Compressive strength of delaminated and repaired composite plates

Compressive strength is a critical concern in the design of fiber-reinforced adhesive matrix composite plates. This is mainly due to the fact that compressive strength is generally lower than tensile strength for most advanced fiber-reinforced composites, e.g., 180 Ksi versus 200 Ksi for a graphite/epoxy composite T300/976 (HYE-1076E). In this study, the compressive strength is used to assess the effect of delamination and repair of T300/976 graphite/epoxy composite plates. The sequence and dimension of composite test plates are [0/45/90/-45/-45/90/45/0]s and 4 x 6 in., respectively. A peel ply is used to separate the plies and to make the delamination across the test plate. The delamination is located at the center and between the 8th and 9th plies. The sizes of delamination are 1/4, 3/4, 1, 3 and 6 in. The compression test of delaminated plates is performed and the effect of delamination on strength is estimated from the compressive strength. The adhesive injection method is the primary approach for repairing delamination without removing the delaminated materials. A two-part low viscosity adhesive (EA9394) is injected into the delaminated area and re-bonds the damaged area. The repair efficiency is assessed by compressive strength of repaired composite. The experimental results show that the compressive strength of delaminated composite plate is reduced as the delaminated area increases, and the repair efficiency of repaired plate is also reduced as the re-bonded area decreases. If the adhesive can fully fill and re-bond the delaminated plies, the repair efficiency can be as high as 98% and satisfy the repair requirement. As a result, the adhesive injection method is seen to be a useful repair method for the delaminated composites.