Defective Repairs of Laminated Solid Composites

Abstract

This paper presents an experimental evaluation of the defective patch repairs of solid laminated composites. The study uses both destructive and nondestructive tests on full-scale repaired panels to evaluate the repair performance under static tension loading conditions. While most reported studies use small coupon specimens, this paper presents test results of full-scale panels that allow strain field monitoring around the patch. The experimental results presented in this paper are the baseline for more advanced study to evaluate the performance of defective repairs in severe loading conditions (fatigue) that is underway by the authors. The nondestructive tests are performed by Iowa State University while the destructive tests are performed by North Carolina A&T State University. The testing program consists of 14 panels of six-ply (300 mm 675 mm) ((60/60/0)s) quasi-isotropic laminates: three pristine (undamaged parent material panels), three damaged panels without repair, three good repairs, three defective repairs due to inserted engineered flaw, and two repairs with mismatched fiber orientation. Two types of defective repairs are investigated: inserting 1-in. circular disbond between the sixth ply and the parent material forms the first type while the second type is formed by fiber mismatching between the patch and the parent material. Based on the evaluation performed in this study, the restored tensile strength of both defective and good repairs is within 80% of the strength of the pristine panels.