Binary titanium alloys are often composed of several phases. The phase fraction changes with content of alloying element and influences on mechanical properties. In this study, solution treated metastable binary titanium-niobium alloys with different niobium content were prepared and their uniaxial and biaxial compressive plastic deformation behaviors were investigated, focusing on the ratios of α (hexagonal close packed structure) and β (body centered cubic structure) phases. It was revealed that α phase gradually decreased and β phase increased with increasing niobium content. The primary plastic deformation mechanism changed from crystal slip to stress induced martensite transformation and deformation twinning with the change of phase fractions. The increase of β phase lowered the compressive stress and thus, the relationship between the phase fraction and the compressive plastic deformation behavior was discussed.

We conducted crystal plasticity analysis of a bicrystal model using a crystal plasticity finite element method (CPFEM), and the activities of slips systems in the α-phase of Ti-6Al-4V alloys (Ti-64) under cyclic loading were investigated. The crystal orientations were set such that prismatic <a> and basal slip systems were the primary slip systems in the crystal grains, respectively. The results showed that the occurrence of work hardening in a crystal grain decreased the volume of deformation and increased those of elasto-plastic deformations in neighboring crystal grains. The phenomenon leads to activation of slip systems in neighboring crystal grains. Thus, although the prismatic <a> slips initially operates under a cyclic loading, the basal slip system in the neighboring crystal grains displays a potential for activation by work hardening on the prismatic <a> slip system. The mechanism of changes in activities of slip systems by the interaction between crystal grains can be explained by the wedge disclination-type deformation field.

In the present study, the two-step deformation behavior in a commercially pure titanium sheet was studied by means of experiments and crystal plasticity finite-element simulations. Two-step loading tests with various pre-strains and loading conditions were carried out. When pre-tension was given in the first loading and the tensile deformation was given along the RD in the second loading, the 0.2% proof stress in the second loading decreased with the increase in the angle between the first and second loading directions. Experimental and numerical results showed that the activity of {1012} detwinning increased with the increase in the angle. These results suggested that the 0.2% proof stress in the second loading was affected by the twinning formed in the first loading.

Magnesium has low specific gravity and high specific strength. Also, since it has excellent recyclability, magnesium is expected to be applied as a structural material for the purpose of reducing the weight of transportation parts. In order to apply magnesium to structural material, it is necessary to grasp fatigue characteristics. Fatigue tests were conducted at stress ratio = -1 using specimens cut out parallel to the rolling direction of rolled AZ31 Mg alloy under high stress amplitude. Fatigue tests were also conducted in each case of starting the tensile load and starting the compression load. The result was compared with a specimen cut out perpendicular to the rolling direction. Then, fatigue life of both specimens shortened at the start of compression loading. However, deformed twins are prefer to be formed during tensile load perpendicular to the rolling direction. In addition, it is suggested that the deformation twinning affects fatigue properties near the fatigue limit. Therefore, under high stress amplitude, it is considered that the activity of the slip system other than the deformation twinning also affects the fatigue properties.

The influence of the start loading direction (from tension and compression) on the fatigue life was investigated by performing the axial fatigue test. An axial fatigue tests were conducted with a stress ratio R = -1 and a stress amplitude σ_a= 100 MPa to 140 MPa. We used the rolled AZ31 magnesium alloy machined in the direction L parallel to the rolling direction in this study. The 0.2% proof stresses of tension and compression are 129 MPa and 78 MPa, respectively. This rolled AZ31 magnesium alloy shows an anisotropy. At all stress amplitudes, the fatigue life of the start from tension loading becomes longer than that of the start from compression loading. In the case of the stress amplitude of 140 MPa, the fatigue life of the start from tension loading was 3,717 cycles, and the fatigue life of the start from compression loading was 3,393 cycles. In particular, stress amplitude of 100 MPa, the fatigue life of the start from tension loading was 30,472 cycles, and the fatigue life of the start from compression loading was 26,360 cycles. In the case of a stress amplitude of 100 MPa, there is a great difference between the fatigue life of the start from the tensile and the compression loading, and the difference of fatigue life was approximately 4,000 cycles. Therefore, it is considered that the start loading direction affects the fatigue life in the L direction under high stress amplitude. The fracture surface of the specimens were observed using SEM. The fatigue crack initiated at the surface of the specimen. Fatigue crack propagated in the T direction.

View of improvement of Quality of life (QOL) for senior citizens, implant treatment that embed prosthesis into a living body has advanced as a method of treating for deterioration or a lesion part. Recently, addition of Hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂, HAp) coatings onto titanium alloy has been developed to reduce duration of treatment and improve strength of treated part. However, adhesion property between such coatings / substrates isn't well known. The purpose of this study is to establish evaluation method of interfacial strength for such coatings system. In this study, plasma-sprayed HAp coating specimens were investigated by means of both tensile adhesion strength test and shear adhesion strength test. The influence of evaluation method and pre / post heat treatment on interfacial strength of plasma-sprayed HAp coating was discussed.

In order to investigate the influence of SiC film thickness on interfacial fracture toughness, SiC films with thicknesses of 1μm, 2μm and 3μm were sputter coated on stainless steel rings with a diameter of 20mm, and a micro ring-compression test was carried out by gradually applying horizontal compression load to the specimen with observing deformation and delamination behavior. The result showed that the curvature of the specimen increased with increasing compression load, and delamination of the SiC film occurred with further increasing load after cracking of the film perpendicular to the loading direction. Scanning electron microscopic observation result showed that delamination of the SiC film occurred from the interface. Obtained interfacial fracture toughness monotonically increased with increasing film thickness. To discuss the reason for the change of the interfacial fracture toughness, X-ray residual stress measurement was carried out. The result showed that compressive residual stress was introduced in the films and the amount of the compressive residual stress increased with increasing film thickness. It was presumed that the interfacial fracture toughness was increased by the compressive residual stress.

Thermal Barrier Coating (TBC) is applied to gas turbine components to protect from high temperature environment. TBC system is composed of top coat (TC) as thermal barrier layer and bond coat (BC) for improving oxidation resistance and adhesion strength. In this study, we develop TBC system with high oxidation resistance and adhesion strength by grit blasting with Al₂O₃ grits. The idea is based on formations of Al₂O₃ layer at TC/BC interface for protecting an oxygen diffusion into BC and roughen BC surface for improving adhesion strength. TBC samples with different TC/BC roughness were prepared by grit blasting using different sizes of Al₂O₃ grits. From cross-sectional observation results by scanning electron microscope (SEM), uniform distribution of fine Al₂O₃ particles of diameter less than 1 μm was observed along TC/BC interface of blasted TBC specimen (which named B-TBC). High-temperature exposure treatment led to homogeneous Thermally Grown Oxide (TGO) growth in B-TBC sample in contrast to complex TGO formation in non-blasted standard TBC (S-TBC). It is presumed that TGO grows at TC/BC interface surface as if filling out the valley in B-TBC. It is confirmed that both Al₂O₃ layer and homogeneous TGO growth are effective for protecting from oxygen diffusion into BC.

The CoNiCrAlY coated Ni-base superalloy was exposed at 1000 and 1100°C for up to 1000h. The morphology and residual stresses in the Thermally Grown Oxide (TGO) layer on the CoNiCrAlY coating were examined by microscopic observation and luminescence spectroscope. The low pressure plasma sprayed CoNiCrAlY coating (LPPS) shows the thinnest TGO layer and lowest residual stress. Residual stress declined the longer the thermal exposure time, it was found that depending on the morphology of TGO layer. Further, the morphology of the TGO layer is likely to depend on the distribution of elements Yttrium to generate the Alumina layer / mixed oxide layer interface was found.

In order to apply silicon carbide (SiC) fiber reinforced SiC matrix (SiC/SiC) composite, which has light weight and superior heat resistance, for high-pressure turbine materials for aircraft engines, development of environmental barrier coatings (EBC) for SiC/SiC composite is essential. EBC is fabricated by depositing several layers on SiC/SiC composite and cooling it to room temperature. During the cooling process, the temperature gradient appears to occur due to the difference of thermal conductivities of EBC layers and substrate. The purpose of this study is to establish a theoretical framework for predicting energy release rate (ERR) for interface crack initiation due to thermal stress, taking into account the temperature gradient in an EBC model (Yb₂SiO₅ : Yb₂Si₂O₇ = 100:0, 80:20, 50:50, 20:80, 0:100/Mullite/Si-based bond coat/CVD-SiC). We conducted heat-transfer finite element method (FEM) analysis to obtain the temperature distribution in the EBC model during the cooling process. The result reveals that salient temperature gradient does not appear in the EBC layers and substrate. Thus, we can regard the temperature in the EBC as uniform. Thermal stress FEM analysis was also conducted to calculate ERRs for interface crack initiation due to thermal stress in EBC during the cooling process. We compared ERRs obtained by the FEM analysis and a simple theory for interface crack where ERR is estimated as the sum of nominal strain energies in the coating layers multiplied by a dimensionless factor. We found that the dimensionless factor is no longer a constant but is determined by thicknesses of Mullite, Si-based bond coat and CVD-SiC layers.

Cold spraying (CS) is a kind of deposition techniques that form a film by solid particle impingement onto the substrate at high velocity. This technique is considered that solid particles by CS, which are able to form coatings for removing native oxide film and forming active nascent surface by large plastic deformation at the time of impinging onto the substrate. On the other hand, surface activated bonding (SAB) is a bonding technique that it removes the oxide layer and form active nascent surface by using a fast atom beam (FAB) in a vacuum. There are a few similarities in bonding mechanism between CS and SAB. Conventional studies show that Al particles deposit on Fe substrate by CS, but Fe bulk did not bond Al bulk by SAB. The reason that both bulks do not bond by SAB is considered contact area of materials, but its detailed mechanism is not revealed yet. Therefore, the bonding of Fe foil and Al foil, and Fe bulk and Al bulk was carried out by SAB. Micro tensile tests in focused ion beam (FIB) equipment was used to measure the bonding strength. Micro tensile tests are able to measure the bonding strength of Fe foil and Al foil. The result showed that the bonding strength was proportional to contact pressure. In addition, the average roughness and Vickers hardness to confirm the deformation of foils and bulks were measured. These result suggested that foils and bulks did not deform. Consequently, it is suggested that it is important for SAB to increase contact area.

In order to investigate the fundamental process of residual stress development in thermal barrier coating during thermal spray, a model experiment was conducted using a paraffin wax. The melted paraffin wax was dropped onto a circular substrate of type 430 stainless steel, and strain and temperature were measured on the back surface of substrate. The model experiment revealed that tensile quenching strain was developed during solidification and adhesion process and it was increased with the number of droplets. Development of the quenching strain and failure of paraffin coating were significantly influenced by substrate temperature. The lower substrate temperature caused the larger quenching strain, and facilitated cracking, delamination and debonding of the coating. Findings in a series of the model experiments showed some similarities to actual phenomena during thermal spray, and will provide a helpful suggestion to optimize various process parameters in thermal spray.

Young's modulus of thermal barrier coating (TBC) is an essential mechanical property as it is required to design the superior TBC system. In this study, we evaluated Young's modulus of TBC at from room temperature to 900 °C based on the primary bending resonance of a TBC system specimen with a substrate. TBC was made by air plasma spray, and preheat treatment was applied at 1000 °C in air or vacuum. As a result, the Young's modulus of the preheat-treated TBC in air was higher than that in vacuum. It was found that the sintering is accelerated by oxygen in pre-heat treatment atmosphere.

TBC (Thermal Barrier Coating) protects 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 the CMAS component. In this study, thermo-mechanical tests on the CMAS infiltrated APSed YSZ TBC specimens were conducted. Changing point on a thermal strain curve of the CMAS infiltrated TBC top coat was observed around 700 °C. The temperature corresponds to the glass transition temperature of CMAS grass. Significant decrease in linear expansion coefficient of the CMAS infiltrated top coat was also observed. These results indicated that the thermo-mechanical characteristics of CMAS infiltrated top coat were strongly influenced by that of the CMAS, and such characteristics play an important role to develop a thermal stress and failure mechanism of TBCs.

In order to develop the environmental barrier coating for ceramic matrix composite, effect of high temperature aging on the pore structure and the mechanical properties of an atmospheric plasma sprayed Mullite (3Al₂O₃-SiO₂) coating and BSAS (BaO-SrO-Al₂O₃-2SiO₂) coating was investigated. In this study, the free-standing Mullite and BSAS coating specimens were prepared and the cross-sectional SEM observation was carried out to analyze the pore structure of coating. The elastic modulus and the fracture strength of the coatings were evaluated by means of the micro-indentation test.

We have established the torsion pin test method with tension to evaluate shearing delamination strength of thermal sprayed coating under tension-torsion combined stresses, recently. Apparent delamination strength depends on the diameter of the pin, so the stress distributions around the interface edge between the top-coat and the bonding coat have to be analyzed by using the finite element analysis based on the experimental results to see the real delamination strength. Before analyzing, the deformation propertiesofthe thermal sprayed coating have to be known. In this report, macroscopic nonlinear elastic deformation properties of the four kinds of porous Thermal Barrier Coating (TBC) is investigated experimentallyand analytically. First, the indentation tests were performed to obtain the load-depth curves, and secondarilyYoung's modulus were explored and then the coefficients A and n in the expression σ=Aε_nlⁿ which means the stress-nonlinear elastic strain relation were also explored as the results of the inverse analysis by using FEM analysis with Karman filter. And finally the coefficient B in the expressionσ=A(1+Bε_nl)ε_nlⁿ was explored in the same way as the final deformation properties for the four kinds of porous thermal barrier coatings.

Effects of hydrogen on fracture behavior in Al-Zn-Mg alloy have been crystallographically assessed using diffraction contrast tomography (DCT), which provides a description of the 3D crystallographic orientations of individual grains and the grain shape in polycrystalline materials. In this study, the fracture surface was mostly intergranular cracking, except some parts of no quasi-cleavage fracture. The intergranular crack initiated at a grain boundary surface perpendicular to the loading axis and adjacent to big grain.

Porous aluminum is a multifunctional material with ultra light weight and high energy absorption properties. In our past study, pure Al dense pipe were fabricated and combining it with ADC12 porous Al by applying friction welding. Precursor of ADC12 porous Al was fabricated by adding blowing agent powder into ADC12 plates by means of applying friction stir processing. The precursor was put into the fabricated pure Al pipe, and the rotating tool was pressed into the precursor. Friction heat was generated and ADC12 precursor / pure Al dense pipe composite materials were fabricated by friction welding. It was shown that metal bonding between porous Al and pure Al pipe of the composites can be realized. In this study, ADC12 porous Al / pure Al bilayer pipe were fabricated to combine ADC12 porous Al to the outside of pure Al pipe by applying friction welding. The specimen with porosity of 74.5 % was successfully fabricated.

A load-controlled fatigue test was performed at R = 0.1 in low cycle region in a dual phase Ti-6Al-4V alloy. In situ computed tomography was employed to measure short crack growth rates in the α, β phase and interphase for two crack length regions. Afterwards, a post-mortem serial sectioning coupled with electron backscattering diffraction (EBSD) was conducted to identify the crystallographic orientations of the α phase. Crack mainly propagates through the α phase in a facet-like growth in the first region. As crack follows the basal planes with high basal Schmid factors its growth rate increases, however, this rate decreases by following the prismatic planes with low factors. In the second region, crack follows mainly the prismatic planes with high prismatic Schmid factors in a tortuous-like growth.

Functionally graded porous aluminum (Al) was fabricated by spark plasma sintering process. In this process, the mixture of Al alloy powder, TiH₂ powder and Al₂O₃ powder (powder I) and the mixture of pure Al powder and sodium chloride (NaCl) powder as spacer particle (powder II) were used as starting materials. The powder mixtures were sintered by spark plasma sintering. Pores were formed by foaming and dissolution process. In this study, pore structures of obtained porous Al were nondestructively observed by X-ray computing tomography (CT).

In cast aluminum alloys, it is found from an experiment that a fatigue crack is initiated from the fracture of Si particles. We have been investigating a methodology to evaluate the particle fracture life from the geometrical parameters of Si particles. By using the synchrotron radiation CT, the geometrical parameters of Si particles were measured, and the image-based finite element analyses were also performed to evaluate the mechanical parameters of Si particles. A few effective geometrical and mechanical parameters were selected to determine the fracture of Si particles. The particle fracture life of Si particle was determined from the chronological observation of CT images. Then, the relationship between the particle fracture life and the geometrical and mechanical parameters were learned by the artificial neural network to predict the particle fracture life of unknown Si particles. In practice, forty three Si particles including the fractured and nonfractured particles were selected from five fatigue specimens, and used for the finite element analysis to evaluate the mechanical parameters. Their geometrical and mechanical parameters were used as the training data for the neural network. The validity of the predicted particle fracture life was examined through the comparison with the actual parameters of fractured particles.

A porous aluminum (Al) is ultra-light weight and has good energy absorptivity and sound insulation property. However, the tensile strength and bending strength of porous Al are lower than those of dense materials. A sandwich structure, which is consisted of porous Al core and dense metallic face sheets, is promised for using a porous Al as a structural component. In this study, a sandwich structure consisting of A6061-ADC12 functionally graded (FG) porous Al core and A1050 Al face plates was fabricated by friction stir welding (FSW) route precursor foaming method. Moreover, the porous Al core parts of the fabricated sandwich structures were observed by X-ray computed tomography (CT) and those pore structures were evaluated using X ray CT images. Through the observation and evaluation results, it was indicated that FG porous Al core sandwich structure, which has two layers of different alloys with good pore structure, can be fabricated by selecting appropriate foaming conditions in FSW route foaming method.

The fatigue crack initiation mechanism of cast aluminum alloy has been addressed by using the synchrotron radiation which gives a high resolution CT images to visualize the microstructure. By the 4D imaging, we have observed the crack initiation and propagation by low-cycle fatigue where the source of crack was the fracture of Si particle or debonding of Al-Si interface. The micromechanical finite element analysis can be performed with the precise microstructure based on the CT images. To investigate the effect of a small uncertainty in the applied cyclic loading on the stress and strain around the silicon particles which were fractured and initiated a crack in the fatigue test, the elastic-plastic finite element analyses was carried out with ten cycles of loading. The fractured silicon particles were identified from chronological CT observation. A method to make a reasonable waveform with precise mean and standard deviation was proposed. The small uncertainty coming from the experimental error was considered, and two types of cyclic loading waveform was made and used in the simulation. From those results, we found that the small uncertainty of applied stress had an significant effect on the maximum stress in silicon particles and increased it gradually by the cyclic loading.

Fatigue crack is initiated by the fracture of Si particles or debonding of Al-Si interface in low-cycle of cast aluminum alloys. To fully utilize the synchrotron X-ray CT image and evaluate the precise stress and strain in the microstructure under a cyclic loading, a large-scale finite element model was constructed based on the CT image. The outer surface, pores, Si particles and intermetallics were fully considered in this model. The voxel finite element was employed for simulation with stabilization. The number of finite elements was about 150 million. The analysis and post-processing were performed on the supercomputer by the massively-parallel computing with the domain decomposition techniques. The material and geometrical nonlinearities were considered, and the two cycle of loading was calculated. The result showed that the effect of free surface was predominant on the accumulation of plastic strain in matrix phase and the gradual increase of stress in silicon phase. The availability of massively-parallel computing to the large-scale micromechanical analysis was demonstrated. Moreover, the geometrical analyses of silicon particles were performed, then the correlation between mechanical and geometrical parameters were investigated statistically, where we found that the high stress concentration was occurred on silicon particles with complex shape and ones at the near of which other particle was present.

In this paper, a stochastic homogenization analysis is applied to composite material with three-dimensionally woven structures. Firstly, the parameters of the variability or uncertainty in composite materials were defined. Physical parameters were decided from the material property of fiber and matrix and the volume fraction of fiber and void in each yarn. Geometrical parameters were decided from the size and the waviness of yarn. Secondly, stochastic homogenization analysis and sensitivity analysis with respect to the yarn in z direction were carried out. The probability density was obtained for each component of the homogenized elasticity tensor. Among three geometrical parameters for the yarn in z direction, its cross-sectional area was mostly influential on the results.

The thermo-elasto-viscoplastic behavior of carbon fiber-reinforced thermoplastics (CFRTP) was evaluated using the homogenization theory taking into account the time dependence of the relation between stress and strain. The thermo-elasto-viscoplastic constitutive equation was newly proposed by introducing temperature dependence into the elasto-viscoplastic constitutive equation of a thermoplastic resin. The thermo-elasto-viscoplastic analysis of the CFRTP laminates was then performed by the finite element method based on the homogenization theory. In the demonstration, uniaxial tensile tests of the CFRTP laminates were performed to confirm the validity of the proposed method. The numerical results showed a good agreement with the experimental results in the elastic and viscoplastic regions for all temperature and loading conditions.

In this study, creep analysis of plain-woven glass fiber-reinforced plastic (GFRP) laminates using a triple-scale homogenization method is conducted. In the triple-scale homogenization method, first, an analysis model is defined, in which a plain-woven laminate is regarded as a macro structure, plain fabrics and a matrix as a meso structure, fibers and a matrix in fiber bundles as a micro structure. Then, a nonlinear time-dependent homogenization theory is applied to the macro/meso and meso/micro problems, respectively. This method can directly take into account not only the creep properties of fiber bundles but also those of fibers and matrix materials in the fiber bundles. Using the present method, creep analysis of plain-woven GFRP (E-glass/epoxy) laminates subjected to on-axis (0°) and off-axis (15°, 30°, 45°) loading is performed at 25°C and 80°C, respectively. It is shown that the present method can take into account the effects of creep behavior of the epoxy in fiber bundles on the macroscopic creep properties of the plain-woven GFRP laminates. It is also shown that the temperature change greatly affects the creep behavior of the laminates.

Composite materials are applied to aerospace structures because of its unique material properties. Since the kind of composite materials is inhomogeneous and anisotropic materials, the numerical analysis is used for evaluation of composite’s deformation behavior as well as damage progression. We used an unidirectional carbon fiber reinforced plastic (CFRP) specimen to measure the elastic constants of a CFRP laminate. Resonant ultrasound spectroscopy (RUS) method is an experimental/analytic technique to determine the elastic constants by measuring the natural frequencies of solid specimens. In this study, we measured the natural frequencies of the unidirectional CFRP specimen, and the elastic constants of that were investigated by using the finite element method and the optimization technique using the quasi-Newton method and the golden section method. Moreover, we estimated the elastic constants of the unidirectional CFRP by the homogenization method. We compared with the elastic constants obtained from the RUS method and the homogenization method to estimate the elastic constants of the carbon fiber in the unidirectional CFRP laminate. The elastic constants of the carbon fiber were overestimated compared with previously-reported values, because the anisotropic of the carbon fiber is not considered for the analysis of the natural frequencies of the specimen. It is considered that accurate estimation of the elastic constants of the carbon fiber is possible by accurate measurement of the natural frequencies in RUS method.

Micromechanical analysis is performed to the composite material containing many misoriented reinforcements. Then macroscopic total strain and overall interaction stress occurred in the composite are expressed explicitly by considering the continuous distribution of zenithal angle of reinforcement which covers from unidirectional distribution to 2-dimensional random one via 3-dimensional random one. In the analysis, the azimuth angle and the rotation angle in the y-convention of Euler's angle are assumed to be uniform. Moreover, by introducing the stereological concept into the model, the distribution of aspect ratios of profile of reinforcement appeared in the cross section can be related with the macroscopic properties of the composite.

Research and development of game-changing ultrahigh reliability ceramics composite material has been conducted to resolve the reduce carbon dioxide emissions. This material is called self-healing fiber-reinforced ceramics (shFRC), and it consists of three layers: a base material layer called a matrix, a fiber layer called a fiber bundle, and an interlayer containing a material called a “self-healing agent”. When the microcracks owing to foreign object collision occur, the rapid fracture is suppressed by crack bifurcation at the interlayer. It is also possible to suppress brittle fractures by the effect of frictional resistance. Further, when a crack propagates in the interlayer subsistent self-healing agent, self-healing autonomously occurs owing to high-temperature oxidation. However, to effectively demonstrate the self-healing function, a crack bifurcation have to be controlled. In this study, the crack propagation is investigated using the Finite Element Analysis (FEA). In FEA, the microscopic structure of shFRC having three-layer construction is discretized. Using FEA, ideal relationships of fracture parameters between fiber bundle and interlayer considering with composite ratio of each layer, sintering characteristics and its dispersion are examined. In this results, depression effect of fiber bundle fracture was increased by porosity decreased. It may be possible to propose guide of back-casting about porosity, thickness and fracture parameter of interface layer to what extent expected at the structural design of shFRC.

Recently, replacing conventional metal components with CFRP has been promoted in automotive industry to realize weight saving. CFRTP whose matrix resin is thermoplastic has advantage of productivity comparison with conventional CFRP. Therefore, it is expected that CFRTP applies to production vehicles. However, it is necessary to develop lightweight and efficient methods of jointing dissimilar materials like CFRP and metal. Heat welding is one of the solution. So, we manufactured CFRTP/Metal composite beam by using heat welding and conducted DCB test and single lap shear strength test. Fracture toughness of interface calculated by BEM analysis and shear strength of interface showed differences of adhesive properties in press temperature. And we examined jointing mechanism by observing cross section of jointing part and fracture surfaces.

In this study, we apply the previously proposed constitutive model to a series of healing-damage processes in self-healing ceramics. The numerical model is imitated a series of experiment of alumina/15 vol.% SiC composites. In the FE analysis, first, an initial damage region due to Vickers indentation is healed under certain temperature and oxygen partial pressure conditions. We then perform the three-point bending analysis, to consider the self-healing effect. Based on FEA results, it is confirmed that the material strength and stiffness in the bending test depend on the healing time and environment as observed in the experiment.

In recent years, applications of fiber-reinforced plastics (FRPs) to large marine structures are expected to improve their performances due to the high specific strength and stiffness and the corrosion resistance. However, the creep lifetime of FRPs in seawater environment has not been made clear so far. Objective of this study is to predict the creep lifetime of FRPs in seawater environment based on the accelerated test results and reveal the fracture mechanism. In this study, creep tests were carried out using the plain-woven GFRP and CFRP laminates under seawater environment and time-temperature superposition principle (TTSP) was used to predict the long-term creep rupture life. It was shown that the rupture time decreased with increase of the seawater temperature and the applied stress, and it was suggested that decrease of the strength was mainly caused by degradation of the interfacial shear strength between the fibers and the matrix. By using Larson-Miller parameter (LMP) as time-temperature parameter, the analytical results showed good agreement with the experimental results. For the GFRP laminates, behavior of the prediction curves varied in the lower applied stress because the glass fibers deteriorated in seawater. On the other hand, deterioration of carbon fibers was not observed in seawater so that the rupture time showed a consistent tendency to decrease for the CFRP laminates.

The relation between mechanical properties of discontinuous carbon fiber reinforced plastics (CFRP) and the length and orientation of reinforcements were investigated. In this work, the blend of chopped CF (6 mm length) and polyamide 6 (PA6) were extruded and were pressed in order to prepare CFRP sheet. The orientations of CF in the CFRP were estimated by the X-ray diffraction of graphite in CF. The tensile modulus and bending modulus of those CFRPs depended on the orientations estimated by X-ray diffraction pattern. It was shown that X-ray diffraction is available for discussion about relation between mechanical properties and fiber orientations in the discontinuous CFRP.

A composite material called Carbon Fiber Reinforced Plastic (CFRP), one of the advanced materials, is lighter, higher strength and higher rigidity than iron. However, it is weak against impact, internal damage such as delamination occurs, and the mechanical properties may decrease. It is difficult to evaluate damage and to distinguish by external inspection. CFRP is known to generate heat when CFRP is subjected to impact loading and fracture. In the present study, the CFRP laminate was subjected to falling weight impact loading and the temperature change of the CFRP laminate at impact loading was measured by infrared thermography. In addition, we investigated the relationship between internal damage and temperature distribution and investigated the possibility of non-destructive inspection for falling weight impact damage within CFRP laminate. As a result, CFRP laminate generated heat with failure. The maximum temperature of heat generation increased as the impact energy increased. The longer the crack length, the larger the heat generation area and the larger the heating value. As the number of cracks increased, the heating value increased. Therefore, there was a clear relationship between heat generation and internal damage of CFRP, and it was confirmed that internal damage can be evaluated from the change of temperature distribution.

The energy absorbing performance of glass fiber reinforced thermoplastics was evaluated by progressive crushing tests with the Split Hopkinson Pressure Bar (SHPB) apparatus. Two types of specimens, one was injection molded glass long fiber reinforced polyamide 66 (GF/PA66), the other was twill weave glass fiber reinforced polyamide 6 (GF/PA6), were prepared as specimens. As for injection molded plates of the GF/PA66, it was investigated the influence of the fiber orientation on the impact mechanical behavior of the test specimen cut out from the different position of the plate. Also, the impact behavior of injection molded the GF/PA66 plates and that of twill weave GF/PA6 laminates were compared in order to investigate the influence of the variation of reinforcing types. As a result of the progressive crushing tests at -30, 23, 90°C, it is revealed that the energy absorbing performance has no temperature dependency regardless of the fiber orientation and the reinforcing types. The reason that the SEA of the GF/PA66 increases with the mechanical properties was discussed from the comparison of the specific energy absorption (SEA) and the compressive strength. In the comparison of injection molded the GF/PA66 and the GF/PA6 laminates, the specimens were reinforced by the different mechanisms; therefore, it seems that influence of mechanical properties on the SEA is not critical because those fracture modes are different.

In order to evaluate the fracture strength of a composite reinforced pressure vessel (CRPV), a full-scale vessel test is required by standards ASME BPVC-VIII-3-2017, and KHKTD 5202. However, such a test consumes a considerable amount of time and money. In evaluating the fracture strength of the CFRP layer using a plate specimen, there are some problems (e.g. stress concentration at the grip). In this paper, internal pressure burst tests using a small CRPV specimen were conducted in order to establish a method of evaluating the fracture strength of the CFRP layer.

The study is to investigate the mechanical properties, cracks behaviors and the effect of matrix cracking on the mechanical properties of angle-ply FRP laminates. Three types of materials were tested for this purpose: 1. CFRP (T700SC/2592, Torayca), 2. CFRP (T700SC/2500, Torayca), 3. GFRP (GE352G135SB). FRP laminates with laminated structures of [θm⁽²⁾/ θn⁽¹⁾]s are monotonically loaded to obtain its mechanical properties. In order to obtain more cracks on specimen, notches were made at the edges of some specimens to create artificial cracks before tested by tensile test machine. Cyclic loading tensile test were also done at certain stress points after inlinearity started to form. As the laminates are loaded and unloaded back to 0 MPa, strain became non-zero due to the existence of residual strain, where laminates are plastically deformed. Cracks observation for CFRP laminates was done by using X-ray machine while for GFRP laminates, due to its semi-transparent properties, cracks formation can be viewed in real time by using DSLR camera. The experimental results of stiffness reduction and crack density relationship agreed well to analytical results. Understanding the damage behavior in cross-ply and angle-ply laminates is important so that damage behavior and its effects in laminates with more complex configuration such as quasi-isotropic laminates can be predicted.

Polymer matrix composites (PMCs) that have high specific strength and specific rigidity have been used in aerospace fields. Fiber-reinforced composite laminates exhibit specific fracture processes such as transverse cracks (cracks in a direction parallel to the fiber), delamination, and breakage of the fiber. In these fracture processes, transverse cracking occurs in the earliest stage. Therefore, it is important to clarify the mechanical behavior of laminate including transverse cracks. To evaluate the relationship between the mechanical behavior of composite laminates and transverse cracking, we formulated the continuum damage mechanics model for predicting the stiffness reduction of composite laminates including transverse cracks and the transverse cracking progression model in laminate including 90° plies. For development of the present models, stress field model, which takes into account thermal residual strain for plies including transverse cracks, was formulated based on micromechanics. Then, the damage variable in the direction normal to the fiber of a ply including transverse cracks and the energy release rate associated with transverse cracking were calculated using stress field model for plies. Finally, we compared the results obtained from present models to those of the finite element analysis (FEA) and experiment results reported in previous studies. Consequently, present models could predict the FEA results and experiment results quantitatively.

Since the fiber/matrix interface significantly affects the fracture behavior of composite materials, the interfacial properties must be properly evaluated for long-term safety of structures. Cohesive zone model has been widely used to evaluate the interfacial strength because it avoids the stress singularity along the interface by effectively including the damage process zone. Among various cohesive zone models, Ma-Kishimoto model is not only practical but also physical because it was established based on a continuum damage mechanics. In this study, material parameters of Ma-Kishimoto model are determined to evaluate fiber/matrix interface of composite material. Analytical model of boundary element method was developed for a single fiber fragmentation test, whose interfacial parameters are reduced to three parameters of initial interfacial rigidity K_t⁰, critical interface damage D_c, and critical interface separation λ_c. A boundary element method was applied to investigate the relationship between these parameters and interfacial strength t₀, interfacial fracture energy G_c, and stress distribution along interface. The numerical analysis clarified the influence of D_c on debonded length along interface under constant t₀ and G_c.

Weldlines are one of the major defects in plastic injection molding (PIM). The weldlines have an influence on not only the strength of product but also the appearance, so it is important to reduce the weldlines as much as possible. The melt plastic will be quickly solidified with the low weldline temperature, that makes the weldlines long. Then, we consider that the weldline temperature will be an important factor for the weldlines reduction. Clamping force also affect the product quality, but the relationship between the weldlines and the clamping force is rarely discussed in the literature. In this paper, the minimum weldline temperature is maximized for the weldlines reduction, whereas the clamping force is minimized for the high product quality. Therefore, a multi-objective design optimization is performed and the pareto-frontier between them is identified. Numerical simulation in PIM is generally so intensive that a sequential approximate optimization (SAO) using a radial basis function (RBF) network is used to identify the pareto-frontier. Through the numerical simulation, the trade-off between the minimum weldline temperature and the clamping force is clarified. Based on the numerical result, the experiment is carried out in order to examine the validity of the proposed approach. Through numerical and experimental result, the validity of the proposed approach is confirmed.

Process parameters in plastic injection molding (PIM) such as the packing pressure, the melt temperature and the cooling time have a direct influence on the product quality. It is important to determine the optimal process parameters for high product quality. In addition to the product quality, high productivity is required to plastic products. This paper proposes a method to determine the optimal process parameters in the PIM for high product quality and high productivity. A constant packing pressure during the PIM is conventionally used, but the multistage variable packing pressure profile that the packing pressure varies in the packing phase is adopted as the advanced PIM. Warpage and cycle time are taken as the product quality and the productivity, respectively. Then, these are simultaneously minimized and the pareto-frontier between them is identified. Numerical simulation in the PIM is so intensive that a sequential approximate optimization using radial basis function is adopted. It is found through the numerical result that the multistage variable packing pressure profile can improve both the warpage and the cycle time, compared with the conventional PIM approach. It is confirmed through the numerical result that the proposed approach is valid for minimizing the warpage and the cycle time.

In plastic injection molding (PIM) is one of the most manufacturing process for producing plastic product. In PIM, warpage and weldline are major defects and they should be minimized for high product quality. Process parameters such as melt temperature, injection time, packing pressure and cooling time strongly affect product quality. It is important for minimizing warpage and weldline to determine the optimal process parameters. This study considers the box type product and proposes a method to determine the optimal process parameters for minimizing the warpage and maximizing the minimum weldline temperature. It is difficult to measure the length of weldline directly, and other method is needed to evaluate the weldline indirectly. The higher the minimum weldline temperature is, the shorter the length of weldline is. So, the minimum weldline temperature is maximized to minimize the length of the weldline. Numerical simulation in the PIM is so intensive that a sequential approximate optimization is used to identify the pareto-frontier. Through the numerical result, it is confirmed that there is trade-off relationship between the warpage and the minimum weldline temperature. In addition, it is identified that the melt temperature and the injection time have influence minimum weldline maximization and the packing pressure has influence warpage minimization.

This study focuses on thermoplastic resin impregnation behavior in carbon fiber reinforced thermoplastic polyimide (CFRTP). The objective of the present study is to clarify the relationship between molding conditions and resin impregnation to fiber bundle and the effect of resin impregnation on the mechanical properties of the composites. Specimens were prepared using micro-braiding, film stacking and powder methods. The analytical prediction for resin impregnation showed a good agreement with the impregnation ratio experimentally-obtained. In addition, the void content inside the fiber bundle could be drastically reduced by pressurized cooling.

This study examines the apparent interlaminar shear strength of spread carbon fiber (SCF)/epoxy (EP) laminates containing hollow silica particles. Short beam shear specimens of unidirectional SCF/EP laminates containing hollow silica particles were fabricated and tested. The effect of hollow silica particle concentration and diameter on the apparent interlaminar shear strength of the laminates was discussed. The damage area of specimens was also examined by an optical microscope. The results demonstrated that the apparent interlaminar shear strength of SCF/EP laminates containing hollow silica particles was higher than that of SCF/EP laminates with urea-formaldehyde microcapsules. In addition, procedures for making microcapsules of hollow silica particles was investigated.

This study examines the mechamical properties of hydrophobizing agent treated cellulose nanocrystal (CNC)/polypropylene(PP) composites. We discovered new hydrophobizing agent(HA) that enables interactions between CNC surfaces. HA helps CNCs dispersion in polyolefins. To form interface between CNC surface and polypropylene, maleic acid polypropylenes were added. Using twin-screw extruder operating at 130rpm and 200°C, CNC/PP composites were prepared by melt-compounding. Tensile tests were carried out to assess the effects of CNC content on the mechanical properties of the CNC/PP composites.

High strength properties of cellulose nanofiber (CNF) are well known, and it has also been already reported that the strength of CFRP could be improved by dispersing CNF in the matrix resin. However, in the previous work, hydrophobic treatment was required to disperse CNF due to its hydrophilicity. In this study, based on a novel manufacturing method of CFRP by using electro-activated deposition resin molding, CNF without hydrophobic treatment was well dispersed on the surface of CFRP. The process was, firstly, the non-crimp carbon fiber fabric was immersed in an electro-activated deposition solution which includes epoxy groups. And, the fabric was electrically energized and electrodepositioned. Secondly, the CNF dispersion was applied and coated to the surface of CFRP. The electrodeposition solution used in this method is an environmentally friendly aqueous solvent. CNF has good dispersibility in water, hydrophobic treatment was not necessary. After heat curing, the three-point bending test was conducted to confirm the strength properties. As a result, it was found that the flexural modulus was improved by 49% and the bending strength was improved by 41%, comparing to the CFRP without CNF on the surface.

In this study, based on the curved beam theory, the bending tests of fingernails were performed, and the structural elasticity of fingernails was determined. The determined value of the structural elasticity of fingernails was about 2.0 GPa. On the other hand, that of the manicured fingernails was about 0.9 GPa, and the manicured fingernail was found to have lower structural elasticity compared with the normal fingernail.

Viscoelastic models are necessary to simulate the behavior of time-dependency materials such as polymer industrial products and biological tissues. Indentation test have been widely used in the many study because of its simplicity for estimate of local mechanical properties of bulk materials. This study obtained analytical solution of relaxation indentation problem of viscoelastic thin layer bonded on rigid substrate indented by flat-ended cylindrical punch using elastic-viscoelastic corresponding principle for axisymmetric elastic contact problem. The relaxation indentation test is conducted for two different polymer materials which are polymethyl methacrylate (PMMA) and polyvinyl chloride (PVC) and bovine articular cartilage of the femoral head. For bovine articular cartilage, normal cartilage treated by collagenase after relaxation indentation test and test is conducted again. The standard linear solids model is chosen as viscoelastic model in this study, then viscoelastic parameters of the model are determined by fitting experimental data collected from the relaxation indentation test. As results, the values of Root Mean Squared Error (RMSE) which indicate the error between experimental data and analytical solution show 0.59, 0.37 for respectively PMMA, PVC and 0.78, 0.52 for respectively normal and treated bovine articular cartilage. The results indicate articular cartilage needs more complicated viscoelastic model than the standard linear solid model. The analysis provide a fundamental basis for evaluating viscoelastic parameters of thin layer with the relaxation indentation test.

This paper presents a formulation and solution of a problem to identify the muscle activities when a deformation of boundary with respect to an organ are given. An aim of this study is to investigate the mechanism of swallow motion and cause of aspiration. Using a model of tongue consisting of hyper elastic body, we consider that the given deformation is realized by the compulsory displacement on the boundary which shape is known, and that muscle activity is assumed as inelastic principle strain generated in the direction of minimum principle strain of the hyper elastic deformation. The identification problem of muscle activities is formulated using the inelastic principle strain as design variable and the work done by the compulsory displacement as cost function of minimization. Solution of the problem is presented based on the scheme using the H¹ gradient method for topology optimization problem of density type. A numerical example done in the previous study is introduced to show the validity of the present theory.