共查询到20条相似文献，搜索用时 215 毫秒
1.
| 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. |
2.
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. |
3.
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. |
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.
| 1. | The structures of the nodal sections of the dished ends designed in accordance with the compensation principle and design restrictions of the standards are charcterized by the permissable level of the maximum working stresses. |
| 2. | In varying the fraction of the reinforcing metal of the nozzle section situated in the wall of the dished end from 50 to 80% the level of the maximum stresses in the section changes only slightly. |
| 3. | The structures containing 70–80% of reinforcing metal in the wall of the nozzle are more rational from the viewpoint of reducing the metal requirement and have sufficient strength at the same time. |
| 4. | The permissible value of the ratio d/D specified by the standards can be increased from 0.3 to 0.5 without reducing the strength of the nozzle section. |
6.
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. |
7.
| 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. |
8.
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. |
9.
| 1. | A qualitative connection is established between creep and the departure of electrons from a surface for various forms of electronic emission. |
| 2. | The observed phenomena are explained on the notion that changing the emission of electrons from a surface disturbs the equilibrium between the components of the structure. |
| 3. | The method of investigation that is proposed utilizes an action on the surface of a mass spaced at a distance from the sample under test and connected with the sample solely by a metal wire. |
10.
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. |
11.
Building bridges, windows and cultures: Mediating mechanisms between team heterogeneity and performance in global teams 总被引：1，自引：1，他引：0
Abstract and Key Results
相似文献
| – | While research on teams shows evidence that heterogeneous composition and global dispersion creates difficulties, it has yet to holistically address how to over-come those difficulties without losing the intended benefits. |
| – | We describe four mechanisms to mediate the difficulties created by heterogeneous composition and global dispersion on global teams. |
12.
G. M. Okhrimenko Yu. M. Rodichev T. Sh. Shagdyr V. P. Slin'ko 《Strength of Materials》1976,8(8):915-921
| 1. | It was found that the moire-band method that the stress-strain state in the working part of biaxially compressed samples of glasses and pyroceramics, whose ends are cemented into the grooves of rigid metal bearing races, has satisfactory uniformity throughout the entire stage of loading, whereas the principal stresses coincide in direction with the loads applied to the contour. |
| 2. | The average compressive stresses in a biaxially compressed sample plate whose ends are cemented into the grooves of metal races, loaded over at least 95.5% of the lateral surface, may be calculated by dividing the applied load by the area of the contact surfaces between the sample and races. |
| 3. | The accuracy of experimental deformation diagrams, plotted from the results of interpreting moire-band patterns obtained in systems of parallel lines with 0.02-mm spacing, is higher by a factor of 1.5–2 than that of such diagrams plotted from tensometric data. |
| 4. | When brittle glass- and pyroceramic-type materials are compressed by smooth metal punches, high contact stresses appear, and stress concentrators are formed which cause premature fracture of the samples and understated results. |
| 5. | Owing to the possibility of maintaining the initial end conditions up to high working stresses on compression of glass and pyroceramic samples whose ends are cemented into the grooves of metal races, samples for testing other brittle, high-strength materials, e.g., high-alumina ceramics, porcelain, etc., are promising. |
13.
| 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. |
14.
B. A. Kolachev 《Materials Science》1992,28(5):395-398
| 1. | A general method of improving the composition of the HSA by complex alloying has been proposed. |
| 2. | Systems of alloying the HSA on the basis of intermetallic compounds TiFe, TiCo, TiCr2, TiMn2 have been described and characterized. |
| 3. | It is shown that not all possibilities of complex alloying have been exhausted to improve the properties of the HSA based on titanium. |
15.
| 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. |
16.
| 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. |
17.
Joshua D. Shackman 《Management International Review》2007,47(4):479-504
Abstract and Key Results
相似文献
| ▪ | In this paper I test the theory that internal capital markets are a motivation for both corporate diversification and vertical integration. I use a sample of 1560 firms from 39 countries. |
| ▪ | Using this data I also test theories about vertical integration and capital market development. I also test agency cost and taxation theories of diversification and vertical integration. |
| ▪ | I find a significant and negative relationship between corporate diversification and capital market development |
| ▪ | I find a significant and positive relationship between vertical integration and capital market development. |
18.
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. |
19.
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. |
20.
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. |