Experimental Investigation on Mechanical Characterization of Epoxy-E-Glass Fiber-Particulate Reinforced Hybrid Composites

Abstract

The present investigation focuses on the manufacturing and mechanical evaluation of epoxy-based composites reinforced with fiberglass with and without various particle fillers. The study explores the potential use of industrial wastes, such as coal powder (CP), coal fly ash (CFA), bagasse ash (BA), palm fruit ash (PFA), ash from rice husks (RHA), bone ash (BoA), marble/granite powder (MP), combinations of coal fly ash and coal powder (CFACP), blends of coal fly ash and marble powder (CFAMP), and combinations of coal fly ash and bone ash (CFABoA).The use of industrial factory wastes as a filler in polymer composite materials is becoming more and more common due to the improvement in structural characteristics compared to the pure epoxy-e-glass fiber composites. Composite manufacturing costs might be drastically reduced by using the above industrial wastes as reinforcing material, which would also solve the problems related to their disposal and ecological pollution. In previous research investigations, the comparative mechanical characteristic analysis of hybrid composites filled with two or more fillers has not been studied, which motivated us to take up the research on incorporation of the above listed industrial wastes as fillers. Different concentrations of these fillers are investigated, and the composites are formed successfully using a manual hand-layup approach. The mechanical properties assessed in accordance with ASTM Standards include micro-Vickers hardness (Hv), impact strength (IS), bending strength (TS), flexibility or flexural strength (FS), and interlaminar shear strength (ILSS). The form and amount of filler provided to the composite are considered when comparing each property of particle-loaded glass-reinforced epoxy composites. Some key findings from the investigation include: (1) Tensile Strength: unfilled composites exhibit a tensile strength of 252.19 MPa, marble powder causes the greatest drop in tensile strength, and CFACP-filled composites at 5 wt % yield the highest tensile strength of 251.42 MPa. (2) Flexural Strength: CFABoA-filled composites exhibit the highest peak bending strength of 860.22 MPa at 10 wt % and Peak ILSS of 34.317 MPa at 5 wt % is observed with CFABoA-filled composites. (3) Impact Strength and Hardness: CFACP-filled composites at 10 wt % show the maximum impact strength (2100 J/m) and hardness (62 Hv). (4) Effect of the Filler Percentage: mechanical characteristics of composites improve with increasing weight percentage of filler material, and Glass fiber-reinforced epoxy composites can be replaced with glass fiber-reinforced and particle-filled polymer-based hybrid composites for structural purposes. (5) Cost Considerations: hybrid composites based on CFACP-filled E-glass fiber-reinforced epoxy can be used instead of E-glass fiber-reinforced epoxy composites to reduce fabrication costs and “ER” epoxy resin usage. (6) Application Recommendation: the study suggests the use of CFACP-filled E-glass fiber-reinforced epoxy composites for constructing end posts in rail insulation junctions. In conclusion, the investigation provides valuable insights into the mechanical properties of epoxy-based composites with various fillers, offering potential applications in structural components with improved characteristics and cost-effectiveness.

1. Introduction

It is accurate that composite materials, especially those reinforced with synthetic fibers and filled with industrial and agro wastes, have gained significant popularity in various manufacturing, construction, and structural applications. The use of such composites is driven by their impressive combination of high strength-to-weight ratio, stiffness, and durability properties.¹⁻³ The shift toward polymers, particularly in the form of Fiber-Reinforced Polymers (FRP), instead of traditional metals and materials is indeed a prevalent trend in engineering and structural applications. Several advantages contribute to this shift:

• Ease of Processing: polymers can be molded and processed more easily than many traditional materials, providing flexibility in design and manufacturing.

• Directional Mechanical Properties: the mechanical properties of polymers can be tailored to specific directions, making them suitable for applications where strength and stiffness need to be optimized along particular axes.

• High Dimensional Stability: polymers often exhibit good dimensional stability, maintaining their shape and size under varying conditions.

• Light Weight: one of the key advantages is the lightweight nature of polymers, which is crucial for applications where weight reduction is a primary consideration.

• Excellent Fatigue and Corrosion Resistance: FRP materials generally have good resistance to fatigue and corrosion, enhancing their durability in various environments.

• High Specific Strength and Stiffness: despite being lightweight, FRP can offer high specific strength (strength per unit weight) and stiffness, making them suitable for applications requiring these properties.

• Low Thermal Expansion Coefficients: polymers often have lower thermal expansion coefficients compared to metals, making them more dimensionally stable under temperature variations.

The applications of FRP span across diverse industries, including:

• Aerospace: manufacturing of helicopters, satellites, aircraft, and spacecraft benefit from the lightweight and high-strength properties of FRP.

• Civil Infrastructure: FRP is used in civil engineering for structures such as bridges, buildings, and pipelines.

• Chemical Processing Equipment: due to their corrosion resistance, FRP materials find applications in the chemical industry for manufacturing tanks, pipes, and other equipment.

• Marine: FRP is used in the construction of ships and submarines, benefiting from its resistance to corrosion in marine environments.

• Automobiles: lightweight components in automobiles contribute to fuel efficiency, and FRP materials are employed for this purpose.

• Medical Prosthetics: the biocompatibility of certain polymers makes them suitable for use in medical prosthetics.

• Electronics and Sports Goods: FRP is used in microelectronics devices and sports equipment due to its specific properties.

In summary, the unique combination of properties offered by composite materials, particularly FRP, has led to their widespread adoption in various industries, driving innovation and advancements in engineering and manufacturing. Since the last couple of decades, the highly intense research is going on toward ceramic filled polymer composites. To reduce the cost and enhance the stiffness of commercial engineering applications, the polymers filled with inorganic fillers are considered.⁴⁻⁶ As polymer modifiers or fillers, the researchers are making use of a wide variety of industrial waste materials, such as dust from coal transportation, cement bypass dust, fly ash, ashes created from burning agriculture wastes in industries, and so on.⁷⁻⁹ The composites with particulate fillers also have efficient characteristics with real operational conditions.

The researchers concluded that hybrid composites filled with industrial waste might be the right material for components used in aquatic settings after completing mechanical characterization and water absorption tests.¹⁰⁻¹² At present, researchers have concentrated on the effect of particle dimensions and size, which affects the mechanical and physical properties.¹³⁻¹⁵ The mechanical properties of composites are enhanced greatly by adding the particles with the change in volume fraction, size, and shape of those particles.

Srivastava et al.¹⁶ expressed that, by the addition of fly ash particles as fillers to “ER” epoxy resins, the fracture toughness has been enhanced. The tensile properties of composites are affected by the size, interfacial bonding, and packing characteristics of fillers. The shapes of the particles and the size distribution are reflected by the maximum volumetric packing fraction.^17,18

Garcia et al.^19,20 primarily introduced the method of adding fillers to the surrounding substance to enhance the dominant medium properties of fiber-reinforced composites. According to this method, whiskers, microfibers, or particulates incorporated to the matrix proceeding to impregnation of resin. Jang et al.^21,22 identified that, by adding ceramic whiskers or particulates, impact energy of the hybrid composite is enhanced. The researchers use numerous industrial waste materials as polymer modifiers or fillers, such as cement bypass dust, fly ash, ashes produced by burning agro-wastes in industries, coal transportation dust, and so on.^23,24 Using these fillers on an extensive level might decrease pollution to the environment and issues with disposal and further enhancing the mechanical properties of composites.²⁵

The findings mentioned above underscore a discernible knowledge gap in the existing research landscape, particularly in the realm of composite materials. While considerable efforts have been invested in understanding the mechanical properties and erosion wear responses of composites reinforced with either fibers or particulates, there exists a conspicuous lack of investigation into composites filled with two distinct types of fillers, in conjunction with “E” glass fiber as the reinforcement and “ER” epoxy resin as the matrix material.

Despite the wealth of research on composite materials, comparative analysis of the mechanical characterization of epoxy-based composites filled with various combinations of fly ashes and marble powder remains largely unexplored in the literature. The absence of such comparative studies represents a noteworthy research gap that has implications for a broader understanding of composite material behavior and performance.

In light of these identified gaps, the primary objectives of the present research are set to:

• 1.Investigate Mechanical Properties: conduct a comprehensive study on the mechanical properties of epoxy-based composites filled with different combinations of fly ashes, marble powder, “E” glass fiber, and “ER” epoxy resin.
• 2.Comparative Analysis: conduct a comparative analysis of the mechanical characteristics of the developed composites, focusing on the synergistic or contrasting effects of the two different fillers in conjunction with the reinforcing fiber and matrix material.
• 3.Optimization: identify optimal combinations of fillers and proportions that yield enhanced mechanical performance in the composite materials.

Through these objectives, the research endeavors to address the identified knowledge gap and advance the understanding of multifiller epoxy-based composites, thereby providing valuable contributions to the field of composite material science.

2. Materials and Methods

2.1. Matrix Material

Because of their superior electrical and mechanical properties, good stability at prominent temperatures, and excellent adhesion to various types of fibers, “ER” epoxy resins are the most widely used polymers for most advanced composites. They also have excellent chemical resistance and contain a small amount of shrinkage due to curing. Because “ER” epoxy resins have the aforementioned advantages over other thermoset resins, they can be used as the matrix material for composites in ongoing research projects. Synthetic epoxy (LY556) is categorized under the epoxide family and goes by the general name “bisphenol-A-diglycidyl-ether”. In this study, the matrix material considered is “ER” epoxy resin combined with the appropriate hardener provided by Kotson Engineering Corporation Private Limited.

2.2. Fiber Material

Woven Roving (WR) E-glass strands from Kotson Engineering Corporation Private Limited, Vijayawada, are being used for strengthening in the composites due to their desirable properties, such as good mechanical properties, insulation, cost-effectiveness, and high chemical resistance. Additionally, to facilitate the easy removal of composite slabs from the mold, a common practice involves applying either white wax polish or silicone spray to the inner surfaces of the mold. This step aims to prevent the composite material from sticking to the mold, making demolding smoother and reducing the risk of damage to the composite structure.

2.3. Particulate Filler Materials

It is rare to see industrial waste used as epoxy modifiers. Therefore, a variety of fly ashes from industries, including coal dust, coal fly ash, bagasse, rice husk ash, palm fruit ash, bone ash, and marble powder, are gathered in the current work and used as particulate fillers for epoxy composites. Their potential for reinforcement can be assessed in terms of wear and mechanical characteristics.

The Dr. Narla Tatarao Thermal Power Station in Vijayawada, India, provided the coal powder that was utilized as a filler in this project. When coal is sent to ball mills for pulverization via conveyor belts, coal powder is produced and collected. It is also known as coal dust and is harmful to the environment and public health. By using it as a filler in large-scale polymer matrix composites, this can be somewhat mitigated. The coal fly ash utilized as fillers in this project was obtained from the Dr. Narla Tatarao Thermal Power Station, which is situated in Vijayawada, India. Fly ash, which is a finely split powder obtained in vast amounts during the burning of coal for power production in coal-based power plants, is collected and classified as Class F fly ash. A combination of ceramic minerals, including SiO₂, TiO₂, Al₂O₃, and Fe₂O₃, is known as coal fly ash.

Rice Husk Ash (RHA) is prepared by burning the agricultural waste “Rice Husk” at a controlled temperature of 680 °C for 6 h. This rice husk ash is used in the preparation of bricks and wooden panels. In the current work, rice husk ash is utilized as a potential reinforcing filler for polymer composites, which is collected from Venkateswara rice mill in Davuluru, India. The burning of rice husks produces ash and alumina. Palm fruit ash (PFA) is an agricultural waste produced by burning the palm bunch and palm kernel shells after extraction of the oil in the palm oil industry. Palm fruit ash is collected from Ruchi industries in Veeravalli, AndhraPradesh. Palm fruit ash is also a blend of ceramic or earthenware materials such as Fe₂O₃, Al2O3, SiO₂, TiO₂, etc.

Bagasse ash (BA) is an agricultural derivative waste produced by the burning of bagasse in boiler combustion chambers for power and steam generation in sugar factories. Bagasse ash is collected from KCP Sugar and Industries Corporation Limited., Vuyyur, and bagasse ash is also a mixture of ceramic materials. Bone ash (BoA) is prepared by heating the bones to about 10,000 °C in an oxygen-rich environment. It consists of 55.82% CaO, 42.39% P4O10, and 1.79% H2O, and the density of bone ash is 3.10 g/mL. The chemical formula for bone ash is Ca₅(OH) (PO₄)₃. The bone meal to prepare the bone ash is supplied by A.P.Gramadhyog, Hanumanghar, and marble sludge is collected from the local marble cutting industry in Vijayawada and crushed to get marble powder.

Coal powder (CP), marble powder (MP), and bone ash (BoA) are combined in the proper amounts with coal fly ash (CFA) to create CFACP, CFAMP, and CFABoA, which are further utilized as particle fillers. Figure 1 displays the particle fillers that were employed to make the epoxy-glass composites.After being purged of any remaining moisture using an oven heated to 110 °C, all of the fillers are sieved to a consistent particle size of between 38 and 60 μm.

Figure 1.

Particulate fillers as epoxy modifiers (source: the photograph is taken by Author Dr. Raffi Mohammed¹).

2.4. Fabrication of Composites

A releasing agent, such as silicone spray or wax, is sprayed on the working side of the mold for simple composite removal, and an hour before the fabrication process begins, a G.I. sheet measuring 300 mm × 300 mm × 5 mm3 is used to prepare the mold. Figure 2 shows the systematic process of manufacturing the composite slabs using a traditional manual layup method and preparation of samples as per ASTM Standards, eight layers of 300 × 300 mm2 glass fiber, “ER” epoxy resin, and particle fillers are used to fabricate the composite plates. The compositions of these resources are listed in Table 1.

Figure 2.

Systematic process for the fabrication of composite laminates and specimens by manual hand-layup technique for mechanical characterization (source: the image is prepared by author Raffi Mohammed¹).

Table 1. Designation and Composition of Composites.

designation of composite	composition
EG50	50 wgt. %“E” glass fiber +50 wgt. %“ER” epoxy resin
EG40	40 wgt. %“E” glass fiber +60 wgt. %“ER” epoxy resin
EGCP2.5	50 wgt. %“E” glass fiber +47.5 wgt. %“ER” epoxy resin +2.5 wgt. %coal powder
EGCP5	50 wgt. %“E” glass fiber +45 wgt. %“ER” epoxy resin +5 wgt. %coal powder
EGCP10	50 wgt. %“E” glass fiber +40 wgt. %“ER” epoxy resin +10 wgt. %coal powder
EGCFA2.5	50 wgt. %“E” glass fiber +47.5 wgt. %“ER” epoxy resin +2.5 wgt. %coal fly ssh
EGCFA5	50 wgt. %“E” glass fiber +45 wgt. %“ER” epoxy resin +5 wgt. %coal fly ash
EGCFA10	50 wgt. %“E” glass fiber +40 wgt. % “ER” epoxy resin +10 wgt. %coal fly ash
EGBA2.5	50 wgt. %“E” glass fiber +47.5 wgt. % “ER” epoxy resin +2.5 wgt. %bagasse ash
EGBA5	50 wgt. %“E” glass fiber +45 wgt. %“ER” epoxy resin +5 wgt. %bagasse ash
EGBA10	50 wgt. %“E” glass fiber +40 wgt. %“ER” epoxy resin +10 wgt. %bagasse ash
EGPFA2.5	50 wgt. %“E” glass fiber +47.5 wgt. %“ER” epoxy resin +2.5 wgt. %palm fruit ash
EGPFA5	50 wgt. %“E” glass fiber +45 wgt. %“ER” epoxy resin +5 wgt. %palm fruit ash
EGPFA10	50 wgt. %“E” glass fiber +40 wgt. %“ER” epoxy resin +10 wgt. %palm fruit ash
EGRHA2.5	50 wgt. %“E” glass fiber +47.5 wgt. %“ER” epoxy resin +2.5 wgt. % ice husk ash
EGRHA5	50 wgt. %“E” glass fiber +45 wgt. %“ER” epoxy resin +5 wgt. %rice husk ash
EGRHA10	50 wgt. %“E” glass fiber +40 wgt. %“ER” epoxy resin +10 wgt. %rice husk ash
EGBoA2.5	50 wgt. %“E” glass fiber +47.5 wgt. %“ER” epoxy resin +2.5 wgt. %bone ash
EGBoA5	50 wgt. %“E” glass fiber +45 wgt. %“ER” epoxy resin +5 wgt. %bone ash
EGBoA10	50 wgt. %“E” glass fiber +40 wgt. %“ER” epoxy resin +10 wgt. %bone ash
EGMP2.5	50 wgt. %“E” glass fiber +47.5 wgt. %“ER” epoxy resin +2.5 wgt. %marble powder
EGMP5	50 wgt. %“E” glass fiber +45 wgt. %“ER” epoxy resin +5 wgt. %marble powder
EGMP10	50 wgt. %“E” glass fiber +40 wgt. %“ER” epoxy resin +10 wgt. %marble powder
EGCFACP5	50 wgt. %“E” glass fiber +45 wgt. %“ER” epoxy resin +5 wgt. %CFACP
EGCFACP10	50 wgt. %“E” glass fiber +40 wgt. %“ER” epoxy resin +10 wgt. %CFACP
EGCFAMP5	50 wgt. %“E” glass fiber +45 wgt. %“ER” epoxy resin +5 wgt. %CFAMP
EGCFAMP10	50 wgt. %“E” glass fiber +40 wgt. %“ER” epoxy resin +10 wgt. %CFAMP
EGCFABoA5	50 wgt. %“E” glass fiber +45 wgt. %“ER” epoxy resin +5 wgt. %CFABoA
EGCFABoA10	50 wgt. %“E” glass fiber +40 wgt. %“ER” epoxy resin +10 wgt. %CFABoA

Prior to the corresponding glass fiber mats (GFM) armored into the matrix, the fillers are completely mixed with the “ER” epoxy resin (LY556). Then, the corresponding hardener (HY951) is combined in a proportion of 10:1 by heaviness as suggested in manufactures catalog. After evenly applying the aforementioned mixture to the mold’s working side with a brush, the glass fiber mat is inserted into the mold. A matrix system made of epoxy, hardener, and filler is then applied to the mat, trapping any trapped air bubbles and removing them through rolling, leaving the mold cavity-free. The manufacturing process is carried out at ambient temperature, and the manufactured slabs are subjected to a uniform weight of 25 kg and maintained at the same temperature for a duration of 72 h. After this period, the slabs are extracted from the mold. The slabs are cut into specimens according to ASTM standards to perform various mechanical characterizations.

2.5. Mechanical Characterization

The specimens are prepared by machining the composite slabs or plates obtained from the manual hand-layup process for mechanical characterization as per ASTM Standards as shown in Figure 3, and the specimens are loaded in to the respective testing equipment for mechanical characterization. Density is a crucial attribute in weight-sensitive applications, and composites have lower densities compared to traditional materials such as metals and ceramics. Polymer composites possess the potential to serve as engineering materials in numerous applications. The density of the composite mostly depends on the kind of matrix and reinforcement as well as their compositions. Theoretical and experimental densities of produced composites exhibit disparity, with the discrepancy serving as an indicator of the void content inside the composites. This void content has the potential to impact the mechanical characteristics of the composites.

Figure 3.

Specimens for mechanical characterization as per ASTM Standards (source: the photograph is taken by Author Dr. Raffi Mohammed¹).

2.5.1. Vickers Micro Hardness

The Leitz microhardness analyzer, seen in Figure 4a, is used to measure the composite laminates’ hardness. Using a diamond-shaped indenter, a full force “F” is delivered to the material surface for 10–15 s. As seen in Figure 4b, the indenter creates an indentation on the substrate with diagonals d1 and d2 when the load is applied, and their mean L1 is measured. In the experiment, a load of F = 24.54N is taken into account, and its Vickers hardness number (VHN) is calculated using the subsequent formulas.

Figure 4.

(a) Leitz micro hardness analyzer, (b) Vickers indentation and measurements of impression diagonals (source: the photograph is taken by author Raffi Mohammed¹ at Vignan University, Guntur).

2.5.2. Tensile Strength

For tensile tests, flat specimens are often utilized. There are two kinds of flat specimens. Two types are available: rectangular and dog-bone types with end tabs. In the current investigation, specimens with the standard ASTM D 638-III are prepared and loaded in the UTM (HEICO) to perform the test at 10 mm/min cross-head speed. The outcomes are used to determine the “TS-tensile strength” of composite specimens. A tensile load of F newtons is applied at the two ends of the sample during the experimentation. A tensile test specimen made in compliance with ASTM standards is shown in Figure 5a. The specimen loading procedure and UTM utilized for the tensile test are depicted in Figure 5b. For every component, three specimens are tested to determine the “TS-tensile strength” of the composite; the mean result is utilized. The tensile modulus, which is also calculated for each kind of composite, is the ratio of the specimen’s tensile stress to its tensile strain under tensile loading.

Figure 5.

(a) Dimensions of the tensile sample as per ASTMD638-III, (b) sample loading for the tensile test (source: the image is taken by author Raffi Mohammed¹ at Vignan University, Guntur).

2.5.3. Flexural Strength and Interlaminar Shear Strength (ILSS)

The term “flexural strength” refers to the composite’s upper limit of tensile strength that it can sustain when bent earlier than breaking. A 3-point bending test at a cross-head speed of 10 mm/min is performed by a universal testing machine on a specimen that has been prepared in accordance with ASTM D-790 and has dimensions of 127 × 12.7 × 3.2 mm³. Figure 6a,b illustrates the specimen dimensions and the loading of the test specimen.

Figure 6.

(a) Flexural test sample as per ASTM D-790, (b) sample loading for the flexural test (source: the image is taken by author Raffi Mohammed¹ at Vignan University, Guntur).

The test is continued three times for each composition, and the mean or average value of the FS-flexural strength and ILSS is found. The following formulae be capable to determine the flexural strength and ILSS.

where l is the samples length in among the two supports in mm, F is the maximum force applied in Newton’s, b is the sample width in mm, and t is the sample thickness in mm.

2.5.4. Impact Strength

According to ASTM D256, the Izod impact tester (shown in Figure 7a) measures the impact strengths of all of the composite types for specimen sizes of 63.5 mm × 12.7 mm × 3.2 mm. The middle of the specimen has a V-notch that is drilled to a depth of 10 mm, as seen in Figure 7b. When the pendulum hammer impacts the notched specimen that has been put in the impact tester’s specimen clamp, the impact strength of the specimen may be immediately viewed from the dial indication of the impact tester.

Figure 7.

(a) Izod Impact tester, (b) Izod impact specimen as per ASTM D256 (source: the photograph (panel a) is taken by Author Dr. Raffi Mohammed¹ at Vignan University, Guntur).

3. Results and Discussion (Mechanical Characterization of Epoxy-Based Hybrid Composites)

Any filler material or particle filler added to epoxy-based E-Glass fiber-reinforced composites will have a persuasive effect on their mechanical and physical properties. Here, the mechanical characteristics of a variety of unfilled and partially filled glass epoxy composites are examined based on experimental data as shown in Table 2.

Table 2. Mechanical Properties of Epoxy-Based Hybrid Composites (Final Results are the Average of Three Identical Samples)^a.

S.No	composite designation	TS (MPa)	TM (GPa)	FS (MPa)	ILSS (MPa)	IS (J/m)	VH (Hv)
1	EG50	252.18	6.29	666.58	20.507	687.50	32
2	EG40	230.02	2.77	620.34	19.084	625.00	27
3	EGCP2.5	250.67	3.02	448.60	13.8013	1362.5	39
4	EGCP5	249.00	5.22	488.40	9.013	1850.0	47
5	EGCP10	181.78	5.66	750.54	25.188	1750.0	51
6	EGCFA2.5	240.00	3.86	422.50	4.6765	1220.0	34
7	EGCFA5	234.47	5.85	525.42	9.696	1340.0	41
8	EGCFA10	175.13	7.82	693.07	24.247	1250.0	48
9	EGBA2.5	239.40	3.85	390.54	12.015	1220.0	36
10	EGBA5	220.50	3.55	419.60	12.909	1312.5	39
11	EGBA10	215.42	6.63	800.17	27.99	1604.0	45
12	EGPFA2.5	203.45	2.34	393.90	12.118	1497.8	28
13	EGPFA5	187.88	3.02	488.62	15.032	1604.68	32
14	EGPFA10	177.01	3.35	590.40	18.1638	1711.9	41
15	EGRHA2.5	198.82	3.20	418.32	12.869	218.75	27
16	EGRHA5	180.14	3.14	502.42	15.457	234.375	30
17	EGRHA10	160.42	3.09	572.81	17.6227	250.00	34
18	EGBoA2.5	235.20	3.96	612.89	18.855	1430.2	36
19	EGBoA5	218.36	4.58	674.40	20.748	1489.7	44
20	EGBoA10	201.40	6.75	794.82	24.452	1536.5	47
21	EGMP2.5	169.45	2.73	250.92	7.7196	1279.5	33
22	EGMP5	142.40	2.86	213.46	6.567	1476.7	35
23	EGMP10	119.68	2.97	319.23	9.821	1642.6	39
24	EGCFACP5	251.42	5.93	624.36	19.208	1974.0	51
25	EGCFACP10	242.56	6.72	702.48	21.612	2100.0	62
26	EGCFAMP5	229.16	4.23	518.86	15.9629	1643.0	49
27	EGCFAMP10	211.41	5.14	690.36	21.239	1728.0	57
28	EGCFABoA5	249.46	5.78	734.28	34.317	1983.0	53
29	EGCFABoA10	218.36	6.26	860.22	33.21	1875.5	60

^aWhere TS is the tensile strength in MPa, TM is the tensile modulus in GPa, FS is the flexural strength in MPa, ILSS is the interlaminar shear strength in MPa, IS is the impact strength in J/m, and VH is the Vickers hardness number (Hv).

The average values of mechanical properties of all the identical samples for three trails are tabulated, and the reasons for variation of mechanical properties are discussed in next sections in detail with the help of graphs for each and every mechanical property.

3.1. Vickers Micro Hardness (VH)

One of the key elements influencing the erosive wear resistance of any material is its hardness, which determines its resistance to wear or wear resistance. Figure 8 displays the Vickers hardness of each of the 29 epoxy-glass composites that are filled with particles. It is quite possible to observe that, regardless of the kind of filler used, the hardness values of all composites have grown with the addition of filler material from 0 to 10%. This is due to the fact that, in the Vickers microhardness test, compressive stacking forces the grid stage/matrix phase and fortification phase (i.e., glass fiber and filler) to wedge together tightly. This increases the interface’s ability to transfer pressure, which improves hardness. When compared to other filled or unfilled composites, the composite filled with CFACP at 10 wt % had the highest microhardness of 62 Hv. The matrix distributes some of the applied stress to the particles, which carry a portion of the load and account for the high hardness levels.

Figure 8.

Type of composite vs Vickers micro hardness number.

With the exception of EG40 and EGPFA2.5 composites, all particle-filled composites showed greater hardness compared to pure composites. These particle fillers may have little to no effect on composite microhardness levels. It may be due to the presence voids and holes in the material that can be studied in detail by SEM analysis, which is not included in the present investigation. Based on the results of this study, we may take into account CFACP-filled composites for prospective uses for which the highest level of wear resistance is necessary. From the previous findings,²⁶ it is observed that the results obtained for vickers micro hardness were in good argument with the present investigation results and the maximum values of hardness were obtained in the epoxy composites filled with the mixture of rice hush ash and saw wood dust ash at 10 wt %age.

3.2. Tensile Characteristics/Tensile Strength (TS) and Tensile Modulus (TM)

Regardless of the type of filler added, an increase in filler material results in a decrease in tension strength for the composite, as shown in Figure 9. The tension strength of an unfilled glass fiber loading is 252.19 MPa, and it decreases to 230.02 MPa for composites with 40 wt % of glass fiber loading without filler. Composites filled with different fillers show varying tensile strengths at different filler weight percentages. The composite filled with CFACP at a weight percentage of 5 wt % exhibits a maximum tensile strength of 251.42 MPa. The uniform dispersion of regular-shaped CFACP fillers in the “ER” epoxy resin is suggested as a reason for excellent interfacial adhesion. Composites EGCP2.5, EGCP5, EGCFACP5, and EGCFABOA5 demonstrate a minimal difference in tensile strength compared to the unfilled composite EG50. The study indicates that the choice of filler material and its uniform dispersion in the epoxy resin significantly influences the tensile strength of the composite. CFACP at 5 wt % emerges as a promising filler for enhancing tensile strength, possibly due to its favorable interaction with the epoxy resin.

Figure 9.

Type of composite versus tensile strength in MPa.

The investigation involved adding marble powder as a filler to composites in varying weight percentages (2.5 to 10%). The most significant drop in tensile strength was observed when the marble powder content increased, particularly from 2.5 to 10%. The tensile strengths for composites with marble powder were reported as follows: EGMP2.5:169.45 MPa; EGMP5:142.4 MPa; EGMP10:119.68 MPa. Regardless of the type of filler used, all composites exhibited a consistent pattern of tensile strength loss. Similar findings from earlier research were also mentioned, indicating a recurring trend. The presence of irregular shapes with sharp corners in the fillers may lead to a stress concentration in the matrix. Pores at the interface between particulate fillers and “ER” epoxy resin could contribute to the reduction in tensile strength. These pores may result in weak interfacial adhesion between the epoxy resin (matrix) and the filler. The observed decline in tensile strength is likely attributed to the stress concentration and poor interfacial adhesion caused by irregular filler shapes and pores at the interface. Above reasons may lead to decline in tensile strength, the exact reasons for failure and reduced strengths can be better studied in detail through microstructural investigation by SEM. In the present investigation, only the effect of various industrial wastes in the form of fine ashes on mechanical properties have been studied.

From the previous investigations done by the researchers,¹² the composite filled with CDCFA at 2.5 weight percentage has given the maximum tensile strength of 249 MPa and this value is nearly equal to the value obtained in present investigation for the composite filled with CFACP at 5 wt %age.

Figure 10 shows all of the composites’ tensile modulus data, both with and without the addition of different fillers. The tensile modulus is shown to rise with an increase in the weight percent of the filler in the matrix material. The composite EGCFA10 demonstrated the highest tensile modulus of 7.823 GPa. On the other hand, the unfilled composite has a tensile modulus of 6.292 GPa.

Figure 10.

Type of composite vs tensile modulus in GPa.

When compared with other filler-filled and unfilled composites, the composite filled with palm fruit ash, rice husk ash, and marble powder had the lowest tensile modulus. According to suggestions, the tensile modulus of glass epoxy composites rose somewhat when a combination of coal powder and coal fly ash was added to the “ER” epoxy resin at a weight percentage of 10%. It is hypothesized that, because of the comparatively low stresses of the composites during the tension test, the addition of a combination of coal powder and coal fly ash at a weight percentage of 10% to the “ER” epoxy resin raised the tensile modulus of glass epoxy composites substantially.

3.3. Flexural Test (FS)

The three-point bending test was employed to measure the flexural strengths of the composites. Several composites, including EGCP10, EGCFA10, EGBA10, EGBoA5, EGBoA10, EGCFACP10, EGCFAMP10, EGCFABoA5, and EGCFABoA10, demonstrated higher flexural strengths than the unfilled composites as shown in Figure 11. Among all composites, EGCFABoA10 exhibited the highest flexural strength at 820.22 MPa, suggesting that the inclusion of particle fillers significantly enhances the composite’s strength. Composites filled with marble powder showed decreasing flexural strengths at 2.5, 5, and 10 wt %, with values lower than the unfilled composites. This decrease may be attributed to poor adhesion, voids, dispersion issues, and fiber-to-fiber interaction. The decrease in flexural strength for composites filled with various fillers at 2.5 and 5 wt % can be attributed to poor adhesion between the matrix and reinforcement, the presence of voids, dispersion issues, and fiber-to-fiber interaction. However, at 5 wt %, composites filled with bone ash (BA) and a mixture of bone ash and coal fly ash (CFABoA) did not exhibit a decrease in flexural strength. The text mentions that the size, shape, and type of particles play a role in influencing the flexural strength of the composite. In summary, the inclusion of particle fillers generally increases the flexural strength of glass epoxy composites, with EGCFABoA10 showing the highest strength. However, the impact of fillers on strength varies, and factors such as filler type, concentration, and particle characteristics play a crucial role in determining the composite’s flexural strength. From the past investigations,¹² it is observed that the flexural strength of the composites filled with CDCFA at 10 wt %age is 703.4 MPa and nearly 1% of decrement is observed in flexural strength with the incorporation of CPCFA in epoxy composites at 10 wt %age in present investigation and the other results are also comparatively good.

Figure 11.

Type of composite versus flexural strength in MPa.

Flexural strength is a crucial mechanical characteristic of any structural member or component. Basically, when they bend, structural parts composed of composite materials are more likely to break. It is imperative that new classes of composites with better flexural characteristics are developed and used to address these failure-related issues. It may be suggested, based on the flexural strength data, to utilize a combination of bone ash (BoA), bagasse ash (BA), and coal fly ash (CFABoA) as fillers for creating composites to get the highest possible flexural strength.

3.4. Interlaminar Shear Strength (ILSS)

To find the interlaminar shear strength (ILSS), epoxy-glass composites loaded with various fillers at various weight proportions are subjected to a brief beam shear test. Figure 12 displays the ILSS findings for epoxy-glass composites that contain filler. Table 2’s ILSS column demonstrates that, irrespective of the filler type, ILSS improves with an increase in the weight fraction of filler material. However, the tendency toward rising ILSS is not seen in composites filled with coal powder (CP), marble powder (MP), or a combination of bone ash and coal fly ash (CFABoA).

Figure 12.

Type of composite versus ILSS in MPa.

EGCFABoA5 shows the maximum ILSS; EGCFA2.5 shows the lowest ILSS. The composite filled with marble powder (MP) shows the lowest mean ILSS. In composite materials, the ILSS is crucial for understanding the material’s resistance to interlaminar shear forces. The variations observed could be due to different factors such as the type and concentration of filler materials as well as the presence of voids in the matrix.

3.5. Impact Strength (IS)

Impact strength refers to a substance’s ability to both absorb and release energy in the event of shock or impact loading. The computed impact strength (IS) values and results for a range of composites discovered during the impact test are displayed in Figure 13. The impact loading resistance of epoxy-glass composites is raised by the use of microfillers. The impact strength of the composite has been seen to increase in comparison to unfilled composites, with the exception of rice husk ash (RHA)-filled composites, due to the amalgamation of particle fillers in the matrix material and E-glass fiber reinforcement.

Figure 13.

Type of composite vs impact strength in J/m.

The composite filled with a mixture of coal powder and coal fly ash (CFACP) at 10 wt % exhibits the maximum impact strength of 2100 J/m due to the interfacial reaction, which acts as an effective barrier for pinning and bifurcating the advancing cracks. The impact strengths of the other filled composites are lower because the stiffer and harder composites reduce their resilience and toughness, which, in turn, results in lower impact strengths. As a result, the suitability of these composites will be determined by standard design parameters and energy-absorbing qualities for the desired applications of an efficient and safe structure design. Composite materials to be used in various engineering applications are expected to have impact loads or high strain rates. In previous investigations,¹² the composites filled with CFACP exhibited the average impact strength of 2009.275 J/m; compared to this, the impact strength obtained in present investigation is 2037 J/m. the variation seen in the results is equal to 28 J/m.

According to the experimental results of the shock tests conducted in this analysis, mixtures of coal fly ash and powder (CFACP) and coal ash and bone ash might be used as filler materials in hybrid composite structures for future applications.

4. Conclusions

This experimental and analytical investigation work done on the glass epoxy composites unfilled/filled with various micro fillers gives the following conclusions:

• 1.Epoxy resins are widely used in composite materials due to their excellent mechanical properties and adhesive characteristics. Hybrid composites typically involve the combination of different reinforcement materials to enhance specific properties. E-Glass fibers are known for their high strength and stiffness, making them a common choice as reinforcement in composite materials. Coal powder (CP), coal fly ash (CFA), bagasse ash (BA), palm fruit ash (PFA), rice husk ash (RHA), bone ash (BoA), marble powder (MP), and mixtures of these industrial wastes have been used as fillers in the composite fabrication process. The industrial wastes are used in the form of particulate fillers or micro fillers, which can enhance specific properties of the composite materials. The composites are fabricated using a manual hand-layup technique, indicating a cost-effective and practical approach to manufacturing. The utilization of industrial wastes in composite fabrication helps in reducing environmental pollution by repurposing these materials. By replacing a portion of the epoxy resin with industrial wastes, the overall cost of composite fabrication is reduced, contributing to economic sustainability.
• 2.It is interesting to note that, while other mechanical properties show enhancement, tensile strength (TS) does not. This could be due to various factors, such as the type and amount of filler used, the dispersion of fillers in the matrix, or the interaction between the filler and matrix. The choice of filler material is crucial in achieving the desired composite properties. Different fillers can have varying effects on mechanical characteristics. Factors to consider when selecting filler materials include their composition, size, shape, and compatibility with the matrix material. Depending on the application, it is essential to choose fillers that align with the specific requirements of the composite. For example, in applications where impact resistance is critical, fillers that enhance impact strength may be preferred.
• 3.The addition of filler materials, particularly marble powder, and CFACP at 5 wt %, led to a decrease in tensile strength. However, the composite EGCFA10 had the highest tensile modulus among the studied materials. The specific fillers, such as palm fruit ash, rice husk ash, and marble powder, resulted in lower tensile modulus compared to other fillers and the unfilled composite.
• 4.The composite EGCFABoA10 demonstrated the highest flexural strength at 820.22 MPa compared to other filled/unfilled composites, irrespective of the type of filler used. Composites filled with marble powder exhibited the lowest flexural strength, with values of 250.92, 213.46, and 319.23 MPa at 2.5, 5, and 10 wt %, respectively. These values were lower than the flexural strength of unfilled composites. The decrease in flexural strength for composites filled with various fillers at 2.5 and 5 wt % (except for BA and CFABoA at 5 wt %) is attributed to factors such as poor adhesion between the matrix and reinforcement, presence of voids, dispersion issues, and fiber-to-fiber interactions. Particle size, shape, and type of filler also play a role in influencing the flexural strength of the composites. Poor adhesion between the matrix and reinforcement can lead to a reduction in flexural strength. The presence of voids and dispersion problems may contribute to the overall weakening of the composite material.
• 5.The composition and percentage of fillers in composite materials play a significant role in determining their mechanical properties. The presence of voids in the matrix phase can contribute to a decrease in ILSS, affecting the overall strength of the composite material. It appears that the combination of coal ash and bone ash at 5 wt % demonstrated the highest ILSS, while 2.5 wt % of coal fly ash and marble powder led to lower ILSS values.
• 6.The impact strength test of a composite material filled with a mixture of coal fly ash and coal powder (CFACP) at 10 wt % indicates the maximum impact strength of 2100 J/m. Additionally, the shock tests in the current investigation suggest that both the mixture of coal fly ash and coal powder (CFACP) and the mixture of coal fly ash and bone ash show potential as filler materials for future hybrid composites.
• 7.The micro hardness of the composite filled with CFACP at 10 wt % is measured at 62 Hv. This value represents the maximum hardness compared to other filled/unfilled composites studied. Generally, all the composites, except EG40 and EGPFA2.5 composites, showed increased hardness compared to unfilled composites. The mentioned EG40 and EGPFA2.5 composites did not exhibit the same level of hardness improvement. The presence of voids and pores in composites may be a potential reason for the little or marginal impact of particulate fillers on the micro hardness of EG40 and EGPFA2.5 composites. This implies that the effectiveness of the particulate fillers in enhancing hardness might be hindered by the presence of voids and pores in these specific composites. The CFACP filled composites, due to their maximum wear resistance, are suggested for potential applications where high wear resistance is crucial. The findings imply that the specific characteristics of the filler and the composite matrix play a role in determining the effectiveness of the filler in enhancing micro hardness. Overall, this investigation suggests that CFACP filled composites could be promising for applications requiring the maximum wear resistance, but the presence of voids and pores in certain composites may affect the overall impact on hardness. Further research may be needed to understand the specific interactions and mechanisms involved in the composite materials.

Author Contributions

R.M.: conceptualization, investigation, writing original. I.A.B.: methodology, formal analysis, reviewing manuscript. A.S.S.: data curation, validation, visualization. S.K.: formal analysis, supervision, reviewing manuscript. A.A.K.: data curation, resources, visualization.

The authors declare no competing financial interest.