During the fatigue tests, a sequence of surface replicas were intermittently taken at the same position in the middle of a specimen surface. Since longitudinal splitting tends to occur at the edges of unidirectional coupons, principally as a consequence of fibre misalignment, the replicas were taken on the unpolished surface across the width. A cellulose acetate film was softened with an acetone-based solution and then pressed onto a predesignated position on the specimen surface for one minute.