PSI - Issue 42

Ayse Cagla Balaban et al. / Procedia Structural Integrity 42 (2022) 284–291 Ayse Cagla Balaban et al. / Structural Integrity Procedia 00 (2019) 000 – 000

285

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1. Introduction Composite materials are now the most preferred materials in marine, automotive, aerospace, civil engineering applications and navy industries. They possess high specific strength, high absorption, high bending stiffness, high load carrying capacity and thermal insulation as well as good sound reduction, they are light, and they provide significant advantages in application areas compared to traditional composites. Due to the increasing use of composite sandwich structures in different engineering applications, the failure criteria need to be well understood (Toygar et al., 2019; Klepka et al. 2013). Sandwich structure is a special form of laminated composite bonded together with a relatively thick, light and weak core. Many researchers have studied sandwich structures, (Zenkert, 1995; Balaban et al., 2019; Noor et al., 1991) however; only limited number of studies deal with the unsymmetrical sandwich composites (Castanie et al., 2002; Polyakov, 2001). Unsymmetrical sandwich structures appear to offer a real opportunity for the design of lightweight structures to be used in different industries due to their high specific strength (Castanie et al., 2002). Unsymmetrical sandwich technology provides an alternative to the classical approach of construction and marine industries. As an example, sandwich structures can be used, made of a thicker facesheet that suits to bear the loads and foam core that reduces vibration and noise while the thinner facesheet eases the junction with the other components of a boat (Di Bella et al., 2012). Furthermore, scenarios such as cracks, damages, and delamination from the core to the surface during production or service time can cause failures in structural integrity of the material. These scenarios should be estimated and analysed well in order to minimise the possible damages in the usage of sandwich composite materials during the service time (Balaban and Tee, 2019). Materials such as honeycomb, foam and polyurethane are commonly used as core materials in sandwich composites in order to reduce the weight and increase the strength of the material (Guler and Uyar, 2010). Although there are studies in the literature on the mechanical behaviours of different sandwich composites, studies obtained from composite materials with Carbon Fibre/Epoxy facesheets, and PVC foam core are quite promising for different industrial applications. Therefore, the examination of the mechanical properties of such materials, the analysis of their behaviour under different loading conditions and the pre-analysis of the failure scenarios will both fill the gap in the literature and prevent the catastrophic consequences that may occur in the areas of use of these materials in the future (Hayman et al.,2008). In this paper, sandwich composite materials manufactured by using PVC as core material and Carbon Fibre/Epoxy facesheets with different thicknesses are examined. The selection of PVC foam for this study is motivated by its wide use in load bearing components in different industries. Failure styles of the structure in compression, shearing and bending were revealed by sandwich flatwise tension, core flatwise compression, and sandwich edgewise compression tests. The detailed experimental process and calculations are provided. The experimental results according to ASTM standards are discussed. 2. Material In this study, the composite sandwich specimens are manufactured by using vacuum-assisted resin infusion moulding process (VARIM) by manufacturing company IZOREEL in Izmir, Turkey. Different thicknesses of lower and upper laminates are preferred due to similar examples used in marine applications. The upper and lower laminates are manufactured by nineteen and seven woven laminas with a unit mass of 200 gr/m 2 . The mechanical properties of upper and lower laminates and foam core are given in Table 1 and Table 2, respectively.

Table 1. The mechanical properties of upper and lower facesheets Facesheets Layer of Lamina

Fibres

Unit Mass (kg/m 2 )

2x2 Twill 3K Carbon Fibre Cloth

Upper Facesheet

19

0.20

2x2 Twill 3K Carbon Fibre Cloth

Lower Facesheet

7

0.20