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1.
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. |
2.
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. |
3.
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. |
4.
| 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. |
5.
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. |
6.
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. |
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.
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. |
9.
| • | Employing detailed industry-level data, this paper examines the country-of-origin effects of foreign direct investment in China. |
| • | The analysis demonstrates that there are significant differences in behaviour between investors from non-Chinese Western (NCW) source countries and those from Hong Kong, Macau and Taiwan (HMT). |
| • | The findings show that NCW investors target local market, while HMT investors are export-oriented. Furthermore, NCW firms are more responsive to local labour quality and technological capability than their HMT counterparts. |
10.
| 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. |
11.
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. |
12.
| • | This paper explores the organizational adjustment in host regions when MNCs switch from their original strategy to a regional strategy. |
| • | MNCs set up sub-regional headquarters (e.g., Greater China sub-regional headquarters) under a regional headquarters (e.g., Asia regional headquarters). A sub-regional headquarters replaces a regional headquarters directly managing subsidiaries within the sub-region. |
| • | The emergence of sub-regional headquarters is in response to the need for a balance between global integration and local responsiveness. An increasing number of decisions are made by sub-regional headquarters, instead of by subsidiaries, a parent, or regional headquarters. |
| • | Industry characteristics and firm’s specific advantages (FSAs) affect the delegation of authority from a parent to regional and sub-regional headquarters. |
13.
A new perspective on the regional and global strategies of multinational services firms 总被引：1，自引：0，他引：1
Abstract and Key Results
相似文献
| • | We explore the differences in international strategy between multinational enterprises (MNEs) in services and manufacturing, especially in terms of their international diversification, as measured by their sales and asset dispersion. |
| • | Our longitudinal data show that the largest MNEs in services have a much stronger home-region orientation than manufacturing MNEs. Large MNEs in the services sector average 83.9 percent of their sales in their home region, which is significantly higher than large manufacturing firms at 65.6 percent. |
| • | We explore the possible reasons for the relative lack of globalization of services firms. The two main reasons are: the difficulty of adapting separately upstream activities and downstream activities in high distance host environments, and the difficulty of selecting activity locations as a function of supply side criteria. |
| • | We offer a refinement of regional strategy theory applicable to services MNEs. |
14.
Yoshitaka Yamazaki 《Management International Review》2010,50(1):81-108
| • | This study investigates expatriate adaptation using a sample of Japanese expatriates in the US. For a comprehensive understanding, home managers in Japan and host managers in the US were also used. |
| • | This study is unique in that it examines expatriate adaptation through an analysis of the change of a fit between 12 learning skills and the skills demands. |
| • | The degree of expatriate adaptation increased in accordance with the length of the current overseas assignment tenure in the host country, along with an increase in job satisfaction. |
15.
Understanding Decisions to Internationalize by Small and Medium-sized Firms Located in an Emerging Market 总被引：1，自引：0，他引：1
| • | We examined perceptions differentiating key Colombian decisionmakers in 168 SMEs who decided to either internationalize or remain domestic. An integrative model compares managerial perceptions of competitive, macro-environmental and neo-institutional factors. |
| • | Foreign MNEs in the home market significantly differentiated decisions to internationalize, as well as the presence of internationalizing domestic competitors, anticipated product acceptance, and internationalizing suppliers. |
| • | The lack of findings for some institutional and macro-environmental factors may reflect important contextual features of the Colombian business environment. |
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. |
17.
| 1. | The long-term strength of polygonized aluminum at 100°C depends on the subgrain size and on the dislocation density within the subgrains, while that of the recrystallized metal depends on the grain size: The long-term strength of aluminum increases (at least for lives up to 1000h) with reduction in the grain or subgrain size and with increase in the density of internal dislocations. |
| 2. | The rate of loss of strength (the tangent of the angle of slope of the long-term strength curves) decreases with increase in the grain or subgrain size of aluminum; this leads to the convergence of the long-term strength curves of metal with different subgrains (or grains) at long lives. |
| 3. | An analogy has been found between the behavior of polygonized and recrystallized in long-term strength tests at relatively short times to failure and that in short-term tensile tests. |
18.
| 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. |
19.
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. |
20.
Christos N. Pitelis 《Management International Review》2009,49(1):95-120
| • | We explore the role of foreign direct investment and (its relationship to) clusters for the competitiveness (and catching-up) of small(er) developing countries. |
| • | We suggest that while size per se need not matter, small(er) developing countries need to explicitly account for any liabilities of smallness when devising and implementing strategies for competitiveness and catching-up. |
| • | We claim that international strategic management scholarship can add insights on this important issue, by complementing extant literature and contributions by international trade and economic development scholarship. |
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