PSI - Issue 13

O. Plekhov et al. / Procedia Structural Integrity 13 (2018) 1209–1214 Author name / Structural Integrity Procedia 00 (2018) 000–000

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(a) (b) Fig. 1. Biaxial testing system Biss BI-00-502 (a), geometry of samples (b) (all sizes in millimeters).

3. Experimental results The heat flux sensor measures the integral heat flux during the experiment and verifies the infrared thermography data. The infrared thermography method was used to obtain the temperature field and the field of heat sources distribution in the region of the crack tip. The infrared thermography data treatment gives us the shape and size of the zone of intense plastic deformations. At the beginning of data processing procedure, the first frame was subtracted from the film to eliminate the influence of infrared radiation from the camera lens on the determined temperature field. Due to the relative motion of the specimen with crack and infrared camera lens under cyclic tests, there is the problem of motion compensation in order to obtain the correct temperature data at a given point on specimen surface. Figure 2 presents the characteristic results of the experiments with constant stress amplitude under uniaxial loading. The evolutions of heat source at crack tip and crack rate versus time of the experiment for different stress amplitudes are presented in figure 2.a and 2.b, respectively.

(a) (b) Fig. 2. Two stage of flux dependence under uniaxial test with constant stress amplitude (a), crack length versus time of the experiment (b)

The characteristic evolution of heat source for all tested stress amplitudes can be divided into three parts. The first part corresponds to increasing of heat flux and constant crack length. The second part is characterized by constant heat flux value. The last part is characterized by rise of heat flux. This part of the experiment is finished by critical, unstable regime of crack propagation.