Kinetics Of Damage Accumulation Research Articles

Effect of the form of stressed state on the kinetics of damage accumulation and crack resistance of body steel 15Kh2MFA under different conditions. Communication 1. Stagewise process of steel KP60 failure

The kinetics of body steel KP60 failure are studied in the final stages of deformation with static tension for smooth specimens and with stress concentrators. Attention is concentrated on features of the generation and start of separation macrocracks in test specimens. Common and distinctive features of damage formation in the test steel are noted taking account of the form of stressed state.

Evaluating the reliability of predictions of the rupture strength of metallic materials for long service lives

It is shown that characteristics of plastic strain in the case of delayed fracture (DFPS) under creep conditions reflect fundamental laws governing the temperature- and time-dependent fracture of metallic materials if these characteristics are functions of stress and temperature. The laws governing the change in DFPS are different for different classes of metallic materials. For the unalloyed steels studied in the present investigation, DFPS characteristics increase with a decrease in stress and then — if the time to fracture is very long — decrease. In the case of chromium-nickel steels, a decrease in stress (an increase in time to fracture) is accompanied by a decrease in these characteristics. However, this decrease slows after the passage of certain stress regions which exist for each test temperature. Two laws of development of DFPS are established for the above steels in tests lasting 100,000 h or more. The rupture strength of these steels for times greater than 100,000–200,000 h can be reliably predicted only with allowance for the kinetics of damage accumulation in the material, which is qualitatively reflected by the laws which govern DFPS development in relation to stress and temperature. Numerical solutions are presented for prediction problems for periods of 300,000 h or more. The reliability of the solutions is evaluated.

Kinetics of deformation and damage accumulation in concentration zones with nonisothermal low-cycle loading

Data are given for endurance with nonisothermal loading of steel 15Kh2MFA specimens with elastic stress-concentration factors of 2.5 and 3.5. Results and test procedure are given in detail. Specimen heating was carried out in a lowintertial furnace with a quartz-halogen lamp of the KGM type. It was established that the heating method used provides quite a uniform field around the concentrator in the specimen plane. In order to isolate the thermal component of deformation, prior thermal cycling was carried out without a load. The authors note that the difference in endurance values for the test material in concentration zones with isothermal and nonisothermal loading schedules is caused by deformation properties of the material in the temperature range considered.

Investigating the failure of composites in a plane stressed state by the method of mechanical luminescence

1. The experimental results that we have cited indicate that the method of mechanical luminescence can be used to investigate the failure of structural composite materials. Both the initial stage of material failure, and the laws governing the kinetics of damage accumulation are determined by this method. 2. It was first established by comparison of results of theoretical computations of the initiation of crack formation in the components of composites with resultant experimental data that mechanical luminescence reflects initial failure processes in fiberglass both in a simple, and complex stressed state.

Kinetics of damage accumulation of rock salt during creep : Kovalev, O V; Litov, Y N; Emanovski, Y I Int J Engng Sci, V19, N3, 1981, P451–454

Kinetics of damage accumulation of rock salt during creep : Kovalev, O V; Litov, Y N; Emanovski, Y I Int J Engng Sci, V19, N3, 1981, P451–454

Kinetics of damage accumulation of rock salt during creep

Microfracturing of rock salt specimen were detected experimentally using the method of impulse electromagnetic radiation (IER). The number of IEE signals was chosen as a measure of damage accumulation in rock salt during creep in uniaxial oompressive experiments. Using the results of these expermients the rupture curve of rock salt is given and the kinetics of damages accumulation is derived.

Strain Criteria for Fatigue Fracture of Metals at High-Cycle Loading

Abstract The paper deals with the features of inelastic straining and fatigue fracture of metals in high-cycle loading. It is shown that the use of cyclic strains enables one to study the kinetics of cyclic deformation and fatigue damage accumulation with different loading histories, to consider the stress-strain state of structural elements with stress concentration, to formulate strain criteria for the fatigue fracture of metals involving various factors, and to develop methods for the accelerated determination of the fatigue limit.

Deformation-induced intergranular creep cavitation in alpha-iron

AbstractThe nature of cavitational damage accumulation has been analysed on the basis of quantitative measurement of the processes contributing to creep deformation in alpha-iron at 700°C. An assessment of the damage accumulation kinetics during steady state dislocation creep has demonstrated that the overall rate of increase in intergranular cavitation is directly related to the process facilitating grain boundary deformation. The rate at which cavities are nucleated has been related to the creep deformation rate, and observations on the cavity distribution together with -the effect of prior deformation at room temperature are interpreted in support of a mechanism in which cavity nucleation is promoted by slip impingement at selective grain boundary sites. Cavity stability may be achieved by local enhancement of the vacancy supersaturation brought about by grain boundary deformation which relaxes the associated stress concentration. Results favour a process in which subsequent cavity enlargement occurs p...

Analysis of fracture surfaces in polymethyl methacrylate tested in bending with rotation

Typical fracture surfaces are examined for polymethyl methacrylate specimens subjected to multicycle fatigue testing in circular cantilever bending at T=20, 40, and 60°C. It is established that the fatigue life of smooth specimens is very closely correlated with the size of the diffuse fracture zone. The kinetics of damage accumulation with increase in the number of cycles are investigated by rapidly fracturing prefatigued specimens. The decisive role of diffuse fracture in the fatigue-fracture process is demonstrated. A method of estimating the mean main crack propagation velocity in circular bending is described.