Journal of the Society of Materials Science Japan

Online ISSN: 1880-7488
Print ISSN: 0514-5163
Fatigue crack initiation and growth characteristics under mixed mode loading have been investigated on aluminum alloys 2017-T3 and 7075-T6, using a newly developed apparatus for mixed mode loading tests. In 2017-T3, the fatigue crack initiation and growth characteristics from a precrack under mixed mode loading are divided into three regions—shear mode growth, tensile mode growth and no growth—on the ΔKI-ΔKII plane. The shear mode growth is observed in the region expressed approximately by ΔKII > 3MPa√m and ΔKII/ΔKI > 1.6. In 7075-T6, the condition of shear mode crack initiation is expressed by ΔKII > 8 MPa√m and ΔKII/ΔKI > 1.6, and continuous crack growth in shear mode is observed only in the case of ΔKI/ΔKII, ≅ 0. The threshold condition of fatigue crack growth in tensile mode is described by the maximum tensile stress criterion, which is given by Δσθmax √2πr ≅ 1.6MPa√m, in both aluminum alloys. The direction of shear mode crack growth approaches the plane in which KI decreases and KII increases towards the maximum with crack growth. da/dN-ΔKII relations of the curved cracks growing in shear mode under mixed mode loading agree well with the da/dN-ΔKII relation of a straight crack under pure mode II loading.
Hot Isostatic Pressing (HIP) of Si3N4 powders with and without additives was performed using a glass container, and various kinds of pressureless-sintered Si3N4 were HIP'ed without a container. The effects of HIP treatment on density, microstructure, flexural strength, microhardness, and fracture toughness on Si3N4 ceramics were studied. Using a glass container it was difficult to reach theoretical density. The microhardness of HIP'ed Si3N4 without additives was low, and the fracture toughness of HIP'ed Si3N4 with and without additives was 22 to 25 W/m-K, and it decreased with increasing the amount of additives. The density and flexural strength, and hardness of pressureless-sintered Si3N4 which contained Al2O and Y2O3 as oxide additives were remarkably improved by HIP treatment using nitrogen as a pressure transmitting gas. It is very important to select the sintering conditions for fabricating the presintered body of Si3N4 in order to improve the mechanical properties of Si3N4 by HIP treatment.
Two kinds of carbon felt reinforced carbon composites, C/C-A and C/C-B, containing respectively pitch carbon fibers and PAN carbon fibers, have been developed to enhance the fracture mechanics properties. The fracture toughness values of these new composites were measured as a function of temperature up to 2400°C. These results are compared with those of a carbon fiber cloth reinforced carbon composite containing rayon fibers (C/C-C) and a fine grain isostatic graphite (IG-11). Major differences among these materials and their distinctive features are discussed.
Numerical and experimental results are presented on the pullout phenomenon in composite materials at a high rate of loading. The finite element method was used, taking into account the existence of a virtual shear deformation layer as the interface between fiber and matrix. Experimental results agree well with those obtained by the finite element method. Numerical results show that the interlaminar shear stress is time dependent, in addition, it is shown to depend on the applied load time history. Under step pulse loading, the interlaminar shear stress fluctuates, finally decaying to its value under static loading.
It is shown that the creep deformation resistance of a variety of metals is reduced by repeated reversed deformation at temperatures above 0.4 Tm, where Tm is the absolute melting temperature of each metal. The reduction of creep deformation resistance due to stress reversals is most prominent at approximately 0.5 Tm where the average creep rate may increase by as much as a factor of twenty due to 50-100 stress reversals. Metallographic studies show that the observed acceleration of creep at high temperatures is in part due to the enhancement of grain boundary sliding as a result of gradual grain boundary migration toward planes of maximum shear stress during reversed creep deformation.
Failure criteria are derived for several modes of failure (in unaxial tensile or compressive loading, or biaxial combined tensile-compressive loading) in the case of closely woven plain fabric, coarsely-woven plain fabric, or roving glass cloth reinforcements. The shear strength in the interaction formula is replaced by an equation dealing with tensile or compressive strength in the direction making a 45 degree angle with one of the anisotropic axes, for the uniaxial failure criteria. The interaction formula is useful as the failure criterion in combined tension-compression biaxial failure for the case of closely woven plain fabric laminates, but poor agreement is obtained in the case of coarsely woven fabric laminates.
The fatigue tests of two types of 3-D Tyranno fiber reinforced SiC matrix composites were conducted at frequencies between 20 and 0.02Hz with a sine wave form and a stress ratio of 0.1 at room temperature. It was shown that the fatigue life of CVI composite was cyclic-dependent between 20 and 0.2Hz, but time-dependent between 0.2 and 0.02Hz. However, the fatigue life of PIP composite was strongly time-dependent between 20 and 0.2Hz. The reduction of Young's modulus and sliding stress of interface during fatigue was analyzed. The cyclic-dependent behavior was dominated by wear of interphase during cyclic loading-unloading. The time-dependent behavior was controlled by stress corrosion cracking of fiber and matrix.
rights: 本文データは社団法人日本材料学会の許諾に基づきCiNiiから複製したものである The effect of microstructure on creep and creep-fatigue behavior at 773K was studied in the Ti-6Al-4V alloy having three different microstructures. The three types of microstructures prepared using different heat treatment conditions included the equiaxed α structure, lenticular α structure and bimodal(composed of equiaxed α and lenticular α)structure. Creep tests were carried out under constant load conditions at 773K in air. Creep-fatigue tests were carried out under total strain controlled conditions using a trapezoidal waveform with hold times of 2min and 10min at 773K in air. Creep rupture strength of the alloy with equiaxed α structure was similar to that of the alloy with lenticular α structure and was higher than that of the alloy with bimodal structure. The number of cycles to failure under creep-fatigue condition of the alloy with lenticular α structure was lower than that of the other two structures. The effect of microstructure on crack propagation life was small as compared with crack initiation life under creep-fatigue conditions. The fracture mode of the alloy with equiaxed α and the bimodal structures was transgranular under creep-fatigue condition. On the other hand, the crack of the alloy with lenticular α structure was initiated and propagated at the interface between the α layer precipitated at the grain boundary and the lenticular α structure.
To evaluate the computational accuracy of the boundary element method used to estimate the galvanic corrosion and cathodic protection in an actual and complex field, a galvanic field with a screen plate was analysed by using the single and multiple-region methods. It was found from two-dimensional analyses that the computated results obtained by both methods were well matched by reducing element size. Three-dimensional analyses were also done on cast iron and stainless steel cylindrical vessels with a screen plate. Good correspondence between the computated and experimental results were also obtained.
In order to propose a new movement of the material design, the load dispersion of the solid–air composites caused by the hydrostatic pressures is investigated by applying numerical analysis. To simplify the evaluation of the load dispersion, the solid–air load transmission is supposed, where each mechanical field of closed cell is independent and that two different fields being in both sides of a cell wall satisfy the equilibrium of forces through the cell wall. The nonlinear deformation under indentation was incrementally simulated by using the finite element formulation based on displacement method. The effect of adhesive film on the load dispersion is considered in the numerical model. It was shown that the assumption of the solid–air load transmission is useful in evaluating the static load dispersion because the numerical results were well in agreement with the experimental ones. And it was clarified that a few structural design parameters become effective for the load dispersion.
The microstructure and mechanical properties of 0.1 wt.% Mg-added and Mg-free Cu–2.0 wt.% Ni–0.5 wt.% Si alloys aged at 400 °C have been examined. The addition of Mg promotes the formation of disk-shaped Ni2Si precipitates. The Cu–Ni–Si–Mg alloy exhibits higher strength and resistance to stress relaxation than the Cu–Ni–Si alloy. The higher strength or stress relaxation resistance is attributable to the reduction in inter-precipitate spacing by the Mg addition or the drag effect of Mg atoms on dislocation motion. The Cu–Ni–Si alloy with a large grain size of 150 μm shows higher stress relaxation resistance than the alloy with a small grain size of 10 μm because of a lower density of mobile dislocations in the former alloy.
Effects of a texture and atmospheric moisture on fatigue properties of an extruded bar and a drawn one of age-hardened Al alloy were investigated under rotating bending in relative humidity of 25% and 85%. The extruded alloy had a marked texture of (111) plane, but the drawn one did not have a specified orientation. Fatigue strength was largely decreased by high humidity in both alloys. The decrease in fatigue strength was larger in the extruded alloy than in the drawn one. Macroscopic growth mode of a crack of the extruded alloy was a shear mode inclined 35° to the specimen axis in high humidity, though those were a tensile mode in low humidity and in both humidity in the drawn alloy. The fracture surface yielded by the shear mode crack was occupied by many slip planes and voids and was (100) plane, though the fracture surface formed by the growth of a tensile mode crack was mainly covered with striations. The shear mode crack was related to the marked texture of the extruded Al alloy and promoted by high humidity.
Sodium yttrium calcium-oxyhydroxyapatites powders with compositions of {[Ca9.98-0.9xY0.9Na0.02](PO4)(6)[(OH)(1.98-0.9x)O(0.9)square(0.02)],x=0.1.0(here square denotes vacancies at OH lattice sites} were synthesized by the wet process. Porous (Ca, Y, Na)-Ap (here Ap denotes apatite) ceramics having apparent porosities of around 33% were prepared at high temperature under steam flow. On the basis of the results of X-ray diffraction, all the obtained ceramics exhibited almost single-phase (Ca, Y, Na)-Ap with hexagonal structure, The impedance for all samples linearly changed from 106 to 104 Omega at 50degreesC in the humidity range of 40-95%RH. Apatites produced by substituting Y3+ and Na+ for Ca2+ in apatite structure showed an excellent conductivity. This is attributed to both ordinary protonic conduction caused by the self-dissociation of physically adsorbed water and another conduction caused by OH vacancies introduced by substituting Y3+ and Na+ for Ca-sites.
The low-cycle fatigue properties of quenched and tempered 0.17%C-21%Ni steel which contains about 18 and 27 volume percent of retained austenite were investigated mainly by the X-ray diffraction technique. The fatigue tests were carried out at 20℃ under constant total bending strain ranges of ±0.9, ±1.3, and ±1.6% with zero mean strain. The results obtained are summarized as follows : (1) The strain-induced transformation of retained austenite depends not only on the strain range but also on the tempering temperature. (2) Stability of retained austenite during fatigue test is maximum in the specimens tempered at temperatures between 250 and 350℃. This dependence of the austenite stability on the tempering temperature is similar to that of stabilization for subzero treatment. (3) The changes of half-value breadth, the particle size and microstrain in martensite during fatigue tests are quite similar as well in the martensitic steels containing 18 and 27 volume percent of retained austenite as in medium carbon martensitic steel without retained austenite. (4) The values of half-value breadth, particle size and microstrain in martensite phase are various in any stage of strain cycling dependent on the tempering temperature and strain range. Therefore, these values are at the present time far from adequate to be taken for the reliable estimate of the fatigue damage in martensitic steel. (5) Fatigue microcracks formed at the early stage of crack formation, are observed not only at non-metallic inclusions and in prior austenite grain boundaries, but along the edges of martensite leaves. Growth of these microcracks is sometimes prevented by their crossing to other martensite leaves or prior austenite grain boundaries.
Second-harmonic generation in thermally/electrically poled transparent BaTiO3 thin films, prepared by dip-coating method, was investigated. The thickness of BaTiO3 thin films dip-coated four times was found to be 0.6 μm by scanning electron microscopy (SEM). X-ray diffraction (XRD) patterns of thin films showed no splitting of the (002) or (200) reflection. XRD verified that there was no difference in the crystal structure or orientation of the crystalline phase before and after thermal/electrical poling.
We have investigated mechanical properties of bimodal networks, which have a two-peak distribution of the length of the network chains between crosslinks, in equilibrium swollen state. The bimodal networks were prepared by end-linking mixtures of short and long poly(dimethylsiloxane) (PDMS) chains with tetra-functional crosslinker. The ratio of molecular mass of the short and long PDMS chains was ca. 11. The stress-strain relationships have been investigated as a function of molar fraction of short chains. The networks with more than 98 mol% short chains are brittle and they have high elastic moduli. When the molar fractions of short chains fall below 95 mol%, the networks become markedly extensible. The stress-strain relations of unimodal networks and bimodal network with small fraction of short chains obey the prediction of the classical theory of rubber elasticity, while those of other bimodal networks deviate from the theoretical prediction. The dependence of network structure on the composition of precursor chains has been estimated from the analysis of the stress-strain behavior. The structure model proposed in small angle X-ray scattering (SAXS) study on bimodal networks has been re-examined on the basis of the results of mechanical experiments in this study.
In the aim of tissue regeneration of an alveolar bone, we developed three-dimensional fabric structural composite scaffolds using a bioabsorbable polymer. This scaffold consists of a polylactic acid (PLLA) resin fiber and a 75/25 poly L-lactide-co-glycolide (PLGA) copolymer resin coat. Scaffold is woven on a new-type of three-dimensional loom, has high porosity (89%) and continuous hole. The compressive rigidity and collapse strength of scaffold are increased due to the resin bonding between fiber intersections. The strength of scaffold that did a dip to phosphoric acid buffer solution (PBS) decreased in half due to the hydrolysis in six weeks. Mouse osteoblast-like cells (MC3T3-E1) were seeded onto the scaffolds and cultured in vitro for six weeks. The cells proliferated during in culture and formed a space-filling tissue between polymer fibers. Bone regenerative messenger ALP/DNA levels remained high compared with those one of culture dish. Mineralization of the deposited collagen on scaffold was initially observed at four weeks. Culture of cell on scaffold constructs for six weeks led to formation of a bone tissue.
The influence of the slip between the inclusion and the matrix during the plastic deformation of inhomogeneous material with elliptic inclusions is investigated. The material is assumed to be rigid-plastic. The boundary slip region is modeled by assuming lower yield stress for the thin boundary region than those of the inclusion and the matrix. The rigid-plastic finite element method is used for the numerical calculation under the plane strain condition. The effects of the aspect ratio of the inclusion, the yield stress of the boundary region, and the volume fraction of the inclusion on the deformation mode are studied. The patterns of the strain concentration and the averaged flow stress of the inhomogeneous material are also discussed. The results may be helpful for understanding creep or superplastic deformation of metals with inclusions.
The electrical resistance of a single crystal of cadmium sulfide was measured at pressures up to 40kbar and at temperatures up to 700°C in a cubic compact anvil high pressure apparatus.The electrical conductivity of CdS of either the atmospheric wurtzite phase or the high-pressure rock salt phase is semiconductive. In the high-resistivity samples used in the present experiment the electrical resistance increased with pressure in either phases, the wurtzite or the rock salt. From the measurements of electrical resistance as a function of temperature, it is found that a band gap of CdS of the wurtzite phase is about 2.5eV. For the CdS of the rock salt phase a band gap of about 0.8eV is obtained.
Effects of loading rate on mode II interlaminar fracture behavior of unidirectional CF/conventional-epoxy (T300/2500, Toray) and CF/toughened-epoxy (IM600/133, Toho Rayon) composite laminates were investigated over a wide range of loading rate from quasi-static to impact at room temperature (displacement rate, δ = 10-7-101 m/s). A newly developed experimental method using the SHPB (Split Hopkinson Pressure Bar) technique and the ENF (End Notched Flexure) specimen was employed for measuring the accurate fracture toughness at very high loading rates. The mode II fracture toughness at the onset of crack growth showed positive rate dependence (fracture toughness increased with increasing loading rate) at lower loading rates, while it showed negative rate dependence (fracture toughness decreased with increasing loading rate) at higher loading rates; there existed a local maximum value of fracture toughness at intermediate loading rates. The impact fracture toughness was about 13 and 29% lower than the local maximum value for the conventional epoxy composite and toughened epoxy composite, respectively; the toughened epoxy composite was more sensitive to the loading rate than the conventional epoxy composite. Microscopic observation showed that the debonding of fiber/matrix interface was dominant at lower loading rates and that the cohesive fracture of matrix resin was dominant at higher loading rates. The transition point of microscopic fracture morphology approximately coincided with the local maximum point of macroscopic fracture toughness. In addition, the load-displacement relation was non-linear just before the onset of crack growth at lower loading rates but almost linear up to the maximum point at higher loading rates.
To make clear the reflection characteristics at fillet parts, the energy reflection coefficient from the fillets is measured. The fillet is composed of the same material as the structure. A semiconductor strain gauge is used to detect single stress pulses. Different from the conventional method where the energy reflection coefficient is the summation of the transfer function obtained by the Discrete Fourier Transform, the coefficient is calculated using strain energy measured by changing the duration of a single stress pulse and the curvature of the fillet. The effectiveness of the new method is confirmed by comparing the results obtained by conventional and new methods. Les caractéristiques de la réflexion d'une onde sur un épaulement sont mesurées. L'épaulement est composé du même matériau que la structure. Une jauge à fil résistant semiconducteur est utilisée pour détecter l'impulsion de contrainte. Le coefficient de réflexion est calculé directement par l'énergie de déformation en changeant la durée de l'impulsion et la courbure de l'épaulement. Cette méthode est différente de la méthode conventionnelle où le coefficient de réflexion est obtenu par sommation de la fonction de transfert par la transformation de Fourier. L'efficacité de la nouvelle méthode est confirmée comparant les résultats obtenus par les deux méthodes.
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.
The mechanism of decrease in the corrosion resistance of Cr-plated parts when they are subjected to a heating process and measures for preventing the degradation are studied. When postfinishing is performed after the Cr-plating process, cracks in the Cr layer are closed as a result of plastic flow on the topmost surface layer. When the residual stress in the Cr layer becomes compressive due to the postfinishing, the cracks are completely closed, resulting in a high corrosion resistance. The residual stress in the Cr layer changes from compressive to tensile following heat treatment. When the residual stress becomes tensile, the cracks in the Cr layer which were closed during postfinishing open once again, resulting in a decrease in the corrosion resistance. We speculated that the change of residual stress from compressive to tensile is caused by the shrinkage of the Cr layer due to heat treatment and the difference in the coefficients of thermal expansion between the substrate (steel) and Cr layer, as well as the release of residual stress generated during processing. In order to prevent the decrease of corrosion resistance under heat treatment, it is effective to apply compressive stress which exceeds the level of change in residual stress due to heat treatment to the Cr layer during postfinishing, after the Cr plating process.
Morphology of thin films of natural rubber (NR), which had been crystallized under molecular orientation, was examined by transmission electron microscopy (TEM). Thin films of NR (RSS#1) were made by casting its solution (2.0wt%) in benzene onto the water surface, stretched by a strain of about 200%, and then mounted on carbon-coated grids for TEM. The specimens thus prepared were introduced into a TEM column by using a cryo-transfer specimen-holder and crystallized there isothermally at -25°C. Selected-area electron diffraction of the NR film gave a well oriented h0l-pattern, which illustrated that the chain axis (c-axis) of NR was oriented parallel to the prestretching direction and also the (010) lattice plane was parallel to the film surface: uniplanar axial orientation. The dark-field image of such a film taken using the 200 equatorial reflection showed that narrow bright striations were oriented perpendicular to the prestretching direction and some of them were stacked in that direction to make row structure or shish-kebab-like structure. Each of these striations, namely of "α-filaments" by Andrews, was concluded to be an edge-on lamella which had been grown plausibly in the [100] direction.
High-resolution electron microscopic (HREM) observation with a transmission electron microscope (TEM) is a powerful experimental method to clarify complicated fine structures, if specimens can endure electron irradiation. Though polymer crystals are very sensitive to electron irradiation, it has turned out possible to observe them by high-resolution electron microscopy at molecular dimensions. If we perform our experiment carefully enough, the resolution limit predicted from the durability against radiation damage can be achieved even for the polymer crystals. One should recognize that HREM images are composed of lattice fringes which are formed by the interference between and scattered and scattered electron waves. Several factors determining performance of the TEM itself should be known. Then the optical systems of the TEM must be aligned carefully and they must be stabilized before taking HREM images. Photographic films are still the best medium to record HREM images. In HREM observation of polymer crystals, reducing the total amount of electron dose given to the specimen before taking an HREM photograph is the most important. A low-dose function which can focus the specimen at a position remote from the region to be photographed in the specimen is useful to reduce the radiation damage during focusing. The condition to record an HREM image is determined by the durability of each specimen against radiation damage. The method to increase the durability of a specimen to electron irradiation by cooling can improve the resolution limit of the specimen. HREM observation of the β-form single crystals of syndiotactic polystyrene is an example. Arrangement of molecular stems both in the solution-grown single crystal and in the melt-grown one was revealed by the HREM observation.
Specimens of 0.38%C steel and Fe-25%Ni alloy were put to test of their low-cycle fatigue, tensile and hardness properties, both in their tempered state. The maximum bending strain on their surfaces under which the fatigue was tested was controlled at between 1.0 and 1.6%. The X-ray diffraction and thin film electronmicroscopy methods and some other techniques were employed for the purpose. The results obtained may be summarized in two phenomena. One is similar to the contrast of annealed metals versus cold-worked metals, and the other is what is considered to characterize the tempered martensite. Both materials in tempered condition present a remarkable variation in microstructure, and the difference in microstructure is almost leveled out only in the low carbon 25%Ni alloy by the fatigue and this phenomenon is similar to the contrast of annealed metals versus cold-worked metals. But in the 0.38%C steel the difference is not leveled out even after the fatigue to failure. The results obtained are not yet adequate enough to explain the correlation between the microstructural variation and the damage fraction in a tempered martensite. The crack initiation and propagation in the 0.38%C steel and 25%Ni alloy are often related longitudinally to the edges of martensite leaves.
Our molecular design of the polymer solid electrolyte based on rubbery state of polymer is presented. Biocompatible segmented polyurethane elastomers with poly(oxyethylene)-poly(oxytetra-methylene)-poly(oxyethylene) segments were used at first for the matrix of solid electrolyte. Next, oligomeric poly(oxyethylene) (PEO) chains were grafted to polysiloxane main chain to afford rubbery matrix for ion conduction when doped with lithium perchlorate. The latter showed higher conductivities than the former. However, the mechanical properties of the latter were poor, and its crosslinking resulted in the lower conductivity. Copolymer polymerized from ethylene oxide and epichlorohydrin was evaluated as a solid electrolyte. The epichlorohydrin units did not contribute to the ion conduction resulting in relatively low conductivities, though it was good in term of mechanical properties. Our final molecular design of the ion conductive matrix was the high molecular weight comb-shaped PEO with oxyethylene segments as side chains. Both main and side chains are oxyethylene units and the molecular weight was in the order of 106. The side oxyethylene units discouraged crystallization of PEO. Excellent conductivities were observed on doping with lithium salts.
A new method of simultaneous measurements of the changes in stress and infrared dichroism on elongation of polymer films was devised by using a double beam infrared Spectrometer. The film was installed in a stretching apparatus and was placed in front of the entrance slit of the spectrometer where both the sample and the reference beams came together. Two polarizers were used: one was placed in the sample beam and the other in the reference beam. Thus the sample and the reference beams were polarized to have the electric vectors in parallel and perpendicular to the stretching direction of the film, respectively. With this arrangement the spectrometer responded only to a difference in the transmittance of the two beams. Then, by setting the spectrometer at one of the wave numbers of the absorption maxima one could record the change in its dichroism continuously during the mechanical treatment of the film. The stress generated by the mechanical treatment was transformed to the electric signal by means of a strain gage pasted on the stretching apparatus and was recorded after having been amplified.According to the theoretical considerations of this method, it is concluded that for the sample of unilateral orientation the quantity T recorded by the spectrometer is related to the orientation function F of the transition moment with respect to the stretching direction by the equation, F=1/3Aodo/dnlog1/T, where Ao is the absorbance of the unstretched film and do and dn are the thicknesses of the unstretched and n% stretched films, respectively.The method was applied to the stress relaxation phenomena of vulcanized natural rubber. The simultaneous measurements of stress and infrared dichroism were made at constant elongations less than 600% at room temperature. The absorption bands examined were those observed at 1664, 1380, 1361, 1129, and 844cm-1, where the last one was a crystallization-sensitive band of natural rubber. When the film was elongated, all the bands gave rise to the instantaneous dichroism to some extent, which was followed by the gradual increase except for the band at 844cm-1. These results show that there is some correspondence between the dichroic change and the stress relaxation. It is concluded that the stress relaxation observed is attributable to the molecular orientation in the amorphous region rather than the crystal orientation which is completed almost immediately after the elongation.
The concentration dependence of the viscosity of disperse systems has been fully investigated by many workers, and especially by Rutgers24. The effect of shear rate has not, however, been further investigated since the work of Powell and Eyring22 and Cross23.This paper discusses the flow patterns of disperse systems based on measurements over a very wide range of shear rates, and concludes that such systems obey “Ostwald” or “modified Ostwald” flow patterns. Yielding properties and dilational characteristics are also discussed using these flow patterns.
TiN films with the(111)and(200)preferred orientations were formed on Si(100)and sapphire(0001)substrates by ion-beam-assisted deposition. The difference in the mechanical properties between the(111)and(200)preferred orientation in TiN thin films was clarified by the nano-indentation technique with the trigonal diamond tip. The experiments revealed significant differences in hardness H and modulus E^* irrespective of the substrate materials. The measured values were H=16 GPa, E^*=316 GPa for the(200)preferred orientation and H=9 GPa, E^*=192 GPa for the(111)preferred orientation. The behavior of the plastic deformation in the TiN films was estimated by the cross-sectional SEM observation and the TEM analysis. These microstructural analyses showed significant difference in cross-sectional views of the plastic deformation and the intergranular fracture mechanism.
この論文は国立情報学研究所の学術雑誌公開支援事業により電子化されました。 The effects of the environmental condition on the relaxation modulus of wood as a porous anisotropic material was discussed with the help of the numerical value of n, which is an index of anisotropy decided by both the geometrical feature of the deformable unit of wood at macroscopic level and its volume fraction. It was found that the numerical value of n was independent on time, temperature and moisture. Therefore, it may be considered that the relaxation process of wood is due to that of wood substance. Furthermore, strain dependence of n is descussed. It was found that n is almost independent on the strain in the tangential direction.
In the previous works, the criterion for the fatigue strength of unnotched specimens under combined stress was proposed and treated separately from that of notched specimens, but it has been found that the former criterion is a special case of the latter. It has been also found that as long as the torsional fatigue strength is determined carefully, the same criterion can be applied to the results of both fracture and nonfracture tests, although the criterion was originally proposed for the case where the fatigue strength is defined to be the stress below which no 0.1 mm slip-band cracks initiate. Slip-band cracks were found fractographically to correspond to the so-called stage I cracks. From several experimental results appeared in the literature, the criterion has been confirmed to be also applicable generally to the rolled steel products in spite of the fact that rolled metals possess inevitably the anisotropy due to rolling. Finally, it was concluded that the proposed criterion alone can be used successfully to estimate the fatigue strength under the combined stress state of bending and torsion, within experimental errors, for both ductile and brittle materials instead of using different empirical formulae which had been adopted previously
The following conditions that affect the flow properties of blood are discussed in brief from the rheological point of view.(1) Volume fraction of erythrocytes-hematocrit value: -The simple Einstein relation between relative viscosity and volume concentration of suspended particles is not valid for blood. The observed relative viscosity is greater than that calculated, owing to the interaction between the erythrocytes and a increase in the effective hematocrit value produced by enclosing and immobilizing of a certain amount of plasma within the collided erythrocytes groups. The asymptotic minimum viscosity of blood is given by a modified Hatschek's equation, over a wide range of hematocrit values.(2) Temperature: -The relative viscosity of a disperse system should not be affected by temperature unless the volume fraction and the shape of the dissolved or suspended particle changes. The relative viscosity of blood is, however, affected by temperature. It rises by about 10per cent by decrease in temperature from 37°C to 17°C. This rise is considered to be due to a small increase in the volume of individual erythrocytes, together with a change of shape towards a more spherical and less disc-like form.(3) Perfusion pressure: -If the perfusion pressure head is sufficiently large, the rate of flow of blood through a rigid vessel increases in proportion to the increase in the applied pressure head. As the pressure head is lowered, the plotted points indicating the relation between the rate of flow and the applied pressure lie on a smooth curve, which is convex to the pressure axis. The convexily becomes more and more prominent with decrease in the pressure head. Blood, therefore, is not a Newtonian fluid. It will appear to behave as a Newtonian fluid only in the limiting conditions in which the mean shearing stress is quite large and the flow still remains laminar. In order to explain the non-Newtonian flow of blood under low pressure head-the reduction in its apparent viscosity with increase in the shearing stress and rate of shear-the following factors should be taken into account.(a) Orientation of the erythrocytes. Increase in the rate of shear leads to an increase in the fraction of erythrocytes which are orientated parallel to the flow axis and, as a result, it brings about a decrease in apparent viscosity.(b) Coherence resistance and marginal slippage layer.“Coherence resistance”between the erythrocytes in addition to the viscous resistance and plug flow of unsheared blood moving down the vessel within a thin, peripheral plasmatic zone under the low pressure head might be responsible for the observed non-Newtonian property of blood. The plasmatic zone is considered to be produced by the wall effect and the axial accumulation of flowing erythrocytes.(4) The radius of the vessel: -In a narrow vessel of which radius is less than 300μ, the apparent viscosity of the blood is found to be less than the value observed in larger vessels. The smaller the radius is, the lower becomes the apparent viscosity. This effect (sigma effect) is observed not only in the blood but also in various suspensions in which the suspended particles are large enough to be comparable in size with the radius of the vessel.
A series of conferences are being organized from the viewpoint of continuation of science and technology by the corrosion and prevention committee of the Society of Materials Science, and this is one of the reports presented at a conference to point out the importance of development of new materials. © 1994, The Society of Materials Science, Japan. All rights reserved.
Superplastic behavior of 5083+0.12Zr alloy was investigated in the temperature range from 783 to 843K and in the strain rate range from 8×10-5 to 3×10-3S-1 at constant strain-rate tensile test. Maximum elongation of 580% was obtained at 823K and at strain rate of 1×10-4S-1, where m value retains its initial value of 0.5 up to a large strain of 1.3 and where minimum cavitation occurs. The large elongation is due to stable deformation caused by retaining the initial m value up to large strain. The alloy showed strain hardening which is induced by dynamic grain growth. Dynamic grain growth rate increased with decreasing strain rate. Decreasing of m value with true strain may be attributed to decreasing grain boundary caused by cavitation and grain growth.
In order to clarify the coaxing process of aged materials, rotating bending fatigue tests were carried out on the 0.15%C steel aged after quenching at low temperature under various aging conditions and optical microscopic observations were made successively during the coaxing process by using the plastic replica method. The main results obtained are as follows: (1) The knee-point in the S-N curve coincides nearly with the point where a micro-crack stops propagating. (2) As the aging power gets greater, the knee-point on the S-N curve moves toward the lower number of stress cycles and the length of non-propagating cracks becomes longer. (3) When the fatigue limit is raised by coaxing effect, the non-propagating micro-crack formed under the first stress level propagate in some degree and then stops by each stepping-up of stress level. (4) As the aging power gets greater, both the rate of increase in fatigue limit by coaxing effect and the increase in crack length becomes greater. (5) The coaxing effect of an aged material is more remarkable in the case where the non-propagating micro-crack under the first stress level is short. © 1980, The Society of Materials Science, Japan. All rights reserved.
The fatigue test has been carried out on 0.18%C carbon steel in order to investigate the effect of atmosphere on its fatigue strength. The experiments were conducted under reversed plane bending at the vacuum levels ranging from ambient pressure to 8 x 10-5 Torr. The difference of fatigue failure modes at these environmental conditions was observed by means of electron- and scanning electron microscopies, and furthermore, the surface roughness of specimens subjected to stress cycling was traced using a surface profilometer. The influence of atmospheric-corrosion on the fatigue failure of low carbon steel was discussed from mechanochemical viewpoints. The main results obtained are as follows: (1) The fatigue life of carbon steel has prolonged with evacuating the air surrounding of a specimen. The endurance limit was observed in the specimens in vacuum in which the value of applied stress at the endurance limit was higher than that in air, and the number of cycles to the endurance limit observed in vacuum was not so much different from the value in air. (2) The prolongation of fatigue life of carbon steel, which was found to be dependent on the degree of test pressure, was analyzed theoretically using a capillary model. (3) The surface roughness of specimens subjected to fatigue stressing has increased in three stages. The surface roughness of specimens tested under a constant stress level has increased with reducing the pressure of test environment. (4) Many cracks of trans-granular type were observed in the specimens tested in vacuum, while those of inter-granular type existed in the specimens tested in air. © 1977, The Society of Materials Science, Japan. All rights reserved.
The paper reports on a study into the effect of laser case hardening on fatigue strength by using 0. 2%C carbon steel specimens with five different types of U and V notches and by applying laser case hardening treatment on the notch part of each specimen. Laser case hardening method was effective to increase the fatigue strength of notched specimens whose stress concentration factor is in the range of less than 4. An increase in fatigue life of structural elements can be expected sufficiently by applying this method at locations considered as the initiating part of fatigue failure, because the stress concentration factor scarcely exceeds the value of 4 in service structural elements.
In order to study the physical basis of scatter in fatigue life, fatigue tests were carried out on the smooth specimens of a normalized 0.21% C steel. Fifteen specimens were fatigued at each stress level and the behavior of all cracks which led to the fracture of the specimens was examined. Fatigue data were analyzed statistically by assuming the Weibull distribution. The results show that the scatter in the number of cycles required to attain a crack length 0.2 mm is particularly large. There is only slight scatter for the propagation life from 0.2 mm up to fracture. The distribution relating to all phases of lifetime can be expressed by the three-parameter Weibull distribution. The values of the coefficient of variance, CV, for the initiation life of a crack length of 0.2 mm and fatigue life increase with decreasing stress level. However, CV for crack growing from 0.2 mm to failure shows only a slight dependency on the stress level. The scatter in fatigue life is due mainly to the behavior of microcracks. The influence of microstructure on microcrack propagation is especially large at lower stress levels, i e. near the fatigue limit. © 1993, The Society of Materials Science, Japan. All rights reserved.
To establish the influence of heat treatments and notch sharpness of specimens upon the notchedbar creep rupture strength of a Cr-Mo-V steel for steam turbine rotor forgings, creep rupture tests were conducted with variously heat treated and notched bar specimens. Three ways of austenitization were employed, i.e., heating at 950°C for 20hr (Sample A), heating at 1000°C for 20hr (Sample B), and heating at 1000°C for 20hr, followed by cooling to 950°C and holding at the temperature for 1hr (Sample C). All the specimens were tempered at 675°C for 24hr. Two kinds of notch sharpness were used, one had a notch with elastic stress concentration factor kt of 6.5 and another of 2.5. The creep rupture tests were conducted with these specimens for about 4000hr at 550°C. The results obtained were as follows. (1) The sample B showed the highest plain bar creep rupture strength of theses three samples, the sample C was second to the sample B, and the sample A was the poorest. (2) Both the sample A and the sample C were notch strengthened within the range of this investigation. However the sample B austenitized at 1000°C was notch weakened at about 1300 hr for kt of 2.5 and about 500hr for kt of 6.5. (3) The plain bar creep rupture properties of the sample C were similar to those obtained with the sample B, while for the notched bar specimen the sample C showed a similar behavior to the sample A. From these results it was found that austenitizing at 1000°C was effective for the plain bar creep rupture strength, and cooling from 950°C was effective for the notched bar creep rupture strength. (4) The rupture time ratios of notched bar specimens for kt of 2.5 were higher than those for kt of 6.5 in all the three samples. (5) From the results of observation of cracks at the notch root, it was found that in specimens for kt of 6.5 cracks were formed in comparatively earlier stage of test, i.e., within 300 of rupture life, while in the specimens for kt of 2.5 no crack could be observed within 900 of rupture life. Consequently, it was supposed that in the specimens for kt of 6.5 almost all of rupture lives were consumed by the propagation of cracks, while rupture lives of the specimens for kt of 2.5 were decided by initiation of cracks. © 1965, The Society of Materials Science, Japan. All rights reserved.
Age-hardened A1-.1 mass %Mg2Si-0.4 mass % Si alloy specimens were deformed to 0.4% strain at room temperature. The accurate surface topographies of the grain boundaries and folds were observed by a scanning tunneling microscope. Large steps which accompanied a straight fold were clearly observed at the grain boundary. Frequently a diffuse and broad fold was also generated from the similar type of grain boundaries. Two types of folds as mentioned above were also generated from a different type of grain boundaries that might be slided parallel to the specimen surface. It was found by the detailed observation of the latter two types of folds that a deeply sinked surface exists always between a grain boundary and fold. In most cases, the direction of straight folds coincided with a slip trace in the grain. Formation of such straight folds can be estimated by using the stress transmission factor NSf with a few exceptions. © 1993, The Society of Materials Science, Japan. All rights reserved.
Acceleration of crack propagation occurred in 0. 45%C steel as in the case of 0. 15%C steel previously reported, when the crack length was more than 50 mu m. The lower limit of understress that caused such an acceleration was reduced steeply as the crack length became longer. In the cases of short cracks (below 200 mu m) and long cracks (above 200 mu m) loaded with low understress, the microscopic fracture surface consisted of small facets, which were supposed to be related to the crystal structure of steel, and cracks observed on the specimen surface propagated intermittently, suggesting that microstructure had a significant effect upon crack propagation under intermittent overstressing. In the case of long cracks loaded with high understress, the microscopic fracture surface consisted of large facets and cracks propagated steadily, indicating that microstructure had less effect. Additional study results are discussed.
Recently, wire electric discharge machining method has been applied to the working and the cutting of parts as well as to die machining. Also in research of strength of materials, in processing of a minute specimen, a wire electric discharge machine will demonstrate great help. Therefore, the data concerning the relationship between the surface layer caused by wire electric discharge and fatigue strength are beginning to be required but we cannot find so many reports of the data concerning on this theme. So, plane bending fatigue tests were carried out on heat treated and annealed 0.45% carbon steel specimens machined by wire electric discharge. The fatigue strength of the heat treated 0.45% carbon steel processed by rough cutting with a wire electric discharge machine decreases approximately 44% from that of the unprocessed material. However, in the annealed 0.45% carbon steel, the decrease of the fatigue strength was only 10%.
We synthesized Eu doped (Zn2-yEuy)(TixSn1-x)O4 (0 < x < 1, 0 < y < 0.5) phosphors using polymerized-complex and coprecipitation methods. As a result, those synthesized by the polymerized-complex method emitted brighter. Red emission was observed around 600 nm by the 4f-4f transition of Eu³⁺ ion in the range from x = 0 to 0.7. With increasing the Ti content over x = 0.9, the emission color shifted to the green color. The green emission was caused by defects in the crystal of the host materials. The crystal structure and morphologies were characterized using powder X-ray diffraction (XRD) and a scanning electron microscope (SEM), respectively. We assumed that the difference in the emission color was caused by the difference in the occupation-site for Eu³⁺ ion in the crystal structure.
The coaxing effect in plane bending fatigue was investigated on the plain specimens of annealed 0. 5%C steel under zero and positive mean stresses. The main results obtained are as follows: (1) The mean stress has hardly any effect on crack initiation, but crack propagation is remarkably affected by the value of mean stress. (2) The Fatigue limit, in the case where the mean stress is positive, is controlled by the limiting condition for propagation of a micro-crack. This is closely related to the coaxing effect. (3) The Coaxing effect of a plain specimen, in the case where a non-propagating micro-crack formed under the first stress level is short, is more remarkable than that in the case where the micro-crack is long. (4) The coaxing effect of a plain specimen is bigger in the case of positive mean stress than in the case of zero mean stress. © 1982, The Society of Materials Science, Japan. All rights reserved.
Top-cited authors
Keisuke Tanaka
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Masao Sakane
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Kenji Suzuki
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