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This study proposes a model that relates the carbon fiber arrangement and orientation in CFRP to the dark-field images captured by X-ray Talbot-Lau interferometer (TLI). X-ray TLI visualizes X-ray ...

In this study, the mechanisms governing compressive strength in quasi-isotropic carbon-fiber reinforced-plastic laminates were clarified to gain an understanding of the results of non-hole compress...

The fiber length distribution (FLD) is one of the factors that determine the mechanical properties of discontinuous carbon fiber reinforced plastic (CFRP). However, accurate sampling for FLD evalua...

The paper proposes a numerical multiscale homogenization method for carbon fiber reinforced composites, where fiber alignment is disturbed due to unintended imperfections (fiber waviness). Imperfection is introduced as input to the calculation, and the calculation is always done using idealized perfect geometry. This has a distinct advantage in numerical calculations where the same mesh can be used for a series of imperfect geometries. The calculation is based on second-order perturbation method in order to capture the anisotropy which is the feature of CFRP. The proposed method is validated by comparing the results to those of a conventional calculation. The results demonstrate that the proposed method can accurately capture the stress distribution when the amplitude of the imperfection is small.

This paper proposes a finite element modeling method for textile composite, in which fiber bundle and matrix resin are separately meshed, and they are connected by using discontinuous Galerkin (DG) method. The fiber bundle geometry is often complex in the textile composite. In the conventional FEM, it causes small, distorted resin elements surrounded by the fiber bundles, because the resin must be meshed along the fiber bundle geometry. These distorted elements result in the increased effort to meshing, computing cost, and degraded accuracy. In the proposed method, we apply the DG method to the 3-dimensional analysis of the textile composite. DG method is a method which can connect two separately divided meshes in the FEM. The method proposed in this paper has a distinct advantage, because matrix resin has not to be meshed along the fiber bundle geometry. Moreover, regular cubic grid mesh can be used for matrix resin. In the present paper, the formulation of the DG method is presented first. The method and results of the microscopic stress analysis for textile composite is then described. The results agree well with those of conventional FEM, and validity of the proposed method is demonstrated.

In the present paper, we proposed a methodology that can predict the number of applied load cycles in tension-tension fatigue test of CFRP laminates from microscopic damages and test conditions. It is difficult to predict the fracture of CFRP laminates and to estimate the remaining life of CFRP laminates for ensuring the long-term reliability of the CFRP components because the fracture process of CFRP laminates is quite complex. The damage process of CFRP consists of various microscopic damage such as matrix cracks, fiber/matrix interfacial debondings, delamination and so on. In order to quantitatively estimate the remaining life of CFRPs, we focused on the degree of the microscopic damages and relate that to the remaining life of them. The tension-tension fatigue tests of CFRP cross-ply laminates were carried out, and we suspended the tests at arbitrary cycles. When the tests were suspended, we counted the number of transverse cracks occurred on the specimens by a replica method, and measured the stiffness degradation of the specimens. We formulated an equation that can predict the stiffness degradation using fatigue test conditions. The predicted stiffness degradation to the number of cycles using the formula agreed well with the experimental results. The result demonstrated that the formula can predict the number of subjected cycles from fatigue test conditions and transverse crack density.

Measurement of the elastic moduli of carbon fiber-reinforced plastics (CFRP) can be difficult owing to the anisotropic and viscoelastic characteristics of CFRP. In this study, a technique based on ...

In this study, a through-the-thickness negative Poisson's ratio of an angle-ply carbon fiber-reinforced plastic (CFRP) laminate is experimentally investigated using a 3D digital scanning method. For this, an image-based measurement method using a 3D digital scanner is developed to obtain the thickness change of CFRP laminates. The thickness change is used to calculate the through-the-thickness Poisson's ratio of CFRP laminates. Then, a tensile test of a [±θ°] angle-ply CFRP laminate is performed, and the through-the-thickness Poisson's ratio is measured based on the developed method. The results obtained suggest that the through-the-thickness Poisson's ratio exhibits negative values which become increasingly negative as (visco)plastic deformation progresses in the laminate, as demonstrated in our previous analysis.

The shear and tensile strengths of carbon fiber-reinforced thermoplastic (CFRTP) laminate joints by ultrasonic welding were investigated by lap shear tests (LSTs) and cross tensile tests (CTTs). The adherends were the cross-ply and the twill woven CFRTP laminates, and the flat energy director (FED) was used to clarify its effectiveness. A modified jig and testing method for CTTs were newly proposed. In each test, the strengths were calculated in two ways: by indicators of “welding efficiency” and “welding quality.” From the experimental results, the strengths of the cross-ply laminate joints were saturated at high welding energy, and the “welding quality” was improved by FED. On the other hand, higher strengths of the twill woven laminate joints were obtained as the welding energy increased, and the effectiveness of FED was confirmed mainly for the “welding efficiency.” The fracture surfaces were then observed to clarify the fracture mechanisms of the joints., ファイル公開：2021-01-01

In this study, the negative through-the-thickness Poisson’s ratios of [±θ] woven laminates were analyzed based on the homogenization theory for elasto-viscoplastic materials. A [±θ] woven laminate model with the fiber bundle cross angle ±θ was considered and its diamond-shaped domain of analysis was defined. The elasto-viscoplastic homogenization analysis was performed to investigate the negativity of the through-the-thickness Poisson’s ratios for the [±θ] carbon fiber/epoxy and glass fiber/epoxy woven laminates. The through-the-thickness Poisson’s ratio of the [±30°] carbon fiber/epoxy woven laminate was negative in both the elastic and viscoplastic regions. However, that of the [±30°] glass fiber/epoxy woven laminate was positive in the elastic region but became negative in the viscoplastic region. The negative through-the-thickness Poisson’s ratios of the [±30°] woven laminates were caused by the compressive stress with respect to the in-plane direction and the viscoplastic deformation of the matrix., ファイル公開：2020-10-01

In the present paper, the interface fracture toughness between a Ti coating film and Al-alloy substrate is evaluated using a laser spallation method and a boundary element method. The fracture toughness can be estimated using inverse analyses by the boundary element method using a transfer function computed from the history of the displacement of the specimen. In the present study, an alternative boundary element program is developed for unsteady state vibration of an axi-symmetric solid body. The mode I interface fracture toughness between the Ti coating film and Al-alloy substrate is confirmed to be about 0.66 MPam1/2 from the present investigation.

The recent status of Japan's government-driven project to establish carbon fiber reinforced thermoplastic composites (CFRTP) technology for automotive applications conducted in the National Composites Center (NCC) Japan is introduced first. The baseline technology is discontinuous carbon fiber reinforced thermoplastic composites (C-LFT-D: carbon – long fiber thermoplastic-direct) using press compaction. All the components of the target car chassis made of aluminum alloy are replaced by C-LFT-D components and a 10% weight reduction with the same rigidity has been verified. The basic physics of the fiber length distribution mechanism and the experimental procedures to measure fiber length distributions are proposed. A basic theory to predict the flow behavior of extruded raw material of the mixture of melted resin and thermoplastics is proposed, and sophisticated CAE software to predict the flow patterns of the raw material is established. Measured elastic moduli of processed LFT-D plates show strong dependency on local fiber orientations and strong correlations between bending strengths and bending modulus are found. Hence, prediction of fiber orientation in the press compaction is a key point of the design of LFT-D components. The viscoelastic properties of C-LFT-D materials are characterized by using established theories. Certain important parameters, such as the shift factors, are identified by theory and experiments. The basic concepts of joining technology are also established, where ultrasonic fusion bonding is selected as the primary method. Joining procedures are defined and mechanical properties of the joints are evaluated. The essence of the other project conducted in the University of Tokyo for CFRTP applications to automobiles is also introduced. Several new composites are developed and evaluation technologies are developed.

In this article, the interlaminar tensile strength between CFRP prepregs with [0°/90°]s lay-up was evaluated with pulse laser spallation method. Transformation functions were applied to obtain the interlaminar stress in the inverse analyses. The pulsed laser spallation test was used to investigate the dynamic interlaminar strength and the static interlaminar strength was determined by the static stud-pull-test. Two different curing conditions (100 °C and 130 °C) were selected to track the curing degree using via interlaminar strength. Additionally, Arai et al. used in one configuration a carbon nanofiller interlayer film between the 0 and the 90 layer to increase the fracture toughness. The location and behaviour of the delamination was determined by fracture images. The results show that the dynamic interlaminar strength of the CFRP laminates was approximately 30 % higher than that of the static ones. The strength of the specimen cured at 100 °C was 20 % lower than that cured at 130 °C.

This paper deals with the damping characteristics of symmetrically laminated plates with transverse shear deformation. First, the effect of laminate configuration on the damping characteristics is ...

Biaxial stress tests of carbon fiber-reinforced plastic (CFRP) laminates were performed to investigate failure criteria under biaxial loads. Specimens of unidirectional CFRP laminates were subjecte...

The deformation behavior of cementite in drawn pearlitic steel and spheroidal cementite steel, which have hypereutectoid composition, was investigated by X-ray diffraction using synchrotron radiation. A detailed analysis of diffraction peak profiles reveals that the deformation behavior strongly depends on the shape of cementite in steel. The unit cell volume of the cementite in the drawn pearlitic steel compressively and elastically deforms by 1.5 to 2 pct of the initial volume at the early stage of drawing, whereas that in the drawn spheroidal cementite steel is compressed by 1 pct of the initial volume even at a large true strain. The cementite in the drawn pearlitic steel fragments into small pieces with increasing the true strain, and these pieces change to amorphous cementite. The dislocation densities of the cementite in the drawn pearlitic steel and in the drawn spheroidal cementite steel are estimated to be ~1013/m2 before drawing and ~1014/m2 after drawing. Although the large strain is induced in the cementite by drawing, the maximum strain energy in the cementite is too small to contribute to the dissolution of the cementite.

The elasto-viscoplastic behavior of slanting-weft woven laminates, the fiber bundles of which are not crossed at a right angle, is investigated both macroscopically and microscopically. For this, an analysis model for the [±θ] slanting-weft woven laminate with a cross angle ±θ and its diamond-shaped unit cell are considered. Then, a basic cell, which is quarter of the unit cell, is defined as an analysis domain by considering the point-symmetry of the internal structure. For the basic cell, the homogenization theory for nonlinear time-dependent composites with point-symmetric internal structures is applied. Using the present method, the elasto-viscoplastic analysis of the [±θ] slanting-weft woven laminates subjected to an in-plane uniaxial tensile load is performed. From the analysis results, the macroscopic elasto-viscoplastic behavior and the microscopic stress and strain distributions of the laminates are investigated.

In this study, a two-scale thermoelastoviscoplastic analysis method for carbon fiber-reinforced plastic (CFRP) laminates is proposed based on a homogenization theory for time-dependent composites. For this, macroscopic and microscopic boundary value problems for CFRP laminates are derived to discuss the relation between the two problems. Using the relation, a two-scale thermoelastoviscoplastic analysis method is constructed, and then applied to the analysis of thermal behavior of an unsymmetric cross-ply carbon fiber/epoxy laminate. The laminate is subjected to a macroscopic temperature change from 180°C to 20°C. It is shown that quite high residual stress and strain occur both macroscopically and microscopically in the laminate, resulting in large macroscopic warpage of the laminate.

The present paper deals with the damping characteristics of symmetrically laminated plates. First, the effect of laminate configuration on the damping characteristics is investigated for cantilevered laminated plates. To examine the effect of laminate configuration, the concept of specific damping capacity is introduced and the damping characteristics are represented on the lamination parameter plane, where the damped stiffness invariants are newly proposed in this paper. Next, the optimal laminate configurations for the cantilevered laminated plates with maximal damping subjected to the constraints on the natural frequencies are determined by using differential evolution in which lamination parameters are used as intermediate design variables. The relation between the laminate configurations and the damping characteristics is discussed based on the concept of lamination parameters.

Improvement of interlaminar mechanical properties in Al/CFRP laminates, fabricated by carbon fiber reinforced plastic (CFRP) prepregs combined with Al alloy sheets, was studied experimentally and numerically. Three toughening methods including acid etching and mechanical patterning for surface treatment of Al alloy sheet, as well as addition of nanofiller (i.e., vapor grown carbon fiber (VGCF)) to the interface of CFRP and Al sheet, were investigated. Experimental results of double cantilever beam tests show the improvement on the interlaminar mechanical properties of Mode-I fracture in terms of much higher critical load PC and fracture toughness GIC. The highest GIC was obtained in the specimens with the combination of acid etching on Al sheet and 10 g/m2 VGCF addition, which was 41 and 6.5 times higher than those of the pristine samples without any treatment and the samples with only acid etching, respectively. Although further mechanical patterning had a positive effect for the case without VGCF addition, the minor effect was observed for the case of VGCF addition because of difficult dispersion of VGCF. Crack propagation and fracture surface were also observed to interpret the improvement mechanism. Moreover, by using the above experimental GIC, finite element analyses were carried out based on cohesive zone model to numerically simulate delamination propagation. The numerically predicted interlaminar tensile strength of Al/CFRP laminates also shows great improvement of interlaminar mechanical properties using the above toughening methods.

Mode-II interlaminar mechanical properties of CFRP/Al(aluminum) laminates were improved by acid treatment to an Al plate and adding vapor-grown carbon fiber (VGCF) between the Al plate and a CFRP layer. The influence of VGCF addition on the Mode-II interlaminar mechanical properties was explored by end-notched flexure tests. The experimental results demonstrated that the critical load and Mode-II fracture toughness of the specimen with acid treatment and 10 g/m2 addition of VGCF increase by 73.66 and 175.76 %, respectively, compared to those of the specimen with acid treatment only. The improvement mechanisms were investigated by the observation of crack propagation path and fracture surface under laser scanning and scanning electron microscopies. Moreover, finite element analyses were undertaken based on the cohesive zone model to verify the experimental fracture toughness and to predict the interfacial shear strength between the Al plate and the CFRP layer.

In the present study the effect of carbon nanofiber interlayers on the fatigue crack propagation of woven fabric CFRP laminates made by VaRTM is investigated. Double cantilever beam (DCB) tests are carried out to determine the mode I static fracture toughness and mode I fatigue crack propagation curve. The experimental results clearly show that the interlaminar fracture toughness and the fatigue crack growth resistance can be substantially improved by the addition of CNF interlayers to the CFRP laminates. In more details, as far as the mode I fatigue crack tests are concerned, thanks to the addition of MWNT-7 interlayers the number of cycles to failure becomes 1.5 or more times greater than that of base laminates. Furthermore, it is found that the fatigue fracture toughness G Imax (the upper limit of the energy release rate in a fatigue test) is increased by about 300%.

Axial compressive simulations are performed on defective and non-defective multiwalledcarbon nanotubes (MWCNTs) using the molecular dynamics method, and the effectof defects upon the buckling behavior is discussed. In our previous study, changes in atomicstresses in MWCNTs with three layers were evaluated until buckling occurred. That studysuggested that the transition from homogeneous stress distributions to inhomogeneous onesplays an important role in the occurrence of buckling in MWCNTs, though the critical stressesor strains relating to buckling are dependent upon the structure and location of defects. In thepresent study, the atomic elastic stiffness of each atom, Bij , is evaluated to discuss the onsetof local buckling in MWCNTs with five layers. The det(Bij) of all atoms is found to change toa negative value long before buckling occurs, while the second smallest eigenvalues of Bij forsome atoms change to a negative value just prior to buckling. The existence of dense regions ofatoms that have two negative eigenvalues of Bij are found to vary as a function of the defectlocation, and to correspond with onset points of local buckling.

Non-destructive and non-contact analysis has been in demand on numerous occasions. Confocal micro X-ray fluorescence analysis enables depth-selective elemental analysis of solid samples in the laboratory. In this paper, we applied this technique for imaging elemental distributions in solutions. A low-carbon steel sheet was placed in artificial seawater (NaCl: 3.5 mass%), and the corrosion process in the solution was observed. A depth image of Fe Kα intensity in the NaCl solution was obtained by using this technique. The Fe Kα intensity in the solution was measured with corrosion time by sequential line analysis at a fixed lateral position. The corrosion of Fe from the steel sheet, the migration of Fe ions in solution, and their condensation near a polymer window were successfully monitored. Copyright © 2014 John Wiley & Sons, Ltd.

A confocal micro-X-ray fluorescence (XRF) method with a vacuum chamber was used for investigation of underfilm corrosion that occurs on a painted steel sheet used for automotive applications. A painted steel sheet was prepared by applying electrodeposition coating onto an electro-galvanized steel sheet with a zinc phosphate conversion coating. The spatial resolution of the confocal micro-XRF was about 10.9 ?m at an energy of 17.4 keV. The phosphorus signal from the zinc phosphate layer was able to be observed nondestructively by measuring under the vacuum condition. Each layer of the painted steel sheet was observed from the depth profile analysis of the characteristic elements of each layer. The painted steel sheet was scratched to expose the substrate surface, and then the sheet was then immersed in a NaCl solution for 10 days. The in-depth elemental map of Ti of the corroded steel sheet revealed blister-type corrosion around the scratch. The in-depth elemental maps of Zn and P suggested that the zinc phosphate layer dissolved from the scratched part into the NaCl solution.

形態: カラー図版あり, Physical characteristics: Original contains color illustrations, Accepted: 2019-06-27, 資料番号: PA2020011000

Thermal imprinting of glass-optical devices and its numerical simulation using the finite element method were investigated. The constitutive equation of the glass material was estimated using compression creep tests based on conventional thermoviscoelastic theory. The relaxation modulus of D263 glass was approximated by the generalized Maxwell model. For glass thermal imprinting, a glassy carbon die was used on which line and space or microlens array patterns were machined with a focused ion beam (FIB). The optimum molding-temperature condition that gives precise transcription profile was investigated in detail. Finite element analyses were performed to simulate the experimental glass thermal imprinting. In comparing experimental and numerical results, the transcription heights of groove or microlens obtained by experimental tests approximately agreed with numerical values. Finite element analyses using thermoviscoelastic property of glass are reliable in estimating suitable conditions for glass thermal imprinting.

Although the electrical-resistance-change method is useful for monitoring delamination cracking of carbon-fiber-reinforced plastic (CFRP) laminates, the method requires many experiments or FEM analyses to obtain the relationship between the electrical resistance changes and parameters describing delamination cracking. In our previous studies, one of the authors proposed using an anisotropic electric potential function to analyze electric current density in CFRP laminates. The function was applied only to thick CFRP laminates. In the present study, the method is expanded to thin CFRP laminates using an image method. The number of images is determined using the electric current analysis of thick CFRP laminates. The electric potential changes caused by delamination cracking can be calculated using an anisotropic doublet line. The associated method is applied to calculate the electric voltage change at the surface of a thin CFRP laminate. The results are compared with an FEM analysis, and, overall, the method...