PSI - Issue 50

Mikhail Nadezhkin et al. / Procedia Structural Integrity 50 (2023) 206–211 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

208

3

modes and has the following technical characteristics: strain resolution 10 -4 , sampling frequency 50 Hz, and scanning area 200×200 mm. Speckle images were acquired using a PixelLink PL -B781 digital video camera at a rate of up to 1 frame per second. The system of reference points in the form of a speckle field on the gauge surface of the deformed specimen was produced by a monochromatic light source with a wavelength of 635 nm. 3. Results and discussions It was found that the strain-time curves ε(t) have three stages, where the first stage corresponds to unsteady or damped creep and then follows a straight portion of steady-state creep (Fig. 1). The third stage corresponds to accelerated creep, followed by necking (Pelleg (2013). Figure 1 shows the creep curve at a constant stress level of 57.5 MPa. Table 1 gives the ranges of steady-state creep strains  in tests with different stress levels  c for different specimens, as well as the creep rate έ , which varies widely depending on stress. In further analysis, we focused on stages of steady-state creep, whose rate έ  const can be correlated with the evolution parameters of the localized strain distributions.

Fig. 1. Creep curve of 1050A aluminum at the stress  = 57.5 MPa: (I) damped creep, (II) steady-state creep (III) accelerated creep.

Table 1. Creep parameters of 1050A aluminum in steady-state creep  c , MPa  , % ἐ 10 -6 , m/s 51 23.1-25.8 (2.7) 0.057 53.5 22.8-25.4 (2.6) 0.5 54.3 23.7-27 (3.3) 0.53 57 25.6-28.2 (2.6) 1.2 58.5 22.2-24.9 (2.7) 4.4

Using the DIC and DSSP methods, we studied macroscopic plastic strain localization at the stage of steady-state creep with constant rate έ by analyzing the time dependences X(t) (chronograms) and distributions of local elongations  xx along the tensile axis (Fig. 2).