13th International Conference on Fracture June 16–21, 2013, Beijing, China -4- The stored energy was obtained as difference between accumulated plastic work (Eq. 3) and accumulated heat dissipation energy (Eq. 4) calculated at the point of the crack tip x0 during all time moments of experiment as follows: ( ) ( , ) it p p 0 0 W t w x t dt (3) ( ) ( , ) it 0 0 Q t s x t dt (4) The time dependence of accumulated plastic work, dissipative energy and stored energy that was calculated at the moving fatigue crack tip is shown in Fig. 5. Comparing time evolution of the plastic work and dissipative energy, the deformation process during cycling loading can be divided into three parts. The first one is about 1.3 seconds when two curves have a good correlation that can be connected with thermoelastic effect and existence the elastic part of the mechanical work. Figure 5. Time dependence of plastic work, heat dissipation energy and stored energy. From 1.3 second to 5 second, dissipation energy increases slower than plastic work. In this period stored energy is monotonically accumulated in deformed material and spent on the potential energy of lattice distortion. At the last moments before fracture the heat dissipation energy increases explosively and reaches the value of the plastic work. The stored energy aims to the zero and material goes to the fracture stage when macroscopic displacements play important role and it is accompanied significant energy dissipation. Data obtained for studied material displays that value of the stored energy increases to a critical point after that all mechanical energy goes to the heat and stored energy decreases explosively to zero, which ultimately leads to the destruction. 4. Conclusion The effect of heat dissipation at the crack tip under cyclic loading has been studied based on the infrared thermography. To calculate the values of heat dissipation at crack tip an original data processing algorithms were applied. The algorithms include the relative motion compensation and spatial-time filtration procedures. As a result of infrared data treatment we determine the characteristics associated with the heat dissipation processes at the crack tip, which allowed us to propose method for determining the current values of the heat dissipation energy and stored energy
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