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Moisture absorption and desorption by a matrix resin, and the resulting deformation, exert a critical adverse effect on the shape stability of carbon fiber reinforced plastic (CFRP) space structures. This study evaluates the effect of the moisture content of prepreg sheets on the life-cycle behavior of the prepreg-based CFRP. After evaluating the moisture absorption and desorption characteristics of the prepreg sheets, the cure-induced strain and moisture absorption and desorption deformations were measured, employing embedded optical fiber sensors. Furthermore, to investigate the relationship between the moisture absorption and desorption behaviors and the chemical structure of the matrix resin, its structure was analyzed by Fourier-transform infrared spectroscopy (FTIR). Since absorption and desorption are dependent on the matrix resin, two types of resins were evaluated: epoxy resin and a low moisture absorption cyanate resin. Finally, recommendations for the manufacture and operation of CFRP space structures are offered, with respect to maintaining their long-term shape stability. [ABSTRACT FROM AUTHOR]

Self-healing composites using microvascular channel networks have been intensively studied. Microvascular networks in composite in-plane directions are normally utilized to deliver healing agents to damaged areas. However, this channel configuration is not optimal to form robust networks and to infuse large damaged areas. This study proposes a self-healing system using multiple short microvascular channels in the through-thickness direction. First, the advantage of using this channel configuration was confirmed through delamination filling tests. Next, the feasibility of this channel configuration was evaluated by tensile tests and four-point bending tests. Double cantilever beam tests were then conducted to confirm its healing function. Finally, this system was applied to composite stiffened panels and the healing performance was evaluated using compression testing following panel indentation. The healing system almost fully recovered the original strength, confirming its high potential under practical conditions. Additionally, the weight reduction potential of the self-healing system was discussed through a strength comparison of specimens with different thicknesses. [ABSTRACT FROM AUTHOR]

L-shaped composites are fundamental parts of complex-shaped structures, and it is well-known that shape distortion (i.e., spring-in deformation) arises after curing due to the orthotropic nature of composites. This residual deformation increases the manufacturing costs, attracting significant attention to the mechanisms of spring-in deformation. Meanwhile recent aerospace-grade composites include inter-laminar toughened layers composed of thermosetting resin and thermoplastic particles to enhance the inter-laminar fracture toughness and to improve the impact resistance. Even though the inter-laminar resin layers can affect the process-induced strain and deformation, their effects have not yet been studied in detail. Therefore, this current study performed fiber-optic-based internal strain measurement and evaluated the residual deformation of L-shaped parts with inter-laminar resin layers. Through-thickness cure shrinkage strain at the corner part was relaxed and the spring-in angle decreased by holding the parts at the cure temperature, indicating that viscoelasticity of the thermoplastic particles is important. Viscoelastic finite element analysis supported this finding and indicated that the effect of inter-laminar toughened layers on the residual deformation should be considered to optimize curing processes. [ABSTRACT FROM AUTHOR]

CFRP pipes are used in spacecraft to support heavy optical instruments. CFRPs' low coefficients of thermal expansion and high stiffness improve the instrument performance. However, significant through-thickness strain arises in thick CFRP pipes in curing and operation at low temperature, resulting in delamination failure. In this study, we developed a fiber-optic-based life-cycle monitoring system to measure through-thickness strain development. First, we addressed the mechanism of strain development using a theoretical approach and finite element analysis (FEA). We confirmed that geometrical constraint arising from the cylindrical shapes causes significant out-of-plane stress in the through-thickness center, and the stress increases with increased thickness and stiffness. A fiber Bragg grating (FBG) sensor was then embedded at the through-thickness center of a pipe during lay-up. Non-axisymmetric strain change in the FBG sensor was continuously measured using the birefringence effect throughout the life cycle, including curing and simulated operation in a low temperature environment. Through comparison between pipe and plate specimens, it was clearly demonstrated that the system could sensitively capture through-thickness strain development and detect delamination failure in the pipe. In addition, FEA was conducted and the result agreed well with the experiment data, confirming the validity of the experiment results. [ABSTRACT FROM AUTHOR]

A crack arrester was recently developed to suppress crack propagation along the interface between the facesheet and the core in a foam-core sandwich structure. The crack arrester is a semi-cylindrical stiff material inserted into the interface. The crack arrester decreases the energy release rate at the crack tip by suppressing local deformation around the crack. If the arrested crack can be instantaneously detected, the damage tolerance of foam-core sandwich structures can be dramatically improved. This study establishes an innovative crack detection technique using two fiber Bragg grating (FBG) sensors embedded at both edges of the arrester. The change in strain distribution in the crack arrester induced by arresting the crack is evaluated using reflection spectra from the FBG sensors. The proposed technique enables an effective application of the crack arrester and significantly improves the reliability of foam-core sandwich structures. [ABSTRACT FROM AUTHOR]

This article describes the dewatering of sewage sludge using liquefied dimethyl ether (DME), which clarified the effect of sludge type and its particle size. Changes in the heating value of the dewatered sludge were also examined. In addition, the change in dewaterability upon reuse of the liquefied DME was investigated experimentally. Regardless of the nature of the sludge, its dewatering behavior was similar. The amount of dewatered water could be increased by decreasing the diameter of the sludge cake. Complete drying of the sludge cake via DME dewatering resulted in retention of approximately 96% of the heating value (17.7 MJ/kg-sludge) of the original sludge cake dry base (18.4 MJ/kg db). The DME could be recovered after extraction, and reuse experiments showed that liquefied DME dewatering performance was unchanged after five reuses. [ABSTRACT FROM AUTHOR]

In this study, we evaluated the applicability of the dimethyl ether (DME) dewatering method originally developed for high-moisture coal to superabsorbent polymer (SAP) and disposable diapers. It was found that liquefied DME successfully extracts water from SAP and disposable diapers. However, the polypropylene outer film and polyurethane used in diapers tended to dissolve in the liquefied DME and were subsequently released with the water discharged. These compounds are highly viscous, making it difficult to remove them from the drain outlet of the prototype. Therefore, the mechanics of the drain outlet should be considered in future studies. [ABSTRACT FROM AUTHOR]

The present study investigated, both experimentally and numerically, the improvement of low-velocity impact damage resistance of carbon fiber reinforced plastic (CFRP) laminates due to through-the-thickness stitching. First, we conducted drop-weight impact tests for stitched and unstitched laminates. The results of damage inspection confirmed that stitching did improve the impact damage resistance, and revealed that the improvement effect became greater as the impact energy increased. Moreover, the stitching affected the through-the-thickness damage distribution. Next, we performed FEM analysis and calculated the energy release rate of the delamination crack using the virtual crack closure technique (VCCT). The numerical results revealed that the stitching affected the through-the-thickness damage distribution because the stitch threads had a marked effect on decreasing both the modes I and II energy release rate around the bottom of the laminate. Comparison of the results for models that contained delaminations of various sizes revealed that the energy release rate became lower as delamination size increased; therefore the stitching improved the impact resistance more effectively when the impact energy was higher. [ABSTRACT FROM AUTHOR]

FBG (Fiber Bragg Grating) sensors and optical fibers were embedded into CFRP dry preforms before resin impregnation in VaRTM (Vacuum-assisted Resin Transfer Molding). The embedding location was the interface between the skin and the stringer in a CFRP-stiffened panel. The reflection spectra of the FBG sensors monitored the strain and temperature changes during all the molding processes. The internal residual strains of the CFRP panel could be evaluated during both the curing time and the post-curing time. The temperature changes indicated the differences between the dry preform and the outside of the vacuum bagging. After the molding, four-point bending was applied to the panel for the verification of its structural integrity and the sensor capabilities. The optical fibers were then used for the newly-developed PPP-BOTDA (Pulse-PrePump Brillouin Optical Time Domain Analysis) system. The long-range distributed strain and temperature can be measured by this system, whose spatial resolution is 100 mm. The strain changes from the FBGs and the PPP-BOTDA agreed well with those from the conventional strain gages and FE analysis in the CFRP panel. Therefore, the fiber-optic sensors and its system were very effective for the evaluation of the VaRTM composite structures. [ABSTRACT FROM AUTHOR]

In this research, optical fiber sensors and shape memory alloys (SMA) were incorporated into sandwich panels for development of a smart honeycomb sandwich structure with damage detection and shape recovery functions. First, small-diameter fiber Bragg grating (FBG) sensors were embedded in the adhesive layer between a CFRP face-sheet and an aluminum honeycomb core. From the change in the reflection spectrum of the FBG sensors, the debonding between the face-sheet and the core and the deformation of the face-sheet due to impact loading could be well detected. Then, the authors developed the SMA honeycomb core and bonded CFRP face-sheets to the core. When an impact load was applied to the panel, the cell walls of the core were buckled and the face-sheet was bent. However, after the panel was heated over the reverse transformation finish temperature of the SMA, the core buckling disappeared and the deflection of the face-sheet was relieved. Hence the bending stiffness of the panel could be recovered. [ABSTRACT FROM AUTHOR]

This study experimentally and numerically investigated the tensile damage progress in stitched laminates. In particular, it focused on the effects of stitching on the damage progress. First, we experimentally confirmed that ply cracks and delamination appeared under load regardless of stitching. We then performed damage-extension simulation for stitched laminates using a layer-wise finite element model with stitch threads as beam elements, in which the damage (ply cracks and delamination) was represented by cohesive elements. A detailed comparison between observation and the simulated results confirmed that stitching had little effect on the onset and accumulation of ply cracks. Furthermore, we demonstrated that the stitch threads significantly suppressed the extension of the delamination. [ABSTRACT FROM AUTHOR]

We propose a stochastic process analysis for predicting the strength and reliability of a unidirectional fiber-reinforced ceramic matrix composite. The analysis is based on a Markov process, in which it is assumed that a state of damage in the composite is developed with each fiber breakage. When the Weibull distribution is used to describe the strength distribution of the fiber, the probability of being in each state can be solved analytically in a closed form. Using the solutions of the probabilities, a discussion about damage tolerance of the composites is quantitatively developed, from the viewpoint of materials reliability engineering. To compare the proposed stochastic process analysis with previously proposed strength models in the basis of classical bundle theory, we obtained the expected value and variance in the composite stress from solutions of the probabilities of being in the states. The expected value and variance both consist of two terms, equivalent to the effects of both bundle structure and stress recovery in broken fibers. These are surprisingly in agreement with the solutions analyzed by Phoenix and Raj [9]. The effect of stress recovery in broken fibers produces a positive in the expected value and a negative in the variance and is thus a significant mechanism for increasing the strength and reliability of the composite. In addition we predicted the expected values of composite strengths and variances from the solutions. The corresponding value of normalized fiber stress to obtain the expected value in strength and the variance agreed relatively well with the value predicted by Hui et al. [13]. We further verified that the composite strength obeys a normal distribution, which has the expected value and standard deviation predicted above. Finally, we predicted the probabilities in strength of the composites with various sizes and concluded that the ceramic matrix composite is quite reliable in strength when the number of fibers corresponds to that in practical use. [ABSTRACT FROM AUTHOR]

This paper presents a part of the feasibility study for employing a damage monitoring system using a PZT actuator/FBG sensor. The goal of this research is to improve the present safety level of aircrafts by ensuring structural integrity and reducing maintenance/operation costs of advanced composite materials that will be employed for the primary structures of the new generation aircraft. Our novel sensor system employing a PZT actuator and an FBG optical fiber sensor can detect several types of damage, such as delamination and debonding, which are expected to occur in the highly efficient bonding structures of an aircraft wing box when the main/tail wing section is designed using composite materials. In this system, elastic waves will be transmitted into the structure by PZT actuators and received by small-diameter FBG optical fiber sensors that are embedded in the critical section of the primary structure of an aircraft. The onset and growth of damage can be detected with a very high accuracy through the change in the received elastic waves. In this study, a conceptual design was implemented in order to employ the novel system. We also selected the optimum application candidate area in order to verify the effects of the system. Further, the investigation and experiment on the novel sensor system that uses a bonded PZT actuator and an FBG sensor was carried out, and the basic damage detection technique was established based on the experimental results of the received elastic wave. Furthermore, compressive tests were carried out using the coupon specimen with an embedded small-diameter or standard-diameter optical fiber sensor. It was verified that the coupon specimen with an embedded small-diameter optical fiber suffered no degradation of its material properties. [ABSTRACT FROM AUTHOR]

The effect of transverse cracks on the ultimate tensile strength (UTS) was experimentally and analytically studied for carbon fiber reinforced plastic (CFRP) cross-ply laminates. For coupon specimens of various cross-ply stacking sequences, quasi-static tensile tests were carried out and transverse cracks were observed. The experimental results showed that the measured fiber bundle strength of 0° ply was almost constant, which indicated that transverse cracks had little influence on the notch sensibility of the bundle strength. Then, we proposed a new numerical model based on the finite element method to investigate the damage extension to the fracture. This model considered the elastoplastic behavior of epoxy matrix and the fiber breakages. Using this model, we applied a Monte-Carlo method to the damage extension simulation. It was found that the plastic region at the tip of the transverse crack reduced the stress concentration due to the crack, and that the bundle strength was barely affected by transverse cracks. [ABSTRACT FROM AUTHOR]

Ti-Ni shape memory alloy (SMA) foils are embedded into carbon fiber reinforced plastic (CFRP) cross-ply laminates in order to suppress the occurrence and progress of the transverse cracks in the laminates. When the pre-strained SMA foil is heated, the shape memory effect produces appropriate recovery compressive stress in the direction to suppress transverse cracks. However, Ti-Ni SMA foil has these specific characteristics due to the existence of a rhombohedral phase (R-phase). Thus, in this research, in order to use this SMA foil as an actuator, an extended Brinson model was proposed to clarify complicated behaviors of SMA. Then, for the determination of the parameters in the constitutive equation in this model, experimental tests were performed for the SMA foils. Using this model, several simulations were conducted and compared with experimental results. The agreement indicated that this model could express the thermo-mechanical behavior of the Ti-Ni SMA foil adequately. Finally, the behavior of the SMA foil during the CFRP manufacturing process was calculated on the basis of this model. The calculation results proved that the recovery stress already existed after the manufacturing process and the embedment of 4% pre-strained SMA into CFRP cross-ply laminate had the effect of suppressing the occurrence of transverse cracks. [ABSTRACT FROM AUTHOR]

In this research, shape memory alloy (SMA) foils were embedded into carbon fiber reinforced plastic (CFRP) cross-ply laminates. When the tensile pre-strained SMA foil is heated, the SMA produces appropriate compressive stress (recovery stress) to suppress the transverse cracks in the laminates. In order to investigate the damage suppression effect, tensile loading–unloading tests were conducted for the CFRP cross-ply laminates. The test results implied that the recovery stress of embedded SMA foil suppressed the occurrence and the progress of the transverse crack. Then, to confirm that the damage suppression effect was caused by the embedded SMA foil, the one-dimensional (1D) shear-lag model considering the behavior of SMA was newly derived. Using this model, the progress of transverse crack density was predicted probabilistically. The simulation results showed the same tendency as the experimental results. As a result, it was proved that the embedment of SMA foils into CFRP laminates is effective to suppress the occurrence and growth of the transverse cracks. [ABSTRACT FROM AUTHOR]

The Japanese Smart Materials and Structures System Project started in 1998 as a five-year program funded by the Ministry of Economy, Trade and Industry (METI) and supported by the New Energy and Industrial Technology Development Organization (NEDO). This project was primarily conducted by the Academic Institutions Centered Program, a collaborative research and development project among universities, industries, and national laboratories. Initially, this project consisted of four research groups: structural health monitoring, smart manufacturing, active/adaptive structures, and actuator material/devices. Two years later, two demonstrator programs were added in order to integrate the developed sensor and actuator elements into the smart structure system and to verify the research and development results of the four research groups. The application target of these demonstrators was the airplane, and two demonstrators whose shapes simulated the fuselage of a small commercial airplane (for example, Boeing B737) were established. The first demonstrator integrated the following six innovative techniques: (1) impact monitoring using embedded, small diameter optical fiber sensors newly developed in this program, (2) impact monitoring using integrated acoustic emission (AE) systems, (3) whole-field strain mapping using the BOTDR/FBG integrated system, (4) damage suppression using embedded shape memory alloy (SMA) films, (5) maximum and cyclic strain sensing using smart composite patches, and (6) smart manufacturing using the integrated sensing system. The second demonstrator was for suppressing vibration and acoustic noise generated in a composite cylindrical structure. In this program, high-performance PZT actuators/sensors (developed in this project) were also installed. All tests and evaluations were completed. This paper outlines the demonstrator programs. [ABSTRACT FROM AUTHOR]

This paper presents an overview of the damage growth suppression effects in CFRP laminates using embedded SMA foils, and was conducted to technically verify the application to aircraft structures. In previous studies, the authors confirmed the damage growth suppression of CFRP laminates with embedded pre-strained shape memory alloy (SMA) foils through both coupon testing and structural element testing. Through detailed observation of the damage behavior, we determined that these effects occurred due to the suppression of the strain energy release rate based on the suppression of the crack opening displacement caused by the recovery stress of SMA foils. These results were verified in this study using a demonstrator test article, which was a 1/3-scaled model of a commercial airliner's fuselage structure (B737 class). To demonstrate the damage growth suppression, the lower panel, which was dominated by tension load, was selected as the evaluation area. The evaluation area was an integrated panel including both the 'smart area' (CFRP laminate with embedded pre-strained SMA foils), and the 'conventional area' (standard CFRP laminate), for direct comparison of the damage behavior. The demonstration was conducted at 80°C in the smart area, and room temperature (RT) in the conventional area using a quasi-static load-unload test method. The demonstrator test article identified that the damage onset strain in the smart area was improved by 30% over that in the conventional area. [ABSTRACT FROM AUTHOR]

We conducted theoretical and practical studies for applying the Brillouin optical timedomain reflectometer (BOTDR) to an aircraft structural-health-monitoring system. First, we measured strain and temperature independently and simultaneously using a combined system of the BOTDR and fiber Bragg grating (FBG) with wavelength division multiplexing (WDM). Second, we used Brillouin spectrum analysis and processing to enhance up to 0.5 m the spatial resolution of the distributed strain measured by the BOTDR. Finally, we verified the proposed improvement of the BOTDR measurement by manufacturing and testing a composite structure. [ABSTRACT FROM AUTHOR]

The mechanical properties of composites subjected to out-of-plane impact decrease markedly from even barely visible damage. In this study, three damage detection technologies are explained: (1) Technologies for the arrangement of embedded small-diameter optical fibers that have no serious effect on the mechanical properties of composites; (2) Technologies for the egress of the optical fibers using 'the embedded connector for smart structures' that can be trimmed without damaging the optical fibers; and (3) Technologies for a damage detection system that has data acquisition and analysis functions, evaluates the initiation and the position of damage, and visualizes damage information. We conducted an impact test using the composite airframe demonstrator. FBG sensors are embedded in the upper panel of the 1.5 m diameter, 3 m long stiffened cylindrical composite structure for strain measurement, and optical fibers are embedded for optical loss measurement. Damage detection in composite structures using the developed damage detection system was demonstrated. [ABSTRACT FROM AUTHOR]

Experimental and theoretical investigations have been conducted to study the dependence of fiber fragmentation behavior on matrix yielding properties. The cured Epikote 828 resins with two types of curing agents have almost similar elastic moduli, but different tensile yield strengths. The interfacial chemistry between fiber and epoxy resin is unchanged due to the same constituent of the epoxy resin. The experimental results indicate that the fragmentation behavior of the fibers embedded in the matrix is significantly different for the tested glass fiber treated by γ-glycidoxypropyltrimethoxysilane. The average fragment length decreased with increasing tensile yield strength of resin, which suggests that the interfacial shear strength determined in the fragmentation test should be different depending on the tensile yield strength of resin used. The important phenomenon observed is the transition of the micro-damage mode from matrix crack to interfacial debonding. An elastoplastic shear-lag model was used to calculate the shear stress and fiber tensile stress distributions considering different plastic behaviors of the matrices. The theoretical results indicate that the plastic behavior of the matrix has a large influence on stress transfer. Based on elastic and plastic properties of the matrix, the fiber fragmentation behavior in the matrix is predicted. Experimental and theoretical results are favorably compared. [ABSTRACT FROM AUTHOR]

The R & D status of our structural health-monitoring group (SHMG) in 1999 is summarized. Activities of the SHMG are conducted as a university-industry collaboration program at the University of Tokyo, along with ten research organizations. Research themes include (1) the development of high-performance sensor system technology with newly developed sensors, (2) the development of a damage detection and self-diagnosis system for structural integrity based on micromechanical damage identification, and (3) the development of application technology for model structures. The sensor technology includes (1) the development of a small-diameter optical fiber sensor, (2) damage suppression in composite laminate systems with embedded shape-memory alloy films, and (3) the development of maximum strain memory sensors with electrically conductive composite systems. The sensor output is correlated with the underlying damage evolution in structures such as aircraft, satellites, high-speed trains, and large-scale civil infrastructures. [ABSTRACT FROM AUTHOR]

Presents a study which applied the concept of a flexible interphase to braided composites with cut and uncut resin. Methods; Results; Conclusion that the cut specimin was improved in fracture load and displacement because the progress of debonding the fiber bundle was interrupted.

A damage mechanics analysis is applied to predict the relation between laminate stress and strain in composite laminates containing transverse matrix cracks. First, the transverse crack density as a function of laminate stress is predicted based on both energy and average stress criteria. Next, the laminate strain increment caused by transverse cracking is also derived as a function of applied laminate stress and transverse crack density, and then the relation between laminate stress and strain is predicted considering matrix cracking. The analytical prediction of the relation between laminate stress and strain is compared with the experimental results. The analytical prediction slightly underestimates the laminate stress because the strain increment associated with transverse crack opening displacement is overestimated in this analysis. An advantage of the present method is that it can be applied to laminates with arbitrary stacking sequences. [ABSTRACT FROM AUTHOR]

Microscopic damage progress in high temperature CFRP cross-ply laminates under thermal cycling was investigated. Two types of laminate configuration were tested to study the effect of ply thickness. Matrix cracks initiated in both 0° and 90° plies and the number of cracks increased as the number of cycles increased. The saturated number of cracks in 90° plies was twice as large as that in 0° plies. To discuss these experimental results, shear-lag analysis was used to evaluate both the energy release rate associated with matrix cracking and the thermal residual stress in cracked plies. It was implied that the effect of the maximum thermal residual stress as well as the energy release rate range were significant in the quantitative evaluation of the matrix cracking induced by the thermal cycling. [ABSTRACT FROM AUTHOR]

Textile composites have been used extensively as industrial materials because of the excellent mechanical properties resulting from the continuously oriented fiber bundle. In a study of the mechanical properties, it is important to consider the fiber/matrix interface property as for other composite materials. In a recent study, the fiber/matrix interface is regarded as an interphase that has its own material constants and thickness; consequently, the mechanical properties of a composite can be controlled by specifically designing the interphase. In this study, we applied this concept to braided composites with flexible resin as interphase for the purpose of designing the interphase. In a static tensile test, though there were no improvements in Noncut specimens (normal braided composites), but a Cut specimen (each side of the Noncut specimen was cut) with flexible interphase was improved in fracture load and displacement. The observation of the specimen edge was carried out and it was confirmed that the progress of debonding at the fiber bundle intersection was interrupted by a flexible interphase, and a matrix crack did not occur in the Cut specimen with flexible interphase. In a fiber bundle pull-out test, it was confirmed that debonding progressed not into the fiber/resin interface but into the flexible interphase in the specimen with flexible interphase, and the interfacial property at the fiber bundle intersection was improved. [ABSTRACT FROM AUTHOR]

Transverse crack behavior in quasi-isotropic interleaved CFRP laminates was observed by an optical microscope and a soft X-ray radiography system. Seven symmetric laminates composed of the same combination of ply orientations were tested to clarify the effect of stacking sequence on transverse crack behavior in 90° plies. The thickness of 90° plies and the modulus of adjacent plies were found to be most influential in their effect on transverse cracking behavior. To model the experimental results, damage mechanics analysis was used. The predictions of transverse crack evolution based on both energy and average stress criteria were compared with the experimental results. The validity of the present analysis was confirmed. The advantage of this analysis was its applicability to general laminate configuration, once the critical values were determined. [ABSTRACT FROM AUTHOR]

In recent years, interlaminar-toughened laminates have been developed in which resin rich layers are placed in interlaminar regions in order to enhance the interlaminar fracture toughness of CFRP laminates. In the present study, a predictive method is developed for transverse cracking in CFRP cross-ply laminates with interlaminar resin layers at 0/90° interfaces under static tensile loading. The analysis is based on a two-dimensional approximate elastic analysis considering the interlaminar resin layers and thermal residual stresses. To predict transverse cracking, both energy and stress criteria are used. The change in thermoelastic properties of a laminate due to transverse cracking is also predicted. To investigate the validity of the analysis, loading-unloading tests are performed to obtain Young's modulus reduction as a function of the transverse crack density. The predictions of transverse crack density as function of the laminate strain are compared with our previous experimental results. A good agreement is obtained which implies the validity of the present analysis. [ABSTRACT FROM AUTHOR]

Presents a study which investigated the multiple cracking phenomena in silicon oxygen thin films deposited on polyethylene terephthalate substrates during tensile test. Materials that were used; Experimental details; Background of modified shear-lag analysis; Results and discussion.

Microscopic damage progress under static tensile loading in quasi-isotropic CFRP was observed by an optical microscope and a scanning acoustic microscope (SAM). Material systems used were toughened-type CFRP, T800H/3631 and newly developed CFRP with interlaminar-toughened layers. T800H/3900-2. The laminate configurations were quasi-isotropic [0/45/90/—45][sub g2] for T800H/3631 and [0/45/90/—45][sub s] for T800H/3900-2. Both plain specimens and specimens with a circular hole were tested. By the edge observation of the plain specimens, transverse crack density was measured as a function of laminate strain. The effect of interlaminar-toughened layers on the behavior of the microscopic damage was clarified experimentally. By the SAM observation of specimens with a hole, delamination onset and growth were detected. To discuss the delamination onset from the edge of the open hole, the energy release rate associated with delamination growth was calculated following O'Brien and Raju. The energy release rate predictions of delamination onset and growth was qualitatively consistent with the experimental observation. [ABSTRACT FROM AUTHOR]

In recent years, to enhance the interlaminar fracture roughness of CFRP laminates, interlaminar-toughened laminates have been developed in which resin rich layers are placed in interlaminar regions. In the present study, stress and displacement fields in interlaminar-toughened cross-ply laminates with transverse cracks are analyzed. The analysis is based on a two-dimensional model which assumes that generalized plane strain conditions prevail. Account is taken of thermal residual stresses arising from a mismatch in thermal expansion coefficients of the 0° ply, interlaminar resin and 90° ply. The analytical results are shown for the laminates with interlaminar resin layers of various thicknesses. The analysis will be a basis for the optimal design of laminates with interlaminar resin layers. [ABSTRACT FROM AUTHOR]

Focuses on the duodenum-preserving reconstruction in the pancreas for the treatment of chronic pancreatitis in Japan. Division of the pancreas over the portal vein; Postoperative course of the patient; Techniques for the drainage of pancreatic juices.

Introduces several articles about smart materials and structures.