Abstract

The post-impact strength of composite materials is one of the main design parameters of aeronautical structures in terms of damage tolerance. During the low-velocity impact test, from a threshold energy, the laminate only partially returns the energy received during the impact to the indenter (elastic recovery). The remaining energy is absorbed by the laminate and dissipated in the form of damage (interlaminar and intralaminar), plastic deformation of the polymer matrix and breakage of the carbon fibers. To date, few authors have attempted to quantify the participation of each of the damage mechanisms in the overall energy absorption process of the laminate due to their experimental difficulty. In this work, a methodology has been developed capable of performing damage of similar extent and location to that produced in a low-velocity impact, but without damaging the fibers, through the application of local induction heating. For this purpose, the residual strength and stiffness of AS4/PEEK laminates, subjected to impacts over a wide range of energies (30-70J), have been compared with those obtained in laminates damaged by electromagnetic currents, for equivalent damage extensions. The results reveal that the breakage of carbon fibers has a great influence on the loss of stiffness of the laminate, but not on its strength, confirming the role of delamination as the main responsible for the loss of the strength capacity of the damaged material.

Abstract

Primary structures fabricated with carbon/epoxy pre-impregnates has become very popular, especially in aeronautics and automotion. Despite the excellent properties of resistance and stiffness, composite materials present a high sensitivity to impact damage which can cause a sudden drop of mechanical properties affecting the service behavior and reducing the useful life. Here is where damage tolerance concept is introduced.In this work, firstly impact tests have been made in composite lamintes reinforced with carbon fiber, and then, the residual strength for the different stacking sequences have been evaluated using CAI (Compression After Impact) tests.

Abstract

In order to alleviate the adverse impact of the air transport on the environment, the UE has shown great interest in increasing the efficiency and safety of aircrafts, which covers the complete life cycle of aircrafts (design, production, maintenance, repair and update).Composite structures show high susceptibility to low-velocity impacts in the perpendicual direction to the plane of the laminate. The complete replacement of damaged components is not always possible due to the high level of integration of the structures and the large size of the components in many sectors (i.e. aeronautics). In this regard, the repair and subsequent put into operation of structures made of composite materials must be a cost-effective and time-saving process.Adhesive repairs present advantages in relation to mechanical repairs. There is a lack of knowledge in their behaviour under impact loads; therefore, the main goal of this work is to analyse the damage tolerance of composite repaired structures. To this end, an experimental study has been carried out on intact and repaired laminate specimens that allows comparing the structural response of both configurations.This study involves the generation of damage through low-velocity impacts (using a drop-weight tower), and subsequent compression tests in order to determine their residual stenght.