GFRP laminates modified with a viscoelastic layer for improvement of the response under low velocity impacts

Abstract

High speed crafts made of glass fibre reinforced polymers (GFRP) suffer in-service structural damage due to the slamming impacts, when the bottom surface impacts against the water. It is important to quantify the extend of the damage and progression during the service life of the ship. In this work, it is presented a methodology using non-destructive evaluation for the assessment of the level of damage in the laminated panels. It is also investigated the effect of the introduction of a viscoelastic layer, composed of two polymeric material with different stiffnesses, designed specifically to dissipate the impact energy. The combination of these polymers with different deformation response under compression, and due to the confinement of the elastomer in small cell surrounded by the rigid polymer, constitutes an effective mechanism of energy dissipation due to impacts, protecting the plies beneath the viscoelastic layer and minimizing the damaged generated in the laminates due to slamming. Test specimens have been prepared using GFRP prepregs cured Out-of-Autoclave (OoA) and impacted using a specifically designed device that apply pressure peaks in the laminates that resemble very closely those that appears in the hull due to slamming loads, and compared with and without viscoelastic layer in the laminate. Changes in panel compliance are used for monitoring the evolution of damage in the material, as a function of the number of repeated impacts imposed on the panel for every load condition. Drop weight tests have been also used to understand the percentage of the income energy that is generating damage in the material, and to establish threshold levels for damage initiation both for unprotected panels and those with viscoelastic shielding layer.