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Abstract

Fused Filament Fabrication (FFF)-based PLA composites reinforced with short glass fibers offer enhanced mechanical properties and processability. However, their vibration response, dynamic mechanical behavior, and wear resistance remain underexplored, despite being critical for load-bearing and impact-sensitive applications. This study addresses that gap by evaluating the combined effects of infill geometry and density on the mechanical, vibrational, viscoelastic, and tribological performance of 3D-printed PLA/Glass Fiber composites. Three advanced infill structures, Cubic, Octet, and Cubic Subdivision, were tested at infill densities of 50%, 70%, and 90%, using seven experimental methods including free vibration and dynamic mechanical analysis (DMA). Results show the Cubic pattern yielded the highest tensile strength and modulus (24.65 MPa, 0.95 GPa), while the Octet pattern showed superior flexural stiffness and the highest natural frequency (41.5 Hz). The Cubic Subdivision pattern offered the best damping performance, with the highest Tan δ (3.35), loss modulus (985.2 MPa), and Tg (77.21°C). Wear resistance and hardness increased with infill density across all patterns. These insights demonstrate that optimized infill design significantly improves both structural and functional performance. The findings are directly applicable to lightweight, vibration-sensitive components such as drone frames, orthopedic implants, vehicle interiors, and protective equipment.

Keywords

FFF PLA Glass Fibre vibration impact

Introduction

Additive Manufacturing (AM), or 3D printing, refers to a family of processes that build components layer by layer from digital models,¹ offering distinct advantages over traditional subtractive manufacturing,² particularly for complex geometries.³ AM encompasses several categories, including Vat Photopolymerization, Material Jetting, Binder Jetting, Material Extrusion, Powder Bed Fusion, Sheet Lamination, and Directed Energy Deposition, each suited to different applications based on precision and material requirements.⁴ Among these, Material Extrusion—particularly Fused Deposition Modelling (FDM),⁵ also known as Fused Filament Fabrication (FFF)—is the most widely used process due to its affordability,⁶ simplicity, and compatibility with common design software.⁷ In FDM, thermoplastic material is extruded through a heated nozzle to form objects layer by layer,⁸ making it ideal for rapid prototyping and low-volume production. The mechanical properties of printed parts, such as tensile strength, fatigue resistance, surface finish, and dimensional accuracy, are highly dependent on processing parameters.⁹

Recent studies have broadened the understanding of how material composition, reinforcement type, and printing parameters influence the multifunctional properties of polymer composites fabricated via FDM. For example, Paul Rodrigues et al. demonstrated that optimized combinations of graphene and clay content, print speed, and nozzle temperature significantly enhance the yield and impact strength of PLA-based composites.¹⁰ Similarly, Menderes Kam et al. revealed that varying infill structures and occupancy rates strongly affect the damping response and dynamic stability of FDM-fabricated components.¹¹ In addition, Praveenkumara Jagadeesh et al. emphasized that basalt filler content and tribological parameters play a vital role in improving wear resistance and reducing specific wear rate in sustainable PLA composites.¹² Collectively, these studies highlight the critical role of internal configuration and process optimization in enhancing FDM-printed composite performance.

Recently, short fiber–reinforced composite filaments have attracted considerable attention in AM, especially in FDM. By incorporating fibers such as carbon, glass, or natural fibers into the polymer matrix, these materials significantly enhance mechanical properties, including tensile strength and stiffness, while maintaining good processability.¹³ Short fibers offer easier processing than continuous ones, making them ideal for extrusion-based systems. For example, Tekinalp et al.,¹³ demonstrated significant improvements in strength and modulus by incorporating carbon fibers into ABS, without losing the ease of fabrication. A crucial factor influencing the mechanical properties of FDM-printed parts is the internal infill structure.¹⁴ Infill patterns and densities directly affect the distribution of stress within the part, thereby influencing strength-to-weight ratio and energy absorption characteristics. Stoia et al.,¹⁵ reported that triangular and gyroid infill structures outperform conventional rectilinear ones under tensile and flexural loading. Similarly, Lubombo et al.,¹⁶ found that mechanical strength and stiffness increase with the number of wall shells and infill density, with reinforced square diagonal patterns showing better performance than honeycomb designs. Further, Ganeshkumar et al.,¹⁷ compared several infill geometries—including truncated octahedron, gyroid, rhombus, and honeycomb—and identified the hexagonal honeycomb as superior in tensile performance. Bani et al.,¹⁸ explored the impact strength of PLA parts and discovered that a 3 mm thickness at 50% infill offered an optimal balance between material usage and impact resistance. SEM and FTIR analyses showed negligible chemical changes but revealed interlayer voids affecting brittleness.¹⁹ Birosz et al.,²⁰ studied grid and honeycomb infill designs, concluding that optimized infill pattern sizing can reduce printing time without compromising flexural properties. Grid patterns showed stable mechanical performance across variations, while honeycomb patterns were more sensitive to structural scaling.²¹ Environmental degradation effects on FDM-printed PLA were studied by Hedayati et al.²² Their results indicated that auxetic and gradient cores provided superior impact resistance and retained structural integrity over time. Gradient designs, in particular, offered balanced energy absorption even under environmental wear.

Fiber-reinforced composites also continue to be investigated for improved performance. Begum et al.,²³ evaluated glass fiber-reinforced PLA with varied infill densities and raster angles. The highest mechanical performance occurred at 60% infill and 0°/90° orientations, with minimal wear at 0° raster angle. In another study, Ma et al.²⁴ assessed the impact resistance of PLA sandwich panels with different infill patterns, finding that cubic and gyroid structures performed best under high-velocity impacts—ideal for lightweight, high-impact applications. Begum et al.²⁵ further examined the compressive stiffness and porosity of PA2200 SLS-fabricated scaffolds, identifying a significant discrepancy between simulated and actual porosity, affecting mechanical predictions. Sivagnanamani et al.²⁶ introduced eggshell particles into PLA and identified an optimal 10% filler at 40% porosity for maximum compressive strength. Prajapati et al.²⁷ focused on the dry sliding wear behavior of 3D-printed PEEK, identifying 90% infill density as optimal. Lower density resulted in higher surface roughness and wear but reduced temperature rise, which may prolong bearing life. Increased porosity reduced friction but increased material loss. Despite significant progress in additive manufacturing, especially with reinforced composites,²⁸ research largely focuses on 2D infill geometries and basic mechanical properties. There remains a knowledge gap in understanding how advanced 3D infill structures affect viscoelastic behavior, wear resistance, vibration response,²⁹ and damping—critical for functional or load-bearing applications. While tensile and flexural strength are important, these overlooked properties often dictate the performance of components subjected to real-world dynamic and mechanical stressors.

Vibrational and Dynamic Properties investigations on the influence of three-dimensional infill geometries at different densities are limited, especially for structures like Cubic, Octet, and Cubic Subdivision across 50%, 70%, and 90% infill levels. This study bridges this gap by systematically assessing the mechanical, tribological, viscoelastic, and vibrational behavior of PLA/Glass Fiber composites with these infill configurations. By revealing pattern-specific performance and sensitivity to density variations, it provides novel guidance for optimizing infill design, enabling the development of lightweight, vibration-sensitive, and wear-resistant 3D-printed composite components.

Materials and methods

Methodology

The findings from the literature review were used to identify the gap in research, which further was used as the starting point for experimental framework development. Figure 1 shows the proposed methodology for the fabrication and characterization of 3D printed PLA/GF PLA composites. The Cubic, Cubic Subdivision, and Octet infill configurations were selected to represent distinct internal architectures with varying connectivity and load paths. While the Cubic and Cubic Subdivision share a common base geometry, the latter introduces additional diagonal elements that modify stress distribution and damping behavior. The Octet pattern, with its space-frame topology, offers a contrasting deformation and vibration mechanism.³⁰ As previous studies have shown, internal configuration significantly affects mechanical and dynamic performance, with Octet lattices exhibiting higher stiffness and energy absorption compared to cubic topologies³¹ This combination enabled a comprehensive comparison of how geometric complexity influences the mechanical, vibrational, and tribological responses of FFF-printed PLA/glass fiber composites. The three infill patterns were investigated at three equal but different levels of density, viz., 50%, 70%, and 90%, to establish the effect of material distribution within the composite structure. The 90% infill density was chosen to explore the transitional region between semi-hollow and nearly solid FFF structures. While this level approaches the density of a fully solid (100%) part, small internal voids and filament overlaps that remain at 90% can still affect stress distribution, vibration damping,³² and interlayer bonding. Earlier studies have shown that mechanical and dynamic properties in FDM composites continue to evolve nonlinearly beyond 80% infill, suggesting that 90% serves as a meaningful threshold for assessing performance before full densification.³³ In addition, this infill level strikes a practical balance between mechanical strength, material efficiency, and printing time, qualities that are highly desirable for lightweight, high-performance components. Specimens were prepared as per relevant ASTM standards to achieve reliability and consistency of the results. Seven experiment tests were performed to determine the response of the composite under various loading and environmental conditions. These experiment tests included tensile, flexural, impact, hardness, free vibration analysis, dynamic mechanical analysis (DMA), and wear testing. This comprehensive testing methodology was developed to establish the mechanical, viscoelastic, vibrational, and tribological response of the material, hence enabling comprehensive characterization of the infill geometry and density effect.

Figure 1.

Proposed methodology for the fabrication and characterization of 3D printed PLA/GF PLA composites.

Procurement of PLA/GF composite

The glass fiber–reinforced PLA (PLA/GF) filament employed in this study was purchased from Macfos Limited (India), the supplier of the commercial-grade material. The filament is made up of PLA and 16% glass fibers by weight. The addition of glass fibers provides tiny structural reinforcement, improving the material’s capacity to distribute mechanical stress more uniformly and thereby increasing tensile strength. When the fibers are aligned with the direction of loading, they increase the filament’s rigidity and impact resistance, resulting in a composite that is much more durable and suited for high-demand applications than unmodified PLA.³⁴ The filament characteristics are shown in Table 1 which was obtained from the manufacturer catalogue. To reduce the influence of moisture absorption by the filament, silica gel is utilized to capture moisture in the sealed bag, allowing the filament to be stored at ambient conditions.

Table 1.

Material properties of PLA/GF filament.

Sl. No.	Property	Values
1	Density (g/cm³)	1.31
2	Melt flow index (g/10min)	6.36 (190°C/2.16 kg)
3	Filament tensile strength (MPa)	59.27
4	Elongation at break (%)	7.99

Fabrication PLA/GF parts using FFF

The CAD modelling of various mechanical tests samples as per ASTM standard dimensions are done using CREO Parametric 8.0 software. Slicing is performed using Ultimaker Cura 5.4.0 software. The software constructs the 3D printing tool path depending on the layer thickness, layer number, raster angle, infill pattern, and infill density. Based on the created tool path, the slicing software produces G-codes. The model used two wall layers, two bottom layers and two top layers. Fused Deposition Modelling (FDM) is an additive manufacturing process in which a thermoplastic filament is melted and injected via a nozzle to lay down each layer of cross section to generate the required geometry. FDM technology is regarded for being low-cost, clean, and easy to use. The experiments were carried out using a Creality Ender 3 printer with a bed size of 220 × 220 × 240 mm, equipped with a 0.4 mm nozzle capable of reaching a maximum temperature of 255°C, a maximum print speed of 120 mm/s, and suitable for printing thermoplastic materials. The printing parameters are shown in Table 2. The printing parameters were constant for all the testing parameters. The printing parameters like the infill density, layer thickness, print speed and Extrusion temperature play a crucial role in the strength of the printed material. The Sliced model of various mechanical test samples with the selected infill patterns along with the various infill densities are printed using FDM- Creality Ender 3. Figure 2(a)–(f) shows the Infill structure and infill density used in this research and the printed samples for mechanical testing.

Table 2.

Printing parameters for printing tensile test samples.

Parameters	Value
Bed temperature	60°C
Nozzle temperature	230°C
Layer thickness	0.2 mm
Print speed	60 mm/s
Nozzle diameter	0.4 mm

Figure 2.

(a) Infill structure and infill density used in this research (b) Tensile test – ASTM D638, (c) Flexural test – ASTM D790, (d) Charpy impact test – ASTM 6110, (e) Wear test – ASTM G99, (f) Dynamic mechanical analysis – ASTM D7028.

Mechanical testing

Tensile test

Tensile test is conducted to investigate the tensile properties of different infill patterns. The test was done with Shimadzu AGS- 2000G UTM with load capacity of 2 Tones which is available at MIT – Rubber and Plastics Department, Anna University, India. Specimens are prepared according to ASTM D638 standard. Five specimens were prepared and tested in accordance with standard practice. Test is performed with strain rate of 1 mm/min.³⁵ The images of samples before tensile and after tensile test are shown in Figure 3.

Figure 3.

Before and after failure of the printed PLA/GF composites images (a) tensile, (b) flexural and (c) impact test.

Flexural test

The flexural test was performed to measure the bending strength of the infill patterns by applying a bending force at three points. The test was done with Shimadzu AGS- 2000G UTM with load capacity of 2 Tonnes available at MIT – Rubber and Plastics Department, Anna University. Test was done according to standard ASTM D790. Five specimens were prepared and tested in accordance with standard practice. Test was performed with 50 mm span length and strain rate of 1 mm/min.³⁶ The images of samples before and after test are shown in Figure 2.

Charpy impact test

Charpy Impact test was conducted to understand the toughness of the infill patterns. The test was done with Charpy Impact tester available at MIT – Rubber and Plastics Department, Anna University. Test was done according to standard ASTM D6110. Five specimens were prepared and tested in accordance with standard practice. The images of samples before and after test are shown in Figure 2.

Hardness test

The hardness test was conducted to evaluate the hardness behavior of 3D printed composite specimens produced utilizing PLA and Glass Fiber reinforcement, taking into account the influence of varying infill patterns. The Shore D Durometer was applied to the measurement of the hardness, available from the Rubber and Plastics Department, Anna University, MIT. The test adhered to the ASTM D2240 standards for the Shore D hardness measurement, a technique that is primarily applied to measure the Shore D hardness of stiffer polymers.³⁷ For uniformity in the results, the specimens were tested at a minimum thickness of 5 mm. To improve accuracy and account for surface roughness variations, hardness was measured at five points on each specimen.

Free vibration test

The free vibration test using an impact hammer in the transverse mode is performed to determine the natural frequencies and damping of the various infill patterns. Test was done according to standard ASTM E1876 – 15. The impact hammer excites multiple natural frequencies simultaneously. This allows for efficient measurement of all dominant modes of vibration in a single test.³⁸ The hammer impact and the response measured using accelerometer is used to calculate Frequency Response Functions (FRF). The clamping is done such that the length of the cantilever is 100 mm.³⁹ In this research, only the first natural frequency was analyzed because preliminary trials showed substantial variability in higher modes due to fixture sensitivity and boundary condition effects. Since the first mode is the most sensitive to global stiffness and internal defects, it was selected as the primary indicator of dynamic behavior.

Dynamic mechanical analysis

The Dynamic Mechanical Analysis (DMA) is carried out to analyse the viscoelastic behaviour of PLA/GF composite for various infill patterns. The Dynamic Mechanical Analysis was performed in the DMA 242 E Artemis, available at the Centre for Composite Testing, IIT Madras. The test followed the ASTM D7028 standard. The tests were conducted in 3-point bending mode, across a temperature range of 30°C to 90°C, and at a frequency of 1 Hz.⁴⁰ Four parameters were studied. They are Storage Modulus (E′), Loss Modulus (E″), Tan δ (Loss Factor), and Glass Transition Temperature (T_g).

Wear test

Wear test was performed to evaluate the wear resistance of 3D-printed PLA/GF composite, with a focus on the effect of different infill patterns and infill densities. Wear tests were conducted using the pin-on-disc apparatus, available at Adhi College of Engineering. The test was conducted according to ASTM G99 standard at a load of 20 N, a sliding distance of 1000 m, and a sliding velocity of 40 m/s.⁴¹ The mass loss was measured and used to calculate the wear rate in g/N·m.

Results and discussions

Tensile strength

The stress strain curves for PLA/GF composite samples printed at various infill patterns and densities are plotted and shown in Figure 4(a)–(c). Influence of infill pattern and density over the tensile property of the material is studied with the stress strain curve. The strain at fracture remained almost the same irrespective of infill patterns at higher infill densities of 70% and 90%. At a lower infill density of 50%, the cubic subdivision pattern showed substantial strain of 4.88%. This is 1.44% greater than the sample with cubic infill pattern. The results observed were in agreement with the work of Rismalia et al.,⁴² who observed almost similar strain at fracture for the infill patterns of concentric, grid and tri-hexagon using PLA material. The cubic infill pattern consistently shows the highest tensile strength and modulus across all infill densities, suggesting it provides better structural integrity under tensile loads. The tensile strength and tensile modulus of the three infill patterns at three infill densities are shown in Figure 4(d) and (e). The octet pattern shows intermediate tensile strength and modulus values, slightly lower than cubic but higher than cubic subdivision. The cubic subdivision infill pattern generally shows the lowest tensile strength and modulus. Increasing infill density from 50% to 90% leads to a noticeable improvement in tensile strength and modulus for all patterns. The change in tensile strength is most prominent in the octet pattern, where it rises from 19.12 MPa at 50% infill density to 23.14 MPa at 90% infill density. The change in tensile modulus is most prominent in the cubic subdivision pattern, where it rises from 0.67 GPa at 50% infill density to 0.83 GPa at 90% infill density. Figure 5(a)–(c) presents the FESEM micrographs of fractured PLA/glass fiber composites with cubic infill structures at 50%, 70%, and 90% densities. At 50% infill (Figure 5(a)), numerous fractured fibers and fiber pull-outs are observed, indicating weak interfacial bonding and inefficient stress transfer between fibers and the PLA matrix. This corresponds to the lower tensile strength recorded at this density. The 70% infill specimen (Figure 5(b)) exhibits relatively fewer voids and improved fiber–matrix adhesion, suggesting enhanced load transfer efficiency and contributing to the moderate increase in tensile performance. However, the presence of residual voids still acts as stress concentrators, initiating premature failure under tension. At 90% infill (Figure 5(c)), the microstructure shows fiber agglomeration and pull-out regions, implying that excessive packing and uneven filament deposition may hinder uniform resin flow during printing. Although this configuration enhances stiffness, the localized agglomeration may restrict matrix mobility and reduce ductility. Overall, the microstructural observations support the mechanical test results, showing that optimized infill density promotes better fiber dispersion and adhesion, which directly influence tensile strength and failure behavior.

Figure 4.

Tensile stress strain curves of PLA/GF samples at different infill patterns and densities (a) 50%, (b) 70%, (c) 90%, and (d) Tensile strength and (e) tensile modulus of PLA/GF samples at different infill patterns and densities.

Figure 5.

FESEM fracture analysis based on different infill density with cubic infill structure (a) 50%, (b) 70% and (c) 90%.

Flexural testing

The flexural stress strain curves for PLA/GF composite samples printed at various infill patterns and densities are plotted and shown in Figure 6(a)–(c). Influence of infill pattern and density over the flexural properties of the material is studied with the stress strain curve. From Figure 6(a)–(c), it can be inferred that the cubic subdivision pattern exhibited greater strain at fracture when compared to the other two infill patterns. At 90% infill density the cubic subdivision pattern showed substantial strain of 5.46%. This is 1.27% greater than the sample with cubic infill pattern. The cubic and octet infill patterns consistently show the highest flexural strength across all infill densities except at 90%. The results observed were in agreement with the work of Birosz et al.,⁴³ who observed almost similar flexural strength for the honeycomb, grid and gyroid infill patterns at higher infill densities using PLA material. The flexural strength and flexural modulus of the three infill patterns at three infill densities are shown in Figure 6(d) and (e). The variation of flexural strength is minimum for cubic and octet patterns at different infill densities. The flexural strength of the octet pattern increased from 35.62 MPa at 50% infill density to 39.42 MPa at 90% infill density, representing an increase of only 9.64%. Similarly for cubic pattern the increase in strength is only 8.64%. The cubic subdivision infill pattern showed large variation in flexural strength of 25.75 MPa at 50% infill density to 39.62 MPa at 90% infill density which is a relatively large increase of 35%. At 90% infill density all the three infill patterns had almost similar strength. From the Figure 5(e) it can be inferred that the octet pattern consistently showed the highest flexural modulus followed by the cubic pattern and the cubic subdivision pattern showed the least flexural modulus across all infill densities. The octet and cubic patterns achieved almost 98% of the strength and modulus at 70% infill density when compared with 90% infill density. For the cubic subdivision pattern there was substantial variation in strength and modulus with respect to infill density.

Figure 6.

Flexural stress-strain curves of PLA/GF samples at different infill patterns and densities (a) 50%, (b) 70%, (c) 90%, and (d) Flexural strength and (e) Flexural modulus of PLA/GF samples at different infill patterns and densities.

Impact and hardness strength

The impact strength of PLA/Glass Fiber composite at different infill patterns with various infill densities are compared in the Figure 7(a). The octet pattern consistently showed the highest impact strength followed by the cubic pattern and the cubic subdivision pattern showed the least impact strength across all infill densities except at 90%. Across all infill patterns, increasing the infill density from 50% to 90% results in higher impact strength. While impact strength increases with infill density, the rate of increase slows down, suggesting diminishing returns in strength gain. This is more prominent in Octet and cubic patterns. The octet and cubic patterns achieved almost 97% of the impact strength at 70% infill density when compared with 90% infill density. The difference in impact strength between the three patterns is less pronounced at 90% infill compared to lower densities, indicating that their structural advantages become comparable at high densities. The impact strength of the Cubic Subdivision pattern increases significantly from 4.08 KJ/m² (50% infill) to 5.5 KJ/m² (90% infill), suggesting that this pattern gains more structural integrity as density increases compared to the other patterns. The results observed were in agreement with the work of Mishra et al.,⁴⁴ who observed maximum impact strength at 85% infill density for the line, zig-zag and concentric infill patterns using PLA material.

Figure 7.

Impact strength (a), Shore D hardness (b) of PLA/GF samples at different infill patterns and densities and (c) FESEM fracture images of impact specimen at 90% infill density with cubic subdivision.

The Shore D hardness of PLA/Glass Fiber composite at different infill patterns with various infill densities are compared in the Figure 7(b). The hardness increases consistently with the increase in infill density across all patterns.⁴⁵ Cubic infill pattern exhibits the highest hardness values across all infill densities. Octet pattern shows the second-highest hardness at all infill densities followed by Cubic Subdivision pattern. At 90% infill, Cubic Subdivision surpasses the other two patterns, achieving the highest hardness value of 84.6. The sharpest increase in hardness with increasing infill density is observed in the Cubic Subdivision pattern.⁴⁶ From 70% to 90% infill, Cubic Subdivision jumps from 77.4 to 84.6, which is a 9.3% increase, highlighting how its performance peaks only at high densities. The findings were in agreement with Ansari et al.,⁴⁷ with their CF-reinforced PLA composites. Figure 7(c) FESEM images shows fiber pull-out and fractured glass fibers, suggesting efficient stress transfer and fiber participation during impact. These features confirm that higher infill densities improve fiber–matrix interaction, contributing to improved impact resistance and surface integrity. Although variations in tensile, flexural, and impact strength were observed among the tested infill configurations, these differences were within a narrow range. Further experimental repetitions with larger sample sets are recommended to statistically validate these trends and confirm their reproducibility.

Free vibration analysis

The frequency response function of one of the sample (Cubic 50% infill) is plotted in the Figure 8(a). The natural frequency of each sample is identified from the acceleration versus frequency plot. The damping ratio is found from the logarithmic decrement from the acceleration versus time plot. The natural frequency and damping ratio of the three infill patterns at various infill densities are depicted in Figure 8(b) and (c). From Figure 8(b), it can be concluded that the natural frequency for the three infill patterns rises as infill density is increased. This is an indication that the greater volume of material contributes to greater stiffness,⁴⁸ hence greater resistance to transverse vibrations. Notably, the Octet pattern consistently has the highest natural frequency for all infill densities, with the highest recorded frequency of 41.5 Hz at an infill density of 90%. This is an indication that the Octet pattern is the stiffest and vibration-resistant compared to Cubic and Cubic Subdivision patterns. On the other hand, the Cubic Subdivision pattern consistently has the lowest natural frequencies for all infill densities, with the lowest recorded frequency of 34.56 Hz at an infill density of 50%. The three infill patterns have a similar rise in natural frequency as a function of rising infill density. This trend suggests a linear relationship between infill density and the enhancement of stiffness. With natural frequencies rising with infill density, relative differences between Octet, Cubic, and Cubic Subdivision patterns are relatively stable. This stability suggests that each pattern retains its structural characteristics irrespective of density. From Figure 8(c), it is concluded that, in contrast to natural frequency, the damping ratio does not show a linear increase with increasing infill densities. Rather, it shows a peak or decline depending on the infill pattern, which implies that the internal structure governs energy dissipation in a nonlinear manner. While both Cubic and Cubic Subdivision patterns show increasing damping ratios, the Octet pattern shows a decline at higher densities. Such a finding implies that optimal damping occurs at specific density levels, and adding more material does not always lead to higher energy dissipation. The Cubic pattern shows the highest damping ratio (0.0222) at 90% infill density. On the other hand, the Octet pattern shows its highest damping ratio (0.0206) at 70% infill density, only to decline to 0.0183 at 90%. The Cubic Subdivision pattern, however, shows a linear and continuous increase in the damping ratio as infill density increases. The damping trends realized in the different patterns suggest that material properties and geometric configuration contribute to the modulation of damping behavior.

Figure 8.

Frequency response function of free vibration test (a), Natural frequency (b) and Damping ratio (c) of PLA/GF samples at different infill patterns and densities.

Dynamic mechanical analysis

Storage modulus

Storage Modulus (E′) represents how much energy is stored elastically when the material is deformed under cyclic loading. The storage modulus curves for PLA/GF composite samples printed at various infill patterns and densities are plotted and shown in Figure 9(a)–(c). Storage Modulus decreases with temperature for all infill patterns, as expected, indicating a transition from the glassy to rubbery region. At all infill densities, the Octet pattern consistently shows the highest E′ values, indicating superior stiffness and load-bearing ability under cyclic load. Cubic pattern comes second with slightly lower E′ which was followed by the cubic subdivision pattern with the lowest storage modulus, across all temperature ranges. As infill density increases from 50% to 90%, the overall storage modulus increases for each pattern due to increased material content and internal support. The drop in E′ occurs sharply between 55°C and 65°C, indicating the glass transition temperature (Tg) zone, consistent across all densities and patterns. The Cubic Subdivision curve drops earlier compared to Octet and Cubic, especially at 90%, implying slightly lower Tg or earlier onset of molecular mobility.

Figure 9.

Storage modulus curves of PLA/GF samples at different infill patterns and densities (a) 50% (b) 70% and (c) 90%.

Loss modulus

Loss Modulus (E″) is a measure of the energy dissipated as heat when a material is elastically deformed during dynamic loading. The loss modulus plots of test samples of PLA/GF composite printed with different infill patterns and densities are shown in Figure 10(a)–(c). All three patterns show an abrupt rise of E″ around 50°C, followed by a maximum at approximately 60°C, which corresponds to the glass transition region. The Cubic Subdivision pattern shows a very much higher baseline E″ at the glassy state (∼700 MPa) compared to Octet (∼270 MPa) and Cubic (∼240 MPa) patterns. At every density level, the Cubic Subdivision consistently shows a very much higher maximum compared to Octet and Cubic patterns, often doubling the latter’s value. The Octet and Cubic patterns have very similar shape curves with practically negligible divergence at the glassy region.

Figure 10.

Loss modulus curves (a)–(c) and Maximum loss modulus (d) of PLA/GF samples at different infill patterns and densities.

The maximum peak loss moduli of infill patterns are presented in Figure 10(d). Cubic Subdivision possesses a maximum peak loss modulus among infill densities at 985.2 MPa for 50% infill. Raising infill density from 50% to 90% makes loss modulus reduce for all the three patterns. Cubic Subdivision’s maximum E″ declines from 985.2 MPa (50%) to 910.5 MPa (90%), decreasing by 7.6%, the lowest decline of the three. Cubic pattern possesses the minimum peak E″ values in total, declining from 538.4 MPa to 458.5 MPa, with a 14.8% decline. Trend suggests denser structures restrict the molecular mobility and reduce the potential of the material to dissipate energy. Results were consistent with Arunprasat et al.,⁴⁹ with grid pattern ABS material.

Loss factor (Tan δ)

The Loss Factor (Tan δ) measures the ratio of energy lost to energy stored during cyclic deformation. It reflects how viscoelastic a material is combining both elastic (spring-like) and viscous (fluid-like) behaviour. The Tan δ curves for PLA/GF composite samples printed at various infill patterns and densities are plotted and shown in Figure 11(a)–(c). The non-homogeneous Tan δ curves observed across the samples arise from the different viscoelastic responses produced by changes in infill pattern and density. At lower infill densities, the printed PLA/GF structures contain more heterogeneous internal regions, causing broader Tan δ peaks due to local variations in the glass-transition behaviour. As infill density increases, the material becomes more uniform and structurally consistent, resulting in narrower peaks and a slight shift of the Tan δ maximum toward higher temperatures. The peak values of Tan δ of the infill patterns are compared in Figure 11(d). Cubic Subdivision consistently shows the highest Tan δ peak values at all infill densities, confirming its superior damping performance across the board. The peak Tan δ values decrease progressively with increasing infill density for all structures, indicating a loss in damping ability as the material becomes denser and stiffer. At 50% infill, the Cubic Subdivision has the highest overall peak (3.35), suggesting this combination has the best capacity to dissipate energy. Octet structure shows the lowest Tan δ peaks at all densities, indicating it is the least effective for damping among the three geometries. The rate of decrease in Tan δ peak from 50% to 90% is most noticeable in Cubic Subdivision, showing that its damping efficiency is more sensitive to infill density.

Figure 11.

Tan δ curves (a)–(c) and Maximum tan δ (d) of PLA/GF samples at different infill patterns and densities.

Glass transition temperature (Tg)

The glass transition temperature (Tg) is the temperature range over which a polymer transitions from a hard, glassy state to a soft, rubbery state due to increase in molecular mobility. Tg is identified as the peak of the Tan δ curve. The Tg values for PLA/GF composite samples printed at various infill patterns and densities are plotted and shown in Figure 12. The observed rise in Tg with increasing infill density is attributed to reduced free volume and the restricted molecular mobility in denser structures. As the internal geometry becomes more compact, polymer chain segments require more thermal energy to initiate motion, causing the glass transition to shift to higher temperatures. Cubic Subdivision shows the highest Tg across all densities, suggesting that its intricate structure offers the greatest resistance to thermal motion. Octet consistently has the lowest Tg, which implies a more flexible internal geometry that permits earlier onset of segmental motion. The rate of Tg increase is steepest for Cubic Subdivision (from 71.2°C to 77.21°C), suggesting this structure is most sensitive to infill density changes.

Figure 12.

Tg of PLA/GF samples at different infill patterns and densities.

Wear analysis

The wear versus time plot and the frictional force versus time plot of one sample (Cubic Subdivision 70% infill) are shown in Figure 13(a) and (b). For different infill densities, the volume wear rate from the depth of wear in μm is less precise than the mass wear rate.

Figure 13.

(a) Wear versus time plot and (b) Frictional force versus time plot of wear test sample, wear rate (c) and Coefficient of friction (d) of PLA/GF samples at different infill patterns and densities.

The friction coefficient and wear rate of the three infill patterns at three different densities are indicated in Figure 13(c) and (d). From Figure 12(c), we can observe that the wear rate decreases as the infill density increases for all three infill patterns, indicating improved wear resistance at higher densities. While the wear rate decreases with increased infill density, the variations among the infill patterns at the same density are minimal, particularly at higher densities. This indicates that wear resistance is influenced more by infill density than by the shape of the infill pattern. From Figure 13(d), we can observe that the coefficient of friction (CoF) decreases with increasing infill densities for all the infill patterns. For 50% infill, the highest CoF (0.332) is for the Octet pattern, which means greater resistance to sliding. The greater CoF at lower infill densities is due to more rough surfaces and bending during sliding. Highly dense structures (90% infill) give greater stability and less bending of material, hence lower friction. These findings are consistent with Liow et al.,⁵⁰ who investigated their ABS composite material with a zig zag pattern. Based on the results of all seven experimental investigations, the following Table 3 summarizes the most suitable infill pattern for each tested property, highlighting the strengths of each pattern in specific performance aspects.

Table 3.

Optimal infill patterns for evaluated properties.

Test	Property evaluated	Best performing infill pattern	Pattern showing highest response to infill density
Tensile test	Tensile strength	Cubic	Cubic subdivision
Tensile test	Tensile modulus	Cubic	Cubic subdivision
Flexural test	Flexural strength	Cubic & octet	Cubic subdivision
Flexural test	Flexural modulus	Octet	Cubic subdivision
Charpy impact test	Impact strength	Octet	Cubic subdivision
Hardness test	Hardness	Cubic	Cubic subdivision
Free vibration test	Natural frequency	Octet	Octet
Free vibration test	Damping ratio	Cubic subdivision	Cubic
Dynamic mechanical analysis	Storage modulus	Octet	Cubic
	Loss modulus	Cubic subdivision	Cubic subdivision, octet and cubic
	Tan δ	Cubic subdivision	Cubic subdivision
	T_g	Octet	Cubic subdivision, octet and cubic
Wear test	Wear rate	Cubic subdivision, octet and cubic	Cubic subdivision, octet and cubic
Wear test	Coefficient of friction	Cubic subdivision, octet and cubic	Cubic subdivision and octet

Conclusion

This study comprehensively evaluated the mechanical, viscoelastic, tribological, vibrational, and damping behaviors of PLA/Glass Fiber composites with Cubic Subdivision, Octet, and Cubic infill patterns at three densities (50%, 70%, and 90%).

Tensile properties showed strong dependence on pattern and density. The Cubic pattern exhibited the highest tensile strength and modulus (24.65 MPa and 0.95 MPa, respectively). Strength improved significantly across all patterns with higher infill, particularly in the Cubic Subdivision design. Flexural strength and modulus peaked in the Octet and Cubic patterns. Cubic Subdivision demonstrated the highest improvement, from 25.75 MPa at 50% to 39.62 MPa at 90%. Impact strength increased with infill density across all patterns, but gains plateaued at higher densities. The Octet pattern recorded the highest values—4.91 KJ/m² at 50% and 5.4 KJ/m² at 90%. Hardness rose with density, with the Cubic Subdivision pattern reaching a maximum of 84.6 at 90% infill—the highest among all.

Natural frequency increased with density; Octet consistently achieved the highest (41.5 Hz). Damping behavior varied: Cubic had the highest damping at 90%, while Octet peaked at 70%. Dynamic mechanical analysis revealed that Octet had the highest storage modulus, while Cubic Subdivision led in loss modulus and damping (Tan δ). Cubic Subdivision also had the highest glass transition temperature (77.21°C). Wear resistance improved with infill density. Both wear rate and friction coefficient declined, with infill density emerging as the dominant factor. These insights suggest that by carefully tuning infill geometry and density, PLA/GF composites can be engineered for specific high-performance applications, such as drone airframes requiring lightweight yet stiff structures, orthopedic implants benefiting from tailored damping and hardness, automotive interior components needing enhanced wear resistance, and protective gear where impact absorption and vibration damping are critical.

Footnotes

Declaration of conflicting interests

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

ORCID iD

Saravana Kumar Murugesan

Data Availability Statement

The experimental datasets obtained from this research work and then the analysed results during the current study are available from the corresponding author on reasonable request.*

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Vibrational and dynamic properties of PLA/GF composites influenced by the synergistic effect of infill geometry and density

Abstract

Keywords

Introduction

Materials and methods

Methodology

Procurement of PLA/GF composite

Fabrication PLA/GF parts using FFF

Mechanical testing

Tensile test

Flexural test

Charpy impact test

Hardness test

Free vibration test

Dynamic mechanical analysis

Wear test

Results and discussions

Tensile strength

Flexural testing

Impact and hardness strength

Free vibration analysis

Dynamic mechanical analysis

Storage modulus

Loss modulus

Loss factor (Tan δ)

Glass transition temperature (Tg)

Wear analysis

Conclusion

Footnotes

Declaration of conflicting interests

Funding

ORCID iD

Data Availability Statement

References