Mode I fatigue fracture toughness of woven laminates: Nesting effect

The mode I fatigue delamination onset and growth is evaluated for two carbon fibre T700-epoxy reinforced woven laminates with a different tow size (3K/12K). Three different nesting/shifting configurations are applied to the plies at the fracture surface. The nesting differences show little effect on the delamination onset fracture energy threshold limits, but normalised results show higher values for the smaller unit cell size. Analysing the normalised Paris diagrams it is concluded that the unit cell size and the nesting configuration does not affect the slopes for the Paris plot. However a smaller unit cell size shifts the normalised Paris diagram to the right. The non-homogeneity of the delaminated surfaces of textile materials leads to irregular slopes.