# Modelling of Failure Behaviour of 3D-Printed Composite Parts
## 1 Introduction  
Additive manufacturing (AM) technology, also known as 3D printing, usage is increasing for many engineering applications [1]. Material extrusion-based AM technology is rising in popularity for producing large-scale composite structures [2], and further, the technology is versatile and can even process metals [3]. However, this latest manufacturing technology has certain limitations and challenges while processing composite materials, including voids, weak bonding of reinforcements and matrix, process-oriented properties, and weak interfacial properties [4; 5]. Furthermore, the material properties of the printed parts are not the same as those of virgin material, which is used for 3D printing and anisotropy is introduced in the properties [6]. Such variation in the properties of 3D-printed parts leads to complex failure behaviour, and further, it is crucial to understand design calculations. Therefore, our work is focused on developing an efficient computational methodology for accurately capturing the failure behaviour of 3D-printed composite parts. Several experimental works have focused on investigating the performance of 3D-printed parts under different mechanical loadings and its relation to the factors associated with the 3D printing process. Investigation of 3D-printed parts revealed that the process parameters, such as printing direction and build orientation, significantly influenced impact behaviour [7] and compressive behaviour [8]. Further, printing conditions, such as the temperatures of the bed and extruder, influenced the fracture properties of 3D-printed composites [9]. The interfacial fracture toughness of bimaterial composites can be enhanced with increased extruder temperature, but the increase in bed temperature can negatively affect the toughness. It was found that the angle-ply printing strategy exhibited bettertoughness than that of the cross-ply. However, the fatigue behaviour of 3D-printed composites with an angle ply printing strategy showed early stiffness degradation compared to other printing strategies [10]. Anisotropic performance is typical in 3D-printed lattice structures due to the variation in printing direction [11]. Investigation [12], on the flexural behaviour of printed composite parts, revealed that the composite material's distribution of reinforcements significantly influenced the parts' flexural response. The printed parts exhibited linear and nonlinear behaviour before fracture. The above studies indicated that the material behaviour of the printed parts is significantly influenced by the printing conditions, process parameters, printing strategies, and materials. Failure behaviour in 3D-printed parts is complex and is not a much-explored research topic. Understanding the failure of materials is important for the effective design of parts. Therefore, assessing the failure behaviour of the printed parts subjected to different mechanical loadings is gaining interest in recent times. [PERSON] et al. [13] employed fracture mechanics techniques, such as J integral and crack tip methods, to quantify the crack initiation and propagation in 3D-printed parts. [PERSON] et al. [14] utilized acoustic emission technology to investigate the damage behaviour. The investigation revealed that matrix buckling and interface failure are the primary failure modes in 3D-printed composite parts subjected to flexural loading. Furthermore, microscopic examination using a micro-CT scanner revealed that the parts also have other damage modes, such as matrix buckling, debonding, delamination, and fibre breakage. On the other hand, the predominant failure modes in 3D-printed honeycomb sandwich structures are indentation, bending of face sheet and core, and core shear [15]. It is clear that different failure modes occur in 3D-printed parts, and no single failure mode is primarily responsible for the ultimate failure of parts.