GPPS/Glass fiber composite?

18 March 2024 1 8K Report

I am preparing general purpose polystyrene (GPPS) glass fiber composite. I want to know what coupling agent can be used and what glass fiber grade would be suitable for GPPS

Suresh Ahuja

Effect of Short Glass Fiber Addition on Flexural and Impact Behavior of 3D Printed Polymer Composites

Mohankumar H R*
,
Maha Gundappa M. Benal
,
Pradeepkumar G S
,
Vijay Tambrallimath*
,
Keshavamurthy Ramaiah
,
T. M. Yunus Khan
,
Javed Khan Bhutto*
, and
Mohammed Azam Ali

Cite this: ACS Omega 2023, 8, 10, 9212–9220

Publication Date:March 1, 2023

https://doi.org/10.1021/acsomega.2c07227

CC-BY-NC-ND 4.0.

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SUBJECTS:

Composites,
Deformation,
Fibers,
Filaments,
Materials

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ACS Omega

Abstract

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Fused deposition modeling (FDM), one of the most widely used additive manufacturing (AM) processes, is used for fabrication of 3D models from computer-aided design data using various materials for a wide scope of applications. The principle of FDM or, in general, AM plays an important role in minimizing the ill effects of manufacturing on the environment. Among the various available reinforcements, short glass fiber (SGF), one of the strong reinforcement materials available, is used as a reinforcement in the acrylonitrile butadiene styrene (ABS) matrix. At the outset, very limited research has been carried out till date in the analysis of the impact and flexural strength of the SGF-reinforced ABS polymer composite developed by the FDM process. In this regard, the present research investigates the impact and flexural strength of SGF–ABS polymer composites by the addition of 15 and 30 wt % SGF to ABS. The tests were conducted as per ASTM standards. Increments in flexural and impact properties were observed with the addition of SGF to ABS. The increment of 42% in impact strength was noted for the addition of 15 wt % SGF and 54% increase with the addition of 30 wt % SGF. On similar lines, flexural properties also showed improved values of 44 and 59% for the addition of 15 and 30 wt % SGF to ABS. SGF addition greatly enhanced the properties of flexural and impact strength and has paved the path for the exploration of varied values of reinforcement into the matrix.

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1. Introduction

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3D printing, also known as additive manufacturing (AM), according to ISO/ASTM 52900:2015, is defined precisely as a fabrication process used for the creation of 3D models by assimilating the material layer by layer taken from the data developed by the 3D model software. (1) The 3D model is extracted from the computer-aided design software. (2) Utilizing the methodology of AM helps in the development of lightweight and complex parts, the manufacture of which is difficult by conventional methods of manufacturing. (3,4) One of the most widely used technologies presently of AM is based on extrusion technology, known as fused deposition modeling (FDM). The utilization of this technology is gaining popularity due to commercial and sustainable advantages, such as optimized material utilization, better energy efficiency, development of any complex geometry, and enhanced life cycle of the fabricated products. (5) The process of FDM works by feeding the filament into the nozzle; the filament melts in the heating chamber before entering the nozzle. The nozzle deposits the material layer by layer on the print bed, which is controlled by a numerical control program. (6) The material deposition takes place until the complete model is built.

The majority of FDM materials are thermoplastics, including polycarbonate, polylactic acid, and acrylonitrile butadiene styrene (ABS). These thermoplastics provide low stiffness and strength to the fabricated parts, leading to their use as prototypes as opposed to functional materials. (7) Numerous researchers have attempted to improve the properties of thermoplastics by incorporating various reinforcements. The most prevalent reinforcements are fibers, tubes, powder, and nanoparticles. (8) Studies by Caminero (9) revealed that reinforcement improved the mechanical properties compared to unreinforced materials. Recent research has centered on the addition of short fibers or continuous fibers (CFs) to thermoplastic materials, which has been shown to improve their mechanical properties. (10,11) In contrast to the addition of long fibers as reinforcement, the utilization of short fibers plays a significant role in filament development in terms of economic benefit and practicability. Numerous studies have been conducted on the utilization of short fibers as reinforcement in filament development. Caminero et al. (12) have demonstrated the viability of developing a graphene-reinforced polylactic acid polymer composite filament, which is then evaluated for the mechanical, dimensional, and surface roughness properties of 3D-printed composites. Tambrallimath et al. (13) demonstrated the successful synthesis and characterization of a graphene-reinforced polycarbonate (PC)–ABS polymer composite extracted as a filament for fused deposition modeling. Surface roughness and dimensional accuracy measurements were superior for PC–ABS with additives. By combining short glass fibers (SGFs) with the ABS polymer, Zhong et al. (14) created a novel composite material. It was observed that the addition of SGFs increased the tensile strength and surface rigidity. This study led to the significant conclusion that the addition of a plasticizer or the optimal amount of glass fiber increased the composite’s toughness. Tekinalp et al. (15) measured the tensile testing of 3D-printed CF/ABS polymer composites with fiber content ranging from 10 to 40% by weight. Fragmented specimens suggested an increase in internal porosity due to an increase in fiber content. With increased fiber content, however, Young’s modulus and tensile strength values increased. It was discovered that fiber orientation was a significant factor in determining the properties of 3D-printed components. In a similar study of CF addition to ABS conducted by Ning et al., (16) the fiber length increment increased the tensile strength.

Tian et al. (17) discovered that at higher temperatures, the surface accuracy of continuous carbon fiber reinforced in PLA would decrease. Increasing the temperature to extremely high levels during printing will result in the formation of pores on the inner surface of the printed part, thereby diminishing its strength. (18) According to Nazan et al., (19) warping is observed at very high printing temperatures due to high nozzle temperatures. Based on these temperature-related studies, the optimal printing temperature should be set so that the material can flow and fuse, rather than completely melt.

Tambrallimath et al. (20) reported that the addition of carbon nanotubes to a PC–ABS matrix resulted in an increase in tensile and impact strength. Experimentally analyzing the flexural behavior and impact strength of SGF-reinforced PLA composites is the focus of the current study, which investigates the wide range of research conducted on fiber-reinforced polymer composites developed via FDM.

As there are currently very few relevant studies on the addition of SGFs as reinforcement and the amount of fiber to be used as reinforcement, the experimental study focused on the development of 1.75 mm filaments with 15 and 30 wt % SGF added to PLA. Flexural and impact specimens were manufactured in accordance with ASTM standards. For fabrication, the optimal printing process parameters were selected, and property studies with build direction, infill density, and orientation were prioritized. This would greatly facilitate the printing process and make possible outcomes clear. Authors were able to examine the dispersion characteristics of SGFs in polymer matrices using scanning electron microscopy (SEM). Microstructure analyses of FDM-printed parts provide greater insight into the structure of specimens. This would aid numerous researchers in the development of new models by serving as a reference study.

2. Materials and Methods

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2.1. Raw Materials

Pellets of ABS procured from M/s (Messrs) GLS polymers, Bangalore, India, were utilized as the matrix material for this study. M/s Tespo International, Bangalore, India, was approached for procurement of SGFs.

Before the start of extrusion of filaments, pellets were dried at a temperature of 120 °C for 2 h. SGFs and dried ABS pellets were mixed in a pre-mixer at a rotor speed of 60 rpm at a temperature of 225 °C. Compounding and twin-screw extrusion machines were adopted to extract a filament of 1.75 mm diameter. Filaments with the addition of 15 and 30 wt % SGF were developed. A pure ABS filament was also developed by maintaining an extrusion temperature of 220 °C. The twin-screw extrusion setup was utilized by varying the temperature at various zones and for smooth extraction. The developed filaments of 1.75 mm diameter were used in the FDM machine.

2.2. Methods

To establish the consistency of filament diameter to be used in FDM, a vernier caliper was used. Numerous trials were conducted at various lengths of the filaments and the dimensions were observed. The device had a tolerance value of 0.1 mm. Under NTP (normal temperature and pressure) conditions, the SGF mixture to the ABS filament provided an even diameter throughout the filament, suggesting that the amalgamation of the reinforcement into the matrix had been to an excellent level without any protrusion of fibers. Macro inspection did not reveal any flaw or crack. The smoothness of the material was in comparison to pure ABS.

Microstructure analysis of energy-dispersive X-ray and SEM of the SGF was done using a scanning electron microscope of make JSM 840a Jeol. The accelerating voltage of SEM was in the range of 1 kV–10 kV. To make FDM samples conductive for microscopy, they were first mounted on stubs and then coated with a thin layer of gold. The technique known as spin-coating was utilized to deposit a thin layer of the conductive coating on the polymer samples. Fabrication of parts by FDM uses layer by layer technology to completely develop 3D models. A Pramaan printer from Global 3D Labs, Bangalore, India, was used for fabrication. Flexural and impact test specimens were developed using the machine. The optimal parameters considered for development of parts are infill density of 100%, 1.2 mm top and bottom layer thickness, 6 mm/s printing speed, 0.1 mm of layer thickness, and 0.4 mm shell thickness.

The impact test was used to assess the ability of FDM parts to sustain a load as the fiber content increased using an ASTM D256 methodology. The test was conducted using Fuel Instruments and Engineers Private Limited equipment along with a 0–60-ton capacity. Flexural specimens were designed and developed according to the ASTM D790 standard. The test methodology helps in the analysis of material flexural strength for research domains, confirmation of the desired quality, and relevant specifications. The experiment involves a three-point loading system for the application of load on a simply supported specimen. The tests have been performed using the universal tensile material testing system with a crosshead speed of 3 mm/min. (21−23)

3. Results and Discussion

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3.1. Microstructure Analysis of Printed Parts

Figure 1 shows the SEM images of FDM-printed ABS and ABS-composite parts with varying SGF contents. The primary purpose of SEM analysis was to examine the surface quality and bonding quality. Figure 1c shows that the surface of ABS in its natural state is quite rough and exhibits a considerable number of wavelike characteristics. The bonding between the raster and layers is not visible in the micrograph; therefore, a high-magnification SEM micrograph was taken to obtain a clear image. As seen in Figure 1c, the interlayer adhesion is quite good, apart from a few microporosities. The thermal energy of ABS as it is extruded through the nozzle of the FDM printer determines the adhesion or formation of bond between the ABS rasters and layers. This suggests that temperature plays a significant role in bond quality. There are two primary temperature-driven bonding mechanisms, such as molecular diffusion between rasters at the interface and neck growth governed by surface tension, which determine the quality of the bond. (24) Both mechanisms play an important role in achieving a strong connection between the raster and layers. Throughout the duration of the deposition process, the temperature of the ABS raster remains above its glass-transition temperature. This condition facilitates intermolecular diffusion across the interface, and at some point, the interface disappears or tends to cease where triangular-shaped voids can be observed. In the section on fracture analysis, the termination of interfaces and observation of triangular-shaped voids will be discussed. In addition, as the temperature of the raster remains above the glass-transition temperature, neck growth occurs between adjacent ABS rasters. The deposition of rasters at the optimal temperature of 230 °C resulted in a larger neck growth and improved molecular diffusion, reducing the number of voids observed at the interface of the rasters or layers (see Figure 1a). In contrast, the ABS composite filament containing 15% SGF, as shown in Figure 1a, exhibited a slightly rougher surface with some microporosities between the layers. Aside from this, the adhesion between the layers was quite good, with no significant gaps observed (see Figure 1b). It is common knowledge that the addition of fibrous material to a polymer can result in the formation of voids as some of the fibers decompose during twin-screw extrusion or printing. Take for instance the jute fiber used as a reinforcement for the ABS matrix, which decomposes when the processing temperature reaches 180 °C. (25)

Figure 1 📷Figure 1. SEM micrographs of (A) ABS + 15% SGF, (B) ABS + 30% SGF, and (C) ABS.

This causes the degradation of cellulose and the production of combustion gases, which leads to the formation of voids. In the present instance, however, the SGF is used as the reinforcing phase due to its superior heat resistance, chemical stability, and thermal insulation qualities. The degradation temperature of the SGF is well above 1000 °C, and the material does not begin to lose strength until 400 °C. (26) Therefore, the likelihood of SGF decomposition, which could have otherwise initiated void formation in the composite, is extremely low. However, there is not much of a difference between ABS and an ABS/SGF composite as the surfaces of both are nearly identical. Figure 1 shows the SEM images of FDM-printed ABS/30% SGF composite parts (b). It can be seen that as the SGF content increased from 15 to 30%, the appearance of printed parts became considerably smoother. In contrast to ABS and ABS/15% SGF composites, the surface is smoother and the number of pores observed is minimal. Despite the high weight percentage of SGF, ABS appeared to have uniformly covered the fibers and led to minimal pore formation at the rasters’ or layers’ interface. Observations indicate that the average pore density ranges between 0.35 and 0.4 mm and 0.26 and 0.3 mm for 15 and 30 wt % composite filaments of 100% infill, respectively. As shown in Figure 1c, the adhesion between the layers was quite good, with no significant gaps or pores between them.

The method used for measuring the porosity of the material is carried out by the classical Archimedes principle. The parts developed by AM use this method for measuring the density (porosity). (27) The equation used to measure the density of the sample is

𝜌={MaMa−Mw}𝜌𝑤

where Ma is the measured mass of the cylinder, measured in air; Mw is the measured mass of the cylinder, measured in water; and ρw is the density of water, which we assume to be 1.0 g/cm3.(1)

3.2. Flexural Strength

The effect of adding SGFs to ABS at different weight percentages of 15 and 30% was investigated using a flexural test. The flexural strength is determined by conducting a flexural test in accordance with ASTM D790 standards at a crosshead speed of 3 mm/min. Although flexural strength is not a fundamental material property, it is critical for structural applications. This is because it provides an overview of a material when it is subjected to three fundamental material stress states.

When composites are subjected to flexural testing, it is frequently observed that they fail at the compression surface. This is because the majority of composites possess a very high tensile strength but a low compressive strength. Failure of composites under compression during the flexural test is primarily due to fiber buckling. In this work, we will investigate how an FDM-printed ABS composite fails under bending load. In addition, it will be fascinating to investigate how SGFs contribute to the composite’s resistance to bending deflection. Table 1 provides the values of flexural strength for ABS and composites with the addition of SGFs.

Table 1. Flexural Strength of ABS, ABS + 15 wt % SGF, and ABS + 30 wt % SGF

SGF (%)flexural strength (MPa)ABS39.2 ± 2ABS + 15% SGF54.5 ± 3.5ABS + 30% SGF62.4 ± 3

Figure 2 shows the flexural strength of ABS and SGF-reinforced ABS composites. ABS exhibited a flexural strength of 39.2 MPa, which is well within the literature-reported range. Addition of SGF at 15 wt % has led to increase in flexural strength by 30.4% in comparison to ABS, having a value of 56.4 MPa. Similarly for 30 wt % addition of SGF to ABS, the increase in flexural strength was 37.2% in comparison to ABS, having a value of 62 MPa. Consider Weng et al., (28) who investigated the flexural strength of ABS utilizing an ASTM D790-03-compliant sample. After testing, the 3D-printed ABS sample was found to have a strength of 42.6 MPa.

Figure 2 📷Figure 2. Flexural strength of ABS and the SGF-reinforced polymer composite.

Vidakis et al. (29) examined the flexural strength of two distinct ABS sample types printed at different angles (0 and 90°). The production grade special ABS had the highest flexural strength of the two, measuring 38 MPa, even though the printing orientation had little effect on its strength. Another study determined the flexural strength of FDM-printed ABS to be 10.5 MPa, significantly lower than the present study’s findings. (30) The authors of the same paper created ABS using compression molding, and the resulting flexural strength was nearly identical to that of FDM-printed ABS. As stated previously, different studies have reported vastly different flexural strength values for ABS in its natural state. The value is quite high in comparison to the current work. In addition, incorporating 15% SGF increased the flexural strength of ABS to 55 MPa. In comparison to pure ABS, the increase in strength was approximately 40.3%, a significant increase. As a result of the SGF’s toughening properties, the flexural strength improved. However, the addition of SGF alone does not increase the strength of ABS composites; the strength of ABS composites also depends on the bonding between the constituents and the dispersion of SGFs in ABS. SEM micrographs of the composite filament and FDM-printed parts revealed that the interfacial bonding was quite strong and that the dispersion of SGFs in the ABS matrix was uniform, with no indication of agglomeration. In these regions, the interface was found to be clean and continuous, with no microporosities. The transmission of stress from the ABS matrix to the high-strength SGF is quite efficient and enhanced by a strong bond. Consequently, the composite was able to support a greater load, which is subtly reflected in its increased flexural strength value. This observation is supported by Liang’s (31) research on hollow glass bead-reinforced ABS. The author found that increasing the volume fraction of hollow glass beads from 0 to 15% increased the flexural strength from 35.5 to 38.4 MPa. Excellent adhesion between the ABS matrix and the hollow glass beads was responsible for the increased strength. Nevertheless, reinforcements do not always increase the flexural strength of the ABS matrix. With the addition of leather powder particles to ABS, the flexural strength values decreased. ABS’s strength decreased from 61.43 to 54.33 MPa when percent leather powder particles were incorporated. The polarity difference between the materials resulted in insufficient interfacial bonding. (32) The intensity changes of the scattered light from a blank ABS sample as a function of the calculated wavenumber include many characteristic peaks. One such characteristic peak from the Raman spectrum of blank ABS is at 1352 cm–1. The shift to 1324 and 1307 cm–1 for varied load percentages of loading multiwalled carbon nanotubes was observed. This shift can only be explained with the reinforcement loading ratio and their affinity with the ABS molecules. (33)

ABS/30% SGF composites exhibited the highest flexural strength of 62 MPa, which is considerably higher than that of ABS alone. The ABS composite is found to be more resistant to abrasion when the SGF content is increased from 15 to 30%. When a high proportion of basalt fiber (20 wt %) was added to an ABS matrix, (34) a comparable significant increase in strength was observed. The compressive strength of unreinforced ABS was 76.71 MPa, while that of the basalt fiber-reinforced composite was 90.72 MPa. The authors made an interesting observation when they stated that the increase in flexural strength was due to the incorporation of basalt fiber and that adhesion between the ABS matrix and basalt fiber was irrelevant or negligible. In many instances, however, increasing the weight percentage of the reinforcing phase had no positive effect. Vidakis et al. (35) reported on the addition of nano- and micron-sized ZnO particles to ABS and studied their flexural strength. ABS in its purest form exhibited a compressive strength of 46.82 MPa, while ABS composites reinforced with nano- and micron-sized ZnO particles exhibited compressive strengths of 43.20 and 46.13 MPa, respectively. Although the authors did not specify why the flexural strength values decreased for composites containing such a high proportion of ZnO particles, it is primarily due to particle clustering in such cases. Particle clusters serve as stress concentration zones, thereby facilitating the initiation of cracks. The overall increase in flexural strength values of ABS composites due to the addition of SGFs can be attributed to the SGFs’ excellent interfacial bonding and dispersion in the ABS matrix. (32)

3.3. Fracture Analysis after the Flexural Test

All specimens were photographed immediately after the flexural test, and the results are shown in Figure 4. Sample 1, which represents pure ABS, shattered into two pieces in a precise manner. This explains why it could not withstand a large bending deflection and broke as the load was increased. Alternatively, samples 2 and 3 correspond to ABS/15% SGF composites and ABS/30% SGF composites, respectively. As depicted in the figure, the composites were capable of withstanding significant bending deflections. The addition of SGFs to ABS proved advantageous as the composites pictured were able to withstand significant bending deformation. The ABS composite with the highest SGF content (30 percent) displayed the greatest deflection, which was in line with its flexural strength. SGF is primarily responsible for the greater deflection of composites compared to ABS. It is common knowledge that SGF has a significantly greater modulus than ABS, allowing composites to carry most of the load. In a similar study, Chen and Lin (36) reported on the flexural properties of cotton/epoxy composites. Photographic evidence revealed that the composite exhibited a significant breaking stress, as discovered by the author. The composite’s significant deformation under bending load was made possible by cotton’s soft texture. Close inspection of the composites shown in Figure 3 reveals that during the initial stages of deflection, small cracks appear on the tension plane, especially in the composites, where the transverse broken line appeared irregular rather than straight. Particularly when the fiber was perfectly parallel to the loading direction, the fracture line followed the path of the first fiber fracture. The crack path deviation may have been caused by random fiber distribution in the ABS matrix. Nevertheless, despite the random orientation of the fiber, the initiation of small cracks occurred directly in the middle of the span, as observed in ref (37). This indicates that the composites were extremely dense and devoid of any appreciably large pores that could have contributed to their failure under bending stress. Even though these statements appear to be assumptions at this point, they are well supported by SEM evidence in the discussion that follows. In addition, it is extremely challenging to explain the effect of FDM parameters on fracture behavior currently as the failure of samples is comparable to that of injection-molded samples. These small cracks in the midspan region may have originated in the ABS-rich region but spread along the interface of the SGF/ABS and fiber-fractured regions. Moreover, if we examine the broken line, we can see that in the case of ABS that broke in a brittle manner, the line was quite straight.

Figure 3 📷Figure 3. Photograph of failed samples of ABS and its composites after the flexural test.

To gain a better understanding of the failure behavior, an SEM analysis was conducted, and the resulting micrographs are shown in Figure 4. This analysis facilitates the examination of the print quality and internal structure of the composite samples. Figure 5 shows the SEM of the fractured surface of ABS that has not been processed (a). It is interesting to note that the raster patterns of printed ABS are not visible in this micrograph, but certain micropores are visible. These pores are not those that are formed during FDM printing as their occurrence is not periodic and there is no partial neck growth between the rasters. Probably, these pores formed between the rasters when the sample was subjected to a bending load. In most instances, the interface plays a significant role in the propagation of stress, and in this context, the interface is the region between the rasters. As the number of bending increases, weak regions such as pores or any discontinuity may cause the material to fracture. In the case of ABS, however, the interface was the first to fail as micro-voids began to form at the rasters’ interface. In such conditions, it is simple for a crack to initiate and spread throughout the material. As the crack propagates, adjacent rasters begin to separate, and this sequence continues until the final fracture occurs. Overall, ABS exhibits all the characteristics of brittle failure under bending stress. In the case of the ABS/15% SGF composite, the fracture surface, as shown in Figure 4b, revealed fiber breakage, and it is reasonable to assume that this was one of the contributing factors to composite failure. In addition to SGF fragmentation, the micrograph reveals matrix pull-out in several resin-rich regions, which contributes to failure. To comprehend the SGF fracture, we must first examine the interface between the ABS matrix and SGF. It is well known that stress propagation occurs from the ABS matrix to the SGF if the interfacial bonding between them is strong. In this instance, the microstructure analysis revealed strong bonding between the two. This explains why the flexural strength of ABS/SGF composites is greater than that of ABS alone. However, it must be noted that the ABS and SGF coefficients of thermal expansion differ greatly, resulting in high stress concentration in these regions. When a bending load is applied to a composite, stress concentration at the interfaces occurs, leading to the formation of cracks and fiber fracture. Yao et al. (38) reported comparable findings in their study of the bending properties of metal–resin composites. Due to the difference in the coefficient of thermal expansion between the steel fiber and the unsaturated polyester resin, it was discovered that the stress concentration at the interface regions increased, causing fiber necking and fiber pull-out. Figure 4c shows the fracture surface of the ABS/30 percent SGF composite, which is nearly identical to that of the ABS/15 percent SGF composite. The fracture surface is characterized by broken SGF and ABS matrix pull-out. The ABS matrix pull-out began in matrix-rich regions and extended to the SGF/ABS interface. Saeed et al. (39) made comparable observations in their work on the 3D-printed carbon fiber-reinforced polymer composite. The fracture surface analysis revealed that the failure of the composite was primarily attributable to fiber rupture. The majority of samples exhibited porosity between fibers and between printed layers, but the primary cause was still fiber breakage and fiber pull-out. Overall, in the present case, ABS showed brittle failure, while both composites failed primarily due to SGF fracture.

Figure 4 📷Figure 4. Fracture surface of (a) ABS, (b) ABS + 15 wt % SGF, and (c) ABS + 30 wt % SGF.

Figure 5 📷Figure 5. Impact strength of ABS and composites reinforced with SGF at 15 and 30 wt %.

3.4. Impact Properties

The impact properties of SGF-reinforced and neat ABS were studied and the obtained results are shown in Figure 5. However, prior to discussing the impact strength of ABS/SGF composites, one must understand that the most determining factor in dictating the impact strength is the reinforcing phase or fibers. This is mainly because in composites, the fiber is the phase which carries most of the load applied during the impact test. Especially if the fiber possesses a high tensile strain to failure property, it could significantly enhance the impact strength of the composites. In this regard, SGF is known for exceptional mechanical properties, and its addition to ABS could also improve the impact strength of the resulting composites. Table 2 provides the summarized results of the impact strength for ABS and its composites developed by the addition of SGFs.

Table 2. Impact Strength of ABS, ABS + 15 wt % SGF, and ABS + 30 wt % SGF

materialimpact strengthABS0.93ABS + 15% SGF2.22ABS + 30% SGF2.86

From Figure 5, it is seen that the impact strength of neat ABS was 0.92 J/mm2, and when comparing this value with previously published literature, it is extremely high. (40,41) For instance, Vidakis et al. (40) reported the impact strength values of the ABS polymer developed using the fused filament fabrication method. The impact strength was found to be in the range of 24–37 kJ/m2. In another work, Huang et al. (41) studied the impact strength of FDM-printed ABS samples developed by adopting different process parameters such as varying thickness (0.1–0.3 mm), printing speed (20–60 mm/s), and build orientation (vertical, horizontal, and lateral). The impact strengths obtained for different combinations of process parameters were in the range of 4.64–21.51 kJ/m2. The values obtained in these works are comparatively lower than the impact strength for neat ABS obtained in the present work. Further, when the 15% SGF is added to the ABS matrix, the impact strength of neat ABS increased to 2.25 J/mm2. This implies that addition of 15% SGF content has resulted in 144% improvement in the impact strength for the ABS matrix. With further increase in the SGF content from 15 to 30%, the impact strength increased to a value of 2.85 J/mm2. Compared to neat ABS and ABS/15% SGF, the percentage improvements in impact strength are 209.7 and 26.7% respectively. The increment in the impact strength is quite significant especially when compared to neat ABS. Strictly from the material point of view, the addition of SGFs has resulted in a substantial increase in impact strength of the ABS matrix. In a similar work, Kuo et al. (42) reported the impact strength of ABS composites with filler materials like starch, styrene-maleic anhydride copolymer, and carbon black. The neat ABS showed a value of 15 J/m, while the composite with 15% starch, 2% styrene-maleic anhydride copolymer, and 5% carbon black showed a value of 18.35 J/m. Keeping the reinforcing phase mechanical attributes in mind, it is obvious that the enhancement in impact strength was minimal. In another work, Caminero et al. (43) studied the impact behavior of nylon and its carbon-, glass-, and Kevlar fiber-reinforced composites. The neat nylon samples showed the highest impact strength of 40.12 kJ/m2, while the carbon-, glass-, and Kevlar fiber-reinforced composites showed values of ∼55, ∼120, and ∼270 kJ/m2, respectively. From this work, it was confirmed that glass fibers showed better impact strength than Kevlar- or carbon fiber-reinforced composites. Therefore, in the present case, the significant enhancement in the strength of ABS/15% SGF and ABS/30% SGF when compared to neat ABS can be attributed to the presence of glass fibers. The high mechanical properties impart their strength to the whole composite in such a way that they acquire impact resistance. Microscopically analyzing the reason for impact strength enhancement showed that the dispersion and interfacial bonding of SGF with the ABS matrix were quite good. Due to good interfacial bonding, the load applied to the sample was efficiently transferred from the ABS matrix to the SGF. Overall, inclusion of SGF to the ABS matrix has led to significant enhancement in the impact strength values.

3.5. Impact Fracture Analysis

After the impact test, failure analysis was performed on all fractured samples. Photographs of failed samples were taken to obtain a macrostructural overview of the fracture mechanism they reveal. Figure 6 shows the photographs of ABS and its composites’ impact samples that failed. In contrast to tensile specimens, where a transition from ductile to brittle fracture behavior was observed, all these samples exhibited a brittle mode of failure. After an impact test, materials can generally be classified as brittle, semi-plastic, or plastic. If the fracture surface of a material exhibits a clean break and no signs of plastic deformation, the material is considered brittle. If, on the other hand, the fracture surface exhibits a small amount of plastic deformation that is localized, the material is referred to as semi-plastic. When a significant amount of plastic deformation, deep scars, and layer pull-out are observed on the fracture surface, the material is referred to as plastic. In the present case, the absence of any indications of plastic deformation and the zigzag path of the crack were the primary indicators of brittle failure. Nonetheless, according to several studies, the material will fail brittlely if voids and local defects are present in composites, particularly at the matrix/fiber interface or between rasters/layers. (43,44) In the present case, however, neither the microstructure nor the fracture surface displayed defects. This indicates that a high number of SGFs not only increased the composites’ strength but also induced stiffness, resulting in brittle failure in all composites. Table 3 shows comparative results of different reinforcements to the polymer matrix in line with the present study.

Figure 6 📷Figure 6. Impact fracture photographs of (a) ABS and (b) ABS + 30 wt % SGF.

Table 3. Comparative Results toward Impact and Flexural Strength

authormaterialresultsMuthu Natarajan et al., (45)PLA + 25% Acacia concinnalayer thicknessflexural strength (MPa)impact strength (kJ/m) 0.0835.5615.3463 0.1646.6116.669 0.2443.9716.283Prajapati et al., (22)Onyx + HSHT fiberglassfiber layersimpact strength (J/m) 1192448.3 592113.3 291566.03 Ansari et al., (46)Onyx + GFfiber wt %flexural strength (MPa) 35.538.016 27.343.2 26.165.8

4. Conclusions

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SGF-reinforced ABS composites were developed through the fused deposition modeling process and examined for impact and flexural strength. A comparison of properties of ABS, ABS + 15% SGF, and ABS + 30% SGF was conducted. With the addition of SGFs to the ABS matrix, flexural strength and impact strength were increased. In order to achieve the desired results, fiber orientation along the print path was crucial to the process. It was possible to improve the resistance to impact by using the matrix’s and fiber’s combined strength. Impact strength increased by 42% with the addition of 15 wt % SGF and by 54% with the addition of 30 wt % SGF. In parallel lines, the addition of 15 and 30 wt % SGF to ABS improved the flexural properties by 44 and 59%, respectively. The incorporation of SGF has significantly improved the flexural and impact properties of the matrix and paved the way for the investigation of various reinforcement levels.

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Corresponding Authors Mohankumar H R - Department of Mechanical Engineering, Government Engineering College, Kushalnagar 571234, India; Email: [email protected] Vijay Tambrallimath - Department of Aeronautical and Automobile Engineering, Manipal Institute of Technology, Manipal Academy of Higher Education, Manipal 576104, Karnataka, India; 📷https://orcid.org/0000-0001-5153-9143; Email: [email protected] Javed Khan Bhutto - Department of Electrical Engineering, College of Engineering, King Khalid University, P.O. Box 394, Abha 61421, Saudi Arabia; Email: [email protected]
Authors Maha Gundappa M. Benal - Department of Mechanical Engineering, Government Engineering College, Kushalnagar 571234, India Pradeepkumar G S - Department of Mechanical and Automobile Engineering, CHRIST (Deemed to be University), Bangalore 560029, India Keshavamurthy Ramaiah - Department of Mechanical Engineering, Dayananda Sagar College of Engineering, Bangalore 560078, India T. M. Yunus Khan - Department of Mechanical Engineering, College of Engineering, King Khalid University, P.O. Box 394, Abha 61421, Saudi Arabia Mohammed Azam Ali - Department of Mechanical Engineering, College of Engineering, King Khalid University, P.O. Box 394, Abha 61421, Saudi Arabia
Author ContributionsConceptualization was achieved by M.H.R., M.G.M.B., P.G.S., K.R., and T.M.Y.K.; methodology was carried out by V.T., K.R., M.H.R., and M.G.M.B.; validation was done by K.R., J.K.B., and M.A.A.; formal analysis was conducted by V.T., K.R., M.H.R., and M.G.M.B.; investigation was completed by V.T., M.H.R., M.G.M.B., P.G.S., and T.M.Y.K.; resources were procured by T.M.Y.K. and J.K.B.; writing─original draft preparation was performed by M.H.R., M.G.M.B., P.G.S., and V.T.; writing─review and editing was finished by T.M.Y.K. and J.K.B.; project administration was taken on by T.M.Y.K.; funding acquisition was done by T.M.Y.K.; research support was extended by K.R., V.T., J.K.B., and M.A.A.; writing─review and funding acquisition were implemented by M.A.A. and T.M.Y.K. All authors have read and agreed to the published version of the manuscript.
NotesThe authors declare no competing financial interest.

Acknowledgments

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The authors extend their appreciation to the Deanship of Scientific Research at King Khalid University, Saudi Arabia, for funding this work through the Research Group Program under grant no. R.G.P. 1/214/43.

References

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📷 Abstract Figure 1 📷Figure 1. SEM micrographs of (A) ABS + 15% SGF, (B) ABS + 30% SGF, and (C) ABS. Figure 2 📷Figure 2. Flexural strength of ABS and the SGF-reinforced polymer composite. Figure 3 📷Figure 3. Photograph of failed samples of ABS and its composites after the flexural test. Figure 4 📷Figure 4. Fracture surface of (a) ABS, (b) ABS + 15 wt % SGF, and (c) ABS + 30 wt % SGF. Figure 5 📷Figure 5. Impact strength of ABS and composites reinforced with SGF at 15 and 30 wt %. Figure 6 📷Figure 6. Impact fracture photographs of (a) ABS and (b) ABS + 30 wt % SGF.

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