in use the slots may be filled with radial fibres these will add centrifugal strength to the blade but are weak in the direction of bending on impact in a carbon fibre reinforced polymer cfrp blade these may be unidirectional carbon fibres the carbon fibres may be coated for example with nickel or titanium boride when used with aluminium to prevent them reacting with the material in a metal matrix composite mmc these may be metal boron silicon carbide or organic fibres fig4 provides a further cross section of a blade 50 in accordance with the invention slots 51 provide discontinuities within the blade 50 these discontinuities may be voids or the slots 51 may be filled with a material of a lower circumferential strength than the blade 50 or not be bonded such that the blade 50 will flex and crack under impact loads dissipating energy prior to further fragmentation of the blade 50 it will be appreciated that the slots 51 provide dislocations as indicated within the blade 50 these dislocations may extend along the blade 50 such that an original three slot format as depicted in fig3 may extend through branching into multiple slots 51 as depicted in fig4 the.