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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.
A. Lamure S. Mezghani M. F. Harmand C. Lacabanne 《Journal of materials science. Materials in medicine》1996,7(3):175-179
Thermally stimulated current spectroscopy has been applied to the investigation of molecular mobility in human calcified tissue. A comparative study of extracts and residues at various stages of demineralization is presented. Results show that:
Biomaterials for orthopaedic prostheses require the same morphology in order to phenomenologically reproduce the same dynamic behaviour. 相似文献
| – | the matrix (collagen) is in a glassy state at physiological temperature; |
| – | the filler (apatite) increases the static modulus; |
| – | the interfaces/interphase (non-collagenous proteins and particularly proteoglycans) ensure cohesion and ductability for the composite. |
3.
| 1. | A method was developed for transforming quasilinear equations of viscoelasticity constructed on the basis of the strain summation principle. |
| 2. | It was shown that a simplified variant of the equations containing two creep kernels can be used to describe experimental data. |
| 3. | The structure of the relations that were obtained shows that, as in the linear theory of viscoelasticity, equations having resolvent creep operators are the simplest to transform. |
4.
M. Arita 《Strength of Materials》1976,8(11):1274-1280
| 1. | The energy absorption by a ship damaged as a result of a collision can be found by static experiment, and the effect of the collision velocity on energy absorption can be corrected in accordance with the increase of the material constant due to the enhanced strain rate. |
| 2. | There exist two fracture mechanisms during collision: one called piercing fracture mode, the other called crushing fracture mode. |
| 3. | During crushing fracture mode the energy absorption is large until fracture of the side skin but then decreases catastrophically. |
| 4. | During piercing fracture mode energy absorption continues to increase, roughly in proportion to the, square of the penetration depth, even after fracture of the side skin. |
| 5. | From the viewpoint of energy absorption during collision, a structure preventing fracture of the piercing mode is more suitable in the case of large critical values of the penetration depth than a structure preventing fracture of the crushing mode. One can change the mode of fracture by varying the dimensions of the deck plates and the side skin and of the stiffeners used in the structure. |
| 6. | In the presence of a scale factor the load and energy absorption in the penetration depth function are proportional to 2 and 3, respectively. |
5.
| 1. | Singular elements with a notch of an arbitrary angle were constructed to determine the stress fields near through notches. |
| 2. | 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. |
| 3. | 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. |
| 5. | 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. |
6.
| 1. | Steel strengthened by phase work-hardening is distinguished by a ratio of fatigue limit to tensile strength (–1/u=0.55–0.60) significantly greater than that of dispersion hardening steel. |
| 2. | The surface treatment method (grinding, turning, surface plastic deformation to a definite intensity) does not have a significant effect on the fatigue strength of N26T steel strengthened by phase work-hardening. |
| 3. | Combined strengthening of phase work-hardenable steel by surface plastic deformation, which causes the formation of 15–25% phase on the surface, and subsequent aging at 350–400°C is an effective means of increasing life. The use of this method makes it possible to increase the fatigue limit by 20% for uniform cross section samples and by 200% for those with a notch. |
| 4. | The increase in the fatigue limit with the use of combined strengthening (surface plastic deformation and aging) is related to the increase in the strength of the surface layers as a result of the increase in the dislocation density and fixing of them by the particles of Ni3Ti precipitated in aging and also to the decrease in peak microstresses. |
7.
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. |
8.
T. B. Buzovkina A. N. Sofronkov L. I. Korolenko S. A. Lyaskovskii I. A. Kuznetsova 《Materials Science》1993,28(4):354-358
| 1. | Unstable peroxides are formed when sea water reacts with a nonpassivating steel surface, which results in passivation. |
| 2. | The pH shifts as far as 13 in sea water in a real static crack in 15KhN5 steel, which is accentuated as the stress level increases, the crack lengthens, and the tip is approached. |
| 3. | The alkalinization in sea water above steel turnings is much less than in a crack but the pH dynamics are the same. |
| 4. | Metabolites from aerobic fouling organisms (bicarbonates and oxygen) retard the decomposition of hydrogen peroxide at the surface, which raises the pH and Eh; the metabolites from aerobic bacteria (hydrosulfides) reduce the hydrogen peroxide concentration, which reduces the pH and Eh. |
| 5. | The hydrogen release overvoltage is reduced on peroxide films on steel surfaces of 15KhN5 type, and the cathodic reaction of depolarizer reduction is retarded. |
9.
Dimitris Manolopoulos Pavlos Dimitratos Stephen Young Spyros Lioukas 《Management International Review》2009,49(1):43-60
| • | The purpose of this study is to investigate the influence of two categories of sources of technology on subsidiary performance. These technology sources can be associated either with the internal Multinational Enterprise (MNE) system; or, the local environment in which the subsidiary is based. |
| • | A questionnaire-based survey was carried out on 88 subsidiaries located in Greece and results were derived through the use of ordered probit analysis. |
| • | Internal MNE technology sourcing has a positive impact on subsidiary performance, which is stronger than that of local (Greek) technology sourcing. Contrary to our expectations, technology sourcing linked to the local context primarily has a negative influence on subsidiary performance. |
10.
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. |
11.
M. N. Georgiev N. Ya. Mezhova E. M. Morozov V. A. Reikhart 《Strength of Materials》1988,20(9):1133-1138
| 1. | It was establised that crack resistance limit Ic determined in full-profile nonheat-treated rails with cross fatigue cracks of area 10...30% of the rail head cross-sectional area is practically constant. The breaking stress c in all the cases is lower than the elastic limit c of the materials, in view of which, its crack resistance limit can be considered as a critical coefficient of the stress intensity for a plane deformed state, i.e., IcKIc. |
| 2. | For the non-heat-treated rails P65 with cross fatigue cracks (defect-21) KIc=37.5 MPa m. |
| 3. | The KIc values determined in full-profile non-heat-treated rails with cross fatigue cracks of area 10...30% of the rail head cross-sectional area practically does not differ from the results obtained as per GOST 25.506-85 in specimens taken from the same rails. |
| 4. | The KIc values for the non-heat-treated rails P65 with cross fatigue cracks decrease on the average by 40% for a test temperature drop from –253 to –333°K. |
12.
L. N. Molchanov 《Strength of Materials》1976,8(6):651-655
| 1. | In choosing a type of steel for conditions involving repeated impacts, it is essential to allow for the reliable working reserve of the structure or the constituent elements subjected to this loading. |
| 2. | The external form of the fractures enables us to determine the character of the breaking load. For static and single impact loading there are three zones of plastic yield situated on the three sides of the cross section (a part from the notch side). Under conditions of repeated impact loading, a fatigue crack necessarily arises, together with only two zones of plastic yield (on the vertical sides of the cross section). The area of the zones of plastic yield is much smaller than in the first two cases of loading and depends on the value of Aim. |
| 3. | By considering the form of the fracture surface we may judge the number of loading cycles. For a small number of cycles and a high impact energy, the final fracture zone occuples a large area, the cross section has an undulating structure, and the zones of plastic yield are considerable. For low impact energies the area occupied by the fatigue crack is greater, the final fracture less undulating, the zones of plastic yield smallish, the front of the fatigue crack directed with its convexity upward, and the relaxation lines more sparsely evident. The fractures confirm that for large impact energies the fracture bears a quasistatic character and for small energies, a fatigue character. |
| 4. | After 5·104 cycles and static completion of the fracture by bending all the samples had macro-or microfatigue cracks, so that the breaking load and the work required to complete the fracture by bending diminished. |
13.
| 1. | The optimum design theory was used to derive equations for optimizing the stress-strain state in the thick-walled pipe with the elasticity modulus varying along the radius and loaded with the internal pressure. |
| 2. | A numerical method of determining the law of the optimum distribution of the elasticity modulus along the radius of the thick-walled pipe was proposed. |
| 3. | The results show that by corresponding changes of the elasticity modulus in the given range along the pipe thickness it is possible to reduce the maximum annular stresses on the internal surface of the pipe. This stress reduction in a ratio expressed in per cent is approximately equal to the variation range of the elasticity modulus. |
| 4. | The minimum annular strains were recorded in the homogeneous pipe produced from the material with the maximum possible elasticity modulus. |
14.
A. Ya. Krasovskii I. V. Orynyak A. V. Naumov V. N. Krasiko 《Strength of Materials》1989,21(5):585-590
| 1. | The flexibility of the contact-zone/block system is determined experimentally from impact tests. In the case when high loading rates are used and massive specimens are tested, plastic deformations develop in the contact zone; this leads to effective values on the low side. |
| 2. | The duration and total amplitude of the resultant KI-t and P-t curves for supportfree tests are determined primarily by the flexibility of the specimen, while their character (the number of peaks, and their amplitude) is determined by the ratios of the flexibilities of specimen and block. |
| 3. | A method of calculating KI for a support-free impact loading is theoretically substantiated and experimentally confirmed. |
| 4. | During the impact testing of specimens on supports, separation of the specimen from the supports occurs at the initial time, i.e., these tests are actually support-free at the initial time. The moment of repeated contact between the specimen and the supports of the impact-testing machine corresponds approximately to time required for the force to reach the local minium. |
15.
| • | Both scholars and practitioners have paid much attention to the impact of retaining top-performing knowledge workers on organizational effectiveness. |
| • | This study hypothesizes and analyzes how a bundle of high-commitment human resource practices (HCHRPs) influence affective organizational commitment, a strong predictor of employee turnover, of top performers versus ordinary employees. |
| • | This study suggests that HCHRPs may enable organizations to retain not only ordinary employees but also top performers through their positive impact on employees’ organizational commitment. |
| • | Using a sample of middle level managerial and R&D workers in 11 subsidiaries of a multinational conglomerate located in East Asia, this study showed that a bundle of high commitment human resource practices was positively related to the affective organizational commitment of top performers more than that of lower performers. |
16.
E. I. Nesis 《Journal of Engineering Physics and Thermophysics》1991,61(1):934-939
| 1. | The process of effervescence of liquids consists of three successive stages with different regimes of operation of active centers, intensities of heat transfer, and characters of the temperature and acoustic fields. |
| 2. | The heat-transfer coefficient increases continuously during the entire period of effervescence, and at the boundaries of the stages its rate of growth increases abruptly, i.e., aIII>aII>a. The markedness of this effect depends directly on the magnitude of the heat flux q. |
| 3. | The bubble-formation processes observed during the second and third stages of effervescence are distinguished by the composition and detachment rate of the bubbles — in the region II they are gas-vapor bubbles and in the region III they are purely vapor bubbles; the detachment rate fIII is more than an order of magnitude higher than fII. |
| 4. | All stages of effervescence are accompanied by acoustic emission, but the character of this emission (loudness, spectrum, timbre) differs significantly in them. This makes it possible to employ the acoustic methods for remote control of the process of effervescence and the intensity of heat transfer between the heater and the adjoining liquid. |
17.
| • | 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. |
18.
Laszlo Tihanyi Robert E. Hoskisson Richard A. Johnson William P. Wan 《Management International Review》2009,49(4):409-431
| • | 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. |
| • | Results indicated a curvilinear relationship (an inverted U-shape) between technological competence and international diversification. |
| • | In line with agency theory, contingent pay (stock options and bonuses) was positively related to international diversification. |
| • | Beyond these direct effects, both contingent and non-contingent pay (cash compensation) moderated the relationship between technological competence and international diversification. |
19.
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. |
20.
| 1. | An algorithm was developed which employs a finite-elements method to solve problems characterized by large dimensions. The algorithm makes it possible to determine the stress-strain state of GTE rotors and to evaluate their load-carrying capacity. |
| 2. | The proposed method of formulating boundary conditions from the results of calculations performed for the assembled rotor makes it possible to determine the stress-strain state of the individual elements with allowance for their interaction. |
| 3. | The results of calculations for the assembled rotor can be used to reliably determine the clearances in the seals. |
| 4. | To reduce the bending strains in cantilevered disks, it is recommended not only that sloping disks be used, but also that the body of the disks be offset relative to the rim. |