Observation of static strength and fatigue life of repaired graphite/epoxy using a tensile coupon

The static strength and fatigue life of repaired graphite/epoxy laminates was observed using a tensile coupon. The lay-up of investigated laminates was [0°/±45°/90°]s. Static strength was measured from the specimens prepared by various repair techniques such as cosmetic treatment, precured-single patch, precured-double patch and cure-in-place patch methods. The strength was recovered to the extent of 60-70% of unnotched case. Fatigue life was also measured from the laminates repaired with cure-in-place patch method. Hwang and Han's MFLPE I (modilied fatigue life prediction equation (1)), which is based on the fatigue modulus degradation model and reference modulus, was chosen for fatigue life prediction of the repaired specimen and compared with the conventional fatigue life equations such as the S-N curve and Basquin's relation. The MFLPE 1 agrees more closely with experimental data than the S-N curve or Basquin's relation.