An optimization procedure is proposed for design of fibrous composite plates having angle-ply for maximum bending stiffness. Strain energy was taken as the objective function, while the lamination parameters by which a general laminate construction can be considered were taken as the design variables. Deformation analysis was carried out using the Rayleigh-Ritz method for bending under any loading conditions. Numerical results are presented for graphite/epoxy symmetric laminates, resting on simple supports and subjected to either distributed or concentrated loading. As a result, it was found that the application of the present optimization procedure yielded an optimum design of a laminate construction, and the effects of the loading condition and aspect ratio became clear.
It has become now possible to analyze by a personal computer even complicated problems with required a large sized computer before, because of remarkable development of personal computers. In the present study, the personal computer program of F.E.M. by triangular elements has been developed in order to analyze the stresses in composite materials. It is shown that the mechanical behavior of composite materials can be analyzed by the developed computer program. As the accuracy of analysis by triangular elements depends strongly on the number of nodes and elements, the program by isoparametric elements which have good accuracy of calculations has been also developed. And the formulation has been evaluated by the comparison between theoretical value and calculational one under bending conditions of isotropic and anisotropic plates. In case of stress analysis for isotropic materials by isoparametric elements, the computational results were in good agreement with the theoretical ones. In case of triangular elements, the computational results agreed with the theoretical ones when the number of nodes was more than 150. The stress analysis for anisotropic materials, however, the computational results by both isoparametric and triangular elements were similar. Therefore, the F.E.M. by triangular elements is considered reasonable for composite materials. The pre- and post-processing programs utilizing the graphics capabilities of the personal computer have been also developed. As the results of the present study, it is recognized that the developed personal computer program is very useful for structure design of composite materials.
The impact damage behaviour by low velocity impact of graphite/epoxy laminated composites was studied and residual mechanical properties tests were conducted after impact. The laminates were fabricated into 8 ply sheets of (0°/±45°/90°)s with about 2mm thickness from commercially available prepregs (Besfight, Toho Rayon). The falling impact tests were carried out varying the drop height and the weight diameter. Impact damage of the specimens was inspected using a new type of ultrasonic imaging system and the three point bending tests were performed with an Instron type machine. The maximum bending stress decreased due to the impact delamination. The residual maximum bending stress showed lower values with a larger weight diameter as impact energy was increased. The impact reduced the residual elastic modulus. The residual elastic modulus by the back face loading was larger than that by the front face loading in lower impact energy. On the contrary, residual elastic modulus by the back face loading was lower than that by the front face loading in the larger impact energy. Therefore, residual elastic modulus depends on impact energy.
In order to apply composite materials fabricated by filament winding for a shock absorber under impact loading, their toughness should be improved. To overcome the problem, it is necessary to develop the configuration suitable for the object. The ring shape made by filament winding with some of notches along the internal circumference was investigated in this paper to increase the toughness by delamination effect under the equivalent value of impact load. The analytical results developed in this paper considering the propagation of stress waves were verified by the experimental results.
A functional composite material was developed to improve its thermal characteristics by the addition of metallic fibers under Vf=1% into fiber reinforced plastics. The metallic materials used were electrolytic copper and brass-plated steel fibers of several tens μm in diameter. They were inserted between chopped strand mats parallel to the longitudinal direction. The thermal diffusivity in the longitudinal direction was improved by following the law of mixture. The static strength of the new materials increased about 50% as compared with that without metallic fibers. A similar increase in fatigue strength was also recognized. The increase in strength of the composite with metallic fibers was maintained even at a high-temperature environment about 200°C, and the heat-resistant property was improved. The reason of such improvement was considered that the shear plastic deformation of composite material both in-plane and inter-ply became difficult due to the presence of metallic fibers.
Glass fiber reinforced plastic bolt (FRP bolt) has been applied to several equipments or structures, as it has good chemical, mechanical and electrical properties such as a corrosion resistance or a large strength/density ratio. Recently, according to the development of super conducting technology, its fatigue property at low temperatures also has become important. In this report, the FRP bolt which had a center roving and a braid structure was chosen and its fatigue behavior at R.T. and 77K was investigated. As the results, the following conclusions were obtained: (1) Although the fatigue strength was hardly dependent on a reinforcement fiber structure in FRP bolt, it was increased at 77K compared with at R.T.. (2) The fatigue fracture of FRP bolt was caused by the initiation and the propagation of 3 types of cracks. The first was on a reinforcement fiber bundle/resin matrix interface, the second was in a reinforcement fiber bundle and the third was in resin matrix. (3) As these cracks were considered to be initiated depending on stress state, it was clarified that the first type crack above mentioned was formed easily at a high shear stress field.
Fatigue damage of interfacial delamination of notched CFRP has been observed by a scanning acoustic microscope (SAM), and the delamination resistances against fatigue cycles are discussed. By using a pulse wave of 50MHz, the delamination images at each interfacial site were clearly observed by a SAM. The delamination was quite different at each interface, and the interfacial delamination ahead of a notch was hardly observed between the 1st and the 2nd laminae but firstly observed between the 2nd and the 3rd laminae. The length of interfacial delamination evaluated in terms of specimen compliance was well corresponded with the saw-cut notch of the equal length, and the delaminated portion lost its load carrying capacity. Axial splits in 0° plies had the effect of separating the 0° plies into two outer strips containing the notch and an inner strip without a notch, thereby reducing the notch-tip stress concentration. The growth rate of interfacial delamination judged in terms of the compliance change was accelerated with an increase in notch length as well as with an increase in maximum ligament stress. The notch sensitivity of CFRP was quite different from the one of uniform materials.
It was recognized that the corrosive behavior of the waste water from leather industry is characterized in: (1) The pH value of effluent from the waste water pretreatment facility at its outlet varies from 4.4 to 13.3. (2) The effluent is rich in sulfide and sulfate ions, the former generates H2S due to the change of pH from basic to acidic merely, and the latter is converted to H2S by the action of sulfate-reductive bacteria. Corrosion proofness of a FRP lining to be applied to the interior surface of concrete sewer pipeline which is scheduled to flush the above-mentioned waste waster, was evaluated by various testing methods. Visual observation, dye penetration test, microscopic observation of surface and cross section, weight change, Taber abrasion test, Barcol hardness, thickness check and measurement of adhesion strength were all valuable for the purpose. However, the last one of these methods still leaves a room for further study in terms of the accuracy and the correspondence between actual lining and test result.
Thermal image furnace melting and twin roller quenching were used to prepare the high fluoride conducting oxyfluoride glasses in the systems of ZnF2-PbF2-SiO2, BiF3-PbF2-SiO2 and MnF2-PbF2-SiO2. The dc electrical conductivities of these glasses were measured as a function of temperature. In all the systems, it was possible to find the glass compositions with high conductivitiy more than 10-4Scm-1 (200°C). The good correlation between logσ and the average polarizability calculated from the constituent cations was observed.
Chemical processing of mullite/4mol% yttria-zirconia (4Y·ZrO2) composites was investigated with the surface modification through the hydrolysis of metal alkoxides on the surface of mullite particles. Mullite particles were coated with yttrium-zirconium hydroxide particles formed by preferential hydrolysis of yttrium and zirconium isopropoxides on the surfaces of mullite particles, which can lead to the preparation of highly homogeneous composite particles of mullite/4Y·ZrO2. It was clarified from the BET measurement and the TEM observation that original mullite particles were homogeneously coated with zirconia particles. The mullite/4Y·ZrO2 composite particles were consolidated by colloidal filtering pressing to give highly homogeneous green compacts, being sintered at 1500°C for 1hr to fully densed bodies with a homogeneous distribution of fine zirconia particles. The fracture toughness, K1c, and Vickers hardness, HV, of mullite/4Y·ZrO2 sintered bodies were remarkably improved to the values higher than 5.6MPa·m1/2 and 13.7GPa, compared with those of sintered mullite body, 2.2MPa·m1/2 and 9.8GPa, respectively. The crack in mullite/10 vol% 4Y·ZrO2 sintered bodies with zirconia grains of a few micrometer was propagated by the crack deflection to give the relatively high toughness, whereas the cracks in mullite/20vol% 4Y·ZrO2 with larger zirconia grains of-5μm traversed through several zirconia grains in mullite matrix.
A metal/ceramic graded composite for reducing the thermal stress generated across the jointed interface was fabricated by a hot-forging process. Powders of magnesium oxide mixed with SUS304 stainless steel in different ratios or the stack of the mixed powders having a stepwisely controlled compositional gradient from metal to ceramics were capsulated in a molybdenum mold with the dimension of 20φ-10φ×25hmm. The mold was preheated at 1250°C for 8 minutes, and was press-forged in a few seconds under an uniaxial compressive load. The deformation ratio of the mold was about 30% of the original height, and the maximum load was about 12ton. By comparing some properties of the products with those of normally sintered materials, it was confirmed that the hot-forging process was effective to prepare the functionally gradient materials of metal-ceramics systems.
The variation of gel forming region with heat-treatment and the variation of melt quenched glass forming region under various cooling rates were compared in the binary and ternary systems of B2O3 -Na2O-TiO2. In the B2O3-Na2O system, only one gel forming region was obtained at 50°C in the composition range of 60-90mol% B2O3, while two glass forming regions existed in the composition ranges of 100-60mol% and 30mol% B2O3 by the melt quenching method. By heat-treatment up to 800°C, both of the gel and glass forming regions became narrower and the thermally most stable region of gel formation was found to be almost coincided with that of glass formation. A water solubility test was conducted on the glasses in order to correlate their solubility with the stability of the gels formed. It was found that the less dissolving composition showed gelation but the soluble composition crystallized in hydrate precipitates. A similar experiment was performed on the ternary systems and the role of TiO2 addition in gellation and vitrification behaviors in the B2O3-Na2O-TiO2 system was discussed.
Natural lime containing 1.45wt% impurities produced from limestone and high-purity lime (99.9%) produced from calcium carbonate were used as the raw materials for the present study. These limes were molded into a circular disk or a plate by cold isostatic pressing (CIP) or uni-axial dust pressing, and then fired at 1800°C. Strength measurements by three-point bending test, estimation of the Weibull parameter and hydration test were carried out on the fired bodies. The following results were obtained: (1) The mean bending strength for the bodies made of natural lime was from 74 to 86MPa, while for the bodies made of high-purity lime the mean strength was 135MPa. (2) The Weibull parameter evaluated for the natural lime bodies was from 11 to 13, while for the high-purity lime bodies the parameter was 17. It was found that the high-purity lime body was more uniform in microstructure than the natural lime body. As for the natural lime bodies, the Weibull parameter of the samples obtained from the CIP-molded green body was higher than that of the samples from the uni-axially pressed green body. (3) The weight gain of the high-purity lime body under a saturated water vapor pressure at 8°C was less than 3wt% after two months, while the natural lime body showed as much as 3wt% of gain only after two weeks under the same testing condition. This result showed clearly that hydration resistance of the high-purity lime body was much higher than that of the natural lime body.
Many kinds of advanced cermaics, which have been recently developed, are considered to have much possibility for engineering applications as structural materials in high temperature water environments. In the previous report, fundamental corrosion behaviors of 14 kinds of sintered polycrystalline ceramics in 290°C high purity water with or without dissolved oxygen were clarified. In the present study, pH and immersion time dependences of corrosion behaviors of sillicon carbide and stabilized zirconia were discussed. Silicon carbide showed high corrosion resistivity, and the corrosion rate increased at higher pH and oxygenated solution. Time dependence of corrosion weight loss obeyed a power law with the power of 0.7 to 1.3 depending on pH value. Surface silica layer formation was not detected by X-ray diffractometry and Auger electron spectroscopy. These results suggest simultaneous hydrothermal oxidation and dissolution, rather than two step oxidation and dissolution with a protective silica layer. Stabilized zirconia with 6mol% and 8mol% of yttria also showed excellent corrosion resistance, especially the corrosion weight loss for 8mol% yttria stabilized zirconia was below the detection limit in oxygen-free neutral and pH 10 solution.
To develope the design concept for a typically hard and brittle material of fine ceramics, its fatigue properties in static and cyclic loading conditions must be systematized especially from the reliability point of view. Though the number of papers on its fatigue behavior is not so many as compared with those on static strength or fracture toughness because of difficulty in conducting fatigue tests, the results obtained hitherto indicate that the scatter of fatigue life is very large presumably depending on the distribution of pre-existing defects. In order to evaluate the cyclic fatigue strength characteritics of fine ceramics systematically, a new pneumatic resonance type plane bending fatigue testing machine with a loading rate of about 80Hz was trially manufactured. With this testing machine, statistical fatigue tests were carried out by using sintered silicon nitride thin plate specimens of simple shape. Excellent performance of the testing machine was confirmed through the experiments, and the results indicate that the distribution of the fatigue lives obeys a 3-parameter Weibull distribution function.