Burst test of Type-3 FW vessel (Practical maximum pressure: 19.6MPa, Capacity: 2.1L) wound in different tension were examined. Observing the cross section of the CFRP layers, microscopic structures such as fiber volume fraction Vf and the edge part of the hoop layer was measured. Analyzing the stress by FEM model considering microstructure the burst pressure was predicted.

Purpose of this study is to investigate fracture mechanisms and an influence of impact load on mechanical properties of shoulder part of composite pressure vessels experimentally and analytically. CFRP laminates which were simulated as shoulder part of composite pressure vessels, were made by FW method and were subjected to out-of-plane impact load. Impacted specimens were inspected by cross-sectioning and X-ray photography. Tensile tests were carried out on some specimens. Finite element analysis that simulates the impact test was also conducted. The experimental results showed that the impact load induced matrix crack, delamination, and splitting. Tensile strength was slightly reduced by impact loading. From the result of finite element analysis, dominant stress component for initiation of damage on backface of laminate was suggested as τ_xz.

For low cost design of high pressure hydrogen tank with reliability, an accurate fracture model of carbon fiber reinforced plastic (CFRP) is indispensable. The accuracy is to be ensured by taking account of meso-scopic structure of fiber bundle and matrix resin, which causes local strain enhancement. Authors have approached to the fracture model of helical layer in CFRP tank by means of the meso-scale finite element model. Quasi-biaxial tensile tests are performed by employing cruciform specimen, and the breakage strength is predicted by the finite element method with different material model. The consideration of orthotropy in the bundle results in adequate feature mode prediction of the specimen.

In order to prove the details of reduction of tensile properties in CFRPs by fiber waviness, experimental evaluation has been performed for local strain and stress around fiber waviness in unidirectional composites under tensile loading. Unidirectional composites of continuous fibers with in-plane sinusoidal waviness in a matrix were composed. Strain distributions were measured by using DIC (Digital Image Correlation) method. Stress distributions in fibers on the cross section perpendicular to the tensile loading were evaluated by means of micro-Raman spectroscopy. It was found that longitudinal strain concentration was observed at the inflection point of fiber waviness and transvers strain in tension arose around the top of the wavy fiber. In addition from the stress distribution in fibers across the loading direction less load shearing was observed at the inflection point in the wavy fibers compared with that in straight fibers located next to the wavy fibers.

This study sought to align multiwalled carbon nanotubes in uncured ultraviolet ray curing resin suspension by applying traveling electric field in the whole area. The suspension coated on a 18mm × 18mm size cover glass and the coated cover glass were put on the multiple-electrode which was constructed with 24 long and slender electrodes. Rectangular and six-phase voltages were applied to the multiple-electrode. The applied voltage in one electrode had the phase differences of ±60 degrees among the voltages applied to the both side electrodes. The multiwalled carbon nanotubes in the suspension were rotated to the direction perpendicular to the electrodes. After the rotation ceased, UV rays were irradiated to the suspension for resin curing. In this way, aligned carbon nanotubes/ ultraviolet curing resin composites were produced. The electrical resistivities of the composites were measured in parallel and vertical directions to the aligned carbon nanotubes.

This paper studies the Mode I fatigue fracture and damage sensing of bonded carbon fiber reinforced polymer (CFRP) composite joints with carbon nanotube (CNT)-based polymer adhesive layer. Mode I fatigue tests were conducted on double cantilever beam (DCB) bonded joint specimens. The responses in the electrical resistance of the bonded joint specimens were measured during the tests. The effective crack length estimated from the specimen compliance was introduced to describe the fatigue damage development, and an analytical model based on the electrical conduction mechanism of CNT-based polymers was used to predict the electrical resistance change of the bonded joint specimens during fatigue loading. A comparison of the predicted results with the experimental data showed that the analytical model captures the electrical resistance behavior.

In this study, based on the linear fracture mechanics, we proposed the Finite Element Analysis method to consider with stochastic uneven sintering effects on strength of ceramic matric composite. Using proposed method, we can examine the fracture behavior depending on the sintering effects which corresponds to the relative density, the initial defect (pore size), and the grain size. In addition, it is shown that the Weibull distribution of 3-point or 4-point bending tests can be analyzed within the framework of FEA.

In this study, to analyse both damage and healing phenomena of self-healing ceramic materials within the framework of FEM, a novel constitutive model is developed. The damage process is formulated based on a fracture mechanics, while the self-healing process is formulated based on an oxidation kinetics model of self-healing time. Then, we apply the proposed constitutive model to FE analyses of alumina/ SiC nanocomposites materials, in which the unevenness of material properties are considered. The super-healing phenomena of self-healing ceramic matrix composite is demonstrated using proposed FE analysis scheme.

This study examines interlaminar shear strength and self-healing of spread carbon fiber (SCF)/epoxy (EP) laminates. Self-healing is accomplished by incorporating a microencapsulated healing agent and catalyst within the epoxy matrix. Short beam shear specimens of self-healing SCF/EP laminates were prepared and tested. The healing efficiency was evaluated by the strain energies of virgin and healed specimens. The effect of addition of carbon nanomaterials to the matrix on the apparent interlaminar shear strength and the healing efficiency are discussed. The damage area of the healed specimens was also examined by an optical microscope.

In this study, a biaxial test of CFRP laminates was performed to investigate a failure criterion under biaxial loading. The specimens were composed of unidirectional CFRP prepreg sheets and subjected to a tensile load in the fiber longitudinal direction and a compressive load in the fiber transverse direction, respectively. The dedicated test jig was used to perform the biaxial test with a commonly used single-axis testing machine. For the biaxial test, a displacement ratio, which is a ratio of compressive displacement to tensile displacement, was controlled. Then, maximum tensile and compressive stresses were calculated using a constitutive equation with respect to three displacement ratios. From the results of the biaxial test, tensile strength in a fiber longitudinal direction markedly decreased with compressive stress in a fiber transverse direction increased.

The contact condition of the fiber-matrix interface is a key factor for mechanical characteristics of composite materials. The characteristics of second-harmonic generation due to nonlinearity at the interface have a possibility to be a measure of the interfacial condition. In this study, the characteristics of second-harmonic generation at the fiber-matrix interface were investigated. Influence of the interfacial condition on the fundamental wave field was also examined. As a result, it was shown that directivity pattern of scattered second-harmonic wave was varied by the interfacial stiffness. This result indicated the possibility that the interfacial condition was monitored by directivity pattern of scattered second-harmonic wave. The interfacial stiffness also affected the stop-band.

CFRP is known to its high specific strength and stiffness, and widely applied in many fields. However, because of its orthotropic mechanical properties, fiber orientation have to be considered in the design process. In addition, recently a new manufacturing method 3D printing of CFRP have developed. Which enabled to place carbon fiber filament curvilinearly. Thereby degree of freedom for design is outstandingly increased. Consequently, there is possibility of products, which have higher fracture strength than conventional one by controlling orthotropic properties in a ply. Thus in present paper, optimization of in-plane curvilinear fiber placement for the 3D printing and discussion of the manufacturability was conducted. As a result strength was significantly improved in terms of Tsai-Wu failure criteria after the optimization, and placement of the CFRP filament for the 3D printing was obtained

Carbon fiber reinforced polymer (CFRP) composites for an aircraft structure have resin-rich layer at the interlamina to prevent a delamination. Resin-rich layer is an electrical insulator, and it limits the contact regions of conductive carbon fibers. Electrical conductivity in the through-thickness direction of CFRP composites, therefore, is very low compared with that in the in-plane direction due to resin-rich layers. When an airplane made of CFRP composites is struck by a lightning, high electric current flows into the CFRP components, which has some influences on structural materials mechanically and electrically. In the present study, the change of electrical conductivity caused by electric current flow in the through-thickness direction was investigated experimentally. Observation of temperature distribution during the current input test by a thermography camera revealed that a temperature increases only at the fiber contact regions, which leads to the increase of electrical conductivity in the through-thickness direction.

Interfacial adhesion strength of composite plate is evaluated by using laser spallation technique. The composite plate specimen is composed of Al-alloy and resin coating film containing carbon nanotube as reinforce material. Interfacial delamination was induced by various laser irradiation. Displacement velocities of specimen back surface were measured by a laser Doppler vibrometer. Interfacial stress was analyzed by 3 dimensional wave propagation simulation using Boundary Element Method. The interfacial adhesion strength between Al-alloy and resin coating was estimated to be 40.9MPa. The obtained value is compared with result from stud pull test.

This study aims to evaluate adhesion quality and surface damage of DLC film as a releasing agent with a thermal shock test. To imitate a practical glass press molding process, DLC specimen was vacuum-encapsulated with a glass tube, and then they were heated up to 610oC using the electric furnace and were quenched to 20oC in water. After eight cycle thermal shock test, localized surface damage and exfoliations were observed, and expanded with the cyclic number. Moreover, the ratio of G-peak to D-peak (ID/IG) in Raman spectra suggesting the degree of graphitization of DLC for the samples after the test increased. These results show that the proposed thermal shock test is useful to evaluate the adhesion quality and surface damage of the DLC film at high temperature.

Tungsten carbide (WC) has high hardness and wear resistance, and powder metallurgy method is applied to form products together with metallic powder, e.g. cobalt (Co), because its formativeness is poor. Recently, application of WC by coating forms has been watched from viewpoints of reduction of tungsten (W) / Co usage and arbitrarily of products design. The purpose of this study is establishment of brand-new formation process for WC-Ni hard coating materials, which is based on wet plating and is constructed with both carbon supplying and diffusion heat treatment. In the current report, influences of both the procedure of carbon supplying and the condition of heat treatment for microstructure of the coating were discussed. In addition, hardness of the film was evaluated by using a instrumented hardness tester.

In order to evaluate interfacial fracture toughness of hard films, a micro ring-compression method is newly proposed. Micro ring-compression test was carried out using a newly fabricated apparatus. SiC films with thicknesses of 1 and 2 μm was sputter coated on stailless steel rings as a specimen. The result showed that the curvature ot the specimen increased with increasing compression load, and delamination of the SiC film occured with further increasing load after plastic deformation of substrate. Scanning electron microscopic observation result showed that delamination of the SiC film occured at the interface. Obtained interfacial fracture toughness was in the range of 140-220J/m2, and increased with increaseing film thickness.

The objective of this study is to investigate the effects of the diameter of spherical indenter 2R on the ring crack initiation strength of ceramic thin film evaluated by cyclic sphere indentation test. Cyclic sphere indentation tests were carried out for 3 type ceramic thin films; TiAlN, “DLC by PVD” and “DLC by CVD”, by using Si₃N₄ balls of 4 types of diameter 2R, 5.96 mm, 7.93 mm, 9.53 mm and 12.6 mm. For all films, the ring crack initiation strength decreased with the increase of 2R. The decrease in “DLC by PVD” was smaller than the other films. The influence of the substrate on the ring crack initiation strength of TiAlN film was also investigated by using two type substrates, WC-Co and high-speed tool steel.The ring crack initiation strength obtained by small indenter changed with the substrate, however, the strength obtained by the indenter 2R = 12.6 mm, did not depend on the substrate material.

It is necessary for a damage evaluation of Thermal Barrier Coatings (TBCs) to understand temperature and thermal stress in turbine blade. In the gas turbine, turbine blade surface temperature vary randomly due to fluctuation in combustion temperature. For the purpose of improving reliability of TBC and Porous-TBC (P-TBC) damage evaluation, the effect of harmonic oscillation on an unsteady state thermal stress of TBC and P-TBC was clarified. As a result, it was found that the position and geometry of pore is related to thermal stress.

It is necessary for a damage evaluation of Thermal Barrier Coatings (TBCs) to understand temperature and thermal stress fields in turbine blade. In the gas turbine, turbine blade surface temperature vary randomly due to fluctuation in combustion temperature. For the purpose of improving reliability of TBC and Porous-TBC (P-TBC) damage evaluation, the effect of harmonic oscillation on an unsteady state temperature field of TBC and P-TBC was clarified. As a result, it was found that the heating wave was reflected from pores, and surface temperature amplitude was attenuated. Furthermore, it is confirmed that the temperature amplitude decreased toward the interface.

TBC (Thermal Barrier Coating) plays an important role to protect structural components from high temperature environment of gas turbines. The TBC consists of ceramic top coat and metallic bond coat, deteriorate by the high temperature operating condition. CMAS (CaO-MgO-Al₂O₃-SiO₂) infiltration into the top coat is also one of degradation mode for TBCs. Damage mechanism associated with the CMAS are significant in the novel turbine system, which operates at higher temperatures than the melting point of CMAS component. In this study, CMAS infiltration tests were conducted. Delamination of the top coat was observed under the CMAS infiltrated layer. The delamination path varied with coating process as well as CMAS infiltration rate. Structural analysis was also conducted. The result indicated that a characteristic stress state that can promote the delamination was developed around the CMAS infiltrated top coat.

Longitudinal elastic modulus of thermal barrier coating (TBC) is one of the most important mechanical properties which is essential to the calculation such as thermal stress, etc. The elasticmodulus of segmented TBC was evaluated by the static and dynamic bending of composite beam. As a result, it was found that the static elasticmodulus was lower than the dynamic elasticmodulus, and the staticmodulus by low strain range showed a tendency to approximate to the value of dynamic modulus. In addition, the compressive elasticmodulus by static bending was slightly higher than the tensile elasticmodulus. They were because of the nonlinearity of segmented TBC. On the other hand, the dynamic elasticmodulus of the other conventional TBC coincided with the static elastic modulus. Further, the compressive elastic modulus by static bending coincided with the tensile elasticmodulus.

In order to investigate the fundamental process of residual stress development in thermal barrier coating during thermal spray, a model experiment is conducted using a paraffin wax. The melted paraffin wax was dropped onto a circular substrate of type 430 stainless steel, and the strain and temperature were measured on the back surface of substrate. Measured strain includes the thermal strains caused by the difference of linear expansion coefficient between substrate and strain gauge, as well as induced by temperature distribution in the circular substrate. These strains were compensated from the measured strain and temperature distribution in the substrate. The compensated strain at the substrate back surface was tensile when the paraffin wax was dropped and solidified. The tensile strain was increased with the number of the droplets and three or four droplets resulted in de-bonding of the solidified wax layer. The strain was converted into the stress in the coating using FEM. It was revealed that the radial component of the stress in the coating was 10-20 MPa in tension.

Graphite is a candidate material for heat sink, because it has extremely high thermal conductivity, and low density. On the other hand, graphite has low solderability. Therefore, it is required to improve solderability by means of a copper bond layer on the graphite surface. The conventional coating methods as represented by CVD and PVD need high vacuum environment and those deposition rates are very low. In this work, we discuss the applicability of Low-Temperature Plasma Spray (LTPS) for thin coating production onto the graphite surface. LTPS is a kind of plasma spray technique, it has high deposition rate, 10 μm/s in an atmospheric environment. The LTPS copper coating, however, does not have highly adhesion strength. However, LTPS titanium coating shows enough adhesion strength on the graphite substrates. Therefore, insertion of Ti bond layer for improvement of adhesion strength between copper coating and graphite is considered. In this study, in order to optimize coating conditions, we make some specimens in different conditions and measure particle temperature and particle velocity and flame temperature. As a result of measurements, Ti particle temperature was over 2800°C between 20 and 60mm from spray nozzle, and particle velocity was 60~100m/s. Experimental results indicate that as spray distance decrease, porosity size in a coating is smaller.

The CoNiCrAlY coated Ni-base superalloy was exposed at 1000 and 1100°C for up to 1000h. The morphology and element distribution in the mixed oxide and alumina layer in the Thermally Grown Oxide (TGO) layer of CoNiCrAlY coating were examined by microscopic observation and elemental analysis. thickness of alumina layer was found to be dependent on the form of a thermally sprayed coating of CoNiCrAlY alloy. In addition, damage such as cracking and peeling was found to be that strong factors other than the thickness of TGO layer.

In order to investigate the effects of new surface modification method “Laser quenching after coating” on the rolling contact fatigue strength of ceramic coated steels, 3 types of ceramic coated steels (CrAlN, TiAlN and CrN) were processed by this method under various laser power conditions, and the thrust type rolling contact fatigue tests were carried out for these specimens. It was found that the delamination initiation life of CrN coated specimen was longer than those of the other specimens, and the reason why was explained by the quite high adhesive strength of CrN coated specimens obtained by laser quenching after coating process.

The pore structure of thermal spray coatings affects their mechanical properties, such as the elastic modulus, tensile strength and etc. In this study, the finite element analysis was performed to investigate the effect of pore structure on the anisotropic elastic modulus of a porous material. An empirical equation to predict the anisotropic elastic modulus of pore structure which consists of ellipsoidal pores was proposed. The anisotropic elastic modulus predicted by using of the proposed equation was compared with the experimental results for some thermal spray coatings.

This paper presents the preliminary investigation of repairing method for CFRP based on TASC (Thermal Activation of Semi-Conductors) technique by removing the matrix resin and inserting the reinforced thread in the target area of CFRP. In order to optimize the joining process, temperature effects on decomposition rate and fiber damage during the decomposition process was studied. The decomposition rate increased as temperature increased whereas the decomposition rate was constant at the temperature of more than 450 °C. By contrast, carbon fiber damaged at the temperature of more than 460 °C. Hence, the optimal temperature of decomposition process was revealed. Decomposition process have been optimized by developing the heating configuration. Homogenous heating was achieved by using radiator and shielding plates with optimal heat source distance from the heating objective. Finally, it is possible to carry out the strength evaluation test using single-lap test specimen created by the proposed method.

Polyhydroxyalkanoate (PHA) which is biodegradable plastic shows the brittleness. Therefore, our group has conducted the research to improve mechanical properties by blending Polycaprolactone (PCL) which shows high ductility. As a result, it was shown that ductility was improved slightly when 50% of PCL was blended. This research aimed at the further mechanical properties improvement in dynamic tensile test by adding the additives to blend materials. When the additives were added, it was confirmed that the maximum stress and fracture strain increased together, and, the usefulness of the additives was showed.

For the collision safety improvement of the vehicle, it is necessary to examine not only the mutual accident of the vehicle but also the collision damage by the motion after the accident. However, the verification by the collision test is not reported on the vehicle motion after the accident, though the theoretical analysis has been attempted. In this study, in order to clarify the vehicle motion after the collision, the motion after side collision was investigated by carrying out the model collision test. The motion of vehicle was compared by the difference of the tire rotational state. The rotational of the tire affects most the rotational angle in the vehicle motion.

In order to improve the systems for vehicle control, traffic accident prevention and autonomous driving and so on, the measurement of the friction coefficient between a tire and the road surface is required. Therefore, various studies were conducted on intelligent tires that can detect the road surface conditions. However, most of them needed complicated systems and costly equipment. This study proposes a method for measuring the vertical and friction loads from the strains induced on a side surface of a tire. The proposed method has possibility to develop an easy and low cost intelligent tire systems.

This paper reports an experimental result of shock wave propagation phenomena in a thin plate by induced shock wave visualization for understanding shock wave propagation in a solid phase. The process of induced shock wave from a thin plate was visualized by shadowgraph method in water, by schlieren method in air and recorded by a high-speed video camera. The sequential optical visualization images show that the measured induced shock wave was generated by propagation of shock wave at longitudinal wave speed of sound in acrylic thin plate.

The aim of this study is to investigate strain rate effect of indentation with different indenter control. In this report, numerical simulations were performed by the finite element method. Material properties of pure aluminum 5N (purity 99.999%) from impact and quasi-static experiments were incorporated in the simulation. Cowper-Symonds equation was used in order to consider strain rate effect. Conical indenter of half apex angle 70.3° was used. Two indenter control methods, constant loading rate and constant indentation strain rate were used and both results were compared. Strain rate diagrams were also obtained for both indenter controls. Whereas values of strain rate decreased for the constant loading rate, those remained the same for the constant indentation strain rate. Obtained strain rate diagrams showed that hemispherical and high strain rate regions were observed from the edge of indenter.

Geckos have attractive adhesive abilities such as anisotropic adhesion, self-cleaning, attaching to a variety of surfaces, and being able to use repeatedly, which inspired researchers to fabricate mimetic adhesive devices. Especially to get anisotropic adhesive properties, tilted micro-pillars and ones with spatula heads have been produced. Micro-pillars-shaped dry adhesive devices with asymmetric cross-sections, such as triangle, also have anisotropic adhesive properties. It is easier to be fabricated and expected to have higher productivity than other ways. However, the effect of cross-sectional shapes of micro-pillars on their adhesive properties is still unclear. In this study, micro-pillars arrays with a various cross-sections were fabricated. The effect of cross-sectional shapes of the micro-pillars on anisotropic adhesive properties is investigated by measuring adhesions and frictions of these adhesive devices.

Plate impact experiments have been performed to determine the dynamic compression behavior of mortar. To investigate the effect of static strength to shock response, three types of mortar, which are denoted as low-strength, mid-strength and high-strength mortar, have been used. The static compression strength of each mortar is 40.3, 78.5 and 174 MPa. Longitudinal stress induced by impact loading have been directly measured by means of embedded polyvinylidene fluoride (PVDF) gauges. The longitudinal stress profile of each mortar shows the inflection of stress-wave front associated with the compaction of pores. The dynamic compression strength of each mortar is determined to be 115, 257 and 895 MPa. The ratio of dynamic to static strength is increased with an increase in the static compression strength.

The purpose of study is to estimate the surface condition, such as dry, wet, ice and snow, by using the ultrasonic method. As a first step, the aluminum plate with smooth surface and the asphalt plate with rough surface were used as the specimen for examination and verification of the possibility of estimation by the ultrasonic. The ultrasonic wave (the center frequency of 40kHz) which propagated to the specimen in the air reflects at the surface by the difference of an acoustic impedance and surface condition, and it is received the ultrasonic transducer. Aluminum specimen has bigger value for the mean of maximum amplitude and the dispersion of the measurement result is wide for the asphalt specimen. In the comparison of both parameters in two specimens, it is clear to show the different result by the surface condition and the difference of acoustic impedance.

Through experiments that the spherical projectile collided against structures that simulate aircraft structure, we confirmed fracture behavior around the riveted lap joint parts. We also tried to reproduce the fracture behavior using FE-Analysis. In addition, we discussed the fracture behavior around the riveted lap joint of the structure, based on the results of the experiment and simulations.

Adhesively bonded joints have been widely used in various engineering products, such as automobiles, ships and airplanes, due to the advantages of adaptation for dissimilar materials bonding. The strength of the joints is one of the important factors in terms of product safety. Double cantilever beam (DCB) test is a standardized evaluation method for the mode I fracture energy (G_IC) of the adhesively bonded joints under quasi-static conditions. Also under impact conditions, various tests have been introduced because of the importance of impact resistance for the safety of the vehicles. However, impact loading makes it difficult to measure the G_IC, and the evaluating techniques under impact loading conditions have not well established. In this study, the DCB tests under impact loading conditions were conducted using a falling-wedge impact-testing machine and a high-speed camera, and the change in the fracture energy G_IC was investigated in comparison with the results under the static loading conditions.

The fracture life, especially, crack growth life under the condition of creep (Time dependent, TD) and fatigue (Cycle dependent, CD) interaction, is mainly dominated by TD in the region of higher temperature and low load frequency and is dominated by CD in the region of lower temperature and high load frequency. In the mediate region, it is considered to be dominated by interactive effect of TD and CD. However, the interactive effect of load frequency on fracture life shows various characteristics. Therefore, it is not feasible to designate under what condition such interactive load frequency characteristic of fracture life appears. In this paper, on the basis of systematic experiments and chaos analysis, a method of theoretical representation on the phenomenological occurrence mechanism of the interaction between TD and CD of fracture life under creep and fatigue condition was discussed.

Lotus leaves are well known for its high water repellency. Lotus leaves have microstructure composed of micro-rods on a surface and when a water drop sit on a leaf, micro-rods keep air layer between surface and drop. Therefore, drop contacts by extremely small area and it can be seen as if it floats on a surface. The micro-rods are not uniform, i.e. micro-rods with various diameter and height are randomly distributed. In this paper, the characteristics of micro-structure on lotus leaf surface and water repellency were investigated by observation and numerical simulation.

A simulation result on the Electromagnetic Flux Generation is presented using a finite element analysis code with multi-physics capability. The difference between simulation results reported last year and this year is discussed from view point of the electrical conductivity as functions of temperature and relative volume.

The influence of stacking sequence on the generation characteristics of ultrasonic band gap of carbon fiber-reinforced composite laminates is investigated theoretically. The energy transmission spectrum of unidirectional, cross-ply, and quasi-isotropic laminates with spring-type interlayer interfaces immersed in water is calculated by using the stiffness-matrix method. The location of the band gaps in which the transmissivity becomes relatively small in the spectrum is found to be significantly influenced by the laminate lay-up and the angle of incidence. The energy transmission spectrum is experimentally measured by the immersion through-transmission technique. The band gap formation observed in the experimental results is shown to be favorably compared with the theory.

In the present study, the effect of strain rate on compressive properties of open-cell metal foams was investigated. A commercial open-cell Ni foam was used. New impact testing machine with opposed load cell, which can detect the load at both ends of specimen in only one test, was developed. The same accuracy was obtained by using this testing machine in comparison with the split Hopkinson pressure bar method. Additionally, the impact and quasi-static test at the strain rate of 4.5×10² s^-1 and 8.3×10^-4 s^-1 were compared. In the Ni foam, the elastic response, plateau deformation and densification were observed regardless of the strain rate. The compressive stress of the Ni foam did not increase when the strain rate increased.

Fiber reinforced thermoplastics (FRTPs) are promising for automotive structures because they enable us to reduce the weight and shorten the process time. For these applications, the materials are usually welded because they can melt at high temperature. In contrast, to join the FRTPs to other materials such as metals, adhesive bonding is often utilized because of its versatility for dissimilar material joining. Thermoplastics are poorer in adhesion property than thermoset ones due to the low surface energy of the matrix resins. Surface treatment before bonding is one of the candidates to overcome the disadvantage. Several types of methods have been proposed for thermoplastics. However, it is still unclear which methods is the most appropriate for FRTPs. In this study, to find appropriate method for the surface treatment of FRTPs, mode-I and mode-II critical energy release rate of adhesively bonded joints has been investigated.

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 known as the MR effect. The application of these fluids for automobiles and buildings for viscous dampers has shown excellent performance for shock absorption. In this study, impact experiment was conducted with a cylindrical projectile in a water-filled tank to test its shock absorption performance. The pressure signals inside water were recorded as well as the velocity profile and the validity of the experiment was discussed in this paper.

In order to improve the tensile properties, natural fiber was added to PLA/PBAT/PEEHEXA polymer alloy. We have done researches on effects of chemical treatment to the fiber and physical treatment to the polymer alloy ,the mixing ratio of PLA/PBAT as well. Also the tensile properties of specimens were measured using split Hopkinson pressure bar method at high strain rates.

In this study, the effect of hydrogen on micro-indentation properties in 7075 aluminum alloys was experimentally investigated. The micro-indentation test using a Berkovich indenter was performed at loading rate of 70 mN/s. The indenter was loaded to a maximum value of 1200 mN, and then was maintained for 30 s. The amounts of hydrogen for 7075 aluminum alloys were 0.12 cc/100g (Low-H material) and 0.46 cc/100 (High-H material), respectively. As a result, the loading curvature of Low-H material coincided with that of High-H material in the early deformation. However, the loading curvature of High-H material decreased in comparison with that of Low-H material from a certain displacement. It was clarified that the micro-indentation properties was affected by the interaction of the thermal activation of dislocations and the hydrogen diffusion with the aid of hydrogen transportation by dislocations.

High speed penetration experiments have been practiced in many fields, and impact experiments were performed using the powder gun within a velocity of 150-510 m/s. Packing density of sand is varied several kinds. Impact and penetration speed of a projectile were measured by coil method that is contactless. The behavior of projectile changed at transition speed and the acceleration of projectile was expressed two equations depending on the speed region. In this research, calculateing coefficient related to forces to act projectile was conducted, and try to make clear forces of projectile during high-speed penetration in sand.

Experiments and simulations on sharp head projectile impact to circular plates made of aluminum alloy 2024-T3 were carried out. The crack limit velocity, perforation limit velocity and deformation of the plates were measured. These experimental results were compared with simulations using material properties experimentally obtained. The fracture mechanisms of impact point were discussed.

In the present study, quasi-static and dynamic bending behavior of CFRP (carbon fiber reinforced plastics) with soft epoxy matrix was investigated. CFRPs were fabricated with the soft epoxy matrix and a standard carbon woven fabrics. The carbon woven fabrics of 5 layers were laminated to be quasi-isotropic. The impact three-point bend testing machine based on the split Hopkinson pressure-bar technique was developed. The bending tests were performed by a universal testing machine for low deflection velocities, a cam plastometer for middle ones and the impact testing machine for high ones. The experiments reveal that the bending modulus of the CFRPs strongly depends on the deflection velocity.