Original Article Study of influence of interlocking patterns on the mechanical performance of 3D multilayer woven composites Muhammad Umair 1 , Syed Talha Ali Hamdani 1 , Muhammad Ayub Asghar 1 , Tanveer Hussain 1 , Mehmet Karahan 2 , Yasir Nawab 1 and Mumtaz Ali 1 Abstract Three-dimensional multilayer woven composites are mostly used in high-performance applications due to their excellent out-of-plane mechanical performance. The current research presents an experimental investigation on the mechanical behavior of three-dimensional orthogonal layer-to-layer interlock composites. The glass filament yarn and carbon tows were used as reinforcement in warp and weft directions respectively, whereas epoxy was used as a resin for composite fabrication. Three different types of orthogonal layer to layer interlock namely warp, weft, and bi-directional interlock composites were fabricated and the effect of interlocking pattern on their mechanical performance was evaluated. The evaluation of the mechanical performance was made on the basis of tensile strength, impact strength, flexural strength, and dynamic mechanical analysis of composites in warp and weft directions. It was found that warp and weft interlock composites showed better tensile behavior as compared to bi-directional interlock composite both in the warp and weft directions, due to the presence of less crimp as compared to the bi-directional interlock composite. However, the bi- directional interlock composite exhibited considerably superior impact strength and three-point bending strength as compared to the other structures under investigation. These superior properties of bi-directional interlock composites were achieved by interlocking points in warp and weft directions simultaneously, creating a more compact and isotropic structure. Tan delta values of dynamic mechanical analysis results showed that bi-directional interlock composite dis- played the highest capacity of energy dissipation in the warp and weft directions while weft interlock structures displayed highest storage and loss moduli in the warp direction. Keywords Three-dimensional orthogonal layer-to-layer interlock, bi-directional interlock, three-dimensional woven composites Introduction Woven fabric structures are divided into two catego- ries, i.e. two-dimensional (2D) and three-dimensional (3D) multilayer interlocks. 1–3 The 2D woven structures have substantial length and width with very small thickness, while multilayer interlock (3D) structures have a significant value of thickness too. Such fabrics are produced with the yarns oriented along the X-axis (longitudinal), Y-axis (cross), and Z-axis (vertical). 4,5 The 2D structures generally serve as reinforcement for laminated composites, which have optimal in- plane performance but their out-of-plane properties are poor. 6 The multilayer interlock structures have Z yarns along thickness, which provide the strength and stiffness in the out-of-plane direction. Therefore, com- posites reinforced with multilayer interlock structures show excellent performance properties as compared to 2D fabrics. 7 1 Textile Composite Materials Research Group,Faculty of Engineering and Technology, National Textile University, Faisalabad, Pakistan 2 Vocational School of Technical Sciences, Uludag University, Gorukle, Bursa, Turkey Corresponding author: Yasir Nawab, Textile Composite Materials Research Group, Faculty of Engineering and Technology, National Textile University, Sheikhupura Road, Faisalabad, Punjab. Email: yasir.nawab@yahoo.com Journal of Reinforced Plastics and Composites 0(0) 1–12 ! The Author(s) 2018 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0731684417751059 journals.sagepub.com/home/jrp