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1.
Comparing the fracture toughness temperature curves evaluated at static and rapid loading on larger (SENB, 1CT) specimens with the fracture toughness curve determined on precracked Charpy specimens at impact loading, the following conclusions can be drawn:
Published in Fiziko-Khimiches-kaya Mekhanika Materialov, No. 3, pp. 54–60, May–June, 1992. 相似文献
| – | both rapid and impact loadings cause the shift of fracture toughness temperature curve to higher temperatures in accordance with the concept of critical tensile stress criterion; |
| – | the transition temperature region with brittle (cleavage) initiated fracture after some ductile crack growth is, at rapid loading, shifted to higher temperature as well; |
| – | at the impact loading of small PC specimens the whole transition region is reduced to one transition temperature only and therefore sharp increase from the lower shelf fracture toughness region to the upper one occurred. This ductile to cleavage initiation transition temperature is, in spite of the impact loading, lower than that of the larger 1CT specimens loaded at a much smaller loading rate; |
| – | for cleavage initiated fracture of low alloy steel only lower shelf fracture toughness values can be measured by employing the PC specimens and the impact loading. |
2.
V. T. Troshchenko V. V. Pokrovskii P. V. Yasnii V. G. Kaplunenko V. V. Burdakov V. P. Leonov Yu. A. Nikonov 《Strength of Materials》1988,20(9):1138-1145
| 1. | On the basis of the experimental investigation of the effect of the test temperature (153–293°K) on the rate of FCG in steels IP-1, IP-2, and IP-3 with a coefficient of load cycle asymmetry R=–2, –1, 0, and 0.5 it was established that lowering of the test temperature has an ambiguous effect on the rate of fatigue crack growth in the mentioned steels. In most cases the rate of FCG is practically insensitive to the test temperature although we can see a general tendency of the coefficient m of the Paris equation increasing with the test temperature being lowered from 293 to 153°K. |
| 2. | A change of the coefficient of load cycle asymmetry in the range –2–0 does not have a substantial effect on the rate of FCG, and in the range 0–0.5 it reduces this rate (in coordinates d/dN-Kmax) at 213 and 293°K, particularly substantially at 213°K. |
| 3. | For the investigated chrome-nickel-molybdenum steels in the temperature range 293-153°K a single dependence was established; it describes the decrease of the coefficient m with rising level of fracture toughness under static loading. |
| 4. | With the test temperature rising from 113 to 153°K, the characteristics of fracture toughness of all the investigated steels increase monotonically under static and cyclic loading, and also in the case of stopping of the crack. |
| 5. | Cyclic loading reduces substantially (to one half) the fracture toughness of steels IP-1 and IP-2 in the temperature range 113–153°K and does not change the values of K1 fc compared with KIc for steel IP-3. |
| 6. | In steels IP-1, IP-2 at temperatures of 113–153°K the fracture toughness under cyclic loading corresponding to final fracture of the specimen practically coincides with the fracture toughness at the instant of stopping of the crack. |
| 7. | In the temperature range 100–183°K of the three investigated steels steel IP-1 has the highest resistance to brittle failure under static loading and at the instant of stopping of the crack, steel IP-2 has the lowest resistance. |
3.
A. Ya. Krasovskii V. A. Makovei G. N. Nadezhdin V. L. Svechnikov G. V. Stepanov 《Strength of Materials》1988,20(2):137-142
| 1. | The velocity dependence of dynamic fracture toughness can be evaluated by the method of quantitative stereoscopic fractography within a broad range of loading rates. |
| 2. | For steel 40Kh the ascending branch of the velocity dependence of KId is determined by fragmentation of the structure causing ramification of the crack which, in the final analysis, increases fracture toughness. The reduced size of the microcrack in fragmentation is directly connected with the weakening of the dependence of crack resistance on the loading rate [19], which in our experiments corresponds to the range of impact speeds of 300–600 m/sec. |
| 3. | Removal of microsegregations from the boundaries forming upon fragmentation of blocks in the structure (by means of diffusion) increases the surface energy of such boundaries, impedes the formation of microcracks on them, and consequently increases fracture toughness. |
4.
J. Davidov 《Materials Science》1993,28(1):62-67
| 1. | With respect to low-cycle fatigue behaviour the increasing of iron quantity from 0.12% to 0.38% results in a decrease of cyclic ductility of AlSi7Mg alloy but this decrease is not very significant. |
| 2. | The alloy with 0.12% Fe shows better low-cycle fatigue resistance then other materials investigated due to its relatively higher cyclic ductility. |
| 3. | The structure with 0.29% Fe shows the best fatigue crack growth resistance which is due to the best combination of its mechanical properties and relatively ductile type of fracture. |
| 4. | With regard to the low-cycle fatigue behaviour and fatigue crack growth resistance investigations carried out in this work have shown AlSi7Mg alloy with 0.29% Fe seems to be the most appropriate material for manufacturing counterpressure cast car wheels of the particular design investigated because the decrease of cyclic ductility for this structure is not very significant. |
5.
I. D. Abushenkov A. I. Alekseev V. Ya. Il'ichev N. I. Mokryi A. I. Telegon V. K. Chernetskii 《Strength of Materials》1988,20(5):698-702
| 1. | Equipment was developed and the test procedure proposed for fracture toughness testing compact specimens of structural materials in off-center loading at low temperatures down to 4.2°K. |
| 2. | The strain gauges and dynamometer operating-directly in the cryogenic liquids were produced and calibrated at various temperatures. These devices can be used to record the (P–V) and (P–f) diagrams during testing. |
| 3. | Preliminary tests were carried out on the specimens of 03Kh18N16G4A and 03Kh18N6G4 steels at 300, 77, and 4.2°K. The cracking resistance of the tested specimens at 4.2°K was evaluated on the basis of the values of KIc whereas the parameters KQ and K C * were used for evaluation at 77 and 300°K. |
| 4. | The results show that 03Kh18N16G4A steel at 4.2°K has the optimum high values of both the yield stress (1600 MPa) and fracture toughness (104 MPa·m1/2). Having relatively high values of 0, 2 (1400 MPa), 03Kh18N6G4 steel has at 4.2°K unacceptably low freacture toughness parameters indicating that the steel fails by brittle fracture in these conditions. |
6.
| 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. |
7.
| 1. | In the presence of longitudinal cracks of varied length (40–160 mm) and varied amount of elastic energy of the compressed air model (1400–9400 kgf·m) the failure of models on thin-walled shells 0.5 mm thick, when loaded by an internal pressure, has a ductile character, independently of the fitting of transverse tires located at different distances from the crack tip (from 20 to 105 mm). |
| 2. | As the initial length of crack increases, its subcritical growth in thin-walled shells increases linearly. |
| 3. | As the crack length increases, the failure stress (gross) is substantially reduced (from 22 to 9 kgf/mm2). At the same time the character of failure is altered: a straight-line propagation of the crack along the generator of the cylinder is replaced by a curvilinear propagation that approximates the failure direction to the circumferential direction. |
| 4. | With a reduction by a factor of two the amount of elastic energy contained by the compressed air model has almost no effect on the strength and geometrical features of the fracture. A dominant effect on the character of fracture is exerted, apparently, by the magnitude of the failure pressure which alters the relationship of the velocities of propagation of the crack and the waves of elastic unloading. |
| 5. | The limitations on the applicability of the existing calculation methods of the fracture mechanics, for the estimation of the resistance to a ductile failure of thin-walled cylindrical shells, is revealed, and appropriate corrections are proposed. |
| 6. | The effectiveness of the use of transverse tires to stop a started ductile failure of shells loaded by an internal pressure, depends on the distance between the tire and the vertex of the initial crack. This distance leads to a transition from the stoppage of the moving crack to its direction being altered. |
8.
A. V. Prokopenko Yu. K. Petrenya V. N. Ezhov I. A. Makovetskaya M. M. Ivakhov 《Strength of Materials》1989,21(1):39-43
| 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. |
9.
N. M. Grinberg V. A. Serdyuk A. M. Gavrilyako V. A. Zolot'ko E. L. Miloslavskaya L. E. Gorelkova 《Strength of Materials》1989,21(7):859-865
| 1. | In the AMg6 aluminum alloy the fatigue crack growth rate at 293 K decreases as compared with the same value in air and parameters Kth and K* increase in vacuum. |
| 2. | With a temperature drop from 293 to 140 K the fatigue crack growth rate decreases especially at low Kmax values, while the Kth and K* values increase. |
| 3. | Each region of the kinetic diagram of fatigue fracture is characterized by a definite micromechanism of fatigue fracture which for the investigated alloy does not change in vacuum even at temperatures falling to 140 K. |
| 4. | On the basis of the dependence of groove pitches on Kmax for the AMg6 alloy in region II of the kinetic diagram of fatigue failure, coordinates K* and A of the transition point which divides this region into sections IIa and IIb were determined. Ordinate A=SIIa does not depend on the medium and temperature and is for this alloy (1.8–2.0)·10–7 m. |
| 5. | Since K* is an important practical characteristic of cyclic crack resistance, the experimental method of its determination must be based on recording the transitional character of one of the physical processes taking place in this point. |
10.
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. |
11.
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. |
12.
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. |
13.
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. |
14.
| 1. | Sheets of the Zr- 1% Nb alloy were used for the first time to show by experiments the crystallographic reorientation of the grains at the tip of the moving crack. |
| 2. | The effects detected by x ray diffraction examination in the vicinity of the fracture of the specimens with the notch, were compared with the effects recorded in the volume of similar smooth specimens subjected to tensile loading. According to the estimates, in the layer up to 20m thick, adjacent to the fracture surface, the average strain of the material in tensile loading is 15–20% for the RD specimen and 3–5% for the TD specimen. |
| 3. | Anisotropy of the cracking resistance and development of the zone of plastic deformation at the tip of the moving crack are determined by the activating mechanism of plastic deformation of alpha zirconium whose special feature is the strong dependence on the crystallographic orientation of the grains. |
15.
I. M. Rozenshtein 《Materials Science》1992,28(5):421-424
| 1. | The critical temperature of arrest of brittle cracks can be interpreted as a partial case on the critical temperature of brittleness in crack initiation. |
| 2. | A method of determining the correlation between the CTABC and the critical brittleness temperature at crack initiation was determined. |
16.
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. |
17.
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. |
18.
B. N. Sinaiskii M. S. Belyaev N. D. Zhukov A. D. Panteleev 《Strength of Materials》1989,21(3):322-329
| 1. | It was shown that heat-resistant nickel alloys subjected to high-cycle loading under conditions of thermal activation undergo fatigue damage and fracture with the participation of the micromechanisms characteristic of creep. This provides grounds for describing high-cycle fatigue characteristics at elevated temperatures and large endurances by means of temperature-time relations used to describe rupture strength and creep. |
| 2. | Experimental data on the high-cycle fatigue strength of heat-resistant nickel alloys ÉI867, ZhS6U, and VZhL12U in the range of service temperatures (three-five levels of temperature) and the endurance range 104–109 cycles was analyzed on a computer. The analysis showed that the mean values of the above characteristics are satisfactorily approximated by the Larson-Miller, Scerby-Dorn, and Manson-Saccup parametric methods and the temperature-time relation for strength within the temperature range above the threshold value (Tth0.55–0.6Tmt). |
| 3. | The investigated parametric methods describe experimental results with different degrees of accuracy and require preliminary evaluation to determine their applicability for a given case. The equation used here which expresses the temperature-time dependence of strength proved to be stable in approximating the above-examined experimental data. |
19.
| 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. |
20.
| 1. | Multiple regression analysis was used to determine a strong correlation between the composition and physicomechanical characteristics of the high-manganese steel alloyed with boron and vanadium. |
| 2. | The correlation of abrasive and impact-abrasive wear resistance with each mechanical characteristic is very weak and in certain cases does not exist at all. |
| 3. | A correlation was found between each type of wear and the remaining characteristics. Abrasive resistance can be increased only by increasing hardness and impact-abrasive wear resistance can be increased by increasing hardness and bending strength. Impact toughness has no effect on wear resistance in both types of wear. |