Abstract

A numerical approach has been developed for modelling the behaviour of a carbon fibre woven laminate under low-level energy impact. The model results have been compared with dart drop tests under sub and supercritical impact energies in fibre carbon textile laminates of different thickness.The models were developed using Ls-Dyna explicit finite element code. The validation approach was based in increasingly complexity approach. First models were developed and compared with subcritical impact energy test. Afterwards, supercritical impact energy has been applied in the laminates and delamination failure has been considered. In order to model delamination damage, cohesive law has been applied using Ls-Dyna cohesive and contact elements. The validation of the model has been carried out by comparing force and displacements.

Abstract

Carbon/epoxy pre-impregnated has become one of the most demanded materials for some aeronautics structures. Boeing 787 and Airbus A350 are pioneers in incorporating carbon fiber-reinforced composite materials in primary structures as wings and airframe. Tailoring the laminate ply sequence involves a difficult challenge owing to the rigorous design and operational criteria. Given that composite materials present a high sensitivity to impact loads, it has been indispensable to examine the influence of different factors in the failure mechanisms after an impact event. In this work, the effect of impact energy, stacking sequence and thickness on the impact damage resistance of CFRP composites was investigated. Damage response parameters as peak force, absorbed energy and delamination threshold were obtained from the impact curves. Then, a C-Scan imagen showed the damage extension using the non-destructive inspection Phased Array.

Abstract

RESUMEN

En el presente trabajo se estudia un nuevo eco-composite tipo FWL (“Fiber-Wood Laminate”) obtenido mediante la hibridación de fibras naturales y láminas de madera. Para ello, se han fabricado laminados por infusión de bioepoxi (SuperSap®) reforzada con tres capas de fibra de lino bidireccional y dos chapas de madera de pino, una en cada cara del eco-composite. Posteriormente, se realizaron ensayos de tracción, impacto de baja energía (E₀=1J-25J) y se inspeccionó el daño mediante ultrasonidos. Igualmente, se repitió la caracterización para laminados sumergidos un periodo de bioactividad marina de 6 meses.

Los resultados muestran que el FWL presenta un aumento del módulo elástico del 58% frente al biocomposite de lino (FFRB). Tras la inmersión en agua de mar, se observa que la absorción de humedad provoca una caída de la rigidez del 4,6% y del 6,9% en el FWL y FFRB, respectivamente.

Por otro lado, los umbrales de penetración y perforación del FWL son un 29% y 32% inferiores a los correspondientes del FFRB. Después de la inmersión, dichos umbrales se desplazan a valores superiores en ambos eco-composites, más significativamente en el FFRB, debido al efecto plastificante de la absorción de humedad que se pone de manifiesto en los distintos patrones de daño observados por inspección mediante ultrasonidos.

En conclusión, las láminas de madera del FWL aumentan la rigidez a tracción del nuevo eco-composite y ejercen un efecto barrera frente a la absorción de humedad debido a la inclusión de la bio-resina en la estructura celular de la madera.

ABSTRACT

The present work explores a new concept of eco-composite named FWL (“Fiber-Wood Laminate”) obtained by combining natural fibres and wood sheets. The studied FWL configuration consisted of a single thin pinewood veneer at each of the outer layers of a bidirectional flax fibre-reinforced bio-epoxy (SuperSap®) manufactured by infusion. Tensile and low energy impact (E0=1J-25J) tests were performed and the damage was analysed by ultrasonic inspection. Furthermore, the last characterization was also conducted on laminates after being immersed during a marine bioactivity period of 6 months.

The results showed an increase in the Modulus of Elasticity by 58% in the FWL compared to the flax-reinforced biocomposite (FFRB). After seawater immersion, the stiffness decreased by 4.6% and 6.9% in the FWL and FFRB, respectively. The penetration and perforation energy thresholds of the FWL obtained by falling weight impact tests were 29 and 32% lower than those of the FFRB, respectively. The effect of seawater immersing entailed a displacement to higher values of the energy thresholds, mainly in those of the FFRB. The plasticizing result of moisture absorption was evident in the different damage patterns observed by ultrasonic inspection.

In conclusion, the thin pinewood veneers increased the tensile strength of the new eco-composite. The epoxy matrix filled the cellular structure of the wood, which acted as a barrier to reduce the water absorbed by the flax fibres.