Hydroxyapatite (HAp) contained in fish scales was dissolved in citric acid solution and needle-like HAp crystals were synthesized hydrothermally. In this case, heating for a period of more than 4 hours at 200°C was necessary to obtain the needle-like crystals. Size of the crystals was 1.6-3.1μm long, 0.07-0.2μm thickness and 10-41 aspect ratio. These crystals gathered mutually and formed fan-shaped lump.
The effect of porosity on the elastic constants for X-ray stress analysis in sintered alumina was analyzed on the basis of four micromechanics models: Reuss' model, Voigt's model, Mori-Tanaka's model (MT model) and Self-consistent model (SC model). The X-ray elastic constant E'X/(1+v'X(E'X=Young's modulus, v'X=Poisson's ratio) decreases with decreasing bulk density or increasing porosity. SC model gives the best prediction for the effect of bulk density on the X-ray elastic constants. The prediction based on SC model requires the mechanical elastic constants of sintered alumina as a composite and the X-ray elastic constants of diffracting phases. It is not necessary to know the properties of secondary phases. When the mechanical elastic constants are not known, the bulk density can be used to estimate the X-ray elastic constants of ceramics.
Simplified theoretical formulae have been developed to predict the maximum and the peak depth of the compressive residual stress due to shot peening from the shot peening parameters and materials properties. These formulae put the base on the motion equation of a shot and the analytical model proposed by Li, who used a Hertz theory of elastic contact and a simplified elasto-plastic theory. For experimental verifications, several conditions of shot peening were carried out with the shots made of cast steel, fused zirconia and glass, which had three les distribvels of shot diameter respectively. The residual stresutions were measured by X-ray diffraction method. The predicted maximum and the peak depth of the compressive residual stress by the proposed formulae were agreed well with the experimental values in the wide range of shot peening condition.
Because of high specific strength and stiffness, fiber-reinforced plastics have been used as structural members in various fields, and hence analysis of thin laminated structures is important. In this paper, the problem of dynamic stability of angle-ply laminated cylindrical shells under impact external pressure is described. First of all, the motion of cylindrical shells under impact external pressure is defined as axially symmetric motion. Following this definition, certain perturbations are superimposed on this motion and their effect on the behavior of the shell is investigated. The symmetric state of motion of the shell is called stable if the perturbations remind bounded. The solutions for the prebuckling motion and the perturbed motion are obtained using the Galerkin's method. Stable regions are examined by utilizing the Mathieu's equation. The inevitability of dynamic unstable behaviors is proved analytically and the effects of various factors, such as external pressure ratio, lamination angle, dynamic unstable mode and dimensions of cylinder, are clarified.
To clarify the effect of sodium environment on mechanical properties of FBR Grade Type 316SS (316FR), creep and fatigue tests were carried out both in sodium and in air at elevated temperatures. The creep strength in sodium was slightly lower than that in air at the stresses corresponding to the rupture time of 1000 to 10000 hours. At the lower stresses the strength was equivalent in both the environments. The fatigue strength in sodium was higher than that in air at total strain ranges above 0.5%, and was equivalent to that in air at the strain ranges below 0.5%. Metallurgical examinations showed that the strength reduction in sodium was caused by the precipitation of σ-phase on grain boundaries close to the surface of a specimen, and that in the case of creep tests at the lower stresses, rupture in sodium was caused by grain boundary cracks in the bulk of a specimen. In the main loading mode of FBR's, which is creep-fatigue loading at low stress levels with long hold periods, the mechanism of failure is considered to be similar to that of creep at low stress levels rather than creep at high stress levels or fatigue. Therefore, it was considered that the sodium environment has limited effects on the creep-fatigue strength of 316FR in FBR's. This was verified by the fact that internal grain boundary cracks were also found in the specimens that were subjected to creep-fatigue tests in sodium.
Fatigue tests have been conducted on a duplex stainless steel, SUS329J4L, in order to clarify the influence of volume fraction of ferrite and austenite phases on crack growth behaviour in room air and in 3%NaCl solution. Three materials with different volume fractions were prepared with solution treatment at 1050°C, 1150°C and 1250°C, resulting in the volume fractions of austenite phase of 50%, 28% and 12%, respectively. In room air, when the data were characterized in terms of δK, the crack growth rates decreased considerably with increasing solution treatment temperature, Ts. After allowing for crack closure, i.e. evaluated by δKeff, all materials showed almost the same growth behaviour, indicating that the observed difference in crack growth resistance was attributed to crack closure derived from residual stress and crack path deflections. In 3%NaCl solution, the crack growth rates for all materials were enhanced in high δK or δKeff region. Cleavage fracture in ferrite phase was responsible for the enhanced crack growth, which increased with increasing Ts and δK.
In the present study, fracture toughness at various strain rates was measured as well as fatigue crack propagation properties to investigate the effect of addition of calboxy terminated copolymers butadiene-acrylonotrile (CTBN) on mechanical properties of glass particles reinforced epoxies. Glass transition temperature decreased with increasing rubber content. Both tensile strength and yield stress decreased with increasing rubber content. Fracture toughness and fatigue crack propagation resistance were strength improved by adding CTBN. These improvements are due to an increase of intrinsic ductility brought by add CTBN. The dynamic fracture toughness showed the minimum value between the loading velocities of 4m/s and 10m/s. The loading velocity where the dynamic fracture toughness becomes increases with increasing the CTBN content. According to fracture surface observation it was fund test crack is attributed to interface decohesion between the epoxy matrix and the SiO2 particles. However, cracks grew through the matrix and CTBN when consolidated CTBN particles were large.
Fatigue tests of plane-woven SiC/SiC composites, which had carbon layer as the interphase on the surface of the fiber, were carried out at room temperature in air and at 1473K in vacuum and also creep tests at 1473K in vacuum. At room temperature, the S-N relation was almost flat and the level was slightly lower than the static strength, showing the fracture mechanism was similar to that of static fracture. On the other hand, at 1473K, fracture behavior was mainly caused by time-dependent creep mechanism. The fracture surface showed that debonding occurred between matrix and carbon interphase in the case of static tests at room temperature. On the other hand, in the cases of static, creep and creep fatigue tests at 1473K, debonding occurred between fiber and carbon interphase because of creep deformation of fiber. Delamination was also dominant for all cases. The length of delamination and debonding was longer in creep fatigue test at 1473K than in fatigue test at room temperature and creep test at 1473K because of reduction in sliding resistance of interface caused by cyclic loading. Thus, stress concentration caused by breakage of fiber and matrix was weaker in creep fatigue test than in creep test. The relation between the test time and the creep strain in creep tests could be evaluated quantitatively using the stress power law.
Alumina fiber (ALF)/epoxy composites are possible candidates for the structural components of superconducting magnets because of their low thermal conductivity in addition to their higher specific strength and modulus. Since laminate structures are applied to the load support system for superconducting magnets, the evaluation of interlaminar strength both under static and fatigue loadings is essential from the view point of structural integrity. In the present study, mode I and II interlaminar fracture toughness and delamination fatigue crack growth behavior were investigated with unidirectional ALF/epoxy laminates using double cantilever beam specimens and end notched flexure specimens both with a special loading device. The fracture toughness values and the fatigue crack growth resistance of ALF/epoxy laminates were higher than those of CF/epoxy laminates with similar matrices. The analysis of the stress-ratio dependency showed that the contribution of the maximum stress was higher for ALF/epoxy than that for CF/epoxy laminates. The fractographic observation indicated that the interfacial fracture was dominant on the fracture surfaces of fatigue fracture, suggesting that the microscopic mechanism was different from that of CF/epoxy laminates.
The stress-ratio effect on the propagation behavior of interlaminar fatigue cracks was studied with unidirectional graphite/epoxy laminates, T800H/#3631, under mixed mode (I+II) loading. Fatigue tests were conducted under the stress ratios of R=0.2 and 0.5 with several mixed-mode ratios, GI/GII, by using the mixed mode bending method. For each R value, the crack propagation rate, da/dN, was higher for higher GI/GII ratios at the same value of the maximum total energy release rate, Gmax. Under a constant value of the GI/GII ratio, both the maximum load and the load amplitude affect the crack propagation rate. For high propagation rates and high GI/GII ratios, the crack propagation rate is mainly controlled by the maximum load, while for low propagation rates and low GI/GII ratios, the contibution of the load amplitude is large. For both R values, the relation between the mode I and II maximum energy release rates, GImax and GIImax, at the fatigue threshold is approximated by the following equation: GImax/GImaxth+GIImax/GIImaxth=1, where GImaxth and GIImaxth are the threshold energy release rates for pure mode I and II loadings and decrease as the R value decreases.
Cyclic tensile fatigue tests were conducted for Si3N4/S45C joint specimens with copper interlayer at room temperature in order to clarify fatigue strength properties of ceramic/metal joint, considering the influence of residual stress in ceramics induced during joining process. Not only the joining process residual stress but also the residual stress behavior due to cyclic tensile loading was analyzed by using the three-dimensional elastic-plastic finite-element method. All experimental data obtained in this study were tried to arrange as the relationship between the normalized testing stress and the effective loading time by using the unified estimation method with considering effective volume and effective loading time. However, even if using the unified estimation method, the normalized strengths in the cyclic fatigue tests were clearly lower than normalized tensile strength at fracture probability of 50%. The difference of both normalized strengths was caused by the increase of the residual stress redistributed during cyclic fatigue tests. The redistributed residual stress was due to the reversible plastic deformation made in the interlayer of copper, but tended to saturate after second cycles. Then, if modifying not only the effective loading time but also the time-strength by using the unified estimation method against the superposing stress of the testing stress and the redistributing residual stress in cyclic fatigue tests, the cyclic tensile fatigue strengths agreed well with the normalized tensile strength for ceramic/metal joints as well as for monolithic ceramics. All cyclic fatigue strengths containing tensile fracture strength can be estimated well as the normalized strength with scatter properties of Weibull distribution.
TiN films with the (111) and (200) preferred orientations were formed on Si(100) and sapphire (0001) substrates by ion-beam-assisted deposition. In order to clarify the relationship between the preferred orientation of the TiN films and the mechanical properties of the hardness H and the elastic moduli E*, nano-indentation studies with a Berkovich indenter were carried out. Their experiments revealed significant differences in H and E* irrespective of substrate materials; i.e., Hav=9GPa, E*av=192GPa for the (111) preferred orientation and Hav=16GPa, E*av=316GPa for the (200) preferred orientation. It could be considered that these differences were attributed to the intrinsic crystallographic anisotropy in a TiN crystal.
Formation of perovskite-type oxides on the surface of fluorite-type oxides by high temperature chemical reaction and their electrochemical properties were studied. A dense and tightly contacted thin layer of BaZrO3, SrZrO3, CaZrO3 and BaCeO3, SrCeO3-based solid solution could be formed on yttrium stabilized zirconia and yttrium doped ceria, respectively. The electromotive phenomena as an electrolyte of the gas cell using the ceramics behaved in a different manner from that of the non-coated cell. Using this character, new type hydrogen-sensing devices with the standard electrode of oxygen can be fabricated.
In this paper, a method for determining the distribution of residual stress on the surface of a coarse-grained material was studied. The method used in this study was a combination of the method based on the cosα method with an imaging plate (IP-cosα method) and the computerized tomography (CT). In the present method, mean stresses over many different irradiated linear area are measured using the IP-cosα method first. Second, the distribution of stress on the surface of the material is reconstructed through the CT approach. A method for determining the least distance, which is needed to obtain mean stresses accurately was also studied and the fractal analysis was applied to diffraction image for this purpose. An experiment was performed using a steel which consisted of grains having diameter around 200μm. It was found from the experiment that the distribution obtained from the present method almost agreed with that obtained from the sin2ψ method using both the parallel beam and the oscillation methods. The present method has a feature that the measurement is easier because the analytic method for polycrystalline materials can be used. In principle, the method is applicable to more coarse-grained materials as long as the material is large enough to keep the irradiated area more than the least distance and thus it will be useful to obtain actual residual stress state on coarse-grained materials.
Stresses in a single crystal specimen or any individual grain of polycrystal specimen were measuerd by the use of one dimensional position sensitive proportional counter (PSPC). A problem on such project is how to measure stresses experimentally because continuous Debye-Scherrer (DS) diffraction ring is only just a spot from a grain and appeared on an imaginary DS circle from polycrystal specimen. Therefore, it is important to convert from such a spot to measurable diffraction curve. We adopted a PSPC and a specimen oscillating mechanism in the present study. Large grained 3% silicone iron specimens were prepared and 211 diffractions on each grain under elastic loading were measured by Cr-Kα x-rays radiation after determination of orientation (n1n2n3) [w1w2w3] on each grain by Laue method. A specimen stage with the ψ and φ rotating attachment was oscillated upon the x-ray irradiated point on the specimen surface in ψ and ψ+90°directions by the use of two stepping motors. The oscillating areas were ±3°in the ψ direction and ±0.5°in the ψ+90°direction, respectively and a measurable diffraction intensity, curve from a DS spot was converted by this operation. Stresses under uniaxial loading were measured by this technique and we concluded that stresses in a grain can be measured without the use of lattice parameters on the non-stresses condition.
A coating method for measuring large surface strains of three-dimensional bodies using the scattered-light technique was proposed associated with an investigation of photoviscoplastic behavior of properly mixed polyester resin. A major advantage of this method is that interference fringes at the boundary between a real specimen and coatings can be observed directly. Two components of shearing strains on the surface of the real specimen in axi-symmetrical torsion problems could be calculated using two kinds of scattered-light fringe patterns obtained by two different incidences of polarized light. For the demonstration of effectiveness of the proposed method, this method was applied to analyses of surface strains of solid and circumferentially notched cylindrical specimens made of aluminum alloy with polyester coatings under torsion. Shearing strains on the surface of solid specimens were estimated, which were well consistent with ones calculated from twisting angles. For the notched specimen, shearing strains on the notch surface were estimated and the distributions were well consistent with FEM analyses.