Long-term Strength Characteristics Research Articles

Changes in the physicomechanical characteristics of VT14 titanium alloy in the process of long-term loading

We study the influence of long-term loading on the behavior of physicomechanical characteristics of VT14 high-strength titanium alloy. The long-term holding of specimens (up to 21 yr) under loads close to the fracture load confirmed the stability of the long-term strength characteristics of the material.

Strength, Durability, and Safety of Engineering Systems

The evolution of approaches to the solution of machine dynamics and strength problems on the basis of determining static and dynamic nominal and local stresses of the operating load is discussed. It is shown how the material strength and plasticity characteristics, the cyclic strength characteristics in the high-cycle and low-cycle fatigue regions, the high-temperature long-term strength and creep characteristics, and the linear and nonlinear characteristics of fracture mechanics were sequentially used as the basic criterial parameters of the deformability and strength of structural materials. Particular emphasis was given to the results of studies on machine safety and catastrophe mechanics. Integrated approaches to the solution of strength and safety problems of potentially dangerous facilities (nuclear power stations, spacecraft complexes, aircraft, chemical plants, etc.) by analysis of all stages of their life cycle, including design, manufacture, testing, and operation, are discussed.

Dependences of the characteristics of creep and long-term strength on the cross-sectional dimensions of specimens

We analyze the available experimental data according to which a decrease in the cross-sectional dimensions of specimens leads to a significant increase in the creep rate and a decrease in the service life. This sclae effect is explained by the corrosion fracture of the surface layers of a metal. We propose a procedure for the phenomenological description of these data based on the concept of Rabotnov. According to this procedure, we consider two time-dependent kinetic parameters, namely, the thickness of a destroyed surface layer and the degree of damage to the material distributed over the remaining part of the cross section. It is shown that the application of proposed equations to the analysis of the experimental data significantly (by a factor of 3–12) decreases the overall discrepancy between the experimental and theoretical characteristics of creep and long-term strength as compared with the use of the standard equations in which the scale effect is neglected.

Corrosion resistance of austenitic steels and alloys in high temperature water

An ampoule corrosion tests technique is presented for making a comparative corrosion-proof estimation of austenitic steels and alloys which are candidate materials for the ITER first wall and shield blanket. Influence of Cl − on the rate and character of corrosion cracking has been determined. The dependence of time before destruction on Cl − contents was obtained by experiments in twice-distilled water at a Cl − content value of less than 0.05 mg/l. Kinetics of a corrosion crack growth has been determined by way of acoustic emission and measurement of electrical resistance. It has been revealed, that corrosion cracking of 316L and 316Ti steels in water with 100 mg/l of Cl − takes place at temperatures over 50°C. For 316L (Russian analogue), 316Ti, 08Cr18Ni10Ti (type 304), 00Cr16Ni15Mo3Nb (type 316) steels and CrNiMo-1 (42–47%Cr, 1%Mo, Ni-base) alloy corrosion long-term strength and crack-resistance characteristics were obtained. Results of tests show, that corrosion characteristics are near the same for all austenitic steels under investigation with CrNiMo-1 alloy being the exception. It was not destroyed during ampoule tests.

Characteristics of the long-term static strength of monocrystalline materials

The use of simplified methods for determining the long-term static strength characteristics within the assigned temperature and durability ranges is considered. An equation which describes by means of a unique parameter the scattering of long-term static strength characteristics of monocrystalline materials with different orientations under tensile stress is derived.

Prediction of the full operating life of steam pipe materials in heat and power enginering

1. The methods of linear summation of relative durabilities in the form discussed above cannot be used for solving problems pertaining to the remaining life without suitable modifications. 2. In using the long-term strength characteristics of a material in the initial state or after prolonged operation, only the time to failure of specimens, rather than the remaining life of the material in structural elements, is determined, regardless of the method employed to obtain a solution. For transition from the heat-resistance characteristics determined experimentally on specimens to the heat-resistance characteristics determined on structural elements, it is necessary to determine or postulate the safety factors on the basis of the generalized experience gained in operation. There are no recommendations to this defect at present. 3. The most economic and reliable way of finding the remaining life of the material in a structural element is to determine it after prolonged operation, using continuous data on the increase of remanent strain and the creep rate, obtained from tensometric measurements directly on the structural elements (steam line pipes).

Effect of nitrogen and heat treatment of the structure and properties of high-temperature steel 31Kh19N9MVBTL

1. Alloying steel 31Kh19N9MVBTL with 0.07–0.13% nitrogen excludes the possibility of forming σ-phase, causing embrittlement and leading to cracking, from ferrite. 2. Short-term and long-term strength characteristics for steel alloyed with nitrogen are 10–15% higher than for steel without nitrogen at normal and operating temperatures. Ductility and impact strength for steel with nitrogen, although somewhat lower than for steel without nitrogen, all the same satisfy the TU specifications. 3. Austenitizing at 1200–1220°C both for steel without nitrogen, and alloyed with nitrogen, provide higher mechanical properties than austenitizing at 1180°C.

Parametric methods of describing and extrapolating the characteristics of long-term strength of refractory matherials

Parametric methods of describing and extrapolating the characteristics of long-term strength of refractory matherials

Effect of reactor irradiation and dissociating N2O4 coolant on the creep resistance of rupture strength of steel OKh16N15M3B

1. In high-temperature tests with static loads, the presence of dissociating heat-transfer agent N2O4 helps increase the service life and creep resistance of steel OKh16N15M3B. 2. Under conditions of reactor irradiation, an N2O4 medium does not decrease the longterm strength characteristics of steel OKh16N15M3B at a temperature of 923°K and radiation intensity Φmax=7.2·1016 neutrons/m2·sec.

Effect of alloying with nitrogen on the long-term strength characteristics of welded joints in molybdenum-based alloys

Effect of alloying with nitrogen on the long-term strength characteristics of welded joints in molybdenum-based alloys

Automated measuring and recording systems to investigate the effect of reactor radiation on the creep and longterm-strength characteristics of structural materials in power reactors

Automated measuring and recording systems to investigate the effect of reactor radiation on the creep and longterm-strength characteristics of structural materials in power reactors

Rating and predicting the statistics of the characteristics of long-term strength of heat-resistant metallic materials

Rating and predicting the statistics of the characteristics of long-term strength of heat-resistant metallic materials

Interpolation calculation of the characteristics of long-term strength of metals using the method of generalized curves with the use of the computer

Interpolation calculation of the characteristics of long-term strength of metals using the method of generalized curves with the use of the computer

Computer prediction of long-term strength characteristics for metals by a generalized-diagram method

Computer prediction of long-term strength characteristics for metals by a generalized-diagram method

The classification of high-temperature materials and the prediction of their long-term strength characteristics

1. The proposed methods — one of which is based on the direct or indirect use of comparable temperature and load conditions, while the other takes into account in addition structural features of the material that are governed by the short-term ductility characteristics — are practically equivalent to the Larson and Miller method as regards accuracy and reliability of prediction. 2. The classification of materials employed in the theory of high-temperature strength may promote the development of rapid methods of predicting the long-term strength and deformation properties by also taking into consideration the state of the material characterized by the short-term mechanical properties.

Some engineering methods of assessing long-term strength characteristics

1. As regards accuracy, the considered methods of assessment are practically equal. 2. The determined characteristics of the accuracy and reliability of assessing (δ=25%, P=90%) are apparently the limiting values for a direct assessment of the long-term strength from the long-term strength characteristics only.

Determination of long-term strength characteristics from crack-growth-kinetics data

The basic concepts of the quasi-stationary approximation of the kinetic theory of long cracks and a model of thermal-fluctuation crack growth are examined. The known experimental results on crack kinetics are discussed and it is shown that these results can be interpreted within the framework of the above-mentioned theory. Certain questions of methodology are considered.

The mechanical properties of rocks in three-dimensional states of stress with various rates of deformation

1. The graph of the strength of a rock vs the deformation rate (with the latter varying over 12 orders of magnitude), when plotted in semilogarithmic coordinates, has at least one horizontal part where the strength is independent of the rate of deformation and of the time, and also a part with a small slope (against the log\(\dot \varepsilon _1\) axis) and a part with a large slope (against the log\(\dot \varepsilon _1\) axis) where the strength depends most markedly on the deformation rate. These relations cannot be represented analytically by a single equation (2), such as that following from the kinetic theory of strength. In this case the kinetic theory of strength requires modification. 2. The authors derive an equation of the limiting state (strength), taking account of the deformation rate and the form of the state of stress. This equation gives the strength characteristics for various deformation rates and also the long-term strength characteristics on the basis of a minimum number of necessary experiments. 3. The authors experimentally establish and investigate an effect of anomalous increase in the plasticity and loosening of rocks with increase in\(\dot \varepsilon _1 = 10^{ - 2} - 10^2 \sec ^{ - 1}\). These deformation rates occur in shock bumps, rock bursts, and other dynamic phenomena in coal mining, in blasting and earthquakes, and also during drilling and breaking of rocks by cutting and percussive tools, etc. 4. In the range\(\dot \varepsilon _1 = 10^{ - 3} - 10^{ - 5} \sec ^{ - 1}\) there is a minimum in the plasticity and loosening of rocks. This range of rates is characteristic of mechanical tests on rock specimens in normal laboratory presses. This rate occurs in rocks near extraction operations. 5. At low deformation rates (from 10\t-5 to 10\t-10 sec\t-1), the plasticity and dilatation of the rocks again increase. In this rate range, creep processes occur. These rates occur in pillars and in rocks surrounding development and main workings, etc. 6. The authors have found and investigated the strength and deformation indices and the effects are of fundamental importance. In many cases they can exert a decisive influence on the energy balance of deformation and fracture and on the stability and mechanical state of the rocks. The effects influence the stress distribution, for example, in the abutment pressure zone, the behavior of rock during blasting, the occurrence of shock bumps, rock bursts, tectonic processes, earthquakes, etc.

Use of relaxation characteristics for predicting the characteristics of creep and long-term strength

Use of relaxation characteristics for predicting the characteristics of creep and long-term strength