16th International Conference on Composite Structures ICCS 16 A. J. M. Ferreira (Editor) AN INDEX FOR THE INDENTATION SENSITIVITY OF COMPOSITE LAMINATES Giancarlo Caprino, Valentina Lopresto, Claudio Leone Department of Materials and Production Engineering, University of Naples “Federico II”, Piazzale Tecchio, 80, 80125 Naples (Italy) e-mail: caprinonina.it , loprestonina.it , leonenina.it Keywords: impact damage, indentation depth, impact energy, composite laminates. Summary. Many factors, impactor shape and energy, constraint conditions, target thickness and laminate stacking sequence, may influence the permanent indentation of a composite panel subjected to low velocity impact [1]. Using a hemispherical tup 12.7 mm in diameter, D t , in [2] the evolution of indentation depth, I, as a function of impact energy, U, was measured CFRP laminates of various lay-ups and thicknesses. As expected, I increased with increasing U and larger indentations were measured for lower thicknesses. The previous experimental data were then re-examined [3] and the effect of panel thickness can be eliminated if the ratio of the impact energy, U, to the perforation energy, U p , is considered. Plotting the indentation depth against U/U p all the I-U curves pertaining to different laminate thicknesses converged to a single master curve having equation: I = I 0 ⋅ U U p β 1) where I 0 , β are material constants to be experimentally determined. It was shown that the two parameters actually influencing I 0 and β are the fibre type and content. Additional indentation results were generated in a subsequent work [4] where a more effective formula, given by: I = k ⋅ 10 γ U/U 0 ( ) - 1 (2) was find to better describe the trend for higher U/U p values. In equation 2, the constants k, γ has to be experimentally determined. In this work, the effectiveness of a new empirical model, aiming to predict the indentation depth resulting in a composite laminate from a hemispherical tup impacting it at low velocity, is verified: I =α⋅ D t ⋅ U/U p 1 - U/U p (3)