共查询到20条相似文献，搜索用时 25 毫秒
1.
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Under irradiation conditions at 700°C the long-term strength of Kh18N10T steel and KhN77TYuR alloy is approximately the same if the time to fracture does not exceed 500 h. For a time base of more than 500 h the strength of KhN77TYuR alloy is lower than that of Kh18N10T steel, this difference incresing with an increase in the test base. From the point of view of the characteristics being considered, preference should evidently be given to canning of Kh18N10T steel.
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With a decrease in grain size from 35–50 to 10–25 in KhN77TYuR alloy its long-term ductility under irradiatioin increases, while the long-term strength does not vary.
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To explain the radiation effects observed it is advantageous to conduct in-pile creep tests. 相似文献
2.
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The temperature-time relationship of the allowable mechanical loads of a thermal transducer protection tube was established.
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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.
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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.
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Electric Temperature Measurement Special Design Office, Lvov. Translated from Problemy Prochnosti, No. 12, pp. 111–113, December, 1988. 相似文献
3.
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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.
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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.
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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
4.
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Improved strength and working life in sintered hard alloys can be provided by shot blasting under optimal conditions.
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One of the major factors governing the improved strength in such treatment is the production of compressive residual stresses in the surface layer.
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相似文献
5.
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High-temperature thermomechanical treatment and microalloying with 0.1% La raise the fatigue and corrosion-fatigue strength of steel 1Kh17N2.
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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.
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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
6.
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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.
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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.
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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.
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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.
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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
7.
| 1. |
The structure of the surface layer exerts a significant influence on the fatigue strength of alloy ÉI437BVD.
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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.
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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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相似文献
8.
| 1. |
Singular elements with a notch of an arbitrary angle were constructed to determine the stress fields near through notches.
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To increase the accuracy of the solution, we constructed transitional singular elements which increase the size of the region re in which singularity is modeled and decrease the incompatibility between the regular and notched singular elements.
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A procedure was developed for determining the stress field near notches under dynamic loadings.
| | 4. |
The stress intensity factor near small-angle notches differs negligibly from the stress intensity factor near cracks of the same length under static and dynamic loadings.
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The finite elements that were constructed make it possible to reliably solve linear fracture mechanics problems by the finite elements method with the use of very coarse idealizations.
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The above approach was realized in the program system POLIFEM for the ES series computer (by MOFAP Gosstroya SSSR). 相似文献
9.
| 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.
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Irkutsk Scientific-Research Institute of Chemical Engineering. Institute of Engineering, Moscow. Translated from Problemy Prochnosti, No. 2, pp. 78–82, February, 1989. 相似文献
10.
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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.
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The measuring accuracy has been increased.
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Recording of the parameters of vibrations in combination with other parameters characterizing the operation of the engine is provided.
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The process of interpreting and treating the test results has been accelerated.
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11.
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This paper examines the FDI location strategies of firms from one of the Asian NIEs (Taiwan) in a rapidly emerging market
(China). Although there is a substantial literature on FDI location choice, most studies model the choice as a function of
a range of location-specific attributes such as local market size, labour costs etc. Few studies consider the impact of firm-specific
characteristics, other than potential country-of-origin effects.
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Yet locations, and especially those in emerging markets where institutions are weak and capital markets are immature, also
differ in terms of their risk. Different shareholder constituencies within the parent company will typically have different
preferences with regard to risk, and are therefore likely to favour some locations over others.
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We find that the ownership structure of the parent company matters with regard to its FDI location decision and, in particular,
that both family and non-family insider shareholders exert influence over the choice of location.
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Furthermore we show that firms’ location and entry mode choices are inter-related, and establish that the extent of their
resource commitments in their foreign affiliates leads parent companies to favour locations where the perceived risks are
lower.
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Finally we show that the efficacy of firms’ external relational linkages varies according to the strength of the cultural
and historic ties between the location of the foreign affiliate and the home country.
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相似文献
12.
Abstract and Key Results
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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.
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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.
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I find a significant and negative relationship between corporate diversification and capital market development
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I find a significant and positive relationship between vertical integration and capital market development.
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13.
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We explore the role of foreign direct investment and (its relationship to) clusters for the competitiveness (and catching-up)
of small(er) developing countries.
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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.
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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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相似文献
14.
| 1. |
Cracking occurs in tubular specimens of U8 steel hydrogenated to high hydrogen concentrations mainly because the gaseous hydrogen affects the steel.
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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.
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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.
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Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 28, No. 4, pp. 63–69, July–August, 1992. 相似文献
15.
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: | – |
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;
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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;
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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;
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the structure of the metallic matrix in the cast irons with vermicular graphite particles does not effect the CCT;
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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;
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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;
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the cast irons with nodular and vermicular graphite inclusions are capable of competing with the structural steels in respect of their CCT.
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Translated from Fiziko-Khimicheskaya Mekhanika Materialov, No. 3, pp. 33–40, May–June, 1990. 相似文献
16.
| 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.
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相似文献
17.
| 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
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.
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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
19.
Abstract and Key Results
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After thirty years of research on the relationship between internationalization and firm performance, findings on direction
and magnitude are still contradictory. This paper quantitatively reviews prior research in an attempt to reconcile the fragmented
results.
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We address the question if and how internationalization relates to firm performance by integrating findings from 36 studies
(41 samples, N = 7,792) using the method of meta-analysis.
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We find empirical support for a significant positive relationship at the aggregate level. Equally important, meta-analysis
reveals that the relationship is moderated by R&D intensity, product diversification, country of origin, and firm age and
size.
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相似文献
20.
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This paper shows that the role of managerial incentives is highlighted by a relatively complex relationship between technological
competence and international diversification. By studying a sample of Standard & Poor’s 500 member firms, we explore the relationships
between technological competence, managerial pay, and international diversification.
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Results indicated a curvilinear relationship (an inverted U-shape) between technological competence and international diversification. |
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In line with agency theory, contingent pay (stock options and bonuses) was positively related to international diversification. |
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Beyond these direct effects, both contingent and non-contingent pay (cash compensation) moderated the relationship between
technological competence and international diversification.
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