In this study, the origin of amounts of localized strain in basal textured Magnesium alloy sheets was investigated. First, grid patterns were drawn on a top surface of sample by Focus Ion Beam system. And then, a distribution of crystal orientation from same area was observed by SEM/EBSD. From these methods, the relationship between the localized strain and crystal orientation was revealed. In generally, the amounts of strains are dependent on the crystal orientation, which means the facility of slip deformation. However, my results show that localized strain is dependent on the existence or absence of twins and twin types, and but not on the Schmid factor of basal slip. And I suggest that {1012} type has the roll of strain accommodation to satisfy the strain compatibility with neighbor grain in primary deformation stage and continue to cancel the strain of slip during deformation. So the grain with {10-12} type slightly deformed. On the other hand, {10-11} type has the roll of accommodation strain component to conform to externally applied stress. But {10-11} twin easily generate double twin. And the grain with double twin localized severely deformed and formed surface steps or cracks.

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A thermodynamics-based constitutive model, which accounts for both crystallographic slip and deformation twinning, is developed for a single crystal of hcp metals within the framework of finite crystal plasticity. While the volume fractions of stress-free twin deformations are introduced as internal variables, the free-energy involves the bulk energy of separate phases and the surface energy at twin interfaces, which are introduced as functions of the internal variables, in addition to the standard hardening-related energy in crystal plasticity framework. After the formulation is described in detail, a series of numerical examples is presented to verify the performance of the proposed model in predicting the deformation twinning, the successive deformation process and the twinning-induced stress responses. The results are studied with reference to the theoretical consequences and the experimental results reported in the literature.

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This paper presents a crystal-plasticity finite-element simulation of deformation behavior during unloading in a magnesium alloy sheet considering twinning and detwinning. A detwinning model proposed by the authors was employed. The detwinning model could be employed in the framework of a twinning model proposed by Van Houtte (1978), with which shear strain and lattice rotation due to detwinning could be taken into account in the crystal-plasticity finite-element simulation. The material parameters were determined so as to obtain reasonable fits with stress-strain curves obtained from experiments of a rolled AZ31 magnesium alloy sheet. A loading-unloading process under in-plane compression was simulated, focusing on the activities of twinning and detwinning. A pronounced inelastic deformation arose during unloading in the simulation, and this tendency was in good agreement with the experimental result. We found that the pronounced inelastic deformation arose because of not only the activation of detwinning during unloading but also the dispersion of crystal orientations owing to the activity of twinning during loading.

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Deformation twinning is one of the primary mechanisms in the deformation of hexagonal close-packed crystals. In this study, using first-principles calculations and empirical interatomic potential, we carry out energetic analysis of the twin boundaries and the twinning dislocations in Mg, and investigate effects of impurities such as yttrium. The dislocation energy and the Peierls potential barrier of the twinning dislocation of {101^^-2} twin are significantly small, compared to {101^^-1} twin. The impurity energy of a substituted yttrium atom is correlated with the averaged interatomic distance and the impurity atoms are more stable at a sparse site of the inhomogeneous atomic configuration of the twin boundaries, compared with at a homogeneous matrix site.

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Effects of backup ring (BR) and squeeze ratio on sealing performance and fracture behavior of cylindrical static seals were investigated under cyclic exposure to high-pressure hydrogen gas. The O-ring specimen was made of a filled silicone rubber. Two types of BRs, BR1 and BR2, were prepared.BR1 was composed of one BR, which was made of polyamide (PA), and BR2 was composed of two BRs, which were made of polytetrafluoroethylene (PTFE) and PA. The squeeze ratio was set to be 10 % or 20 %. Under these sealing conditions, pressure cycle tests of the cylindrical static seals were performed at 100 cycles under hydrogen gas of 70 MPa and temperature of 30 ℃ by using a durability tester. In spite of the sealing conditions, no drastic gas leakages were observed after the pressure cycle tests. The fracture morphology caused by extrusion of the O-ring was clearly influenced by BR, and BR2 prevented the extrusion fracture on the surface at a low-pressure side, different from BR1. This is presumed to be due to a large deformation of PTFE used for BR2. Furthermore, BR equipped at a high-pressure side also prevented the extrusion fracture on the surface at its side.

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The 70 MPa class high-pressure hydrogen tank applied for FCV(Fuel Cell Vehicle) system requires seal durability of rubber O-ring with pressurized and decompressed hydrogen cycles. When rubber composites are used under high-pressure gas, internal cracks (blister) sometimes occur, and the sealing performance degrades with the blister growth. In this study, we evaluated a long-term seal durability of rubber O-rings in hydrogen pressure cycles from 70 to 0.5 MPa at 30 ℃ using compact pressure vessel. EPDM, VMQ and HNBR rubber O-rings designed on hardness at JIS A80 were employed for the pressure cyclic test. These O-ring specimens were installed in a flat face static sealing groove for internal pressure application and were subjected to cyclic hydrogen pressure of 5,500 cycles. No blisters were observed on the cross-section of the O-ring specimens after the test, and the cyclic hydrogen pressure hardly influences their repulsion force for sealing. This result implied that the sealing performance was maintained at this condition.

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The rubber belt for CVT in scooter is subjected to the complex loadings, because the CVT performs as the variable speed device and as the power transmission. Therefore, the failure mechanism of the CVT rubber belt is considerably complex, and therefore the failure mechanism has not sufficiently been understood. There are three major failure modes for the CVT rubber belts. There are three major failure modes for the CVT rubber belts, namely tension rubber crack, bottom land crack and adhesive rubber crack. Moreover, the adhesive rubber crack was classified into the surface-crack and the de-bonding of the interface. In this study, the author evaluated the fatigue life based on the shearing stresses in the adhesive rubber layer. Moreover, the initiation mechanism of the bottom land crack was discussed by using the failure observation.

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We investigated the effect of rubber-block shape on the localized buckling of sliding surface. The plane-strain finite deformation field subjected to both compression and shear is determined under the assumptions that the rubber block is incompressible, neo-Hooke material. By comparing the applied strain with the critical strain addressed in [H. Hohlfeld and L. Mahadevan, Phys. Rev. Lett. 106 (2011) 105702.], we estimate the onset of the localized buckling of the block in connection with the rubber-block shape.

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Boundary value problems involving contact are of great importance in industry related to mechanical and civil engineering, but also in environmental and medical applications. While the rubber materials so called elastomer admit to deform large deformation in a practical manner. Therefore it is needed the choice of excellent numerical procedure for contact problem. This paper refers the various contact models, and shows the numerical result of the hollow rubber ball which has the enormous difficulty of contact condition.

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Based on the Persson's mathematical model, we propose the procedure of estimating the friction coefficient for a rubber block sliding on a road surface with multiscale asperities. In our model, we create a new methodology of determining the wavenumber range for the calculation from the standpoint of elasticity limit of rubber. Comparing the estimated friction coefficient with that of experiment, we also discuss the some factors of the rubber friction due to hysteresis loss, adhesion and local temperature increase.

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When handling the rubber like materials, it is necessary to understand their complex phenomena, such as static behavior as well their dynamic behaviors and damage behaviors. We performed several measurements for natural rubber material applying digital image correlation (DIC) method. On these cases, we found that DIC is an useful tool with high accuracy for measuring covering from narrow to wide visible range.

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For identifying a constitutive model of an incompressible hyperelastic material such as rubber, tensile tests under three deformations (simple tension, pure shear and equibiaxial tension) are sometimes performed by using an in-plane biaxial tensile tester. In the typical in-plane biaxial tensile tester, uniform deformation is not obtained in a rubber specimen due to stress concentration caused by clamps; however, its influence is often ignored to calculate stress and strain at uniformly-deformed region in the specimen. This study indicates a method for accurately estimating stress and strain at the uniformly-deformed region in the specimen by using the typical biaxial tensile tester. A unique rubber specimen with holes was prepared based on the analysis by FEM; then, their tensile tests were performed under three deformations (simple tension, pure shear and equibiaxial tension). The experimental stress and strain data were successfully fitted by a polynomial Mooney-Rivlin model. A biaxial tensile test of a cross-shaped specimen was also performed, and the relationship between force and displacement of the specimen simulated by using material constants identified from the specimen with holes had a good agreement with the experimental one, different from that simulated by using material constants identified from a conventional specimen without holes.

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In-plane biaxial testing produces a two-dimensional stress-state that can be used to characterize the mechanical behavior of rubber materials. A technique is proposed of calculating nominal stress and strain from the tensile load-displacement data measured in biaxial testing. The technique is characterized by its simple concept and the evaluation formula with high accuracy. The validity of the technique is verified through the 3D Finite Element Method.

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A numerical computation of consistent tangent moduli using complex-step derivative approximation (CSDA) is presented, and it applications to non-linear viscoelastic material model at finite strain are demonstrated. This study shows a simple, robust and efficient numerical approximation of the tangent moduli that can be easily implemented within commercial FE software, Abaqus. The implementation and the accuracy of this approach are demonstrated.

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Polymeric material is used in fields such as electricity and electronic parts. In this report, deformation behaviors of polypropylene after pre-straing are investigated under biaxial stresses to establish the constitutive model. A series of equi-strain loci after tensile and torsional pre-straings can be expressed numerically for various strain rates in Mises type stress plane by considering hydrostatic pressure effect in flow stress. By using the obtained equations of the equi-strain loci and the normality rule with respect to plastic strain incremental vector, stress paths are calculated at loading along various strain paths with a corner of various angle. It is confirmed that rather good agreement can be obtained between experimental and predicted results on stress-strain curves of Polypropylene in reloading after pre-straings.

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Nonlinear stress-strain curve of high polymer material with plastic deformation was estimated from load-deflection curve of 3-point bending test. Equations of curvature and strain were derived from load-deflection curve by applying geometrical relation. An equation was derived for estimating stress from moment and curvature. Finite element analysis was conducted for verifying these equations for estimating stress-strain curve. Deflection of simply supported beam model with rectangular cross-section was calculated for a certain stress-strain relation. The stress-strain relation estimated using the equations showed good agreement with the actual one. We verified that the proposed method for estimating stress-strain relation from the load-deflection curve of 3-point bending test was useful.

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The Natural Strain is obtained by integrating an infinitesimal strain increment on identical line element. Since the rigid body rotation can be removed from the rotating angle of a line element and the additive law of strain on an identical line element can be satisfied, the Natural Strain theory is effective strain expression for representing a large plastic deformation. In the previous report, using the Natural Strain theory, the shape of yield surface and the distribution of modulus of strain hardening h around the yield surface have been examined by conducting the proportional loading tests for tension and torsion after giving the pre-deformation of uni-axial tension or simple shear. In this paper, the shape of the yield surface, which is obtained after giving the pre-deformation of proportional loading for tension and shear, is estimated by examining the modulus of strain hardening h in various directions in the stress space.

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Applicability of constitutive models which are widely used to simulate the dynamic behavior of materials and structures are discussed by comparing the properties of these models with the experimental data which cover not only for the homogeneous deformation but also for the entire deformation reaching the true fracture strain. It is clearly shown that the Tanimura-Mimura model 2009 is effective to simulate the dynamic behavior, and is especially efficient for the case of occurrence of a large deformation reaching fracture.

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The method of finite strain measurement based on the image analysis is suggested by using the Natural Strain theory. The effectiveness of this measurement method is verified by comparing the strain measurement by the image analysis with the conventional measurement based on the displacement meter, and the validity of this method has been examined for uni-axial tension and simple shear. However, in our previous study, the validity of this method was confirmed by the measurements within the uniform deformation, and the local deformation has not been examined yet. So, the measurement under local deformation is examined in this paper. Especially, the measurements of local deformation for simple shear after uni-axial tension are conducted by using the image analysis, and the result obtained at the middle portion of the specimen is compared with the result of upper portion of the specimen.

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For prediction of thermal ratchet deformation on FBR pressure vessels, the inelastic constitutive model is required to simulate both cyclic hardening and its recovery during high temperature operation. In this paper, macro model is examined to simulate the recovery of cyclic hardening, which will be linked with the micro model based on the hypothesis that dislocation structures are dissolved with holding period increasing under high temperature. The structural analysis with the macro model demonstrates that the recovery induces the progress of axial and radial plastic strain. It indicates the necessity to simulate the recovery of cyclic hardness in inelastic constitutive models.

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We estimate effects of ply thickness in mechanical properties and damage evolution of CFRP angle-ply laminates under various tensile loading. It should be noted that the laminate thickness is almost the same, but the ply thickness are quite different. Monotonic tensile tests, cyclic loading-unloading tensile tests and stress relaxation tensile tests are performed on [(±θ)12]s (t-0.05prepreg×48plies), [(±θ)4]s(t-0.15prepreg×16plies) and [(+θ)4/(-θ)4]s (t-0.15prepreg×16plies) T700SC/2500 carbon/epoxy laminates with various fiber directions (θ=30, 40, 45, 50 and 67.5°). Ply thickness is expressed as t-0.05, t-0.15 and t-0.6, respectively. Damage evolution can be determined by cyclic loading-unloading tests. We use mesoscale damage model to investigate damage evolution in CFRP laminates. We discuss effect of ply thickness on mechanical property of angle-ply laminates. Laminates have thin ply thickness showed high strength and fracture strain.

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Structural members of automobiles are required to improve collision safety and reduce weight for the purpose of lower fuel consumption. Therefore a thin-walled cylinder which has excellent energy absorption efficiency and lightweight is used for the shock absorber of structural members. This cylinder absorbs impact energy in the continuous plastic buckling distortion caused by axial impact loading. However the load histories of the axial crushing of the cylinder repeat the periodic variation with the local buckling. That is causing the decrease of energy absorption efficiency. For this reason, the design which suppresses variation of load lead to improved energy absorption efficiency. The purpose of this study is to develop members improved the stability of load. We examined the optimal cross-sectional shape of the cylinder to reduce the load variation with FEM analysis.

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As one of the analytical techniques of mechanical behavior for textile composites, the inclusion element method was proposed. It is possible to analyze them using very simple gird finite elements. In this study, the effectiveness verification was carried out by applying it to the spread woven fabric composites. The full-field strain distribution was measured using the 3D digital image correlation method. The peculiar deformation and strain distribution of woven fabric composites were obtained from the analysis and the measurement. As a result of comparing the analysis with the experiment, both results were compatible with each other. It was proven that the inclusion element method was an useful technique for various textile composites.

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Woven fabric composites with spread tow may induce better resin mechanical properties than the conventional woven architectures. The tow structure makes it possible to insert more carbon fiber into a given volume. And, the straight fibers with reduced crimp angle optimize and strengthen the composite. Furthermore, fewer crimps in the composite reduce the amount of excess plastic, which minimizes weight. However, the mechanism of woven fabric composites with spread tow has not been investigated completely. To estimate the effect of a CFRP woven laminates with spread tow, we have carried out the static bending test for woven fabric composites with/without spread tow. As a result, the characterization of a woven fabric composites with spread tow have characteristics is different from that of conventional woven laminates. And, it is revealed that the mesh superposition method is useful for the estimation of mechanical properties for woven fabric composites with spread tow.

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The spreading tow technique seems promising in application to filament wound or woven composites with advantageous strength enhancement mechanism. We hypothesize that the homogeneous distribution of fibers realized by the spreading tow technique causes suppression of stress concentration of resin in the vicinity of close-packed fibers. The hypothesis is examined through the finite element simulation using micro-scale model with definite separation of fiber and resin. The residual stress and strain after cure and damage propagation under uniaxial loading are investigated by means of newly developed simulation system.

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In the curing process of thick Fiber Reinforced Plastics (FRP) vessels, excessive temperature rise due to self-heating of the resin appears. It is necessary to accurately evaluate excessive temperature rise for avoiding trial and error approach of temperature control to quality guarantee. We have developed a curing process simulator, including the self-heating of the thermosetting resin. In this study, we demonstrate the degree of cure and heat transfer analysis, and investigate abrupt rise of excessive temperature due to small raise of holding temperature.

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We have developed a methodology in a framework of meso-scale model for a precise strength evaluation of filament wound carbon fiber reinforced pressure vessel. The vessel is an indispensable component as hydrogen storage tank for fuel cell vehicle itself and hydrogen filling station. A rational strength estimation is expected by means of the meso-scale model with elemental material property obtained by simple material tests concerning resin and fiber bundle. We demonstrate potential ability of meso-scale strength evaluation in problem of local stress enhancement in bundle cross region of helical filament winding.

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The deformation behavior of textiles for draping simulation requires very different assumption from one for metal forming simulation. By the simulations of Meso-Scale model for uniaxial tensile test, biaxial tensile test and picture frame test, we understood the textile material properties under the each load conditions. One of the implemented material models in LS-DYNA, which is the fully nonlinear and orthotropic material model, was selected and complex draping simulation was carried out. Finally the draping simulation of Meso-Scale model where textile structure was directly modeled could be performed in order to introduce the possibility of large scale model simulation.

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Phase field model for representing mechanical response of the microstructure to mechanical loading is presented. The base model is the multi-phase-field model complemented by additional terms considering the effect of stress and grain-size, and numerical simulations are carried out. The microstructure is distorted according to macroscopic deformation applied, and grain rearrangement is initiated promptly. Consequently, grain distribution with stable hexagonal grains is obtained. Repeated load is also imposed to the model, and it revealed that such loading accelerated the grain stabilization.

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Piezoelectric ceramics are applied to sensors and actuators because of quick response, high efficiency of energy conversion, generation of large force and so on. Therefore, since they are used in situation subjected to cyclic loading in products, it is concerned that change of material properties and cracks due to long-term use may affect measurement as sensors and control of products. In the present paper, focused on the development of internal damage due to compressive fatigue loading and fatigue life of piezoelectric ceramics, formulation to predict fatigue life and damage development with high accuracy was conducted. So, considering the applicability of the formula which has been proposed for metal materials to fatigue life prediction of piezoelectric ceramics, a new damage evolution equation using a fatigue life were proposed. Finally, its validity was examined by comparing the predicted results with the experimental results. As a result, both the internal damage development and fatigue life were able to be expressed.

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To better understand how the electric power generated from PZT piezoelectric ceramics is affected by mechanical loading conditions the power generation was examined during cyclic loading under various loading conditions. The electric power generation was continuously examined using a monitoring system that we have recently developed. This system revealed that the electric power increased with increase of the applied load but then decreased when the applied load exceeded a certain level. In addition, greater electric power was generated with a simple beam condition compared with a cantilevered beam. The change of electric power generation was directly related to the stress direction; high stress in the tetragonal structure parallel to the c-axis gave rise to high electric power generation. On the other hand, material failure, including domain switching and crack generation, caused a reduction of the electric power generated. Based upon our experimental data, suitable loading conditions to give high piezoelectric energy generation have been clarified.

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The domain walls and domain characteristics have been examined experimentally. In this study, a conventional lead zirconate titanate (PZT) piezoceramics were used. The specimen was designed to be a rectangular block shape. The specimens were loaded mechanically and electrically. The domain and domain-wall directions were altered with different direction. The domain direction was switched 90 degree by the mechanical loading, i.e., domain switching, where the (002) peak decreased and the (200) peak increased. In contrast, the domain wall direction was altered 90 degree when loaded electrically. With the applied stresses, domain direction and domain wall direction can be controlled. From the domain properties, it is considered that piezoelectric properties of PZT ceramics can be controlled by the applied stress.

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We conduct numerical experiments of a recently proposed elasto-plastic constitutive model for nonlinear piezoelectric problems, which is based on thermo mechanics. This model is in the same framework of classical elasto-plasticity for metals and hence, computational return mapping algorithm can be constructed for nonlinear electro-mechanical finite element analyses. The numerical experiments under electrical loadings show not only its numerical robustness for large increments but also its capability for the high representation of phenomenological behaviors.

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The perovskite ferroelectric Pb(Zr_xTi_<1-x>)O_3 (PZT) at morphotropic phase boundary (MPB) consist of multiple crystal systems and it shows complicated hysteresis behavior and high piezoelectric responses depending on domain switching and structural phase transition. In the present work, a multiscale nonlinear finite element method based on crystallographic homogenization theory was developed to evaluate nonlinear behaviors at MPB. We employed the incremental constitutive law taking into consideration with material property changes caused by domain switching and structural phase transition and the judgment formulation based on electromechanical energy. Some computational results of typical ferroelectric behaviors were presented for PZT.

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A trade-off problem between cost reduction and reliability enhancement becomes great issue for practical use of Fiber Reinforced Plastics (FRP). Defects formation in resin is inevitable in manufacturing and use. A quantitative estimation of strength degradation caused by defects is indispensable for logical solution of the trade-off problem. We employ meso-scale model, which handles fiber bundle and resin separately, to clarify the effect of the defect to ultimate strength through damage propagation simulation in resin/fiber bundle system. In this study, we reveal acceleration effect of spherical defect and cylindrical defect imitating bubble and crack, respectively, to fibers break by means of the damage simulation with the meso-scale model.

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There has been much interest in Carbon Fiber Reinforced Plastics (CFRP) for its aerospace applications because of its high specific stiffness and strength. For adequate evaluation of its strength, that is indispensable for mechanical design, the authors have proposed meso-scale damage analysis, handling fiber bundle and matrix separately. In this paper, we demonstrate a damage simulation of quasi-static punch test of 12-layered CFRP laminates, which includes resin damage, delamination damage, and fiber bundle failure.

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This study examines the interlaminar shear strength and self-healing of carbon fiber(CF)/epoxy(EP) laminates fabricated by a tow-spreading technology. Healing is accomplished by incorporating a microencapsulated healing agent and catalyst within a polymer matrix. Self-healing is demonstrated on short beam shear specimens of CF/EP laminates and the healing efficiency was evaluated by the strain energies of virgin and healed specimens. The effect of microcapsule concentration on the interlaminar shear strength and healing efficiency is discussed. The damage area of the healed specimens was also examined by an optical microscope.

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The stitching yarn of NCF(Non Crimp Fabric) brings the improvement of out-of plane strength, formability, lower rate of crimp compared with woven fabric. Although numerical method considering the microscopic structures based on the mesh superposition method has been proposed previously, the effects of the stitching parameters on damage development under tension load has not been investigated completely. In this study, test specimens have been prepared with changing the stitching parameters such as stitching pattern, pitch, and direction, and the tensile test under static loading has been carried out. The effects of stitching yarn have been investigated by FE analysis based on the mesh superposition method. The experimental and numerical results of the damage development have been described.

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This paper investigates the interlaminar shear behavior and damage detection of woven carbon fiber reinforced polymer (CFRP) composite laminates at cryogenic temperatures. Short beam shear tests were performed at room temperature and liquid hydrogen temperature (20 K), and the temperature dependence of the apparent interlaminar shear strength was examined. The electrical resistance of the composite specimens was also monitored during the tests. A detailed observation of the tested specimens was made to assess the damage, and the relationship between the damage and the electrical resistance was discussed. In addition, the stress, strain and current density distributions in the short beam shear specimens were determined by the finite element method. The numerical results were used to better understand and explain the experimental findings.

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The purpose of this study is to examine the mechanical properties and corrosion resistance of ADC6 (Al-Mg) alloys. To obtain high mechanical strength and high corrosion resistance of ADC6 alloy, an attempt was made to create the cast samples by heated mould continuous casting (OCC) process. With the OCC process, the microstructure of the ADC6 alloy is formed with fine α-Al grains and small eutectic structures, e.g., Mg_2Si and Si. In addition, the crystal orientation of the α-Al phase is regularly oriented. Due to the tiny microstructural formation, tensile and fatigue strengths are higher than those produced by the conventional gravity casting process. Such a tiny microstructure is also attributed to the high corrosion resistance. The material ductility for the OCC sample is extremely high compared to the gravity casting one because of the uniformly orientated crystal orientation.

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Material damping of polyarylate fiber reinforced plastics is analyzed experimentally and numerically comparing damping capacity. The damping capacities of VFRP are identified by the experimental results. The result of identification was compared with damping capacity of aramid fiber reinforced plastics. It is recognized that the polyarylate fiber reinforced plastics have higher damping capacity than AFRP. Next, the damping capacities of polyarylate fiber and epoxy resin were evaluated by using DMA and vibration test. From the result of experiments, it was found that the polyarylate fiber is high damping material.

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Membrane electrode assembly (MEA) serves as a central component in proton exchange membrane fuel cells. Reliability of the MEA is critical to ensure a proper functioning of the fuel cell. The objective of the present study is to develop a numerical model to predict the onset of MEA crack formation. A finite element model was created to simulate a tensile test, thus predicting the failure criterion of MEA, both for monotonic and cyclic loadings.

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The viscoplastic constitutive equation of epoxy resin reinforced with carbon nanotube (CNT) is evaluated using a numerical approach based on the finite element method (FEM). Homogenization theory is employed to estimate the 'homogenized elastic moduli' of the composite composed of matrix resin and carbon nanotube. Viscoplastic property of epoxy resin was evaluated by experimental test using dynamic tensile tests under several strain rate. Viscoplastic constitutive equation of CNT/epoxy resin composites can be estimated numerically by homogenization theory with FEM. The effectiveness of the present study is verified by comparing the experimental and numerical results of stress-strain relation of the composite changing strain rates.

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As a way to quantify the extent of damage in carbon/graphite fibre-reinforced polymers (CFRP), carbon fibres themselves are used as self-sensing sensors and damage state is estimated via inverse analysis. Here, an error sensitivity analysis is carried out with various data processing schemes to improve the estimation accuracy. In addition, preliminary tests are conducted for actual CFRP laminates with thermal-sprayed electrodes to verify the concept of the proposed method. Although further refinements are necessary, increased resistances due to the damage among electrodes are obtained.

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Carbon fiber reinforced polymer (CFRP) composites have higher specific strength and specific stiffness than conventional metallic materials. The CFRP structures, however, are easily damaged by impact loading. It is quite difficult to detect internal damages caused by impacts by visual inspection. In the present paper, self-sensing time-frequency-domain reflectometry (TFDR) is proposed as a damage detection method for large CFRP structures. In the TFDR a set of high-frequency burst signals is applied to a structure and damage location is calculated from difference in time of arrival between an input signal and reflected signal from the structure end. By using several signals with different frequencies, other information such as dimensions of damage can be obtained. This is one of the great advantages to using the frequency domain reflectometry. The TFDR uses both methods; one estimates damage location and the other identifies its dimensions. The purpose of this study is to verify the applicability of the TFDR to CFRP structures. In the TFDR, after experiment for damage detection using the time domain reflectometry (TDR) with electromagnetic waves flowing in a long UD CFRP (1980 mm×120 mm) in the transverse direction, the frequency characteristics of the wave in the CFRP structure are investigated by the finite difference time domain (FDTD) analysis. As a result, the experiment indicated that the TDR could detect a notch in the CFRP using waves flowing in the transverse direction. The electromagnetic analyses showed that the TFDR was able to detect damage and identify its location and dimensions of CFRP structures.

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A rapid diagnosis method for composite aircraft is required. In this study, a new inspection method using a load sensor which also acts as a lightning protection shield (LPS) is proposed. The load sensor consists of upper layer and lower layer composed of an electrical circuit which has many pressure-sensitive elastomer pills in it. The upper layer is a copper mesh sheet acting as a LPS. The lower layer consists of two kinds of wires. One is high-electrical-resistance nichrome, and another is low-resistance copper. The pressure-sensitive pill changes from an electrical insulator into a conductor when it is compressed. When an impact load is applied to the sensor, the pressure-sensitive pill gives a new electrical path between the two layers at the load point. During the operation of the load sensor, a unidirectional gradient of electrical potential is applied to the lower layer. When a new electrical path is formed between the two layers by the load, potential of the upper layer comes to be equal to that of the indented part of the lower layer. Consequently, measuring the potential of the upper layer provides the X coordinate of the load point. After the X coordinate is acquired, the orthogonal potential gradient is applied to the lower layer to measure the Y coordinate. These XY coordinates can be evaluated within a few milliseconds. In addition, it comes possible to estimate the peak value of the load by measuring the electrical resistance of the pressure-sensitive pill.

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A beamforming array technique with 4 sensors is applied to a cylindrical plate for detecting point of impact. Linear array of acoustic sensors attached to the plate record the waveforms of Lamb waves generated at the impact point with individual time delay. An optimization technique is incorporated into the beamforming technique in order to deal with the direction dependent Lamb wave speeds in a cylindrical geometry. The optimization is carried out using the experimentally obtained wave speed as a function of propagation direction. The proposed technique is experimentally verified by comparing the predicted points with the exact points of impact on a cylindrical aluminum plate and a composite shell. For randomly chosen points of impact the beamforming technique successfully predicts location of the exact acoustic source.

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Detecting crack by using the cross correlation function of the measured vibration responses was carried out. A fast and easy check of machine parts is necessary for mass-production. The method of a fast and easy check of machine parts need (1) simple hold method for clamping the test piece and (2) fast signal processing. In this study, we pay attention to (2) fast signal processing. Real crack in the machine parts was treated as two-dimensional crack model. Test piece size and crack size were varied. Natural frequency of first bending mode was obtained by period derived from result of the cross correlation function. And also, natural frequency of first bending mode was obtained by the result of Fast Fourier Transform (FFT). Natural frequency was changed by test piece size and crack size. Distribution of the natural frequency can be confirmed clearly by the result derived from the cross correlation function.

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Ultrasonic flaw detection and sizing are important issues for ensuring structural reliability of industrial plants. However if the flaws are close to each other, the detection performance becomes lower. The Time-of-Flight Diffraction (TOFD) method is known as the most accurate flaw sizing method. However the TOFD method is unsuitable for sizing of such neighboring flaws because there is scarce beam path difference between the arrival times of diffraction echoes from each flaw. On the other hand, authors suggested a new TOFD method using multiple probes in a previous study. In this study, the flaw size and position are measured by suggested method. As a result, the flaw size and position can be identified by the suggested method though there is nonnegligible identification error if the distance of neighboring flaws is small.

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Accurate sizing of cracks in aging structure is required now. To improve the SN ratio of crack tip in ultrasonic inspection, a subharmonic wave technique is expected to apply the industrial fields especially for a detection of a closed crack. One of the most advanced techniques of SPACE (Subhamonic phased array for crack evaluation) system has been developed in 2007, and apparent improvement of SN ration in crack tip echo can be obtained for some test specimen. In this study, SPACE system was applied for the detection of the crack tip of the several types of dummy cracks of fatigue crack and stress corrosion crack in austenite stainless steel, cast stainless steel and welded inconel alloy to investigate the availability of industrial crack tip measurement.

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