## 1 Introduction  
The aerospace sector is one of the engineering industries where the most importance is given to the innovation of new materials due to the working conditions that aircraft must endure in the distinct phases of flight. The use of composite materials in the aerospace industry has grown since 1980 thanks to their low density, better mechanical properties, and chemical inhibition in comparison to aluminum alloys used, such as 2024, 6061, and 7075 [1, 2]. Unfortunately, composite materials have many defects: one of these is delamination, which is a critical failure mechanism in laminate composites caused by high interlaminar stresses coupled with typically exceptionally low through thickness strength. The phenomenon arises because the fibers lying in the plane of a laminate do not provide reinforcement through the thickness, so the composite transfers all external loads into the weaker matrix [3, 4]. As far as delamination solution goes, several types of manufacturing that drastically improve interlaminar resistance have been studied, such as 3D weaving, z-pinning, braiding, tufting, and stitching [5, 6, 7, 8, 9]. Stitching is one of the most interesting processes since it is much easier to fabricate, and there are also methods used to join different composite parts [10]. There are several types of stitching, such as tufting and lockstitch, modified lockstitch, chain stitch and one side stitching, to name a few [11; 12; 13]. Stitched composites can improve up to 15 times on interlaminar resistance [14]. [PERSON] et al. [15] report that with their stitched method, the fracture toughness can increase 45 times more. Another study made a composite with 0.33 mm diameter steel wires separated by 1.6 mm; this increased interlaminar resistance by 50%, but the manufacturing was non-practical [16]. Another study on carbon fiber/epoxy with Kevlar threads shows that while stitching arrests delamination, there is a variation in tensile strength [17]. Even so, there have been different studies related to issues in formability in stitch composites. Some have shown different methods to fit complex molds by cutting the woven materials and stitching them, which also increases the mechanical properties in the stitch joints [18; 19; 20; 21; 22; 23; 24]. [PERSON] et al. [25] have shown that the density, direction, and pattern of the stitching are critical parameters for optimal mechanical properties. The density of the stitch is particularly important, such as there is a critical stitch density in which a maximum interlaminar resistance is reached. After that, no more resistance gain can be achieved, but a major density stitch can cause a misalignment within the woven material, which then affects its mechanical properties [26]. [PERSON] et al. [23] in their study showed that stitch density is inversely proportional to tensile strength by the creation of stress concentration in the stitching points. [PERSON] et al. [27] have shown that stitched composite increases impact resistance, but the damage zone has shown the formation of wrinkles which the unstitched sample does not have, leaving permanent deformation in some samples and a weak recovery after deformation in comparison to the non-stitched sample. To eliminate this, more layers of stitching must be made, but still, deformation recovery is compromised. The motivation of the present study is to manufacture an unmanned aerial vehicle made of composite material, and since delamination is a concern, the stitching process will be used to increase delamination resistance as it is the process more convenient to us, but more information regarding the effect of the stitching on all the mechanical properties is needed. This investigation is focused on the tensile fracture behavior in four lengths of nylon stitched patterns (0.5, 1.0, 1.5, and 2.0 mm) in a biaxial E-Glass Saertex 830 g/m\({}^{2}\)/Sypon 8086 polyester resin composite. Nylon yarn was chosen because of its low density, tensile and impact strength, and chemically inert property.