PSI - Issue 37

P. Santos et al. / Procedia Structural Integrity 37 (2022) 833–840

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P.Santos et al. / Structural Integrity Procedia 00 (2019) 000 – 000

1. Introduction Greenhouse gas emissions due to the excessive use of fossil resources are at the origin of an increased interest in the development of bio-composites, and in particular materials reinforced with plant (lignocellulosique) fibres (Abderrezak Bezazi et al., 2020; Maache et al., 2017; Saaidia et al., 2017). The use of materials derived from biomass helps to reduce the environmental problems, especially pollution and global warming, and preserves fossil resources. On the other hand, due to the development of sustainable and environmentally friendly materials, the green resins are an alternative to petroleum-based resins to manufacture eco-friendly and biodegradable composites as consequence of their mechanical performances and desirable functional properties that allow chemical modifications. Compared to synthetic fibres, lignocellulosique ones have numerous advantages: biodegradable, low density, relatively low price, available in abundance in the form of fibres, and so on. The number of research devoted to the study of composite materials based on natural fibres obtained from different plants has considerably increased in recent years from an academic point of view and by the multiplication of industrial applications (Abderrezak Bezazi et al., 2014; Boumediri et al., 2019; Fiore et al., 2016; García del Pino et al., 2020; Khelifa et al., 2021). In other words, different lignocellulosique fibres have been proposed by several researchers to replace the traditional synthetic fibres to reduce the environmental impact, which led to a reorientation of research towards this type of natural and biodegradable composites (Amroune et al., 2015; Bouakba et al., 2013; Bouhemame et al., 2021; Manimaran et al., 2018; Vijay et al., 2020). In the same context, cork is a natural and sustainable core material, from the cork oak bark, offering excellent fire, smoke and toxicity properties associated with good mechanical and processing characteristics. Perfectly aligned with the new green classifications, its closed air cell’s structure promotes low water absorption, high rot resistance and good impact tolerance. The industrial processing of cork covers a wide field ranging from bottle stoppers to thermal and acoustic insulation in buildings and homes, for rolling and space vehicles (Silva et al., 2013). Sandwich panel composite materials are generally composed of two thin skins bonded to a thick, low-density core and have been used extensively in several fields of engineering. Usually, the skins are made of aluminium alloys or fibre reinforced laminates, and the most used core materials are PVC, Rohacell, metallic foams, aluminium honeycombs, cardboard, aramid, etc. (A. Bezazi et al., 2007, 2009). Sandwich panels have many advantages including excellent high strength/weight ratio, fire resistance, thermal insulation, sound insulation and cost-effectiveness (Reis et al., 2013). Regardless of the benefits reported above, literature shows that composites reinforced with natural fibres are sensitive to low velocity impact loads (i.e., low impact resistance), while composites reinforced with cork powder absorb more energy (Santos et al., 2020; Silva et al., 2019). Therefore, the main goal of this study is to develop two novel types of bio-composites: a laminate and a sandwich. The laminate is produced from date palm leaflet and a green epoxy resin, while the sandwich is manufactured from the same type of laminate and a cork core. The choice of the palm leaflet is mainly justified by reasons of availability in Algeria, which has more than twenty million date palms, and good tensile strength (Bouhemame et al., 2021). Both the bio-laminate and the bio-sandwich that were developed are, subsequently, subjected to impact tests with three different energy levels. The results are presented and discussed in this paper in terms of load-time and energy-time diagrams. 2. Materials and Methods Date palm leaflets were used in this study, and the manufacturing process of the composite laminates is summarized in Fig. 1. After manual harvesting and separation from the rachis, the leaflets were washed with water to remove dust/impurities and, subsequently, air-dried in a shaded place for 7 to 8 days. The length of the leaflets was measured using a ruler, while for the width (measured in two distinct regions: inferior and intermediate) and for the thickness, a digital caliper with 0.01 mm precision was used. Average values of 450 mm were obtained for the length, 0.4 mm for the thickness and 27.2 and 32.5 mm for the inferior and intermediate width, respectively. Fig. 1a) shows the leaflets prepared to be inserted into the composite with 350 mm long. Posteriorly, these leaflets were manually aligned, one by one as shown in Fig.1b), along four layers to produce the final laminate and, between each layer, an amount of predefined resin was inserted. This assembly was carried out inside a cardboard frame to contain the resin and maintain the alignment of the leaflets. A SR Greenpoxy 56 resin and a SD Clean hardener, both supplied by Sicomin, were used as matrix in this bio-based composite. Finally, the system was placed inside a vacuum bag and a