Increase of contact radius due to deflection in low velocity impact of composite laminates and prediction of delamination threshold load

An analytical method is proposed to calculate the increase of contact radius due to the deflection of the laminate subjected to low velocity impact with respect to that calculated with Hertz contact law. The method is validated with finite element method (FEM). The model of delamination threshold load (DTL) is improved based on the corrected contact radius. The low velocity impacts were conducted on a composite wing box, and the DTLs of skins were measured under the impacts of three indenters variant in diameter. The linear model was fist employed to prediction the DTLs, the maximum error of which reaches 27%. The increase of contact radius was calculated for each impact, which is ranging from 41% to 44%. The DTL were then recalculated based on the revised contact radius, and the prediction errors are lower than 6.5%. The presented method is less time consuming in comparison to the FEM and is applicable to predict the DTLs of a laminate family when the interlaminar shear strength is given.