Mechanism And Effect Of Defect On Main Crack In γ-TiAl Alloy

Micro-crack and micro-hole are regarded as two chief factors which have a great inference on fatigue life of materials, a large stress concentration would be caused by these defects under the complex load and fatigue crack, and fatigue cracks are easier to produce in these areas. Besides, these factors also have an inference on the behavior of extension path of fatigue crack.The main crack model which included micro-crack and micro-hole defects at micro scale is simulated based on extended finite element method(XFEM), γ-TiAl alloy was adopted to research effects of single micro-crack in the horizontal and double micro-crack on SIF of main crack tip,and the effects of different position and orientation of micro-hole on the main crack are also studied. The path of crack propagation by micro-crack of offset direction is simulated. The main results are as follows:1.The interaction between collinear single micro-crack and the main crack was studied. The models of collinear single micro-crack in horizontal direction and main crack are built using extended finite element method, and the interaction between single micro-crack in different direction and the main crack is simulated. The results showed that the influence of collinear single micro-crack on the crack tip stress field of the main crack is mainly manifested as a sharp enhancement in a short distance, and it nearly has no influence in a long distance.2.The effect of offset double micro-crack on SIF of main crack tip is studied. The results show that the effect of SIF on the main crack tip of double micro-crack would change with increase of time as periodic fluctuation of equal amplitude, and its fluctuation is caused by the enhancement and shielding effects of micro-crack on the main crack. The closer the distance between micro-crack and main crack is, the larger the effect was, and the effect was little when the distance between micro-crack and main crack is far.3. The effect of crack tip micro elliptical hole in different position and orientation on SIF of main was studied, and its mechanism was analyzed. The results showed that the effect is related to the position of the main crack and its own orientation, and changed with these two factors, the effect of micro elliptical hole on the crack tip of the main crack is manifested as enhancement and shielding effects, which could be coexist.4.The effect of offset single micro-crack on the propagation path of the main crack is studied. The results show that the unilateral offset micro-crack would change the propagation direction of the main crack, which lead to the crack propagation toward the direction of micro-crack, and reduce the propagation rate of the central main crack; the extension deflection angle of the main crack decreased and the extension rate increased by the increase of offset distance.