Microbuckle initiation from a hole and from the free edge of a fibre composite

Microbuckle initiation from an open hole, from a filled hole, and from the free surface of a unidirectional fibre composite is examined by a finite el ement method. The role of fibre bending resistance is included in the formu lation so that a hole size effect is predicted. It is found that the open h ole knocks-down the compressive strength to the order of 20 tau(Y), while t he filled hole reduces the strength to about 40 tau(Y), where tau(Y) is the in-plane shear modulus of the composite. Pre-existing fibre waviness adjac ent to the hole gives a further reduction in the compressive strength. The role of in-plane shear stress and transverse stress in reducing the open ho le compressive strength is examined: the compressive strength is reduced by the presence of shear and transverse tension, but the effect is less prono unced than that observed previously for the case of a circular patch of wav iness. The study concludes with an investigation of the influence of the fr ee surface on microbuckle initiation from a band of waviness and from a sem i-circular patch of waviness a negligible effect of the free surface on the compressive strength is predicted. (C) 2000 Elsevier Science Ltd. All righ ts reserved.