Osteoporosis is a disease caused by an abnormal bone metabolism. In this paper, it was attempted to explain the progressive rate of osteoporosis based on the product of bone remodeling activity and morphological parameters of the trabecular structure of the cancellous bone. The main results obtained were as follows. As the bone formation became slow, the bone volume gradually decreased and the cortical bone was thinned. Furthermore, the porosity of the cancellous bone increased abnormally. These changes greatly impaired the mechanical properties of the bones. These abnormalities may also cause such a bone fracture as intracapsular femoral neck fracture. The value Vf obtained by the equation (13) is considered to represent the progressing behavior of osteoporosis at the proximal end of the femur. From the measurment of the metabolic activity and quantification of the morphological properties of cancellous bone structure, it was concluded that the highest progressive rate of resorption appeared in bar/bar like trabecular structure. The plate/bar like structure was the next and the plate/plate like structure was most insensitive.
Recently, the basic oxygen furnace slag produced in a new steel-making process aiming at energy and resource saving is being supplied as fine particles under 5mm size because it breaks down itself due to its high content of f-CaO. In future, this type of basic oxygen furnace slag is anticipated to replace the conventional basic oxygen furnace slag. The objective of this study was to investigate the applicability of this powdered basic oxygen furnace slag as a subbase material. Firstly, the changes in physical and chemical properties, the surface texture and the hydrated products of the basic oxygen furnace slag naturally weathered outdoors. were determined by X-ray diffraction, differential thermal analysis (DTA) and SEM-EDXA analysis. Secondly, the strength test, the CBR test and the expansion test of the compacted basic oxygen furnace slag mixtures were carried out in order to clarify the strength characteristics of the powdered basic oxygen furnace slag as a subbase material and the effect of weathering outdoors on reducing its unfavorable self-deterious properties. The main results obtained are summarized as follows; (1) The major compounds of the powdered basic oxygen furnace slag were β-C2S, C2F, C2S-C3P, Wustite and a considerably large amount of f-CaO and Ca(OH)2. (2) In the powdered basic oxygen furnace slag naturally weathered outdoors, the hydration of β-C2S and f-CaO slowly progressed with age, resulting in the formation of C-S-H gel, Ca(OH)2 and CaCO3 on the surface of particles. (3) The powdered basic oxygen furnace slag became a stable material not showing self-deterious property by weathering outdoors for about three months, and thus it can be used as a subbase material.
The reinforcing steel bars which are one of the structural rolled steels for construction can be classified into two types as blast furnace reinforcing steel bars and electric furnace reinforcing steel bars. Electric furnace reinforcing steel bars are utilized for about 85 per cent of all reinforcing steel bars at present. In this study, firstly, the Charpy impact characteristics of the above-mentioned two types of material SD35 were investigated. Secondly, the correlations between the Charpy impact characteristics and various factors such as chemical compositions, rolling conditions, and optical microstructures were studied using the multiple regression analysis method. As a result, the apparent differences in Charpy impact characteristics were found between the two types of bars. That is to say, the electric furnace steel bars had energy transition curves or fracture transition curves with more gentle slopes, lower shelf energies (vEshelf), and higher energy ransition temperatures (vErE) or higher fracture transition temperatures (vTrs) than the blast furnace steel bars. Therefore, it has been realized that these differences in characteristics depend on Mn, Cr and N Contents as well as on reduction ratio. It has also been realized that vTrE and vTrs shift to lower temperatures as the ferrite perlite structures become lamellar.
Fracture mechanics tests have been made on high strength, controlled rolled steel in a wide temperature range. Fracture toughness, fatigue fracture toughness and separation initiation properties have been investigated in detail by using compact tension and three points bending specimens. The main conclusions obtained are as follows: (1) Anew separation index i, e, separation depth index (S.D.I.), was proposed, and this index was shown to be a good parameter because of its sensitivity to plastic constraint and temperature. (2) The test material was found to indicate singular ductile-brittle transition behaviour. The J integral at the transition temperature was about 0.02MJ/m2, which is about two figures smaller than that of ordinary weldable structural steel. (3) The singular ductile-brittle transition behaviour of the controlled rolled steel is caused by the rapid decrease of plastic constraint ahead of the notch which results from the initiation of separation.
The effects of partial or perfect unloading on the crack growth initiation life and the threshold stress intensity factor in delayed failure under repeating load were investigated on the precracked specimens of SNCM 439 steel quenched and tempered at 473K. The main results obtained are as follows: (1) The crack growth initiation life and the threshold stress intensity factor in delayed failure under repeating load were markedly increased by partial or perfect unloading method, the effect of which was larger when the stress intensity factor range superposed became smaller. (2) The reason why the delayed failure strength under repeating load was increased by both prestressing methods can be explained by the decrease of effective stress intensity factor at the precrack tip, which will suppress the repeating slip and the corrosion reaction and thus prevent the invasion of hydrogen into material. There exists a relation of η=Rum at Ru≥0.7 between the decrease rate of effective stress intensity factor η(=Km·eff/Kma) and the unloading stress ratio Ru(Kma/Kp), where Kma and Km·eff are the average stress intensity factor (apparent value) and the effective one after partial unloading, respectively, Kp is the stress intensity factor at preloading, and m is a constant. (3) The change of fractographs supports the conclusion that the effective stress intensity factor at the crack tip is decreased by partial unloading.
Although some case hardening methods, e.g. high frequency induction quenching, cementation and nitriding, are being applied to increase the fatigue strength of carbon steels, these methods require a troublesome treatment. Laser case hardening method has been developed to avoid the trouble and to increase hardness at a small desired area. The present study was planned to investigate 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. Since it is well known that the fatigue strength in impact fatigue is lower than that in non-impact fatigue, most of the experiments were conducted under impact fatigue load conditions in the wide stress cycles range of 10-107 cycles. The S-N curves under the non-impact load condition and those of the annealed specimens under the impact and non-impact load conditions were also obtained, and the effect of case hardening by laser surface quenching on fatigue strength were discussed by comparing these S-N curves each other, especially from the viewpoint of dependence of strength increase by laser case hardening on the stress concentration factor. The results showed that the laser case hardening method was effective to increase the fatigue strength of notched specimens whose stress concentration factor αis in the range of α<4. In other words, an increase in fatigue life of structual 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.
The effect of a single peak overload on fatigue crack propagation behavior of polycarbonate was investigated. The results obtained are summarized as follows: (1) The amount of crack extension produced by a single peak overload was very large, and the amount of crack extension inside the specimen was about equal to the size of plastic zone at the crack tip produced by a single peak overload under a plane strain condition. (2) The acceleration factor of crack propagation due to a single peak overload was markedly higher than that in metals. (3) The maximum retardation of crack propagation was found to occur immediately after a single peak overload at both the surface and the interior of the specimen. (4) The degree of retardation increased with decreasing baseline stress, and with increasing the ratio of peak to baseline stress. (5) The crack opening ratio U measured at the specimen surface was almost constant before and after a single peak overload. This fact suggested that the crack closure mechanism could not be applied to the retardation in polycarbonate.
As one of the on-going studies to investigate the fatigue crack growth characteristics in impact fatigue, the fatigue crack growth behavior resulting from the single application of impact over-load was investigated by using Dual-Phase steel with ultimate tensile strength of about 800MPa as an experimental material. Discussions were made on the retardation of crack growth rate, crack opening behavior after over-loading and fractographical aspect in comparison with the results obtained through the application of single static over-load with peak stress hold time of 3min. The major conclusions obtained are summarized as follows: (1) Retardation of crack growth rate after impact over-loading was not so distinct when compared with the case after static over-loading. (2) The values of crack opening ratio after impact over-loading were higher than after static over-loading. (3) Fractographical observations showed that abrasions were caused on the fractured surfaces after impact over-loading, but not so after static over-loading. The following speculation on the crack tip plastic deformed zone was needed to explain the peculiar crack growth behavior after im- pact over-loading as mentioned above. In comparison with the condition of the plastic zone constructed by static over-load, the size of the zone constructed by impact over-load is smaller, but the strength of this small plastic zone is higher, in other words, the higher density of slip bands is attained under impact over-load.
In order to investigate the effects of overload history on the behavior of crack growth threshold and the crack closure at the threshold, fatigue crack propagation tests under multi-overload and single overload of four different load patterns were carried out using 784MPa class high-tensile-strength steel bending specimens for the case of R=-1 and R=0. The results obtained were as follows; (1) For the multi-overload tests, the greater the overload stress intensity KOL was, the greater the threshold stress intensity Kthv was, both for the case of R=-1, and R=0. (2) As the result of single overload tests, in the case of R=0, the effect of the overload pattern appeared remarkably and the effect of the tension overload pattern was similar to that of multi-overload. However, in the case of R=0, the effect mentioned above was little. (3) The fatigue crack growth threshold was expressible only by the effective threshold stress intensity range ΔKeffth, independent of the load history tested in this investigation.
The influence of environment on the acceleration of crack growth at peak loading and the retardation after peak loading in room air and 1% NaCl solution was discussed and compared with the results of cyclic loading. The load sequence used consisted of fatigue loading at lower load level (K2) subsequent to 2 cycles at peak load (K1) in rotating bending. The material was SNCM 439 tempered at 200°C. The results obtained are as follows: (1) At peak loading the crack growth rate was accelerated remarkably. The rate was several tens times as fast as that in fatigue loading at the same load level. While the rate in fatigue loading was several times faster in 1% NaCl solution than that in room air, this accelerated crack growth rate was almost the same in both environments. (2) The number of retardation cycles (ND) decreased under peak loading compared with that under cyclic loading. ND in 1% NaCl solution was smaller than that in room air under the same loading condition. (3) The crack growth rate in retardation period was almost equal irrespective of loading conditions. On the other hand, the rate in retardation period was influenced significantly by the test environment. The rate in 1% NaCl solution was about 10 times faster than that in room air.
Corrosion tests were carried out in fresh water containing sodium nitrite inhibitor at 80°C using a Cr-Mo cast steel specimen and a specimen with a crevice which had been introduced artificially. The characteristics of corrosion inhibition of sodium nitrite inhibitor were then investigated. Fatigue tests were carried out in fresh water containing sodium nitrite inhibitor at 80°C using a relatively large specimen with a crevice. The effect of crevice on corrosion fatigue prevention was then investigated. The results obtained were as follows. The critical concentration of sodium nitrite inhibitor required for corrosion inhibition of Cr-Mo cast steel was found to be 1000ppm. Even though sodium nitrite inhibitor was added above the critical concentration level, crevice corrosion occurred on the specimen with a crevice. The specimen had a clear fatigue limit in air or in fresh water containing sodium nitrite inhibitor over the critical concentration level. The fatigue strength of the specimen with a crevice became markedly low due to the crevice corrosion. Corrosion fatigue cracks initiated from corrosion pits caused by crevice corrosion. Crevice corrosion also occurred in the crack propagation area near the crack initiation site, because hardly any fresh water was able to flow on to the crack surface due to obstruction by the O-ring bound to the specimen. On the initial crack propagation area where crevice corrosion occurred, striation was not clear and partial intergranular fracture was observed. Ductile patterns were predominant on the subsequent crack propagation area.
The effect of creep damage on low-cycle fatigue life at high temperatures has been studied with the object of making clear the mechanism of interaction between creep and fatigue of Cr-Mo-V turbine rotor steel. Prior creep tests for introducing the creep damage were carried out under two conditions suitable to cause transgranular and intergranular creep fractures; at 500°C and 32kgf/mm2, and at 575°C and 18kgf/mm2, respectively. In addition to the prior creep tests, isothermal aging tests were conducted at 500 and 575°C. Both the prior creep at 500°C and 32kgf/mm2 and the isothermal aging considerably increased the fatigue life. This increase was explained by the reduction in stress range at half strain cycles to fatigue failure, which is caused mainly by softening during creep or aging. On the other hand, the prolonged prior creep at 575°C and 18kgf/mm2 produced the extensive growth of grain boundary cavities in addition to the softening, and decreased the fatigue life remarkably. Metallographic observation showed that this growth of grain boundary cavities changed the fatigue fracture mode from transgranular fracture with striations to intergranular fracture with grain boundary cracks. It is suggested that grain boundary cavities reduce the fatigue life by their accelerating effects on initiation and propagation of fatigue cracks.
Thermal fatigue characteristics of superalloys for gas turbine components were investigated by a fluidized bed apparatus. Thermal fatigue tests were made using an improved disk-shaped specimen in heat cycles between 850°C and 300°C. The specimen was kept at 850°C with or without holding for 30 minutes. Thermal fatigue resistance was evaluated in terms of the crack initiation cycle number and the crack propagation rate from the standpoints of mechanical properties and precipitates morphology in the superalloys. The Ni-base superalloys (IN939, IN738LC, and René 80) exhibited no cracking even after 1200 heat cycles. This was related to the fact that the yield strength of these superalloys at high temperatutes was larger than that of the thermal stress generated during the heat cycle and no inelastic strain was produced. In the Co-base FSX-414, the yield strength and the creep rupture strength increased with increasing C content in the matrix. The crack initiation of this superalloy depended on the test condition. When a specimen was kept at 850°C for 30 minutes, the heat cycle number to crack initiation increased with increasing its high temperature strength. Without holding at 850°C, this cycle number of the alloy with higher C content tended to decrease. This was considered to result from the crack initiation acceleration due to the stress concentration produced at the tip of relatively large eutectic carbides. The crack propagation in the FSX-414 was significantly affected by the eutectic carbides morphology. With increasing C content in this alloy, the eutectic carbides precipitated in large quantities, forming network structure. When a crack was initiated in higher C content FSX-414 alloys, the crack propagated along this network structure carbides, thereby resulting in a remarkable increase in crack propagation rate.
An X-ray diffraction line broadens considerably when steels transform into a martensitic structure on quenching. By using eight types of steels with carbon contents between 0.38 and 1.06%, quenched and tempered at various temperatures, experimental equations representing the relation between diffraction line width and hardness were obtained as a function of carbon content. The halfwidth and the Gaussian curve parameter (GCP), that is a constant of a Gaussian curve fitted to a diffraction line peak, were used to evaluate the diffraction line width. The curve representing the relation between the line width and hardness had a bend at the tempering temperature of about 400°C. At this temperature the martensitic structure of tempered steels changed into troostite or sorbite, which has a ferritic matrix. The relation between the half-width and the GCP was also given.
Paper handling technology related to sorting, feeding and stacking, has recently become of importance as a result of the development of high-speed, high-resolution printers. Consequently, the clarification of paper processing characteristics is of vital concern. Although there have been numerous reports on metal processing characteristics, very few studies have been carried out on paper processing characteristics such as springback. In the previous paper, a mechanical model for paper behavior was proposed. The present study deals with paper processing characteristics related to stacking. Using the previously proposal mechanical model, an analysis was made of springback in the bending phenomenon for paper and the results were compared with those for metal plates. The results were successfully applied to make clear the correlation between springback and stacking stability in a printer. The main conclusions are as follows: (1) When the strain rate dependency was taken into consideration, close agreement was found between the observed and calculated values of paper in this springback analysis. (2) The stacking stability increased as springback decreased. It was seen that greater paper thickness and the absence of a fixing process results in better stacking characteristics.
The main purpose of the present study was to establish an accurate and stable tensile test method of ceramic materials. The test device was designed to minimize load eccentricity and to eliminate gripping problems. A plate specimen was supported at its upper and lower shoulders by four aluminum pipes each of 12mm diameter, 10mm long and about 2.5mm thick. Large deformation of aluminum pipes absorbs load eccentricity and yields a good contact with the specimen shoulders. Fracture of specimens at shoulders parts is thus completely avoided. Silicon nitride plate specimens were used in the test. It was observed that the eccentricity of load rapidly decreased with the increase of applied load, as was expected, and the percentages of out-of-plane and in-plane bending stresses at fracture were found to be less than 4% and 5%, respectively. The mean tensile strength of sintered silicon nitride was 46.0kg/mm2 which was 50% of the value obtained by the three-point bending test on the same material. The Weibull modulus obtained by plotting the strengths of 38 specimens on the probability paper was 9.2 which was 4.7 less than the value obtained by the three-point bending test. The Young's modulus and Poisson's ratio of sintered silicon nitride were found to be 3.07×104kg/mm2 and 0.260, respectively.
A scanning exoelectron emission microscope (SEEM) was constructed trially, and some observations were made by using the trial SEEM. This trial microscope can be turned into a scanning electron microscope (SEM) by a simple mechanical operation. Therefore, it is easy to observe the same point by both SEM and SEEM. The preliminary observations on aluminum tensile specimens seem to suggest that this scanning exoelectrtron technique will become a unique tool to investigate fracture mechanisms.