Composite Structures 8 (1987) 1-12 Is Fatigue Testing of Impact Damaged Laminates Necessary? R. Jones Department of Defence, Defence Scienceand TechnologyOrganisation, Aeronautical Research Laboratories, PO Box 4331, Melbourne, Victoria 3001, Australia J. F. Williams and T. E. Tay Department of Mechanical and Industrial Engineering, Universityof Melbourne, Parkville 3502, Australia ABSTRACT A major long-term objective in the evolution of advanced fibre composites as aircraft structural materials must be the establishment of a damage tolerance methodology. The availability of this methodology would greatly aid the design of safe, efficient composite structures as well as their management in service. There are, however, many difficulties in meeting this objective, including the multiplicity of failure modes in the composites, the numerous types of potentially significant defects which may arise during manufacture or in service and sensitivity to moisture and temperature. This paper discusses the necessity of fatigue testing of impact damaged composite laminates. Selected experimental studies in the literature are briefly discussed. It is shown that uniaxial S-N curves]or damaged laminates have a generic shape with a pronounced threshold level. Indeed, it is clear that further research is needed to understand the physical reasons ]'or such a threshold value. 1 INTRODUCTION Graphite-epoxy composites have many advantages for use as aircraft structural materials, including their formability, high specific strength and stiffness, resistance to cracking by fatigue loading and their immunity to corrosion. Thus, besides producing lighter, more efficient structures, the l Composite Structures 0263-8223/87/$03.50 O Elsevier Applied Science Publishers Ltd, England, 1987. Printed in Great Britain