3D-printed Composites Research Articles

Biomimetic 3D-printed Composites: Ballistic Impact Resistance with Nacre-Inspired and Tubulane Structures

This research delves into nature-inspired designs for creating materials with exceptional impact resistance, leveraging cutting-edge 3D printing techniques. Our composite design features a nacre-like outer layer combined with a tubulane-resembling core, aiming to enhance energy dissipation significantly. By emulating the dense aragonite structure found in natural nacre and the unique porosity of tubulane, to enhance ballistic impact resistance. To validate its effectiveness, we conducted ballistics tests using a 40-grain lead-tipped .22 LR bullet at an initial velocity of 330.7 m/s, with a specialized chronograph setup to measure both initial and post-penetration bullet velocities, quantifying energy absorption precisely. This study opens new frontiers in aviation safety, structural engineering, and personal protective equipment, showcasing the transformative potential of biomimicry and additive manufacturing in advancing public safety and material science.

Impact of pyrolysis heating methods on biochars with enhanced CO2/N2 separation and their incorporation in 3D-printed composites

N-doped biochars, derived from chitosan sourced from waste crustaceous shells, were produced via microwave-assisted pyrolysis at temperatures ranging from 400 to 800 °C to enhance CO2 and N2 separation. Their performance was compared with biochars from conventional pyrolysis. Microwave-derived biochars exhibited superior CO2 adsorption capacity at 25 °C and 100 kPa (0.78 – 1.56 mmol g−1) compared to conventionally produced ones (0.55 – 1.43 mmol g−1). Increasing the pyrolysis temperature up to 600 °C significantly improved biochar properties, including surface area, pore volume, and CO2 adsorption capacity. Microwave-derived biochar featured enhanced surface area, larger pore volumes, and unique morphologies, requiring, on average, 61 % less preparation time. The higher ultramicroporosity and N-species concentration correlated with superior performance in the biochar produced at 600 °C. In gas mixture experiments (20 % CO2 and 80 % N2) under flow conditions, these biochars showed rapid adsorption/desorption rates due to enhanced macroporosity at samples produced at 600 and 800 °C, facilitating gas diffusion along the ultramicropores. Adsorption heat analysis indicated that the CO2 adsorption is predominantly driven by physisorption, supported by complete sample regeneration when applying N2 flux or increasing the temperature during desorption. The study also explores the feasibility of 3D-printing a composite using the most effective biochar and inorganic polymers sourced from waste, presenting potential benefits for industrial applications.

Evaluation of the Properties of 3D-Printed Onyx-Fiberglass Composites.

This study evaluated the properties of 3D-printed Onyx-fiberglass composites. These composites were 3D-printed with zero, one, two, three, and four layers of fiberglass. Ten samples of each configuration were printed for the tensile and flexural tests. The average tensile strength of the Onyx specimens was calculated to be 44.79 MPa, which increased linearly by approximately 20-25 MPa with each additional fiberglass layer. The elastic moduli calculated from the micromechanics models were compared with the experimental values obtained from the tensile tests. The experimental elastic modulus increased more significantly than the model prediction when more fiberglass layers were added. The flexural modulus of Onyx was 17.6 GPa, which increased with each additional fiberglass layer. This quantitative analysis of composites fabricated using 3D printing highlights their potential for commercialization and industrial applications.

Near pixel-level characterisation of microfibres in 3D-printed cementitious composites and migration mechanisms using a novel iterative method

Microfibre reinforcement is widely used for additively manufactured composites, however, it remains a challenging task to resolve the 3D distribution of microfibres in the matrix with low contrast and resolution for image analysis. To address this challenge, we propose a novel iterative destruction–filtering–repairing (DFR) image processing method, and take glass microfibre-embedded extrusion-moulded cementitious filaments (EMCFs) as an example for 3D structural analysis with X-ray computed tomography. Results show that the DFR method enables near pixel-level microfibre diagnosis with high accuracy beyond the ordinary image processing method. The glass microfibres are unevenly distributed in the EMCFs and their orientations are different between the filament body and the interfacial zone, uncovering the mechanisms of extrusion-affected material migration, collision, and redistribution. Our findings make a breakthrough in image analysis with limited resolution and contrast, providing a broad path towards better understanding the microstructure of 3D printed fibre-reinforcement composites.

Mechanical Properties of Additive-Manufactured Composite-Based Resins for Permanent Indirect Restorations: A Scoping Review.

The introduction of 3D printing technology in dentistry has opened new treatment options. The ongoing development of different materials for these printing purposes has recently enabled the production of definitive indirect restorations via 3D printing. To identify relevant data, a systematic search was conducted in three databases, namely PubMed, Scopus, and Web of Science. Additionally, a manual search using individual search terms was performed. Only English, peer-reviewed articles that encompassed in vitro or in vivo research on the mechanical properties of 3D-printed composite materials were included, provided they met the predefined inclusion and exclusion criteria. After screening 1142 research articles, 14 primary studies were selected. The included studies mainly utilized digital light processing (DLP) technology, less commonly stereolithography (SLA), and once PolyJet printing technology. The material properties of various composite resins, such as VarseoSmile Crown Plus (VSC) and Crowntec (CT), were studied, including Vickers hardness, flexural strength, elastic modulus, compressive strength, tensile strength, fracture resistance, and wear. The studies aimed to compare the behavior of the tested additive composites to each other, conventional composites, and subtractive-manufactured materials. This scoping review examined the mechanical properties of composites used for 3D printing of definitive restorations. The aim was to provide a comprehensive overview of the current knowledge on this topic and identify any gaps for future research. The findings suggest that 3D-printed composites are not yet the first option for indirect restorations, due to their insufficient mechanical properties. Due to limited evidence, more research is needed in this area. Specifically, there is a need for clinical trials and long-term in vivo research.

Nanoindentation creep: The impact of water and artificial saliva storage on milled and 3D-printed resin composites.

This study evaluated the effects of artificial saliva and distilled water on the nanoindentation creep of different 3D-printed and milled CAD-CAM resin composites. Disk-shaped specimens were subtractively fabricated from polymer-infiltrated ceramic network (EN) and reinforced resin composite (B) and additively from resin composite (C) and hybrid resin composite (VS) using digital light processing (DLP). Specimens from each material were divided into two groups according to their storage conditions (artificial saliva or distilled water for 3 months). Creep was analyzed by nanoindentation testing. Statistical analysis was done using two-way ANOVA, one-way ANOVA, Bonferroni post hoc tests, and independent t-test (α = 0.05). The main effects of material and storage conditions, and their interaction were statistically significant on nanoindentation (p<0.001). Storage condition had the greatest influence (partial eta squared ηP 2 =0.370), followed by the material (ηP 2 = 0.359), and the interaction (ηP 2 = 0.329). The nanoindentation creep depths after artificial saliva storage ranged from 0.34 to 0.51µm and from 0.50 to 0.87µm after distilled water storage. One of the additively manufactured groups had higher nanoindentation creep depths in both storage conditions. All specimens showed comparable performance after artificial saliva storage, but increased nanoindentation creep after distilled water storage for 3 months. The subtractive CAD-CAM blocks showed superior dimensional stability in terms of nanoindentation creep depths in both storage conditions. Additively manufactured composite resins had lower dimensional stability than one of the subtractively manufactured composites, which was demonstrated as having higher creep deformation and maximum recovery. However, after artificial saliva storage, one of the additively manufactured resins had dimensional stability similar to that of subtractively manufactured.

Piezoresistive modeling of orthotropic 3D-printing composite line extrusions with non-affine reorientation of fibers

This work introduces a micromechanical semi-analytical model to estimate piezoresistive constants in 3D-printable short-fiber composites, extending the Mori–Tanaka scheme with two innovative components. Firstly, the model incorporates non-affine reorientation of fibers, controlled by a parameter η, which significantly impacts texture coefficients. This parameter introduces an additional layer of complexity, modifying texture coefficients beyond traditional affine fiber reorientations. Observational data illustrate a linear relationship between piezoresistivities and η, leading to the development of a statistical model that calculates η based on the fiber aspect ratio. Secondly, the model accounts for preferential fiber orientation in the undeformed state, resulting in an orthotropic material model. This anisotropy is quantified using an Orientation Distribution Function (ODF) derived from X-ray scans, which is parameterized to maintain symmetry across three orthogonal planes. Initial investigations indicate that the inherent anisotropy introduced by the printing process substantially affects the initial resistivity of 3D-printed composites. Utilizing a Gaussian transversely isotropic model, we find that neglecting this anisotropy could lead to significant errors in understanding and predicting piezoresistive behavior. The model’s incorporation into advanced nanocomposite frameworks offers preliminary reconciliation with experimental data. Additionally, our results emphasize the necessity to refine wavy fiber models by incorporating non-affine rotations, particularly crucial for fibers with small aspect ratios, thereby enhancing predictive accuracy. The findings lay a robust foundation for future research, emphasizing the need for comprehensive experimental validation and setting the stage for nuanced applications in piezoresistive composite materials.

Study on the microwave absorption properties of FeCoNiCrMn/PLA 3D printed composites

The work in this paper is dedicated to the study of wave-absorbing materials for applications in extremely harsh environmental conditions such as seawater and oil. In this paper, FeNiCrMn high-entropy alloy material with corrosion resistance and polylactic acid (PLA) material with high strength and high modulus were used to prepare more environmentally adaptable FeNiCrMn/PLA electromagnetic(EM) microwave-absorbing materials by two-step method of ball milling and melt extrusion.The physical phases, microscopic morphology, EM parameters and mechanical performance of FeCoNiCrMn/PLA composites were characterized using XRD, SEM, Vector Network Analyzer and Universal Testing Machine respectively. The microwave-absorbing properties of FeCoNiCrMn/PLA composites were investigated, and the effects of their components and micro-morphology on the microwave-absorbing and mechanical performance were discussed. The results show that when the FeCoNiCrMn content reaches 25 wt% and the thickness is 4.5 mm, the minimum reflection loss of FeCoNiCrMn/PLA composites reaches −24.58 dB, and the effective microwave-absorbing bandwidth is 2.51 Ghz. The maximum tensile strength and elongation at break of the composites could reach 23.83 MPa and 7.12 %, respectively. The microwave-absorbing ability of FeCoNiCrMn composites is mainly due to their rich EM loss mechanisms, including dielectric losses such as dipole polarization, interface polarization, defect-induced polarization, etc., as well as magnetic losses such as natural resonance, exchange resonance, and eddy current losses. Finally, the wide-angle microwave-absorbing characteristics of FeCoNiCrMn/PLA 3D-printed composites were investigated, the results showed that the composites with FeCoNiCrMn content of 25 wt% had Radar Cross Section (RCS) values lower than −10 dBm² within the microwave incidence angle of −90° < θ < −6° and 6° < θ < 90°, which indicated that the composites had wide-angle microwave-absorbing capability. The materials have microwave-absorbing properties along with a certain degree of mechanical strength, and at the same time have good environmental adaptability. The FeCoNiCrMn/PLA composite wire can be used in FDM technology to prepare structural microwave absorbers, realizing the integration of “material-design-manufacturing”, which has a broad application prospect in the field of EM microwave absorption and 3D printing.

Dynamic analysis of 3D-printed CF-PETG composites with different infill densities

Dynamic analysis of 3D-printed CF-PETG composites with different infill densities

Optimizing the Dielectric and Mechanical Performance of 3D-Printed Cellulose-Based Biocomposites and Bionanocomposites through Factorial Design for Electrical Insulation Application.

Materials for low-permittivity and electrical insulation applications need to be re-engineered to achieve sustainable development. To address this challenge, the proposed study focused on the dielectric and mechanical optimization of 3D-printed cellulose-based composites for electrical insulation applications. Two different fillers, microcrystalline cellulose (MCC) and nanocrystalline cellulose (NCC), were used to create biocomposites and bionanocomposites, respectively, blended into a polylactic acid (PLA) matrix. The effects of infill ratio, printing temperature, and filler content on dielectric and mechanical properties were measured using an incomplete L9 (3^3) factorial design. The findings showed that the infill ratio was the most significant factor influencing the properties tested, directly attributable to the increase in material availability for polarization and mechanical performance. The second most influential factor was the filler content, increasing the polarity of the tested composites and decreasing the toughness of the biocomposites and bionanocomposites. Finally, printing temperature had no significant effect. Results for the biocomposites at a 50% infill ratio, 200 °C printing temperature, and a weight content of MCC of 15% gave a 60% higher tensile-mode stiffness than neat PLA printed under the same conditions, while exhibiting lower dielectric properties than neat PLA printed with a 100% infill ratio. These results pave the way for new lightweight materials for electrical insulation.

Volume-Metallization 3D-Printed Polymer Composites.

3D printing polymer or metal can achieve complicated structures while lacking multifunctional performance. Combined printing of polymer and metal is desirable and challenging due to their insurmountable mismatch in melting-point temperatures. Here, a novel volume-metallization 3D-printed polymer composite (VMPC) with bicontinuous phases for enabling coupled structure and function, which are prepared by infilling low-melting-point metal (LM) to controllable porous configuration is reported. Based on vacuum-assisted low-pressure conditions, LM is guided by atmospheric pressure action and overcomes surface tension to spread along the printed polymer pore channel, enabling the complete filling saturation of porous structures for enhanced tensile strength (up to 35.41MPa), thermal (up to 25.29Wm-1K-1) and electrical (>106Sm-1) conductivities. The designed 3D-printed microstructure-oriented can achieve synergistic anisotropy in mechanics (1.67), thermal (27.2), and electrical (>1012) conductivities. VMPC multifunction is demonstrated, including customized 3D electronics with elevated strength, electromagnetic wave-guided transport and signal amplification, heat dissipation device for chip temperature control, and storage components for thermoelectric generator energy conversion with light-heat-electricity.

3D printed fabrication of ultra‐structured composites of carbonyl iron powder@carbon@carbon black/polylactic acid for efficient microwave absorption

AbstractDesigning an electromagnetic wave absorber that can meet the needs of wide frequency, high efficiency, wide‐angle absorption and strong mechanical bearing capacity is still a challenge. In this paper, a core‐shell structure Carbonyl iron powder (CIP)@Carbon (C)@Carbon black (CB) composite material was prepared by coating and vacuum carbonization process. Using it as a filler, PLA as a matrix to prepare 3D printing composites. The unique structure and material distribution of CIP@C@CB gives the composite a variety of loss mechanisms that greatly improve microwave absorption capacity. Superstructure electromagnetic wave absorbers with integrating broadband microwave absorption and good mechanical bearing performance were designed and prepared by using CIP@C@CB/PLA 3D printing composites. By optimizing the parameters of this superstructure absorber, an EAB of 5.5–18 GHz is realized, and its yield limit reaches 11.5 MPa. In addition, the superstructure absorber also has excellent wide‐angle absorption capacity, with an effective absorption bandwidth (EAB) of 10GHz at 0°–40° transverse radio (TE) and 0–70° transverse magnetic wave (TM). This research offers a straightforward and effective method for crafting broadband wide‐angle absorbers that possess the added advantage of mechanical load‐bearing capacity.Highlights The core‐shell structure was prepared by coating and carbonization processes. The unique structure of CIP@C@CB enhances the interfacial polarization effect. At a thickness of 2 mm, 30% CIP@C@CB/PLA achieves a maximum EAB of 5.0 GHz. The stepped structure achieves 90% effective absorption in the 5.5–18 GHz range.

Path planning and inspection of complex-shaped 3D-printed composites based on robotic pulse-echo laser ultrasonic testing

With the recent advancement in manufacturing, there has been an increasing demand for composite workpieces in the aviation industry. The emergence of composite 3D printing technology that enables the simplification and automation of composite manufacturing processes presents the possibility of replacing the manufacturing process of secondary structures in an unmanned aerial vehicle (UAV). To evaluate the applicability of the technology, a solution for automated non-destructive testing (NDT) that can be applied after the 3D printing process is needed. This study proposes an advanced approach to utilizing laser ultrasonic testing (LUT) for complex-shaped structures fabricated through continuous fiber 3D printing. To ensure accurate defect detection and localization, which are crucial factors in NDT, we propose a method that utilizes a six-degree-of-freedom (6-DOF) robot arm to control the position of the inspection target. By calculating the scan points and path through coordinate transformation and spatial rotation using a quaternion, all surfaces of the targets were inspected. This maintains a constant stand-off distance (SOD) while the sensing laser was vertically incident on the target surface, resulting in a high signal-to-noise ratio (SNR) of the ultrasonic signals. Inspection results have demonstrated the proposed technique to be suitable for detecting defects in complex-shaped 3D-printed structures.

Enhanced interlayer strength in 3D-printed PA12 composites via electromagnetic induction post-processing

Weak interlayer strength remains a critical limitation in the application of material extrusion 3D-printed parts. Herein, a non-contact method, electromagnetic induction post-processing, is proposed to address this issue. This method aims to enhance the weak interlayer strength of 3D-printed PA12 samples by introducing Fe3O4 particles for induced heat generation under alternating magnetic fields. The heat generation characteristics, surface morphology, crystallization behavior, and interlayer performance of 3D-printed samples subjected to induction post-processing are systematically investigated. The results indicate that a remarkable improvement in the interlayer strength of 3D-printed PA12 samples can be achieved through induction post-processing. Tensile strength along the Z-direction (perpendicular to the printing plane) exhibits a distinct increase of 218.3 %, while interlayer tear strength can rise by 328.1 %. Improvement in interlayer strength results from heat generation driving interfacial resin diffusion. Additionally, induction post-processing results in localized surface smoothing and a slight reduction in the crystallinity of the 3D-printed sample. Compared to traditional methods like in-oven heat treatment (annealing), induction post-processing offers higher efficiency by circumventing the initial constraints of heat transfer. Furthermore, the concept of selective induction heating (SIH) is proposed to achieve non-contact, localized heating by adjusting the composition of thermoplastics during printing. SIH holds good promise for applications in 3D-printed continuous carbon fiber-reinforced thermoplastic composites, including mold-free forming, complex surface welding, and repair (particularly in narrow and inaccessible areas).

Numerical modeling of fiber orientation in multi-layer, isothermal material-extrusion big area additive manufacturing

Fiber orientation is a critical factor in determining the mechanical, electrical, and thermal properties of 3D-printed short-fiber polymer composites. However, the current numerical studies on predicting fiber orientation are limited to straight single-strand configurations, while the actual printed parts are often composed of complex multi-layer structures. To address this issue, we conducted numerical simulations of material extrusion in multi-layer big-area additive manufacturing without any post-deposition strand morphology modification mechanism. By examining the effects of material properties and printing conditions when extruding and depositing strands on a fixed substrate as well as previously deposited layers, it was possible to observe the complex interplay between multiple layers and its impact on fiber orientation. The work and methodology presented in this paper can be used to identify optimal extrusion-to-nozzle speed ratios, material rheology, fiber content, and fiber aspect ratio to achieve the desired performance and thermo/mechanical properties of additively manufactured parts. This work is an important contribution towards the manufacture of high-performance, short-fiber polymer composites as the presented methodology can enable engineers to precisely predict and tailor the fiber orientation in 3D printed parts.

Vat photopolymerization of polymer composites with printing-direction-independent properties

The implementation of additive manufacturing techniques for thermal management applications necessitates the development of printable materials with enhanced properties. This study focuses on enhancing the thermal and mechanical properties of 3D-printed polymer composites (UV-based vat photopolymerization; VPP), starting by loading graphene nanoplatelets (GNP) as fillers into a monomer solution. GNP stabilization in the solution is achieved via the addition of sepiolite, a fiber-like clay, that traps them in dispersion. However, the inherent GNP-UV blocking limits its concentration in the VPP-printed composite, and its 2D nature yields parts with undesired anisotropic properties. We overcome this GNP concentration limit by using the excluded volume approach, namely, adding micron-sized diamonds to increase the GNP effective concentration. This approach also transforms the anisotropic VPP-printed composite into an isotropic structure, ensuring consistent thermal and mechanical enhancement regardless of the printing direction. Thermal conductivity (TC) and fracture toughness (FT) are enhanced by 180 % and 100 %, respectively (vs. the neat polymer). However, the electrical conductivity (EC) is also enhanced, which is undesirable in thermal management systems (risk of short-circuiting). Therefore, hexagonal boron nitride is added to reduce the EC, producing composites with enhanced TC and 140 % FT enhancement. Our approach holds promise for various applications, especially in advanced heat management solutions, where enhanced TC, light weight, and low EC are imperative.

Effect of moisture content on the mechanical performance of 3D printed continuous reinforced two-matrix composite

Additive manufacturing, particularly Fused Filament Fabrication, has gained significant attraction in recent years. In order to increase the mechanical performances of several components, continuous reinforcements, such as carbon fibers, can be coextruded with a polymeric matrix.The present study relies on a specific 3D printing process, called towpreg coextrusion, which exploits continuous carbon fibers covered with an epoxy resin and polyamide (PA) as the thermoplastic matrix, thus obtaining a 3D printed two-matrix composite. Since polyamide is a highly hygroscopic material, the impact of moisture content on the mechanical properties of 3D-printed continuous composites was investigated. Tensile and flexural specimens were manufactured and tested under both undried and dried conditions. Drying treatment was carried out at a temperature of 70 °C for 2 h in oven, with weight measurements before and after for quantifying weight loss and then the moisture removal. Additionally, through thermogravimetric analysis, the thermal stability of the material was assessed. It was observed that the drying process allows for a reduction of up to 0.56% by weight of moisture in the specimens. Thus, the drying process led to an improvement in the mechanical properties of the material. Specifically, the tests reveal a 15% increase in tensile strength and an 11.5% increase in flexural strength following the drying process, reaching values of 392.78 MPa and 151.06 MPa, respectively. Similarly, an increase in the tensile and flexural moduli was noted in the treated specimens. Finally, fractured samples underwent optical and scanning electron microscopy analysis, through which different fracture mechanisms of the material and the presence of macrovoids and microvoids attributable to the 3D printing process were observed. Knowledge of deposition defects represents an important starting point for the improvement of the process and the mechanical properties obtained to date. This research provides valuable insights into optimizing 3D-printed continuous composites, emphasizing the importance of moisture control for superior mechanical performance in industrial applications.

Mechanical Characterization and Production of Various Shapes Using Continuous Carbon Fiber-Reinforced Thermoset Resin-Based 3D Printing.

Continuous carbon fiber-reinforced (CCFR) thermoset composites have received significant attention due to their excellent mechanical and thermal properties. The implementation of 3D printing introduces cost-effectiveness and design flexibility into their manufacturing processes. The light-assisted 3D printing process shows promise for manufacturing CCFR composites using low-viscosity thermoset resin, which would otherwise be unprintable. Because of the lack of shape-retaining capability, 3D printing of various shapes is challenging with low-viscosity thermoset resin. This study demonstrated an overshoot-associated algorithm for 3D printing various shapes using low-viscosity thermoset resin and continuous carbon fiber. Additionally, 3D-printed unidirectional composites were mechanically characterized. The printed specimen exhibited tensile strength of 390 ± 22 MPa and an interlaminar strength of 38 ± 1.7 MPa, with a fiber volume fraction of 15.7 ± 0.43%. Void analysis revealed that the printed specimen contained 5.5% overall voids. Moreover, the analysis showed the presence of numerous irregular cylindrical-shaped intra-tow voids, which governed the tensile properties. However, the inter-tow voids were small and spherical-shaped, governing the interlaminar shear strength. Therefore, the printed specimens showed exceptional interlaminar shear strength, and the tensile strength had the potential to increase further by improving the impregnation of polymer resin within the fiber.

Build and raster orientation effects on CFRP onyx/aramid impact absorption

Composite materials fabricated via additive manufacturing are becoming more relevant in ready-for use products used in engineering applications like aerospace structures, propellers, electric vehicles, or sandwich cores. Continuous Fiber Reinforced Polymeric (CFRP) composites are 3D-printed composites with tailor-made properties due to the capability of the printing process to deposit matrix and fiber whenever required. However, CFRP products behave differently and have lower mechanical properties than traditional composites. This study aimed to analyze the impact strength of CFRP specimens with gyroid infill and the effects of two build (flat and on-edge) and two raster (0° and 45°) orientations on impact behavior. The gyroid infill helps to obtain a light-weight structure and it has been used in energy absorption applications showing excellent mechanical behavior in thermoplastic 3D-products. The specimens were manufactured using Onyx as the matrix and aramid fiber as the reinforcement materials. The impact energy absorption of CFRP composites was measured using unnotched Izod impact specimens. The impact tests results were statistically analyzed, revealing that the build orientation directly and significantly affects the impact behavior, resulting in higher impact absorption when flat orientation is used to produce CFRP composites. The impact strength of CFRP composites increased 8 times, and 2 times for flat and on-edge oriented specimens, respectively compared to pure Onyx specimens. The variation in impact energy absorption between raster orientations in both build orientations was not significant, the difference in flat-oriented specimens at 0° and 45° was only 0.2 J, and between on-edge-oriented specimens at 0° and 45° was only 0.089 J. Also, the after impact specimens were analyzed to categorize the different failure modes observed. The after-impact analysis showed poor impregnation between aramid and onyx layers, causing delamination, fiber bridging, and fiber exposure failures. The combination of Aramid, Onyx, and a non-solid infill (gyroid) demonstrated positive results in impact behavior, obtaining high-impact absorption (165 kJ/m2) with no more than 56 % of fiver volume. The impact properties information of CFRP composites made with aramid fibers is still very scarce, joined to the lack of information on the impact properties of CFRP composites with non-solid infill, like gyroids or sinusoidal path infills. The results of this research open the possibility of using non-solid infill in CFR process that can be used to manufacture and test ready-for-use CFRP products in tasks that require high-strength, low-weight structures and impact energy absorption.

3D printing of cementitious composites with seashell particles: Mechanical and microstructural analysis

Seashells are abundantly available as waste products from the seafood industry and from coastal areas. Accordingly, processed shells can be used to partially replace aggregates in traditional concrete. This paper investigates the effects of different proportions of seashell particles on the mechanical and microstructural properties of 3D-printed cementitious composites. The seashells were crushed and milled to be transformed into seashell particles, replacing the river sand at 15 wt% and 30 wt%. It was found that when the seashell particle content increased to 15 wt% and 30 wt%, the mechanical strengths all decreased significantly, which could be attributed to the increasing volumetric proportion of voids and the lower elastic modulus of seashell particles compared to river sand. However, when the seashell particle proportion further rose from 15 wt% to 30 wt%, the mechanical strengths did not continue decreasing substantially. Instead, the compressive and indirect tensile strengths nearly levelled off with minor fluctuations. Based on the microstructural analysis results, it was inferred that the fine seashell powders as part of the seashell particles, which were comprised of aragonite-based calcium carbonate, participated in the cement hydration process that could help with microstructure densification of the cement matrix. This positive effect brought by the fine seashell powders was thought to prevent the further weakening of mechanical properties. Overall, this study aims to understand the role of seashell particles on the mechanical performance of 3D-printed cementitious composites from the perspectives of microstructural characteristics, further promoting the utilisation of waste seashells in 3D concrete printing applications.