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1.
| 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.
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Published in Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 28, No. 1, pp. 73–78, January–February, 1992. 相似文献
2.
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: | – |
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;
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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;
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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.
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Published in Fiziko-Khimiches-kaya Mekhanika Materialov, No. 3, pp. 54–60, May–June, 1992. 相似文献
3.
| 1. |
We derived an equation which can be used to determine the endurance in cyclic loading on the basis of the crack initiation criterion in elastoplastic deformation of the material and the triaxial stress state.
| | 2. |
Rapid fatigue damage cumulation can take place in the material only if the size of the reversible elastoplastic zone is larger than the grain diameter.
| | 3. |
The assumption on the homogeneity of SSS in the structural element makes it possible to describe most adequately the relationship between the strain and fatigue damage of the material.
| | 4. |
We derived an analytical expression linking the threshold value of the stress intensity factor \GDKth with the mechanical properties and grain diameter of the material.
| | 5. |
A model of fatigue crack propagation which is based on the approximate analytical solution of the cyclic elastoplastic problem of the SSS in the vicinity of the crack tip was developed. The model takes into account the special features of deformation of the material in the conditions of the triaxial stress state and also uses the assumption on the homogeneity of SSS in the structural element. The main advantages of the model are as follows:
it can be used to determine the crack growth rate in cases in which the variation of the range of the stress intensity factor in the structural members takes place at the variable loading asymmetry; 相似文献
4.
| 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.
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相似文献
5.
| 1. |
With thermal cycling loading for coated specimens microracks occur in brittle coating layers, and conditions for their formation depend not only on coating composition, but also on the composition of the metal being protected, and operating conditions (time, temperature).
| | 2. |
Propagation of thermal fatigue microcracks into the basic metal is determined not only by the difference in linear thermal expansion coefficients, elasticity moduli of the coating and basic metal, but it also depends on the thickness of the coating, cycle parameters, aggressivity of the corrosive medium, relative position of the cracks formed, and the level of heterogenetiv for the coating itself.
| | 3. |
In order to provide reliable protection for turbine blades from corrosion, coating selection should be carried out with reference to actual operating conditions and the grade taking account of chemical composition) of the basic material.
| | 4. |
Numerical evaluation of the features of surface microcrack growth from coatings into the basic metal with thermal cycling loading should be carried out on the basis of threshold aggressivity of the corrosive medium.
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I. I. Polzynov Central Institute of Boiler Turbines, Leningrad. Translated from Problemy Prochnosti, No. 12, pp. 30–35, December, 1988. 相似文献
6.
| 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.
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7.
| 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.
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Physicotechnical Low-Temperature Institute, Academy of Sciences of the Ukrainian SSR. Komsomol Ukrainy Kharkov Automobile Road Institute. Translated from Problemy Prochnosti, No. 7, pp. 26–32, July, 1989. 相似文献
8.
| 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.
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相似文献
9.
| 1. |
Sheets of the Zr- 1% Nb alloy were used for the first time to show by experiments the crystallographic reorientation of the grains at the tip of the moving crack.
| | 2. |
The effects detected by x ray diffraction examination in the vicinity of the fracture of the specimens with the notch, were compared with the effects recorded in the volume of similar smooth specimens subjected to tensile loading. According to the estimates, in the layer up to 20m thick, adjacent to the fracture surface, the average strain of the material in tensile loading is 15–20% for the RD specimen and 3–5% for the TD specimen.
| | 3. |
Anisotropy of the cracking resistance and development of the zone of plastic deformation at the tip of the moving crack are determined by the activating mechanism of plastic deformation of alpha zirconium whose special feature is the strong dependence on the crystallographic orientation of the grains.
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Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 27, No. 5, pp. 56–61, September–October 1991. 相似文献
10.
| 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.
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Translated from Fiziko-Khimicheskaya Mekhanika Materialov, No. 2, pp. 7–13, March–April, 1992. 相似文献
11.
| 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.
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Translated from Fiziko-Khimicheskaya Mekhanika Materialov, No. 2, pp. 21–27, March–April, 1990. 相似文献
12.
| 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.
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13.
| 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.
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Institute of Strength Problems, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Problemy Prochnosti, No. 5, pp. 108–110, May, 1989. 相似文献
14.
| 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.
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Lvov Polytechnic Institute. E. O. Paton Welding Institute, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Problemy Prochnosti, No. 2, pp. 33–36, February, 1988. 相似文献
15.
| 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.
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Translated from Problemy Prochnosti, No. 9, pp. 8–13, September, 1988. 相似文献
16.
| 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.
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相似文献
17.
| 1. |
The life of coatings by the criterion of fatigue limit is determined by the technology, the materials, parameters and structure of sprayed-on coatings, by adhesive bonds.
| | 2. |
Important parameters affecting the fatigue characteristics are the sequence and kind of sprayed-on powders, the existence and the thickness of the sublayer, the total thick ness of the sprayed-on layer, preliminary heating of the substrate (increases adhesion), residual stresses arising during treatment (with increasing thickness of the coating the residual tensile stresses increase).
| | 3. |
The use of powder PN85Yu15 as sublayer and of power PR-N65Kh25S3R3 as upper layer, with the total thickness of the coating equal to 0.15 mm, increases the fatigue limit of spra coated specimens by 30% in comparison with the same specimens but with the material in the initial state.
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Sergo Ordzhonikidze Moscow Aviation Institute. A. A. Blagonravov Institute of Engineering Science, Academy of Sciences of the USSR, Moscow. Translated from Problemy Prochnosti, No. 11, pp. 39–42, November, 1988. 相似文献
18.
| 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.
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相似文献
19.
| 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.
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相似文献
20.
| 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.
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Strength of Materials Institute, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Problemy Prochnosti, No. 1, pp. 30–33, January, 1989. 相似文献
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