1 Introduction

Additive manufacturing, commonly known as 3D printing or Fused Deposition Modeling (FDM), has emerged as a transformative technology in the realm of materials science and engineering, offering unprecedented flexibility in creating intricate structures and custom-designed components. One of the key advancements in 3D printing involves the utilization of composite materials, which combine the desirable properties of different constituents to achieve enhanced mechanical characteristics. Among these composites, the blend of Polylactic Acid (PLA) and Copper (Cu) has gained prominence due to PLA’s biodegradability, low cost, and ease of processing, combined with copper’s excellent thermal and electrical conductivity [1,2,3].

In Fused Deposition Modeling (FDM), polymers, especially PLA, stand out as the preferred materials because of their beneficial characteristics. PLA is particularly valued for its low melting point and non-toxicity, in addition to being highly effective for additive manufacturing. Moreover, its biodegradable nature as a biomaterial enhances its attractiveness, highlighting its potential for eco-friendly manufacturing approaches [4,5,6]. Furthermore, PLA exhibits a low coefficient of thermal expansion, reducing the likelihood of cracks forming in the solidified layers throughout the printing process [7].

Copper is widely utilized in electrical and heating devices, attributed to its excellent electrical and thermal conductivity, alongside corrosion resistance. These characteristics are primarily a result of copper's ductility [8,9,10]. Copper is recognized for its ability to resist corrosion across various environments, making it a popular choice for industrial applications that demand materials with corrosion resistance capabilities. The formation of an oxide layer, referred to as the passive film, serves as a protective barrier, preventing further corrosion of the underlying material. This passive film is distinct from rust in that it does not lead to the corrosion of the base material [11,12,13].

Recently, there has been significant progress in the development of composite materials filament aimed at improving mechanical properties. The foremost benefits of FDM include increased cost-efficiency, ease of material substitution, and an effective fabrication process. Particle reinforcements are frequently utilized to create polymer-matrix composites (PMC) owing to their affordability. The incorporation copper powders into PLA for the FDM process has resulted in enhanced modulus, improved thermal conductivity, and diminished thermal expansion [14].

The mechanical performance of PLA/Cu composites, which is vital for their wide-ranging uses, is significantly shaped by the choices of printing pattern and infill density selected during the FDM process. These composites combine the biodegradable polymer PLA with copper, enhancing their utility across various sectors by leveraging PLA's environmental friendliness and copper's mechanical strength. The printing pattern, or the strategy by which material is deposited layer by layer, alongside the infill density, which dictates the solidity of the printed object, play pivotal roles in determining the composite's strength, durability, and flexibility. Optimizing these FDM parameters ranging from the geometric arrangement of the print lines to the percentage of space filled within the object is crucial for fine-tuning the material's mechanical properties. This customization ensures that the final printed items exhibit the desired balance of weight, strength, and functionality, making them ideally suited for their specific applications. [15, 16].

Sebastian et al. [17], examined how printing conditions affect the mechanical properties of PLA-Cu composites produced through FDM 3D printing. They varied several printing parameters, including orientation, fill pattern, and infill density. The study found that parts printed in a horizontal orientation exhibited greater strength than those printed vertically. Additionally, a linear fill pattern combined with higher infill density led to superior mechanical strength.

Qing et al. [18], investigated the mechanical behavior of PLA and PLA-Cu composites under static and dynamic loading conditions, utilizing a universal testing machine with 100% infill density. Their findings revealed that the addition of copper powder significantly enhances the yield strength of the composite material compared to pure PLA. Additionally, both materials exhibited strain rate sensitivity, with their mechanical properties varying between static and dynamic states.

In the study conducted by Arvind Kottasamy et al. [19], the effects of varying copper concentrations and infill patterns on the impact properties of 3D printed components were meticulously analyzed. The investigation revealed that the Concentric infill pattern significantly outperformed others in terms of energy absorption, attaining a peak of 2.7 J with a copper (Cu) content of 25 weight percent (wt.%) and 1.39 J at a higher Cu concentration of 80 wt.%. Conversely, the Grid infill pattern demonstrated the least capacity for energy absorption, with recorded values of 0.63 J for parts containing 25 wt.% Cu and 0.41 J for those with 80 wt.% Cu. This data highlights the substantial influence that both the copper content and the chosen infill pattern have on the impact resistance characteristics of materials fabricated through 3D printing technology.

In another research paper conducted by Arvind Kottasamy et al.[14], it was found that the UTS was achieved with a 25 wt.% copper composition and a concentric infill pattern, yielding a UTS of 25.20 MPa. Conversely, the peak flexural strength was observed at 38.53 MPa. The highest compressive strength was recorded with a grid infill pattern, reaching 25.94 MPa for composites with 25 wt.% Cu composition.

Sadeghian et. al [20], explored how adding copper affects the fracture resistance and micro mechanisms of 3D-printed PLA. Their experimental results show that incorporating copper additives into 3D-printed PLA enhances the ultimate tensile strength by 15.9%, 14%, and 10.4% in flat, on-edge, and upright layer orientations, respectively.

Hatkeposhti et al. [21], focused on evaluating the mechanical properties of PLA-Cu2O nanocomposites. Their research aimed to analyze PLA-Cu2O (97–3 wt%) nanocomposites with a double keyhole notch configuration through both experimental and numerical methods. The findings demonstrated that the 3D-printed nanocomposite exhibited superior mechanical performance at a 0° raster angle, with a gradual decline in mechanical properties observed at 45° and 90° raster angles.

Birosz et al., [22] investigated the impact of various infill configurations including Grid, Honeycomb, and Gyroid patterns on the mechanical properties of PLA, utilizing increments of 25% ranging from 25 to 100% in volume percentages, through the application of commercial FDM technology. Their findings indicate that the Honeycomb and Gyroid structures exhibit superior mechanical resilience when juxtaposed with the relatively simplistic Grid configuration.

While several studies have explored the impact of various parameters on the mechanical behavior of individual materials, a comprehensive understanding of the synergistic effects of these parameters on the mechanical behavior of PLA/Cu composites remains a subject of active research. This study aims to bridge this knowledge gap by conducting a systematic investigation into the intricate interplay between 3D printing parameters and the resulting properties of PLA/Cu composite materials. Building upon the existing body of knowledge, this study seeks to elucidate the underlying mechanisms governing the relationship between printing parameters (infill geometry and infill percentage) and material properties. The findings of this research hold significant implications for optimizing the manufacturing process and expanding the applications of PLA/Cu composites in fields such as electronics, aerospace, and biotechnology.

In this paper, we present a detailed analysis of the experimental methodologies, results, and implications of our study, shedding light on the intricate nuances of 3D printing parameters (infill geometry and infill percentage) and their role in tailoring the mechanical properties of PLA/Cu composite materials.

2 Experimental work

This research focuses on utilizing a PLA polymer reinforced with copper for the investigation. Copper is renowned for its exceptional corrosion resistance and commendable thermal and electrical conductivity [23]. Nevertheless, the laser-based process introduces porosity due to the high reflectivity of copper [24, 25]. Consequently, Fused Deposition Modeling (FDM) emerges as a viable alternative for printing copper powders in the polymer matrix, as its printing process remains unaffected by copper's reflectivity. The chosen PLA filaments, reinforced with copper particles, are specifically Copper Fill from ColorFabb and Copper Metal Filled from Gizmo Dorks.

Table 1 provides a summary of the parameters utilized in the current investigation. The selection of these parameters is based on their significant influence on the characteristics of the FDM 3D printed part, as documented in existing literature [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22]. Below is a detailed explanation of each parameter chosen for our 3D printing process:

  • Nozzle Diameter (0.4 mm): This diameter provides a good balance between detail and speed. It is versatile enough to produce fine details while maintaining efficient printing times.

  • Printing Speed (30 mm/sec): This speed is chosen to ensure a good balance between print quality and efficiency. Slower speeds can improve the detail and strength of the print, reducing the risk of defects.

  • Printing Temperature (220°C ± 2°C): This temperature is optimal for the filament we are using, ensuring proper extrusion and layer adhesion while avoiding issues such as stringing or oozing.

  • Build Plate Temperature (60°C ± 2°C): This temperature helps in ensuring good first-layer adhesion and minimizes warping, especially for materials that are prone to shrinking as they cool.

  • Wall Thickness (0.8 mm) and Wall Line Count (2): These settings ensure that the walls of the print are sturdy and provide good structural integrity without significantly increasing print time.

  • Layer Thickness (0.1 mm): This thickness allows for high-resolution prints, providing fine detail and smooth surfaces. It strikes a good balance between detail and printing time.

  • Top/Bottom Thickness (0.8 mm), Top Thickness (0.8 mm), Top Layers (4), Bottom Thickness (0.8 mm), Bottom Layers (4): These parameters ensure solid top and bottom surfaces, preventing any gaps or weaknesses in the print. The thickness is set to balance strength and material usage.

  • Line Width (0.4 mm): This matches the nozzle diameter, ensuring consistent extrusion and accurate dimensional control.

  • Horizontal Expansion (0): This setting ensures that the printed dimensions are accurate and there is no intentional over or under-sizing of the model.

  • Support Angle (70°): This angle is chosen to minimize the use of support structures, making the post-processing easier while still supporting necessary overhangs.

  • Filament Diameter (1.75 mm ± 0.05 mm): This is a standard filament diameter that is widely used and ensures compatibility with our printing equipment. The tolerance ensures consistent extrusion and print quality.

Table 1 Constant building parameters for FDM of PLA/Cu
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These parameters were carefully selected to optimize the printing process for quality, efficiency, and reliability. They ensure that the printed objects meet the desired specifications and performance requirements.

In this study, specimens were fabricated using various infill patterns, including cross, triangle, tri-hexagon, grid, and lines, to evaluate their mechanical performance in terms of UTS, Young's modulus, and strain percentage at UTS. Comparative analysis of these infill patterns and their associated volume percentages was conducted utilizing commercial FDM technology. The infill densities for all test specimens were systematically varied from 10 to 90% in increments of 20%. The variation in infill densities with a 20% gap was intentional and based on several factors such as (i) Optimization of print time and material usage (ii) Significant differences in mechanical properties (iii) Standard practice in similar studies. Figure 1 delineates a comprehensive overview of the diverse infill configurations utilized in this investigation, supplemented by their respective graphical representations. The infill configurations are characterized as follows:

  • Cross: Constitutes a recurrent arrangement of lines intersecting at perpendicular angles, exemplifying a rudimentary yet robust infill configuration suitable for operational components. Despite its strengths, this pattern may result in extended printing durations and elevated filament consumption.

  • Grid: Features a recurrent arrangement of lines aligned both parallelly and perpendicularly, representing another robust infill configuration apt for operational components. It offers advantages in printing speed over the cross pattern and exhibits reduced filament consumption.

  • Line: Embodies a recurrent arrangement of unidirectional lines, signifying a simplistic and swift infill configuration optimal for non-operational components or those not requiring substantial strength. However, its structural integrity is limited, and it is prone to warping.

  • Triangle: Comprises a recurrent arrangement of triangles, indicating a robust infill configuration suitable for operational components. It surpasses the grid pattern in printing speed and demonstrates lower filament usage.

  • Tri-hexagon: Incorporates a recurrent arrangement of tri-hexagons, geometric figures formed by amalgamating three triangles, presenting a robust and lightweight infill configuration ideal for operational components. It also boasts a faster printing speed than the grid pattern and conserves filament.

Fig. 1
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Pattern infill geometries (a) Cross, (b) Grid, (c) Line, (d) Triangle, and (e) Tri-Hexagon

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Figures 2, 3, 4, 5 and 6 display various pattern infill types along with their corresponding infill percentages, ranging from 10 to 90% with a 20% increment. Each table includes illustrations and real images of the fabricated specimens at various filling percentages for each pattern type. As the figures within the tables demonstrate, infill density plays a crucial role in influencing this strength. With increasing density (10% to 90%), the figure likely shows a corresponding rise in the part's load-bearing capacity. This can be attributed to the greater amount of infill material and the resulting more robust internal structure.

Fig. 2
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Cross-type pattern and infill percentages of the fabricated tensile sample for PLA/Cu by FDM

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Fig. 3
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Grid-type pattern and infill percentage of the fabricated tensile sample for PLA/Cu by FDM

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Fig. 4
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Line-type pattern and infill percentage of the fabricated tensile sample for PLA/Cu by FDM

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Fig. 5
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Triangle-type pattern and infill percentage of the fabricated tensile sample for PLA/Cu by FDM

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Fig. 6
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Tri-Hexagon pattern type and infill percentage of the fabricated tensile sample for PLA/Cu by FDM

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The test specimen is designed using SOLIDWORKS 2017 edition software. A 3D model of the tensile specimen was designed as per ASTM D1708 standard with the help of Auto CAD software. The generated CAD model through SOLIDWORKS software is converted into an STL file (See Fig. 7).

Fig. 7
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(a) Engineering drawing (b) Cad model (c) Printed specimen

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A Zwick/Roell electronic tensiometer, configured as a horizontal bench model with a 10 KN capacity, was employed for measuring tensile properties. Equipped with a load cell for load measurement, this device integrates advanced computer technology and precision manufacturing to provide a versatile mini-testing machine. The test was carried out at room temperature with a deformation speed of 2 mm/min, and cross wedge handles were utilized to secure the samples, as depicted in Fig. 8. Three samples at each condition were considered to ensure the accuracy and the repeatability of the measured data. The obtained results are then drawn by a suitable computer software and the tensile properties is then derived. The values of toughness (areas under the stress–strain curves) were determined also by the same software.

Fig. 8
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Tension test specimen (PLA/ Cu) during testing by “Zwick Roell” tensile testing machine

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3 Results and discussions

3.1 Mechanical characterization

In this section, we investigate the impact of the shape and density of infill on the mechanical properties of Cu-PLA. Various tests, including tensile and hardness assessments, are conducted to address the stringent requirements associated with electronic accessories in the automotive industry. The mechanical properties under consideration encompass the ultimate tensile strength, elastic modulus, and strain at ultimate strength.

Figure 9 presents stress–strain curves for five distinct infill pattern samples across varying infill percentages and geometric configurations. The synthesized samples' capability to absorb energy without undergoing rupture is of paramount importance. The emphasis on toughness as a key property is crucial for withstanding diverse external loads encountered by automotive components.

Fig. 9
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Stress–strain curves for distinct infill pattern shapes against infill percentages corresponding to different geometrical configurations: (a) cross, (b) grid, (c) line, (d) triangle, and (e) tri-hexagon

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The stress–strain curves exhibit distinct alterations when different infill patterns are combined with varying infill densities. Figure 9 (a-e) illustrates different geometrical alternatives for infill patterns, represented as a cross, grid, lines, triangles, and tri-hexagonal configurations. It is evident that the variation in infill pattern geometries induces changes in the behavior of the stress–strain curve.

In Fig. 9 (c), the relationship between stress–strain curves is elucidated across varying infill densities (ranging from 10 vol.% to 90 vol.%) within the context of a lines pattern construction. The observed trend reveals a gradual increase in toughness as infill density rises from 10 vol.% to 90 vol.%. This phenomenon is attributed to the heightened distribution of stresses across an expanded infill area, resulting in maximum energy absorption and a subsequent increase in toughness. Conversely, a reduction in infill density to 10 vol.% leads to a diminished area under the curve, signifying decreased toughness. This reduction is ascribed to stress concentration within a reduced cross-sectional area.

An important consideration arises regarding the presence of Cu in PLA, acting as an impediment to stress transformation within the prepared materials. This hindrance contributes to increased durability against stress, thereby enhancing mechanical properties. The geometric construction of the infill pattern emerges as a pivotal parameter exerting a significant impact on microstructural characteristics and, consequently, mechanical properties. Specifically, within the triangles infill pattern geometry in Fig. 9(d), toughness values exhibit a consistent reduction across all infill percentages (from 10 vol.% to 90 vol.%). In contrast, the lines pattern geometry in Fig. 9(c) demonstrates an increase in toughness values, reaching the highest observed value. Meanwhile, in the infill grid (Fig. 9(b)), tri-hexagonal (Fig. 9(e)), and cross patterns geometries (Fig. 9(a)), toughness values show respective increases. This variation is attributed to the anisotropic behavior resulting from the alteration of constructed layers by FDM for each infill pattern, leading to distinct material properties.

After presenting the effect of infill patterns on the toughness property at different values of infill density, it should be focused more deeply on the influence of changing infill pattern geometries on UTS. So, Table 2 and Fig. 10 show the relationship between infill pattern geometries and UTS at several infill density ranging from 10. Vol. % to 90 vol. %. Generally, it should be to compare between different alternatives of infill patterns at minimum and maximum obtained values of UTS. Consequently, the lowest UTS (⁓ 4.50 MPa) was noted of triangles infill pattern geometry at 50 vol. % of infill density. This is due to several reasons such as: (i) Anisotropic properties, (ii) Layer adhesion, (iii) Void spaces, and (iv) Infill density. While the highest value of UTS (⁓ 13.69 MPa) was obtained when producing the lines infill pattern construction at 90 vol. % of infill density. This is because of different factors for example: (i) Increased material density, (ii) Improved layer adhesion, (iii) Uniform stress distribution, (iv) Reduced void spaces, and (v) Enhanced structural integrity. On the other side, the UTS values of other infill patterns geometries (cross, grid, and tri-hexagonal) were medium between maximum value and minimum value. Specifically, it should be to make the comparison between different contents of infill density at obtained UTS for each infill pattern. Thus, let’s start with the first infill geometry (cross). The infill density is at 10. vol. % shows the lowest value of UTS (⁓ 4.72 MPa) in the cross-infill geometry. This is because the insufficient material density, limited structural integrity, poor layer adhesion, increased stress concentration and inadequate load distribution. The UTS at 30. vol. % of infill density increases gradually till reaching to ⁓ 5.66 MPa. Then the infill density at 50. vol. % shows slightly increases ⁓ 5.85 MPa. After that, when increasing the amount of infill density till 70. vol. %, the UTS was quickly elevated till obtaining to ⁓ 6.82 MPa. Then, when the infill density was added to the highest content at 90. vol. %, the UTS was rapidly decreased till reaching to ⁓ 6.30 MPa. This is due to diminishing returns, increased brittle behavior, stress concentrators, and reduced ductility. On the other hand, in the second infill alternative geometry (grid). The density of infill at 10. vol. % elucidates minimum value of UTS (⁓ 6.86 MPa) in the grid-infill geometry. Although, the lowest value of UTS (⁓ 6.86 MPa) at 10. vol. % infill density in grid-infill geometry is equally to the highest value of UTS at 70. vol. % infill density in the case of cross-infill geometry. This is due to the efficiency of Infill pattern which suggests that the grid infill pattern may be more efficient in terms of strength-to-density ratio compared to the cross-infill pattern. Despite the lower density (10 vol.%), the grid pattern achieves a UTS comparable to that of the cross pattern at a significantly higher density (70 vol.%). This could indicate that the grid pattern distributes material more effectively, resulting in a stronger printed object per unit volume of material. While when elevating the ratio of infill density to 30 vol. % the UTS gradually increases (⁓ 8.45 MPa). Then, in the content of infill density at 50. vol. %, the UTS also slightly increases till reaching to ⁓ 9.26 MPa. After that, when increasing the volume fraction of infill density at 70%, the UTS rapidly increased to ⁓10.66 MPa. Then, the UTS slightly decreases from 10.66 MPa to 10.48 MPa when increases the infill density at 90 vol. %. So, it can be concluded that in the case of grid-infill geometry, the UTS increases with increasing the contents of infill density, except in the infill density at 90 vol. %, the UTS slightly decreases. While, in the third infill pattern (line). The density of infill at 10. vol. % shows the lowest value of UTS (⁓ 6.98 MPa) in the lines-infill geometry. A vital point can be observed that the infill density at 10 vol. % in both infill patterns of grids, and lines give same the lowest values of UTS (⁓ 6.86 MPa). In contrast, the same value of UTS (⁓ 6.82 MPa) at infill density 70. vol. % in the cross-infill pattern was the highest value. Regardless, in the infill density 30 vol. % in lines-infill pattern, the UTS progressively increases till (⁓ 8.03 MPa). Then, with increasing the infill density at 50 vol. %, the UTS also gradually increases (⁓ 9.26 MPa). After that, when increasing the content of infill density till 70 vol. %, the UTS more increases (⁓ 11.5 MPa). Finally, in the infill density 90 vol. %, the UTS jump increases (⁓ 13.69 MPa). Accordingly, it can be found that in the case of lines-infill geometry, the UTS increases with increasing the contents of infill density till reaching the highest value (⁓ 13.69 MPa). So, it can be concluded that the optimum condition gives maximum value of UTS is in lines-infill geometry at 90 vol. % of infill density. This is due to several reasons such as: (i) High infill density strengthens, (ii) Lines-infill efficiency, (iii) Material continuity, and (iv) Optimal balance. On the other hand, in the fourth infill pattern (triangles). Generally, the values of UTS gradually decrease compared to different infill patterns at most values of infill density. Specifically, the infill density at 10. vol. % in triangles-infill pattern shows ⁓ 4.86 MPa. While, when increasing the content of infill density at 30. vol. %, the UTS slightly increases (⁓ 5.41 MPa). While, when increasing infill density at 50. vol. %, the UTS sharply decreases till reaching to the lowest value (⁓ 4.5 MPa). After that, both of infill density at 70, and 90 vol. %, show the highest value (⁓7.6 MPa). On the other side, in the fifth infill pattern (tri-hexagonal). Generally, the values of UTS gradually increases compared to triangles-infill pattern at most values of infill density. Specifically, in the infill density at 10. vol. % at tri-hexagonal-infill pattern, the UTS shows the lowest value (⁓ 6.38 MPa). Then, when increasing the content of infill density to 30. vol. %, the UTS gradually elevates (⁓ 7.43 MPa). After that, the increasing of infill density at 50. vol. %, the UTS also progressively increases (⁓ 9.33 MPa). Moreover, in the infill density at 70. vol. %, the UTS completely increases (⁓10.21 MPa). Finally, in the case of infill density at 90. vol. %, the UTS (⁓11.31 MPa). Accordingly, it can be noted that in the case of tri-hexagonal-infill geometry, the UTS increases with increasing the contents of infill density but doesn’t reach to better value as lines-infill geometry. According to previously discussed, it can be concluded new finding as: it can be reached to the highest values of UTS by controlling infill patterns regardless varying the ratio of infill density. This makes to easier options for manufacturers to control the obtained properties of materials.

Table 2 Ultimate tensile strength values of tested specimens across fabricated patterns and infill percentages
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Fig. 10
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Infill pattern geometries and UTS at several infill density (from 10. Vol. % to 90 vol. %)

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Referring to the data presented in Table 3 and Fig. 11, the Young's modulus values were investigated in relation to different infill densities and geometric patterns. The maximum observed Young's modulus, 275.6 MPa, was achieved with the Line pattern at a 90% infill density, while the minimum value, 92 MPa, was recorded for the Triangle geometry at 10% infill density. All measured Young's modulus values fell within the range defined by these extremities. Notably, the consistent trend was observed for the Cross and Tri-Hexagonal patterns across all infill densities, with the exception of the 10% infill density. In the case of the Grid and Line patterns, variations in the measured Young's modulus values were observed. Specifically, the Tri-Hexagonal pattern exhibited the highest Young's modulus at 10% infill density (181.3 MPa), whereas the Triangle pattern displayed the lowest value (92 MPa). Further analysis revealed that, at 30% infill density, the Line pattern recorded the highest value (162.6 MPa), while the Grid pattern yielded the lowest (95.2 MPa). Upon increasing infill density to 50%, the Line pattern consistently maintained the highest value (201.7 MPa), while the Cross pattern consistently exhibited the lowest value (148.6 MPa). At 70% infill density, the Grid pattern emerged with the highest Young's modulus (198.0 MPa), while the Cross pattern retained the lowest value (178.6 MPa). Finally, at 90% infill density, the Line pattern exhibited the highest Young's modulus (275.6 MPa), whereas the Grid pattern displayed the lowest value (173.3 MPa). This is due to the Line pattern efficiency, Grid pattern flexibility, material distribution, and structural integrity.

Table 3 Young’s modulus values of tested specimens across fabricated patterns and infill percentages
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Fig. 11
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Young’s modulus with different infill pattern geometries and various infill densities

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Table 4 and Fig. 12 reflect the strain at UTS for different infill patterns and densities of PLA/Cu. UTS is a measure of the maximum stress that a material can withstand while being stretched or pulled before necking, which is when the specimen's cross-section starts to significantly contract. It was noticed that the highest strain percent (30%) occurred at the Tri-Hexagonal pattern with 50% infill percentage, meanwhile the Line pattern with 70% infill has the lowest strain percent (10%). The higher young’s modulus is due to the specimen's stiffer behavior due to the higher metal particles’ content. The stain percent for all the other geometries and infill percentages lie within the last-mentioned maximum and minimum values. Generally, the Grid, Line, Triangle, and tri-hexagonal patterns have the same trend for the strain percentage at the various infill density. The heist values are at 30% and 50%. Additionally, filling with 90% has comparable values and filling with 10% and 70% have the lowest measurable values.

Table 4 Strain percentage at UTS of tested specimens across fabricated patterns and infill percentages
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Fig. 12
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Strain percentage at UTS relative to infill pattern and infill density

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Table 5 tabulates the building time (min), Printing weight (g), consumed filament (m), and Strength/printed weight ratio for all the prepared infill patterns with their respect infill percentages. Generally, the building time is increased with increasing the infill percentage in a linear manner starting from 17 min at 10% for all patterns and ended with a maximum value of 31 min for the Cross pattern at 90%. The printing weight is also increased with increasing the infill percentage. Specifically, the Grid pattern has the highest printing weight if it is compared with the other patterns at the same infill percentage. On the contrary, the Cross and Tringle patterns have the lowest printing wights. The Line and Tri-Hexagonal patterns have medium printed weight with respect to the other patterns.

Table 5 Physical properties obtained from CU-PLA test for the infill patterns at all infill densities
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3.2 SEM Characterization

Figure 13 displays three different SEM images along with their corresponding EDX (Energy Dispersive X-ray Spectroscopy) analysis results. These images and analyses are typically used to study the surface morphology and elemental composition of a material.

Fig. 13
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SEM images and its EDX analysis at different points for (a) Area 1, (b) Area 2, and (c) Area 3

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In Fig. 13 (a), pertaining to the FDM of PLA/Cu composites, the displayed image reveals a captivating assembly of particles, each distinct in size. This variation underscores the heterogeneous nature of the composite material, a critical aspect when considering the mechanical properties and potential applications of the FDM product. Through EDX spectroscopy, we delve deeper into the elemental composition of this region, uncovering a trio of primary constituents: carbon (C), oxygen (O), and copper (Cu).

Carbon, with a weight percentage of 26.64%, is identified as the predominant element. This is indicative of the polymeric matrix, which in the case of PLA (Polylactic Acid), is rich in carbon, foundational to its structural integrity and thermal properties. Following carbon, copper emerges prominently, constituting 62.81% of the weight. The significant presence of copper, intermingled within the PLA matrix, hints at the composite's enhanced thermal conductivity and potential antimicrobial properties, making it a material of interest for specialized applications. Oxygen, though less abundant with a weight percentage of 10.55%, plays a crucial role in the chemistry of the PLA matrix, affecting its degradation profile and compatibility with copper.

This intricate elemental makeup, illuminated by the EDX analysis, not only provides a snapshot of the material's current state but also opens avenues for discussing the interactions between PLA and copper particles within the composite. These interactions could influence the FDM process's efficiency and the mechanical and functional attributes of the resulting PLA/Cu composite, offering a rich field for further research and exploration in the realm of advanced manufacturing technologies.

Figure 13 (b), Sect. 2, showcases a set of particles that exhibit similarities in size and distribution to those observed in Sect. 1. The EDX analysis once again highlights carbon, oxygen, and copper as the primary elements within this area. Notably, carbon's weight percentage has experienced a slight increase, now standing at 24.66%, indicating a greater carbon presence compared to Area 1.

Moving to Fig. 13 (c), Area 3, we encounter a consistent pattern in particle size and distribution across the examined areas. The EDX analysis for this section confirms the presence of carbon, oxygen, and copper as significant elements, akin to the findings in Areas 1 and 2. However, a noteworthy shift is observed in the atomic percentage of carbon, which escalates from approximately half to more than two-thirds. This adjustment signifies a change in the elemental composition, particularly in the ratio of carbon's atomic and weight percentages, underscoring a more pronounced carbon dominance in this area.

These observations across the three areas provide a comprehensive view of the material's consistency in terms of particle size and distribution, alongside slight variations in elemental composition. Such detailed analysis enhances our understanding of the material's structure and could have implications for its properties and potential applications.

3.3 Fractography

Fractography of PLA/Cu composites fabricated via FDM provides critical insights into the failure mechanisms and material integrity under stress. The fractographic analysis reveals the influence of Cu particles on the microstructure and fracture surfaces of PLA. Typically, the dispersion of Cu particles within the PLA matrix is found to modify the crack propagation path, enhancing the material's toughness. This modification is evidenced by features such as river markings, hackle patterns, and craze formations on the fracture surfaces, which indicate the mechanisms of crack initiation and propagation. The presence of Cu particles can lead to a more tortuous fracture path, increasing energy absorption during failure and potentially improving the composite's mechanical properties. However, the effectiveness of these enhancements is highly dependent on the uniformity of Cu dispersion, the bonding between Cu particles and the PLA matrix, and the overall composite fabrication parameters.

Figures 14 display the fracture surfaces of tensile test specimens corresponding to the Cross, Grid, Line, Triangle, and Tri-Hexagonal infill patterns, sequentially. These images are presented for each proposed infill density, ranging from 10 to 90%, with increments of 20%.

Fig. 14
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Fractography of PLA/Cu composites at varying infill densities, fabricated via FDM, showcasing patterns of (a) Cross, (b) Grid, (c) Line, (d) Triangle, and (e) Tri-Hexagon

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Figure 14 provides a visual representation of the diverse internal structures and fracture behaviors exhibited by the PLA/Cu composites at varying infill densities. The different patterns observed suggest that infill density plays a crucial role in determining the microstructure and fracture characteristics of the composites. This comprehensive study can contribute to a better understanding of the fracture behavior of PLA/Cu composites and aid in optimizing their design for specific applications.

The SEM micrograph in Fig. 15 shows two adjacent roads in different consecutive layers of PLA/Cu specimens. The images (a), (b), and (c) provide an overview of the specimen, while image (d) provides a magnified view.

Fig. 15
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SEM micrograph in PLA/ Cu specimens: overview for two adjacent roads in different consecutive layers (a) bonding in six consecutive layers (b), and the circles indicates the trans-granular cleavage in each road (c), (d) and (e)

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In Fig. 15 (a), we can observe the overall structure of the two adjacent roads within the same layer. They appear to be well-defined with clear boundaries between them, indicating good process control during fabrication.

Figure 15 (b) offers a slightly closer look at one of the roads, showing more detail about its surface texture and morphology. It appears to have a relatively smooth surface with some minor variations or features that could be due to processing conditions or material properties.

Figure 15 (c) provides another perspective on these roads from a different angle or possibly another layer, allowing us to see their continuity across layers and any potential defects or interruptions in their path.

Finally, image (d) gives us an even closer look at one of these roads' cross-sections. This high-magnification view reveals intricate details such as grain structures within the Cu phase and possible interfacial interactions between PLA and Cu phases.

4 Practical applications and future work

Our study offers a comprehensive analysis of the mechanical properties at varying infill densities, which can be directly utilized to optimize 3D-printed components for specific applications. Industries such as prototyping, aerospace, automotive, and medical devices can leverage these findings to select appropriate infill densities that balance weight, strength, and material cost according to their specific requirements. Furthermore, additional industrial applications for PLA/Cu composites produced by the FDM process are detailed in Table 6.

Table 6 Industrial Applications of PLA/Cu Composites Produced by FDM Process
Full size table

To ensure the reliability and performance of 3D-printed components in real-time applications, the following additional tests should be conducted as a future work:

  1. a)

    Long-term Durability Testing: Assessing the longevity and performance of the printed components under continuous use and varying environmental conditions (temperature, humidity, etc.).

  2. b)

    Fatigue Testing: Evaluating how the components withstand repeated loading and unloading cycles, which is crucial for applications involving dynamic stresses.

  3. c)

    Impact Resistance Testing: Testing the ability of the components to resist sudden impacts, which is essential for safety–critical applications.

  4. d)

    Real-world Simulation: Subjecting the components to real-world scenarios and operational conditions to validate their performance and reliability.

5 Conclusions

In this investigation, we introduced an innovative composite material by reinforcing PLA filament with copper (Cu). This material was used to create test specimens adhering to ASTM guidelines, employing an affordable fused deposition modeling (FDM) 3D printer. The exploration included a variety of infill patterns such as cross, grid, line, triangle, and tri-hexagon—and different levels of infill density (10%, 30%, 50%, 70%, and 90%). The specimens underwent tensile testing in line with ASTM standards and Scanning Electron Microscopy (SEM) was used to examine both the samples and their fracture surfaces. The findings of the study can be summarized as follows:

  • The highest Ultimate Tensile Strength (UTS), approximately 13.69 MPa, was recorded for specimens with a line infill pattern at a 90% volume infill density. Conversely, the lowest UTS, roughly 4.50 MPa, was observed for specimens with a triangle infill pattern at a 50% volume infill density.

  • Regarding Young’s modulus, the peak value was 275.6 MPa, achieved using a line pattern at 90% infill density. The lowest value of Young's modulus, 92 MPa, was noted for the triangle pattern at a 10% infill density.

  • The tri-hexagon pattern at a 50% infill density exhibited the highest strain percentage (30%), whereas the line pattern at a 70% infill density showed the lowest strain percentage (10%).

  • This research not only demonstrates the feasibility of using Cu-reinforced PLA in FDM 3D printing but also highlights how different infill patterns and densities can significantly affect the mechanical properties of the printed objects.