Issue 24

A.Yu. Fedorova et alii, Frattura ed Integrità Strutturale, 24 (2013) 81-88; DOI: 10.3221/IGF-ESIS.24.08 81 Special Issue: Russian Fracture Mechanics School A study of the stored energy in titanium under deformation and failure using infrared data A.Yu. Fedorova, M.V. Bannikov, O.A. Plekhov Institute of Continuous Media Mechanics of the Ural Branch of the Russian Academy of Sciences, 614013, Ac. Koroleva Street, 1, Perm, Russia poa@icmm.ru A BSTRACT . The work is devoted to the experimental study of heat dissipation caused by plastic deformation and failure processes taking place in a titanium alloy Ti-4.2Al-1.6Mn. To investigate the spatial and time evolution of temperature, a set of experiments has been carried out on plane titanium smooth specimens and specimens with pre-grown centered fatigue cracks. The original mathematical algorithm for experimental data processing has been applied to obtain the rate of heat dissipation generated by plastic deformation and stored energy. It is shown that the stored energy is accumulated in titanium specimens undergoing fatigue tests, and at the time of damage to fracture transition it is equal to zero. K EYWORDS . Heat dissipation; Infrared thermography; Stored energy. I NTRODUCTION t is well known that real metals have a complex structure, which is a hierarchy of different scale levels [1, 2]. Under deformation, the structural evolution is observed at all scale levels and leads to irreversible deformation and failure that is accompanied by energy accumulation and dissipation. Investigation of thermodynamics of deformation and failure is a key issue in solid mechanics. These studies allow one to develop a universal material failure criterion for estimating different stress-strain states (including multi-axial ones) and loading histories. The experimental and theoretical study of the energy balance during deformation is based on an extensive bibliography. The importance of this problem was originally shown by J. H. Lambert in 1779 in his work concerning the energy similarity of mechanical and thermal failure processes of solids. The essence of this similarity is that the mechanical failure of metals can occur when the relative deformation in at least one direction reaches a value equal to the linear thermal expansion at the melting point. A substantial contribution to the development of these ideas was made by V.S. Ivanova, who proposed the structure-energy theory of metal fracture [3]. A detailed analysis of thermodynamic effects produced by cyclic deformation and failure in metals was carried out by V.T. Troshchenko and V.V. Fedorov. A review of strength energy criteria was given in [4, 5]. To analyze the thermodynamic characteristics of deformation processes in solids, it is necessary to take into account the fact that the plastic deformation work is converted into two parts: heat energy caused by the movement and annihilation of defects at various structural levels, and hidden (stored) energy of plastic deformation accumulated in the elastic fields of defects. The energy is dissipated in the surrounding environment by conduction, convection and radiation and also stored in the material as thermal energy that increases due to the self-heating effect. The main difficulty encountered in the analysis of deformation and failure processes is a choice of thermodynamic parameters required to determine the exhaustion degree of material deformability. In work [5] published in 1979, it was experimentally shown that an endurance limit can be determined by using almost any thermodynamic characteristics of the process: inelastic deformation per one load cycle, irreversibly consumed energy per one load cycle, self-heating I