Issue34

E. Marcisz et alii, Frattura ed Integrità Strutturale, 34 (2015) 379-386; DOI: 10.3221/IGF-ESIS.34.42 384 187.5, 232, 233, 255 MPa, values of elastic energy have been calculated according to linear-elastic model of solid (W a =  a 2 /2E), obtaining W a = 0.23, 0.28, 0.34, 0.36, 0.42 MJ/m 3 . Figure 9 : The fatigue characteristic of 2024 aluminum alloy under bending with a controlled amplitude of the 1 – energy parameter with Eq. (1), 2 – energy parameter with linear-elastic model of solid. The results of fatigue tests have been subjected to statistical analysis, and calculated according to relations (2) and (3), coefficients of regression equation and correlation are shown in Tab. 3.    log f a N A m W (2)     log f a N A m (3) where: W a - amplitude of energy parameter,  a - amplitude of nominal stress, N f - number of cycles to failure, A i m - coefficients of the regression equation Material A B r Type of research 2024 7.030 -7.216 0.960 Controlled energy parameter amplitude - Eq. (2) 2024 10.293 -0.022 0.981 Controlled bending moment amplitude - Eq. (3) Table 3 : Coefficients of the regression equation and correlation at a significance level,  = 0.05 with a controlled amplitude of the nominal stress. Cracks of specimens from aluminium with  phase structure occur in the slip plane {111} under shear stress, which are almost independent of grains space orientation. In the specimen (Fig. 10) it is observed the main, zigzag crack developed through transcrystallic  phase grains. This crack is changing direction on grain boundaries. It can also be noticed some side, short cracks running in parallel to the main crack. The characteristic feature of the main crack are slips occurring under angle 45° to specimen axis.