PSI - Issue 18

A. Vshivkov et al. / Procedia Structural Integrity 18 (2019) 608–615 Author name / Structural Integrity Procedia 00 (2019) 000–000

611

4

2 d y t dt

2 ( )

(1)

( )

q t



2

3 1

  

  

( )

dy t dt



where q(t) is the time dependence of the heat flux, t is time.

a) b) Fig. 2. Heat dissipation during fatigue crack propagation in uniaxial mode (a) and biaxial mode (b).

Paris curves during fatigue test are presented in figure 3. Circles markers show the point, where second stage of heat dissipation is starting. This point is located in the middle of linear part. Therefore that stress intensity factor can’t fully describe the propagation of fatigue crack.

a) b) Fig. 3. Two stages in the Paris curve for uniaxial mode (a) and biaxial mode (b).

The analysis of the experimental data in the light of the hypothesis about the stages of fatigue crack propagation allowed us to derive characteristic relationships between the crack growth rate and the energy dissipation in both stages. At the first stage, the crack rate is proportional to the power of heat flux and the crack length 1 1       da ~Q a dN ,