13th International Conference on Fracture June 16–21, 2013, Beijing, China -5- The crack opening contour for a nearly 17mm average crack length under two different stress level is shown in Fig. 6. It can be seen that crack opening contour increase significantly with a higher stress level. On the other hand, Fig. 7 display the relationship between saw-cut length and crack opening contour. The crack opening contour in a larger 15mm saw-cut length is slightly larger. 2.2. Delamination shape and size Past studies[2, 16] have described the crack length and delamination in each layer for AHL in detail, as shown in Fig. 8. The outer aluminium alloy sheet, adhesive film and inner aluminium alloy sheet own the same longer length crack without delamination inside. There is a large delamination size between inner aluminium alloy sheet and prepreg, and the sharp point of the delamination locate in the same place with the crack tip of inner aluminium alloy sheet. Crack in central aluminium alloy sheet is obviously shorter than other layers, meanwhile there is a smaller size delamination between prepreg and central aluminium alloy sheet. Figure 8. Crack and delamination in each layers The delamination between inner aluminium alloy sheet and prepreg affect the fiber bridging effect markedly for its large scale, determine the fatigue crack propagation property of AHL, and thus is selected as the study object for delamination behavior. The results are shown in Fig. 9(a-c). Similar with above, the direction of axis x represents the direction of crack propagation and the point in axis x=0 and axis y=0 is the location of the saw-cut tip. Fig. 9(a-c) indicates the variation of delamination between inner aluminium alloy sheet and prepreg. With the increase of crack length, delamination grows larger while remaining a similar shape: the size close to zero in the crack tip, increase from crack tip to saw-cut tip, and decrease slightly near the saw-cut tip. Considering the symmetry of the delamination shape, delamination data were grouped and compared after adding together the data from two sides of crack. As shown in Fig. 10, data in axis d represent the width of the delamination shape in Fig. 9, that is d=|y1-y2|, in which y1 and y2 separately indicate the data of upper and lower delamination boundary. (f) (a) (b) (c) (d) (e) (a), (b) and (c) (d) (e) (f) outer aluminium alloy sheet outer aluminium alloy sheet inner aluminium alloy sheet inner aluminium alloy sheet central aluminium alloy sheet
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