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1.
S. I. Yakovenko A. P. Guk V. I. Lakh V. N. Kryzhanovskii 《Strength of Materials》1988,20(12):1682-1684
| 1. | The temperature-time relationship of the allowable mechanical loads of a thermal transducer protection tube was established. |
| 2. | For a preliminary evaluation of the strength of a thermal transducer in relation to service time it is necessary to use the temperature relationship of the modulus of elasticity or of the stress-rupture strength of the materials used. |
| 3. | Failure of the protection tube of a thermal transducer in long high-temperature loading occurs as the result of development of pores primarily at grain boundaries. |
2.
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. |
3.
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. |
4.
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. |
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. |
6.
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. |
7.
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. |
8.
| 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. |
9.
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. |
10.
| 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. |
11.
| a) | The study describes the basic fracture micromechanisms of porous materials with dominantly ferritic matrix structures. |
| b) | Quantitative fractography is used to describe the basic mechanisms of crack propagation in the porous body corresponding to the non-monotonous temperature dependence of fracture toughness values. |
| c) | Behavior of fracture toughness values and relevant fracture micromechanisms indicate that the state of plane deformation in microvolumes in front of the crack tip cannot be reached at higher porosities and temperatures. This piece of information corresponds to the knowledge of independence of fracture toughness values of porous materials on the specimen thickness, as is presented in the literature [5]. |
12.
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. |
13.
Conclusion Through metallurgical SEM analysis, it was found that 42% of failures occurred due to corrosion plus erosion-corrosion, 16.5%
were due to inclusions and stress gaps that could be correlated oto fatigue, 16.5% had traces of production impurities, and
25% showed fatigue via ductile-type failures. The results/reasons correlation can be summarized as follows:
As a result of the analysis of various implant materials, the main reasons for failure are corrosive attack, manufacturing
defects, and nonstandard-caused failures. Biocompatible inorganic materials, such as hydroxy-apatite coating with some binders,
would make the dissolution of metal ions difficult and so may delay corrosion and wear and also minimize the loosening of
implants from bone. 相似文献
| – | • In the investigation of a total hip prosthesis, the fracture was multiorigined, probably due to the presence of manufacturing defects in both surfaces of the device; was associated with poor design of the component; and introduced points of high stress concentration. |
| – | • The study revealed that the failure of the stainless steel femoral compression plates occurred by a fretting-fatigue mechanism under the action of low nominal stresses and unidirectional bending. |
| – | • The failure of femoral compression titanium plates occurred by corrosion fatigue promoted by the presence of intense localized corrosion and intergranular cracking. |
| – | • The failure of hollow spinal rods occurred by overload caused by the intense formation of pitting corrosion during service. The pitting was associated with the presence of superficial manufacturing routes. |
14.
O. N. Romaniv A. N. Tkach T. Ya. Yus'kiv V. I. Ovchinnikov V. A. Sharkov 《Materials Science》1990,26(3):274-281
The presence of the graphite inclusions in the structure of the cast iron greatly affects the cyclic cracking resistance as a result of an increase of the dissipation of energy during crack growth and its closure. The dissipative processes lead to branching, blunting, and deviation of the crack from the plane of action of the highest normal stresses. This inhibits crack propagation. The effect of these processes is maximum at low crack growth rates and decreases with increase in AK. At FCG in cast irons failure takes place both in the graphite particles and at the matrix-graphite interface boundaries with the graphite inclusions displaced to the fracture surface. Being the highest elements of the relief of the fracture surface, the graphite particles increase its roughness and determine the mechanism and level of the CC. The described special features of the behavior of graphite in the cast irons during FCG indicate the following:
Translated from Fiziko-Khimicheskaya Mekhanika Materialov, No. 3, pp. 33–40, May–June, 1990. 相似文献
| – | at low crack propagation rates (below 10 -9 m/cycle) the CCT of the cast irons is, irrespective of the form of the graphite inclusions, higher than in the steels with similar structures; |
| – | at rates higher than i0 -s m/cycle, the CCT of the cast irons with matrix of the same structure depends not only on the form of graphite but also on the crack growth rate; |
| – | the specific features of FCG in the cast irons with plate-shaped inclusions of graphite (high AKth and curvature KDFF) causes that GCI cannot be used for machine components operating under cyclic loading conditions; |
| – | the structure of the metallic matrix in the cast irons with vermicular graphite particles does not effect the CCT; |
| – | in cast irons with nodular graphite, the CCT at low rates of FCG increases with an increase of the size of globules and strength of the matrix; |
| – | in the cast irons with the nodular and vermicular graphite with the same structure of the matrix, the CCT depends on the strength of the matrix and its capacity to relax local stresses; |
| – | the cast irons with nodular and vermicular graphite inclusions are capable of competing with the structural steels in respect of their CCT. |
15.
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. |
16.
V. I. Bolobov K. M. Makarov A. A. Prokof'ev 《Journal of Engineering Physics and Thermophysics》1992,62(3):327-330
| 1. | We determined the critical deflagration pressure for titanium samples of various form during failure in oxygen. For like samples, we estimated the exposure rate of juvenile metal surface using the results of photographs of crack propagation during failure. |
| 2. | We proposed an empirical equation which describes the critical deflagration pressure of titanium samples during failure in oxygen, as a function of the rate of exposure of juvenile metal surface. |
| 3. | We suggested that this dependence of the critical deflagration pressure on sample configuration can be explained by the difference in the rates of exposure of juvenile metal surface during the failure of the titanium samples in oxygen. |
17.
| 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. |
18.
| 1. | As a result of introduction of the system, the possibility of loss of information on the vibration condition of an engine has been eliminated, especiallyin short time appearance of vibrations in failure situations when the vibrations increase very rapidly. |
| 2. | The measuring accuracy has been increased. |
| 3. | Recording of the parameters of vibrations in combination with other parameters characterizing the operation of the engine is provided. |
| 4. | The process of interpreting and treating the test results has been accelerated. |
19.
| 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
20.
G. M. Okhrimenko Yu. M. Rodichev T. Sh. Shagdyr V. P. Slin'ko 《Strength of Materials》1976,8(8):915-921
|