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1.
| 1. | The described general method of designing structural elements (a type of thin nonsloping shell of revolution) under cyclic loading, which has been approved for the case of a spherical notched shell, is effective, and can also be employed for other types and shapes of thin-wall designs of constant or variable thickness. |
| 2. | Stabilization of the stress state during cyclic loading is heavily dependent on the applied-loading rate and occurs (according to the results of the design and experiments under consideration) during the 2–10th loading cycle for a load range of 10q25 kg/cm2. |
| 3. | As the loading in the shell increases, the stress concentration diminishes from a value k=3.5, which corresponds to the elastic state, to 1.3 at which point the strain concentration reaches a maximum value with q=15 kg/cm2 for the material in question, and then decreases; this is associated with the transition of the shell into the plastic state. These results can be used to evaluate the low-cycle strength of standard structural elements, and to determine the factors of safety and the bearing capacity under cyclic loading. |
2.
| 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. |
3.
| 1. | In dependence on the strain-hardenability of material determined by the type of crystal lattice, the test temperature, by alloying and work-hardening, loss of stability may cause either strict localization of deformation in the neck or smooth transition from uniform deformation to concentrated deformation in static tension of a smooth cylindrical specimen. |
| 2. | In compression, torsion, bending, tension in a state of plane stress and other kinds of tests, the margin of strength of the part and its technological and design strength are determined chiefly by the magnitude of the ratio of yield strength to true tensile strength (and not ultimate tensile strength), and also by the magnitude of relative contraction, i.e., by parameters characterizing the capacity of material to the nucleation and development of flaws in it under plastic deformation. |
| 3. | Uniform deformation and the magnitude of the ratio 0.2/u play an important role in ensuring the load-bearing capacity of a structure, in particular, when cylindrical parts are subjected to tensile loads. In that case loss of stability of uniform deformation leads to reduced strength of the part, and essentially it is the onset of failure. |
4.
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. |
5.
| • | This paper examines the conditions under which corporate social responsibility (CSR) is related to value creation in the multinational enterprise (MNE). |
| • | Following prior work by Burke and Logsdon (1996), we examine the relationship of centrality, appropriability, proactivity, visibility, and voluntarism to value creation. |
| • | The results of a survey of 111 MNEs in Mexico suggest that centrality, visibility, and voluntarism are related to value creation. |
6.
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. |
7.
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. |
8.
| 1. | The dependence of the growth rate of a fatigue crack on the stress intensity coefficient at the tip of the crack is described by an exponential function of the da/dN=CKn type for all zones of a welded joint. For a given applied stress and realizable values of K the index n in this function has a constant value, differing for each particular zone. |
| 2. | The instantaneous and average crack velocities reach their maximum values in the heat-affected zone and their lowest values in the seam metal. The crack growth rate in the parent metal is close to that in the heat-affected zone. |
| 3. | The fatigue life of a weld subjected to cyclic (fatigue) loading may to a first approximation be estimated by the n and C values of the parent metal. |
9.
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. |
10.
V. T. Troshchenko P. V. Yasnii V. V. Pokrovskii Yu. V. Tkach 《Strength of Materials》1988,20(10):1281-1286
| 1. | Fatigue crack propagation between the brittle jumps consists of the incubation period, during which the crack length is constant, and the period of continuous crack growth in which the crack propagates in each cycle. |
| 2. | With increasing maximum SIF of the cycle the duration of the incubation period and of the period of continuous FCP decreases. Depending on the ratio of the crack extension between the brittle jumps l y and continuous crack extension l c in the block, we can determine the following sections: l y/l c>1; l y/l c=1; l y=l c=0. |
| 3. | Stable fatigue crack propagation in 15Kh2MFA steel between the brittle jumps takes place as a result of fatigue damage cumulation. |
11.
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. |
12.
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. |
13.
| 1. | The strength of an unnotched specimen after both natural and artificial aging is higher in biaxial tension than in axial and for both structural conditions is 1.12t of the material. |
| 2. | The sensitivity of the material to these stress raisers in axial tension is revealed more strongly for D16T1 alloy and is 0.9t of the material while in biaxial tension for both structural conditions is greater than t of the material (1.04–l1.16t). |
| 3. | In axial and biaxial (2/1=0.5) tension of sheet in the plastic area the rivet body does not participate in deformation of the material all the way to failure of it (Fig. 2). |
| 4. | It was established that in both methods of loading the presence of a rivet both without and with interference leads to redistribution of the deformed condition, and the lower the plasticity of the material, the more sharply it occurs. For example, for D16T1 alloy the curve of the deformed condition on the edge of the rivet has the minimum value (Fig. 1), and for D16T alloy the maximum. |
14.
G. S. Neshpor V. P. Gusev G. D. Kudryavtseva M. I. Zhukova A. D. Petrov 《Strength of Materials》1989,21(8):998-1004
| 1. | In a plate of alloy 1163T the mean rates of fatigue crack growth increase from 3.2 to 8.6 mm/kc with when the thickness of the specimens increases from 3 to 15 mm, and the characteristics of static crack resistance attain their maximum when the thickness of the specimens is t* (KIc/0.2)2 10 mm. |
| 2. | With increasing thickness of the specimens, the pitch of the fatigue grooves and the proportion of elements of static failure increase in the fatigue fracture. In a static fracture there is failure by shear, intragranular pitting and ductile grain boundary failure, and with increasing thickness of the specimens the proportion of grain boundary (low-energy) failure increases. |
| 3. | The transition from plane strain to plane state of stress is effected in the region of increase of crack length equal to the thickness of the specimen. |
15.
| 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. |
16.
| 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
17.
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:
18.
19.
M. Arita 《Strength of Materials》1976,8(11):1274-1280
20.
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:
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