In this study, we investigated the applicability of the combination of the laser cleaning and cold spraying technique for corrosion repair. Zinc coating was applied to the corrosion substrates which were treated by the laser cleaning and conventional shot-blast cleaning techniques. The corrosion resistance property was evaluated by a salt spray test for 168 hours. The results showed that zinc coating was deposited successfully on the substrates treated with the laser cleaning and conventional shot-blast cleaning. As a result of the corrosion test, no corrosion of the substrate was observed, and the corrosion resistance was achieved by the cold sprayed zinc coating. In addition, a compound of zinc, chlorine, and oxygen was generated on the surface of the zinc coating, which may improve the corrosion resistance of the zinc coatings.

This study deals with an inverse elastodynamic problem in a functionally graded thin plate composed of piezoelectric and magnetostrictive materials. All response quantities are considered to be initially zero. It is assumed that the top surface of the thin plate is fixed to a flat rigid body and the bottom surface is subjected to an unknown impact pressure and that an induced voltage between the top and bottom surfaces is known. The material properties are assumed to vary in the thickness direction according to a power low distribution. This elastodynamic problem is solved numerically by employing the method of charateristics and then the particle velocity and stress are obtained for the case where the materials at the top and bottom surfaces of the thin plate are taken to be CoFe₂O₃ and BaTiO₃ , respectively. Finally, time histories of the impact pressure and dynamic stress are presented graphically.

Fiber orientation of the short fibers in composites fabricated by injection molding will be difficult to be perfectly controlled, and it will be randomly distributed. In particular, the random fiber orientation will not distribute uniformly, and it will take certain conditions such as filling speed and cavity pressure. For this problem, an influence of a biased distribution of the random fiber orientation on the homogenized elastic properties should be investigated. In this paper, a stochastic homogenization analysis using Monte Carlo simulation considering biased random fiber orientation distribution of short fibers in fiber reinforced composites is performed, and the influence the biased fiber orientation distribution is discussed.

In recent years, the demand for weight reduction in the field of transportation equipments has been increasing along with the rise of global environmental issues. Although, due to issues such as productivity, CFRP is rarely used as a stand-alone material and is generally used in the right places for the right materials. Therefore, the joining of dissimilar materials with metallic materials is essential. In this study, dissimilar material joints between CFRP and A6061 were fabricated using the punching rivet method with the impulsive load. Compared to the conventional riveting method, the punching rivet method does not require drilling of the material to be joined, and the punching and fastening can be performed almost simultaneously. To increase the seating pressure and improve joint strength, the tip of the rivet shaft was inclined to promote the outward deformation of the tip of rivet shaft. The part of rivet holder hole was chamfered. From the experimental result, joint strength was improved.

Currently, polymeric materials are used as key materials in a wide range of fields, for example chemical, industrial and medical products, etc. Most polymeric materials are petroleum-derived plastics that do not decompose in the natural environment. Recently, these marine pollution, such as microplastics, they have become an global environmental issue. Cellulose nano fiber (CNF) is attracting attention as an alternative material of petroleum-derived plastics. The mechanical and optical properties of these polymers greatly depending on their orientation, therefore it is important to evaluate their orientation. Raman spectroscopy is useful to evaluate molecular orientation of polymer materials. In this study, we evaluated Raman spectrum and the molecular orientation of various CNFs were evaluated using a polarized micro-Raman spectroscopy. In Raman spectrum some typical peaks were observed in four types of CNFs. Next, in polarization measurement, periodical change of peak intensity of some Raman shift was obtained. Therefore, it is possible to evaluate molecular orientation of CNFs using micro-Raman spectroscopy.

In recent years, various new semiconductor materials have been studied to replace silicon due to the limitation of silicon’s physical properties. Graphene is one of the next-generation material because of its high performance in electrical and thermal conductivity and mechanical strength. Graphene also has different properties depending on the number of layer. Therefore, the evaluation of the number of layer is very important for industrial use. Raman spectroscopy is the one of the powerful tool to evaluate the physical properties of carbon materials. In this study, we have studied the effects of the number of layers of graphene on Raman spectrum by using first-principles calculations. The intensity of Raman spectrum increased with increasing the number of graphene layers. This result indicates one of the effective prediction method to evaluate the number of graphene layers by Raman intensity.

To develop processing technology for functional containers, forming technology for pure titanium containers and titanium alloy clad containers using deep drawing technology has been developed so far. In the present study, an attempt was made to form corrugated clad cups with voids that resemble the cross-sectional structure of corrugated paper. This unique shape of cup has never been fabricated before, and it is a completely new forming technology. The test material was commercially available pure titanium, ultralow-carbon steel, and stainless steel. The shape of the blank was a disc with a diameter of 80 to 85 mm. The deep drawing machine used was a hydraulic machine. The clad cup was formed by a composite die with a structure consisting of the roller ball die sandwiched between two regular dies. The formability of the cups was evaluated by measuring thickness strain and compressive strength. Load-displacement measurements were also taken to investigate the forming transition. As a result of the deep drawing process using a combination of ferrous metals of SPCC and stainless steel, it was found that it was possible to form corrugated cups. No fracture occurred in the forming of the corrugated cup.

Shock absorbing members such as crash boxes are mounted on the front and rear of an automobile to absorb the shock in the traffic accident. This shock absorbing member is required to have a large amount of energy absorption while suppressing the peak load at the initial stage of collision, and to suppress the load fluctuation during crushing. In this study, impact crushing analysis is performed using the finite element analysis software LS-DYNA® for a lattice structure having cubic unit cells positioned at different angles, and investigated the arrangement angle of unit cells that can have a large amount of energy absorption in both frontal collision and oblique collision. As a result, it was found that the lattice structure is suitable for the shock absorbing member of an automobile because the initial peak load is suppressed, and the load fluctuation is suppressed at any collision angle by changing the arrangement angle of unit cells.

The consideration of the decrease of the friction coefficient with the increase of the normal contact stress is required for the analysis of the sliding behavior for a wide range of the normal contact stress. The explicit equation of the subloading-friction model is extended to describe this fact in this article.

High-strength steel sheets for automobiles with a tensile strength of more than 980 MPa have been required to reduce the car weight and improve collision safety. Delayed fracture or hydrogen embrittlement becomes a serious problem for the high-strength steel sheets. In this study, delayed fracture behavior of TRIP-aided martensitic (TM) steel was investigated, and the effects of residual stress and plastic strain on the occurrence of delayed fracture of a hole-expanded specimen of the TM steel were discussed. Delayed fracture cracks were initiated and propagated concentrically with the punched hole in the TM steel. A finite element analysis revealed that the high tensile residual stress in the radial direction was applied in the portion where the delayed fracture crack occurred although the equivalent plastic strain was not so high in comparison with that at the punched hole edge. It is considered that the high tensile residual stress was preferential factor for the occurrence of delayed fracture in the TM steel specimen.

The authors have developed finite element analysis (FEA) programs in order to simulate non-linear behavior of refractories with cracking. FEA programs are based on implicit method (IM), damage mechanics technique (DM, DMR) and explicit method (EM). In this study, the authors focused on the composite beam consisted of brittle material and bottom steel sheet. In addition, the authors derived theoretical load versus displacement relation based on the beam theory. This study aims to demonstrate the validity of FEA programs by comparing numerical results with theoretical values of the composite beam. Also, this study aims to clarify accuracy and efficiency of FEA programs. As a result, all FEA programs except for the program based on IM showed generally good agreement with theoretical value. However, the programs based on DM and DMR consumed much time than the program based on EM because of the iterative calculation by occurrence of the crack.

The aim of this study is to clarify the generation mechanism of the fracture sound for tensile test. A SS400 steel specimen was attached to a universal testing machine. Tensile load was applied to the specimen until right before breaking the specimen and then unloaded. In order to investigate the sound pressure at breaking the specimen, a microphone was set at a 200 mm distance from the specimen. A high speed video camera was also set to focus on necking region of the specimen. White smoke was used to visualize the air flow near the necking region of the specimen. Tensile load was applied to the specimen again until breaking the specimen. As a result of the acoustic analysis of the fracture sound of the specimen, negative sound pressure was initially detected at breaking point. Subsequently, positive sound pressure was also detected. As a result of the image analysis for the image captured from the movie taken with the high speed video camera, the air flow to the fracture region was observed. Both results indicate that vacuum region occurred at breaking point. The air near the specimen rapidly expanded to vacuum region and shrunk. Thus, the fracture sound of the specimen for tensile test would be caused by that the air near specimen rapidly expands to the vacuum occurred at fracture region and shrinks.

In this paper, the effect of hardness on the tensile strength of hot die steel JIS SKD61 in a high temperature environment was investigated by a tensile test using an extensometer. The tensile test was performed under four conditions from room temperature to 500℃. The hardness of the experimental material is in the range of 41.4HRC to 51.4HRC under five conditions. As a result of the experiment, the following was found. Regardless of the test temperature, the tensile strength and 0.2% proof stress increase as the hardness of the test specimen increases. In addition, the relationship between the strength (tensile strength and 0.2% proof stress) and hardness at each temperature can be approximated by a linear regression, whose slope is nearly independent of the temperature. Under the environment at 100℃ and 300℃, the strength ratio of tensile strength and 0.2% proof stress is almost equal, and the strength ratio shows almost constant value regardless of hardness. In an environment at 500℃, the strength ratio of 0.2% proof stress and tensile strength is different, and the strength ratio of 0.2% proof stress is smaller than that of tensile strength.

In recent years, higher performance and higher reliability of power devices have been required. Therefore, it is necessary to develop a technique to evaluate the strain field in micro-order regions of power devices. In our laboratory, polarized Raman spectroscopy with a multi-point simultaneous spectroscopy system has been developed in order to measure stress and strain in several 10 μm square region, but the spatial resolution was reduced. In this study, the structured illumination method was applied to the Raman spectroscopic imaging system. In this method, a stripe illumination with a periodic intensity distribution was formed by laser light through diffraction optical elements (DOE). An interval between the bounds of the interference was good agreement with theoretical value. We detected Raman scattered light of (111) silicon irradiated by stripe laser light.

In discontinuous carbon fiber reinforced thermoplastics molded by kneading resin and carbon fiber, controlling fiber length, dispersion and orientation state is an issue because those dominant mechanical properties of them. Therefore, the methods to measure fiber orientation distribution in the composites are indispensable. X-ray structure analysis is an effective means for the measurement. Because it allows us to acquire data in a short time without destruction of specimens. We established the method for estimating the fiber orientation distribution from the X-ray diffraction image of carbon fiber reinforced PA6 (CFR-PA6). The X-ray diffraction image shows overlapped signals correspond structures form carbon fibers and PA6, respectively. We assumed that the intensity distribution of each signal can be express Gaussian function in diffraction and azimuthal angle direction. To extract signal of carbon fibers from the image, the waveform separation in diffraction angle direction was carried out. Subsequently, the extracted intensity distribution was converted to fiber length distribution by the waveform separation in azimuthal angle direction. This method was applied to CFR-PA6s with known and simple orientation distributions such as pseudo-isotropic and the estimated results almost correspond to the expected values.

To realize highly efficient dissimilar jointing of CFRTP, we have studied the ultrasonic welding of CFRTP and aluminum alloy. In this study, we searched for the optimum conditions for ultrasonic welding of CFRTP / A5052 to clarify the correlation between welding conditions and bonding strength. We considered the relationship between the bonding strength and the input energy, the total sinking as the welding conditions by the sinking control. As these results, we showed the effectiveness of the sinking control as the optimum condition settings and realized stable bonding of CFRTP / A5052 by ultrasonic welding.

Carbon fiber reinforced thermoplastics (CFRTP) are suitable as structural material for automobiles due to their high specific rigidity and strength. However, these materials have random fiber orientations and volume fractions for each part, which makes it difficult to predict the material’s mechanical behavior. In this study, a new non-destructive inspection method called Talbot Lau interferometer was applied to CFRTP inspections and fiber orientations in a CFRTP plate were quantified, making a color map of fiber orientations. Tensile tests of CFRTP specimens and the color map intended that relatively weak specimens had break along the fiber orientation at their break point. Additionally, finite element models using quantified fiber orientations were generated and tensile test of FEM had been done. The result clearly showed the difference of elastic modulus in a specimen corresponding its fiber orientation. The comparison of FEM and digital image correlation showed that the specimen has a concentrated strain at its break point just before it broke although in FEM a part of specimen apart from the break point had the maximum strain.

In this study, the critical buckling temperature of a lattice sandwich panel was investigated by using FEM. In particular, the effects of geometric properties, for example a core height h, a core length L, and the number of cells N_c on the buckling temperature, were discussed. It was revealed that there are mainly two types of buckling modes of sandwich panels: global and local buckling mode. The critical buckling temperature for each mode can be estimated by using the equivalent shear modulus of the core, material properties of the panel and unit-cell length.

In this study, a plane-packed tessellated structure for modelling the natural structure of living organisms is discussed to find an alternative material that is tougher than currently used materials such as ceramic matrix composites. Hence, we generalize a method for generating a plane-packed tessellated structure of a regular polygon comprising n-tips and then develop a numerical procedure for analyzing the stress field in the tessellated structure based on the continuous distributed dislocation (CDD) method. The effects of n-tips and the loading direction, which is defined as the azimuthal angle measured from the side of the polygon, on the fracture toughness values are examined based on the fractal dimension D. It is revealed that the crack propagation path deflects significantly as the loading angle approaches the value of (2−n)π/2n. In this study, the deflected crack shape is characterized by D. It is discovered that D changed with the loading angle, and that the fracture toughness values changed with the loading angle, similar to the trend of D changing with the loading angle. The relation between the polygon shape and loading angle shows that the fracture toughness increases with D, which characterizes the complexity of the crack path, and increases with the number of vertices in the polygon. Therefore, it can be concluded that controlling D and plane geometry can effectively improve the fracture toughness of materials.

Carbon fiber reinforced plastic (CFRP) laminates are expected to be expanded as structural members due to their excellent mechanical properties. It is essential to evaluate very high cycle fatigue properties to ensure long-term reliability and durability. However, conventional hydraulic fatigue test requires a huge amount of time, so accelerated testing by ultrasonic fatigue test using resonance phenomenon has been conducted. Since the stress distribution applied to the specimen is typically in the hydraulic fatigue test, but not in the ultrasonic fatigue test, it is necessary to obtain the stress distribution when transverse cracks occur in the ultrasonic fatigue test. In this study, the stress components of the CFRP cross-ply laminates with transverse cracks subjected to ultrasonic vibration were calculated by the variational approach considering thermal residual stress. As in the case of typically loading stress, the 90° layer stress decreased to zero at the location of the crack, and it was confirmed that the 0° layer stress increased by sharing the mechanical stress that the 90° layer carried.

In this study, the deformation and fracture behaviors of carbon materials in composites were investigated by numerical simulations using the molecular dynamics method. We have performed compression analysis of nano-composite models of graphite and polyethylene (PE). Graphite structures in models were not only flat against the compression axis, but also wavy, to investigate the difference in stress state at the interface and the associated change in the atomic structure. As a result, it is clarified that the bonding change on Graphite/PEinterface occurs due to densification of PE in the late stage of compression. In addition, a slight difference in the bonding change was observed depending on shapes of graphite surface.

Infrared thermography has been proposed as a method to detect the configurations of prepreg/tape lay-ups and process-induced defects in the manufacturing process of CFRP (Carbon Fiber Reinforced Plastics) laminated structures. For this purpose, the transient responses were measured and compared with the theoretical or numerical models, to detect the change from the reference solution to the heat conduction characteristics of CFRP. Here, high-speed image processing is necessary for the application to the actual manufacturing sites. The present study attempted to employ the Proper Generalized Decomposition (PGD) method for obtaining computationally efficient solutions of heat conduction problems required in the thermography inspection of CFRP. We also presented a method to evaluate heat conduction characteristics in the preforming process using CFRP layup tapes with AP-PLY configuration as an example. The results demonstrated that the proposed method could capture the variation in the heat conduction inside the material depending on the contact state between the tapes.

With the development of electronic information technology, there is an increasing demand for materials with high thermal conductive. In this report, BN and CNT are used as mixed fillers to improve the thermal conductivity and maintain the insulation of silicone rubber. This is mainly because BN can destroy the conductive network formed by CNTs while ensuring the integrity of thermal conductive network. After the thermal conductive silicone rubber was obtained, the thermal conductivity of silicone rubber is measured by a thermal conductivity tester and the electrical conductivity is measured by a four-probe tester. As expected, the addition of thermal conductive filler can improve the thermal conductivity of silicone rubber. When the BN content up to 10 wt%, the thermal conductivity of silicone rubber reaches 0.404 W/(m*K). However, due to only simple mixing, the interface thermal resistance between BN and CNT cannot be ignored. The thermal conductivity of silicone rubber decreases with the increase of CNT content. At the same time, the conductivity has not changed significantly, and the silicone rubber is still insulating.

Carbon Fiber Reinforce Plastic (CFRP) is one of the composite materials of carbon fiber and the plastic. For maximization of the mechanical properties of CFRP, it is necessary to improve the adhesion strength at the interface of carbon fiber and plastic. Controlling the surface morphology grown by carbon nanomaterials has been researching as one of the effective methods to improve the adhesive strength at the interface of the carbon fiber and plastic. We have investigated the growth method of Carbon Nano-Walls (CNWs) on the carbon fiber surface by using the microwave plasma device without any catalyst or expensive gas. In this study, we evaluated the tensile strength of single carbon fiber grown by CNWs on the carbon fiber surface. Additionally, we fabricated the micro droplet device and measure the Interfacial Shear Strength (IFSS) of the sample. The tensile strength of the carbon single fiber grown by CNWs on the carbon fiber surface was 93 % of that of the as-received carbon fiber. The IFSS of the carbon single fiber grown by CNWs on the carbon fiber surface was 120 % of that of the as-received carbon fiber.

Cellulose nanofibers are nanofibers that can be produced from plants and are attracting attention as a new material with low environmental impact. It is known that yarns made of cellulose nanofibers can be continuously produced by injecting cellulose nanofiber suspension into an acetone bath. In this study, cellulose nanofiber yarns were produced by changing the concentration of cellulose nanofiber and the flow rate of injection, and tensile tests were conducted to investigate the effect of the production conditions on the tensile properties of yarns.

Polylactic acid (PLA), a bioplastic, has attracted attention as an alternative material to conventional plastics, but it suffers from low flexibility and impact resistance. This paper has explained the change of mechanical properties and morphologies of PLA by filling epoxidized soybean oil (ESO), a plant-derived plasticizer, and nano-calcium carbonate (nano-CaCO₃) a high-stiffness filler, to PLA. As a result, PLA increased its fracture strain by up to 180% while maintaining its stiffness and improved its flexibility.

In agriculture, there is a demand for the development of biodegradable capsules to contain seeds and other materials. In this paper, the combined effects of poly (vinyl alcohol) (PVA) to poly (lactic acid) (PLA) were investigated as a function of their mechanical properties and disintegration in water to use as the biodegradable capsules. PVA/PLA composites prepared using a twin-screw extruder were molded to the JIS standard specimens by injection molding and subjected to characterization test. The results show the composition of PVA/PLA composites that exhibit excellent mechanical properties and disintegration in water.

Although composites using cellulosic plant fibers as filler contribute to the realization of a low-carbon society, they have poor interfacial adhesion with non-polar polymers such as polypropylene (PP), resulting in decreased mechanical properties. Maleic anhydride-modified polypropylene (MAPP) as a compatibilizer was filled to PP/rice straw composites to improve interfacial adhesion. Observation of the fracture surface showed that the addition of MAPP improved the interfacial adhesion between rice straw and PP. As a result, the tensile strength was greatly improved by filling MAPP and was higher than pure PP.

A tricalcium phosphate (TCP)/poly(lactic acid) (PLA) composites have attracted the attention as bone fixation screws in the maxillofacial region because of their bioabsorbability and osteoconductivity. However, the application of TCP/PLA composites has been limited to the low-loaded region because of their low strength. Therefore, molecular orientation in PLA was focused since improve the strength of TCP/PLA composites in this study. TCP/PLA screws were prepared through kneading, casting, and die forging. Effect of TCP content and drawing by the die forging on shear and torsional strength of TCP/PLA screws was investigated. The extruded screws were prepared through kneading and casting at 200 °C by using a single-screw extruding machine. The drawn screws were prepared through kneading, casting, and die forging. Casting billets were molded at 200 °C by using the single-screw extruding machine. Then, these billets were extruded at drawing temperature 130 °C and draw ratio 2 and molded simultaneously into the screws by die forging. The annealed screws were prepared by heating to 130 °C and pressing the extruded screws. As a result, the screws with different molding methods showed distinctly different fracture behavior. In 0 mass% of TCP content, shear and torsional strength of the annealed and the drawn screws were higher than that of the extruded screws. On the other hand, in 30 mass% of TCP content, the torsional strength of the drawn screws was higher than that of the annealed screws.

Biodegradable composites have been designed with biopolybutylene succinate (BioPBS) and thermoplastic starch (TPS) to investigate their mechanical properties and biodegradability in natural seawater. The biodegradability of their composites in seawater was verified by measuring the biochemical oxygen demand (BOD) in our laboratory using natural water collected from the port of Yurihonjo City, Akita, Japan. The results show the composition of BioPBS/TPS composites that exhibit excellent mechanical properties and marine biodegradability.

In this paper, the fracture problem of a functionally graded piezoelectric material strip (FGPM strip) containing a crack perpendicular to the interface between the FGPM strip and a homogeneous layer under an electric load is considered. Material properties are assumed to be exponentially dependent on the distance from the interface. The superposition technique is used to solve the governing equations. The stresses induced by the electric load in the uncracked laminate are calculated, and the obtained normal stress is used as the crack surface tractions with opposite sign to formulate the mixed boundary value problem. By using the Fourier transforms, the electro-mechanical fracture problem is reduced to a singular integral equation, which is solved numerically. The stress intensity factors of the internal crack and the edge crack are computed and presented for the various values of the nonhomogeneous and geometric parameters.

This study examines the effect of laminate configuration and microcapsule concentration on the mechanical properties of carbon fiber/epoxy (EP) laminates containing microcapsules. The reinforcements used in this study were spread carbon fiber (SCF) and woven carbon fiber (WCF). SCF/EP, WCF/EP and SCF/WCF/EP laminates were evaluated by short beam shear testing and four-point bending testing to assess apparent interlaminar shear strength and apparent bending strength. The apparent interlaminar shear strength and apparent bending strength of WCF/EP and SCF/WCF/EP laminates with microcapsules was higher than that of SCF/EP laminates with microcapsules.

Mechanical properties of spread carbon fiber reinforced polymer containing microcapsules were predicted by using representative volume element (RVE) models. Firstly, we employed finite element analysis (FEA) to discuss the effects of microcapsule volume fraction, dispersion state and diameter on the elastic properties of RVE models of spread carbon fiber reinforced polymer containing microcapsules. Then, FEA of short beam shear testing was performed using the predicted elastic properties from the RVE models, and the analytical results were compared with the experimental results to validate the RVE models. Finally, we investigated damage progression behavior of the RVE models to study the damage distributions within the spread carbon fiber reinforced polymer containing microcapsules. The results indicated that comparisons with the analytical and experimental results showed reasonably a good agreement. Therefore, the RVE models were effective to predict the mechanical properties and can contribute the design of microstructure for self-healing spread carbon fiber reinforced polymer.

Talc is used to improve the mechanical properties of thermoplastics. In this study, the effect of shape and size of talc on the mechanical properties of talc/polypropylene composites was investigated. Three-dimensional finite element analysis was performed using a representative volume element (RVE) model to calculate stress distribution and Young’s modulus of talc/polypropylene composites. The results showed that the stress distribution did not depend on the shape and size of talc but Young’s modulus of talc/polypropylene composites was influenced by the shape and size of talc.

Carbon fiber reinforced composite material (CFRP) is widely used for structural members of aircraft and automobiles because of its advantages such as high specific strength, corrosion resistance, and fatigue resistance. On the other hand, it is required to clarify the fatigue / deterioration generation mechanism to extend the design life. In this report, a new method was proposed for evaluating fatigue damage of CFRP laminates by the lock-in thermography. The results of verifying its validity with tensile test pieces with different fatigue processes was reported. A significant decrease in the in-plane thermal diffusivity was confirmed. However, it was suggested that it should be corrected by the amount of change of the fiber orientation angle. Out-of-plane thermal diffusivity results showed that the amount of decrease was small compared to the in-plane direction. Although it was suggested that it may have captured the occurrence of local fatigue damage. In the future, it will be necessary to investigate the effect of local fatigue damage on the thermal diffusivity using a numerical analysis model.

In this study, the structural characteristics of CFRP plates with an optimal free-material orientation, which was determined by the optimization method in advance, were evaluated by testing, where static rigidity and frequency response characteristics were measured. In addition to the CFRP specimen with optimal material orientation, two types of linear orientation and resin-only specimens were fabricated and tested for comparison. All specimens except for the resin-only were fabricated using Tailored Fiber Placement (TFP) based on a stiching technique. It was confirmed that the CFRP plate fabricated based on the optimal material orientation calculation has the best performance on the rigidity and the frequency response.

The curvilinear print path generation technique for 3D printed carbon fiber composites was proposed. The anisotropic Swift-Hohenberg equation (SHE), which is a generalized mathematical model for periodic patterns in organisms, was applied to generate the evenly spaced 3D print paths. Parameters of SHE that control the convergence of the periodic pattern were optimized for maximizing the structural performance based on the vector field. Then, a 3D print paths were obtained. A carbon fiber reinforced thermoplastic was 3D-printed based on the curvilinear print paths.

Piercing and trimming are essential because composite structures are usually manufactured in a near-net shape to reduce machining operations. Punching and shear cutting using out-of-plane shear loading are expected to increase productivity. Nevertheless, little is known about the effects of such operations on polymer-matrix composites. This study presents on the characterization of anisotropic piercing damage in typical carbon fiber reinforced plastic (CFRP) cross-ply laminates [0°₂/90°₂]_s after punching using drop-weight impact (DWI) loading. During DWI punching, amount of piercing damage can be reduced, and the difference in amount of damage due to anisotropy associated with edged punching was smaller.

In this study, a small sphere impact test was carried out using a short fiber reinforced composite material to investigate the effect of sphere material on sphere impact damage. After impact test, the bending test was carried out and the residual strength was investigated. As the results, in the case of 4mm WC sphere, 6mm WC sphere, 4mm SUJ2 sphere and 4mm Al sphere, the number of radial cracks, the indentation diameter, indentation depth and residual strength ratio can be well organized by impact energy regardless of the sphere material. But it was found that the 2mm WC sphere has a different tendency from other spheres. This reason is that the 2mm WC sphere has a different inpact damage mechanism from other spheres. The fracture positions after the 4-point bending test could be classified into 3 types according to the damage by indentation and the influence of radial cracks.

CFRTP are becoming of interest to mass production industries. In this study, we investigate the capability of energy absorption and its mechanism of new concept CFRTP under impact loading by experiment and calculation. New concept CFRTP improved both static and impact characteristics was manufactured by laminating prepregs which inserted reinforced layer dispersed elastomer particles in the resin and controlled its direction. The experiments were conducted drop-weight impact test at a key impact energy (120J) for different elastomer-volume fractions. An LS-DYNA finite element analysis model of drop-weight impact test were implemented by 4 methods. By comparing load-displacement curves and damage behavior between experiment and numerical predict, we aimed to establish highly accurate analysis method and tried to clarify the main factors in improving the impact characteristics.

Stress intensity factor (SIF) under mode I and mode II mixed-mode loading is considered. SIFs under various conditions (which are the plus/minus sign of K_I and K_II, the ratio of K_I to K_II and crack width) are evaluated using a circular disk specimen. Fracture toughness determined by the caustic method is compared with the calculated value through the fracture load K_C(Load). As a result, it is revealed that K_C(Load) is extremely overestimated under the minus sign of K_I condition. Moreover, pure mode II tensile test with the crack closing load P_t is carried out. Consequently, tensile fracture load Pfract is increased with the rise of P_t, but fracture toughness measured by the caustics is constant regardless of P_t and P_fract. Finally, attempt for determining the mode I compressive fracture toughness is made with a V - notched specimen.

Cold spraying is a surface coating technique in which a powder material is impacted on a base material at high speed without melting to form a dense coating layer. The advantage of cold spraying is that the base material is not exposed to high temperatures, which prevents oxidation and thermal alteration of the coating layer. However, the stress-strain relationship in an ultra-high strain rate range from 5000 to 100000 /s which is required for cold spraying, has not yet been fully determined, and the mechanisms of the formation of coating layers have not been elucidated. In this study, the stress-strain relationship at ultra-high strain rates from 5000 to 20000/s was experimentally identified for pure nickel as a powder material in order to clarify the coating layer formation process by numerical simulation. We also identified the stress-strain relationship in the range from quasi-static strain rate to medium strain rates of the 10²/s order, and developed a rate sensitive constitutive equation based on T-M2009 model covering a wide strain rate range from 10^-2/s to 10⁴/s.

The Jump-out caused by the shear failure of the threads is one of the ductile failure modes of the premium threaded connections for Oil Country Tubular Goods (OCTGs). However, actual testing results of the premium threaded connections with the shear failure of the threads were not agreed with the prediction results by the conventional method. In this study, the novel prediction method for the shear failure of the threads on the premium threaded connections was proposed. In this prediction method, it is assumed that shear failure will be occurred when the equivalent plastic strain of the thread exceeds the ductile crack initiation limit. The equivalent plastic strain of the thread was evaluated by finite element analyses which simulated the actual tensile tests of the premium threaded connections. The ductile crack initiation limit was determined by the 3-point bending tests. As a result, this prediction method made it possible to predict the shear failure of the threads on the premium threaded connections occurred at an actual tensile test more accurately than the conventional prediction method.

As a simple and highly accurate axial force management method during manufacturing and maintenance of bolt-fastened structures, we examined a method to calculate the axial force from the image of the bolt head. In this method, the axial force is calculated using the strain on the bolt head measured by digital image correlation (DIC) technique from the image of the bolt head and strain results database by finite element analysis (FEA) that organizes the relationship between the strain and the axial force. We examined this method through two comparisons. The first was to compare the strain on the bolt head measured by DIC with data by strain gauges on the bolt head. The second was to compare the axial force calculated by using the relation database with data by strain gauges on the bolt side. As a result of comparing measured strain by DIC on M10 bolt head with data by strain gauges, the higher the axial force, the smaller the error between the two, and the error was less than 10% at the proof load 18kN in strength category 4.8. We confirmed that the strain on the bolt head generated its fastening can be measured with high accuracy using DIC. Axial force was calculated by using the relation database value of case in which the strain by FEA was being equal as the strain by DIC. The axial force calculation based on DIC measurement for a M10 bolt with 15.4kN fastening force showed 16.5kN, thus the error was 6.9%. We confirmed that the axial force calculation result based on the measurement strain on bolt head by DIC indicated much better accuracy than 30% in error by typical conventional torque management method.

In metallic materials, the flow stress significantly depends on the strain rate. At high strain rates exceeding 10⁴ s^-1, the flow stress tends to increase drastically with increasing strain rate. However, the conventional split-Hopkinson pressure bar method is difficult to evaluate the strain rate dependency of the flow stress at higher than 10⁴ s^-1. In this study, a simple estimation method for the material constant C in the Johnson-Cook flow stress model, which is associated with the strain rate dependency, was proposed. In this method, the material constant C is estimated from the indentation sizes formed via a ball impact test and an instrumented ball indentation test. The fundamental equation was theoretically derived based on the energy conservation and the heat conduction equation during impact process. Then, the average strain rate during impact process was determined via a finite element analysis. The verification with the finite element analysis revealed that the strain rate dependency can be accurately estimated at higher than 10⁴ s^-1 by the proposed method.

It is a well-known fact that there is significant difference in magnitude of flow stresses and work hardening rates of Polycarbonate and ABS between in tension and compression. There is a possibility that hydrostatic pressure is involved in this asymmetry to the loading axis, in which case volume change occurs in plastic deformation. The aim of this study is to measure the variation of plastic Poisson’s ratio by means of Digital Image Correlation method to clarify the existence of the plastic compressibility of Polycarbonate and ABS. The authors conducted tensile tests of thin strip specimens, and measured the axial and lateral strains by DIC method, then, plastic Poisson's ratio was derived. The result showed that plastic Poisson’s ratio of Polycarbonate was smaller than the value of 0.5, that result in the existence of plastic compressibility in this material. The Vickers hardness measurement for a gauge length was also performed to clarify the strength distribution of a specimen, and the results showed that the necking part of the materials was softened.

Polarizing microscopes visualize the optical retardation of light transmitted through a substance and show the anisotropy of the refractive index of that. However, it is difficult to quantitatively evaluate the anisotropy of the refractive index field. Therefore, in this study, by combining a high-speed camera with a laser photoelastic method using a photoelastic modulator (PEM), we acquire a quantitative optical retardation field together with a microscopic image. To verify the performance of the apparatus, the stress distribution at the edge of a semicircular notch in a glass plate was measured under a 20 N tensile load. Then, it was compared with the FEM analysis value. As a result, stresses of about 3 MPa were distributed at the notch edge in both cases, and the results were generally consistent with each other. However, there is a room for improvement such as a stress being detected where the optical retardation should be zero.

The applicability of the specimens with drop-like holes aligned to the polygonal line for generating intended acoustic emission (AE) signals to evaluate the performance of AE measurement systems was investigated. The stress distribution of the specimen subjected to a tensile load determined by finite element analysis demonstrates that high-stress areas appear along the line from the tip of the hole to the center of the arc of the next hole. This fact implies that cracks will generate in the direction toward the hole tip so that the location of the crack generation is enlarged by aligning such holes in two-dimension. It was found that intermittent crack generation is expected for the specimen with the holes having an angle of not small since the degree of stress concentration decreases monotonically in the order lined up, while multiple cracks might generate simultaneously for the small-angle due to a slight difference in the degree of stress concentration between some holes. The result of a tensile test shows that multiple load decreases appeared under loading, and generations of cracks between each hole were observed at the time of load decreases. A large number of AE counts with high amplitude were measured at the time of load decreases, and those sources were located around the tip of holes and the notch. Therefore, one can obtain AE signals caused by cracking at the intended location. Consequently, it was revealed that the specimens are suitable to evaluate the systems from the viewpoints of AE parameters and source location.