It is important to develop numerical methods for the prediction ofthe residual strength of damaged structures in damage tolerancedesign. The buckling and postbuckling strength of stiffened compositeplates with impact damage are studied numerically and experimentally.The delamination distributions through the thickness due to lowvelocity impact are predicted by finite element analysis. Thedelamination failure criterion under impact loading is modified forstiffened composite plates. The predicted delamination distributionsare compared with experimental ones those are detected by an improvedultrasonic technique. To predict residual strength, a progressivefailure model with degradation of elastic moduli in damaged region isadopted in a nonlinear finite element method. The degradation ratioin each sublaminate is determined by delamination distributionsthrough the thickness of laminates. The predicted buckling andpostbuckling residual strength show good agreements with experimentalresults. The impact damage and the postbuckling residual strength ofblade stiffened composite plate are discussed.
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