Ageing effect on the low-velocity impact response of 3D printed continuous fibre reinforced composites

Ageing effect on the low-velocity impact response of 3D printed continuous fibre reinforced composites L.M. Ferreiraa,b, M.T. Arandaa, M. Mu˜noz-Rejaa,b, C. Coelhoc, L. T´avaraa,∗ aGrupo de Elasticidad y Resistencia de Materiales, Escuela T´ecnica Superior de Ingenier´ıa, Universidad de Sevilla, Camino de los Descubrimientos s/n, 41092 Sevilla, Spain bEscuela Polit´ecnica Superior, Universidad de Sevilla, c/ Virgen de ´ Africa 7, 41011 Sevilla, Spain cUnidade Departamental de Enegnharias, Escola Superior de Tecnologia de Abrantes, Instituto Polit´ecnico de Tomar, Rua 17 de Agosto de 1808, 2200-370 Abrantes, Portugal Abstract This paper aims to analyse the low-velocity impact performance of 3D printed continuous carbon fibre reinforced composites manufactured by fused deposition modelling. Moreover, the effect of ageing on the impact properties and visual damage is studied. This evaluation is crucial for understanding the long-term behaviour and durability of these materials, enabling better design and engineering decisions in various applications where impact resistance is paramount. Low-velocity impact tests were conducted on specimens aged 1, 7, 15 and 30 days. An instrumented drop-weight testing machine was employed for the tests. The dimensions and layup sequence of the composite specimens were designed following the recommendations outlined in the ASTM D7136/D7136M standard for unidirectional composite tapes. Results showed that the initial elastic part slightly reduces with age. In addition, the severity of visual damage in the specimens clearly varied with age. The older specimens present the less visible damage but also the lower impact energy absorption. Keywords: 3D printing, Fused deposition modelling, Composites, Ageing, Low-velocity impact ∗Corresponding author. Tel.: +34 954487299. Email addresses: [email protected] (L.M. Ferreira), [email protected] (M.T. Aranda), [email protected] (M. Mu˜noz-Reja), [email protected] (C. Coelho), [email protected] (L. T´avara) Preprint submitted to Journal of L A T EX Templates June 1, 2023 Manuscript File Click here to view linked References 1. Introduction Additive manufacturing (AM) or 3D printing has transformed the traditional manufacturing process by enabling the development of intricate designs that were previously challenging to produce using conventional manufacturing methods [1]. One of the most widely used AM techniques is Fused Deposi-5 tion Modelling (FDM), which utilises thermoplastic based filaments to fabricate parts. FDM stands out for its affordability and its ability to generate robust and functional components [2, 3]. In parallel with the advancements in AM, there has been a surge of interest in developing reinforced materials. These materials possess internal structures10 that can be precisely engineered to meet specific mechanical performance requirements [4]. By incorporating reinforcements, such as particles [5], short fibres [6], or continuous fibres [7], 3D printing of polymeric materials can produce composites with enhanced mechanical properties. The utilisation of 3D printed continuous fibre filaments offers the flexibility to tailor fibre orienta-15 tion and arrangement according to specific design requirements, including the creation of sandwich structures with core materials [8, 9]. In recent years, significant efforts have been dedicated to analyse the mechanical properties of these reinforced components. Justo et al. [10] performed tensile, compression, and shear tests to examine the properties of 3D printed20 components reinforced with continuous carbon and glass fibres. Their study demonstrated that specimens reinforced with continuous fibres exhibited superior mechanical properties compared to non-reinforced ones. Another study by Pertuz et al [11], focused on exploring the effects of various reinforcement fibres (carbon, glass, and Kevlar®) on the static and fatigue behaviour of 3D printed25 specimens. Compressive and flexural mechanical properties of continuous fibre AM specimens were also evaluated by Araya-Calvo et al. [12]. Numerous works have also been conducted to study the methods and process parameters. Caminero et al. [13] focused on the effect of the layer thickness and 2 fibre volume fraction on the interlaminar bonding behaviour of printed speci-30 mens. In a similar line, Chac´on et al. [14] analysed the effect layer thickness and feed rate on the mechanical properties of PLA samples. Additionally, printing directions have been also found to play a role, as demonstrated by Aranda et al. [15], showing that the fracture toughness increased by printing the fibres vertically instead of horizontally in structured interfaces in adhesive joints. With35 respect to the anisotropic behaviour inherent to the FDM process, Zhang et al. [16] presented an improved aligned deposition method or Sangaletti and Garcia [17] analysed reinforced filament deposition path capabilities on V-notch and Open-Hole specimens. Nevertheless, factors such as the fibre content and interlaminar adhesion40 within the material have a significant influence on the impact resistance of 3D- printed composites. Understanding the impact damage in composite materials has generated significant interest and it has been extensively studied for traditional composites [18], and remains an ongoing challenge [19, 20]. Frequently, composite structures are subjected to low and/or high-velocity45 impact loads over their service life, e.g. aircraft structures or wind turbine blades may be subjected to hit by hail or a bird strike [21, 22]. These types of load are usually classified as low or high-velocity impact depending on the contact time between the projectile and the target, the mass of the projectile, and the way the structure absorbs the kinetic energy [23, 24].50 In the context of structures exposed to low-velocity impact loads, the overall energy absorption capacity of the structure plays a critical role. The ability to dissipate kinetic energy effectively is influenced by various internal damage mechanisms that depend on the composite material’s mechanical behaviour and geometric characteristics. These mechanisms include matrix-cracking, delami-55 nation and fibre failure [25, 26, 27]. It is important to note that the resulting damage may not be readily visible on the structure’s surface, which can lead to a reduction in the component’s residual strength while it remains in service. The significance of these internal damage mechanisms becomes even more crucial as they can compromise the energy absorption capability of the composite struc-60 3 ture. The accumulation of damage can result in a reduced capacity to absorb impact energy, thereby increasing the risk of catastrophic failure or decreased performance over time. The response of structures under low-velocity impact loads has been extensively studied for thermoset composite materials manufactured by different65 curing methods in recent years. However, research focused specifically on 3D printed composites, particularly in terms of understanding the low-velocity impact damage behaviour has received very scarce attention. Some significant efforts regarding the dynamic behaviour of components produced by 3D printing were provided by Papa et al. [28] in which the low-velocity impact behaviour70 of four kind of specimens (combining Nylon®, Onyx®and glass fibre reinforced layers) were examined. Also a non-destructive evaluation was done in order to estimate the impact damage tolerance. Caminero et al. [29] also studied the impact strength of 3D printed continuous fibre reinforced thermoplastic composites by means of Charpy tests, employing nylon based composite specimens75 reinforced with different fibres such as carbon, glass and Kevlar®. The results revealed that glass fibre-reinforced composites exhibited the best impact performance while carbon fibre resulted in the lowest impact resistance, leading to a more brittle behaviour. Additionally, another relevant factor to consider during the analysis of the80 impact behaviour in 3D composites is related to the ageing effect on the properties of the specimen. According to T´avara et al. [30], 3D printed material properties can be affected over time. These experimental results showed the influence of some hygrothermal properties due to the nature of polyamide (PA /Nylon®), resulting in an ageing effect even for standard environmental condi-85 tions. Specifically, the Young modulus, the elastic limit values and the ultimate tensile strength were lower for the older specimens while the ultimate tensile strain where higher for the older coupons. Finally, the fracture toughness values remained similar through the different ageing stages. Therefore, the motivation of the present research is twofold:90 4 (i) First, stemming from the scarcity of previous studies on the low-velocity impact behaviour of 3D printed composites, as recalled above, the objective is to evaluate this impact response of the 3D printed composite laminates reinforced with continuous carbon fibres. By focusing on this aspect, the study aims to provide valuable insights into the impact per-95 formance of 3D printed composites, which is essential for their practical applications. (ii) Motivated by the findings reported in [30] regarding the ageing effect in 3D printed short carbon-fibre composites, the second objective is to explore whether similar ageing effects would also occur in 3D printed composites100 with continuous fibre reinforcement. By specifically considering continuous fibre reinforcement, which represents a significant aspect of composite materials, the study aims to advance the knowledge in this field associated with the long-term performance of 3D printed composites. The document is organised as follows. The experimental procedure is de-105 scribed in Section 2, including the specimen design and manufacturing as well as the experimental set-up. The results are compared and discussed in Section 3. Finally, the main conclusions are summarised in Section 4. 2. Experimental procedure The composite specimens used in this study were manufactured by FDM,110 using a Markforged®MarkTwo 3D printer. This equipment uses a single print head with a dual-extruder heated setup and two dedicated nozzles (for different kind of filaments). One of them is dedicated to a composite base filament which includes a thermoplastic matrix and a tow of embedded continuous fibres (e.g. glass, carbon and kevlar). The second nozzle is used to print a Nylon filament115 that may be reinforced (or not) with short carbon fibres. Both filaments are deposited over an unheated bed. In the present study, two kind of filaments were used: (a) Nylon including short carbon fibres (Onyx®) and (b) continuous carbon fibre reinforced polymer 5 (CFRP), both of them supplied by Markforged®. These filaments were used at120 the different layers of the analysed composite specimens. The properties of the filaments extracted from the manufacturer datasheet are listed in Table 1. Figure 1: Tested specimens: (a) Geometric dimensions; (b) Lay-up sequence. The design dimensions of the specimens, represented in Fig. 1 (a), are denoted as length l=150 mm, width, w=100 mm. While, the actual specimen thickness is h=2.11±0.03 mm. The lay-up sequence, shown in Fig. 1 (b), was125 defined according to the ASTM D7136/D7136M standard [31], for unidirectional tape composites, that is, [45/0/-45/90]s. The manufacturer’s 3D printer slicer software Eiger®was used to import a previously generated STL file with the specimens’ three dimensional surface geometry. Eiger®also defines a few slicing parameters, such as material se-130 lection, layer thickness, total number of layers, fibre angles and infill pattern. The deposition temperature of the material and the feed rate are defined by the software and cannot be changed. Some of these parameters are known to affect the mechanical performance of the specimens [14, 32]. The most relevant printing parameters used in the manufacturing of the specimens are presented135 6 Table 1: Properties of the filaments used to manufacture the specimens by FDM (supplied by Markforged®). Property CFRP filament Onyx® Tensile Modulus (GPa) 60 2.4 Flexural Modulus (GPa) 51 3.0 Tensile Strength (MPa) 800 40 Flexural Strength (MPa) 540 71 Density (g/cm3) 1.4 1.2 Filament diameter (mm) 1.75 1.75 in Table 2. It should be noted that the minimum number of roof and floor layers allowed by the printer is 4 layers and that the raster angle used in those layers can not be changed too. The printing time for each specimen was approximately 5 hours. The instrumented drop-weight testing machine IMATEK-IM10 shown in Fig-140 ure 2, was employed to conduct the low-velocity impact tests. This machine uses a guided mass system to ensure the correct positioning of the impactor throughout the test, a second impact prevention system to avoid rebounding impacts, and a clamping system that follows the ASTM D7136/D7136M [31] requirements. The impact energy is controlled by the drop height and the impactor’s145 mass. The machine control (height, velocity or energy), data acquisition parameters (sample rate) and data visualisation are carried out via a PC using IMATEK ImpAcqt software. The impact force is measured with a piezoelectric load cell mounted immediately behind the impactor, and the impact velocity is measured through the time of flight of the impactor using a laser/photo-diode150 detector. Based on this captured data, the software calculates the displacement (or deflection) of the plate using the definite integral of the acquired velocity function v(t), and the impact energy is measured from the kinetic energy of the impactor. A hemispherical shaped impactor with a 10 mm diameter and a mass of 2820155 7 Table 2: Printing parameters Parameter Value Infill pattern Solid fill Fibre fill type Isotropic Layer thickness 0.125 mm Roof (Onyx®) layers 4 Floor (Onyx®) layers 4 Onyx raster angles 45/-45/45/-45 CFRP filament layers 8 Fibre angles 45/0/-45/90/90/-45/0/45 Temperature at nozzle — Onyx®265◦ Temperature at nozzle — Carbon fibre 255◦ g was used in this study. This configuration provides an impact energy of 5.2 ±0.1 J corresponding to an impact velocity of 1.92 m/s. A total of 20 specimens were tested, with 5 specimens related to each test condition (following the guidelines outlined in [31]). The test conditions were determined based on different ageing periods, that is, 1, 7, 15 and 30 days ±1160 day. All the experiments were performed at room temperature. 3. Results and discussion This section presents a comprehensive analysis of the effect of ageing on the low-velocity impact response of the 3D printed composite laminates. Thus, the experimental force-time, force-displacement, and energy-time curves for ageing165 periods of 1, 7, 15, and 30 days were obtained, see Figs. 3, 4, and 5, respectively. These figures depict representative curves of the tested specimens, along with the upper and lower limits of the experimental data, providing a comprehensive overview of the low-velocity impact response. In the force-time and force-displacement curves, it can be observed the dis-170 tinct oscillations that arise from the vibrations experienced by the specimens 8 Figure 2: Instrumented drop weight testing machine: (a) Main machine systems and components; (b) Detail of the specimen‘s clamping. during the test [33, 34, 35]. These oscillations are a result of the dynamic nature of the impact event and reflect the structural response of the composites. By capturing these vibrational patterns, the curves provide valuable insights into the behaviour and performance of the laminates under low-velocity impact175 conditions. Table 3 complements the graphical representations by presenting the maximum values obtained for the force, displacement, contact time, absorbed energy, and impact bending stiffness. These quantitative measurements offer a concise summary of the impact response for each ageing period, facilitating a compari-180 9 Figure 8: Comparison of effect of ageing on the force-time histories a reduced severity. The damage patterns on both the top and bottom faces are comparable, indicating a slightly improved resistance to impact forces with increased ageing time. On the other hand, the specimens aged for 15 days exhibit noticeably distinct damage modes, as seen in Fig. 7. On the top face, a small depression is observed260 at the impact point, without any puncture or surface buckling. Similarly, the damage on the bottom face appears as a barely visible dent. These damage modes indicate a different response of the composite material to the impact, suggesting an enhanced ability to distribute and dissipate the impact energy over a wider area.265 Furthermore, extending the ageing time from 15 to 30 days does not result in substantial differences in the damage modes, as shown in Fig. 7. The damage response remains relatively consistent, with no significant increase in severity. This finding suggests that the ageing process may have reached a saturation point in terms of its influence on the damage response, and eventually further270 ageing does not lead to a substantial worsening of the damage. The energy histories presented in Fig. 9 and Table 3 provide additional support for these findings. It is well-established that damage severity increases as the absorbed energy increases [34]. Accordingly, the energy analysis reveals 16 Figure 9: Comparison of effect of ageing on the energy-time histories that the specimens aged for 1 and 7 days absorbed an average of approximately275 93% and 91% of the impact energy, respectively. In contrast, the specimens aged for 15 and 30 days absorbed an average of approximately 75% and 69% of the impact energy, respectively. These energy absorption percentages further confirm the trend observed in the visual inspection, where the severity of damage decreases with increased ageing time.280 Collectively, the visual inspection and impact response curves provide evidence that the ageing process has a substantial influence on the severity of damage in the 3D printed continuous carbon fibre reinforced composites. The findings highlight the importance of considering ageing effects when evaluating the impact performance and durability of these materials, as well as their285 potential application in industries where resistance to damage is critical. A plausible explanation for the observed behaviour of the 3D printed composite laminates with respect to ageing is the plastification of the matrix due to moisture absorption. It is important to note that the base material of 3D printed CFRP layers is a hydrophilic polymer (nylon). Additionally, the spec-290 imens include top and bottom layers made of Onyx®(nylon reinforced with micro carbon fibres). As hydrophilic materials, they have an inherent affinity for water. 17 Figure 10: Comparison of effect of ageing on the force-displacement histories In this context, when exposed to a moist environment, water molecules can penetrate the polymer matrix and establish interactions with the poly-295 mer chains. This interaction leads to a reduction in the cohesive forces between the chains. The moisture acts as a plasticity agent, effectively increasing the mobility and ductility of the polymer chains within the polymer matrix [38, 39]. The plastification effect induced by absorbed moisture can increase the overall ductility of the composite, allowing for greater deformation during a low-300 velocity impact event. This increased ductility may contribute to the observed decrease in the severity of damage as the ageing period extends. 4. Conclusions This study aimed to assess the influence of ageing on the low-velocity impact performance of 3D printed continuous carbon fibre reinforced composites305 manufactured using fused deposition modelling technique. The investigation is focused on evaluating the impact properties of the composite specimens over a range of ageing time. To ensure standardisation and comparability, the dimensions and layup sequence of the composite specimens were designed following the recommenda-310 18 tions outlined in the ASTM D7136/D7136M standard for unidirectional composite tapes. This standard provides guidelines for creating uniform and reproducible test specimens, thereby facilitating accurate assessment of material properties. The specimens were subjected to an ageing process, during which they were315 stored for 1, 7, 15 and 30 days. This allowed examination of the effect of time-dependent changes on the impact mechanical behaviour of the 3D printed composite specimens. Ageing can often lead to alteration of material properties, making it crucial to understand its effect on the performance of 3D printed carbon fibre reinforced composites.320 To evaluate the low-velocity impact response of the aged specimens, an instrumented drop-weight testing machine was employed. This testing apparatus enabled the measurement of the load and energy histories experienced by the composites under controlled conditions. The force-time and force-displacement curves showed that all tested specimens exhibited similar behaviour until the325 force approached its peak. However, a sharp drop in the impact force occurred near the peak, indicating substantial damage to the specimens. However, the magnitude of this jump decreased with ageing, suggesting different damage mechanisms occur for the different configurations. The impact bending stiffness was found to decrease with ageing. This finding is more significant for the330 specimens aged for 15 and 30 days, as they demonstrate a more pronounced reduction in IBS compared to 1 and 7 days. The severity of damage observed in the specimens also varied with age. The specimens aged for 1 day displayed the most severe damage, while those aged for 7 days showed comparable but less severe damage, characterised by punctured335 areas and surface buckling near the impact point. Notably, the specimens aged for 15 days exhibited distinct damage modes, including a small depression at the impact point without puncture or surface buckling, accompanied by barely visible dent damage. Extending the ageing period from 15 to 30 days did not yield substantial differences in the damage response. It is also remarkable that340 the energy impact absorption decreases when the age of the coupons increases. 19 A plausible explanation for these observations is the plastification of the matrix resulting from moisture absorption during ageing. The absorption of moisture by the matrix can lead to changes in its mechanical properties, affecting the impact response and damage mechanisms of the matrix.345 The ageing process significantly influenced the low-velocity impact performance of the 3D printed continuous carbon fibre reinforced composites. Understanding the effects of ageing on the mechanical behaviour and damage modes of these materials is crucial for their reliable and efficient utilisation in various applications, aiding in the design and engineering decisions to ensure long-term350 durability and performance. Further research can delve into the specific mechanisms behind the observed damage modes and explore mitigation strategies to enhance the impact resistance in this type of composites. Acknowledgements This study was partially supported by the Junta de Andaluc´ıa and European355 Social Fund (P20-00595), and the Spanish Ministry of Science and Innovation and European Regional Development Fund (PID2020-117001GB-I00, TED2021- 131649B-I00, PID2021-123325OB-I00). References [1] A. Nazir, O. Gokcekaya, K. Md Masum Billah, O. Ertugrul, J. Jiang,360 J. Sun, S. Hussain, Multi-material additive manufacturing: A systematic review of design, properties, applications, challenges, and 3d printing of materials and cellular metamaterials, Materials & Design 226 (2023) 111661. doi:https://doi.org/10.1016/j.matdes.2023.111661. [2] P. K. Penumakala, J. Santo, A. Thomas, A critical review on the fused de-365 position modeling of thermoplastic polymer composites, Composites Part B: Engineering 201 (2020) 108336. doi:https://doi.org/10.1016/j. compositesb.2020.108336. 20 [3] T. N. A. T. Rahim, A. M. Abdullah, H. Md Akil, Recent developments in fused deposition modeling-based 3d printing of polymers and their com-370 posites, Polymer Reviews 59 (4) (2019) 589–624. [4] F. Mashayekhi, J. Bardon, V. Berth´e, H. Perrin, S. Westermann, F. Addiego, Fused filament fabrication of polymers and continuous fiberreinforced polymer composites: Advances in structure optimization and health monitoring, Polymers 13 (5) (2021). doi:10.3390/polym13050789.375 [5] G. Griffini, M. Invernizzi, M. Levi, G. Natale, G. Postiglione, S. Turri, 3d- printable cfr polymer composites with dual-cure sequential ipns, Polymer 91 (2016) 174–179. [6] J. Reverte, M. Caminero, J. Chac´on, E. Garc´ıa-Plaza, P. L´opez, J.-P. B´ecar, Mechanical and geometric performance of PLA-based polymer composites380 processed by the fused filament fabrication additive manufacturing technique, Materials 13 (04 2020). doi:10.3390/ma13081924. [7] P. Zhuo, S. Li, I. A. Ashcroft, I. A. Jones, Continuous fibre composite 3d printing with pultruded carbon/pa6 commingled fibres: Processing and mechanical properties, Composites Science and Technology 221 (2022) 109341.385 [8] I. Papa, A. Silvestri, M. Ricciardi, V. Lopresto, A. Squillace, Effect of fibre orientation on novel continuous 3d-printed fibre-reinforced composites, Polymers 13 (2021) 2524. doi:10.3390/polym13152524. [9] K. Sugiyama, R. Matsuzaki, M. Ueda, A. Todoroki, Y. Hirano, 3d printing of composite sandwich structures using continuous carbon fiber and fiber390 tension, Composites Part A: Applied Science and Manufacturing 113 (2018) 114–121. doi:https://doi.org/10.1016/j.compositesa.2018.07.029. [10] J. Justo, L. T´avara, L. Garc´ıa-Guzm´an, F. Par´ıs, Characterization of 3d printed long fibre reinforced composites, Composite Structures 185 (2018) 537–548.395 21 [11] A. D. Pertuz, S. D´ıaz-Cardona, O. A. Gonz´alez-Estrada, Static and fatigue behaviour of continuous fibre reinforced thermoplastic composites manufactured by fused deposition modelling technique, International Journal of Fatigue 130 (2020) 105275. [12] M. Araya-Calvo, I. L´opez-G´omez, N. Chamberlain-Simon, J. L. Le´on-400 Salazar, T. Guill´en-Gir´on, J. S. Corrales-Cordero, O. S´anchez-Brenes, Evaluation of compressive and flexural properties of continuous fiber fabrication additive manufacturing technology, Additive Manufacturing 22 (2018) 157– 164. [13] M. A. Caminero, J. M. Chac´on, I. Garc´ıa-Moreno, J. M. Reverte, Interlam-405 inar bonding performance of 3d printed continuous fibre reinforced thermoplastic composites using fused deposition modelling, Polymer Testing 68 (2018) 415–423. [14] J. Chac´on, M. Caminero, E. Garc´ıa-Plaza, P. N´u˜nez, Additive manufacturing of PLA structures using fused deposition modelling: Effect of process410 parameters on mechanical properties and their optimal selection, Materials & Design 124 (2017) 143–157. doi:10.1016/j.matdes.2017.03.065. [15] M. T. Aranda, J. Reinoso, I. G. Garc´ıa, On different 3d printing methods and fracture performance in dcb composite specimens including structured interfaces, Theoretical and Applied Fracture Mechanics 122 (2022) 103552.415 [16] K. Zhang, H. Zhang, J. Wu, J. Chen, D. Yang, Improved fibre placement in filament-based 3d printing of continuous carbon fibre reinforced thermoplastic composites, Composites Part A: Applied Science and Manufacturing 168 (2023) 107454. [17] S. Sangaletti, I. Garc´ıa, Fracture tailoring in 3d printed continuous fibre420 composite materials using the phase field approach for fracture, Composite Structures 300 (2022) 116127. 22 [18] S. Safri, M. Sultan, N. Yidris, F. Mustapha, Low velocity and high velocity impact test on composite materials - a review, International Journal of Engineering and Sciences 3 (2014) 50–60.425 [19] P. Reis, P. Sousa, L. Ferreira, C. Coelho, Multi-impact response of semicylindrical composite laminated shells with different thicknesses, Composite Structures 310 (2023) 116771. doi:https://doi.org/10.1016/j. compstruct.2023.116771. [20] L. M. Ferreira, C. Coelho, P. Reis, Numerical simulations of the low-velocity430 impact response of semicylindrical woven composite shells, Materials 16 (04 2023). doi:10.3390/ma16093442. [21] F. Santos, H. Rebelo, M. Coutinho, L. Sutherland, C. Cismasiu, I. Farina, F. Fraternali, Low velocity impact response of 3d printed structures formed by cellular metamaterials and stiffening plates: PLA vs. PETg, Com-435 posite Structures 256 (2021) 113128. doi:https://doi.org/10.1016/j. compstruct.2020.113128. [22] Y.-T. Kao, A. R. Amin, N. Payne, J. Wang, B. L. Tai, Low-velocity impact response of 3d-printed lattice structure with foam reinforcement, Composite Structures 192 (2018) 93–100. doi:https://doi.org/10.1016/j.440 compstruct.2018.02.042. [23] W. Cantwell, J. Morton, Comparison of the low and high velocity impact response of cfrp, Composites 20 (6) (1989) 545–551. [24] W. Cantwell, J. Morton, Impact perforation of carbon fibre reinforced plastic, Composites Science and Technology 38 (2) (1990) 119–141.445 [25] M. Richardson, M. Wisheart, Review of low-velocity impact properties of composite materials, Composites Part A: Applied Science and Manufacturing 27 (12) (1996) 1123–1131. doi:10.1016/1359-835X(96)00074-7. 23 [26] R. Olsson, Low-and medium-velocity impact as a cause of failure in polymer matrix composites, in: Failure Mechanisms in Polymer Matrix Composites,450 Elsevier, 2012, pp. 53–78. [27] R. Olsson, Analytical prediction of damage due to large mass impact on thin ply composites, Composites Part A: Applied Science and Manufacturing 72 (2015) 184–191, publisher: Elsevier. [28] I. Papa, E. Manco, G. Epasto, V. Lopresto, A. Squillace, Impact behaviour455 and non destructive evaluation of 3d printed reinforced composites, Composite Structures 281 (2022) 115112. doi:10.1016/j.compstruct.2021. 115112. [29] M. Caminero, J. Chac´on, I. Garc´ıa-Moreno, G. Rodr´ıguez, Impact damage resistance of 3D printed continuous fibre reinforced thermoplastic compos-460 ites using fused deposition modelling, Composites Part B: Engineering 148 (2018) 93–103. [30] L. T´avara, C. Madrigal, M. T. Aranda, J. Justo, Anisotropy and ageing effect on the mechanical behaviour of 3d-printed short carbon-fibre composite parts, Composite Structures (2023) In Press.465 [31] Standard Test Method for Measuring the Damage Resistance of a Fiber Reinforced Polymer Matrix Composite to a Drop Weight Impact Event., Standard, American Society for Testing and Materials (2005). [32] M. Fernandez-Vicente, W. Calle, S. Ferrandiz, A. Conejero, Effect of infill parameters on tensile mechanical behavior in desktop 3d printing,470 3D Printing and Additive Manufacturing 3 (3) (2016) 183–192. doi: 10.1089/3dp.2015.0036. [33] L. M. Ferreira, C. A. C. P. Coelho, P. N. B. Reis, Numerical simulations of the low-velocity impact response of semicylindrical woven composite shells, Materials 16 (9) (2023). doi:10.3390/ma16093442.475 URL https://www.mdpi.com/1996-1944/16/9/3442 24 [34] P. Reis, P. Sousa, L. Ferreira, C. Coelho, Multi-impact response of semicylindrical composite laminated shells with different thicknesses, Composite Structures 310 (2023) 116771. doi:10.1016/j.compstruct.2023.116771. [35] L. Ferreira, C. Coelho, P. Reis, Impact response of semi-cylindrical compos-480 ite laminate shells under repeated low-velocity impacts, in: 2022 Advances in Science and Engineering Technology International Conferences (ASET), 2022, pp. 1–5. doi:10.1109/ASET53988.2022.9735043. [36] O. David-West, D. Nash, W. Banks, An experimental study of damage accumulation in balanced cfrp laminates due to repeated impact, Composite485 structures 83 (3) (2008) 247–258. [37] Study on visual inspection of composite structures, Tech. rep., European Aviation Safety Agency, J. Baarab (2009). [38] E. Woldesenbet, N. Gupta, J. Vinson, Determination of moisture effects on impact properties of composite materials, Journal of Materials Science 37490 (2002) 2693–2698. [39] M. Johar, W. Chong, H. Kang, K. Wong, Effects of moisture absorption on the different modes of carbon/epoxy composites delamination, Polymer Degradation and Stability 165 (2019) 117–125. 25