Issue 49

A. Vedernikova et alii, Frattura ed Integrità Strutturale, 49 (2019) 314-320; DOI: 10.3221/IGF-ESIS.49.31 318 a) b) Figure 4 : (a) Infrared thermography data vs heat flux sensor data; (b) Time dependence of heat dissipation and stored energy (Eqn. 4). The parameters Q and  p E can be derived via Eqn. (6) using the experimental surface temperature measurements and the room temperature data, provided that the heat transfer coefficient  and the surface emissivities  are known. In our case, the specimen surface was coated with a thin layer of amorphous carbon, and the emissivity coefficient was equal to 0.92. The following three different formulae were used in order to evaluate the heat transfer coefficient in the case of natural convection [11]:   2 1/6 8/27 9/16 1/4 4 1/2 1/4 1/4 0.387 0.825 , 0.492 1 , , 2.43478 4.884 4.95283 0.667 , 0.952 , a Ra Nu Pr Pr Nu A Gr Pr A Pr Pr Pr Nu Ra Pr L Nu                                                        (7) where Gr , Nu , Pr , Ra are the non-dimensional Grashof, Nusselt, Prandtl and Rayleigh numbers, L is the length of the examined part of the specimen, and  a is the thermal conductivity of the air [W/(m K)]. It has been established that these formulae give very similar results and the mean value of heat transfer coefficient   3.7 W/(m 2 K). Based on the obtained results, we can conclude that conduction is the predominant heat transfer mechanism for titanium alloy Grade 2 specimens (Fig. 5a). The curve describing stored energy evolution during the mechanical test is presented in Fig. 5b. This plot coincides with the curve obtained according to Eqn. (4), which confirms the possibility of using the stored energy value as a reliable parameter for diagnosis of fracture. C ONCLUSION volution of irreversible deformation in the material is accompanied by the processes of energy accumulation and dissipation. In this work, we analyzed the energy balance of the material during the deformation process by two methods: infrared thermography technique and the method which uses the heat flux sensor. The infrared scanning E