In this paper, mechanical ratcheting of 6-4 Brass under steady axial stress with cyclic shearing load is investigated experimentally. The amount of the increasing ratcheting strain is formulated precisely as the function of the steady stress, the cyclic strain amplitude and number of cycles. The presented equations are available for the cases with changes in a steady stress and cyclic strain amplitude on the mechanical ratcheting conditions.

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Plastic deformation of metals is typically characterized with the uniaxial tensile test. However, multiaxial loading in sheet metal plastic forming requires more complex test, such as the controlled biaxial test with cruciform specimens. In this study, tensile tests were conducted at high temperature on rolled AZ31 Mg alloy sheets with fine grain, and deformation behavior under biaxial tensile deformation was investigated from the viewpoint of the effects of cavity on tensile strength. In biaxial tensile deformation at high temperature, the effects of flow stress and stress concentration in triple point during deformation were high in comparison with uniaxial tensile deformation. The cavity was formed and growth at various direction with increase of biaxial tensile deformation ratio, because a restriction effect plane.

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A7075 is one of most high-strength material in the aluminum alloys. And so, it was one of the beneficial solutions to energy problem to use the sheet of high strength aluminum alloys. In this study, The alloys was grain refined by multi-axial alternative forging and warm rolling combined by intermediate thermo-mechanical treatment and the microstructure, hardness and tensile yield strength were investigated. The sever plastic deformed samples with grain size between 150 and 200 nm were machined to tensile specimens with their tensile direction parallel to the rolling direction. The yield stress and tensile strength were shown that 470 MPa and 520 MPa respectively. In fact, high strength A7075 alloy was proved by rolling. The relationship of the rolling temperature and high strength were researched the rolling temperature at 292 K, 373 K and 474 K. As result, rolling temperature at 293 K was the highest strength. In other words, strength improved by cold rolling, But, it was not lead to improvement of the elongation.

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To improve the corrosion resistance of magnesium alloys, laminated material coated with aluminum alloys on the surface of AZ31 magnesium alloy, using titanium sheet as inserted material, has been developed by solid-phase diffusion bonding in vacuum hot pressing. After vacuum hot pressing, laminated materials were applied hot rolling to increase bonding strength. The bonding strength of laminated materials fabricated was examined by tensile shear test. The optimal maximum shear stress was 7 MPa at a bonding temperature 623 K, under applied stress 20 MPa and a bonding time 3.6 ks. Bonding strength is influenced strongly by the bonding temperature and applied stress. The mechanical properties of laminated materials were investigated by tensile test, bending test and conical cup test. As results of these tests, developed laminated composite materials were confirmed to have excellent plastic formability properties.

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Mg alloys need to be deformed at high temperatures to develop structural vehicles caused by crystal structure of Mg alloy. In this study, the effects of grain size on the deformation strength of Mg alloys under high-temperature deformation were examined in order to understand the deformation properties of Mg alloys at high temperatures. In this present study, external parameters, namely, the mechanical properties and strain rate, and an internal parameter, namely, the grain size, of the Mg alloy were investigated. Tensile tests were conducted at 623 K on three types of AZ31Mg alloys with different grain sizes at initial strain rates of 1x10^-1 to 1x10^-4 s^-1. It was found that the relationship between deformation stress and grain size is given by σ∝d^b ; this relationship serves as a model of the grain-boundary sliding. It was found that deformation stress was affected by the deformation mechanism. The magnitude of the reduction in the strength increased as the grain-boundary sliding became more dominant, and the internal stress caused by the grain-boundary sliding increased as the grain size decreased.

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Deformation behaviors of aluminum alloys during pre-loading and reloading were measured by Electronic Speckle Pattern Interferometry. In order to reveal the effect of the pre-load condition on the speckle fringe pattern, two-dimensional deformation distributions along the tensile direction (perpendicular) and the horizontal direction to tensile axis were observed, and the speckle fringe pattern in the reloading compared with the fringe patterns in preloading. For the perpendicular fringe pattern in the reloading tends to have concentrated fringes to the neck part of specimen. On the other hand, for the horizontal fringe pattern, the slopes of fringes in reloading were smaller than that in the pre-loading. This tendency appears strongly in the higher pre-load condition.

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A series of fatigue test was carried out under several two step loading waves varied a ratio of high load amplitude to low load amplitude by using a round bar specimen with small hole. The obtained fatigue life was compared with the predicted life by the liner cumulative damage rule from S-N curve that was obtained from the fatigue test under constant load amplitude. Moreover, effective stress ranges under two step loading wave and constant load amplitude were compared. These two comparisons were correlated. Therefore, it was proposed to predict the crack growth fatigue life from the liner cumulative damage rule considered the change of effective stress range due to load variance.

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Local compression fatigue tests of peripherally clamped the honeycomb core sandwich panel (hereafter, HSP for brevity) in consideration of usage condition as a floor panel were carried out. In the fatigue tests, the fatigue property of HSP was investigated by changing the cell wall thickness, the thickness of face sheet contacted the indenter and the maximum load value. As a result, when the thickness of the cell wall is 0.05mm, the fracture pattern changed from the tensile type to shearing type with the increase in the thickness of face sheet contacted the indenter. In the transitional region, the dent type existed. However, when the thickness of cell wall is 0.08mm, the fracture pattern of circumference type was observed instead of the dent type. This is because the increase of buckling strength of cell wall constrained the formation of dent. This situation resulted in the increase in the shearing stress around the dent.

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Nowadays honeycomb core sandwich panel (hereafter, HSP for brevity) is widely used in various structures, such as inner and outer packages of aircraft. HSP is the composite structural material which consists of two face sheets and honeycomb core. Because of high compressive strength due to the buckling of the core, HSP has advantages such as high rigidity and high-performance impact absorption ability. Compressive strength of double wall which is the bonded part in honeycomb core is higher than the single wall, because of the constraint by two cell walls that compose the double wall part. In this study, an influence of the number of laminated cell walls on compression properties of sandwich panel has been investigated for a development of new core structure. The static compression test was carried out by using five core models which metamorphose honeycomb core including the basic core model which consists of only single wall part. From the obtained results, the compressive properties of the core models were evaluated.

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The fatigue and fracture behavior of C/C composites fabricated using fine-woven carbon fiber laminates were investigated in several notched and smooth specimens. Slits and blunt notches were cut in some specimens, and the effect of fiber direction and notch configuration on the fatigue behavior was examined. A bending moment was applied, and the fracture strength and the fracture mechanism were investigated. The fatigue strength was dependent on fiber direction and notch configuration. It was found that the fatigue strength of the notched specimens were higher than that of the smooth specimens. So, the fracture behavior of present material was different from metals and plastics. The local peeling of fiber sheets and local shear deformations are important factors in the evaluation of static and fatigue strength.

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This paper presents finite element analysis for the lamination-type cracked ceramic coatings subjecting to a tensile loading. The analysis was conducted using the program including the nonlinear elastic constitutive equation for ceramic thermal barrier coatings that was proposed by author. The numerical results for stress field showed that stress singularity field can be characterized by HRR field. The results for damage field revealed that micro crack formed near tip of the crack, and relaxed the tip stress in the inner region of HRR field.

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The effect of bolt materials on the bolt load loss behaviour of magnesium alloy AZ91D bolted joint at high temperature were clarified in this study. The bolt load loss tests were conducted under an initial bolt load of 4.5 kN for 100 h at ambient temperature and 100°C using magnesium alloy AZ91D plates assembled with steel SCM435 bolt and magnesium alloy AZ3 lbolt. From the results, magnesium alloy AZ91D bolted jointed clamped with steel bolt and AZ31 bolt showed the same performance of bolt load loss at the ambient temperature. For the tests at 100°C, magnesium alloys AZ91D bolted joint clamped with AZ31 bolt showed higher remained bolt load (66% of initial bolt load) after testing when compared with the one clamped with SCM435 bolt (42% of the initial bolt load). It was found the mismatch of thermal expansion between bolt and clamped part caused an additional tensile bolt load in SCM435 bolt which bolt load corresponded to increasing in an additional compressive stress on magnesium alloy AZ91D plates which played as an important role for driving creep deformation which could lead to the acceleration of bolt load relaxation.

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This research is about FEM analysis of CFRP / Metal plate fastener especially about the mitigation effect for the internal stress of the rigidity and the site of a washer and a bolt. Carbon fiber reinforced plastic (CFRP) has the characteristics of lightweight, high tensile strength and high rigidly. therefore, it is suitable for the large structures like airplanes and space instruments. But in generally, an epoxy resin is used for CFRP, the compression strength is low. Therefore, about the fastener for the CFRP plates, axial force for the bolt /nut tightner must be set as low value compared with fastener for the Metal Plates. To avoid the loosening at the low cycle vibration increment of the allowable axial force for the tightner before failure is important. For the CFRP plate .main failure caused close to the bolt hole is matrix crack kinku and delamination caused by internal stress and sharing stress between analysis

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This study is about the effect of the localized slip to the looseness behavior of CFRP / metal flat plate fastener. In recent years, because of its high stiffness and strength per weight, CFRP becomes applied to large-scale structure. To fastening the CFRP to the large-scale structure, mechanical fastening method like bolt nut joint is desired because of ease of the maintenance. Since compressive strength of the CFRP is low, to prevent the compressive damage, fastening force is set up to low value. Therefore, it is easy to break at around the bolt holes because of the fastening holes side contact. Then in this research, to elongate number of cycle before the hole side contact, experimental observation about under several fastening force condition was conducted. From the observation, effect of the fastening force to the early stage of the loosening process and whole process was examined.

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Acoustic emission (AE) technique is widely used for health monitoring of machines. However, it is difficult to monitor structural components that has rough surface or that is under operating. In order to monitor these components, non-contact AE monitoring system with noise reduction function was developed. The developed system was composed of an air-coupled ultrasonic transducer and a digitizer with a real-time noise reduction function. Two types of digital signal processing for improving signal to noise ratio were embedded in the system. One is a spectral subtraction process for reduction of continuous noise. The other is E-filter process which filters out pulse-like noise. Artificial AE signals were monitored to compare the performances between conventional AE system and developed one. The S/N ratio of the AE signal was improved by 12.3 dB by the developed system.

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Efficient transduction of a circumferential (C-) Lamb wave by a pair of noncontact air-coupled ultrasonic transducers (NAUT) was presented. A line focus type (LFT-) of the NAUT was employed for the efficient transduction. Characteristics of the LFT-NAUT were theoretically and experimentally shown in comparison to those of the conventional plane type (CPT-) NAUT. The efficiency of the C-Lamb wave generated and detected by the LFT-NAUT took about 20 times higher than that by the CPT-NAUT. As for an application of the C-Lamb wave generated by the LFT-NAUT, a novel method of an accurate estimation of pipe wall thickness was introduced and evaluated with a theoretical model. It was confirmed that the averaged error between the experiments and the theoretical model was at less than 10 μm.

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Integrated piezo-electric ultrasonic wave transducer (IUT) which can be driven until about 600 degrees has been developed for high temperature nondestructive evaluation (NDE). To achieve fast NDE or NDE of rotating components, noncontact sensing is highly desirable. Actually, it would be useful if there is such a sensor could detect and receive an ultrasonic wave with more than 10cm-liftoff Then, non-contact sensing system based on the electromagnetic induction method using a commercial type ultrasonic transducer has been studied.

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Excitation of higher-order mode guided waves using a piezoelectric ring-shaped transducer were presented. The principle of the transduction and the experimental verifications of the T(0,1), T(1,1) and T(2,1) mode generations in frequency range from 30 kHz to 80 kHz were shown. It was also confirmed that the circumferential Lamb waves were excited resonantly by the piezoelectric ring-shaped transducer as spurious signals at appropriate frequencies.

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Sensitivity of defect detections in elbow pipes using guided waves was evaluated. The artificial defects introduced at several locations of the elbows were evaluated using the T(0,1) mode at three frequencies (30, 40 and 50 kHz). It was confirmed that, at 30 kHz, the sensitivities of the defects inside the elbow were higher than those outside the elbow while sensitivities of the defects inside the elbow were lower than those outside the elbow at 50 kHz. The experimental results were discussed with the propagation phenomena obtained by the FEM simulations.

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Nondestructive inspection of a high temperature structure is required to guarantee the safety of it. However, there are not any useful sensors for high temperature structure. Some of them can' t work at high temperature over 50°C. Another one is too expensive to use it. The sensing system which can transmits and receives an ultrasonic wave which travel long distance by using a long wave guide has been studied. We could confirm that a guided ultrasonic wave can travel more than 500mm for using a thin bar with 2mm-diameter as a wave guide. However, we are having a difficulty to transmit and receive an ultrasonic wave from a test specimen. We are trying to improve the trial inspection system by using an ultrasonic horn.

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Turbine generator in power plants is an important equipment, and requires its preventive maintenance for normal operation.For the inspection efficiency for turbine generator rotor, the application of ultrasonic testing technique for the keyway in a rotor shaft is demanded. The ultrasonic testing for the keyway in a rotor shaft detects crackings occurred diagonally for rotor axis. For this issue, the authors developed the cracking detection techniques by the phased array ultrasonic testing method using an array probe installed in the distant position from the keyway. The ultrasonic beams propagate three-dimensionally because the rotor shaft is a column. Therefore a control of the beam incident direction is difficult. Therefore the ultrasonic beam angle and the ultrasonic probe position for cracking detection were calculated based on the rotor's geometry. The authors confirmed the possibility of crackings detection in this calculated condition by the experiment using electric discharge machining slit in the specimen simulated a rotor shaft, and ensured the inspection reliability.

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A newly developed method for estimating shape of a defect in piping using the several frequencies of T(0,1) mode guided waves was presented. The theoretical model calculating reflection coefficient at a defect having an arbitrary distribution along the axial direction was first described in the paper. In the estimation, defect shape was assumed to be constant-cross-section at circumferential direction and to be circular cross-section at axial direction. In the method, the calculation model was recursively applied to obtain reflection coefficients for plural circular shapes. The effect shape was finally decided when one of the calculation results takes the closest value to the experimental result. The principle and verification were shown.

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A simple ultrasonic method for measuring surface temperature distributions of heated materials is presented. A laser ultrasound scanning technique is employed for non-contact measurements of surface temperature distributions. The principle of the methods is based on the temperature dependence of a surface acoustic wave (SAW). SAWs are generated at different positions on a material surface consecutively by pulsed laser irradiation scanning (Nd:YAG, wavelength=1064 nm, energy 200 mJ/pulse, pulse width 3 ns) using a one-dimensional galvanometer scanner, and each SAW is detected at a certain position using a laser interferometer based on photorefractive two-wave mixing (Nd:YAG, wavelength=532 nm, energy 200 mW). The ultrasonic method is applied to the surface temperature measurement of an aluminum plate whose single side is being heated. The surface temperature distributions determined by the ultrasonic method almost agree with those measured using an infrared camera. The accuracy of the ultrasonic method is also examined.

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Investigated the accuracy improvement for specimen preparation of Ni-based single-crystal superalloys of elastic property measurement by using IP laue camera. After determining the crystal orientation by IP Laue camera, the specimen and cross goniometer head moved to cutting machine together. Performing the reinforcement of the cross goniometer head stage , also adjusting the granularity of the abrasive the cutting blade, so it was improved the cutting sa d and angle accuracy . Prepared specimen in such procedure verified the accuracy of crystal orientation using by X-ray, ultrasonic and resonance method.

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This paper describes a technique for measuring the thickness of coating on the double-sided coating steel plates by means of acoustic resonant spectroscopy. The both sides of the samples were covered with coatings of epoxy resin, and the thickness of the coatings was from 10 to 40pm. The acoustic resonance related with the top and bottom coatings of all samples were observed by the 100MHz focused ultrasonic transducer, and the thickness of coatings on both side of the plates were successfully evaluated from their resonant frequencies.

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We present an ultrahigh frequency surface acoustic wave (SAW) resonance phenomenon. We fabricated Cu nanowire specimen on (100) Si and glass substrate, and generate vibrations related with nanowires by picosecond ultrasound method. We succeeded in observing high (70-80 GHz) and low (-15GHz) frequency vibrations. They are identified to be thickness resonance of nanowires and SAW resonances, respectively. By changing the wire spacing, we observed dispersion relationship of the ultrahigh SAW and compared them with calculations with the effective mass density by considering the volume fraction of nanowire. This calculation showed good agreements with the measurements when the penetration depth of SAW energy is 6% of wavelength.

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In this study, we applied fatigue damage evaluation in pure copper plates subjected to zero-to-tension fatigue loading through monitoring of with non-contacting NRUS (nonlinear resonant ultrasound spectroscopy), and nonlinear three-wave interaction method, which is a resonance-based technique exploiting the significant nonlinear behavior of damaged materials. In NRUS, the resonant frequency of an object is studied as a function of the excitation level. As the excitation level increases, the elastic nonlinearity is manifest by a shift in the resonance frequency. In nonlinear three-wave interaction method, two intersecting ultrasonic waves produce a scattered wave when the resonance condition is satisfied. The wave amplitude is measured. NRUS and nonlinear three-wave interaction methods exhibit high sensitivity to microstructural change of the damaged material. It rapidly increases from 60 % of fatigue life to the fracture. This noncontact resonance-EMAT measurement can monitor the evolution of NRUS throughout the fatigue life and has a potential to assess the damage advance and to predict the fatigue life of metals.

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Acoustic nonlinearity is known to show higher sensitivity to material's deformation and fatigue damages than linear characteristics such as velocity and attenuation. Previously, we have developed resonance ultrasound microscopy (RUM) to quantitatively measure the local Young modulus and internal-friction using an isolated langasite oscillator. Here, we applied this method to measure the local nonlinearity. The langasite oscillator is excited by the half fundamental-resonance frequency, and the resultant second harmonics component at the resonance frequency is observed. The nonlinearity parameter is defined using the resonance peak height. This paper shows the results on a NbTi/Cu resin superconductive wire composite.

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Conventional ultrasonic techniques are unable to detect material heterogeneities such as local plastic deformation or solidification boundaries of welds which have nearly same acoustic impedance with base materials. To solve this problem, higher harmonic imaging methods using immersion local resonance and backscattered waves are proposed and the validity of the method is demonstrated for local plastic deformation in thin plates and solidification boundaries of spots welds.

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Mechanical Engineering Fuchinobe 5-10-1, Chuo, Sagamihara, Kanagawa, 252-5258The purpose of this study is to evaluate interaction of low-frequency So-mode Lamb wave and rectangular-type defects on a 6-mm-thick steel plate. In order to discuss the effect of width of defect on amplitude of wave reflected with the defects, two dimensional FDTD method and experiment were performed. In calculation, in the case that the defect width is less than 0.4 times wavelength of So-mode Lamb wave, amplitude of wave reflected from the defects depended on width of the defects as well as depth, since an interaction of reflection wave from wall of defect at incident side of Lamb wave and refraction wave at transmitted side. In calculation and experiment, amplitude of wave reflected with defect on the 6-mm-thick steel plate increased with cross-sectional area of the defect. However, the reflection coefficients were slightly smaller than cross-sectional area ratio of defect. It may be due to mode conversion at defect.

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The time reversed method was evaluated with applying to lamb waves propagating in an aluminum plate. Though the detected and re-constructed waves contained some reflected waves, the waveform of re-constructed wave agreed with a source input signal. Next, the time reversed method was applied to tensile test of an aluminum specimen. Macroscopic crack generations could be detected by amplitude changes of either detected or re-constructed waves. But, only the amplitude of re-constructed wave decreased by beginning of the plastic deformation. Therefore, it showed that this method can detect the plastic deformation.

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Measuring internal temperature distributions of a heated material is an important issue in the field of material science and engineering. This is because such temperature distribution often plays an important role in understanding the behavior of materials being processed at high temperature. In our previous work, an ultrasonic technique providing effective measurements of internal temperature profiles of heated materials has been developed and its potential is demonstrated experimentally. In this work, the use of shear wave is attempted to measure internal temperature profile of a heated steel using the ultrasonic technique. It is expected that the use of shear wave may be effective to improve the accuracy in determining temperature because of its relatively slower velocity. An experiment with both longitudinal and shear wave transducers has demonstrated. Two temperature distributions obtained using the longitudinal and shear waves are compared with each other. Although those results almost agree with that obtained using thermocouples, the result using shear wave is not always better than that using longitudinal wave. This is because of the deterioration of the shear wave signal during heating.

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Simulation of alignment of CNTs or VGCFs by the water contraction flow was carried out. The flow was reproduced using ANSYS CFX software and then the dynamic motion of CNTs transported by the flow was calculated. 2D contraction flow with upstream and downstream channel flows was used. And a CNT was modeled as a dumbbell-like element. The orientation angle of the elements at the end of the downstream flow channel was estimated. It is found that the ratio of upstream channel width to downstream channel width is the major factor for the alignment of the elements. And the absolute value of average angle 0.29 degree and minimum standard deviation 4.98 degree were obtained with upstream channel width 25 cm, contraction length 20 cm, downstream channel length 10 cm, and downstream channel width 1 cm.

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Carbon-fiber reinforced epoxy was decomposed using subcritical water and supercritical methanol to reclaim carbon fibers. The tensile strength of the reclaimed carbon fibers was measured. Then XPS alalysis and Raman spectral analysis were conducted to elucidate the change of tensile strength caused by decomposition. The tensile strength decreased by 6% in the case of decomposition with supercritical methanol, and by 18% with subcritical water. Subsequent XPS analysis revealed that functional groups of the carbon fiber surface had been removed. Raman spectral analysis showed decreased graphitization of the carbon fiber surface.

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Thermal conductivity and processability of polymer composites with nano and micro fillers have been investigated. The nano fillers used were carbon nanofibers (CNFs), and the spherical alumina particles and the carbon fibers were selected as the micro fillers. Packing simulations were performed to obtain the random close-packed structure of two filler systems (i.e. two-particle, large-particle/small-fiber, large-fiber/small-particle and two-fiber). In addition, experimental measurements of the thermal conductivity and the viscosity of the manufactured polymer composites with CNFs and the close-packed structure of micro fillers were carried out. The microstructure of the polymer composites was also examined using a scanning electron microscope.

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Nylon 6 clay hybrid (NCH) composite consists of nano-sized Montmorillonite and nylon 6 matrix. Tensile tests at the glass transition temperatures (35 -C, 50 -C, 80 -C) were conducted at a strain rate of 10-2S-1. Fatigue tests were performed with a stress ratio of 0.1 and frequency of 0.1Hz. NCH-2 had highest tensile strength and fatigue strength at room temperature, but NCH-5 had highest tensile strength and fatigue strength at temperatures higher than 35-C. Fracture origin changed from surfaces to interior of specimens with an increase in temperature in NCH-2 and NCH-5.

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In this study, the anisotropic behavior in bending deformation of woven carbon fabrics reinforced PPS thermoplastic laminated composites with various fiber orientation angles under a concentrated and thermal loading was mainly investigated by coordinate measurements. Two parameters for anisotropic evaluation of the bending deformation such as the amount of torsion and degree of anisotropy were used. The anisotropic behavior in bending deformation of woven fabric thermoplastic laminated composites under thermal load was affected strongly by matrix resin segregation on the surface of laminates. The matrix resin segregation arises especially at both ends of the wrap yarn direction on the uncut laminates result from roll forming processes. Also, the distribution of the matrix resin changes by the cutting out position of test specimens.

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This paper deals with mechanical property and damage evolution in CFRP symmetric angle-ply laminates with different ply thickness. Usually, CFRP is made by laminating the fiber direction in many directions. So, it is important to understand effect of ply thickness on mechanical property and damage evolution of CFRP laminates. T700SC/2500 carbon/epoxy laminates with stacking sequence of Rア45)12b, [(ア67.5)121s (t-0.05mm prepregx48plies), R-45)4/(+45)4is, [(-67.5)4/(+67.5)4], (t-0.15mm prepregx16plies) are used as specimens. It should be noted that the laminate thickness is almost the same, but the ply thickness are quite different. In 48-ply specimen each thickness of 45 and -45 ply is 0.05mm. Meanwhile, in 16-ply specimen, the ply thickness is 0.6mm if each (+45)4 or (-45)4 ply is regarded as one blocked ply of +45 or -45 ply. In this regard, the one ply thickness in 48-ply specimen is 12 times thinner than that in 16-ply specimen. Monotonic tensile tests are performed to understand fundamental mechanical properties of each laminate. And we estimate damage evolution from mesoscale damage model with loading-unloading tensile test results. 48-ply specimen has been found to exhibit high fracture strain and strength in comparison to 16-ply specimen.

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In fabricating complicated laminated composite structure by using prepregs, there may be fiber discontinuity in the structure which may influence the mechanical response of the structure. The fiber discontinuity also may act as a source of stress concentration and damage. In this regard, it is very important to understand the effect of fiber discontinuity. In the present study, the effect of fiber discontinuity in CFRP laminate is investigated experimentally. The damage initiation and growth near the fiber discontinuity are also discussed. Laminates which contain fiber discontinuity with different thicknesses are prepared. Tensile tests were conducted to investigate the mechanical response of the laminates. We observed the edge surface of the specimen around the fiber discontinuity. The strain away from fiber discontinuity show almost linear stress-strain relation until a certain stress level. The strain increases rapidly at a stress point, and after that, stress-strain curve shows almost linear stress-strain relation. The strain at the center of the specimens (fiber discontinuity site) shows nonlinear stress-strain relation at relatively low stress range. After the strain away from fiber discontinuity rapidly increased, the stress-strain curves of both points almost agreed with each other. The nonlinear stress-strain relation at the fiber discontinuity site implies that interfacial debonding initiate and progress around the fiber discontinuity in the relatively low stress range. The coincidence of the stress-strain curves from the two points after the sudden increase in the strain implies the delamination development and progress between the continuous and discontinuous layers.

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A method to predict quantitatively the initiation of a transverse crack caused in the various types of [0・90,1 cross-ply carbon fiber reinforced plastic (CFRP) laminates subjected to fatigue loading was proposed. On the basis of the assumption that the mechanism of transverse crack initiation is equivalent to that of transverse crack increase in the earlier stage of fatigue within low transverse crack density, the cycles that a transverse crack initiates are calculated by applying the normalized modified Paris law, which shows the relationship between the transverse crack density growth rate and the normalized energy release rate range associated with the transverse crack formation. Once the constants of the normalized modified Paris law are given with an arbitrary cross-ply laminate, the proposed method makes possible to predict the initiation of a transverse crack in the other various types of cross-ply laminates under fatigue loading by only measuring the stress at which a transverse crack initiates under static tensile loading.

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Effects of variable fatigue loading with alternate R-ratios on the fatigue life of a quasi-isotropic woven fabric CFRP laminate have been studied. First, constant amplitude fatigue tests are performed on plain coupon specimens of the CFRP laminate at different stress ratios in order to obtain a baseline set of fatigue data for this investigation. Then, variable R-ratio fatigue tests are carried out during which the stress ratio of fatigue loading alternates between two values keeping the level of maximum fatigue stress constant. The fatigue life of the composite under variable R-ratio loading is examined not only for different pairs of stress ratios, but also for different levels of maximum fatigue stress. By comparing the fatigue lives under constant and variable R-ratio fatigue loading conditions, the effect of alternation in R-ratio on the fatigue life of the CFRP laminate is elucidated. Experimental results demonstrate that a small change in R-ratio has a degrading effect and affects to reduce the total number of cycles to failure, while a large change in R-ratio brings about a retardation effect in damage accumulation, when the maximum fatigue stress is relatively high. The retardation effect due to variation in R-ratio disappears under fatigue loading with a low maximum fatigue stress. Finally, the anisomorphic constant fatigue diagram is applied to prediction of the fatigue life of the CFRP laminate subjected to the alternate R-ratio loading using representative cumulative fatigue damage rules.

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The off-axis notched strength of a plain woven roving fabric CFRP laminate has been studied with emphasis on its fiber orientation dependence and dominant failure mode. Static tension tests were carried out on center hole specimens with different diameters of a hole and different fiber orientations, respectively. The off-axis notch sensitivity of the woven composite was elucidated on the basic of the experimental results obtained. The three-dimensional digital image correlation (DIC) method with two CCD cameras was used to measure full-field displacement filed and its variation during each tension test until rupture occurs. Local strain distribution, which was calculated on the displacement field measured by the 3D-DIC method, was used to identify dominant failure modes that are responsible for ultimate tensile failure in off-axis notched specimens of the woven CFRP laminate. To prediction of the off-axis notched strength of the woven CFRP laminate, applicability of the anisotropic notch size effect law that takes into account both the effects of fiber orientation and notch size was also discussed.

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In this study, a new welding method which utilizes conductivity of CFRTP (Carbon fiber reinforced thermoplastic) is proposed. Electrical current is applied through the CFRTP single-lap joints in thickness direction. Since resistance of joining surface is the highest in the current path, the joining surface is preferentially heated by Joule heating. In this study, spot welding and surface welding were conducted. By applying constant voltage of 5.0V or ,10.3V, the joint-surfaces were heated above glass transition temperature of the material and were welded. In order to evaluate lap-shear strength (LSS) of welded joints by proposed method, tensile lap-shear tests were conducted. As a result, the tensile lap-shear true stress of spot welding is 31.0MPa and nominal stress of surface welding is 22.0MPa (CF Fabric/PEI) and 21.6MPa (CF Fabric/PPS) . These strengths were comparable to those that were welded by traditional resistance welding (19-22MPa) . It is also found that LSS is changed with welding pressure of joint parts.

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The high modulus pitch-based carbon fiber reinforced polymer-based composite laminates (CFRPs) with 20-30nm-13-SiC nanoparticle and multi-walled carbon nanotubes (MWCNT) were fabricated using a dry method (nano-structure), hand lay-up, no bleeder vacuum bagging technique and autoclave curing. Prepreg consists of pitch-based carbon fiber (K13C) and cyanate ester matrix (EX-1515). Fiber orientation of the CFRPs was set to [0]24. The fiber volume fraction of the CFRPs was 53.1 vol%. Four different volume fractions of 20-30nm-13-SiC nanoparticle (1.0, 2.0, 5.0 and 10 vol%) and four different volume fractions of MWCNT (1.0, 3.0, 5.0 and 7.0 vol%) were used for the inclusion. The interlaminar fracture tests were performed using a universal testing machine. The crosshead speeds of 1.0 mm/min (mode I) and 0.5 mm/min (mode II) were applied. The mode I and mode II interlaminar fracture toughnesses of unfilled CFRP were 145 and 374 N/m. Regradless of nano-structure types, the mode I and mode II interlaminar fracture toughness decreased with increase in the volume fraction of nano-structures.

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Carbon fiber reinforced thermoplastic acrylonitrile butadiene styrene [CFRTP (CF/ABS)] was successfully developed and prepared by solution cast method, which production period tremendously shorter than that by the casting method. Although the samples under room temperature cannot be fractured by using Charpy impact test, the Charpy impact value (auc) under low temperature of 77 K at mid point of fracture probability (Pf) of 0.5 for CFRTP (CF/ABS) was approximately equal to that for carbon fibers in thermo-hardened epoxy resin matrix [CFRP (CF/EP)]. In addition the distribution range of experimental errors of CFRP(CF/ABS) is tremendously smaller than the of CFRP(CF/EP).

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To reduce the cost of carbon reinforced polymer (CFRP) the sandwich structural composite (CFRP/ABS/CFRP) has been proposed and successfully developed. The Charpy impact value at room temperature of CFRP/ABS/CFRP is approximately equal to that of CFRP. The heating improves the CFRP/ABS/CFRP as well as CFRP. The maximum impact value of CFRP/ABS/CFRP was found at 373 K and was more than 40% higher than that of CFRP.

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Photoelasticity is a non-destructive, whole field, stress visualization technique based on birefringence. But this can not tomographically measure the internal stress distribution of sample materials. Recently, Polarization Sensitive Optical Coherence Tomography (PS-OCT) has been developed as a tomographical and non-destructive visualization method of biological tisuue birefringence at the micrometer resolution. In this study, a novel tomographic system of stress detection is proposed on the basis of PS-OCT, applying it to low density polyethylene (LDPE) samples under the loading. As a result, this system can provide the tomographic retardation map determining stress distribution, in which the photoelastic fringe pattern can be depth-resolved and depend on the loading stress. Therefore, the spatial fringe frequency can be calibrated with respect to loading stress. Consequently, it was concluded that the proposed method can non-destructivly visualize the internal stress distribution of non-transparent sample at the micrometer resolution.

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During Resin transfer molding (RTM) process for manufacturing composites, entrapped air may remain as void in a part to bring significant decrease of the mechanical properties. In the past, it has presented that amount of the void formation depends on velocity of resin flow. However, in the case that an anisotropic fabric is applied, directions of the resin flow may also affect on the void formation. In this paper, the effect of anisotropy of fiber on void generation was examined analytically and experimentally. Finally, good agreement was obtained between results of them.

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This paper aims to clarify the off-axis delayed fracture characteristic of woven GFRP laminate by the constant tensile load test in hydrothermal environment. Experimental condition discussed in this paper are air and deionized water at 40 -C. Static tensile tests of woven GFRP laminate were conducted to examine the off-axis directionnal mechanical properties and to determine the stress level for the constant tensile load test. It turned out that the maximum stress, elastic modulus and Poisson's ratio slightly decreased and the fracture strain decreased greatly in deionized water. Constant tensile load tests of woven GFRP laminate were conducted to investigate the delayed fracture characteristics: the strain response and fracture time. The stress level of constant tensile load test was determined to be 15, 30 and 45% of the maximum stress obtained from static tensile tests. As a result of constant tensile load test, it was ascertained that the strain increase with the increase of the applied load and the immersion in deionized water.

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Vacuum assisted Resin Transfer Molding (VaRTM) is a composite molding process by which resin is drawn through fiber preforms using a vacuum pressure. We proposed a method to measure three-dimensional resin impregnation in a VaRTM process on the basis of the ensemble Kalman filter (EnKF). In this method, the resin-impregnated region was estimated by a combination of measuring capacitances from a set of electrodes and a simulation of a VaRTM process. The proposed method was examined by numerical experiments and it was confirmed that the flow velocity reduction in a low permeability region can be estimated.

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