PSI - Issue 54

Wojciech Skarka et al. / Procedia Structural Integrity 54 (2024) 490–497 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

491

2

1. Introduction Airframe structures are comprised of basic elements that are connected to create a pathway for transmitting loads. The joints, or connections, represent potential weak points and play a crucial role in determining the overall effectiveness of the structure. Examples of these connections in airframe assemblies include the attachments between the skin and ribs, as well as between the skin and spars. Numerous researchers have delved into the behavior of these components, especially examining the failure mechanisms of composite laminate and composite T-joints Yap et al. (2002), Kesavan et al. (2006), Blake et al. (2001), Vijayaraju et al. (2004), Kumari and Sinha (2002), as well as sandwich joints Turaga et al. (2000), Zhou et al. (2008). Additionally, there has been considerable attention given to the impact of cutouts in sandwich panels and the reinforcement of cutouts around the free edges, with limited studies addressing this area De Boos et al. (2007), Guo et al. (2008), Guo et al. (2009). The traditional sandwich T-joint design involves incorporating features like a base core drop-off and merging the upper and lower composite faces to create a unified laminate in the joint area. However, this manufacturing process is intricate and expensive. The reinforcement of composite materials, such as carbon, glass, Kevlar, and other synthetic fibers, is crucial. On the other hand, there are fibers like natural fibers Kumpati et al. (2022), biodegradable and easy fracturing process. Natural fibers are widely used in aerospace, automotive, and various other applications. They are eco-friendly and biodegradable. This present study expands on the examination of sandwich T-joint structures, along with experimental work, to suggest design enhancements that facilitate simpler and more affordable manufacturing processes, all while maintaining the overall strength of the T-joint. The bio-composite structure can used for the UAV application. Initially, we have fabricated laminates for validation such as compressive test, tensile test, and flexural tests.

Nomenclature E 1

composite ply modulus in the longitudinal direction composite ply module in the transverse direction composite ply shear modulus in the i-j plane composite ply Poisson’s ratio in the 1 -2 plane tensile strength in the fiber direction compressive strength in the fiber direction tensile strength in the fiber transverse direction compressive strength in the fiber transverse direction composite ply stress in the 1 or 2- direction composite ply shear stress in the 1-2 direction composite ply strain in the 1-2 direction composite ply shear strain in the 1-2 direction

E 2 G ij ν 12 X t X c Y t Y c

σ 1, σ 2

τ 12

ɛ 1, ɛ 2

γ 12

2. Material methods The T-joint configuration consisted of two flat panels, a base panel and a web panel connected at a right angle by means of two L-shaped stringers. The base panel measured 180 mm in width and 260 mm in length, while the web panel had dimensions of 150 mm in height and 260 mm in length, as illustrated in Figure 1. The web panel was composed of a 3.5 mm thick foam adhered to 2 mm thick composite laminate surfaces which were comprised of 6 layers of jute- epoxy woven fabric arranged in a symmetrical [± 45] S layup and each layer having 0.35 mm thick. Each of the composite faces on the base was composed of 6 layers of the same jute-epoxy woven arranged symmetrically in a [± 45/0/ 90] S layup and ply thickness is 0.35 mm. In the joint area, the sandwich base panel featured a transition from foam to a monolithic laminate where the composite faces seamlessly merged. Two L-shaped stingers were affixed to the web faces and the monolithic base laminate to connect the two panels. These stringers were