In the present paper the effective mesoscale failure response of a fibre-epoxy sample is computed from its complex microscale fracture behaviour. The mesoscale failure response is represented by a traction-separation curve derived from numerically homogenizing the fracture response of a periodic fibre-epoxy microstructure loaded under uniaxial tension. The traction-separation curve can be applied in material points of interface elements that are used for simulating mode I mesoscopic fracture in macroscopic laminate failure problems. The effect of the size of the microscopic fibre-epoxy sample on the mesoscale failure response is examined, as well as the effect of local imperfections at fibre- epoxy interfaces.