基于熵产的高温裂纹扩展热力学损伤研究

In order to investigate the thermodynamic damage response of nickel-based superalloy GH4169 during crack propagation process at 873 K，a method of calculating the thermodynamic entropy generation for specimen with a crack within the thermodynamic framework was proposed. The FEM simulation of crack propagation process was conducted，and the method of defining the thermodynamic system was proposed for specimen with a crack. Analyses were conducted to reveal the influence of stress amplitude on cyclic entropy generation rate (CEGR) and accumulated entropy generation，then the ratio of accumulated entropy generation to fatigue fracture entropy (FFE) was defined as the thermodynamic damage of thermodynamic system. The relationship between normalized fatigue life and thermodynamic damage was analyzed. Results showed that the thermodynamic system should include the crack and the crack tip plastic zone all the while. The CEGR of thermodynamic system was not constant at different cyclic numbers when the stress amplitude was kept constant，and the dispersion of CEGR increased as the stress amplitude decreased. The FFE had an approximate quadratic function relationship with stress amplitude. The normalized residual life of the thermodynamic system decreased exponentially with the accumulation of thermodynamic damage.