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1.
J. Davidov 《Materials Science》1993,28(1):62-67
| 1. | With respect to low-cycle fatigue behaviour the increasing of iron quantity from 0.12% to 0.38% results in a decrease of cyclic ductility of AlSi7Mg alloy but this decrease is not very significant. |
| 2. | The alloy with 0.12% Fe shows better low-cycle fatigue resistance then other materials investigated due to its relatively higher cyclic ductility. |
| 3. | The structure with 0.29% Fe shows the best fatigue crack growth resistance which is due to the best combination of its mechanical properties and relatively ductile type of fracture. |
| 4. | With regard to the low-cycle fatigue behaviour and fatigue crack growth resistance investigations carried out in this work have shown AlSi7Mg alloy with 0.29% Fe seems to be the most appropriate material for manufacturing counterpressure cast car wheels of the particular design investigated because the decrease of cyclic ductility for this structure is not very significant. |
2.
| 1. | High-temperature thermomechanical treatment and microalloying with 0.1% La raise the fatigue and corrosion-fatigue strength of steel 1Kh17N2. |
| 2. | The rise in the fatigue strength is due to an increase in the resistance to crack growth resulting from changes in the structure and substructure brought about in the steel by the high-temperature treatment and microalloying with the rare earth metal. |
| 3. | High-temperature thermomechanical treatment of steel 1Kh17N2 and its alloying with 0.1% La raise the corrosion resistance of the steel and reduce its tendency to intercrystalline corrosion. |
| 4. | The increase in the corrosion resistance of steel 1KM7N2 after the high-temperature treatment and microalloying with the rare earth metal is caused by the structural changes produced in the steel by the treatment and the microalloying. |
3.
| 1. | We proposed a method which can be used to examine the kinetics of failure and cracking resistance of the materials taking into account the type of thermal effect. |
| 2. | The results show that the variation of the temperature conditions during macrocrack propagation has a controlling effect on force and energy characteristics of failure and on the change of the failure micromechanisms. This effect differs for different types of materials. |
| 3. | Electron fractographic examination showed that the level and nature of damage in the material obtained in the previous stage of thermal loading greatly affects the relationships governing the propagation of the macrocrack after a temperature change. |
| 4. | It is shown that it is important to take into account the history of thermal loading (direction and temperature variation amplitude) in determining the cracking resistance of materials and structures. |
4.
S. F. Yur'ev V. F. Luk'yanov V. I. Sheiko V. Ya. Kharchenko V. G. Ovsyannikov A. F. Gorbachev 《Strength of Materials》1976,8(4):441-444
| 1. | Cladding of high-strength steel with type 08KhN2GMTA deposited metal aids in increasing the resistance to failure of plate metal under repeated static biaxial bending in a 3% sodium chloride solution. |
| 2. | With an amplitude of operating stresses of 70% of the yield strength of the high-strength steel the cladding layer at first experiences plastic deformation, which leads to the formation of residual stresses and a change in the degree of asymmetry of the subsequent load cycles of the external layers in a favorable direction. |
| 3. | The appearance in the cladding layer of residual compressive stresses and the decrease on the sample surface of the maximum tensile stresses aids in increasing the resistance to the origin and initial growth of a corrosion-fatigue crack. |
5.
V. T. Troshchenko V. V. Pokrovskii P. V. Yasnii V. G. Kaplunenko V. V. Burdakov V. P. Leonov Yu. A. Nikonov 《Strength of Materials》1988,20(9):1138-1145
| 1. | On the basis of the experimental investigation of the effect of the test temperature (153–293°K) on the rate of FCG in steels IP-1, IP-2, and IP-3 with a coefficient of load cycle asymmetry R=–2, –1, 0, and 0.5 it was established that lowering of the test temperature has an ambiguous effect on the rate of fatigue crack growth in the mentioned steels. In most cases the rate of FCG is practically insensitive to the test temperature although we can see a general tendency of the coefficient m of the Paris equation increasing with the test temperature being lowered from 293 to 153°K. |
| 2. | A change of the coefficient of load cycle asymmetry in the range –2–0 does not have a substantial effect on the rate of FCG, and in the range 0–0.5 it reduces this rate (in coordinates d/dN-Kmax) at 213 and 293°K, particularly substantially at 213°K. |
| 3. | For the investigated chrome-nickel-molybdenum steels in the temperature range 293-153°K a single dependence was established; it describes the decrease of the coefficient m with rising level of fracture toughness under static loading. |
| 4. | With the test temperature rising from 113 to 153°K, the characteristics of fracture toughness of all the investigated steels increase monotonically under static and cyclic loading, and also in the case of stopping of the crack. |
| 5. | Cyclic loading reduces substantially (to one half) the fracture toughness of steels IP-1 and IP-2 in the temperature range 113–153°K and does not change the values of K1 fc compared with KIc for steel IP-3. |
| 6. | In steels IP-1, IP-2 at temperatures of 113–153°K the fracture toughness under cyclic loading corresponding to final fracture of the specimen practically coincides with the fracture toughness at the instant of stopping of the crack. |
| 7. | In the temperature range 100–183°K of the three investigated steels steel IP-1 has the highest resistance to brittle failure under static loading and at the instant of stopping of the crack, steel IP-2 has the lowest resistance. |
6.
Comparing the fracture toughness temperature curves evaluated at static and rapid loading on larger (SENB, 1CT) specimens with the fracture toughness curve determined on precracked Charpy specimens at impact loading, the following conclusions can be drawn:
Published in Fiziko-Khimiches-kaya Mekhanika Materialov, No. 3, pp. 54–60, May–June, 1992. 相似文献
| – | both rapid and impact loadings cause the shift of fracture toughness temperature curve to higher temperatures in accordance with the concept of critical tensile stress criterion; |
| – | the transition temperature region with brittle (cleavage) initiated fracture after some ductile crack growth is, at rapid loading, shifted to higher temperature as well; |
| – | at the impact loading of small PC specimens the whole transition region is reduced to one transition temperature only and therefore sharp increase from the lower shelf fracture toughness region to the upper one occurred. This ductile to cleavage initiation transition temperature is, in spite of the impact loading, lower than that of the larger 1CT specimens loaded at a much smaller loading rate; |
| – | for cleavage initiated fracture of low alloy steel only lower shelf fracture toughness values can be measured by employing the PC specimens and the impact loading. |
7.
| 1. | The fracture of heat-resistant alloys and tool steels under the influence of thermal cycling may be quasistatic, fatigue, or mixed in character. |
| 2. | Quasistatic fracture as a result of thermal cycling takes place with the specimen working portion remaining constant (hard loading mode); it is caused by the accumulation of strains of opposite signs in local material volumes. |
| 3. | The accumulation of residual strains in local specimen volumes for thermoplastic strain materials is due to the mismatch of plastic strain fields along the specimens during the heating and cooling cycles. |
| 4. | Under thermal cycling conditions (as in isothermal low-cycle fatigue) the static damage is measured in terms of the accumulated plastic strain (of a given sign), while the fatigue damage is measured in terms of the magnitude of the plastic strain per cycle. Quasistatic fracture takes place in regions of the maximum accumulated plastic strain which is equal to zero in the zone of fatigue fracture. |
8.
| 1. | Multiple regression analysis was used to determine a strong correlation between the composition and physicomechanical characteristics of the high-manganese steel alloyed with boron and vanadium. |
| 2. | The correlation of abrasive and impact-abrasive wear resistance with each mechanical characteristic is very weak and in certain cases does not exist at all. |
| 3. | A correlation was found between each type of wear and the remaining characteristics. Abrasive resistance can be increased only by increasing hardness and impact-abrasive wear resistance can be increased by increasing hardness and bending strength. Impact toughness has no effect on wear resistance in both types of wear. |
9.
S. M. Lyalikov 《Strength of Materials》1989,21(5):687-690
| 1. | It has been established that SPD reduces inelastic strain per cycle for the stress levels studied with any number of loading cycles. |
| 2. | As a result of mechanical strengthening the fatigue limit and endurance of steel 14Kh17N2 specimens increased to a greater extent than for steel 20. |
10.
| 1. | The not earlier noted fact of formation in contact impact on the surface of hardened steel of prismatic and segment chipping fragments was established experimentally. The first are formed in intersection of median cracks and the second in intersection of median and circular cracks. |
| 2. | Simple models based on criteria of fracture mechanics and low-cycle fatigue making it possible to analyze the forms of failure considered are proposed. Using the calculation relationships it is possible to determine the order of magnitude of the separate fragment. |
11.
T. B. Buzovkina A. N. Sofronkov L. I. Korolenko S. A. Lyaskovskii I. A. Kuznetsova 《Materials Science》1993,28(4):354-358
| 1. | Unstable peroxides are formed when sea water reacts with a nonpassivating steel surface, which results in passivation. |
| 2. | The pH shifts as far as 13 in sea water in a real static crack in 15KhN5 steel, which is accentuated as the stress level increases, the crack lengthens, and the tip is approached. |
| 3. | The alkalinization in sea water above steel turnings is much less than in a crack but the pH dynamics are the same. |
| 4. | Metabolites from aerobic fouling organisms (bicarbonates and oxygen) retard the decomposition of hydrogen peroxide at the surface, which raises the pH and Eh; the metabolites from aerobic bacteria (hydrosulfides) reduce the hydrogen peroxide concentration, which reduces the pH and Eh. |
| 5. | The hydrogen release overvoltage is reduced on peroxide films on steel surfaces of 15KhN5 type, and the cathodic reaction of depolarizer reduction is retarded. |
12.
L. E. Matokhnyuk A. V. Voinalovich A. A. Khlyapov V. L. Belov A. B. Pavlova A. V. Kirillova 《Strength of Materials》1988,20(7):861-867
| 1. | Within the range 500–10,000 Hz the cyclic loading frequency has practically no effect on the fatigue resistance of the IMV-2 alloy, while for the AMg6N alloy at an increase of loading frequency to 10 kHz the fatigue limit of smooth specimens increases monotonically. |
| 2. | The effective stress intensity coefficients and the coefficients of the welding effect do not change during transition to higher loading frequencies which permits them to be determined from the results of high-frequency tests on the required loading bases. |
| 3. | On each of the investigated loading frequencies the scatter of fatigue life values of broken welded specimens and of specimens with stress concentrators is greater than that of smooth specimens of the initial material. This must be taken into account in calculating and predicting the cyclic fatigue life of structural elements and machine components. |
13.
A. Ya. Krasovskii V. A. Makovei G. N. Nadezhdin V. L. Svechnikov G. V. Stepanov 《Strength of Materials》1988,20(2):137-142
| 1. | The velocity dependence of dynamic fracture toughness can be evaluated by the method of quantitative stereoscopic fractography within a broad range of loading rates. |
| 2. | For steel 40Kh the ascending branch of the velocity dependence of KId is determined by fragmentation of the structure causing ramification of the crack which, in the final analysis, increases fracture toughness. The reduced size of the microcrack in fragmentation is directly connected with the weakening of the dependence of crack resistance on the loading rate [19], which in our experiments corresponds to the range of impact speeds of 300–600 m/sec. |
| 3. | Removal of microsegregations from the boundaries forming upon fragmentation of blocks in the structure (by means of diffusion) increases the surface energy of such boundaries, impedes the formation of microcracks on them, and consequently increases fracture toughness. |
14.
L. V. Kuksa B. I. Koval'chuk A. A. Lebedev V. I. Él'manovich 《Strength of Materials》1976,8(4):393-398
| 1. | Plastic deformation in polycrystalline copper develops unevenly in the microregions in both the linear and the plane stress state (including plane stress under conditions of complex loading). A higher level of microinhomogeneity in deformation was observed in the plane stress state. |
| 2. | The immobilization and duplication of microcenters of increased and reduced deformation in simple loading is a general property of polycrystalline materials and is in independent of the nature of the material and the type of stress state. |
| 3. | The development of deformations in individual microsectors in conditions of complex loading (axial tension—uniform biaxial tension—transverse tension) differs substantially from that in simple loading. The difference lies in the varying degrees of localization of deformation of fixed microsectors. |
| 4. | In a plane stress state, especially under conditions of complex loading, deformation is due to the action of a larger number of slip systems than in a linear stress state; this must indicate more complex deformation conditions in the individual microvolumes. |
15.
This article presents a failure analysis of 37.5 mW gas turbine third stage buckets made of Udimet 500 superalloy. The buckets
experienced repetitive integral tip shroud fractures assisted by a low temperature (type II) hot corrosion. A detailed analysis
was carried out on elements thought to have influenced the failure process:
The most probable cause of the bucket damage was the combination of increased stresses due to corrosion-induced thinning of
the tip shroud and unfavorable microstructures in the tip shroud region. 相似文献
| a) | the stress increase from the loss of a load bearing cross-sectional area of the bucket tip shroud by the conversion of metal to the corrosion product (scale), |
| b) | influence of the tip shroud microstructure (e.g., a presence of equiaxed and columnar grains, their distribution and orientation), |
| c) | evidence of the transgranular initiation, and |
| d) | intergranular creep mechanism propagation. |
16.
A. E. Andreikiv N. V. Lysak V. R. Skal'skii I. L. Parasyuk O. N. Sergienko 《Materials Science》1993,28(4):378-382
| 1. | Cracking occurs in tubular specimens of U8 steel hydrogenated to high hydrogen concentrations mainly because the gaseous hydrogen affects the steel. |
| 2. | Slow failure occurs by the formation and growth of defects of crack type, which cause the large-amplitude discrete AE signals alternating with continuous AE ones of relatively low amplitude. |
| 3. | Cracking is accentuated by increased pressure during the hydrogenation at a given temperature and by reduction in the cooling time. |
| 4. | High tensile steels saturated with hydrogen are liable to slow failure by the formation and growth of defects of crack type. The main periods in the failure are as follows: a) preparatory period, with plastic strain and corrosion due to the high temperatures and to the residual-stress and strain concentrations on cooling; b) the incubation period, when microcracks are formed at grain boundaries and nonmetallic inclusions; and c) subcritical growth period, where microcracks merge into macrocracks, which grow. |
| 5. | The cracks grow in steps equal to the sizes of the grains or a few grains, and the AE is due to intercrystallite cracking in the zone of stable crack growth in U8 steel. |
17.
N. M. Aptekar' S. L. Babchenko G. M. Vorob'ev G. V. Yashnaya O. D. Smiyan 《Materials Science》1976,11(6):650-652
| 1. | Selective absorption of hydrogen (at active centers) takes place on the working surface of railway crossing points made of steel G13L. |
| 2. | High hydrogen concentrations are found in the metal adjacent to exfoliation; these concentrations reach a maximum in layers situated at a distance of 0.5–1 mm from the exfoliation surface. |
| 3. | In an exfoliation zone the hydrogen concentrations are considerably greater than the initial values. |
| 4. | Splashes of hydrogen concentrations are observed in regions of the surface layers of the crossings in which flakes are not actually visible; the state of the metal can then be described as the preflaking stage. |
18.
M. V. Bol'shakov V. N. Palash V. N. Yus'kiv M. M. Nerodenko E. A. Asnis 《Strength of Materials》1988,20(2):172-176
| 1. | The method of determining the static cracking resistance using, as the criterion, the values of the J-integral is more suitable for testing small specimens of niobium alloys with a high ductility margin. |
| 2. | The static cracking resistance characteristics of the welded joints in 5VMTs alloy with solid-solution hardening are considerably higher than those other welded joints in NTsU heterophase alloy. |
| 3. | When the welding speed is increased from 2.8 to 16.6 mm/sec, with a corresponding reduction of the heat input from 1480 to 760 J/cm, the cracking resistance of both the weld metal and HAZ of the examined alloys increases. |
| 4. | Subsequent heat treatment for 1 h at 1473°K increases the cracking resistance of the welded joints. |
19.
| 1. | The described general method of designing structural elements (a type of thin nonsloping shell of revolution) under cyclic loading, which has been approved for the case of a spherical notched shell, is effective, and can also be employed for other types and shapes of thin-wall designs of constant or variable thickness. |
| 2. | Stabilization of the stress state during cyclic loading is heavily dependent on the applied-loading rate and occurs (according to the results of the design and experiments under consideration) during the 2–10th loading cycle for a load range of 10q25 kg/cm2. |
| 3. | As the loading in the shell increases, the stress concentration diminishes from a value k=3.5, which corresponds to the elastic state, to 1.3 at which point the strain concentration reaches a maximum value with q=15 kg/cm2 for the material in question, and then decreases; this is associated with the transition of the shell into the plastic state. These results can be used to evaluate the low-cycle strength of standard structural elements, and to determine the factors of safety and the bearing capacity under cyclic loading. |
20.
E. I. Aleksenko N. M. Grinberg S. I. Aksenova N. A. Grekov G. I. Arkavenko 《Materials Science》1990,26(2):138-144
| 1. | A reduction of the air pressure reduces the rate of fatigue crack growth and increases the threshold range of the SIF in 3M titanium alloy. |
| 2. | A reduction of temperature in vacuum is accompanied by a nonmonotonic variation of the cracking resistance characteristics of the 3M alloy. At 93 K the rate of fatigue crack growth decreases and the threshold range increases. However, a further reduction of temperature to 11 K results in the reversed effect, with the rate of fatigue crack propagation becomming comparable with that in air. |
| 3. | A variation in the duration of the crack initiation stage with a reduction of the air pressure and temperature correlates with the variation of the threshold SIF. |
| 4. | On the basis of changes in the microstructure of the fracture surfaces, it can be concluded that the energy capacity of fatigue failure increases with a reduction of the air pressure and decreases with a reduction of temperature to 11 K. |