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Strain monitoring of resin during cure process is an effective method to manufacture high-quality FRP products because it is known that residual stress generated during molding decreases strength of final products. Although both cure and thermal shrinkage occur during cure process, it is difficult to measure cure shrinkage of FRP products due to dramatic changes in mechanical properties of resin by cure reaction. Among cure monitoring methods, it is proven that fiber optic embedded strain sensors can measure cure shrinkage of resin. However, quantitative evaluation of cure shrinkage strain measured by optical fiber strain sensors has not been conducted. In the present paper, we monitored curing shrinkage of epoxy resin by an embedded EFPI sensor. Mechanical and thermochemical properties of the resin during cure process were experimentally obtained by several methods. Volume shrinkage of resin during cure process was also measured by a dilatometer. In this paper, a viscoelastic model during cure process was driven and the model was used for FEM analysis of cure shrinkage strain generated in the embedded EFPI sensor. From the results, it appeared that the calculated cure shrinkage strain of the EFPI sensors agreed well with the measured strain especially when the degree of cure was high. Therefore, it was concluded that an embedded EFPI sensor can measure cure shrinkage strain quantitatively.

In the present paper, the impact responses and overall damages of Fibre-Metal Laminates based on titanium alloys and glass fibre-reinforced polymers (Ti/GFRP) as Ti/FRP laminate system were evaluated. Low-velocity impact tests using a drop-weight tower were conducted for the cross-plied GFRP laminates and the Ti/GFRP laminates, and the impact responses during impact loading were obtained. Impact damages such as cracks in titanium layer and delamination of titanium-GFRP interface or matrix cracks and interlaminar delamination in GFRP layer were observed from the impact direction. From the experimental evidence, it was found that the Ti/GFRP laminates showed same impact damage modes as of other types of Fibre-Metal Laminates. Internal damages in the Ti/GFRP laminates were restrained by the reinforcing effect of titanium and adhesive layer compared to the cross-plied GFRP laminates. The Ti/GFRP laminates showed two patterns of the impact responses and damages with the threshold impact energy of about 4.8J. With higher impact energy than this threshold, single crack was presented in titanium layer at non-impacted side. The interlaminar delamination area in GFRP layer increased sharply due to the occurrence of this crack. Numerical analysis model that represent the impact behaviour of the Ti/GFRP laminates using finite element method was suggested based on the damage observations. The impact responses obtained by the dynamic analyses agreed well with the experimental results. The calculated area of interlaminar delamination in GFRP layer as a function of impact energy showed same behaviour as seen in the experiments. As a consequence, it was shown by the analysis as well that the drastic increase in the internal damage area of the Ti/GFRP laminates was induced by the fracture in outer titanium layer under the out-of-plane impact loading.

This study proposes a real-time monitoring method for degree of cure (DOC) of curing resin by refractive index measurement using a single-mode optical fiber based on the Fresnel reflection at the fiber end. First, we particularly present an approach for measuring refractive index of resin in real time without the effects of unexpected backward reflection. We applied this approach to measurement of refractive index of an epoxy resin during cure process, and experimentally confirmed that the change of the refractive index was stably measured in real time. Next, we proposes a new approach to calculate DOC from change of refractive index by eliminating effect of temperature change on refractive index of curing resin. This approach can quantitatively evaluate the DOC in real time, which is not obtained by conventional methods, and provide information in the small region at the fiber end. The experimental results of monitoring cure process of the epoxy resin showed that the DOC could be stably measured by this approach without effect of the temperature change. Furthermore, the DOC obtained by this approach was compared with the DOC curve by the thermal analysis using differential scanning calorimeter. These experiments revealed that the DOC by the present approach represented the curing condition of the resin regardless of the cure pattern and was easily translated into the DOC by the thermal analysis. The present approach of real-time quantitative evaluation of the DOC can be applied to fast cure reaction as well as slow reaction demonstrated in this paper.

** Two pitch based high modulus type carbon fibers with oxidative surface and sizing treatments and without any treatments are used in the present work. These fibers are made under the same process derived from the same pre- cursor. Unidirectional carbon fiber reinforced carbon composites (C/C composites) are prepared from two kinds of these carbon fibers and four kinds of carbon matrix precursors, two thermosetting resins (phenolic and furan resins) and two pitches, (coal-tar and petroleum pitches). The tensile test of the strand specimen of the composites heat- treated at different temperatures is carried out by following JIS R7601. Effects of oxidative surface and sizing treat- ments of carbon fiber on tensile properties of the composites derived from different matrix precursors are discussed. In the case of high modulus type pitch based carbon fiber, it is found that there is almost no effect on the strength of composites by the surface oxidation and sizing treatment of the carbon fiber, except for showing different fracture morphologies of graphitized composites derived from the thermosetting resins between the treated and the untreated fibers.

Recently real-time monitoring technique by using built-in sensors of FRP is expected to reduce the cost and enhance the reliability. In the present paper, built-in FBG fiber optic sensors were applied to cure and health monitoring of filament winding (FW) glass/epoxy pipes. FW pipes were wound by ± 45° helical ± 5° parallel winding methods. The FBG sensors were embedded between helical and parallel layers along axis direction of the pipes. Internal strain monitoring of the FW pipes was conducted during cure and fatigue tests. From the results of the cure monitoring, it was found that FBG sensors could be used for measurement of the curing shrink as well as the thermal residual strain. The results of the fatigue tests showed that strain from the FBG sensors had very good agreement with that from the attached strain gauges. Young's modulus of the pipes measured by the FBG sensor was almost constant during the fatigue tests although transverse cracks occurred in the parallel layers. However, the spectral shape reflected from the FBG sensor was affected by existence of the fatigue cracks. In order to evaluate degree of damages near the sensor, correlation coefficient calculated from the spectral shape was introduced. The experimental results showed that the correlation coefficient was useful for evaluation of damages.

Charcoals were prepared under various conditions of carbonization from three kinds of plants: balsa (Ochroma lagopus Sw), giant ipil-ipil (Leucaena leucocephala (Lam.) de Wit) and mousou chiku (Phyllostachys pubescens). The pore structure of the various charcoals was observed on fractured cross-sections under SEM and was evaluated utilizing mercury porosimetry. The sorption capacity of the charcoals for A-grade heavy oil was determined by direct soaking in oil. It was found that the pore structure of the charcoals depended strongly on, not only, the precursor plants but also carbonization conditions, particularly heating rate. Balsa charcoals prepared with a heating rate of 50°C/min. under vacuum gave a relatively high sorption capacity for A-grade oil, approximately 30g/g of charcoal. The other two charcoals, derived from giant ipil-ipil and Mousou chiku, had a considerably lower capacity, approximately 1.5g/g-carbon. The dependence of pore occupancy, the ratio of volume of oil sorbed to total pore volume, on the average pore radius indicated that pores with a diameter above 1μm were largely responsible for heavy oil sorption.

Accepted: 2003-01-30, 資料番号: SA1003318000

The notched fracture strength using the double edge notched plate tension specimen of the woven C/C composite was calculated by the modified shear lag analysis method, in combination with the average stress criterion (composite fractures when the average stress over the characteristic distance in the fiber bundle at the notch tip reaches the strength of the fiber bundle). The present method could describe the following features experimentally observed in our former work. (i) The fracture strength was lower than the net strength criterion and decreased with increasing width when the debonding at the notch tip was short. (ii) The fracture strength was well estimated by the net strength criterion when the debonding was long. The results of calculation for wider specimens revealed the following; the notched strength remains nearly constant for any width given by the net strength criterion when debonding length is very long; it decreases with increasing width unless the debonding length is very long; the strength-width curve of the composite with finite debonding length is in the range of the upper bound given by the net strength criterion and the lower bound by the fracture toughness one.

The effect of the orientation texture of cross-sectional graphitic layer planes on transverse compressive properties was studied in pitch-based carbon fibers. The finite element analysis indicated that radially oriented fiber could be expected to display higher transverse modulus and lower transverse compressive strength than randomly oriented fiber. The transverse compressive test was carried out by means of direct pressing of single filaments in which each filament's strength and modulus were measured. The cross-sectional orientation texture was identified not only by observation under scanning electron microscope (SEM) but also by torsional modulus measurement. The transverse modules and transverse compressive strength were found to decrease with increasing crystallite size. It was however not possible to find out clear differences between radially and randomly oriented fiber. These transverse properties cannot therefore be attributed to differences in cross-sectional texture. Bonding between crystallites appears to be the dominant factor in determining the transverse modulus, while the strength in the central area of the cross section is expected to determine the transverse compressive strength of the filament.

The effects of interface control and matrix microstructure on the interlaminar shear strength and mode II interlaminar fracture toughness of 5H satin woven C/C composites were investigated by coating bismaleimide-triazine co-polymer (BT-resin) on the surface of carbon fiber and changing the heat-treatment temperature. Three point short beam flexure tests were carried out for the shear strength. End notched flexure specimens were used for the mode II interlaminar fracture toughness tests. Both the interlaminar strength and toughness decreased by coating BT-resin and increasing HTT from 1600°C to 2500°C. However the influence of the BT-resin coating was much larger for the mode II interlaminar fracture toughness than that for the interlaminar shear strength. This difference of the effect of interface control was discussed on the basis of microscopic observation.

Thermal conductivity of a highly porous carbon/carbon composite, known as carbon bonded carbon fiber (CBCF) and used as thermal insulation, was measured and related to the structure investigated by optical microscopy, x-ray diffraction and Raman spectroscopy. It was found that halogen purification of CBCF, that involves heat treatment in chlorine atmosphere, did not result in a greater extent of structural development than heat treatment at the same temperature for the same time in inert atmosphere (unpurified sample). The thermal conductivity of CBCF, both halogen purified and unpurified, was found to increase with temperature in the measured range 1000°C to 2200°C. The experimental thermal conductivity values were in good agreement with those calculated from a model that indicated that in CBCF solid heat transfer was dominant, compared to radiation heat transfer, even at 2200°C. The matrix in CBCF was found to be relatively graphitic as a result of stress orientation on carbonization and as matrix was observed along the fiber length it was tentatively suggested that it may contribute to the effective axial conductivity of the fibers.

In order to investigate the influence of heat treatment temperature on the interfacial shear strength of C/C composites, a pull-out test was carried out on a microcomposite heat-treated at various temperatures which was composed of seven filaments. It was confirmed from SEM observation and Raman spectroscopy that shear fracture proceeded through both interface and interphase. Interfacial shear strength was calculated taking into account the effect of stress distribution. It was found that interfacial shear strength decreased by carbonization until 1200°C. However, it increased by graphitization at 2000°C. At the same time, exfoliation of the matrix from some fibers occurred by graphitization and those samples showed a very low level shear fracture force. Therefore, strengthened parts and weakened parts were mixed in the graphitized C/C composite.

KC8 and KC24 were allowed to react with several unsaturated hydrocarbons. After contact with isoprene, styrene or 1,3-butadiene, potassium—graphite intercalation compounds (GICs) expanded slowly along the c-axis direction. Molecules of unsaturated hydrocarbons are considered to be introduced into the interlayer spacing of GICs and polymerized progressively. When acrylonitrile, 1-butene or isobutene is used as the unsaturated hydrocarbon, the interaction between GICs and hydrocarbons is quite different. Monomer molecules are polymerized only in the vicinity of the sample edge, which enhances the stability of potassium—GICs in water. Two other kinds of interaction between alkali metal—GICs and unsaturated hydrocarbons, i.e. intercalation with and without oligomerization, are also reported elsewhere by several authors. We classified the interaction into four categories mainly according to the reactivity of unsaturated hydrocarbon for polymerization.

Unidirectional carbon fiber reinforced carbon composites (C/C composites) were prepared from a high modulus-type carbon fiber, treated with either silane or titanate coupling agents, and a furanic resin matrix precursor. Regardless of coupling treatments of fibers, a preferentially oriented region parallel to the fiber surface was observed at the interphase in the carbon matrix derived from furanic resin. The matrix interphase was flattened by development of graphitic structure after heat treatment at 2600°C. In the composite fabricated from untreated fiber, the strong adhesion between fiber and matrix resulted in damage of the reinforcing fibers by the flattening of the matrix. The coupling treatments weakened the interfacial adhesion between carbon fiber and carbon matrix, and prevented fiber damage resulting from matrix flattening by separation at the interface. In the graphitized composite fabricated from silane coupling-treated fibers, the interfacial adhesion became so weak that fiber pull-out was observed on fracture. The titanate coupling treatment limited the extent of graphitization of matrix in the composite. For composites fabricated from titanate coupling-treated fiber, the tensile strength increased with increasing heat treatment temperature. The graphitized composites from titanate coupling-treated fibers showed 50% higher strength than the composite from untreated fibers.

There are two major fracture criteria for notched C/C (carbon/carbon) composite materials. One is that the fracture strength is determined by the fracture toughness criterion, and the other is that it is simply decided by the net section stress failure criterion. In the present study, effects of crack depth, specimen size, and the heat treatment temperature on the strength and fracture mechanism of C/C composites were investigated by using double edge cracked plate tension specimen in order to clarify the confusion on the fracture criterion. For the case of carbonized C/C composites (heat-treatment temperature = 1600° C), the notched strength of wider specimens was smaller than the net section stress failure criterion, showing the notch effect. When the ligament length of the notch was shorter than about 8 mm, the fracture strength of notched specimen was well correlated to the net section stress criterion. On the other hand, the notched strength of graphitized C/C composites (heat treatment temperature = 2500 and 3000°C) was well estimated by the net section stress criterion without respect to the ligament length. The strength of smooth specimen for C/C composites was almost the same without respect to the heat-treatment temperature, while the fiber strength decreased by half with increasing the heat-treatment temperature. Thus, the contribution of the fiber strength to composites strength was much higher for the graphitized C/C composites, The change of fracture mechanism in macroscopic and microscopic scale was well correlated to the change of the fracture criterion.

For carbon fiber reinforced plastics (CFRP) using 6 kinds of carbon fibers with different surface conditions, ILSS was measured from 25°C to 200°C at various cross head speeds (CHS), and the influence of surface structure of carbon fiber on the high temperature ILSS of CFRP was investigated. The following results were obtained.(1) ILSS measured at high temperatures was higher for CFRP with surface treated fibers.(2) The logarithmic values of shift factor aT by adopting time-temperature superposition principle were plotted against 1/T. These Arrhenius' plots showed differences among kinds of fibers and those with or without surface treatment. In every case, plots are aligned on a line that bends at a point.(3) In the lower temperature range than the bending point on Arrhenius' plot, the activation energy were from 140 to 230kJ/mol and it increased with the increment of the amount of COOH group obtained from C1s peak of X-ray photoelectron spectroscopy.

The strength by a short beam method of three point bending was measured for some CFRPs with varying fiber and matrix resin combination and their failure states were examined. The strength of every CFRP decreased linearly with increasing temperature. The strength retention at 200°C depended on the glass transition temperature of matrix resin. The retention for PMR-15 matrix resin was the highest, followed by MY720 resin and then EPIKOTE 828 resin. The failure mode of CFRP with EPI-KOTE 828 matrix resin tested at a cross head speed of 5mm/min was a mixture of shear and compression failure below 150°C, but pure shear failure at 200°C. Pure shear failure was also observed at cross head speeds less than 0.5mm/min, while compression failure in addition to shear failure was observed at cross head speeds more than 5.0mm/min. In CFRP with MY720 matrix resin, only shear failure was observed in the range of testing temperatures. In CFRP with PMR-15 matrix resin, buckling failure in addition to shear failure was observed up to 250°C. These differences in failure modes of different CFRPs were related with the ultimate strain of the matrix resin.

Torsional and tensile tests of alumina and silicon carbide fibers from precursors were carried out. Their shear moduli, torsional strengths, Young's moduli and tensile strengths were evaluated and compared. Their shear moduli are about one half of their Young's moduli. Their fracture surfaces show the characteristic feature of isotropic brittle structure. The measured torsional strength of the alumina fiber coincides with that deduced from the tensile strength. Thus, this fiber has extremely isotropic properties of not only structure and moduli but also of strength. However, the measured torsional strength of the silicon carbide fiber is weaker than that deduced from the tensile strength. As for this reason, it is supposed that the sheath is weaker than the core and/or defects are preferentially oriented to the fiber axis.

Effects of fibre/matrix interface and matrix microstructure on the strength and fracture mechanism of C/C composite materials were investigated by coating bismaleimide-triazine co-polymer (BT-resin) on the surface of the carbon fibre and changing the heat-treatment temperature. Here, the high-modulus type carbon fibre was used to avoid the change of fibre properties during heat treatment. For the case of carbonized C/C composites (heat-treatment temperature=1600°C), the notched strength of composites without BT-resin coating was smaller than the net section stress failure criterion. The notched strength of the wider specimen was smaller than the narrower specimens. Thus, the composites indicated clear notch sensitivity. On the other hand, the notched strength of C/C composites with BT resin coating was well estimated by the net section stress criterion. For the case of graphitized C/C composites (heat-treatment temperature=2500°C), the notched strength was well estimated by the net strength criterion without respect to BT-resin coating. The change of the fracture mechanism in microscopic scale was well correlated to the change of the fracture criterion.

Clamping methods for evaluating tensile properties of carbon fibers in a form of strand were studied. When clamped with the three-plates aluminum tab and loaded through pins, the strand specimens in which the carbon fiber was impregnated with resin so as to penetrate fully among filaments exhibited the highest tensile forces. In this case, the strand specimens often broke into several pieces. With the clamping method using abrasive cloth, the strand specimens exhibited 95% of them, but their preparations were less time- consuming.

A wicking method technique to study the sorption behavior of heavy oil into exfoliated graphite packed in a glass column was developed. The weight increase of the exfoliated graphite column during the sorption process was continuously measured. It was found that the sorption speed depended on the viscosity of heavy oils. Sorption of the A-grade heavy oil with a low kinematic viscosity was a hundred times as quick as that of the C-grade oil with a high viscosity. Packed density of the exfoliated graphite in the column affected not only sorption speed but also the sorbed amount of heavy oil, because the size of opening spaces formed among the exfoliated graphite particles and the pore volume per unit weight of exfoliated graphite decreased with increasing the packed density. The exfoliated graphite column with the higher packed density showed quicker sorption of heavy oil. Exfoliated graphite with density of 7kg/m3 showed the largest weight of sorbed oil per unit weight of the graphite. The weight of sorbed oil per unit weight of exfoliated graphite decreased with increasing the packed density. In the saturated weight of heavy oil sorbed into the column, however, the maximum value was found when the exfoliated graphite was slightly densified from 12 to 16kg/m3.