Intralaminar delamination

The saw-tooth fracture surface can be interpreted as a sequence of interlaminar and intralaminar delaminations oscillating back and forth at regular intervals [4], The amplitud(j of the saw-tooth pattern determined from photographs is consistent with the assumption that it is equal to the thickness of the centre 90°-ply of the cross-ply specimens. For the symmetric lay-up with two 90°-plies at the centre, the wave-length of the saw-tooth pattern is more than doubled (factor around 2.1) compared with the non-symmetric lay-up. The steady-state delamination in the cross-ply specimens is oscillating between two 0°-plies on either side of the centre 90°-ply with a wavelength that seems to depend on ply thickness. [Pg.440]

Fig. 7 shows that the values from the second laboratory tend to be lower than those from the first for both types of cross-ply lay-up, while those for the unidirectional lay-up agree fairly well. The scatter still seen in the R-curves for the cross-ply laminates with a single fracture surface topography (Fig. 7) can probably, at least in part, be attributed to different amounts of fibre-bridging (compare Fig. 1). Another factor is micro-cracking in front of the delamination that may make accurate determination of the delamination length difficult. This would also offer an explanation for the steep rise seen in the R-curves of those specimens for which the delamination does not deviate into the unidirectional plies. This is discussed in detail in [6]. Small (local and short-term) deviations of the delamination into the unidirectional plies not recognised in the visual inspection of the fracture surfaces might also contribute to the scatter by temporarily reducing Gic. Finally, the oscillating interlaminar - intralaminar type of delamination propagation could also account for some of the observed scatter. The analysi > presented in [4] concludes that the intralaminar G is considerably smaller than the...

$Fig. 7 shows that the values from the second laboratory tend to be lower than those from the first for both types of cross-ply lay-up, while those for the unidirectional lay-up agree fairly well. The scatter still seen in the R-curves for the cross-ply laminates with a single fracture surface topography (Fig. 7) can probably, at least in part, be attributed to different amounts of fibre-bridging (compare Fig. 1). Another factor is micro-cracking in front of the delamination that may make accurate determination of the delamination length difficult. This would also offer an explanation for the steep rise seen in the R-curves of those specimens for which the delamination does not deviate into the unidirectional plies. This is discussed in detail in [6]. Small (local and short-term) deviations of the delamination into the unidirectional plies not recognised in the visual inspection of the fracture surfaces might also contribute to the scatter by temporarily reducing Gic. Finally, the oscillating interlaminar - intralaminar type of delamination propagation could also account for some of the observed scatter. The analysi > presented in [4] concludes that the intralaminar G is considerably smaller than the...$

Figure 8.2 Schematic presentation of (a) interlaminar (between fibre plies) (b) intralaminar (normal to fibre plies) and (c) tranr-laminar (cutting fibre) delamination in fibre-reinforced composite laminates.

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