Experimental investigation and analysis on the wear properties of glass fiber and CNT reinforced hybrid polymer composites

2.1 Fabrication of CNT-GFRP reinforced hybrid composites by the pultrusion method

The glass fiber was fabricated with reinforced epoxy resin and reinforced CNT. Epoxy is a solid adhesion substance, which is utilized for adhering diverse materials, which are covered upon the surfaces together. Epoxy resin mixture has an extensive range of utilizations, such as coatings of metal in both electronic and electrical components. Industries have high tensioned electrical covers, and structured adhesion is utilized in root canal treatments [15]. For securing, nanotubes of carbon with a composite mixture of resin and glass fiber along with a hardener are utilized. The hardener used in this experiment is Ardur (HY951), which is utilized as a part of the composite parts performance. Ardur (HY951) is cured under normal room temperature alongside a mixture of resin composites, which has a long life and a very low viscous property. This kind of system is simple to handle and has decent properties of fiber impregnation, which shows amazing mechanical properties. It consists of chemical compound resistance against acids at a high temperature raised to 80°C [16]. This resin material composite has a great resistant property towards chemical degradation because of atmospheric conditions. Glass fiber filaments were utilized as a reinforced medium in the present experiment. Glass fibers were treated along with sizing, coupled operating agents to decrease the impact of the abrasion of fiber, that are degraded in the property of mechanical strength for the individual content of fiber. The glass fiber utilized as a part of the experiment has a low alkali base glass. It is composed of the combinations of SiO₂ 5.4 wt%, CaO+MgO 22 wt%, B₂O₃ 10 wt%, Na₂O+K₂O under 2 wt% and Al₂O₃ 14 wt%. Numerous different materials were present as pollutants. Glass fiber has the most astounding strength property with high stiffness, great resistance towards heat, better chemical compound resistance, and insensitivity to moisture [15].

In this experiment, the GFRP composites were prepared for directing the test for wear. GFRP (mixture of resin, CNTs and glass fiber) composite samples were prepared for the investigations. In the primary sample, epoxy resins were blended with CNTs and also with glass fiber reinforcement materials. In the fabrication procedure, the LY-556 mixture of epoxy resin was solidified by utilizing the hardener HY951 at room temperature by the hand pultrusion method in an approximate ratio of 10:1 proportion. In this method, the glass tubes were made to be used as the mould. The dried fibers, mixed with resin and CNTs, were pulled through the glass tubes to produce the CNT composite rods. CNTs 1%, 3% and 5% were considered to fabricate different samples. The prepared proportionate test samples of CNTs with glass fiber, resin, and hardener are shown in Table 1. Figure 1 displays the preliminary arrangement of the composites used for fabrication. Figure 2 displays the scheme for the strategic arrangement of the hand pultrusion process, which was utilized for the composite fabrication procedure. Figure 3 shows the fabricated composite test samples.

Figure 1:

Preliminary arrangement of the fabrication process.

Figure 2:

Strategic arrangement for the fabrication process.

Figure 3:

Fabricated hybrid composite samples.

2.2 The wear testing of hybrid composites

The specimen of the test was a pin with a round tip, which was placed perpendicular to another specimen, which is normally a flat circular disc. A rigidly held composite sample is often used as the pin specimen; it revolves around the disc center. In this case, the sliding path was a circle on the disc surface. The plane was slanted vertically. The specified load was used to press the disc against the pin specimen by means of an arm and attached weights. Since it is a single material, the specimen was used as pin. The wear was determined by weighing the specimen before and after the test and by measuring the linear dimensions of both specimens, which were used in the test, both before and after the test. A suitable metrological technique, such as electronic distance gauging or stylus profiling, was used to measure the length change and shape change of the pin. Appropriate geometric relations were used to convert linear measures of wear into wear volume. The precise loss was measured using linear measures because mass loss is very small.

A pin-on-disc tester with 10 mm diameter and 60 mm length with dead weight loading system was used to keep the pins. The disc piece was 55 mm in diameter and 10 mm in thickness, which was slided at a diameter of 50 mm and was made of hardened steel HV 698. The specimen of reinforced glass fibers was tested at varying applied loads of 29.43 N (3 Kgf), 39.24 N (4 Kgf) and 49.05 N (5 Kgf) at different sliding speeds of 200, 300 and 500 rpm. The sliding distances were 1000, 2000 and 3000 m in the experiment. The test was conducted at room temperature with 50% relative humidity. Figure 4 shows the pin-on-disc wear tester with an experimental arrangement.

Figure 4:

Pin-on-disc wear testing arrangement.

3.1 The influence of sliding distance and applied load on the wear properties

The remarkable mechanical properties of the CNTs have inspired the researchers to produce composites by combining CNTs with glass/carbon fibers. Very little work has been done to describe the sliding wear of CNT-based composites. The CNT content in the composite shows a steady rise in properties. The result indicates that the addition of CNTs decreases the wear rate, but it is observed that up to 3%, the wear rate reduces drastically, whereas a further addition of CNT (5 wt%) did not reduce the appreciable wear as observed earlier.

The study on the COF and the wear of nanocomposite materials is very important for material scientists and manufacturing engineers. Especially, when GFRP nanocomposite materials are to be used for a particular application, the response to wear and COF has to be analyzed [16]. The COF and wear rate of GFRP nanocomposite materials are different from those of polymer composite materials. Wear performance graphs were used to analyze the properties of the composite material. The wear test results for the GFRP (glass fiber+CNTs and epoxy resin) composites under the dry sliding condition are presented in Figure 7. Figure 7 demonstrates the variation of the rate of corresponding wear with respect to loads for the different CNT content in the volume of the GFRP composites. It reveals that there is an increase in wear rate with an increase in the applied load. Table 2 shows the weight loss ratio for the increase of the wear due to the increase of the load for various wt% of CNTs. The weight loss ratio is the ratio between the weights of the specimen after the wear and the original weight of the specimen. If the ratio is high, the weight loss is less, and vice versa.

Figure 7:

Difference in wear rate to applied load for various % of CNTs.

The result indicates that the increase in the CNT percentage decreases the wear rate. The result shows that the CNTs improve the wear performance of GFRP composites. Figure 8 shows the COF for GFRP composites at a sliding speed of 300 rpm with varying load conditions. The outcome shows that the COF increases naturally as the percentage of CNTs increases. The same result is also reported by Johnson et al. [18]. Also, it shows that the COF has a decrement with an increment in the applied sliding load. The force of friction developed during contact is substantially low because of the top layer of the pin-on-disc. Gradually, the increase in rubbing action leads to the wear of the disc and the pin material, because the contact took place between the pin and the disc, which in return causes the impact of ploughing effect. Hence, the COF increases with the increase in the duration of rubbing [19]. The presence of a typical load and sliding speed significantly influences the friction force. Within the observing range, the estimations of the COF decrease along with an increase in a typical load, though the COF increases with an increase in the sliding speed for gear fiber as well as glass fiber slide against the smooth or rough surface of mild steel pin [20].

Figure 8:

Difference in COF with respect to load for different % of CNT.

3.2 The influence of speed and load on wear properties

COF is obtained from the impact of sliding velocity under the same loading condition and wear property of the GFRP composites with varying volume percentage rates of reinforcement. The specimens at the time of sliding are plotted against the sliding speed, which is shown below. It is clear that an increase in sliding speed results in an increase in wear rate. It also shows that an increase in the volume percentage of CNTs with GFRP composites leads to a decrease in the wear rate.

Figure 9 discloses the rise in the rate of wear with an increased sliding velocity under the same load condition. It also shows that a decrement in the rate of wear increases the volume percentage of CNTs in GFRP composites. Table 3 shows the weight loss ratio for the increase of the wear due to the increase of the speed for various wt% of CNTs. The weight loss ratio is the ratio of the weights of the specimen after the wear to the original weight of the specimen. If the ratio is high, the weight loss is less, and vice versa.

Figure 9:

Difference in the rate of wear with respect to sliding speed for variation in % of CNT.

Figure 10 shows a linear increase in the COF during the variation in sliding speeds under the same load conditions. The same figure also shows that the increased volume percentage of CNTs in GFRP composites increases the COF.

Figure 10:

Difference in COF with respect to sliding velocity for different % of CNT.

3.3 SEM analysis

The surface prior to the wear test and the well-used worn-out reinforced surfaces of the material composites of glass fiber are shown in Figures 11–16. Figures 11 and 12 show the SEM examination of the resin casting mixed with the composites of the glass fiber with 1% CNTs before and after the wear test. Figures 13 and 14 display the CNTs, which are not uniformly distributed in the composite matrix. It is observed that there is porosity in the sample. Figures 15 and 16 indicate that there is a worn-out surface which is formed later in the execution of test for wear. This image indicates that the surface formed after wear consists of little pits and abnormalities in the specimen, which is made from reinforced composites of glass fiber. As a result, voids are formed, which are also keenly noted. This is because of the fabrication procedure, and this wear might be reduced by adopting the proper tribological conditions [15].

Figure 11:

GFRP with CNTs 1% before wear.

Figure 12:

GFRP with CNTs 1% after wear.

Figure 13:

GFRP with CNTs 3% before wear.

Figure 14:

GFRP with CNTs 3% after wear.

Figure 15:

GFRP with CNTs 5% before wear.

Figure 16:

GFRP with CNTs 5% after wear.

Figures 13 and 14 show the SEM images of the GFRP composites with 3% CNTs prior to and after the test for wear. Figure 13 shows that the grain size is a little bigger when it is compared with the previous one. The CNTs are sparsely distributed in the matrix. It is keenly noted that the porosity of the test sample reduces with an increase in the fraction volume of CNTs in the composites of GFRP [21]. Figure 14 shows that the wear tracks are observed on the surfaces of the GFRP composites. The graphs clearly indicate how the wear happens on the top layers of the composites. The surface finish is observed better after the wear test. Little voids are observed with the formation of a regular pattern.

Figures 15 and 16 show the SEM images of the composites of GFRP with 5% CNTs prior to and after the test for wear. In Figure 15, a large grain size is observed when it is compared with 1% and 3% CNT-mixed GFRP composites. The CNTs are uniformly distributed in this matrix. It is noted that the porosity of the specimen tends to decrease, corresponding to the increase in the fraction volume of CNTs in the GFRP composites. Figure 16 shows the fine, smooth grain size, which is observed after the wear test, and later, equal distribution of the glass fiber is observed. Minimum wear tracks observed on the surfaces of the GFRP composites have a better surface finish after the wear test. No voids are observed in 5% of CNT-GFRP composites.

3.4 EDAX analysis

Figures 17–19 show the EDAX analysis graph for fabricating composite samples. Figure 17 shows the EDAX report of GFRP composites with 1% CNTs. On the basis of the spectrum analysis, the zones are classified as 0–2, 2–4, 4–6 and 6–8. In zone 0–2, a small number of chemical compositions are observed, and in zones 2–4 and 6–8, only two chemical elements are observed. In zone 4–6, no element is observed. From this figure, it is also noted that the compositions of elements present in the specimen are C, O, Si, Ca, Fe, Mg, Al and Si, which gives information about the undesirable elements other than C, Ca, O, Al, Si and Mg. It is recognized that the mixture consists of high peaks of different elements. This result affects the properties of composite elements because of poor interracial bonding within the fiber and the matrix [22, 23].

Figure 17:

EDAX report of GFRP composites with 1% CNTs.

Figure 18:

EDAX report of GFRP composites with 3% CNTs.

Figure 19:

EDAX report of GFRP composites with 5% CNTs.

Figure 18 shows the EDAX report of GFRP composites with 3% CNTs. On the basis of the spectrum analysis, the zones are classified the same. In zone 0–2, a large number of chemical compositions are observed; in zone 2–4, there is only one element present; and in zone 6–8, only two chemical elements are observed. In zone 4–6, no elements are observed. The same chemical composition is observed other than “Na”, which gives the data that there exist undesirable composite elements other than C, Ca, O, Al, Si and Mg. It is noted that the composites are composed of high peaks of various different elements. The result impacts the properties of composites because of the poor radical blended bond within the fiber and the matrix.

Figure 19 shows the EDAX report of GFRP composites with 5% CNTs. On the basis of the spectrum analysis, the zones are classified the same. In zone 0–2, a large number of chemical compositions are observed compared with the 1% and 3% CNT composites. In zone 2–4, three elements are observed. Two chemical elements are observed in zone 4–6 and in zone 6–8, only two chemical elements are observed. This figure also shows that other elements like K, Cl and Ti exist as undesirable composite elements other than C, Ca, O, Al, Si and Mg. It is noted that the composites comprise the high peaks of various different elements. The result impacts the properties of composites because of the poor radical blended bond within the fiber and matrix. The K, Cl and Ti peaks are generated because of the reinforcement of fibers in the nanopolymer composites. The peaks are generated at different zones with respect to the percentage weight of CNT.

3.5 XRD test

XRD is a technique used to distinguish both the molecular atom as well as the molecular subatomic structure of the specimen, whose crystalline particle of molecular atoms emits lights of incident beams of X-rays that are diffracted into various particular directions, which emits a three-dimensional (3D) pictorial rendering of the thickness of electrons present inside the composite crystal [24]. An XRD examination is completed for reinforced materials with CNT composites. Their crystalline size is measured for the reinforced glass fiber with 1%, 3%, and 5% CNTs with prominent peaks in the diffracted pattern. The observed results for the different compositions are presented in Figures 20–22 .

Figure 20:

XRD analysis of GFRP composites with 3% CNTs.

Figure 21:

XRD analysis of GFRP composites with 5% CNTs.

Figure 22:

XRD analysis of GFRP composites with 1% CNTs.

Phase identification using XRD relies mainly on the positions of the peaks in a diffraction profile and to some extent on the relative intensities of these peaks. The shapes of the peaks, however, contain additional and often valuable information. It is observed from the XRD analysis that the particle size is increased proportionally with the increase in the wt% of CNTs. From the observed results, the XRD pattern shows prominent peaks only at one region. In Figure 22, the XRD patterns show a strong diffraction peak at 20°–30°. The results observed from the XRD test reveal that there are no diffraction peaks existing in the materials, but that there is a broadband observed at 2θ values in the range of 20–30. The spacing between bonding materials was also observed. The XRD pattern of the three different compositions of the nanoparticle inclusion indicates that the bonding is better for the 3% and 5% CNT inclusion.

Figure 23:

AFM analysis of GFRP with 1% CNTs–3D analysis.

The result from the XRD studies further indicates that the intensity observed for the 1% CNT content is higher than that for the 5% CNT content, which reveals the bonding between the molecules of the composites.

3.6 AFM analysis

The AFM study was carried out on the nanoscale to analyze the worn surface of the GFRP composites. The AFM utilizes a sharp pointed tip to scan across the sample. Figures 23, 24 and 25 show the AFM images of the GFRP composites with 1%, 3% and 5% CNTs after the wear test. A commercial AFM was used to obtained topography images for typical nanoparticle distributions. The manipulated study of the nanoparticles with the help of AFM has clearly shown that there is an area of contact depending on the COF [25]. Because of the higher wear rate in the 1% CNTs, the surface roughness was observed to be higher, whereas in the 3% and 5% CNT reinforced samples, the wear rate is comparatively low. For an easy comparison of the surfaces, the length and breadth of the sample were considered to be uniform and were 10 μm.

Figure 24:

AFM analysis of GFRP with 3% CNTs–3D analysis.

Figure 25:

AFM analysis of GFRP with 5% CNTs–3D analysis.

The AFM analysis of the wear properties of GFRP composites shows that the pattern with 1% CNTs has an average thickness of 150 nm, whereas the GFRP with 3% CNTs has an average thickness of 450 nm. However, the GFRP with 5% CNTs has an average thickness of around 0.75 nm. This shows that the % increase in CNTs has an effect on the size of the nanoparticles. The GFRP composites with medium % CNT are more prone to void and wear. Also, the GFRP with 3% CNTs has a rougher surface than the GFRP with 5% CNTs.

The variation in the COF with high CNT concentrations is negligible, with no practical significance. This is because of the absence of the lubricating capabilities of CNTs, but the specific wear rate gradually decreases with an increase in the percentage of CNTs [26]. There are nonuniformity and high roughness after the addition of CNTs because of the agglomeration of nanotubes to some extent. Change in the COF is the contrast to the specific rate of wear. The COF increases in concentrated proportion with an increase in the rate of CNTs.