COMPRESSION FATIGUE BEHAVIOR OF NOTCHED CARBON-FIBER EPOXY LAMINATES

The compression fatigue behaviour has been studied for [(+/- 45/0(2))3]s carbon fibre-epoxy specimens containing either a single hole or two closely spaced holes. For both single-hole and two-hole specimens, fatigue damage consists of ply cracking, delamination and, at loads approaching the static compressive strength, fibre microbuckling. When the applied maximum compressive stress is below 85% of the static compressive strength (denoted throughout the paper as sigma-ult) no fatigue failures occur prior to reaching 10(6) cycles. After fatigue cycling at peak loads smaller than 85% of sigma-ult the residual strength of the specimen was found to increase as a result of longitudinal splitting and associated damage which acts to reduce the stress concentration at the hole edge. This effect has been modelled for the single-hole specimen using a two-dimensional finite element analysis. At peak fatigue loads equal to 90% of sigma-ult fatigue failure occurs as a result of microbuckle initiation and growth. The presence of zinc iodide solution (which is used as a penetrant in X-ray studies) has been shown to accelerate split growth and thereby prolong the fatigue life of the specimens.