Advanced TTT composite materials for aeronautical purposes: Compression after impact (CAI) behaviour

The purpose of this paper is to examine the behaviour of the dry stitched composites when they are subjected to low velocity impact loads. Such composites have been laminated in combination with the Resin Film Infusion (RFI) technique. The experimental results exposed in this document are obtained from the Compression before Impact (CBI) and Compression after Impact (CAI) test efforts. The CAI behavioural determination of such composites is very important in terms of residual strength status after impact because in this case their use in primary aeronautical structures has also to satisfy the stringent Certification Requirements for Airworthiness. Traditional stitching methodologies, using Kevlar 29 threads as a 3-directional reinforcement, are compared to other advanced techniques such as the "tufting" and z-pins insertion. Following the optimization of the needle pass and the pitching line, normalized compression tests have been performed on a number of specimens which have been obtained through the utilization of different fabrication techniques in both before and after impact conditions. This has been done so as to evaluate the strength decay due to the impact damage. The subjec tests' were performed at the Alenia Aeronautica laboratories and in accordance with the AECMA ST Std prEN 6038 standards. Finally a review and a discussion of the experimental results conclude the paper. (c) 2006 Elsevier Ltd. All rights reserved.