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This study presents a simple approach to model unidirectionally arrayed chopped strand (UACS) laminates via the extended finite-element method to represent slits (i.e., fiber cutting lines). This enables the introduction of slits independent of the finite-element mesh and reduces the effort to represent a complex discontinuity pattern when compared to standard modeling using double nodes. The laminated structure was represented by stacking two-dimensional layers, and cohesive elements were inserted into the layer interfaces to predict the extension of delamination. Damage progress in CFRP quasi-isotropic laminates with diagonal continuous slits were analyzed via the present approach, and the effect of the angle between the slit line and fiber direction on the tensile strength was investigated. The predicted strength was in agreement with the reported experiment results within the examined slit angle range. A numerical study revealed that the strength of the UACS laminates was enhanced by a low inclined slit angle.

In particle accelerators, a very effective way to shield an external magnetic field, which affects the beam inside the vacuum chambers, is to manufacture the vacuum chambers using soft magnetic materials with high permeability. We selected a permalloy and a ferritic stainless steel as candidates of those magnetic materials. However, until now the vacuum performance of vacuum chambers made of magnetic material does not yet have a proven track record. Therefore we made a list of items to be examined and verified. These items are listed as follows. 1. General vacuum performance of the magnetic materials. 2. Magnetic annealing condition and its effect on each performance. 3. Magnetic and vacuum characteristic of a vacuum chamber made of soft magnetic material. The outgassing rate of the magnetic materials was equivalent to that of an austenitic stainless steel. A good magnetic shielding performance is obtained by annealing at higher temperatures than 850 °C for both magnetic materials, although the performance declines, if the annealing temperature is too high. Furthermore the magnetic annealing in good vacuum is combined with vacuum heat treatment. The TDS spectrum showed that the reduction of hydrogen outflux from the bulk material near the surface was achieved by this process. Finally, we successfully produced a vacuum chamber with such a magnetic material, which will be used in a beam line at the 3 GeV J-PARC synchrotron, because satisfying magnetic shielding and vacuum performance were obtained.

To safely use turbo-molecular pumps (TMPs) in a magnetic field, it is necessary to reduce the eddy current induced in a rotating rotor. Instead of adding a magnetic shield facility to the TMPs available in markets, we developed a TMP with a magnetic shield function by replacing the housing material of the TMP with a ferromagnetic substrate SUS430. Before and after machining, the SUS430 was vacuum-fired at 700 °C for 10 h in order to attain a good vacuum quality and recover its high magnetic permeability. The magnetic shield efficiency of the TMP with SUS430 housing was then examined. When a perpendicular magnetic field of 9 mT was applied, the field inside the TMP was reduced to less than 0.3 mT. Next, we confirmed that the developed TMP shows good performance in achieving an ultrahigh vacuum in magnetic fields of up to 9 mT. The limit of the magnetic shield efficiency for the developed TMP is also discussed.

The effect of current peening techniques that modify the surface layer of metallic materials on the fatigue strength of those materials has been enhanced by employing a micro-size, high-rate shot impact. The present paper evaluates the effect of impact velocity and impact size on work hardening on the surface of polycrystalline metals subjected to peening. A single-shot impact was modeled based on a polycrystal plasticity finite-element analysis in order to address the effect of grain-order work hardening. Using the finite-element analysis, the effect of the relative size of the shot and the individual grains on the surface work hardening of polycrystalline metal was investigated. Simulated results reveal that the deformation progresses preferentially along the grain boundary rather than inside the grain after a large shot impact, while peening with a small shot can introduce intense work hardening inside the grain just beneath the surface. Moreover, we compared a shot impact and a static indentation whose dimples were almost the same size and confirmed that a high-rate shot impact can generate a significantly work-hardened layer beneath the impacted surface.

In this study, we investigated the influence of base resin and curing agent and their mixture on the curing characteristics by performing experiments and molecular simulations. In the curing experiment of epoxy resin, we used differential scanning calorimetry (DSC) to obtain the conversion by mixing curing agents and base resins. We used the molecular orbital method (MO) and the molecular dynamics method (MD) to simulate the curing reaction in molecular scale and investigate the effect of differences in resin composition on the curing characteristics. This simulation took into consideration activation energy, heat of formation, and polarization in the curing reaction. The simulation captures the trend of curing reaction obtained by the experiment. We found that the selection and mixture of curing agents are very important when controlling the curing characteristics of epoxy resin.

The conundrum of Ptomaphagus (s. str.) sibiricus Jeannel, 1934 (Coleoptera, Leiodidae, Cholevinae, Ptomaphagini) is solved, and it is redescribed and newly recorded in South Korea. A new species is also described from the Russian Far East: Ptomaphagus (s. str.) hayashii sp. n. Relevant morphological characters of the concerned species are illustrated with colour plates, and their known distributions are mapped.

This study proposes the layer-wise method (LWM) as a new approach for predicting the tensile strength of discontinuous fiber-reinforced composites that have arbitrary fiber orientation angles. The LWM assumes the discontinuous fiber-reinforced composites are identical to laminates that are composed of unidirectional fiber-reinforced plies and have the same distribution of fiber angles over the entire laminate. We applied the LWM to discontinuous carbon fiber polypropylene composites and evaluated the effect of fiber length on tensile strength and fracture mode. Simulated results agreed well with those of experiments. In addition, we proposed a simple analytical model based on micromechanics. This analytical model can correctly evaluate the strength and the fracture mode as effectively as the LWM. We also compared these models with a rule of mixture considering the failure criterion of fiber breakage and examined the limitation of the rule of mixture in predicting composite strength.

In this paper we propose an experimental method for estimating the depth to which the surface of a material is modified after being treated by cavitation peening. The estimate is made on the basis of two theories: plate theory and beam theory, in which the plastic strain in the modified layer is considered. As the depth of the compressive residual stress is an important factor for the fatigue strength and for stress corrosion cracking, a simple and straight-forward method to estimate the depth of the modified layer is needed. In the proposed method, measurements of the surface residual stress and the radius of curvature generated as a result of the plastic deformation introduced by cavitation peening are combined with either plate theory or beam theory. The most appropriate theory depends on the thickness of the specimen. The plate theory is more accurate than beam theory in the case of both a thin and thick specimens. The beam theory should be applied only in the case of a thick specimen.

Discontinuous fiber-reinforced composites have better productivity and formability than continuous fiber-reinforced composites. However, their strength is remarkably low. Thus, there is an urgent need to improve the strength of discontinuous fiber-reinforced plastic composites. In this study, we utilized a unit-cell model that considers microscopic damage including matrix cracking and fiber breaking, and incorporates constitutive laws of thermosetting resin or thermoplastic resin for the matrix. The tensile damage and strength of the composite were investigated for various fiber lengths and/or matrix properties. We compared the simulated strengths with experiments for carbon fiber-reinforced polypropylene. The effect of deformation rate on mechanical behavior was also investigated.

For this study we used finite element analysis to show how the residual stress affects the hydrogen concentration around a crack tip in a plastically deformable material after a fatigue process. Following a 9 cycle fatigue process, hydrogen diffusion analysis was carried out at the highest applied fatigue stress. This showed hydrogen invading the crack surface and diffusing into the material. The concentration of hydrogen was higher close to the crack tip and its behavior was largely affected by the residual stress in the material. Tensile residual stress accelerated the hydrogen invasion and increased its concentration, while compressive residual stress simulated as the stress induced by peening clearly suppressed them. This is due to the affect the residual stress has on the hydrostatic stress around the crack tip which is a dominant factor in the hydrogen diffusion behavior. Peening, which is a surface treatment used to introduce compressive residual stress to enhance the mechanical properties of a material, such as its resistance to stress corrosion cracking and its fatigue strength, may, therefore, suppress the embrittlement caused by hydrogen.

The usual way for reduce outgassing of a large structure in vacuum is to bake the whole vacuum chamber containing the structure. However, this method needs a huge heater capacity and there are limits caused by the heat expansion of the chamber. The solution is to raise the temperature of the structure inside without heating the vacuum chamber. This is achieved by installing a heat source inside the chamber and by inserting the heat shield between the structure and the chamber walls to direct the heat to the structure. In the particle accelerator field, it is often required to reduce outgassing of structures inside vacuum chambers. One example is a kicker magnet, which is installed in a vacuum chamber and consists mainly of ferrite and aluminum alloy. As known from former experience the main outgassing component from ferrite is water. We applied the above mentioned method to the outgassing reduction of such a kicker. We are able to direct most of the heat flow toward the kicker magnet by inserting the heat shielding plates and thus outgassing was successfully reduced.

In the present study, we conducted periodic-cell simulations of the thermomechanical cycle of thermally activated shape memory polymer (SMP)-based composites. The present simulation utilizes a micromechanical model for reproducing the discontinuous fibers and SMP. We analyzed the effect of fiber volume fraction, fiber aspect ratio, and fiber end position on the shape fixity and shape recovery of the composite. The simulated results revealed that fiber elasticity is a key factor for the shape fixity of the composite, while both strain concentration near the fiber ends and fiber elasticity play important roles in the shape recovery properties of the composite.

The effect of fiber arrangement on transverse tensile failure in unidirectional carbon fiber reinforced composites with a strong fiber-matrix interface was studied using a unit-cell model that includes a continuum damage mechanics model. The simulated results indicated that tensile strength is lower when neighboring fibers are arrayed parallel to the loading direction than with other fiber arrangements. A shear band occurs between neighboring fibers, and the damage in the matrix propagates around the shear band when the interfacial normal stress (INS) is sufficiently high. Moreover, based on the observation of Hobbiebrunken et al., we reproduced the damage process in actual composites with a nonuniform fiber arrangement. The simulated results clarified that the region where neighboring fibers are arrayed parallel to the loading direction becomes the origin of the transverse failure in the composites. The cracking sites observed in the simulation are consistent with experimental results. Therefore, the matrix damage in the region where the fiber is arrayed parallel to the loading direction is a key factor in understanding transverse failure in unidirectional carbon fiber reinforced composites with a strong fiber/matrix interface.

The present study proposed a method to evaluate the equibiaxial compressive residual stress of a metal surface by means of a depth-sensing indentation method using a spherical indenter. Inverse analysis using the elastic–plastic finite-element model for an indentation test was established to evaluate residual stress from the indentation load–depth curve. The proposed inverse analysis utilizes two indentation test results for a reference specimen whose residual stress is already known and for a target specimen whose residual stress is unknown, in order to exclude the effect of other unknown mechanical properties, such as Young’s modulus and yield stress. Residual stress estimated by using the indentation method is almost identical to that measured by X-ray diffraction for indentation loads of 0.49–0.98 N. Therefore, it can be concluded that the proposed method can effectively evaluate residual stress on metal surface.

We presented a numerical simulation to address the impact-induced deformation and damage of composite plates subjected to soft-body, high-velocity impacts for application to the bird-strike problem of composite fan blades. A new stabilized contact algorithm was developed based on the Lagrange multiplier method to predict appropriate impact forces applied to the plate, in order to solve soft-body impact at high velocity without causing severe numerical instabilities. The bird-strike impact on composite fan blade was simply modeled by discussing the damage characteristics of a unidirectional composite plate. Combining the model of a soft-body impactor with an appropriate contact algorithm, we could capture the transition from the global bending mode at low velocity to the local deformation mode at high velocity, enabling a discussion of the ballistic limit using the damage analysis of the laminate. As the impact velocity increased, the damage in the composite changed from bending-induced matrix-cracking to an intensive fiber-breakage mode causing local shear perforation. The damage mode transition allows us to detect the transition velocity as a ballistic limit, which is one of the critical factors for discussing the bird-strike resistance of composite fan blades.

In order to eliminate stress corrosion cracking, a method of introduction of compressive residual stress using cavitation impacts was proposed, without use of shots. The cavitation impacts were successfully produced by a cavitating jet in air, without the requirement of a water-filled chamber. The injection condition of the jet was optimized and the introduction of compressive residual stress into stainless steel was demonstrated using the jet. The maximum compressive residual stress introduced by the optimized jet was 500 MPa on the surface, while the thickness of the modified layer was up to 400 μm. A method for estimation of the introduced compressive residual stress by the jet as a function of processing time was proposed, considering the stochastic phenomena of the cavitation impacts. Both the intense impact at 0.2 Hz and relatively weak impact at 4.5 Hz affect the introduction of compressive residual stress. The value of the residual stress and the thickness of the modified layer can be estimated by the proposed experimental equation.

We have developed a novel stampable sheet composed of discontinuous carbon mono-fibers and thermoplastic resin for press molding of composite materials. This sheet enables in-plane random orientation and dispersion of carbon fibers in composites. Therefore, complexly shaped products, such as rib structures, are easily fabricated. Moreover, composites having superior mechanical properties can be obtained because the fiber length in composite is easily controlled to be long. This study addressed the effect of fiber length on strength and fracture modes of composites made of the sheet, using tensile tests and micromechanical analyses. To investigate the influential damage for the fracture mode, our analysis utilized Duva-Curtin model for fiber breakage. We incorporated this damage model into an equivalent inclusion model combined with the Mori-Tanaka theory to predict the tensile strength of the composites. The predicted results agreed well with those of the experiments when the fiber length and orientation in the composites were appropriately considered. Our analyses also indicated that 3 mm as the lower-limit fiber length in the composite, below which the damage mode is no longer dominated by fiber breakage and superior strength of the composites cannot be obtained.

This paper experimentally investigates damage mechanisms which is closely related with the bearing failure in bolted joints of CFRP laminates and proposes a finite element model to reproduce those damage mechanisms. First, the damage was observed in the bearing failure of bolted joints, and the main factor of the large stiffness degradation in bearing failure is the fiber kinking damage. In addition, the fiber kinking is suppressed by the bolt clamping, which increases the bearing strength of bolted joints. Then, three-dimensional finite element model was developed for addressing the bearing failure in bolted joints based on the experimental observation. In this model, the initiation and the propagation of the fiber kinking damage which plays an important role in the bearing failure of bolted joints were reproduced and the stress failure criteria were investigated. The variation of the load at the kinking onset due to the bolt clamping was simulated and consequently the load history during the evolution of the fiber kinking damage was simulated.

Carbon fiber-reinforced composites have been recently applied for engine fan blades because of their high specific strength. In the design of the fan blade, bird-strike impact is one of the greatest concerns, since impact-induced damage can lead to the engine stalling. This study presents a numerical method to analyze bird-strike impact as a soft-body impact on a cantilevered composite panel. Especially, we coupled a stabilized dynamic contact analysis, which enables appropriate prediction of impact force on the panel, with laminate damage analysis to predict the impact-induced progressive damage in the composite. This method is verified through a comparison with experimental results. With the numerical method, we investigate the effect of impact condition, blade thickness and shape on the impact-induced damage in a composite fan blade subjected to a bird strike. An intermediate blade thickness and a large blade curvature help to improve the bird-striking impact resistance of the composite.

The authors proposed fiber-optic-based damage monitoring of carbon fiber reinforced plastic (CFRP) bolted joints. Optical fibers were embedded along bolt holes and strain change along the optical fiber induced by internal damage was measured by a Brillouin Optical Correlation Domain Analysis (BOCDA), which is a high spatial resolution distributed strain sensing system. This study began by investigating damage modes of CFRP bolted joints after bearing failure. Effective embedding positions of optical fibers were then proposed and their feasibility was evaluated by finite element analysis simulating the damage propagation in the bolted joint and consequent strain change. Finally, verification tests were conducted using specimens with embedded optical fibers at various positions. It was clearly shown that damage could be detected using residual strain due to fiber-microbuckling (kinking) damage or permanent deformation of neighboring plies. Furthermore, damage size and direction could be estimated from the change in the strain distribution. The system developed is quite useful for a first inspection of large-scale composite structures in aerospace applications.

In the use of hydrogen energy, the hydrogen embrittlement should be investigated, and it is necessary to improve reliability and safety of machine components which are used in hydrogen environment. The hydrogen sensitivity of material depends on material structure, defect and stress distribution. There is a possibility that the hydrogen invasion into material and the fatigue crack propagation with hydrogen embrittlement can be suppressed by introducing compressive residual stress by us- ing surface modification such as cavitation peening. The cavitation peening is a one of the peening technique, and enhancement of the fatigue strength of the mechanical components and structural materials by cavitation peening have been revealed. In this study, the austenite stainless steel JIS SUS316L with precrack were charged by a cathodic hydrogen charging method, and the fatigue test with and without hydrogen charge were conducted by a plate bending fatigue test. The results demonstrated that the fatigue crack propagation with hydrogen embrittlement can be greatly suppressed by cavitation peening.

Cavitation normally causes severe damage in hydraulic machinery such as pumps and turbines by the impact produced by cavitation bubbles collapsing. Although cavitation is known as a factor of erosion, Soyama et al. succeeded in utilizing impacts of cavitation bubble collapsing for surface modification by controlling cavitating jet in the same way as shot peening. The local plastic deformation caused by cavitation impact enhances the fatigue strength of metallic materials, and the surface modification technique utilizing cavitation impact is called “cavitation peening (CP)”. It is well known that the peening improves fatigue strength by introducing compressive residual stress on the surface, but little attention has been paid to the behavior of fatigue crack growth of the material which was modified by CP. In the present study, the fatigue behavior of austenite stainless steel with and without CP was evaluated by a plate bending fatigue test, and the results revealed that the compressive residual stress introduced by CP suppresses fatigue crack growth rate by 70 % compared to that without CP.

This study proposes a technique for enhancing strength and uniformity in unidirectionally arrayed chopped strands (Enhanced UACS). Enhanced UACS is made by introducing slits at small angles to the fiber direction into a unidirectional prepreg. As the angle becomes smaller, the stress concentration around the slit decreases. Therefore, delamination initiated from the slit is effectively suppressed and the final failure is mainly caused by fiber breakage. As a result, the Enhanced UACS laminate achieves excellent tensile, compressive, flexural, fatigue and impact strength, comparable to continuous fiber composites. Moreover, we demonstrate that the laminate can be uniformly stretched without a slit opening when it is formed.

Shape memory polymers (SMPs) are currently investigated as potential materials for large deployable space structures [1–3]. The thermomechanical properties of these polymers significantly change on reaching their glass transition temperature, which yields the excellent feature of shape fixity and shape recovery [4]. As another aspect, the modulus of these materials is not sufficient since they are polymeric materials. In actual applications, the fiber reinforcement is effective for ensuring the sustainability of the deployed structures. However, while the fiber reinforcement has advantages for increasing the stiffness, it has a negative influence on the shape recovery behavior of SMPs. Experimental studies for shape memory polymer composite were conducted by Gall et al. [5, 6] for SiC powder-reinforced nanocomposite, Ohki et al. [7] for short-glass-fiber reinforcement, and Lan et al. [8] for SMP reinforced with plain-weave fabrics, and the increase of residual strain after shape recovery process was confirmed. In order to maximize both the stiffness and shape-recovery behavior of fiber-reinforced SMPs, it is essential to know how the fibers block the shape recovery behavior of polymers. However, the mechanism was not modeled. Therefore, we focus on the mechanism underlying the degradation of shape recovery behavior due to fiber reinforcement. To investigate this mechanism, we first conducted thermomechanical cycle tests for pure SMP and SMP reinforced with short-carbon fibers. We used polyurethane series of thermoset SMP, Diary MP-5510 (curing temperature 100 C), provided by SMP Technologies Inc. The cured polymer has a glass transition temperature of 55 C, and the temperature range of glass transition between glassy state and rubbery state is 30 C. Short carbon fibers T700S (Toray Industries Inc.) were embedded in the polymer. The fibers with approximately 5 mm length were randomly embedded in the prepolymer before curing, and the weight fraction of fibers was set to 0, 2, and 4 wt%. It should be noted that the bundle of carbon fibers (12,000 fibers) was embedded and not dispersed in these model experiments, as also modeled later. After curing, strip specimens were cut out (approximately 40 mm gauge length, 20 mm width, and 2 mm thickness in average). The following thermomechanical cycle was applied to these specimens using a tensile test machine (INSTRON 5566), as shown in Fig. 1

This paper examines the stress distribution around a fiber break in alumina-fiber reinforced aluminum matrix (Al2O3/Al) composites using finite element analysis and predicts the tensile strength using tensile failure simulations. In particular, we discuss the effect of the matrix hardening on the tensile failure of the Al2O3/Al composites. First, we clarify the differences in the stress distribution around a fiber break between an elastic-perfect plastic matrix and an elastic-plastic hardening matrix using finite element analysis. Second, the procedure for simulating fiber damage evolution in the Al2O3/Al composites is presented. The simulation incorporates the analytical solution for the axial fiber stress distribution of a broken fiber in the spring element model for the stress analysis of the whole composite. Finally, we conduct Monte Carlo simulations of fiber damage evolution to predict the tensile strength of the Al2O3/Al composites, and discuss the effect of matrix hardening on the tensile strength of the Al2O3/Al composites. Coupled with size-scaling analysis, the simulated results express the size effect on the strength of the composites, which is seen in experimental results.

This paper proposes a numerical model of the fatigue damage process in short fiber-reinforced plastics. In the fatigue fracture of these composites, the microcracks in the polymer matrix increase with fatigue cycles and dominate the fatigue damage process. Therefore the matrix crack was modeled by the continuum damage mechanics approach while considering the microscopic fatigue damage process in the polymer matrix based on a Kachanov-type damage-evolution law. We applied the model to addressing the fatigue-cycle experiments of short glass-fiber reinforced polycarbonate conducted by Ha et al. The simulated results agreed well with the experimental results. Moreover, the simulation revealed that the dependence of the damage accumulation on the fiber orientation remarkably changes the fatigue life of the short glass-fiber reinforced plastics.

We investigate the effects of the vacancy defects (i.e., missing atoms) in carbon nanotubes (CNTs) on the interfacial shear strength (ISS) of the CNT-polyethylene composite with the molecular dynamics simulation. In the simulation, the crystalline polyethylene matrix is set up in a hexagonal array with the polymer chains parallel to the CNT axis. Vacancy defects in the CNT are introduced by removing the corresponding atoms from the pristine CNT (i.e., CNT without any defect). Three patterns of vacancy defects with three different sizes are considered. Two types of interfaces, with and without cross-links between the CNT and the matrix are also considered here. Polyethylene chains are used as cross-links between the CNT and the matrix. The Brenner potential is used for the carbon-carbon interaction in the CNT, while the polymer is modeled by a united-atom potential. The nonbonded van der Waals interaction between the CNT and the polymer matrix and within the polymer matrix itself is modeled with the Lennard-Jones potential. To determine the ISS, we conduct the CNT pull-out from the polymer matrix and the ISS has been estimated with the change of total potential energy of the CNT-polymer system. The simulation results reveal that the vacancy defects significantly influence the ISS. Moreover, the simulation clarifies that CNT breakage occurs during the pull-out process for large size vacancy defect which ultimately reduces the reinforcement.

Numerical simulation by finite element analysis was used to investigate the relationship between the strength of glass fiber reinforced plastic (GFRP) and fiber length. Load speed dependability was also investigated, since thermoplastic resin used for GFRP exhibits much nonlinear stress—strain behavior and strong dependency on load speed. For this purpose, we conducted a periodic-cell simulation to address the effect of composite microstructure, matrix viscoplasticity, and microscopic damage (fiber break and matrix crack). When the fiber length was varied, the damage pattern was divided into two patterns: fiber-avoiding propagation and fiber-breaking modes of the matrix crack from fiber ends. When the matrix crack easily propagated in a fiber-avoiding way for shorter fiber lengths, the rate-dependent effect of the matrix was significant. Moreover, we considered the length at which the fracture mode changed based on this analysis, and compared it with the conventional critical length given by Kelly. Since the conventional critical length does not ensure improved composite strength, the consideration of the damage mode transition is essential for selecting the appropriate fiber length for strength improvement.

This paper investigated the damage transition mechanism between the fiber-breaking mode and the fiber-avoiding crack mode when the fiber-length is reduced in the unidirectional discontinuous carbon fiber-reinforced-plastics (CFRP) composites. The critical fiber-length for the transition is a key parameter for the manufacturing of flexible and high-strength CFRP composites with thermoset resin, because below this limit, we cannot take full advantage of the superior strength properties of fibers. For this discussion, we presented a numerical model for the microscopic damage and fracture of unidirectional discontinuous fiber-reinforced plastics. The model addressed the microscopic damage generated in these composites; the matrix crack with continuum damage mechanics model and the fiber breakage with the Weibull model for fiber strengths. With this numerical model, the damage transition behavior was discussed when the fiber length was varied. The comparison revealed that the length of discontinuous fibers in ...

In wire electrical discharge machining (WEDM), it is necessary to control the wire orientation accurately. However, the control is difficult because of the complex behavior of the wire during cutting caused by bubble expansion, electrostatic force and electromagnetic force. Therefore, it is important to measure the deflection and vibration of the wire in-process and to predict the machined surface shape. This paper describes the in-process measurement of the wire behavior using a sensor newly developed. The surface shape predicted from the wire behavior coincided well with the surface shape measured after machining.

Discontinuous fiber reinforced plastics have superior productivity and formability in comparison with continuous fiber reinforced plastics. However, their strengths are remarkably low. Thus there is an urgent need to establish a fundamental model in order to improve the strength of discontinuous fiber reinforced plastics. In the present work, we utilized numerical simulations that consider the microscopic damage in the composite and incorporate an individual constitutive law of thermosetting resin or thermoplastic resin. The fundamental mechanism that affected the strength and failure of the composite was investigated when the fiber length and/or matrix properties were varied from continuous glass fiber reinforced plastics to discontinuous glass fiber reinforced plastics. Our results clarified two factors that cause the strength degradation of discontinuous fiber reinforced plastics. One is the low yield stress of thermoplastic resin, which is frequently used for the matrix of discontinuous fiber reinforced plastics. As the other factor, the final failure mode is changed from fiber breaking mode to matrix cracking mode in the case of the low fiber volume fraction of discontinuous glass fiber reinforced plastics. Moreover, we investigated the relationship between fiber length and strength of carbon fiber reinforced polypropylene and the effect of thermoplastic matrix properties depending on the loading rate as well.

Discontinuous-glass-fiber-reinforced plastic (GFRP) composite material is widely used in industrial fields, mainly because glass fiber improves the strength and stiffness of polymer and because it is much less expensive than carbon fiber. It is thought that the use of long fiber is important in more efficiently improving the strength and stiffness of composites. In our previous study [1], we reported that the fracture mode of the discontinuous-fiber-reinforced composite changes from the matrix-cracking mode to the fiberbreaking mode (Fig. 1), when the aspect ratio for the fiber length to the fiber radius exceeds about 150. We also demonstrated that the strength is dramatically improved compared to the strength of the short fiber-reinforced composites and that the global load-sharing (GLS) model can roughly predict the strength (Fig. 2). Recently, Thomason [2, 3] produced the long discontinuous-fiberreinforced composites where the aspect ratio was about 250 and reported the stiffness and strength of the composites. In this article, we applied the GLS model to his experiments and discuss the validity of our models. First, we discuss the strength of unidirectional (UD) discontinuous-fiber-reinforced composites, rUD, based on the GLS assumption [4, 5]. We applied two types of GLS approaches to predict the composite strength. The GLS model focuses on one fragmented fiber (i.e., discontinuous fibers), aligned in the fiber axial direction, and neglects the interaction among fibers in the fiber cross-sectional direction. It predicts the composite’s strength by simulating the fiber damage evolution in such a fiber. One approach is based on Monte Carlo simulation [6] for fragmentation in a fiber in the composites. The other is based on the analytical model by Duva et al. [5]. (Hereafter, we refer to this as the DCW model.) Monte Carlo simulation deals with a detailed fiber stress distribution and fragment distribution, though multiple calculations are required for the prediction because it is a probabilistic approach. In contrast, the DCW model assumes an approximate stress distribution and fragment distribution, but it predicts the composite strength analytically. In simulating the fiber-damage evolution, the first approach utilized Monte Carlo simulation with the elastic– plastic hardening shear-lag model given by Okabe and Takeda [7]. The schematic of the elastic–plastic shear-lag model is illustrated in Fig. 3. The axial length of the model was set to 25 9 lf (lf is the length of discontinuous fiber), and the axial length was divided into 10,000 segments. The fiber ends in discontinuous-fiber-reinforced composites were represented by setting some random segments to the initially broken segments. Thus, the averaged length lf of the discontinuous fibers was related to the density of the initially broken segments introduced in the model. The transverse length of the matrix shear region in the model

The statistical strength distribution of Carborundum polycrystalline SiC fibers was derived from the fragmentation process in a single fiber/epoxy composite. We conducted Monte Carlo simulations of the fragmentation process using an elastic-plastic hardening shear-lag model. The Monte Carlo simulation with the estimated fiber strength distribution reproduces the fragmentation seen in the experiments very well. We also compared these simulated results with those calculated by the elastic shear-lag model with the shear-lag parameter beta tuned as proposed in Curtin et al. [Curtin WA, Netravali AN, Park JM. Strength distribution of Carborundum polycrystalline SiC fibers as derived from the single-fiber-composite. J Mater Sci 1994;29:4718-28] and with an elastic-plastic finite element model. The fiber axial stress distributions in all three models are in close agreement, with the characteristic length beta(-1) used in Curtin et al. consistent with the plastic length around a fiber break in an elastic-plastic hardening shear-lag model. (c) 2008 Elsevier Ltd. All rights reserved.

A numerical model of the progressive damage in cross-ply laminates (e.g., transverse cracks, interlaminar delaminations, and fiber breaks) is proposed. In this model, the embedded process zone (EPZ) model is used for the transverse cracks and interlaminar delaminations; the truss elements are used to express the fiber breaks. First, we describe the formulation and algorithm of this model. Second, we calculate the transverse cracking stress in CFRP [0/90] s laminates and compare it with the experiments by Boniface et al. The comparison validates that our model can appropriately simulate the onset and accumulation of transverse cracks for an arbitrary thickness of the 90° ply to the 0° ply with a set of parameters. Finally, this model is applied to our experiments for GFRP [90/0] s laminates. The simulated results reproduce the complicated progressive damage in GFRP [90/0] s laminates very well.

This paper attempts to quantify the fracture properties (strength and toughness) of the fiber–matrix interface in composites, using the fragmentation process and debonding growth for HI-Nicalon™ SiC single-fiber and T300 carbon single-fiber epoxy (Bisphenol-A type epoxy resin with triethylenetetramine (TETA) as curing agent) composite systems. This method is based on the numerical modeling for the microscopic damage and fragmentation process in single-fiber composite (SFC) tests, with a cohesive zone model (CZM). For the HI-Nicalon™ SiC single-fiber epoxy composite in which the major damage near a fiber break is interfacial debonding, interface properties were reasonably determined as ( T II,max , G IIc ) = (75 MPa, 200 J/m 2 ). In contrast, for T300 carbon single-fiber epoxy composite, we could not determine unique interfacial properties, since the variation of the cohesive parameters hardly affects the microscopic damage process due to the transition to the damage pattern dominated by matrix cracking.

本稿では,教師の専門性について稲垣忠彦氏の「自律性(autonomy)」の概念に注目し検討を加えるものである。自律性から見えてくる教師の専門性の重要性を明らかにするとともに,その醸成としての具体的方策である授業のカンファレンスを例示し,professional developmentと位置付ける教師教育の根幹を描き出していく。さらに,大学における教員養成についてその可能性と方向性を明らかにするものである。, By this report, I add examination to pay attention to a concept of "the autonomy" of Mr.Tadahiko Inagaki about the specialty of the teacher. I clarify importance of the specialty of the teacher from a concept of the autonomy, and I exemplify the conference of the class that is a concrete policy to breed the specialty of the teacher and draw root and trunk of the teacher education to place with professional development. Furthermore, I clarify the possibility and directionality about a teacher training in the university.

This paper proposes a numerical simulation of interlaminar damage propagation in FRP laminates under transverse loading, using the finite element method. First, we conducted drop-weight impact tests on CFRP cross-ply laminates. A ply crack was generated at the center of the lowermost ply, and then a butterfly-shaped interlaminar delamination was propagated at the 90/0 ply interface. Based on these experimental observations, we present a numerical simulation of interlaminar damage propagation, using a cohesive zone model to address the energy-based criterion for damage propagation. This simulation can address the interlaminar delamination with high accuracy by locating a fine mesh near the damage process zone, while maintaining computational efficiency with the use of automatic mesh generation. The simulated results of interlaminar delamination agreed well with the experiment results. Moreover, we demonstrated that the proposed method reduces the computational cost of the simulation.

The tensile strength of unidirectional carbon fiber-reinforced plastic (CFRP) composites was predicted by numerical simulation plus size scaling. The fiber strength distribution used in the numerical simulation was determined from the fragmentation process in a single fiber composite. Since the experimental data obviously did not fit the normal Weibull distribution, we fitted them with the Weibull of Weibull model, considering the statistical distribution of scale parameters of fiber strength in the normal Weibull model. Moreover, the constitutive law of the matrix was derived from the stress–strain curves of the angle ply laminates, utilizing the micromechanics approach proposed by Tohgo et al. [9]. Based on these parameters, we simulated the tensile fracture of unidirectional CFRP composites with the spring element model (SEM). The predicted tensile strength by numerical simulation plus size scaling agreed well with the experimental data. The results also confirmed that the Weibull of Weibull model is i...

A taxonomic revision of the subgenus Calosilpha Portevin, 1920 (of the genus Necrophila KirbySpence, 1828) through Asia is presented. Four valid species are recognized: (1) Necrophila (C.) brunnicollis (Kraatz, 1877), widely distributed from Bhutan and China: Yunnan province to Far East of Russia and Japan (including Ryukyu Islands); (2) N. (C.) cyaneocephala (Portevin, 1914), endemic to Taiwan; (3) N. (C.) cyaniventris (Motschulsky, 1870), widely distributed from northern India to Vietnam and southern China (east to Hainan Island); and (4) N. (C.) ioptera (KollarRedtenbacher, 1844), comb. nov. (ex Calosilpha), widely distributed in Pakistan, India (Himachal Pradesh to Assam) and Nepal. Eusilpha (Calosilpha) bicolor imasakai Nishikawa, 1986 and Eusilpha (Calosilpha) kurosawai Nishikawa, 1986 are confirmed as junior subjective synonyms (sensu ChoLee 1995, Ji 2012) of Silpha brunnicollis Kraatz, 1877. Description of important adult taxonomic characters (including male genitalia) and a key to species is included. Georeferenced records for all four species are mapped. First reliable records of Necrophila (Calosilpha) brunnicollis from China: Hong Kong and Anhui, Fujian, Gansu, Hubei, Jiangxi, Jilin, Qinghai and Zheijiang provinces and Guangxi autonomous region; N. (C.) cyaniventris from India: Himachal Pradesh, Uttarakhand, Meghalaya, Arunachal Pradesh, Nagaland and Manipur; and N. (C.) ioptera from Pakistan, India: Uttarakhand, Uttar Pradesh, Bihar, Sikkim, West Bengal and Assam are given (only imprecise records from "Himalaya" had been published for the last two species). First records of N. (C.) brunnicollis from Bhutan, and of N. (C.) cyaniventris from China: Hainan and Yunnan provinces, Myanmar, Laos and Cambodia are given. Parsimony analysis supports the monophyly of Calosilpha, with two clades, one formed by N. (C.) brunnicollis and N. (C.) cyaneocephala and the other by N. (C.) cyaniventris and N. (C.) ioptera. Geometric morphometrics discriminated four taxa of Necrophila (Calosilpha). Results indicated a sexual dimorphism between sexes in all species. Shape variability was concluded between the taxa. Populations of N. (C.) brunnicollis from continental Asia and three regions of Japan (Honshu + Shikoku, Kyushu and Ryukyus) also were examined. MANOVA was significant and supported shape differences in male and female populations. When testing each pair of groups by discriminant analysis, only differences between male populations from Japan (Kyushu) and those from Japan (Honshu + Shikoku) showed insignificance.

This paper explains previous studies addressing the onset crack or matrix crack in composite materials and presents a brief history of this field for the understanding of readers. Next, the analytic criterion and periodic unit cell analysis are compared for thermosetting or thermoplastic matrices. For both matrix resins, comparisons show that the Tsai-Hill criterion obviously cannot reproduce the results obtained from the periodic unit cell analysis, and the Hashin and Christensen criteria may give an appropriate failure envelope. Furthermore, macroscopic yielding and nonlinear deformation occur due to the plastic deformation of matrix resin before the failure. Thus it is appropriate to consider the elastoplastic or viscoplastic behavior of matrix resin. For thermoplastic resin, macroscopic yielding and nonlinear deformation occur due to the viscoplastic deformation of matrix resin much before its failure. Hence nonlinear deformation including creep may be more important than failure for thermoplastic resin.

This paper examines the stress distribution around a fiber break in alumina fiber-reinforced aluminum matrix (Al 2 O 3 /Al) composites using finite element analysis and predicts their tensile strengths using tensile failure simulations. In particular, we discuss the effect of matrix hardening on the tensile failure of the Al 2 O 3 /Al composites. First, we clarify the differences in the stress distribution around a fiber break between an elastic–perfect plastic matrix and an elastic–plastic hardening matrix using finite element analysis. Second, the procedures for simulating fiber damage evolution in the Al 2 O 3 /Al composites are presented. The simulation incorporates the analytical solution to the stress distribution of a broken fiber in the spring element model for the stress analysis of the whole composite. Finally, we conduct Monte Carlo simulations of fiber damage evolution to predict the tensile strength of the Al 2 O 3 /Al composites. Coupled with a size-scaling analysis, the simulated results express the size effect on the strengths of the composites seen in experimental results.

This paper proposes a numerical simulation of interlaminar damage propagation in FRP laminates under transverse loading, using the finite element method. First, we conducted drop-weight impact tests on CFRP cross-ply laminates. A ply crack was generated at the center of the lowermost ply, and then a butterfly-shaped interlaminar delamination was propagated at the 90/0 ply interface. Based on these experimental observations, we present a numerical simulation of interlaminar damage propagation, using a cohesive zone model to address the energy-based criterion for damage propagation. This simulation can address the interlaminar delamination with high accuracy by locating a fine mesh near the damage process zone, while maintaining computational efficiency with the use of automatic mesh generation. The simulated results of interlaminar delamination agreed well with the experiment results. Moreover, we demonstrated that the proposed method reduces the computational cost of the simulation. � 2006 Elsevier Ltd. All rights reserved.