Accession Number : ADP006813

Title :   Influence Of Edge Effect on Compression-Tension Fatigue of Toughened Graphite/Epoxy Laminates,

Corporate Author : NATIONAL RESEARCH COUNCIL OF CANADA OTTAWA (ONTARIO) INST FOR AEROSPACE RESEA RCH

Personal Author(s) : Komorowski, J. P. ; Heath, J. B. ; Efebvre, D. L. ; Roy, C. ; Masmoudi, R.

Report Date : APR 1992

Pagination or Media Count : 7

Abstract : Results are reported of fatigue tests on a toughened graphite/epoxy (IM6/5245C) using a specimen and grip design that allows a relatively large volume of material to be tested. The loading was compression dominated (R=-3.75). Two different stacking sequences of an 18 ply laminate were tested. The lamination was typical of an aircraft wing skin (0/45/90) (44.4%,44.4%,l 1. 1 %). The specimens were 25.4mm wide, 290mm long with a gauge length of 150 mm. During the test program specimen stiffness and residual strength were measured. In parallel, local damage development was monitored using ultrasonic C-scans, photoelastic coatings and optical microscopy. The use of thin (.25 mm) photoelastic coatings to observe in-situ damage initiation and growth is new. It is based on the sensitivity of coatings to the change in mechanical properties of specimens due to damage. The C-Scan inspection results correlate closely with photoelastic observations. Results indicate that fatigue in composite specimens is dominated by the edge effect. Differences in the fatigue lives of the two stacking sequences used were close to two orders of magnitude. The proper selection of stacking sequence is crucial to achieving long fatigue lives. Under compression dominated loading fatigue damage is a local process. Damage always initiated at the edge and could be related to edge interlaminar shear stresses. The fatigue process consists of a relatively long period before initiation, usually in several locations, followed by a period of growth from one initiation site that finally leads to rapid compressive failure.

Descriptors :   *MILITARY AIRCRAFT, *FATIGUE(MECHANICS), *GRAPHITE EPOXY COMPOSITES, *LAMINATES, AIRCRAFT, COATINGS, COMPRESSION, DAMAGE, EDGES, GRAPHITE, LAMINATES, LENGTH, MECHANICAL PROPERTIES, MICROSCOPY, RESIDUALS, SENSITIVITY, SHEAR STRESSES, STACKING, STIFFNESS, STRESSES, TEST AND EVALUATION, ULTRASONICS, VOLUME, FATIGUE TESTS(MECHANICS), FAILURE(MECHANICS), REPRINTS, STRENGTH(MECHANICS), DELAMINATION, WINGS, AEROSPACE CRAFT, NATO.

Subject Categories : Laminates and Composite Materials
      Aircraft
      Research and Experimental Aircraft

Distribution Statement : APPROVED FOR PUBLIC RELEASE