Prediction of fracture toughness for heat-resistant steels considering specimen dimensions. Report 2. Ductile fracture

A model of ductile failure of a body with a crack has been developed which enables predicting fracture toughness on the upper shelf of the fracture toughness temperature dependence taking into account the influence of the stress state. The model is based on the physical-mechanical model of ductile failure which is controlled by the critical value εf reached by plastic strain at the crack tip ε _i ^ρ . In this case it is assumed that both the ε _i ^ρ value, which precedes the crack growth onset by the mechanism of pore coalescence, and the critical strain εf are functions of specific stress state parameters, namely: the critical strain is a function of the stress state triaxiality σ _m /σ _n (σ _m is the hydrostatic stress, σ _i is the stress intensity), and ε _i ^ρ is a function of the parameter χ introduced, which is an explicit function of all three principal local stresses in the process zone at the crack tip and which defines the degree to which the stress state approaches the plane strain conditions for a body of specified thickness. The model developed has two modifications one of which enables predicting fracture toughness of large-size bodies from the results of testing only small cylindrical specimens without cracks (smooth and with a circular recess) and the other from the results of testing small cylindrical specimens and small specimens with a crack. Translated from Problemy Prochnosti, No. 2, pp. 5–19, March–April, 1997.     

Prediction of fracture toughness for heat-resistant steels considering specimen dimensions. Report 3. Brittle fracture

A model has been developed for predicting fracture toughness characteristics on the lower shelf of the fracture toughness temperature dependence considering the influence of specimen dimensions. The model is based on the physicomechanical model of brittle fracture governed by microcleavage critical stress which in its turn depends on plastic prestraining. This model is also based on the assumption that the change in the body dimensions influences fracture toughness as much as the change in the stress state caused by it, which is evaluated by the introduced parameter χ, and affects plastic deformation preceding brittle fracture by cleavage. According to the given model, in some cases an increase in specimen thickness can lead only to a shift of the brittle-to-ductile transition temperature, and in other cases to both a shift of the brittle-to-ductile transition temperature and a decrease in the critical SIF value at which this transition occurs. The paper also presents further elaboration of the probabilistic approach to the prediction of size effect for the cases of brittle fracture based on Weibull's three-parametric distribution. A distinctive feature of this approach is the determination of one of the parameters of the cumulative distribution function, namely, the parameter of location K_{c min} , directly in the experiment and not by conventional statistical methods. This reduces appreciably the requirements for the size of the sample and simplifies the body of mathematics. In this case, the parameter of location K_{c min} corresponds to the critical SIF value during the first unstable jump of a fatigue crack K _fc ⁽¹⁾ which, according to a large number of experimental data, is minimal and the most invariant among all other critical SIF values obtained experimentally. Translated from Problemy Prochnosti, No. 2, pp. 21–31, March–April, 1997.     

Strength criteria for a solid body taking into account the size effect and the influence of the environment

We develop a procedure for the evaluation of the surface γ and interphase γ _m energy of deformed solid bodies subjected to atomic irradiation or placed in a liquid metal. The characteristic of the surfaces γ _m appears in the Griffith, Griffith-Orowan, Kamdar-Westwood, and Kontorova-Frenkel fracture mechanics criteria and their modifications for the case of the size strength effect. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 35, No. 2, pp. 80–85, March–April, 1999.     

Prediction of residual pipeline resource taking into account the operation loading conditions

An effective energy approach to the evaluation of the residual service life of a pipe of oil pipeline containing a crack on its inner surface for the two-frequency loading mode of biaxial tension-compression has been proposed. The two-frequency variations of pressure in the pipe are caused by the turbulence of the oil flow (high frequency), opening and closing of the gate valves, and the shutdowns of the pumps (low frequency). __________ Translated from Problemy Prochnosti, No. 1, pp. 44–52, January–February, 2009.     

Prediction of fracture toughness for heat-resistant steels considering specimen dimensions. Report 4. Fracture toughness after plastic prestraining of materials with cracks

The paper presents the results of an experimental investigation of the influence of warm prestressing (WPS) on fracture toughness characteristics of large-size specimens. The WPS has been found to be an efficient method for enhancing brittle fracture resistance of large-size bodies from the investigated materials and can be recommended for practical realization in nuclear reactors and other critical structures whose brittle fracture is impermissible both in the process of normal operation and in emergency situations. The optimum temperature-loading regime of the WPS is defined by both the properties of a given material and its thickness which governs the intensity of plastic deformation in the process of WPS. Based on the established mechanisms of the WPS effect, a physicomechanical model has been developed for the prediction of fracture toughness for pressure-vessel heat-resistant steels after WPS taking into account the influence of the stress state at the crack tip. The model makes it possible to predict fracture toughness for large-size bodies subjected to WPS with the given temperature and loading regimes from the results of testing small laboratory specimens. The most optimum regimes of the WPS can also be determined using this model and even those for several materials making up a structural component and subjected to the WPS. Translated from Problemy Prochnosti, No. 3, pp. 39–54, May–June, 1997.     

Investigation of the temperature fields in structural steels taking structural and phase transformations into account

The article presents the solution of the heat-transfer equation in a metal wall subjected to pulsed thermal effect, taking into account the dynamics of a number of structural and phase transformations, both in heating and cooling.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 38, No. 5, pp. 894–902, May, 1980.     

Prediction of the long-term strength of pipeline metal taking account of crack development under creep conditions

A procedure which makes it possible to predict the long-term strength of smooth specimens from the endurance and nominal breaking of cylindrical specimens with a sharp notch without exceeding the working temperature is substantiated theoretically and proved by experiment for pipeline steels (12KhlMF, 15KhlMlFL, 20KhMFL). This prediction makes it possible to reveal more reliably the breaking point on the long-term strength curve and to provide reliable results for evaluating high-temperature strength with much shorter tests. Translated from Problemy Prochnosti, No. 1, pp. 59–70, January–February, 1997.     

Calibration of LR-115 for 222Rn monitoring taking into account the plateout effect

The dose received by people exposed to indoor radon is mainly due to radon progeny. This fact points to the establishment of techniques that access either radon and progeny together, or only radon progeny concentration. In this work a low cost and easy to use methodology is presented to determine the total indoor alpha emission concentration. It is based on passive detection using LR-115 and CR-39 detectors, taking into account the plateout effect. A calibration of LR-115 track density response was done by indoor exposure in controlled environments and dwellings, places where 222Rn and progeny concentration were measured with CR-39. The calibration factor obtained showed great dependence on the ambient condition: (0.69 +/- 0.04) cm for controlled environments and (0.43 +/- 0.03) cm for dwellings.