Elastic–Plastic Transition in Iron: Structural and Thermodynamic Features

The structural and thermodynamic features of the elastic–plastic transition in armco iron and its plastic deformation are studied. Energy storage in iron is shown to have a nonlinear character and be accompanied by wavelike heat dissipation. To describe the energy balance in the plastically deformed metal, a theoretical model is proposed based on a statistical description of the evolution of an ensemble of typical mesodefects (microshears). Moreover, a procedure is developed to experimentally determine the dependence of the potential of the medium on the mesodefect density using infrared scanning data.This work was supported in part by the Russian Foundation for Basic Research, project nos. 05-08- 33652, 07-08-96001, and 07-01-0-96004

On the dependency of the parameters of fatigue crack growth from the fractal dimension of rough crack profiles

A theoretical study based on dimensional analysis and fractal geometry of crack profiles is proposed to establish the relation between their fractal dimension D (1<D<2) and the parameters defining the fatigue crack propagation rate. The exponent m of the Paris' law is found to be an increasing function of the fractal dimension of the crack profile, m=2D/(2-D). This trend is confirmed by a quantitative analysis of fractographic images of Titanium alloys with different grain sizes (different roughness of crack profiles), by a new experimental test and by an indirect estimation of D from crack growth equations accounting from crack-size effects in Steel and Aluminum. The present study can be considered as the first quantitative analysis of fractographic images aiming at relating the morphological features of cracks to their kinetics in fatigue.Comment: 13 pages, 4 figures, post-print of the article published in Proc. IMechE Part C: J. Mechanical Engineering Scienc

In the Land of a Thousand Cities: Evaluating Patterns of Land Use in Bactria through Survey and Remote Sensing

Bactria, a region today comprised of parts of Afghanistan, Turkmenistan, Uzbekistan, and Tajikistan, has historically been the homeland for a wide range of cultural groups that have produced a palimpsest of archaeological sites. Focusing on those parts of Bactria within the northern provinces of Afghanistan, this paper draws on decades worth of archaeological survey and excavation to investigate the history of land use in this region and its relationship to the highly variable landscape. Periods of increase and decline in site frequency are identified which, through analysis of topographic, environmental, and ecological data derived from remote sensing, are examined in respect to where increases are occurring and how that may reflect land-use and subsistence strategies of different groups. By doing so, a better understanding of how these different groups historically utilized the landscape is achieved, while also emphasizing the significant changes that occurred during transitions between different historical periods

A study of the stored energy in titanium under deformation and failure using infrared data

The work is devoted to the experimental study of heat dissipation caused by plastic deformationand failure processes taking place in a titanium alloy Ti-4.2Al-1.6Mn. To investigate the spatial and timeevolution of temperature, a set of experiments has been carried out on plane titanium smooth specimens andspecimens with pre-grown centered fatigue cracks. The original mathematical algorithm for experimental dataprocessing has been applied to obtain the rate of heat dissipation generated by plastic deformation and storedenergy. It is shown that the stored energy is accumulated in titanium specimens undergoing fatigue tests, and atthe time of damage to fracture transition it is equal to zero

Energy dissipation and storage in iron under plastic deformation (experimental study and numerical simulation)

The work is devoted to the experimental and numerical investigation of thermodynamic aspects ofthe plastic deformation in Armco iron. Dissipation and stored energies was calculated from processedexperimental data of the surface temperature obtained by infrared thermography. An original mathematicalmodel describing the process of mesoscopic defects accumulation was used for numerical simulation of thequasistatic loading of iron samples and for calculation of theoretical value of the stored energy. Experimentaland modeled values of the stored energy are in a good agreement

Three approaches to evaluate of the heat dissipated during fatigue crack propagation experiments

This work is devoted to the comparative analysis of three techniques for measurement of energy dissipation in metals under fatigue crack propagation: original contact heat flux sensor, post-processing of the infrared thermography data and lock-in thermography. The contact heat flux sensor allows real-time recording of the heat source value. Non-contact temperature measurements by infrared thermography techniques allows one to calculate the heat source field on the specimen surface using the solution of heat conductivity equation. Lock-in thermography is a well-established technique for measuring of the dissipated energy under cyclic loading based on the analysis of the second harmonic amplitude of the thermal signal. This paper deals with the V-notched flat specimens made of stainless steel AISE 304 subjected to cyclic loading. It was shown that the dissipated energy values estimated by different techniques have a good qualitative agreement. Contact and non-contact measurements can be used for investigation on energy dissipation either in combination or separately. The measured values allows one to propose a relation between the fatigue crack growth rate and dissipated heat near the crack tip

THM-coupled numerical analysis of temperature and groundwater level in-situ measurements in artificial ground freezing

Belarusian Potash salt deposits are bedded under aquifers and unstable soil stratums. Therefore, to develop the deposits a vertical mine shaft sinking is performed using the artificial ground freezing technology. Nowadays, real time observations of ground temperature and groundwater level is applied to control the ground freezing process. Numerical simulation can be used for a comprehensive analysis of measurements results. In this paper a thermo-hydro-mechanical model of freezing of water saturated soil is proposed. The governing equations of the model are based on balance laws for mass, energy and momentum for a fully saturated porous media. Clausius-Clayperon equation and poroelastic constitutive relations are adopted for description of a coupled change in water and ice pore pressure, porosity and a stress-strain state of freezing soil. The proposed model enables us to describe evolution of equivalent water content measured in Mizoguchi’s test and predict frost heave strain in one-sided freezing test. Numerical simulation of ground freezing in the Petrikov mining complex located in Belarus has shown that the model is able to describe field measurements of pore pressure inside a forming frozen wall. Furthermore, the mismatch between hydro- and thermo-monitoring data obtained during the artificial freezing is analyzed

Elastic–Plastic Transition in Iron: Structural and Thermodynamic Features

The structural and thermodynamic features of the elastic–plastic transition in armco iron and its plastic deformation are studied. Energy storage in iron is shown to have a nonlinear character and be accompanied by wavelike heat dissipation. To describe the energy balance in the plastically deformed metal, a theoretical model is proposed based on a statistical description of the evolution of an ensemble of typical mesodefects (microshears). Moreover, a procedure is developed to experimentally determine the dependence of the potential of the medium on the mesodefect density using infrared scanning data.This work was supported in part by the Russian Foundation for Basic Research, project nos. 05-08- 33652, 07-08-96001, and 07-01-0-96004

Infrared thermography study of the fatigue crack propagation

The work is devoted to the experimental study of heat dissipation process caused by fatigue crack propagation. To investigate a spatial and time temperature evolution at the crack tip set of experiments was carried out using specimens with pre-grown centered fatigue crack. An original mathematical algorithm for experimental data treatment was developed to obtain a power of heat source caused by plastic deformation at crack tip. The algorithm includes spatial-time filtration and relative motion compensation procedures. Based on the results of mathematical data treatment, we proposed a way to estimate the values of J-integral and stress intensity factor for cracks with pronounced the plastic zone

Theoretical Approach for Developing the Thermographic Method in Ultrasonic Fatigue

AbstractIn the last years, several approaches were developed in literature for predicting the fatigue strength of different kinds of materials. One approach is the Thermographic Method, based on the thermographic technique. This study is devoted to the development of a theoretical approach for modeling of surface and undersurface fatigue crack initiation and temperature evolution during ultrasonic fatigue test. The proposed model is based on the statistical description of mesodefect ensemble and describes an energy balance in materials (including power of energy dissipation) under cyclic loading. The model allows us to simulate the damage to fracture transition and corresponding temperature evolution in critical cross section of a sample tested in very high cyclic fatigue regime