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951.
A crack-tip screening analysis of cleavage fracture of steel is developed. The analysis incorporates evidence that reinitiation
of an arrested cleavage crack requires less stress intensity than cleavage initiation from a fatigue precrack. Fractographic
evidence as well as metallographic sectioning of arrested cracks have previously shown that the mechanism of rapid crack propagation
by cleavage is affected strongly by partial crack-plane deflection which leaves unbroken ligaments in its wake. The tearing
of these ligaments by dimple rupture is the dominant energy-absorbing mechanism. Earlier etch-pit experiments using an Fe-Si
alloy showed that the crack-tip stress intensity based on plastic zone size is extremely low. These observations are incorporated
into a model in which cleavage crack reinitiation is analyzed using a sharp crack that is shielded by a distribution of pinching
forces along its faces. During reloading of the arrested crack, the ligaments restrict crack-tip blunting, leading to higher
local stresses. As a result, lower stress intensities are needed for reinitiation than for initiation from a fatigue precrack. 相似文献
952.
953.
954.
In this paper we suggest a new statistical method of correcting the results of hot-line experiments for the effects of background sources and we use the new method to reassess the adequacy of three probability distributions proposed in the literature for image spread from line sources. The data are from sources labelled with 125I in semi-thin resin sections 0·4-0·8 μm in thickness. The new method reveals that two of the models describe the empirical distributions more closely than earlier analysis had suggested, and it confirms an increasing relationship between half distance of image spread and the thickness of the source. However, it also confirms that considerable ‘inter hot-line’ experimental variation remains, even after background correction. This suggests that multiple experiments are needed to produce reliable estimates of half distance. 相似文献
955.
956.
N. Ya. Kydryavtseva Yu. N. Gromov V. A. Kotofeev 《Metal Science and Heat Treatment》1991,33(5):349-352
Conclusions Of all of the tested forms of hardening with chemicothermal treatment single-phase boriding and chrome-vanadizing provide the best combination of service properties of 5KhNM steel.Kemerovo Technological Institute for the Food Industry. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 5, pp. 7–8, May, 1991. 相似文献
957.
958.
We report impedance measurements on PVC matrix membranes which contain KBPh4 with varying proportions of valinomycin. In agreement with our earlier measurements the value of the bulk membrane resistance (Rb) is much larger in the presence of valinomycin, indicating that the mobility of K+ is greatly reduced by the valinomycin. Rb shows a linear variation with valinomycin/K+ ratio between 0 and 1, but it is invariant at higher valinomycin/K+ ratios. Thus there is no evidence for a special transport mechanism for K+ in these membranes. 相似文献
959.
D. N. Mukhiddinov Kh. A. Alimov A. I. Yufa A. V. Ulubabyan V. P. Dudanov 《Fibre Chemistry》1985,16(3):204-206
Conclusions The process of drying cellulose triacetate in a vibrating bed has been studied.For final drying of cellulose triacetate before solution, it is recommended to use an industrial specimen of a unit with a vibrating bed having a capacity of 2700 kg/h.This assembly can be used to dry other fibre-forming disperse polymeric materials containing strongly bound moisture.Translated from Khimicheskie Volokna, No. 3, pp. 49–51, May–June, 1984. 相似文献
960.
Conclusions The change in some properties of polyvinyl fluoride during the process of fibre spinning has been investigated.It has been found that during the process of converting PVF powder into fibre, the degree of polymer crystallinity plus its resistance to thermal and thermooxidative degradation is increased; depending on the spinning regime, the densities and physicomechanical properties of PVF fibres are different.Translated from Khimicheskie Volokna, No. 4, pp. 34–35, July–August, 1984. 相似文献