Issue 49

A. Vedernikova et alii, Frattura ed Integrità Strutturale, 49 (2019) 314-320; DOI: 10.3221/IGF-ESIS.49.31 316 The volume-averaged Eqn. (1) is used for estimation of the integral power of the heat source. To this end, a standard averaging procedure was conducted. The difference between the averaged specimen temperature on volume T and the initial specimen temperature 0 T in the thermal balance with the environment is defined as:             /2 /2 /2 0 0 /2 /2 /2 1 '( ) ( ( ) ) ( ) , a b h a b h t T x, y,z,t T dxdydz t T V (2) where a , b , h are the length, width and thickness of the specimen, respectively, and V is the volume. The boundary conditions are expressed as follows: 2 2 /2 0 /2 2 ( , , z, ) ( , , z, ) , ( , , z, ) ( ( , , z, ) ) , a a x x a x a x a T x y t T x y t x x g T x y t k T x y t T dxdydz x a                 (3) where x g means the heat exchange coefficient between the specimen and the environment on the corresponding edge of the specimen. Therefore, integrating Eqn. (1), considering expressions (2) and boundary conditions (3), we obtain relation (4) to estimate the heat source field caused by irreversible deformation:         0 ( ) ( ) ( ( ) ), t S t mc V t T t (4) where  is the average temperature of the examined surface, m is the mass of the representative volume where the average temperature is taken from, ( ) S t is the heat source field (W), and  is the material parameter that determines heat losses associated with the heat exchange with the environment. The parameter  is determined by the additional experiment data from the tests in which the specimen was cooled after pulse point heating. Fig. 2a presents the IR image, which was made during the pulse point heating experiment, and data of the average temperature of the heating area during the cooling process. To calculate the constant  , it is necessary to approximate the experimental data of the average specimen temperature after pulse point heating in terms of the solution of the averaged thermal conductivity Eqn. (4) with a zero source (Fig. 2b). The experimentally obtained value of parameter  is equal to 3.65 · 10 4 . a) b) Figure 2 : (a) IR image of the specimen during pulse point heating; (b) Approximation of the cooling curve of the specimen after its pulse point heating.