Unified model of nucleation and growth of fatigue cracks. Part 1. Use of force parameters of fracture mechanics of materials in the stage of crack nucleation

According to the phenomenological model of nucleation of a fatigue macrocrack, the process is considered as a two-parameter process. The process is described by the local stress or strain range and a certain linear parameter of the material. We propose the corresponding parameters, namely, the local stress range Δσ _y ^* and the characteristic sized ^* of the prefracture zone. The formation of this zone is caused by the anomaly of the yield strength of the material in subsurface layers, the microstructure, the loading amplitude, the cyclic strain hardening, and the environment. The quantityd ^* is a constant of the material, which is independent of the geometry of notch and specimen. the boundary of the prefracture zone is considered as a macrobarrier that determines the growth of microstructurally short and physically small cracks. The moment when a physically small crack oversteps the boundary of the prefracture zone is defined by the quantitative criterion (a ₀=d ^*) of the initial sizea ₀ of a macrocrack in the material. The proposed dependences of (Δσ _y ^* ,N _i ),N _i ) and (d ^*,N _i ) can be regarded as a basis for the determination of characteristics of resistance of the material to the nucleation of a fatigue macrocrack. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 34, No. 1, pp. 7–21, January–February, 1998.     

Study of the law of corresponding states of viscous properties of classical liquids

The law of corresponding states is studied for the coefficients of shear η* _S and volume η* _V viscosities of classical liquids (Ar, Kr, Xe, O₂, N₂, CH₄); the analytical expressions are derived on the basis of kinetic equations for one- and two-particle distribution functions. The reduced iso-frequency coefficients Φ(|r|) and g(|r|) for liquid Ar, Kr, Xe, O₂, N₂, and CH₄ are numerically calculated in a wide range of variations at the reduced temperatures T* and densities ρ*, which satisfy the law of corresponding states, at a definite choice of the intermolecular interaction potential η _S * and radial distribution function η _V *.     

Theory of magnetic cooling of a class of model paramagnets

We have recently conjectured within the framework of the approximate mean-field formalism a cooling process on adiabatic demagnetization of antiferromagnetic systems from accessible initial paramagnetic states of entropyS _i , applied external uniform constant magnetic field strengthH _i , and temperatureT _i , to paramagnetic final states of coordinatesS _f S _i ,H _f H _c , andT _f <T _c (0) orTT _c (0). HereT _c (0) is the spontaneous critical ordering temperature of the system in the absence of magnetic field, andH _c is its critical internal magnetic field strength arising from the relevant fundamental interactions between its constituent particles or spins, which prevents it at all temperatures from undergoing its ordering transformation. In the present work, the above conjecture acquires solid foundation through the exact formalism at very low temperatures of the paramagnetic phase of magnetized, anisotropic, spin–12 systems subject to antiferromagnetic Ising interactions.Work performed under the auspices of U.S. ERDA.     

Investigation of Near-Critical States of Molybdenum by Method of Isentropic Expansion

In this work release isentropes of shocked porous molybdenum were investigated. Samples with an initial porosity m = ρ₀/ρ = 1.4 and 3.1 were studied to achieve near-critical entropy states of metal after shock compression. Compressed samples were expanded into helium with different initial pressures. The brightness temperature of the metal and the helium shock wave velocity were measured with a fast multichannel pyrometer. The helium shock wave velocity was used to determine the final pressure (P_S) of expansion of the metal and the velocity of metal expansion (W_S). Location of peculiarities on the P_S–W_S and P_S–T_P curves of the isentropes gives the location of their entrance into the two-phase region. Estimation of the molybdenum critical temperature and pressure was carried out on the basis of the experimental data. Paper presented at the Fifteenth Symposium on Thermophysical Properties, June 22–27, 2003, Boulder, Colorado, U.S.A.     

Coprecipitation of microamounts of radionuclides on chitosans of various molecular weights in solutions

Coprecipitation of ²³³U, ²³⁹Pu, ²⁴¹Am, ¹⁵²Eu, ⁹⁰Sr, ⁹⁰Y, and ⁶⁰Co on chitosans of various molecular weights (MW) was studied. Low-molecular-weight chitosan (LMWC) with MW of 5 kDa (5 × 10³ g mol⁻¹) proved to be a more effective coprecipitant than high-molecular-weight chitosan (HMWC) with MW of 700 kDa (7 × 10⁵ g mol⁻¹). With HMWC, the degree of coprecipitation (α) was 80% for ¹⁵²Eu and ⁹⁰Y, 99% for ²³³U and ²⁴¹Am, and 85% for ²³⁹Pu. For ⁶⁰Co, α monotonically increased with an increase in the chitosan concentration in solution and reached 40% at [HMWC] = 5 g l⁻¹. For ⁹⁰Sr, α did not exceed 3% in the entire examined range of chitosan concentrations. With LMWC, the α values for An, ¹⁵²Eu, and ⁹⁰Y differed insignificantly (92–99%). For ⁶⁰Co and ⁹⁰Sr, α increased to 40% in the range of chitosan concentrations from 0 to 1 g l⁻¹. The presence of inorganic salts in solution considerably decreases α of UO₂²⁺ with chitosans but does not noticeably affect the behavior of Am, Pu, and Eu. The effect of salts on the efficiency of ²³³UO^2/2+ coprecipitation on HMWC decreases in the order Na₂SO₄ > NaCl > Na₂CO₃ > NaNO₃ > Na₃PO₄. Based on the results obtained, a procedure suitable for expedition conditions was developed for preconcentration of Pu from seawater on chitosan, with simultaneous separation of Pu from U, for radioecological monitoring of natural waters. The specific activity of Pu in samples of near-bottom seawater of gulfs of the Novaya Zemlya archipelago was (150–170) ± 20 mBq m⁻³. The results are well consistent with the published data.     

The variation of thermoelastic properties under conditions of variation of isotopic composition of diamond

The parameters of interatomic interaction in diamonds of ¹²C and ¹³C isotopes are determined. The parameters are determined by two methods, namely, from the elastic modulus (potential no. 1) and from the sublimation energy at T = 0 K (potential no. 2). Based on these parameters, the Debye model is used to calculate the isobaric temperature dependences of the thermoelastic properties for isotopically different diamonds, namely, the coefficient of thermal expansion (CTE), the density, the elastic modulus B _T , and the specific heat capacity. It is demonstrated that the best agreement with the experimentally obtained dependences of the foregoing parameters is obtained when potential no. 1 is used in calculations. The values of CTE, density, and heat capacity increase in the case of transition from ¹²C diamond to ¹³C diamond. It is demonstrated that the inequality B _T (¹²C) < B _T (¹³C) is valid at T = 0 K, which is associated with the reduction of interatomic spacing in the case of transition from ¹²C diamond to ¹³C diamond. However, as the temperature increases, the volumetric isotopic effect in diamond decreases. It is found that the B _T (T) dependences for ¹²C and ¹³C diamonds intersect at a temperature below the Debye temperature. Therefore, at high temperatures, the elastic modulus for light-isotope diamond comes to exceed that for heavy-isotope diamond, B _T (¹²C) > B _T (¹³C). Experimental results are given which confirm this effect. The variation of the properties of isotopically different diamonds with increasing pressure is discussed.     

Estimation of the accuracy of measurements of the corrosion rate by the method of polarization resistance

The method of polarization resistance is extensively used for the determination of the rate of corrosion. At the same time, the accuracy of measurements of the corrosion rate performed with industrial corrosion meters is often not estimated. By using an indicator, we find the accuracy of the measurements of the corrosion rate for 20 steel placed in 1N H₂SO₄ and 0.01N Na₂SO₄ solutions and for 12Kh18N10T steel placed in 1N and 10N H₂SO₄ solutions.Kiev Polytechnic Institute, Kiev. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 31, No. 3. pp. 22–27, May–June, 1995.     

Comparative Assessment of Ambient Air Quality of Major Cities of Pakistan

The deterioration of ambient air quality is one of the emerging environmental problems in developing countries of South Asia. Unplanned urbanization, population growth, degradation of vegetation cover and industrial and vehicular emissions, particularly in urban areas, have resulted in substantial rise in the level of air pollutants and emission sources. This study focused on monitoring of different cities as per traffic volume and flow. Air quality monitoring was conducted on hourly basis to determine the major parameters; i.e. PM₁₀, NO_x, SO₂, CO by using fixed station for 8 h from 1:30 pm to 9:30 pm. All the measuring values were then compared with the National Environment Quality Standards (NEQS) and Air Quality Index (AQI). Results revealed that the concentration of PM₁₀ at the selected areas of these cities ranged from 156 to 390 μg/m³, CO ranged from 1.18 to 6.01 mg/m³, and NO_x ranged from 32.65 to 129.47 μg/m³. It was evident that all these concentration had been higher than the permissible limits of NEQS, whereas only SO₂ was found within the permissible limits (15.60–110.52 μg/m³⁾. Air Quality Index (AQI) of all the designated points of cities was also assessed, and most of the vehicular and commercial areas had shown unhealthy and severe conditions ranging from 191 to 320, respectively.

     

The Distribution of the Maximum Sum of Rank

In this paper a c-sample slippage analogue of the Wilcoxon [11] test is considered. Given a sample of size n for each of c populations, the test rejects the hypothesis that the c populations are identical when max_1≤i≤c σ _k r _ik > λ, where r _i1, …, r _in are the ranks of the observations from the i-th population in the combined sample of size cn. The small and large sample distributions of the test statistic are derived. Tables of the exact distribution are given for c = 2(1)5, n = 2(1)5. Tables of critical values are given for c = 2(1)6, n = 2(1)8 for values of α = 0.001, 0.005, 0.01, 0.025, 0.05, 0.10, and 0.20.     

Unified model of nucleation and growth of fatigue macrocracks. Part 2. Application of deformational parameters of the fracture mechanics of materials in the stage of crack initiation

We propose a new approach to the experimental estimation of local strains at the tip of a concentrator. The approach is based on the measurement of displacement of certain points in the vicinity of the tip of a notch, which is further associated with the effective radius of the notch. Various concentrators in structures are simulated within a wide range of variation in radii of notches (ρ=0.1−6.5mm) and in the geometry of specimens. We establish the main dependences between the value of the range of local strains Δɛ^* and the periodN _i prior to the nucleation of a fatigue macrocrack. Thus, by using the experimental quantity Δɛ^*, we can estimate the periodN _i prior to the nucleation of a fatigue crack of lengtha _i=d^* for structural elements of a complicated geometry. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv. Vol. 34, No. 3, pp. 55–66, May–June, 1998.     

Some New Aspects of Chlorination of Fullerenes

Abstract

The effect of the reagent ratio, reaction time and power of the reagent on the product composition in chlorination of [60]fullerene was studied. Chlorofullerenes C₆₀Cl₆, C₆₀Cl₈, C₆₀Cl₁₀, C₆₀Cl₁₂, C₆₀Cl₁₄, and C₆₀Cl₂₆ were synthesized and characterized by chemical analysis, FTIR, ¹³C NMR, and MALDI TOF mass spectrometry. The experimental data supported the coexistence of several isomers of C₆₀Cl _n (n = 8, 10, 12, 14, 26); the mixtures were not separated so far. Semiempirical calculations (AM1, PM3) were used to analyze the addition patterns and resulted in the most favorable structures of C₆₀Cl_8–26. Chlorination of C₇₀ under various conditions invariably yielded C₇₀Cl₁₀.     

Analysis of different approaches to the study of microelectrochemical heterogeneity of materials

We investigated systems of steel 20 with nickel and zinc coating in a 3% NaCl solution, distilled water, and a 45 · 10⁻³% H₂SO₄ + 0.14 H₂O₂ + 5 · 10⁻⁶% K₂Cr₂O₇ solution using capillary probes filled with these environments. After their use, errors in measurements in the volume of the electrolyte are absent. The low conductance of the electrolyte and the dissolution of the metal in the active state are necessary conditions for adequate measurements of local electrode potentials. It is established that the accuracy of local microelectrochemical measurements in an electrolyte drop is higher than that in an electrolyte film. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 44, No. 3, pp. 126–129, May–June, 2008.     

Methods for the construction of the diagrams of fatigue crack-growth rate of materials

We study different parameters used for the construction of the diagrams of fatigue crack-growth rate of materials in the force, deformation, and energy approaches and tested for 08kp low-strength steel and 60 high-strength steel. The applicability of the dependences known from the literature for the evaluation of the crack-tip opening displacement and local strain energy at the crack tip is analyzed. It is shown that the range of local strains Δε* and the total range of dissipation of local energy in a loading cycle ΔW _t * specify the fatigue crack-growth rate in the material and that the da / dN−Δε* and da / dN−ΔW _t * diagrams are more sensitive to the structural and mechanical characteristics of the materials than the ordinary da / dN−ΔK diagrams. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 43, No. 4, pp. 31–41, July–August, 2007.     

Determination of the rheological properties of whole blood by the nonstationary method of pulsed changing of the rate of shear

Problems associated with the use of the nonstationary method of pulsed changing of the rate of shear for the measurement of important viscoplastic properties of whole blood — the critical shear stress τ₀ and the plastic viscosity μ_p — are considered. The indicated method was compared to the method of stationary rheometry. It is shown that the blood-flow curve obtained by this method, unlike that obtained by the stationary method, characterizes a viscoplastic medium. To calculate the parameters of this medium exactly, it is necessary to take into account the dependence of the rate of shear on the above-indicated parameters. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 78, No. 5, pp. 176–179, September–October, 2005.     

Determination of the half-life of the spontaneous fission of240PU

Two metallic²⁴⁰Pu sources were certified as reference standards of spontaneous-fission activity and neutron flux. The certification results were used to determine the ratio T_&#x03B1;T_s&f of the alpha-decay and spontaneousfission half-lives of²⁴⁰Pu. The ratio was found to be (5.68&#x002B;-0.11)&#x00B7;10^&#x2212;8, which corresponds to T_s&f =(1.16&#x002B;0.02)&#x00B7;1011 yr for an assumed value T_&#x03B1;=6563&#x002B;7yr.Translated from Izmeritel'naya Tekhnika, No. 2, pp. 57&#x2013;58, February, 1995.     

Study of the kinetics of decomposition of goethitein vacuo and pore structure of product particles

The kinetics of decomposition of-goethite were investigated, under vacuum conditions, in the temperature range 170–250° C. The experimental thermogravimetric traces were interpreted according to the shrinking core model for cylindrical particles. The Arrhenius plot of InK (kinetic constant) against 1/T yielded an activation energy of 119±9 kJ mol^–1 at 210° C. The highest specific area,S _BET=118.4±5.5 m² g^–1, of the reaction product-hematite, was obtained by decompsition at 225° C. Information about the formation of micropores and their evolution with temperature was also obtained.     

Molecular dynamics calculation of thermal expansion coefficient of a series of rare-earth zirconates

To develop more reliable and stable thermal barrier coatings, low thermal conductivity materials with higher thermal expansion coefficients (TECs), like rare-earth zirconates (A₂Zr₂O₇, A = La, Nd, Sm, Eu, Gd, Er, Yb and Lu), have been the focus of a great deal of attention in recent years. But the mechanisms underlying the values of TECs are still poorly understood. In this paper, the TECs of a series of rare-earth zirconates are calculated using molecular dynamics. Two typical crystal structures, pyrochlore and fluorite, are considered. By investigating the potential functions and the equilibrium-location deviations between the atoms, it is found that the Zr–O bond is the most important factor that determines the overall TECs, and the A–O bond plays a secondary role. However, O–O has little effect on the TECs. In addition, the fluorite structure has a relatively higher TEC due to a weaker Zr–O bond. Calculated values are consistent with the experimental observations. Using the method presented in this study, two doped zirconates (Gd_0.4Sm_0.5Yb_0.1)₂Zr₂O₇ and Sm₂(Ce_0.3Zr_0.7)₂O₇ are designed and compared. As expected, both of them have higher TECs than undoped Sm₂Zr₂O₇, and doping at the A-site is more efficient than doping at the Zr-site.     

Effect of mechanical properties of material on rate of fatigue crack propagation

Many experimental and analytical equations on a rate of a fatigue crack propagation have been proposed. However, it seems that they can not fully express its complex behavior. There are still many problems remaining to be solved in order to clarify its mechanism. One of them is to clarify the relation between the rate of the crack propagation and the mechanical properties of material. In this paper, the rate of the crack propagation is analysed to clarify this problem. This analysis is based on the observation results of the fatigue crack propagation behavior previously by the authors. The analytical result is compared with the experimental one to make sure that they agree with each other. The conclusion obtained is; the rate of fatigue crack propagation is expressed by using the stress intensity factors as

$\text{dl}\text{dN}\text{= {}\text{c}\text{[Y}{}^2\text{F}{}^{\mathrm{a}}\text{E}{}^{\mathrm{a(1?n)}}\text{]}\text{} (K}{}_{\max }\text{)}{}^2\text{(K}{}_{\mathrm{a}}\text{)}{}^{\mathrm{a(2?n)}}$

. where C is a constant; E, Young's modulus; F, plastic coefficient; Y, yield stress; K_max and K_a, maximum and amplitude of the stress intensity factor, and α and n, exponents of the Manson-Coffin's law and work-hardening.     

Specific features of the interaction of alloys of the didymium-iron-boron system with hydrogen

We study the interaction of alloys of the Dd-Fe-B system [M-82, M-83, M-84, and M-85 alloys with a mass content of 33–40% didymium, up to 0.5% aluminum, and 1–1.25% boron (the rest is iron)] with hydrogen using volumetric, X-ray phase, and differential thermal analysis. If the initial hydrogen pressure is 1.0 MPa, hydrides with 0.4–0.6 mass % of hydrogen are formed. The saturation of these alloys with hydrogen is accompanied by an increase in the spacing a of an elementary cell by 1.2–1.4% and in c by 0.8–1.1% (the general increase in volume is 3.2–3.9%). If the initial pressure is 0.15–0.2 MPa, the time of complete saturation with hydrogen is 15–20 min for most alloys. At 973–1033 K, the alloys under study in hydrogen disproportionate into DdHx didymium hydride (a = 0.5449 – 0.5458 nm), -iron (a = 0.2864 – 0.2866 nm), and Fe2 B iron boride (a = 0.5112 – 0.5117 nm, c = 0.4228 nm). An increase in the initial hydrogen pressure from 0.1 to 5.0 MPa is accompanied by a decrease in the disproportionation temperature to 930 K.Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 40, No. 2, pp. 105–112, March–April, 2004.     

Control of microstructure of Fe-B microcrystalline materials

The correlations between hardness, microstructure and heat-treatment condition of Fe-B microcrystalline materials were systematically investigated. The means of controlling microstructure by adjusting composition and, thus, the type of boride was also explored. It was established that the grain size of the matrix phase was determined by the volume fraction of dispersive boride particles, and their size follows the formula: D _max = 4/3 r/f, and, in turn determines hardness which obeys the Hall-Petch relation: H _V = H _o + kd ^–1/2. It was also found that the size of the boride particles increases exponentially with increasing temperature and linearly with the fourth root of holding time. M₃B₂ has a lower coarsening rate than M₂B; therefore, promoting M₃B₂ and inhibiting M₂B is an effective measure to stabilize the microcrystalline structure under hot exposure.