Accession Number : ADA270187

Title :   The Development of Fatigue Damage Around Fastener Holes in Thick Graphite/Epoxy Composite Laminates,

Corporate Author : MATERIALS RESEARCH LABS ASCOT VALE (AUSTRALIA)

Personal Author(s) : Saunders, D. S. ; Galea, S. C. ; Diermendjian, G. K.

Report Date : 1993

Pagination or Media Count : 14

Abstract : This paper discusses the mechanisms by which damage develops and grows around countersunk fastener holes in composite laminates under fatigue loading conditions. Experiments have shown that the erosion of material between ply layers nucleates delaminations which then grow through the laminate under the action of the fatigue loads. The damage at the hole bore surface produces sites for the nucleation of delaminations. The morphology of the delaminations and ply cracking was mapped extensively and from these maps it was found that the volume of material around the fastener hole,.damaged by the fatigue loading, adopted a characteristic shape, the volume of damaged laminate increased towards the faying surface of the laminate and (metal) fixture. This characteristic damage volume was generated by the fastener rocking under the fatigue loads. Growth of the delaminations has been shown to be preceded by intraply cracking and, as fatigue loading proceeded, more delaminations were generated at the hole bore surface. The interfacial region between the composite laminate and the fixture also provided the nucleation site for fatigue cracks in the fasteners. The effects of initial fastener-hole clearances on damage nucleation and growth,. did not appear to follow any clear pattern. However, coupons with excessive initial hole clearances did appear to exhibit greater than expected damage growth after only one sequence block. Composite materials, Mechanically fastened joints, Fatigue loading, Fatigue damage, Damage development, Damage mechanisms, Thick laminates, Graphite/epoxy.

Descriptors :   *COMPOSITE MATERIALS, *DAMAGE, *LAMINATES, *GRAPHITE EPOXY COMPOSITES, BORES, CLEARANCES, CRACKS, DELAMINATION, EROSION, FATIGUE, LAYERS, MAPS, MATERIALS, METALS, MORPHOLOGY, NUCLEATION, PATTERNS, REGIONS, SEQUENCES, SHAPE, SITES, SURFACES, FASTENINGS, MECHANICS, AIRCRAFT EQUIPMENT.

Subject Categories : Laminates and Composite Materials
      Couplers, Fasteners, and Joints
      Mechanics

Distribution Statement : APPROVED FOR PUBLIC RELEASE