International regulations for aerofoils within gas turbine engines require the safe containment of a released aerofoil. The blade fragments must be contained within an engine casing. Smaller fragments will generally be easier to contain within the casing and therefore reduce the weight of that casing. However introducing lines of weakness may result in cavities and holes which are subject to moisture ingress and problems associated therewith. By providing a root section which incorporates a core having shear surfaces, blades can be designed which in normal use are subject to compressive loads and remain operational, but when subject to impact loads or bending forces create tension forces which cause fragmentation along the shear surfaces after initial energy losses by slippage. By providing the shear surfaces in cores their location is encapsulated avoiding problems with moisture ingress.