Fused deposition modelling (FDM) is one of the fastest-growing additive manufacturing methods used in printing fibre-reinforced composites (FRC). The performances of the resulting printed parts are limited compared to those by other manufacturing methods due to their inherent defects. Hence, the effort to develop treatment methods to overcome these drawbacks has accelerated during the past few years. The main focus of this study is to review the impact of those defects on the mechanical performance of FRC and therefore to discuss the available treatment methods to eliminate or minimize them in order to enhance the functional properties of the printed parts. As FRC is a combination of polymer matrix material and continuous or short reinforcing fibres, this review will thoroughly discuss both thermoplastic polymers and FRCs printed via FDM technology, including the effect of printing parameters such as layer thickness, infill pattern, raster angle and fibre orientation. The most common defects on printed parts, in particular, the void formation, surface roughness and poor bonding between fibre and matrix, are explored. An inclusive discussion on the effectiveness of chemical, laser, heat and ultrasound treatments to minimize these drawbacks is provided by this review.

Among various bio-inspired structures, sutures are a prominent structure which has evolved independently to optimize their functionalities. The diabolical ironclad beetle suture-inspired structure was fabricated using multi-material additive manufacturing (3D printing) system with TangoBlackPlus (TBP) as the soft suture layer and VeroWhitePlus (VWP) as the hard material. The print quality of the specimen was assessed through the optical microscope images, and a nanoindentation test was performed to investigate the interfacial hardness between TBP and VWP. Flexural properties of the suture structure when changing the thickness of the soft layers were then studied. Experiments were continued to identify the effect of combining different sizes of suture modules to develop the suture structure. A numerical simulation model was then generated and validated using the experimental results to proceed with the parametric study. A design of experiment (DoE) was developed to analyse the effect of changing the suture geometry to optimize performance. The research concluded that gradually decreasing the size of the suture allowed the structure to withstand higher loads. It was also evident that the deformability of the structure could be increased by incorporating smaller interlocking angles and larger a:b ratios, while larger interlocking angles and smaller a:b ratios generate stiff structures.

Sutures are a ubiquitous feature in biological materials with great impact resistance properties. Sutures promote high energy absorption (EA) during impact loading due to their morphology and composition. The lack of studies on the impact resistance properties of sutures is a great limitation in understanding the potential of the sutures. Therefore, this research work focuses on investigating the behaviour of the suture structures under the drop-weight impact test. Suture design is inspired by the ellipse-shaped medial sutures in diabolical ironclad beetle. Test panels are fabricated from VeroWhitePlus, stiff material and TangoBlackPlus (TBP), rubber-like material using Stratasys PolyJet 3D printing. Five designs with equal volume fractions of TBP are developed and tested under the dop-weight impact test. The damage analysis confirmed that aligning the suture interfaces at different orientations in each layer can enhance the damage tolerance without complete perforation. Results indicated that the designs with suture interfaces parallel to the length of the specimen (Design_2) could provide an optimized structure due to lower reaction force and higher EA with minimum damage under different impact velocities.