscale thickness is used in many electronic devices. Misfit dislocations are caused between dissimilar crystal layers spontaneously, and defects often occur from these misfit dislocations. It is useful to simulate these defects to protect the occurring of these defects. We evaluated the stress field along the interface between Si_0.75Ge_0.25 and Si using the molecular dynamics with MEAM potential. Similar singular stress fields around misfit dislocations were observed along the interface between Si0.75Ge0.25 and Si by the molecular dynamics, the molecular statics and the anisotropic elastic simulation. The molecular statics did not consider the thermal stress, but the influence of thermal stress is much smaller than the stress caused by the lattice mismatch. In this study, the molecular dynamics could not simulate the defects occurring from the misfit dislocations.

The stress intensity factor for an interfacial corner, which are compatible with that for a crack, can describe the singular stress field around it. However, due to the difference of the singular order with the angle of a corner and the combination of materials, we cannot compare the stress intensity factors for different singularity orders. In this study, we estimated the fracture toughness of jointed interfacial corners with different opening angles with their stress intensity factors using the molecular statics. The fracture toughness shown by the stress intensity factors exponentially decreased with the increase of singular orders to 0.5 that is the singular order of a crack. This trend is the same in several models with different materials. According to these results, we will show that the fracture toughness at the jointed interfacial corner can be translated to the equivalent stress intensity factors of a crack.

In baseball, an increasing number of players wear batter helmets extended to the chin, and some pitchers and fielders wear head protector with cushioning material. For pitchers and fielders, a lightweight and flexible head protector that can be worn without a sense of incongruity is required due to the intensity of sports activities. In this study, we examine the application of cushioning material for head protector of soft epoxy foam which is extremely sensitive to strain rate and flexible at low strain rate but has high energy absorption capacity at high strain rate. In particular, assuming that a hard ball for baseball hits the head, the head protection performance of the soft epoxy foam is evaluated by a ball impact test.

Breaking ice with an ice pick is known as one of the ice fracture phenomena. In the previous study, we carried out the percussion test of the ice specimen using the conical and spherical indenter. It has been shown that the indenter shape had an influence on the energy required to fracture ice. In this study, the quasi-static indentation test was performed in a low-temperature environment using a chamber and a cooling system in order to investigate the fundamental deformation and fracture phenomena of ice. The conical indenter of 90° was used. The indentation rate was changed to set to three of 0.02, 0.2, and 2 mm/s. The test was conducted after keeping the temperature in the chamber at 10±1℃ for 360 s. The load-displacement relationship of ice during deformation increased and decreased due to crack formation. When the indentation rate was high, it was observed that the ice pieces were spattered during deformation, but not when the indentation rate was low. It was suggested that the deformation process of ice was changed from melting by friction and pressure to crack formation when the indentation rate was increased. In addition, it was shown that the maximum load, which means fracture load, decreased with increasing the indentation rate.

The Lamb wave reflection and transmission characteristics in bent plates were investigated experimentally. The specimen was fabricated by performing a three-point bending for a flat aluminum alloy plate of 1 mm thickness. The lowest-order symmetric (S0) and antisymmetric (A0) Lamb modes were excited separately for the incident wave to the bent zone in the frequency range lower than the cutoff frequencies of the higher-order modes using a piezoelectric transducer with polymethylmethacrylate (for S0 mode) and polytetrafluoroethylene (for A0 mode) wedges placed on the flat zone of the specimen. The temporal reflection (including the incident wave) and transmission waveforms were then measured on a plate surface on both sides of the bent zone using a laser Doppler vibrometer. The signals corresponding to S0 and A0 modes were extracted from the recorded waveforms using rectangular windows, Fourier transformed, and normalized by the amplitude spectrum of incident wave to obtain the amplitude reflection and transmission spectra. Both S0 and A0 modes were found to be generated in the reflected and transmitted fields even in the case of single mode incidence of either S0 or A0 mode to the bent zone. Furthermore, the reciprocal relation was shown to nearly be satisfied. In other words, the amplitude reflection and transmission coefficients of A0 mode for the S0 mode incidence were favorably compared with those of S0 mode for the A0 mode incidence.

There is a method of sticking a film on a glass plate to prevent the fragments from scattering when the glass plate fractures. This method is widely used because it can be used on existing glass plates simply. Prior research has shown that sticking a polymeric film to a glass plate not only prevents the shattering of the fragments at the time of fracture but also suppresses the crack propagation of the glass plate and improves the strength until fracturing starts. However, the mechanism for strengthening the impact resistance of the glass plate by applying a film has not been fully clarified. The purpose of this study is to elucidate the strengthening mechanism of the glass plate by applying the polymeric film by conducting impact fracture analysis of the glass plate attached by the finite element method. Therefore, we attempted to create a model with high reproducibility of the fracture process by simulating the impact test conducted in the previous research by numerical analysis. In addition, we compared the glass fracture process obtained by analysis and photoelasticity experiment. From the results of numerical analysis, the model was able to follow the strain up to the start of fracture due to the crack opening in the glass plate. However, it is thought that it is necessary to construct a new glass model in the low speed range because the simulation of the fracture mode is insufficient.

In the previous study, authors have investigated the effect of foam structure on compressive properties of foamed PE film using various foam structure specimens. This result suggested that the cell structure, aspect ratio of the cell shape, of the specimen significantly affects compression properties. In this research, based on the past experimental study, the mechanism of the effect of cell structure was investigated using numerical experiment. To investigate of the effect of cell shape, a simple morphology and repetition model was used. A model consists of upper, lower rigid walls and cell wall. Three models with different aspect ratios were prepared to evaluate the effect of cell shape aspect ratio. The compressive numerical experiments were performed by applying the constant velocity in the upper rigid wall. The constant velocities were 0.75 and 7.5 m/s (initial strain rate: 5.0×10¹ s^-1 and 5.0×10¹ s^-1). As a result of numerical examination, it was confirmed that when the aspect ratio of cell shape was different, the deformation mode changed due to the difference in the curvature of the cell wall at the initial stage of the deformation. It was found that the difference in this deformation mode influences the slope of the elastic response. From this result, it was clarified that the slope of the elastic response is caused by the difference of the aspect ratio of the cell.

This study aims to evaluate the interfacial strength of aluminum alloy/epoxy resin adhesive by using two different tests of impact loading and quasi-static loading. For the impact test, laser shock adhesion test (LaSAT) was carried out. This method uses a strong shock wave induced by a laser ablation in order to apply the tensile stress at interface. The shock wave propagates from the back surface of substrate to interface. When the tensile stress wave reaches the critical value of interface, the delamination occurs. Since the magnitude of tensile wave is dependent on pulse laser energy, we gradually increase the laser energy to identify the critical energy for delamination. Moreover, the shock wave propagation was simulated in Finite Element Method (FEM). This numerical simulation calculates the applied tensile stress in the interface when the delamination occurs, and then we estimate the dynamic interfacial strength of Al alloy/epoxy resin. In addition, we carried out the uniaxial tensile test for estimating the quasi-static interfacial strength.

In order to improve the creep resistance to the PTFE gasket, a particulate-filler is compounded. Indentation test was carried out using TMA with Berkovich indenter to evaluate the viscoelastic characteristics of a PTFE based sheet gasket. The time-temperature superposition principle was applied to obtain the master curve of the creep compliance of gasket material at elevated temperature. The shift factor was arbitrarily determined. It is found that the higher the blending ratio gets, the stronger the creep resistance becomes by examining the influence of this particulate-filler blending ratio on creep characteristics of gasket.

Accurate prediction of layer construction consisting of clay, silt, sand and gravel is important to improve the ground for the construction of high-rise buildings, because the process parameters in jet grouting must be controlled to make the improvement structure with high-quality. Even if the core sample is obtained to know the layer construction, it is not uniform over wide area. Therefore, when drilling the ground before inserting a rod equipped with a nozzle for cement ejection, some physical quantities were monitored and used for the prediction of layer construction. Since rapidly oscillating data was obtained in the real ground boring, statistical analysis of the obtained ground boring data was performed. To this end, cumulative probability of the electric current and that of the water pressure were found to be useful to distinguish the soil type.

In this study, the elastic wave propagation characteristics in isogrid structures are investigated by numerical analysis. By applying Bloch’s theorem as the boundary conditions to the unit cell of isogrid structure modeled by the finite element method (FEM), the dispersion surfaces of isogrid stuructures are calculated. As a result, no bandgaps are found in the frequency range of 0 kHz to 8 kHz. It is also found that while the second branch (dominated by in-plane transverse wave) and the third branch (dominated by longitudinal wave) propagate in an isotropic manner, the first branch (dominated by flexural wave) has anisotropic characteristics.

In this study, tensile tests of austenitic stainless steel 304 at room temperature were performed under various strain rate conditions ranging from 0.001/s to 1,000/s using smooth round bar specimens. From experimental stress-strain data, stresses at various strain levels were extracted and the fitting results using the Johnson-Cook strength model were compared. As the strain rate increases, yield strength increases monotonically, but tensile strength decreases and then increases. Uniform elongation also decreases and increases slightly with the increasing strain rate. These trends are related to the strain-induced transformation of metastable austenite γ phase to α’-martensite phase. Because of these complex behaviors, fitting results using the Johnson-Cook strength model vary depending on the strain level.

Fluid–structure interactions (FSI) which are multi–physics between fluid and structure are a crucial consideration in the design of many engineering systems. Considering the fact that most FSI problems are transient and there are few closed–form solutions for the problem, this paper applies normal mode methods to investigate the dynamic transient response of a plate coupled with fluid subjected to impact loadings. The method is available for various types of impact loadings such as concentrated force and surface pressure. Considering a small oscillating induced by the plate vibration in fluid, velocity potential function is used to describe the fluid motion. To validate the theoretical results, an efficient and flexible MATLAB finite element procedure using fully vectorized codes is developed. MITC4 element is used to simulate the plate, and the acoustic pressure element is used to simulate the fluid. At last, the drop test of a plate coupled with fluid is conducted. The results are compared with the transient responses for displacement and natural frequencies.

Re-defined DSGZ model has been proposed to effectively determine stress-strain relationship for thermo-plastic materials especially showing non-uniform deformation such as necking behavior during tensile test. Thanks to Rational Bézier curve, material constants of the proposed model can easily be identified from an experimental result, and adjustable parameters of the proposed model can also be determined by Simplex method. An example result with the proposed model is provided where fitted curve based on the proposed model successfully predicts experimental result.

Foamed resin materials are widely used as a protective cushioning material in sports and daily life. They have been developed according to various purpose. The compressive properties of foamed resin materials depend on base material, cell structure and density. This study proposes a molding method of epoxy foams by using the extraction method. The extraction method makes it easy to produce low density epoxy foams by using sodium chloride as nucleating agent and water as solvent. In addition, this study revealed effect of the density of the molded epoxy foam by changing the mass ratio of main agent, curing agent, and nucleating agent. The density of the epoxy foam can be decreased from 1.1 g/cm³ to 0.15 g/cm³. Compression tests were performed to evaluate density effects on compressive property of foams. The experimental results show that compressive stress decreases as reducing density of epoxy foam. In addition, it revealed that epoxy foams by extraction method have excellent flexibility.

This research work discusses the quality assurance of 3D printed or additively manufactured metal products by stochastic finite element analysis considering uncertainties. The variability of the physical parameters of material and geometrical imperfections should be considered as well as the uncertainties in the boundary conditions in experiment or in practical use. In this paper, a dental prosthesis made by titanium alloy, Ti-6Al-4V, is studied. The elasto-plastic properties were measured by static tensile test using 3D printed dumbbell type specimens. The geometrical model was generated by micro-CT images of printed prosthesis. The experimental results were largely scattered but they were within the predictions when the uncertainties in the constraint condition was assumed. The presented numerical simulation will be useful for both design and quality assurance.

The concrete is the most basic structural material and it is used for various structures. Therefore, many impact experiments have been performed so far. However, most of experiments have been performed for only normal strength concrete. With that kind of background, shock experiments have been performed to obtain the shock compression behavior of ultra-high-strength concrete in this study. The stress wave profiles propagating into the impacted concrete are directly measured by using PVDF and Manganin stress gauges embedded in specimen. The compression-release paths under shock loading are derived from the measured stress wave profiles. The derived loading-unloading paths show large hysteresis. It is found that the ratio of energy consumed by void collapse to the impact energy reaches about 80% in the impact stress range of about 1 GPa. These results indicate that the large part of the work by shock-loading is consumed by the collapse of the pores inside concrete.

Fluid-structure interaction (FSI) is important in the design of plants and piping systems. In the previous studies, it has been observed that cavitation bubbles were incepted at the solid-fluid interface with FSI. It has confirmed that the transmission behavior of the stress/pressure wave across the solid-fluid interface was changed due to the cavitation inception. However, quantitative evaluation of the effect of cavitation generation on wave propagation at a solid-fluid interface with FSI was not sufficient. This study aims to quantitatively evaluate the effect of dynamic cavitation inception on wave propagation at a solid-fluid interface with FSI by considering energy transfer from solid to fluid. An impact experiment was conducted with a free-falling projectile which hit the cylindrical solid buffer placed on top of the water surface within the elastic tube. The surface wettability of the buffer and the surface tension of water were varied to change the intensity of cavitation. It was confirmed that at the interface with worse wettability (large contact angle), energy transmitted into water was consumed by cavitation inception from the solid-fluid interface, thus the potential energy of water in the pipe was reduced. Then, the kinetic energy reduction of the buffer and the potential energy of water in the tube were estimated theoretically. The potential energy of the in-pipe water was 66%, 71% and 72% of the lost kinetic energy of the buffer with contact angles of 93.2°, 77.1°, and 12.5°, respectively. Consequently, the effect of cavitation inception at the solid-fluid interface with FSI on wave propagation could be quantitatively evaluated by considering the energy transferred from the solid to the water in the pipe.

The fatigue life prolonging of an aging advanced building is currently needed. In prolonging fatigue life, it is important to reduce the rate of progress of internal fatigue cracks. The rate of fatigue crack propagation is evaluated by using the effective stress intensity factor which is the ratio of stress at opening and maximum stresses. Based on the Paris law, if the effective stress intensity factor decreases, the rate of progress decreases. Therefore, from the viewpoint of fatigue life prolongation, attention has been paid to a method of reducing the effective stress intensity factor in recent years. In this study, fine particles and pulsed current sintering were used for crack repair. In this research, we applied pulse current sintering to have no particle diameter dependence. At first, a precrack of a test specimen was filled with iron fine particles and pulsed current sintering. In order to confirm the bonding state, the cut surface was observed measured using Scanning Electron Microscope (SEM). After the SEM observation, fatigue test was conducted. These experimental results indicated that our easy repair method prolong fatigue life of precrack.

Polypropylene/Polyamide11 (PP/PA11) alloy has a unique phase structure, which is called “salami structure”, of nano order. It has been found that this material is superior to a polycarbonate alloy known as an impact resistant resin. However, the impact evaluation method is Charpy test or puncture test. Therefore, the compressive strength of PP/PA11 alloy and its strain rate dependence are unknown. In this study, in order to elucidate the compressive deformation properties of Polypropylene/Polyamide11 alloy with unique phase structure at a wide range of strain rates, this dynamic deformation properties are evaluated using a cam mechanism. 100%PP/PA11 alloy (PP/PA11) and 100%PP (PP) were prepared. First, the elastic response of PP is higher than that of PP / PA11. It is considered that the rigidity of the entire specimen is reduced due to the internal PA11 phase. In the early stage of deformation, which exceeds the elastic response and has a strain of approximately 0.2 or less, PP has higher flow stress than PP/PA11. On the other hand, the flow stress of PP/PA11 becomes higher than PP as the strain increases. The difference becomes more prominent as the strain increases. This tendency is similar to the results of the previously reported the impact test.

Measurement of road surface friction coefficient is important to improve vehicle safety. Recently, various advanced driver-assistance systems have been developed for vehicles. Generally, the driver-assistance systems use information obtained from wheel speed sensors, acceleration sensors, yaw rate sensors etc. However, road surface friction coefficients are difficult to be measured accurately in real time by using usual sensors. As a tire of a vehicle is only parts to contact with a road surface, various studies try to develop an intelligent tire capable of measuring road surface friction coefficients. The authors have already proposed a method to measure road surface friction coefficients from strains induced on the tire-sidewall. This study clarifies the effects of the tire pressures and slip ratios on the measurement results of the road surface friction coefficients with the proposed method.

Measurement of road surface friction coefficient is significant to improve advanced driver-assistance systems (ADAS)．Almost of ADAS use the information obtained from wheel speed sensors, acceleration sensors, etc. However, it is difficult to measure the road surface friction coefficients accurately with these sensors. Therefore, in order to develop an intelligent tire capable of measuring the road surface friction coefficients, various studies focus on tires that are the only parts of a car being grounded on road surface. However, such an intelligent tire has not been put to practical use due to the difficulty of stable measurement of deformation induced on a tire and difficulty in estimating the road surface friction coefficients from the deformation of the tire. Therefore, this study focuses on the deformation of a wheel and proposes a method to measure road surface friction coefficients from strains induced on the surface of not a tire but a wheel. The study clarifies the relationship between the strains on a wheel and the loads acting on the tire from the grounding surface by using an experimental apparatus capable of simulating complete slip running. In addition, a simple method of measuring road surface friction coefficients is proposed by means of the obtained relationship.

In this study, shock compression experiments are conducted on polycarbonate and PMMA to investigate their shock responses and spall behavior. The stress wave profiles propagate into samples are measured using PVDF piezoelectric film gauges embedded in samples. The spall strengths are determined by measuring free-surface-velocity profiles by means of the VISAR. Both measurements are simultaneously performed. The obtained relationship between shock velocity and particle velocity in PMMA show the non-linear nature below the particle velocity of 0.4 km/s indicating viscous effects. In the case of polycarbonate, its shock velocity shows bilinear relation with its particle velocity. Even though the tensile and compression strength of polycarbonate and PMMA show the strain-rate hardening, the spall strength itself does not show strain rate dependence in both materials. However, the spall strength obtained in both materials shocked above the point of discontinuity in each shock velocity – particle velocity relationship shows lower value than that obtained below that point. This result indicates that the microstructural change at shocked state effect on the spall behavior although the spallation occur the tensile stress state after compression release.

The purpose of this study is to evaluate the surface condition of road material, such as dry, wet, icy and snowy, by using the ultrasonic system on the moving vehicle. As a first step, we use ultrasonic transducer with a central frequency of 40 kHz, and five kinds of road material were used as the specimen for examination and verification of the possibility of evaluation by the ultrasonic with moving. The ultrasonic wave 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 is moved at a walking speed for measurement. As a result, five kinds of road material was distinguished by using mean value and standard deviation of maximum amplitude.

The target of this study is to clarify the impact behavior of car body structures for railway vehicles, that have double skin panels made of aluminum alloy, in the event of a collision accident by a numerical approach. As the previous step, we carried out the impact compression tests by using the double skin panels. The test specimen was compressed in extrusion direction at an initial speed of about 10 m/s under two conditions: an overall compression condition for compressing the entire cross-section of the specimen and a local compression condition for compressing a part of it. Under the overall compression condition, buckling deformation mainly occurred at the end of the test specimen. In contrast, under the local compression condition, besides buckling deformation, shear fracture occurred. In both conditions, the force-displacement relationship in each case was almost the same until the force reached the maximum value. After that, its relationship was different from each other caused by the difference in the mode of buckling deformation. We also carried out FEM simulations under the same conditions as the tests. A material model that can express the strain rate dependence of the stress-strain characteristics was used for these simulations. As a result of the comparison between the simulations and the tests, under each condition, the maximum force was almost the same, and the transition of deformation and the force-displacement relationship generally agreed.

It is known that the dynamic behavior of polymers depends greatly on not only the strain rates but also the hydrostatic pressure, and the volume change is caused during plastic deformation. It is desirable to apply material constitutive model considering these mechanical properties in numerical simulation for polymers. It is however still not enough to prepare an easy-to-use material constitutive model considering these mechanical properties in general-purpose numerical simulation code. Therefore, we developed a new constitutive model for polymers and implemented using the user subroutine function of the impact analysis code LS-DYNA. And Mimura et al. measured the plastic Poisson’s ratio of Polycarbonate by Digital Image Correlation method.

In this study, we focused on the volume change during plastic deformation of Polycarbonate, applied this measured plastic Poisson’s ratio to this constitutive model and performed numerical simulation using LS-DYNA to verify the validity of this constitutive model and material parameters.

Bamboo is widely used as a functional and natural material in Japan and several other Asian countries. The novel mechanical characteristics of bamboo are its high toughness, stiffness and lightness. Bamboo’s hollowness enables it to be light to grow faster. However, by being light, bamboo indeed becomes vulnerable to strong winds and can also fail to support its own weight. To overcome this limitation, the woody parts of bamboo are reinforced with thin but tough fibers (vascular bundles). Each fiber is considered to be as rigid as steel. This fact makes us realize that bamboo is one of the wonderful naturally-occurring functionally graded materials. From this point of view, we have investigated the relationship between vascular bundle distribution and bending properties of bamboo. It is known that a cross-section of bamboo revealed the non-uniform distribution of fibers in the woody parts. The density of the fibers progressively turns out to become thicker from the inner to the outer surface, pointing out that the outer parts are stiffer and stronger than the inner parts. This shows that bamboo improves their bending strength by appropriately adjusting the distribution of their fibers. Our present study could help develop advanced materials by mimicking the bamboo model for its lightness and toughness.

In this study, shock-compression experiments have been performed to evaluate the shock-response characteristics of engineering ceramics which are Al₂O₃, Si₃N₄, and ZrO₂. By shock-profile measurements using a laser velocity interferometer, it is confirmed that the shock wave which consists of elastic- and plastic- shock parts propagates into a specimen. The values of compression strength under shock-loading, which are named as Hugoniot Elastic Limit (HEL), for each material are determined from the amplitude of the elastic shock part. In the results of Si₃N₄, it is revealed that the stress wave following the plastic shock wave consists of ramp wave followed by steep shock wave. The formation of the ramp wave indicates the existence of non-crystalline intermediate phase between crystalline low pressure phase and crystalline high pressure phase, and the shock-compressed state of high-pressure phase is denser than the state obtained in previous study. By the comparison of this study with previous works, it is shown that the Al₂O₃ with fine grain structure have higher HEL and shock-deformation resistance than usual Al₂O₃ and the pores in ZrO₂ cause a decrease in its shock impedance. These results clearly indicate that further understanding of microstructural effects is important to evaluate the shock-responses of engineering ceramics.

The enforcement braking device which is the equipment for the forcibly stopping the automobile is used for prevention of the traffic accident and for safety protection of the driver and worker in the road construction region. For the performance improvement of the enforcement braking device on the collision safety and reliability, it is necessary to evaluate the braking characteristics and optimize the structure of the device. In this study, on the arm which was one of the components of the enforcement braking device, the influence of the arm shape on braking characteristic was investigated by model collision test and theoretical calculation.

In this study, a focusing method of Lamb waves is shown for a plate structure with thickness variation using the temporal-spatial inverse filter. An actuator is attached on the plate and a sensor is placed at the location which corresponds to the focusing location. Input and output signals of the actuator and sensor are analyzed in the frequency domain, and a Green function is obtained from the input-output relation. The inverse filter is constructed based on the Green function and the target focusing waveform. The waveform obtained by the inverse filter is used as the input waveform into the actuator to focus the Lamb wave at the initial sensor location. In this study, three-dimensional wave propagation analysis is performed by the elastodynamic finite integration technique (EFIT), and the focusing of the Lamb wave in the plate structure is simulated numerically. As a result, the emitted Lamb wave is focused at the initial sensor location and the target waveform is fairly reproduced by the target waveform. The wave focusing by a single actuator becomes possible by utilizing the effect of reflections at edges and steps of the plate. The temporal and spatial characteristics of the focused Lamb wave are shown and discussed.

The SHB method was conducted to investigate the deformation characteristics of carbon steel at high strain rates. Furthermore, the strain rate dependence was obtained by conducting static tensile tests with a strain rate of 1 × 10- / s to 1 × 10^-1 / s and high-speed tensile tests with a strain rate of 1 / s to 1 × 10³ / s. As a result of the SHB test, a slight stress amplitude was observed near the yield point but a good stress-strain curve was obtained. In the case of a plastic strain of 0.1, the strain rate tended to rise almost linearly in the range of 1 × 10- 3 / s to 1 × 10³ / s. At high strain rates the stress wave amplitude in the high-speed tensile was larger test than that in the SHB method, but it was found that the same value as the SHB method can be obtained by smoothing.

The crash safety structure of the railway vehicles is important as one of the safety measures against the train crews and the passengers in the event of a collision accident. It is impractical to perform collision testing many times using the actual train unit in order to design the crash safety structure. Therefore, the numerical simulation is effective and it is important to validate the analytical accuracy. Firstly, the authors performed the impact test using an actual-size partial stainless-steel carbody structure of a railway leading vehicle for the purpose of validating and improving the analytical accuracy of numerical simulation. Secondly, we carried out finite element analysis under the same condition as the experimental test. We compared the numerical result to the experimental one in terms of each compression loads measured by 6 load cells and the time history of velocity of test specimen. As a result, the numerical result was consistent with the experimental result.

In the past two or three decades, I have studied a number of topics concerning plant biomechanics or plant biomimetics, such as structure of folding paper observed in leaves and flowers of plants, folding storage and unfolding manner observed in Sensitive Plant, mechanical functions of sepals and petals observed in lily flower bud, vein structure and mechanical properties of a leaf of Santa Cruz Water Lily, mechanical behavior of tendrils with spiral structure supporting cucumber body, adherence in the column of Stylidium caesupitosum and high speed rotation ... etc. From these researches, several interesting ideas or mechanisms adopted by plants have been clarified. For examples, the unfolding vein angle of regularly corrugated simple leaves is chosen as satisfying smooth and earlier unfolding with relatively small energy, the thick main veins of giant water lily have the cross-section with a tear drop shape including many voids to accomplish simultaneously a large bending rigidity and a body as light as possible, very complicated closing motion of a sensitive plant (Mimosa pudica) leaflet can be carried out by a simple rotation of a small pulvinus and a combination of a few installation angles of leaflet on the mid rib, or the incredibly rapid rotation of Stylidium flower column may be performed by the quick release of strain energy stored in a bending part of column. A number of interesting topics are shown here.

Carbon Fiber Reinforced Plastics (CFRP) is one of composite materials. CFRP is superior in the specific strength and rigidity, which is useful in the fields required to reduce the weight of products. However, CFRP have a problem causing delamination between layers by the impact. Invisible delaminates may cause a serious incident. The impact tests that produce the delamination in the CFRP laminate are made using an air-gun system. CFRP laminates being subjected to bending and twisting loads are imposed on the impact load at each temperature of 298K, 403K and 85K. Scanning Acoustic Microscopy (SAM) is utilized for detecting the delamination area of CFRP laminates. The residual strength of the damaged CFRP laminates is examined by using the three point bending device. The residual strength of the damaged laminates decreases linearly with increasing delamination area. The largest area of delamination is observed at 7/8 layer, and the tendency is more effective at low temperature ranges. The effect of the bending stress is more critical on the delamination and the residual strength of the CFRP laminates.

A quasi-static tensile test and impact tensile tests (tensile speeds: 2 m / s, 5 m / s, 10 m / s) were carried out on hexagon bolts and nuts, and the effect of strain rate on the impact tensile properties were investigated. The actual tensile speed was calculated from the stroke-time diagram obtained from the test results, and the strain rate was calculated by dividing the thread length by the actual tensile speed. Comparing the tensile strength of the quasi-static tensile test with that of the impact tensile test, the tensile strength increased by 8% at 1.9 × 10² /s, 30% at 6.6 × 10² /s, and 51% at 1.1 × 10³ /s. It was also found that the elongation increases only when the strain rate is 1.9 × 10² /s. It was also confirmed that the macro fracture surface changed from a cup and cone shape to a shear shape. From the macro observation of the fracture surface, a large amount of unevenness was formed at the center of the fracture surface, and a fibrous fracture surface was formed at the outer edge of the fracture surface. SEM observation of the fracture surface revealed that equiaxed dimples and elongated dimples mixed at the center of the fracture surface, and elongated dimples were dominant at the outer edge of the fracture surface.

Towards the “Sustainable low CO₂ emission world”, the research findings have been applied to extend to explore a new type of thermal energy storage system, employing a concept of chemical heat pumps. For this purpose a new original facilities have been designed and fabricated. Whereas many advantages were found in the new systems; e.g., high speed thermal energy absorption and generation, high cycle thermal fatigue failures must be always a critical problem for structural reliability in future.

After aluminum alloy A2017-T4 spheres with a diameter of 3.2 mm struck LPSO-type magnesium alloy plates at an impact velocity of 3 km/s, ejecta size distribution and scattering area 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. Forward ejecta from targets were decreased using fiber fabrics. A possibility of LPSO-type magnesium alloy plates to space debris bumpers were discussed.

Crack initiation in cast aluminum alloy under low-cycle fatigue loading is mainly caused by the fracture of Si particles. In this study, the large-scale image-based finite element analysis was conducted to reveal the mechanism of Si particle fracture. The fatigue test and in situ CT scanning were performed at SPring-8. The fracture of Si particle was identified by chronological CT observation. The CT images used for the model was extracted into quarter of horizontal cross section where the fractured Si particle for crack initiation was included. The image-based finite element model with voxel element was generated semi-automatically using the extracted CT images. The number of elements for the finite element model was about 130 million. To evaluate the incremental rate of stress for Si particles under cyclic loadings, 10 cycles of loading were applied in the analysis. The large-scale finite element analysis and its post-processing were performed on the supercomputers by the massively-parallel computing. The result of the finite element analysis showed that the value of the first principal stress for Si particles and its incremental rate under cyclic loadings did not only depend on their shapes but also their position in the specimen. Moreover, it was observed that the increment of the first principal stress for the fractured Si particle near a pore under cyclic loadings was drastically changed.

Crack initiation in cast aluminum alloy under low-cycle fatigue loading is mainly caused by the fracture of Si particles. The fracture of Si particles is influenced by pores, aluminum particle, specimen surface and their interactions. Thus, the stress-strain field on the large part of specimens should be investigated to elucidate the fracture mechanics of Si particle. In our previous study, the large-scale image-based finite element analysis was conducted by using CT images for the large part of a specimen, where the voxel element was employed to generate the finite element mesh definitely and automatically. However, the voxel element caused the lack of accuracy of the stress along the material interface. In this study, we addressed the zooming analysis by using the result of large-scale finite element analysis to achieve the high precision of stress field. The small volume image for zooming analysis was cropped from the entire CT images, where the Si particle for the crack initiation was contained. By using the extracted CT images, the finite element model with ten-node tetrahedral element was generated. The nodal displacement on the surface of the zooming small model was imposed from the result of the finite element analysis. The comparison between the large-scale, zooming small and local small model was performed to investigate the validation of the zooming analysis. As the result, the zooming analysis could reproduce the mechanical effect on the fracture Si particle observed in the large-scale analysis and mitigate the lack of accuracy of the stress due to the voxel element.