Further Considerations Concerning a Mechanism of Fatigue Crack Propagation

X-ray microbeam diffraction technique is a useful one to investigate the features of the crystal deformation in a localized area. That is, this method have been adopted to examine the density and array of dislocation, microscopic lattice strain and macroscopic residual stress. And so, the informations obtained from the tip of the crack during the fatigue process have been correlated with the behaviours of the initiation and propagation of the crack. The authors, in the present paper, investigated a relation between the distributions of the microscopic lattice strains which are calculated and measured by the technique, and suggested the sort of dislocation at the tip of the crack that relate to the fatigue crack propagation. The crack initiated at the notch root of the specimen which was composed of the coarse grain and propagated along the grain-boundary in the early stage under fatigue process of the alternating stress 4.1 kg/mm(2). Thereafter, it changed the propagating direction toward the inside of the grain. The distributions of the micro lattice strain in each reflecting plane which were measuerd at the plastically deformed zone in the vicinity of the grainboundary and at the crack tip agreed well with modes of the strain distribution due to a screw and a edge dislocations by the calculation, respectively. From these results, the authors concluded that the fatigue crack propagation would relate closely to the changing in the sort of the dislocation from the screw to the edge

Yield Strength and Stacking Fault Energy on Fatigue Crack Propagation

It is very important to clarify the question whether fatigue crack propagation will be affected by mechanical propaties or other propaties of materials. In the present paper the authors studied in relation of yield strength and stacking fault energy to rate of fatigue crack propagation. αbrass were chosen for the investigation because they provided sufficient range in both quantities of interest that either could be varied independently of the other. Fatigue tests were carried out under full bending moment of flat specimens with V-shape notch. Chosen stress levels were 0.6 σy and 0.8 σy in which σy is yield strength, rate of fatigue crack propagation was evaluated from the second stage of the curve of fatigue crack propagation. The dependence of the rate on stacking fault energy γ was found to be dl/ dN=G・γ(n). But dl/dN did not systematically to change in yield strength. Thus, γ is concluded to be the controlling variable

X-ray Investigation on the Fatigue Damage of Metals Containing α- and β-Phases (On the Changes in Half-Value Breadth and ResidualStress of 6-4 Brass due to Stress Cycles)

In the field of mechanical engineering, the need for a simple but effective way of evaluating the fatigue strength and lifetime of structural materials is an important problem with which the design engineers have faced. Accordingly, a cunsiderable amount of investigations have been made in this field. However, the basic nature of fatigue damage and the conditions which lead to the initiation and propagation of fatigue cracks are not sufficiently understood. Nor any satisfactory method of assessing the exact state of fatigue damage has yet been found. X-ray diffraction technique is not a new as the method of experimental study, but has often been adopted for direct and non-destructive observations of change in the local structures of crystalline materials at fundamental research. X-ray technique is one of the most powerful means to investigate the changes of microscopic- structure due to external forces, considering the fatigue phenomena occur on the surface of materials. Accordingly, one of the authors have studied the relations of half-value breadth of X-ray diffraction lines, residual stresses and hardness and number of cycles of fatigue stresses in detail for various sorts of engineering metallic materials. In the results of a number of experiments, it has been found that the variation in half-value breadth showed very regular relation with number of stress cycles, the authors have reported that the lifetime of materials in fatigue could be predicted. Consequently, it needs to investigate whether or not this predicting method is fitted for alloy containg α and β phase, moreover, it is interesting to make clear the fatigue mechanism of such materials which are present two phases having the different yield stress and type of crystal structure

Mechanism of Fatigue Fracture (On the Distribution of Plastic Strain around Fatigue Cracks)

Broadly speaking, there are three kinds of approaches to investigate the deformation and fracture of materials, that is, the microscopic (metallurgical), macroscopic(mechanical) and theoretical (mathematical) researches. It is necessary, however, to bridge the gap which persists among of them. Many investigations on the form of plastically deformed zone at a crack tip, the distribution of plastic strain in plastic zone and fracture criterion have been made for the purpose to clarify the mechanism on initiation and propagation of cracks. In this paper, the authors report the studies, from the standpoint of microscopic views, on the crystal deformation at the tip of crac's in notched specimen during fatigue process

On the Development of X-Ray Stress Measurement TechniqueUsing X-Ray Diffraction by Crystal Oscillation Method. I,

In the present paper, to provide information on the stress measurement in coarse grained materials by X-ray micro-beam diffraction technique using a crystal oscillation method, the authors first examined experimentaly and theoretically the relation between the sizes of X-ray beam and crystal to obtain the particular diffraction ring in the case of use of crystal oscillation method. The specimen attachment of X-ray camera used in this experiment can be oscillated automatically around a horizontal and vertical axes with high accuracy centering around an illuminated position on the specimen surface. Accordingly it is possible to increase the number of the diffraction spots without changing the area and position of the specimen illuminated. Experiments were carried out for three kinds of annealed low careon steel with grain sizes of about 15, 30 and 50μ in diameter, and with X-ray beam collimated by pinhole slits of 0.12, 0.30 and 1.00 mm in diameter, using CrKα characteristic X-rays. On the other hand, a theoretical analysis was carried out according to the X-ray diffraction theory which have been proposed by P. B. Hirsch et al. As the conclusion, it is found that the crystal oscillation method is extremely useful for X-ray stress measurement of coarse grained materials. Moreover, the conditions of the crystal oscillating operation were clarified theoretically for any pair of the sizes of X-ray beam and crystal

The Effects of Time Constant and Absorption on Stress Measured by X-ray Diffraction Method

The diffracted intensity of X-ray depends upon several physical and geometrical factors such as structure, multiplicity, absorption and Lorentzpolarization and measuring conditions such as time constant and scanning speed of detector on counter method[l]. For analyzing on the X-ray stress measurement, especially, profile shape of X-ray diffraction which is affected by geometrical factors such as absorption and Lorentz-polarization is very important. In order to eliminate these factors affecting the stress measured by using X-ray, the correcting factors were introduced and those theoretical values were calculated. After this theoretical calculation, it is found that as the half value breadth increases the difference between the stress measured by using X-ray and the corrected one becomes larger and larger under same measuring condition. When the ideal diffracted intensity of X-ray is assumed Cauchy distribution the measured stress depends upon measuring condition for same specimen, but it is independent of measuring condition in Gauss, distribution. Consequently, it is found that the stress measured by using X-ray must be corrected under each measuring condition and the method of correction is made clear and proved experimentally in this paper

Non-LTE Line-Formation and Abundances of Sulfur and Zinc in F, G, and K Stars

Extensive statistical-equilibrium calculations on neutral sulfur and zinc were carried out, in order to investigate how the non-LTE effect plays a role in the determination of S and Zn abundances in F, G, and K stars. Having checked on the spectra of representative F-type stars (Polaris, Procyon, and alpha Per) and the Sun that our non-LTE corrections yield a reasonable consistency between the abundances derived from different lines, we tried an extensive non-LTE reanalysis of published equivalent-width data of S I and Zn I lines for metal-poor halo/disk stars. According to our calculations, S I 9212/9228/9237 lines suffer significant negative non-LTE corrections amounting to <~ 0.2--0.3 dex, while LTE is practically valid for S I 8683/8694 lines. Embarrassingly, as far as the very metal-poor regime is concerned, a marked discordance is observed between the [S/Fe] values from these two abundance indicators, in the sense that the former attains a nearly flat plateau (or even a slight downward bending) while the latter shows an ever-increasing trend with a further lowering of metallicity. The reason for this discrepancy is yet to be clarified. Regarding Zn, we almost confirmed the characteristic tendencies of [Zn/Fe] reported from recent LTE studies (i.e., an evident/slight increase of [Zn/Fe] with a decrease of [Fe/H] for very metal-poor/disk stars), since the non-LTE corrections for the Zn I 4722/4810 and 6362 lines (tending to be positive and gradually increasing towards lower [Fe/H]) are quantitatively of less significance (<~ 0.1 dex).Comment: 33 pages, 7 figures, PASJ, Vol. 57, No. 5 (2005) in pres

Effect of Vitronectin Bound to Insulin-Like Growth Factor-I and Insulin-Like Growth Factor Binding Protein-3 on Porcine Enamel Organ-Derived Epithelial Cells

The aim of this paper was to determine whether the interaction between IGF, IGFBP, and VN modulates the functions of porcine EOE cells. Enamel organs from 6-month-old porcine third molars were dissociated into single epithelial cells and subcultured on culture dishes pretreated with VN, IGF-I, and IGFBP-3 (IGF-IGFBP-VN complex). The subcultured EOE cells retained their capacity for ameloblast-related gene expression, as shown by semiquantitative reverse transcription-polymerase chain reaction. Amelogenin expression was detected in the subcultured EOE cells by immunostaining. The subcultured EOE cells were then seeded onto collagen sponge scaffolds in combination with fresh dental mesenchymal cells and transplanted into athymic rats. After 4 weeks, enamel-dentin-like complex structures were present in the implanted constructs. These results show that EOE cells cultured on IGF-IGFBP-VN complex differentiated into ameloblasts-like cells that were able to secrete amelogenin proteins and form enamel-like tissues in vivo. Functional assays demonstrated that the IGF/IGFBP/VN complex significantly enhanced porcine EOE cell proliferation and tissue forming capacity for enamel. This is the first study to demonstrate a functional role of the IGF-IGFBP-VN complex in EOE cells. This application of the subculturing technique provides a foundation for further tooth-tissue engineering and for improving our understanding of ameloblast biology