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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Fig 5. Two stages of heat flux dependence under biaxial test.

The analysis of the experimental data on the crack rates and heat dissipations confirms the hypothesis about the stages of fatigue crack propagation for biaxial loading. At the first stage, the crack rate is proportional to the power of heat flux and the crack length, in the second stage – power of heat flux. Characteristic dependences are shown in figure 6.

Q 2

(a) (b) Fig 6. Normalized heat flux and crack rate on first (a) and second (b) stages.

4. Conclusions A series of experiments was carried out to study the dissipation of energy from the fatigue crack tip under biaxial loading. The experimental technique used a contact heat flux sensor and method of infrared thermography was developed for measuring the energy dissipation during fatigue test. The results confirm the hypothesis of the existence of two modes of heat dissipation during the fatigue cracks propagation. The first mode corresponds to slow cracks (10 -7 – 10 -5 m/cycle) and is described by the relation 1 1 da ~Q a dN       . The first mode corresponds to slow cracks (10 -5 – 10 -4 m/cycle) and is described by the relation 2 2 ~ da Q a dN       . Based on the experimental results, it is possible to generalize the hypothesis about linear relationship between heat dissipation from the fatigue crack tip and its rate to the case of biaxial loading. The qualitative correspondence of the energy approach to the describing of the fatigue crack propagation and the classical description based on the use of the stress intensity factor is shown.