numero25

A. Shanyavskiy, Frattura ed Integrità Strutturale, 25 (2013) 36-43; DOI: 10.3221/IGF-ESIS.25.06 40 5 2.89 10 A x MPa  1, 2, 3..., 0( 1) s p or   /2 /4 (0) (2 / 3) s p A    (4) In Eq.(3) T m - temperature of melting;  - Poisson factor; - (0)  shear modulus. Figure 3 : Fatigue striation spacing against crack growth in the depth direction for semi-elliptic crack in a specimen of AK6 Al-based alloy. Numbers indicate spacing-values calculated in accordance with Eq.2. a) b) Figure 4 : Scheme of minimum inhomogeneity occurring (a) at the dislocation and (b) crack tip. It is very clear that subsurface cracking in UHCF regime takes place with level of deformation being the same which have to be classified as infinitesimal deformations. That is why quantum-mechanical approach for consideration crack increments quantization has fundamental nature. Another way of consideration for quantum-mechanical approach to fatigue crack growth can be introduced based on well- known relation for time dependent processes of solid body degradation [23]: 0 0 exp( )/ U kT      (5) In Eq.4 U 0 – energy of activation for cracking process;  - constant;  - stress of external loading;  - time for matrix cracking; 0  - time for cracking start. Let be considered crack growth rate in the form 0 ( / ) ( / ) exp( { } / ) i i da dN da d C U E kT        (6) In the case of infinitesimal deformations between stress and strain takes place not uniformly expressed dependence because of (6). Consequently, there will be cascade of crack growth rates constant values with constants energy levels 0 ( ) i U E    , where i  is local deformation at the crack tip. In the case of tests with high frequency measurements of crack increment can be realized now to register average value. That is why most of test results have not evidence of considered nature of crack growth. Nevertheless, in one of the well-