【Special Topic Review】Customized Basalt Fibers and E-Glass Fibers as Reinforcement to Enhance Impact Resistance

Abstract

玄武岩 fiber凭借优异的耐碱性与增强力学性能，在工程领域的应用潜力备受关注；而E-glass fiber reinforced composites have been widely used in the manufacturing of resistive industrial parts such as switches, circuit boards, and protective shells. This study employs vacuum-assisted resin transfer molding technology to fabricate polymer composites with different volume fractions of basalt/E-glass fiber reinforcement, and systematically tests their tensile properties, flexural properties, thermal stability (thermogravimetric analysis), and low-speed impact characteristics.

The test results show that when the volume fraction of basalt fibers is increased to 39%, the impact resistance of the composite material increases significantly by 45%, and the bending performance is also moderately improved; as the volume fraction of E-glass fibers increases to 40%, the tensile and bending performances of the material continue to enhance, reaching 185 N/mm² and 227.87 N/mm², respectively, and the higher the volume fraction of E-glass fibers, the more significant the improvement in these two mechanical properties. The results of the thermogravimetric analysis show that the composite material with PC313534 formula (containing 35 volume% basalt fibers and 34 volume% E-glass fibers) has the lowest decomposition temperature, which is 381.10℃.

The research conclusion shows that the impact resistance and other key mechanical properties of composite materials can be effectively improved by optimizing the mixing ratio of basalt andE-glass fiber. The polymer composites prepared in this study are suitable for applications with high requirements for structural bearing capacity.

1. Introduction

After mining and melting basalt, fibers or fabrics can be made without adding any auxiliary agents, but there are differences in mineral composition and chemical content due to geographical regions, and not all basalt is suitable for spinning process. The research report of the Fraunhofer Institute for Material Research and Testing in Germany points out that basalt fibers are an ideal alternative to glass fibers and carbon fibers, and related research has become a focus of attention in the field of composites.

Birkner and others developed a new silicate polymer matrix that can be embedded with mineral glass fibers and basalt fibers, and prepared composites by a double-polymerization method, which increased the stiffness by 25% and the storage modulus by 260%. Ball and others conducted a performance evaluation of basalt fibers from seven suppliers and found that grains act as fiber defects to reduce the mechanical strength of materials, and clarified the key pain points of fiber quality control. The study by Walter and others showed that the addition of basalt fibers can significantly enhance the flame retardant properties of composites of carbon fibers, glass fibers, and polybenzimidazole.

Over the past decades, composites have seen a continuous growth in demand across various fields such as construction, marine, defense, and aerospace, due to their high strength, customization capabilities, and excellent strength-to-weight ratio.The impact response characteristics of fiber composites are determined by a combination of key parameters including the thickness of the laminates, fiber type, lamination sequence, boundary conditions, and resin matrix. Fiber mixing technology provides an effective approach to customize the mechanical, electrical, and thermal properties of these materials. Fragassa et al. showed that placing basalt fibers on the outermost layer of laminated composites can significantly optimize the mechanical properties of flax fiber/basalt fiber-reinforced vinyl ester resin composites; Masoud et al. focused on the thickness effect of basalt-kevlar composites, establishing the rules of their impact resistance; Malik et al. confirmed that basalt fibers are preferred materials for blast-resistant structure design due to their outstanding compression and fatigue resistance; Boria et al. found that the impact resistance of flax fiber and basalt fiber-reinforced thermoset vinyl ester composites can be increased by 60%.

In the study of mixed fiber systems, The results of Lapena et al. show that the tensile strength of materials can be increased by 45% and the interlaminar shear strength can be increased by 11% when basalt fibers and glass fibers are mixed to enhance; Atmakuri et al. compared the performance of basalt fibers, E-glass fibers and graphite mixed fillers, and confirmed that mixed fillers are better than single fibers, and that basalt fiber strength is higher than glass fiber. In addition, the influence of interface modification and structural regulation on the performance of composites has also been widely concerned:Plappert et al. reported the enhancing effect of epoxy silane surface modification on the fiber-matrix interface performance; Nayan, Vijayan and Natarajan et al. research revealed that regulating the fiber stacking sequence and arrangement mode can effectively improve the mechanical properties of laminated composites; Omid Sam-Dali and Yundong Ji conducted research on glass fiber reinforced polypropylene and silicone modified epoxy/phenolic composites respectively, and both confirmed that process methods and parameters have a significant impact on the mechanical properties of materials.

Yunfu investigated the Weibull parameters of materials under different initial strain rates (25, 50, 100, 200 s⁻¹) and temperatures (-25, 0, 25, 50, 75, 100 °C) using a uniaxial test method, and found that the tensile strength increased linearly by about 49.1% in the strain rate range of 1/600-200 s⁻¹, and the toughness increased by about 109.7% when the load changed from quasi-static (1/600 s⁻¹) to dynamic (25 s⁻¹). Although the application of polymer composites has爆炸性增长， their long-term service performance in harsh environments is still unclear, which restricts the safe and economical development of related designs. Mario found that the mechanical properties of FRP-LVL materials were significantly enhanced after being soaked in water for 48 hours through a carbon fiber and basalt fiber composite impregnation experiment, and the thickness expansion rate of PVAc-CF samples decreased by 19%, which provides a reference for the optimization of material environmental performance.

To this end, the authors of this paper aim to investigate the lamination sequence of basalt-E- glass-reinforced polymer composites and to expound the property effects of mixed fiber reinforced materials. Although research on various mixed polymer composites has attracted attention in the past decade, research on basaltE- glass-reinforced epoxy matrices is still insufficient. This paper presents and discusses the mechanical behavior, such as bending, tensile, low-speed impact properties, and thermal stability performance of the composite.

2. Materials and Methods 

2.1. Sample preparation 

Bought from Mumbai, IndiaCF Composites company's plain E- glass fiber fabric and basalt fiber fabric, with area densities of240g/m² and 160 g/m²; the epoxy resin two-component polymer matrix LY556 and curing agent W152 LR were purchased from local suppliers. The performance of the epoxy resin, basalt fiber and E- glass fiber fabric provided by the supplier is shown in Table1 and Table 2.

Table1. RingOxygen treePerformance of oil and curing agent

Table2. Performance of basalt and E-glass fiber fabrics

To limit the sliding and delamination of the laminated plate, this study employs ordinary bidirectional woven basalt fiber fabric and glass fiber fabric. In the pre-treatment stage, epoxy resin and curing agent are mixed and homogenized in a standard ratio of3:1. Through the vacuum-assisted resin transfer molding process (VARTM), mixed polymer composites containing different volume fractions of basalt fiber and E-glass fiber are prepared (mold size is300mm×300mm).

Before molding, a layer of wax is coated on the mold base plate as a release agent. The basalt fiber fabric andE- glass fiber fabric (300 mm×300 mm) are hand-laid over each other in the open mold until the target thickness of 3 mm is achieved. After the layering is completed, a peel layer and a breathable layer are covered on the fiber layer, and the entire structure is sealed with a polyethylene bag and a sealing tape. Then, the epoxy resin mixture is allowed to flow through the fiber layer under a pressure of 0.1 bar. The vacuum pump draws the resin matrix from the reservoir to the interlayers of the fabric under this pressure, and the excess resin is collected in the liquid collection tray. After the resin is evenly spread, the prepared laminates are allowed to cure at room temperature for 24 hours and then subjected to a 2-hour heat treatment in a 50℃ oven.

To facilitate understanding, basalt fiber fabric andE-glass fiber fabric are marked asB and G respectively. The fiber fabrics are stacked in the order of B-G-B-G-B-G-B-G-B-G-B, with the neutral axis as the symmetry axis, where the basalt fiber fabric constitutes the outer layer, and the E-glass fiber fabric is located in the core layer. The fiber-matrix volume fraction of different mixed structures is calculated using the formula.

Where:f—Fiber, m—Matrix, W—Weight, ρ—Density, B—Basalt fiber, G—E-Glass fiber.

Table3 summarizes the thickness of the laminated plates and the various volume fractions of basalt/E-glass/epoxy resin composites. The designation PC303040 refers to a polymer composite (PC) with an epoxy matrix volume fraction of 30%, a basalt volume fraction of 30%, and an E-glass volume fraction of 40%. Subsequently, samples were cut using water jet machining technology in accordance with ASTM standards for various mechanical tests. Figure 1 shows a schematic of the stacking and sample preparation.

Table3. Thickness and volume fraction of mixed combinations

Figure1. (a) Schematic diagram of the stacking sequence. (b) Vacuum bag setup. (c) Basalt fiber/E-glass fiber polymer composite sample.

2.2. Research Method

The test samples for the uniaxial tensile test were prepared according toASTM D638 standard and tested using a servo-controlled universal testing machine (Instron 8801, Natick, MA, USA), with a test speed of 0.001 to 1.000 mm/min, an axial load capacity of ±100 kN (22,500 lbf), and equipped with a patented Dynacell load cell function to compensate for the inertial load generated by the heavy clamps. Three samples were tested for each configuration to measure the tensile strength, yield strength, and ductility. The bending test samples were prepared according to ASTM D790 standard (80 mm × 13 mm × 3 mm) and tested on the same machine at a crosshead speed of 4 mm/min. Izod and Charpy impact tests were performed simultaneously to analyze the effect of the impact load on the test samples in both horizontal and vertical orientations. The Izod test was conducted using an AIT-300N impact testing machine (ASTM D256 standard), and the Charpy test was conducted using the same machine (ASTM D6110 standard), with the conditions set as: pendulum swing of 600 mm, hammer weight of 18.7 kg, and the highest impact speed of 10 m/s. The failed samples were analyzed using a field-emission scanning electron microscope (FE-SEM) to understand the failure mechanisms caused by the load at different magnifications. The thermogravimetric analysis was performed up to the highest temperature of 600 ℃ (Model: PerkinElmer 2.0, TGA 4000, optimized through Pyris software), to calculate the mass change generated with the increase in temperature.

3. Results

3.1. Tensile test

Figure2 shows the ultimate tensile stress and the corresponding strain values for all five configurations when subjected to tensile loading at a strain rate of 0.1 s⁻¹. PC323929 (E-glass fiber: 29 vol%) had the lowest tensile strength (103.61 MPa), while PC303040 (E-glass fiber: 40 vol%) had the highest tensile strength (185.19 MPa). The results indicate an gradual change in the strain values corresponding to the tensile stress as the volume content of E-glass fiber increases. The 78.73% increase in tensile strength can be attributed to the reinforcing effect of the E-glass fiber; when the polymer composite is subjected to a load, the glass fiber acts as a load carrier, transmitting the load along the fiber direction from the matrix. Tang et al. noted that the tensile strength of pure epoxy resin is about 66 MPa, which is about 300% lower than that of PC303040. This difference results in a more uniform stress distribution, thereby enhancing the strength of the composite. It is worth noting that a high content of basalt reinforcement in the matrix can limit the tensile capacity of the composite. The loss of ductility observed in PC323929 (basalt 39 vol%) resulted in a nearly 83% decrease in its strength compared to PC303040, which may be attributed to the lower silicon content of basalt. The current research results differ from the previously published results using basalt fibers or E-glass fibers. Although this study notes that the tensile strength of epoxy composites reinforced with basalt fibers is higher than that of composites reinforced with E-glass fibers, the combination of different proportions of basalt and E-glass fiber mats with the epoxy matrix has a significant effect on the stiffness of the basalt fiber mats. This mixed composite can generate higher tensile forces before yield.

Figure2. Stress-strain curve after the tensile test of the mixed sample.

3.2. Flexure test

Figure3 shows the bending strength of composites with different filler proportions. It can be seen from Figure 3 that PC303040 (E-glass fiber: 40 volume percent) exhibits the highest bending strength (227.87 MPa) and bending strain (3.39%), with its bending strength being about 128% higher than that of pure epoxy resin (bending strength of 99.88 MPa). In fact, the bending strength of all composites is higher than that of pure epoxy resin.

The highest flexural strength was obtained when the E-glass fiber filler content was highest (40 vol%) and the basalt fiber content was lowest (30 vol%). The increase in basalt fiber content in the polymer matrix reversely reduces the flexural properties of the composites, which may be due to the excessive fiber content restricting the excellent interfacial bonding, and the fiber distribution is often uneven, leading to fiber agglomeration. Fiber agglomeration can cause internal structural defects, weakening the fiber's reinforcement effect on the polymer matrix, and ultimately reducing the material strength. Xiao Xian'an measured the flexural strength of pure epoxy resin to be 81 MPa, and this data has been included in Figure 3 for comparative analysis.

Figure3. Stress-strain curves of the mixed samples after bending load.

3.3. Low-speed impact test

Figure4 shows the test process and broken samples of Izod and Charpy impact tests, and the corresponding results are summarized in Table 4. The energy absorption capacity of the laminates gradually increased with the increase of the basalt fiber reinforcement ratio, and the results of the Charpy impact test showed that the mixed laminates with 39% volume fraction of basalt fiber had better energy absorption performance than other laminates.

In the Izod impact test, the pendulum energy is transferred to the tested polymer composites, and part of the energy is consumed during the fracture process, which is achieved through fiber-matrix interactions (such as sliding, debonding, or fiber pull-out) to dissipate energy. The results of the Izod test in this study show that the higher the content of basalt fibers in the reinforced materials, the better the impact energy absorption performance. When 10 volume percent basalt fibers are used as reinforcement in polymer composites, its Charpy impact energy absorption rate increases by 40-50%, and the Izod impact energy absorption rate increases by 60-70%.

It can be inferred that the surface of basalt fibers has a striped irregular structure, which may enhance the interfacial bonding between the fibers and the polymer matrix. In addition, scanning electron microscopy images of the fracture surface (see the section on fracture surface analysis for details) show significant debonding and拔出 phenomena, both of which are energy dissipation mechanisms that can lead to an increase in the impact strength of composites with high basalt fiber content. On the other hand, in the case of composites reinforced with35 volume percent basalt fibers, insufficient impact energy absorption was observed, which may be due to porosity or fiber debonding issues that occurred during the testing or pre-treatment phase.

Figure4. (a) Schematic diagram of Izod impact test and broken test specimen. (b) Schematic diagram of Charpy test and broken test specimen.

Table4. Energy absorption along fiber orientation

3.4. Thermal Gravimetric Analysis

Figure5 shows the results of the thermogravimetric analysis (TGA) of the basalt/E-glass fiber reinforced polymer composites. It can be seen from Figure 5 that all the composites reinforced with basalt/E-glass fiber show good thermal stability: when all the composites are heated gradually to 320°C, the mass loss is all less than 5%; when the heating temperature is increased to 400°C, the mass loss of all the samples is still less than 10%.

Notably, the ratio change of basalt fibers withE-glass fibers has a significant impact on the glass transition temperature (Tg) of the composites, which means that their physical properties may also change accordingly. For example, the glass transition temperature (Tg) of PC303040 (E-glass fibers: 40 volume%) is 369.1°C, while that of PC323929 (E-glass fibers: 29 volume%) is 328.3°C, the former is about 12.43% higher than the latter.

The increase in Tg for PC303040 can be attributed to the higher content of E-glass fibers used: due to the excellent interfacial adhesion between E-glass fibers and the epoxy matrix, it can effectively restrict the segmental motion of the polymer matrix. The reinforcement with lower content of E-glass fibers (i.e., composites with E-glass fiber volume fractions of 29%, 33%, and 34%) did not show significant differences in Tg, as the content of E-glass fibers was not sufficient to retard or hinder the molecular dynamics of the composites, which is the key factor affecting the Tg of mixed basalt/E-glass fiber reinforced polymer composites.

Figure5. (A) TGA of mixed basalt/E-glass composites with different E-glass fiber content. (B) Enlarged view of the TGA curve, showing a significant weight loss in the range of 300–400 ℃.

4. Discussion

The plot6 shows the Ashby diagram, which is used to accurately describe and classify materials based on their specific strength (strength-to-weight ratio). Most of the mixed-fiber-reinforced polymer composites involved in this study fall within the composite material region of the plot. For example, the specific strength of the composite PC303040 is comparable to that of glass fiber reinforced composites (GFRPs). Due to their high specific strength, E-glass epoxy composites typically exhibit reasonable flexibility along with excellent tensile strength; in addition, basalt fibers, with their enhanced modulus of elasticity, also possess stronger resistance to fatigue, deformation, and impact loading. It is worth noting that there is still room for improvement in the results of this study, and future optimization schemes may yield composites with consistently higher specific strengththanGFRPs, thereby revealing previously unknown material properties.

The results of the tensile and bending tests conducted on the samples with increasedE-glass fiber content showed that the tensile and bending strengths of the material were improved, while the inclusion of basalt fiber increased the impact resistance of the material, thanks to the combination of toughness and durability of the epoxy resin laminates. In a related study, Elmahdy et al. compared the performance of woven basalt fiber and E-glass fiber reinforced epoxy composites under high strain rates, aiming to supplement their application in auxiliary structural components of aircraft. The hybridization treatment of basalt and E-glass fibers can enhance the overall performance of the composites, a property that may offer significant advantages for secondary components in aerospace applications.

Fracture surface analysis

This study employs field emission scanning electron microscopy (FE-SEM) to analyze the fracture surface of composites containing 40 volume percent E-glass fibers (PC303040), the choice of this material being due to its exhibition of optimal tensile and flexural properties. Figure 7 shows that at magnifications of 250-1000 times, the orientation of fiber breakage and various defects in the rock wool fiber/E-glass fiber composite are clearly discernible. Through SEM images, it is observed that the composite contains multiple defects and failure mechanisms such as pores, holes, fiber pull-out, and surface roughness of the matrix.

The SEM analysis results show that the increase of the volume fraction of basalt fibers leads to a decrease in the interfacial bonding performance between the polymer matrix and the reinforcing material, while also increasing the frequency of fracture and the range of crack extension. In addition, the improvement in the flexibility of the material indicates that the connection between the matrix and the reinforcement is firm and the wetting is good, which can be attributed to the pre-treatment process of E-glass fibers and basalt fibers before being embedded in the polymer matrix, as well as the subsequent curing process.

Figure6. Experimental data representation – Eschelby diagram.

Figure7. Field-emission scanning electron microscopy images of 40% E-glass reinforced composites (PC303040): (A) Fracture matrix surface, (B)粗糙 matrix surface, (C) Fracture fiber, (D) Fracture matrix and fiber.

5. Conclusion

This study employs vacuum-assisted resin transfer molding (VARTM) to fabricate composite materials with different fiber volume fractions of hybrid basalt/E-glass fiber reinforced polymers, and the relevant research conclusions are as follows:

1. The experimental results show that when the volume fraction of basalt fiber is increased by 10%, the composite can achieve excellent impact energy absorption effect, with an absorption efficiency of 40-70%.

2. The tensile test results show that the composite with 40 volume% E-glass fiber as the reinforcement has a better tensile strength than the composite with 40 volume% basalt fiber as the reinforcement.

3. The results of the three-point bending test showed that the higher volume fraction of E-glass fibers could enable the composites to obtain a reasonable bending strength, which was 80% higher than that of other laminates prepared in this study.

4. The analysis of the results of the tensile and bending tests shows that the composites with 40 volume% E-glass fiber reinforcement perform better in tensile and bending properties; while the composites with 40 volume% basalt fiber reinforcement are more suitable for applications that need to withstand impact energy.

5. The TGA results showed that PC313534 (with 35 vol% basalt fiber and 34 vol% E-glass fiber) had the lowest decomposition temperature of 381.1°C;同时，该样品 (玄武岩与E-玻璃纤维含量近乎相当) 的热稳定性优于本研究中其他组分的复合材料.

6. The results of this research can be used to design composites with high specific strength, which have practical application value in the field of defense armor and in the application of flaps, slats, fuselage, etc. in the aerospace field.