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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.
A. V. Prokopenko Yu. K. Petrenya V. N. Ezhov I. A. Makovetskaya M. M. Ivakhov 《Strength of Materials》1989,21(1):39-43
| 1. | At high temperatures the fracture surface changes from being brittle and along crystallographic planes to quasiductile both in polycrystalline, and in monocrystalline alloys. This increases the fatigue crack growth rate. |
| 2. | As the temperature is increased from 1073 to 1273 K, the rate of high-temperature corrosion increases, especially in polycrystalline material. |
| 3. | The fatigue crack growth rate is higher in polycrystalline alloys than in monocrystalline alloys with a <111> orientation, and is lower in monocrystalline alloys with a <001> orientation, i.e., they have an intermediate rate in comparison to specific orientations of the grain. |
| 4. | The advantages of using monocrystalline alloys in increasing the fatigue crack growth resistance are only realized when the orientations of its most resistant planes are advantageously aligned along the direction of highest tensile stress both during brittle shear fracture at 293 K and, during quasiductile fracture at 1073-1273 K. |
3.
| 1. | The dependence of the growth rate of a fatigue crack on the stress intensity coefficient at the tip of the crack is described by an exponential function of the da/dN=CKn type for all zones of a welded joint. For a given applied stress and realizable values of K the index n in this function has a constant value, differing for each particular zone. |
| 2. | The instantaneous and average crack velocities reach their maximum values in the heat-affected zone and their lowest values in the seam metal. The crack growth rate in the parent metal is close to that in the heat-affected zone. |
| 3. | The fatigue life of a weld subjected to cyclic (fatigue) loading may to a first approximation be estimated by the n and C values of the parent metal. |
4.
| 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. |
5.
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. |
6.
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. |
7.
A. V. Prokopenko V. N. Torgov Yu. K. Petrenya M. M. Ivakhov 《Strength of Materials》1989,21(7):900-904
| 1. | The relief of the fatigue fracture can be connected with crack growth rate, and the effect of the corrosive action of the medium on the latter can be established. |
| 2. | Cathodic protection with magnesium neutralizes anodic dissolution of the material at the crack tip in the case of a low crack growth rate. The form of the fracture surface in this case is the same as in air. |
| 3. | The fractures of steel 14Kh17N2 are more ductile than those of steel 20Kh13, which can be attributed to the difference in their structures (ferrite-martensite and bainite, respectively). This explains the fact that the CGR is somewhat lower in steel 14Kh17N2 than in steel 20Kh13. |
8.
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. |
9.
| 1. | Single plastic prestraining leads to a decrease of the threshold level of the stress intensity factor range of alloys if they do not form pores or microcracks during deformation. These structural defects cause stress relaxation or crack tip blunting which causes an increase in the threshold level of the SIF. |
| 2. | A material classification is presented which is based on sensitivity of FCG rate in the middle section of the kinetic diagram of fatigue failure to the degree of prestraining Cold deformation, rolling, or tensile tension increases the FCG rate of cyclic hardened materials (u/0.2>1.5) and decreases it for cyclic softened or cyclic stable materials. |
10.
N. M. Grinberg V. A. Serdyuk A. M. Gavrilyako V. A. Zolot'ko E. L. Miloslavskaya L. E. Gorelkova 《Strength of Materials》1989,21(7):859-865
| 1. | In the AMg6 aluminum alloy the fatigue crack growth rate at 293 K decreases as compared with the same value in air and parameters Kth and K* increase in vacuum. |
| 2. | With a temperature drop from 293 to 140 K the fatigue crack growth rate decreases especially at low Kmax values, while the Kth and K* values increase. |
| 3. | Each region of the kinetic diagram of fatigue fracture is characterized by a definite micromechanism of fatigue fracture which for the investigated alloy does not change in vacuum even at temperatures falling to 140 K. |
| 4. | On the basis of the dependence of groove pitches on Kmax for the AMg6 alloy in region II of the kinetic diagram of fatigue failure, coordinates K* and A of the transition point which divides this region into sections IIa and IIb were determined. Ordinate A=SIIa does not depend on the medium and temperature and is for this alloy (1.8–2.0)·10–7 m. |
| 5. | Since K* is an important practical characteristic of cyclic crack resistance, the experimental method of its determination must be based on recording the transitional character of one of the physical processes taking place in this point. |
11.
12.
S. B. Kasatkin 《Strength of Materials》1976,8(11):1346-1350
| 1. | Polycarbonate specimens enable direct observation of the stress-strain pattern during the loading process. |
| 2. | It has been shown that under plane strain and plane stress conditions the crack starts at the boundary of the elastic-plastic deformation zone at the moment when the normal stress component reaches the critical value. |
| 3. | Under plane strain conditions the value cr is determined by the yield point and the radius of the notch n. Under plane stress conditions the strip of plastic deformation functions, as a stress concentrator. Fracture occurs when the normal stress component at the boundary reaches the critical value. |
| 4. | During the intervals when the specimen is not loaded the plastically deformed zones act as concentrators of residual stress. When load is again applied there is interaction between the residual stresses and the externally induced stresses. |
13.
| 1. | The specific energy of plastic deformation characterizes quasibrittle failure of metal structures operating under extreme conditions in the cold climate, and makes it possible to compute the limiting stresses and strains at different stress raisers. |
| 2. | The strength of components and elements of metal structures with stress raisers in elastoplastic deformation can be evaluated on the basis of the energy loss in the zone of strain localization. |
| 3. | The values of the threshold strain for 20 steel, calculated during mechanical tests with determination of the specific energy of deformation and failure, are in the range of exhaustion of ductility determined by x-ray diffraction analysis. |
14.
M. N. Georgiev N. Ya. Mezhova E. M. Morozov V. A. Reikhart 《Strength of Materials》1988,20(9):1133-1138
| 1. | It was establised that crack resistance limit Ic determined in full-profile nonheat-treated rails with cross fatigue cracks of area 10...30% of the rail head cross-sectional area is practically constant. The breaking stress c in all the cases is lower than the elastic limit c of the materials, in view of which, its crack resistance limit can be considered as a critical coefficient of the stress intensity for a plane deformed state, i.e., IcKIc. |
| 2. | For the non-heat-treated rails P65 with cross fatigue cracks (defect-21) KIc=37.5 MPa m. |
| 3. | The KIc values determined in full-profile non-heat-treated rails with cross fatigue cracks of area 10...30% of the rail head cross-sectional area practically does not differ from the results obtained as per GOST 25.506-85 in specimens taken from the same rails. |
| 4. | The KIc values for the non-heat-treated rails P65 with cross fatigue cracks decrease on the average by 40% for a test temperature drop from –253 to –333°K. |
15.
| 1. | The results show that when the temperature is reduced from 293 to 11°K the fatigue crack growth rate in Kh60MVYu nickel alloy decreases only insignificantly and only in the near-threshold region. Under the effect of vacuum the rate decreases to a considerably greater extent and in a wider range. |
| 2. | The threshold stress intensity factor Kth increases under the effect of both the medium and low temperature (11°K). |
| 3. | The size of the plastic zone at the crack tip is independent of the medium and decreases with decreasing temperature. |
| 4. | The size of the plastic zone at the point with the abscissa K* corresponds to 2h=3d, both for 293°K and 11°K. At this point the value m changes abruptly from m2=2 to m1=6. |
16.
| 1. | In the presence of longitudinal cracks of varied length (40–160 mm) and varied amount of elastic energy of the compressed air model (1400–9400 kgf·m) the failure of models on thin-walled shells 0.5 mm thick, when loaded by an internal pressure, has a ductile character, independently of the fitting of transverse tires located at different distances from the crack tip (from 20 to 105 mm). |
| 2. | As the initial length of crack increases, its subcritical growth in thin-walled shells increases linearly. |
| 3. | As the crack length increases, the failure stress (gross) is substantially reduced (from 22 to 9 kgf/mm2). At the same time the character of failure is altered: a straight-line propagation of the crack along the generator of the cylinder is replaced by a curvilinear propagation that approximates the failure direction to the circumferential direction. |
| 4. | With a reduction by a factor of two the amount of elastic energy contained by the compressed air model has almost no effect on the strength and geometrical features of the fracture. A dominant effect on the character of fracture is exerted, apparently, by the magnitude of the failure pressure which alters the relationship of the velocities of propagation of the crack and the waves of elastic unloading. |
| 5. | The limitations on the applicability of the existing calculation methods of the fracture mechanics, for the estimation of the resistance to a ductile failure of thin-walled cylindrical shells, is revealed, and appropriate corrections are proposed. |
| 6. | The effectiveness of the use of transverse tires to stop a started ductile failure of shells loaded by an internal pressure, depends on the distance between the tire and the vertex of the initial crack. This distance leads to a transition from the stoppage of the moving crack to its direction being altered. |
17.
V. T. Troshchenko S. P. Sinyavskii S. S. Gorodetskii A. P. Gopkalo A. K. Rusanovskii 《Strength of Materials》1976,8(7):747-753
| 1. | The strength characteristics of the piston alloys under consideration, measured under conditions of isothermal and thermal fatigue approaching those encountered in actual practice, are considerably lower than the static strength characteristics. This indicates the importance of allowing for the factors in question when calculating the strength of interual-combustion-engine pistons. |
| 2. | Of the alloy studied in the present investigation, the lowest thermal-fatigue strength characteristics corresponding to approximately normal working conditions are those of aluminum alloy AL25. For temperature cycles of 55330°C the breaking stress on a base of 2·104 cycles of heat exchangers falls to 1 kgf/mm2, as compared with the isothermal fatigue limit (6.1 kgf/mm2) and the static tensile strength (12 kgf/mm2) at the same temperature. |
| 3. | Under conditions of combined loading, the fatigue life of alloy AL25 falls more rapidly than would follow from the linear hypothesis of damage summation, allowing for both mechanical and thermal fatigue. A vital factor in this case is the damage associated with interaction between the fatigue and thermal fatigue processes due to multiple-factor effects. |
| 4. | Criteria for the failure of piston materials under multiple-factor conditions call for urgent and more extensive investigation. |
18.
| 1. | The microstructure of the steel has a strong effect on the resistance to low-cycle fracture. The highest fracture resistance in cyclic loading is shown by the steel with the austenitic structure, that of the steel with the ferritic-pearlitic structure is slightly lower, whereas the lowest resistance was recorded for the steel of the transition grade (ferritic-martensitic). This is explained by special features of deformation of their microstructural components and different properties of the crystal lattice. |
| 2. | In low-cycle loading, the austenitic steel shows susceptibility to hardening, the steel of the ferritic-pearlitic grade is stable, and the steel with the sorbitic and ferritic-martensitic microstructure softens. |
| 3. | The low-cycle deformation resistance of the steels of different structural grades depends on the strength properties in static loading: the resistance is always higher In the material with a higher ultimate strength, i.e., in the steel with a martensitic microstructure. |
| 4. | The microstructure of the steel has the maximum effect in the near-threshold region of the fatigue failure diagram. |
19.
| 1. | The structure of the surface layer exerts a significant influence on the fatigue strength of alloy ÉI437BVD. |
| 2. | The fine-grained structure of the surface layer, which is obtained by the method of mechanothermal treatment, is characterized by the complete absence of macro- and microstresses and possesses high thermal stability. |
| 3. | Mechanothermal treatment of the surface layer of components formed from the heat-resisting alloy ÉI437BVD is an effective method of increasing the fatigue strength and operating reserves of components, which can be recommended for turbine and compressor blades. |
20.
| 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. |