Issue 27

A. Kostina et alii, Frattura ed Integrità Strutturale, 27 (2014) 28-37; DOI: 10.3221/IGF-ESIS.27.04 30 0 0.1 0.2 0.3 0.4 0.5 0 50 100 150 200 250 300   , MPa  (  ) 299 300 301 302 303 304 305 306 307 308 Temperature, K T(  ) Figure 2 : Stress – strain evolution of Armco iron specimen (solid line) and local temperature evolution (dash line); strain rate 2·10 -3 s -1 . The plastic wave propagation is finished by the transition to hardening process accompanied by an approximately homogeneous plastic deformation of the sample (the second part of plastic deformation). The last part of the deformation process is characterized by necking heterogeneous temperature distribution of the specimen surface. The second part of the process can be considered as a homogeneous at macroscopic level. The energy balance in specimen at this part of deformation will be simulated in the next part of this paper. All other parts of the process requests the consideration the nonlocal effects in defect ensemble and leads to the more complex model. Heat sources calculation The heat sources evolution can be calculated based on the following equation [4] 2 2 2 2 ( , , ) T T T T s x y t c k t x y                         (1) where T is the temperature, ρ is the density (7870 kg/m 3 ), c is the heat capacity (444 J/(kg·K)), k is the heat conductivity (76.2 W/(m·K)), s is the unknown specific power of heat source (W/m 3 ) and τ is the constant describing the heat exchange process with the surroundings (160 sec) [5]. The definition of heat sources evolution requests the calculation of the space and time derivation of noisy temperature field. It leads to the situation when recorded experimental data of the temperature is not enough suitable to calculate the heat dissipation rate. In this work we use time and space filter for experimental data. To implement filtration procedure it was applied discrete Fourier transform with Gaussian kernel. The peculiarities of filtering procedure are described in [6]. This procedure allows us to smooth spatial and time heterogeneity. Fig. 3 presents field of temperature range before and after processing. a) b) Figure 3 : Temperature range on the surface of specimen before data processing (a) and obtained field of temperature range with zone of interest (b) .