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Enhancing the wear resistance and coefficient of friction of composite marine journal bearings utilizing nano-WC particles

  • Suadad Noori Ghani EMAIL logo , Ali Sadiq Alithari and Hala Salman Hasan
Published/Copyright: July 28, 2025
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Open Engineering
From the journal Open Engineering Volume 15 Issue 1

Abstract

In maritime applications, journal bearings are an essential part in guaranteeing the effectiveness and performance of machinery. Nonetheless, a variety of environmental elements, including wear and friction, have a substantial impact on the bearings’ lifespan and functionality. The development of novel composite materials with enhanced mechanical characteristics is necessary to address these issues. In this context, the use of epoxy reinforced with glass fiber and carbon, with the addition of reinforcing materials such as nano-tungsten carbide (WC), is a promising strategy to improve the performance of bearings. This research contributed to the improvement of the tribological properties of the friction coefficient and wear resistance of journal bearings that are used in marine applications. The research includes preparing samples of epoxy composites reinforced with different weight percentages (1, 1.5, and 2%) of nanoparticles of WC, mixed with 8% chopped glass fibers, 8% chopped carbon fibers, and a mixture of chopped (4% glass + 4% carbon) fibers. The mechanical tests were done according to standard tests to get an idea about the improvement in wear resistance and coefficient of friction for composite samples. The results indicated that pure epoxy had the highest wear rate and friction coefficient compared to the fiber-reinforced samples. The addition of chopped glass and carbon fibers improves the wear and friction properties of the composite. Introducing different ratios of nanoparticles of WC will improve the wear rate and friction coefficient significantly. In this study, the optimum combination was achieved using a mixture of 4% chopped carbon fiber, 4% chopped glass fiber, and 1.5% nanoparticles of WC. Since this ratio revealed a significant friction coefficient value of 1.55 × 10−5 g/m) and improvement in wear resistance by 117.33% at high loading (15 N) and a friction coefficient value of 0.623 × 10−5 (g/m) and improvement in wear resistance by 58.10% at low loading (10 N), respectively. Furthermore, a friction coefficient value of 0.12 and improvement in wear resistance by 83.78% at high loading, and a friction coefficient value of 0.08 and improvement in wear resistance of 86.66% at low loading were observed.

Keywords: wear resistance; friction coefficient; journal bearing; chopped fibers; nano-WC

1 Introduction

Marine bearings, also known as journal bearings [1–3], have played an essential role in many industrial and marine applications due to their frequent exposure to harsh operating conditions that include high mechanical loads, wear, friction, and constant exposure to salty environments [4–6]. These difficult conditions lead to rapid wear of the bearings, which negatively affect their performance and lifespan [7]. Therefore, improving the wear and friction resistance of these bearings is crucial to ensure reliable performance and high efficiency in marine environments [8]. In recent decades, composite materials have become a popular choice for improving bearing properties for their flexibility in modification and the possibility of enhancing their mechanical properties [9,10]. Among these materials, tungsten carbide (WC) has been an ideal choice due to its high hardness and excellent wear resistance [11–13]. When combined with chopped carbon and glass fibers, significant improvements in wear resistance and friction can be achieved [14,15]. In contrast, carbon fiber provided an additional boost in rigidity and durability while reducing the weight [16]. The glass fiber contributes to improving the resistance to abrasion and chemical corrosion [17,18]. The study of the effect of composite and nanomaterials in improving the performance of journal bearings in marine environments has gained attention in recent years. Many researchers have focused on developing composite materials reinforced with different types of fibers with adding nanoparticles to study wear resistance and coefficient of friction. For example, Kishore Mishra et al. [19] investigated the advantage of tungsten carbide to improve the wear resistance and increase the hardness of the coated samples to reduce the material loss due to corrosion. Another study by Akgul et al. [20] compared hybrid epoxy composites containing both glass and carbon fibers with those containing only one type of fiber. The hybrid composites showed better flexural and energy absorption performance, while the carbon fiber-only composites showed better performance in wear resistance. Babu et al. [21] studied the effect of adding WC on the wear of epoxy-reinforced composites. Their results showed that incorporating WC significantly reduces the wear of composites compared to materials without fillers due to improved wear resistance and fiber protection. Chang and Friedrich [22] studied the effect of nanoparticles on improving the wear resistance of short fiber-reinforced polymers. They found that the addition of nanoparticles reduces adhesion and lowers the coefficient of friction, which improves performance under severe sliding conditions. Athith et al. [23] investigated the addition of WC to improve the wear resistance of polymeric composites. Their results show that this addition significantly reduced the abrasive wear compared to unfilled materials. Mohan et al. [24] studied the effect of WC on the wear resistance of glass-epoxy composites. Their work showed that the WC-filled composites had a lower wear rate and less damage compared with the unfilled composites, especially at a 90° impact angle. Note that the recycled carbon fiber offers environmental and economic benefits, contributing to reduced industrial waste and production costs compared to virgin carbon fiber. However, when used in applications such as marine journal bearings, their performance may be lower than virgin carbon fiber due to the potential degradation of their mechanical properties during the recycling process. In this study, virgin chopped carbon fibers were used to ensure the highest level of wear and abrasion resistance, a critical factor in marine bearings subjected to dynamic loads and harsh environments. Although recycled fibers can be a sustainable option, the variability in their physical and mechanical properties may affect the bearing’s performance, making virgin fibers a more reliable option for these critical applications.

The main contribution of this work can be considered in three-fold: (1) utilizing nano-WC to improve the performance of bearings in aquatic environments, focusing on improving wear and friction resistance properties. (2) Combining glass and carbon fibers with nanomaterials represents an innovative approach to enhance mechanical and tribological properties. This combination can lead to composite materials having the advantages of both glass fiber's strength and carbon fiber's flexibility and lightweight, resulting in improvements in wear and friction resistance. (3) Different experiments with various percentages of fiber, nanomaterial, and matrix of the proposed composite are performed. Exploring the effect of different proportions of additives (nano-WC) on the final properties of the composite, which provides new data, will help improve bearing design and select the most efficient materials for superior performance in aquatic environments. This gives the potential to improve the lifespan and performance of the journal bearing.

2 Materials and methodology

2.1 Materials

2.1.1 Chopped fiber

In this research, two types of chopped fibers, namely glass fiber and carbon fiber, were used, focusing on how these fibers, alone or in combination, affect the journal-bearing material. The fiber length used was chosen to be 4 mm for glass fibers and 4 mm for carbon fibers to control the thickness and weight of the composite materials. This is important in applications that require lightweight and strong materials. The chopped glass fiber used is from Jushi Company (China), and the chopped carbon fiber is from Toray Company (Japan), as shown in Figure 1. The technical characteristics of the fibers used are listed in Table 1.

Figure 1 (a) Chopped glass fibers and (b) chopped carbon fibers.
Figure 1

(a) Chopped glass fibers and (b) chopped carbon fibers.

Table 1

Specification of the chopped glass and carbon fibers

Property Glass fiber Carbon fiber
Fiber length 4 mm 4 mm
Fiber diameter 10–20 µm 5–10 µm
Density 2.5–2.6 g/cm3 1.6–2.0 g/cm3
Weight Relatively light Very light
Elastic modulus 70–80 GPa 230–600 GPa
Tensile strength 2–3 GPa 3–7 GPa

2.1.2 Epoxy resin and hardener

The binder component used in this research was a general-purpose epoxy resin [25]. This epoxy resin is from Renfloor HT 2000 (0105) and used at room temperature to provide excellent bonding properties between the fiber layers. The utilized hardener is HT2000(1125), which is used to increase the interface adhesion and strengthen the composite. To obtain the best matrix composition, a 2:1 mixture of resin to hardener is employed [26]. The physical specifications of the resin obtained from the manufacturer Renksan (Turkey) are shown in Table 2.

Table 2

Specifications of the epoxy resin

Physical constants Specification
Shade/colors Transparent
Finish High gloss
Solid by weight (%) 100%
Flash point 130c/266 f
Density 1.05 g/cm3
Viscosity 900–1,200 mPa s
Tensile strength 60–80 MPa
Compressive strength 110–130 MPa

2.1.3 Nano-WC

WC is a very hard material and is difficult to cut. It is widely used in manufacturing due to its superior resistance to wear and corrosion [27,28]. Therefore, different proportions of nano-WC (1, 1.5, and 2%) are added to the composite material, which consists of epoxy as the matrix material and the fibers as the reinforcing part. The WC is obtained from the US Research Nanomaterials Company. The technical properties of the employed WC are listed in Table 3.

Table 3

Specifications of the nano-WC

Material type Nano-WC
Volume 55 nm
Purity 99.9%
Density 15.63 g/cm3
Hardening ∼9 on the Mohs scale
Particle shape Spherical/irregular
Melting point 287°C

2.2 Methodology

The work process is discussed in detail in this section. A Teflon mold was manufactured and coated with a waxy substance (Provaks Plus, Ilkester Company) to ensure that the sample does not stick after removing. A mold, shown in Figure 2, is used to prepare cylindrical samples with a diameter of 4 cm and a height of 1 cm. The work was carried out using 16 samples. Each sample includes a specific combination of epoxy, chopped glass fiber, chopped carbon fiber, and WC with different weight ratios. In the first sample, the epoxy and hardener are mixed at a ratio of 2:1 according to the epoxy manufacturer’s instructions. In the second sample, the epoxy and hardener are mixed, and then the chopped glass fiber is added at 8% of weight of the total mass.

Figure 2 Teflon mold: (a) female mold part and (b) male mold part with a disk.
Figure 2

Teflon mold: (a) female mold part and (b) male mold part with a disk.

The hand layup method was used to form layers of epoxy and chopped glass fiber. Then, the mixture was poured into the mold and left to dry. Sample 3 follows the same steps, but chopped carbon fiber is used at 8% (by weight). Sample 4 is prepared by mixing the epoxy and hardener with a mixture of 4% chopped glass () and 4%carbon fiber (by weight) and ensuring that the fibers are evenly distributed in the sample. In Sample 5, the epoxy and hardener are mixed with 1% WC using a mechanical mixer, and then an ultrasonic device is used to ensure good distribution of the nanomaterial in the epoxy. For Sample 6, the same steps are repeated as for Sample 5, but the tungsten carbide ratio is increased to 1.5%. Sample 7 is also prepared similarly, but with 2% WC. In Sample 8, the epoxy and hardener are mixed with 8% glass fiber and 1% WC and ensuring that the components are evenly distributed in the mixture. Sample 9is prepared similar to Sample 8, but the WC ratio is increased to 1.5%. Sample 10is prepared using the same steps, but the WC ratio is increased to 2%. In Sample 11, the epoxy and hardener are mixed with 8% chopped carbon fiber and 1% tungsten carbide. For Sample 12, the same steps are used, but the WC ratio is increased to 1.5%. Sample 13 is prepared using the same steps, with the WC increased to 2%. In Sample 14, the epoxy and hardener are mixed with 4% glass fiber and 4% carbon fiber mixture and 1% WC. Sample 15 is prepared using the same steps, with WC increased to 1.5%. Sample 16 is prepared using the same steps, with WC increased to 2%. After preparing the samples, they are left for 24 h to completely dry, ensuring that there are no air voids. A summary of the manufactured samples is presented in Table 4.

Table 4

Composition of the samples

Sample no. Composition Sample no. Composition
1 E + H 9 E + H + 8%G + 1.5% WC
2 E + H + 8%G 10 E + H + 8%G + 2% WC
3 E + H + 8%C 11 E + H + 8%C + 1% WC
4 E + H + 4%G + 4%C 12 E + H + 8%C + 1.5% WC
5 E + H + 1% WC 13 E + H + 8%C + 2% WC
6 E + H + 1.5% WC 14 E + H + 4%G + 4%C + 1% WC
7 E + H + 2% WC 15 E + H + 4%G + 4%C + 1.5% WC
8 E + H + 8%G + 1% WC 16 E + H + 4%G + 4%C + 2% WC

E: epoxy, H: hardener, G: glass fiber, C: carbon fiber, WC: nano-WC.

Additionally, the general flowchart is illustrated in Figure 3. Furthermore, the real experimental work steps of the sample preparation are shown in Figure 4.

Figure 3 Work methodology.
Figure 3

Work methodology.

Figure 4 Method of composite sample preparation.
Figure 4

Method of composite sample preparation.

3 Tribological tests

3.1 Wear test

The wear rate can be calculated by measuring the initial weight of the sample before the testing and then exposing the sample to wear conditions for a certain period of time. The final weight of the sample was then measured. The difference between the initial and final weights was determined, which represents the amount of the removed material. The wear rate was calculated using Equation (1) [29] as follows:

(1) W = w 1 − w 2 S d ,

where w 1 is the initial weight value, w 2 is the final weight value, and S d is the sliding distance. The sliding distance S d can be calculated using the following equation:

(2) S d = 2 × π × n × r × t ,

where n is the rotational speed (r.p.m.), r is the radius of impact (m), and t is the time (s).

A pin-on-disc apparatus was used to evaluate the wear rate of the prepared composite samples. The apparatus is from the Pin on Disk Tribometer Company. Two loads, 10 and 15 N, were applied for 12 min, and the wear rate was measured every 2 min to observe the resulting change in wear performance. The rotation speed was set as 400 rpm according to the standard test ASTM G99. The image of the real apparatus is shown in Figure 5.

Figure 5 Wear test apparatus (pin on disc).
Figure 5

Wear test apparatus (pin on disc).

3.2 Coefficient of friction

The coefficient of friction is also calculated using the Pin on Disc apparatus by introducing a vertical force, F n, that is applied to the pin. This force is adjusted using weights by the device settings. When the device is turned on, as the disc starts to rotate, friction is generated between the pin and the disc. This results in a horizontal force as the disc rotates. The device measures the horizontal force F f resulting from the friction between the pin and the disc. From this setup, the coefficient of friction can be calculated utilizing the following Equation (3) [30]:

(3) C . O . F . = F f F n ,

where C.O.F. is the coefficient of friction, F f represents the horizontal force (friction force between the pin and disc), and F n is the vertical force applied to the pin.

The device automatically records the data, and one can collect the results from the system to view and analyze the coefficient of friction.

4 Results and discussion

In this section, the key findings of the study are presented and analyzed in relation to wear and friction coefficient enhancement. The experimental results were analyzed with the aim of evaluating the effect of different variables on the properties of the studied composite material. These results include wear rates and friction values under different operating conditions. The behavior of the composite material was discussed, and the effects resulting from the addition of reinforcing materials at different concentrations under specified environmental conditions were interpreted. The limitations and practical significance of the findings are addressed, providing a comprehensive interpretation of the results.

4.1 Wear test results

The samples were immersed in seawater for 180 days before the wear test. This procedure aims to simulate the real environmental conditions that materials are exposed to during use in marine applications. This step helps to study the effect of long-term exposure to seawater on the mechanical properties of the sample, such as its corrosion resistance and the cohesion of its components, ensuring accurate results that reflect the actual performance in aquatic environments. In this subsection, the wear rates of the wear test results for epoxy with different ratios of chopped glass fiber, chopped carbon fiber, and WC are indicated. The figures present detailed qualitative analyses of the study, which give insight for a deeper understanding of the factors affecting the performance of the material.

Figure 6(a) presents the wear rate for a loading of 10 N. For pure epoxy, the results show that the wear rate increases significantly to 0.3 × 10−6 after about 4–8 min, indicating that pure epoxy is unable to resist wear for a long time. This is because epoxy alone is a flexible polymeric material, but it is not very hard or wear-resistant under mechanical loads. Then, the curve shows an increase in the wear rate with time and continues to increase until the end of the experiment (at 12 min) to 1.49 × 10−5. Over time, the friction between the surface and the epoxy increases, which leads to a rapid deterioration of its mechanical properties, subsequently accelerating the wear rate. The absence of fillers such as WC makes the epoxy susceptible to deformation and direct friction, which reduces its performance in wear resistance. When 1% WC is added to epoxy, it shows improvement in wear resistance compared to pure epoxy due to the high hardness provided by these particles. The wear rate starts to increase slowly after about 4 min, but is lower than the wear rate of pure epoxy. WC acts as reinforcement for the epoxy and distributes stresses better, and reduces deformations in the material, resulting in increased wear resistance for a longer period. Despite the improvement, the low percentage (1%) may not be enough to enhance the wear resistance perfectly; hence, the wear rate increases after a certain period of time. This sample shows the lowest wear rate that remains low for a longer period and starts to increase slowly after about 4 min. Even after 8 min, the wear rate remains lower than those of the other samples (1.38 × 10−5 at 12 min). The 1.5% WC sample seems to represent the ideal balance between hardness and uniform distribution of particles within the epoxy. The hard particles prevent the propagation of cracks or weak points in the material, which improves the material’s resistance to wear to 0.9 × 10−5 at 12 min. This sufficient particle ratio ensures even distribution that reduces stress points and enhances the material’s durability for longer periods of time. The absence of agglomeration or deformation at this ratio helps keep the material durable and effective in resisting wear for a longer period. For 2% WC, it shows an improvement in wear resistance compared to pure epoxy, but the curve shows an increase in wear rate to 1.39 × 10−5 after a short period compared to the 1.5% sample. The wear rate of this sample is lower than pure epoxy but higher than the 1.5% sample. Although increasing the weight percentage of WC to 2% improves the wear resistance compared to pure epoxy, the higher concentration of particles may lead to agglomeration within the composite material. These agglomerations may cause weaknesses within the composition as the particles are not distributed homogeneously. This may lead to the formation of microcracks when the material is subjected to continuous stress. This agglomeration may reduce the positive effect of WC and work as a stress concentration point, which leads to this percentage being less effective than 1.5% in wear resistance. A 33.85% improvement in wear rate was achieved with 1.5% WC added to 8% chopped glass fiber composite, compared to the same fiber content without WC. For 4–8 min, all samples show relatively low wear rates, indicating that the onset of the wear process is slow. For 8–12 min, the wear rate starts to increase clearly with chopped fiberglass (without WC), showing a greater increase in wear compared to the other samples (1.32 × 10−5). This suggests that the addition of WC helps improve the wear resistance. The samples containing 1 and 1.5% WC show a clear improvement in wear resistance compared to fiberglass alone, to 0.97 × 10−5 and 0.78 × 10−5, respectively. However, at 2%, one can see an increase in wear after a certain period, indicating that the high concentration may lead to negative effects, such as particle agglomeration. The results indicate that when 1.5% WC is added to chopped glass fiber, the wear resistance improves by 46.93%, indicating that the wear rate for chopped carbon fiber at different percentages of WC improved at a load of 10 N. Over time, the wear rate increases in all samples. However, there is a clear difference in the behavior depending on the material composition. The sample with 8% carbon fiber and 2% WC shows the highest wear rate with time. This means that adding 2% WC increases the wear rate rather than reducing it. This may be because this high percentage of WC causes the structure of the material to change in a way that makes it more susceptible to wear. The sample with 8% chopped carbon fiber and 1.5% WC showed the lowest wear rate of 0.76 × 10−5 at 12 min, indicating that adding 1.5% WC improved the wear resistance at this load. The sample with only 8% of chopped carbon fiber showed average performance better than the sample with 2% WC but not as good as the sample with 1.5% WC. At low load, adding a moderate percentage of WC (1.5%) seems to improve the wear resistance by enhancing the material cohesion and improving the surface properties. However, adding a higher percentage (2%) may lead to poor performance due to increased hardness or deterioration of the internal structure of the material. As a result, the improvement of adding 1.5% WC with chopped carbon fiber at 10 N is 48.52%. The best wear resistance in samples with (4% glass and 4% carbon) chopped fiber was achieved at 1.5% WC. All samples, for load 10 N in Figure 6(a), show an increase in the wear rate over time. However, there is a clear difference based on the composition. The sample containing 2% WC showed the highest wear rate, indicating that a high percentage of WC leads to a deterioration in wear resistance. The sample containing 1.5% WC showed the lowest wear rate of 0.623 × 10−5 at 12 min, indicating that this moderate percentage of WC enhances the wear resistance of the glass fiber and carbon fiber blend. The samples containing 1% WC showed lower wear rates than the sample containing 2% WC (0.93 × 10−5 and 0.94 × 10−5, respectively) but slightly higher than that of the sample containing 1.5% WC. The sample containing only chopped fibers (no WC) showed an average wear rate, indicating that the addition of WC generally improves the performance, but the optimal percentage is still 1.5% WC. At low load, adding 1.5% WC to the glass fiber–carbon mixture shows the best improvement in wear resistance. The results from adding 1.5% WC show improvement by 58.1% at 10 N. This blend can be considered the best combination for the best enhancement in wear rate results, as presented in Table 5.

Figure 6 Wear rates for 16 samples for different percentages of WC with (a) 10 N loading and (b) 15 N loading.
Figure 6

Wear rates for 16 samples for different percentages of WC with (a) 10 N loading and (b) 15 N loading.

Table 5

Improvements in the wear rate (%) for 10 N loading

WC% Epoxy 8%glass fiber 8%carbon fiber 4% glass + 4%carbon fiber
0 0 11.15 19.60 28.86
1 7.04 34.23 36.25 36.98
1.5 33.85 46.93 48.52 58.10
2 6.277 33.77 35.59 36.79

Figure 6(b) shows the results of wear rates at 15 N loading. Epoxy without additives shows a very rapid increase in the wear rate after about 8 min, with a significant increase in wear until the end of the experiment. The wear rate at this load is much higher than that at low load 10 N due to the fact that pure epoxy is not good at withstanding high loads without undergoing significant deformation. Under high loads (15 N), the epoxy material is subjected to severe mechanical stresses, which lead to a rapid increase in wear (3.8 × 10−5 at 12 min) Under these conditions, the epoxy is more susceptible to deformation due to the lack of any filler to support its mechanical structure. This leads to a significant acceleration of the wear process. For epoxy with 1% WC, the curve shows an improvement over pure epoxy, but the wear rate still increases significantly after 4–8 min. Despite the improvement over pure epoxy, wear still increases rapidly at high loads. Adding 1% WC improves the wear resistance by 3.7 × 10−5 at 12 min compared to pure epoxy, but may not be sufficient at high loads. Under high loads, the low concentration of WC is not sufficient to effectively distribute stresses within the material, causing deformation and wear to occur relatively quickly. In this case, the low concentration enhances performance, but does not completely prevent the increase in the wear rate due to high load. For epoxy with 1.5% WC, the curve of this sample shows the best performance under high load, as the wear rate remains low for a longer period compared to pure epoxy and 1% WC. The increase in wear rate starts after 10 min, but is less severe compared to the sample without additives or with 1% WC. The 1.5% WC content provides the optimal balance between improving the wear resistance to 3.42 × 10−5 at 12 min and the material’s ability to withstand high stresses. WC in this ratio acts as a strong reinforcement to strengthen the epoxy, preventing the propagation of cracks or weak points under high load. In this case, the stress distribution within the material is improved, reducing the effect of high load on the wear rate. For epoxy with 2% WC, despite the improvement compared to pure epoxy, this curve shows a higher wear rate than the 1.5% WC sample at high load. The wear increases significantly after about 8–10 min and continues to increase relatively fast. Adding 2% WC may be too high in this case, leading to agglomeration of particles within the composite. Under high loads, agglomeration may lead to weak points, where particles are not evenly distributed, leading to the formation of microcracks and increased wear rate. Excessive particle concentration limits the performance improvement, and 1.5% appears to be the most efficient. The improvement of adding 1.5% WC to epoxy at 15 N is 42.79% for 15 N loading. At higher loads, wear rates are faster for all samples. At 4–8 min, initially, all samples show good wear resistance. At 8–12 min, the wear rate increases faster due to higher load. Samples containing WC (especially 1 and 1.5%) still show better resistance compared to fiber glass alone, to 2.34 × 10−5 and 1.98 × 10−5, respectively, indicating that WC reduces the effect of high loads. For 2% WC, one can see that increasing WC can lead to greater wear, reinforcing the idea that high concentration can reduce performance due to agglomeration or inhomogeneous distribution. The wear resistance improvement when 1.5% WC was added to chopped glass fiber was 79.67%. As the load increases, the material is subjected to higher stress, which increases the wear rate. However, the optimum WC ratio (1.5%) still shows improved wear resistance, while the higher ratio (2%) leads to increased wear rate due to the weaker internal structure. In general, the sample with 1.5% WC exhibits superior stability against wear over time under higher loads than the sample without WC or the sample with 2% WC. This means that adding WC at a certain percentage provides better mechanical support at high loads, while a high percentage may have negative effects on the resistance. The improvement for 1.5% WC added to chopped carbon fiber at 15 N is 103.98%. All samples showed a greater increase in wear rate compared to the lower load (10 N), which is consistent with expectations, as higher load leads to higher wear rate. The sample with 2% WC, again, showed the highest wear rate. The sample with 1.5% WC showed the lowest wear rate even under a high load of 1.55 × 10−5 at 12 min, which shows an optimum WC ratio and maintains improved performance even at higher loads. The sample with 1% WC showed a similar wear rate to that at low load, but performed less than the sample with 1.5% WC, but better than the sample with 2% WC. The sample containing only chopped fibers showed lower performance than the samples containing WC, indicating the importance of adding WC in improving wear resistance under high loads. Under the highest load, the optimum percentage of WC (1.5%) showed a greater effect, as it maintained the lowest wear rate. A balance is required in the percentage of WC, as increasing its percentage excessively (2%) makes the material less resistant to wear under high load (1.933 × 10−5 at 12 min), while the optimum percentage (1.5%) provides the best resistance, and it improved by 117.33%. Again, this combination shows the best improvement in wear rate results, as presented in Table 6.

Table 6

Improvements in the wear rate (%) for 15 N loading

WC% Epoxy 8%glass fiber 8%carbon fiber 4% glass + 4%carbon fiber
0 0 24.97 41.36 55.76
1 9.18 54.52 82.62 87.03
1.5 42.79 79.67 103.98 117.33
2 6.86 52.40 80.58 86.11

Through the outcomes of the experimental wear tests on composite materials conducted using a pin on disc apparatus, the improvements in wear rate for both loadings, as shown in Figure 6, are summarized in Tables 5 and 6. The best improvement is found for the combination of 1.5% WC, 4% glass fiber, and 4% carbon fiber. The improvement in wear rate for this combination is 58.10% at 10 N loading and 117.33% at 15 N loading, respectively. These values are highlighted in green in Tables 5 and 6. The comparison was made using pure epoxy as a baseline, where the percentage improvement in wear rate (WRI) was calculated using the following equation:

(4) WRI = ( Wear of epoxy − wear of fillers ) / ( wear of epoxy ) .

4.2 Coefficient of friction test results

The friction coefficient of the friction test results for epoxy with various ratios of WC, chopped glass fiber, and chopped carbon fiber is shown in this section. The extensive qualitative analyses are shown in the figures. They provide information to help comprehend the aspects influencing the material’s performance at a deeper level.

Figure 7(a) shows the friction coefficient results at 10 N load for epoxy at different percentages of WC. One can notice that the coefficient of friction is significantly high for epoxy (0.6). This is because epoxy creates a very hard surface, which increases its resistance to slipping. This results in a high ability to adhere to other materials, which contributes to creating a high-friction surface. When 1% WC is added to epoxy, the coefficient of friction is 0.26 compared to that of pure epoxy of 0.6 due to the improvement of the load distribution on the friction surface, which reduces the coefficient of friction. However, when 1.5% WC is added to epoxy, the coefficient of friction is 0.21, which indicates good performance in terms of reducing friction. At 1.5%, a better distribution of particles is achieved, which leads to a greater reduction in the coefficient of friction. The coefficient of friction increases again compared to 1.5% but remains lower than pure epoxy when 2% WC is added to epoxy. At 2%, particle aggregation may occur, which leads to a decrease in the effectiveness of the nanoparticles in reducing friction. Thus, a slight increase in the coefficient of friction can be seen. One can notice that the coefficient of friction is initially high (0.42) when chopped glass fiber is used. This indicates that the chopped glass fiber alone does not provide sufficient resistance to friction. With 1% WC added, the coefficient of friction decreases significantly, which means that the addition of 1% WC helped to reduce the friction to 0.21. The coefficient of friction decreases with this ratio. With the addition of 1.5% WC to chopped glass fiber, the coefficient of friction is 0.2, which indicates that this ratio enhances the friction properties. When 2% WC is added to the chopped glass fiber, we notice that the coefficient of friction starts to increase compared to 1.5 and 1%, but it is still lower than that of the chopped glass fiber alone.

Figure 7 Friction coefficient for 16 samples for different percentages of WC with (a) 10 N loading and (b) 15 N loading.
Figure 7

Friction coefficient for 16 samples for different percentages of WC with (a) 10 N loading and (b) 15 N loading.

The coefficient of friction for only 8% chopped carbon fiber without any additives is 0.38, which is higher than that of the samples with added WC. This could be because the chopped carbon fiber itself has a rougher or more resistant surface, which leads to a higher coefficient of friction. After adding 1% WC, the coefficient of friction decreases to 0.2. This could be because WC enhances the mechanical strength and reduces the surface roughness, which reduces the friction. By increasing the amount of WC to 1.5%, it is observed that there is a further decrease in the coefficient of friction to 0.13, but to a lesser extent than the decrease in the coefficient of friction when adding 1% WC. Here, WC may enhance the homogeneous distribution on the surface, which improves the wear resistance and friction. When the WC ratio is increased to 2%, we notice that the coefficient of friction increases to 0.21, but it is lower than that of the chopped carbon fiber only. This may be due to the saturation of the material, and thus, the WC molecules cannot be distributed optimally. Instead of enhancing sliding, the WC may start to work in reverse due to its inhomogeneity on the surface, leading to increased friction. The coefficient of friction for the blend without any additives is higher (0.36) compared to the samples with added WC. This may be because the carbon and glass blend has a rough and friction-resistant surface due to the absence of any material that contributes to improving sliding or wear resistance. When 1% WC is added, a significant decrease in the coefficient of friction is observed (0.14). This is because WC improves the mechanical properties and reduces the friction. At this percentage, WC particles may be evenly distributed on the surface of the fiber blend, which reduces the contact of rough points and leads to reduced friction. With the addition of 1.5% WC, the decrease in the coefficient of friction is 0.08 and continues to decrease significantly. This indicates that increasing the ratio enhances the effect of WC in reducing the friction. The reason may be that the higher ratio contributes to better distribution of the material on the surface, which reduces the interaction between the fibers and increases the smoothness of the surface. When 2% WC is added, one can notice that the coefficient of friction increases to 0.17 compared to the other ratios (1 and 1.5%). The possible reason for this increase is that increasing the WC ratio may significantly lead to the accumulation of WC molecules in certain areas on the fiber surface instead of distributing them evenly. This accumulation may cause an increase in roughness in some areas, leading to increased friction.

Figure 7(b) shows that the coefficient of friction increased as compared to load 10 N because when the applied force is greater, the coefficient of friction increases to 0.74 for pure epoxy. The high coefficient of friction of pure epoxy is due to the lack of additives that reduce friction, its hardness that leads to greater direct contact with other surfaces, as well as the lack of natural lubricating properties. Epoxy + 1% WC significantly decreases the coefficient of friction to 0.36 compared to pure epoxy (0.74), but epoxy + 1.5% WC shows a greater decrease in the coefficient of friction to 0.29, similar to that at 10 N load, and the effect of tungsten carbide becomes more pronounced. Smaller ratios, such as 1 and 1.5% provide a significant improvement in friction reduction, as the particles help to better distribute the forces on the friction surface. The coefficient of friction increases slightly compared to 1.5% but remains lower than pure epoxy when 2% WC is added to epoxy. However, increasing the ratio to 2% leads to negative effects due to the possibility of nanoparticles accumulating, which reduces their effectiveness in reducing friction. At 15 N load, the chopped glass fiber alone is less capable of bearing loads, and thus the coefficient of friction appears high (0.69), reflecting the poor performance of glass fiber in resisting friction at this load. A significant decrease in the coefficient of friction to 0.27 is observed when 1% WC is added to chopped glass fiber. Due to the added WC, the system’s ability to distribute loads improves, and direct contact is reduced, leading to reduced friction. The ratio of 1.5% provides greater improvement in the friction performance to 0.26 compared to 1%, but at 2%, WC particles accumulate, reducing their effective distribution. One can deduce that, as the load increases, the addition of WC is more effective in reducing friction due to its ability to withstand greater loads and distribute them better on the friction surface.

Under 15 N load, it is observed that the coefficient of friction for the chopped carbon fibers without WC is almost the same as that of the lower load 10 N (0.68); however, when WC is added at different percentages, it leads to results better than that of the 10 N load. This can be interpreted as follows: when the load increases, there is more enhancement of friction properties. Noticing this, the perfect addition ratio of WC is 1.5%. At a higher load of 15 N, it is noticed that the coefficient of friction is much higher than that at 10 N load. This is expected, as increasing the load leads to increased contact between the two surfaces and thus increased friction. Higher loads create greater pressure on the fibers, which increases the resistance resulting from the rough surface of the original blend. When 1% WC is added, a decrease in the coefficient of friction is observed (0.21). In this case, WC helps in reducing friction by improving the surface properties and reducing the direct contact between the fibers. This can be due to the fact that WC begins to form a protective layer that reduces surface roughness and increases wear resistance, which leads to reduced friction despite the increased pressure. At 1.5% WC, the decrease in the coefficient of friction continues; under a high load, it is 0.12 WC due to the better distribution on the surface, which enhances its anti-friction effect. The reason for the continuous decrease may be that WC, in this case, improves the material’s resistance to wear more due to high pressure, which reduces the effect of surface roughness and prevents premature wear of the material, thus reducing the coefficient of friction. With 2% WC, an increase in the coefficient of friction of 0.26 is observed compared to 1 and 1.5%. At 15 N, increasing the WC ratio to 2% may lead to the same problem that occurs at 10 N, which is the uneven accumulation of WC on the surface. With high pressure, the uneven distribution becomes more obvious, which causes an increase in local roughness and a higher coefficient of friction. Increasing the load increases the effect of surface defects. Under high loads, any inhomogeneity or surface roughness becomes more affected by high pressure, which leads to an increase in friction despite the addition of WC. Fibers are not as flexible as carbon fibers, and under high pressure, they can cause increases in rough contact between surfaces. The increase in load causes the glass fibers to distribute the pressure perfectly, resulting in increased friction. At high loads, glass fibers can cause undulations in the surface or additional contact points that increase friction compared to a light load. Although carbon fiber reduces friction significantly at 10 N, at 15 N, one can notice a slight increase in the coefficient of friction. Increasing the load can lead to increased contact between the fibers and the surface they are rubbing against, especially in areas where the fibers are unevenly stacked. Although carbon fiber has excellent wear resistance, increasing the load can lead to surface changes that cause a slight increase in the coefficient of friction. For 4% glass fiber and 4% carbon fiber mixture, at 15 N, the coefficient of friction for this mixture is equal to the coefficient of friction for carbon fiber alone, i.e., 0.68. This means that glass fiber, which normally increases the coefficient of friction, has its effect neutralized by the presence of carbon fiber. Carbon fiber contributes more to load distribution and reduces rough contact, so the effect of glass fiber becomes less pronounced. As a result, the combination of glass and carbon fiber performs as efficiently as carbon fiber alone, with the carbon fiber being responsible for reducing the coefficient of friction.

Tables 7 and 8 provide a summary of the improvement in the friction coefficient for both loading conditions, as shown in Figure 7. The combination of 1.5% WC, 4% glass fiber, and 4% carbon fiber exhibits the greatest improvement, measuring 86.66% at 10 N loading and 83.78% at 15 N loading. These values are indicated in green in the tables.

Table 7

Friction coefficient enhancement (%) with 10 N loading

WC% Epoxy 8%glass fiber 8%carbon fiber 4% glass + 4%carbon fiber
0 0 30 36 40
1 56.66 65 66 76.66
1.5 65 66.66 78.33 86.66
2 55 60 65 71.66
Table 8

Friction coefficient enhancement with 15 N loading

WC% Epoxy 8%glass fiber 8%carbon fiber 4% glass + 4%carbon fiber
0 0 6 8 8.10
1 51.13 63.50 67.56 71.62
1.5 60.81 64.86 79.72 83.78
2 48.61 59.46 63.51 64.86

A comparison was made using pure epoxy as baseline, where the percentage improvement in the coefficient of friction (FCI) was calculated using the following equation:

(5) FCI = ( coefficient of friction of epoxy − coefficient of friction of fillers ) / ( coefficient of friction of epoxy ) .

The 1.5% WC + (4% G + 4% C) composite achieved the best performance in abrasion and friction resistance because this ratio allowed for a homogeneous distribution of WC particles within the polymer matrix, enhancing stiffness without significant agglomeration. The balance between glass fibers and carbon fibers resulted in a combination of the properties of each. Carbon fibers provide high stiffness and mechanical resistance, while glass fibers help distribute stresses and reduce frictional wear. This homogeneous distribution improved the interfacial bond between the fibers and the matrix, reducing separation and gradual wear during testing. Other combinations, however, were less effective due to several negative factors. For example, when WC was increased to 2%, agglomeration increased due to the particles being closer together and not being evenly distributed, creating weak areas in the material and negatively impacting abrasion resistance. Furthermore, when only one type of fiber (either glass or carbon) was used, the synergistic effect between the fibers was not achieved, making the material more susceptible to abrasion due to the imperfect stress distribution. Therefore, a 1.5% WC ratio with mixed fibers (4% G + 4% C) is optimal for achieving the highest abrasion resistance and best friction properties.

5 SEM microstructure analysis

Figure 8(a) shows the microstructure of the pure epoxy sample, where the surface appears relatively homogeneous but lacks obvious mechanical reinforcement. In contrast, Figure 8(b) shows a micrograph of the 4% C + 4% G sample, where the fibers appear intertwined and evenly distributed, enhancing the mechanical strength of the sample. The homogeneity of this sample is also better than that shown in Figure 8(a). Figure 8(c) shows the microstructure of the sample (1.5% WC + (4% G + 4% C)), which shows excellent homogeneity and even distribution of components. This distribution promotes smooth stress transfer, which contributes to the improved wear resistance of the material. The absence of gaps and clusters also enhances the strength of the material and reduces weak points, making this sample the most efficient in wear resistance. Figure 8 (d), (e), and (f) shows the presence of nanoparticle agglomerations, which reduced the homogeneity of distribution within the epoxy. This aggregation negatively affected the wear resistance and coefficient of friction compared to 1.5% WC, which showed a more homogeneous distribution and improved performance.

Figure 8 (a) SEM microstructures of (a) pure epoxy, (b) 4% C + 4% G, (c) 1.5% WC + 4% C + 4% G, (d) 2% WC + 8% G, (e) f 2% WC + 8% C, and (f) 2% WC + 4% C + 4% G.
Figure 8

(a) SEM microstructures of (a) pure epoxy, (b) 4% C + 4% G, (c) 1.5% WC + 4% C + 4% G, (d) 2% WC + 8% G, (e) f 2% WC + 8% C, and (f) 2% WC + 4% C + 4% G.

6 Conclusion

In this study, different weight percentages of nano-WC (1, 1.5, and 2%) were combined with epoxy and different types of chopped glass and carbon fibers to enhance the wear rate and friction coefficient of the marine journal bearing composite material. Many samples were prepared and manufactured to perform different wear and friction tests. Important results were deduced in this study, as stated in Section 4. This section highlights the main points. Epoxy without additives exhibits less wear resistance due to the lack of hardness enhancement. When 1% WC is added, there is a slight improvement in wear resistance, while 2% WC leads to agglomeration of particles, which reduces effectiveness compared to 1% WC. The best performance can be seen with 1.5% WC, 4% glass fiber, and 4% carbon fiber. This can be considered the perfect balance between particle distribution and hardness. According to the study, the optimal wear rate for this combination was 0.623 × 10−5 with an improvement of 58.1%, while the optimal coefficient of friction was 0.08 with an improvement of 86.66%. Under a 15N load, the optimum wear rate was 1.55 × 10−5 with an improvement of 117.33%, while the optimum coefficient of friction was 0.12 with an improvement of 83.78%. In the future, a real journal bearing will be manufactured, according to this combination, and introduced under test in a real marine environment.

  1. Funding information: Authors state no funding involved.

  2. Author contributions: All authors have accepted responsibility for the entire content of this manuscript and consented to its submission to the journal, reviewed all the results and approved the final version of the manuscript. Suadad Noori contributed to writing, investigation, and software; Ali S. Alithari contributed to methodology, validation, and writing; and Hala S. Hasan contributed to conceptualization, review, and editing.

  3. Conflict of interest: Authors state no conflict of interest.

  4. Data availability statement: All images, drawings, and figures contained in the manuscript are entirely the author’s own creation and were produced specifically for the purposes of this research using data and experiments conducted during the study period. No figure or drawing has been borrowed or copied from external sources, and therefore, no citation or permission for use from any third party is required.

Appendix

The images of the SEM are presented for the rest of the samples.

Images (A–D) show the structure of epoxy (E), which has a relatively homogeneous surface that reflects the material’s hardness and ability to provide a solid foundation for reinforced materials. Chopped glass fibers (GF) can be observed with a smooth surface and sharp edges, indicating good distribution within the composite material, which enhances its corrosion resistance and increases its durability. Chopped carbon fibers (CF) have a rough surface and sharp corners, which enhance their adhesion to the epoxy and provide additional resistance to mechanical stresses. Hybrid (glass and carbon) chopped fibers (CGF) show effective integration of the different fibers in the epoxy, indicating a homogeneous distribution that enhances the mechanical and tribological properties.

Images (E–J) show that the addition of 1% tungsten carbide to the epoxy (w1E) contributed to a homogeneous distribution of particles within the polymer matrix, which enhanced the bonding between the components and led to improved hardness. When the concentration was increased to 1.5% (w1.5E), the internal structure of the material improved, as the particles showed better integration with the epoxy, which helped to enhance the mechanical properties. However, at 2% (w2E), the particles began to aggregate and agglomerate, which reduced the distribution efficiency and led to a decrease in homogeneity, although some improvement was still achieved compared to pure epoxy. In the glass fiber-reinforced samples, the 1% tungsten carbide concentration (w1G) showed a good distribution of particles around the fibers, which contributed to enhancing the strength of the material and improving the bonding between the fibers and the matrix. At 1.5% (w1.5G), the interaction between the particles and the fibers was more pronounced, as the interpenetration between the fibers and the particles improved, which led to increased hardness and wear resistance. At 2% (w2G), particle clusters were more pronounced, reducing homogeneous dispersion, but the presence of fibers helped improve the distribution of some particles compared to the fiber-free system, maintaining some level of improvement in the overall performance.

Images (K–P) show that when 1% tungsten carbide was added with the chopped carbon fibers (W1C), the particles were well distributed within the matrix, which enhanced the adhesion between the fibers and the resin, thus improving the material’s resistance to wear and friction. When the concentration was increased to 1.5% (W1.5 C), the density of tungsten carbide particles increased, which contributed to further enhancing the hardness and strengthening the internal bonds. However, when reaching 2% (W2C), the particles began to aggregate, which affected the homogeneity of distribution within the material, although the presence of the fibers helped to maintain a certain level of hardness. For the blend of glass and carbon fibers, at 1% (W1CG), the fibers were homogeneously interwoven with the tungsten carbide particles, which enhanced the hardness and improved the material’s resistance to mechanical loading. At 1.5% (W1.5CGG), greater fusion between the fibers and particles appeared, which increased the material’s resistance to deformation. However, at 2% (W2CGG), excessive agglomeration of particles resulted in a decrease in their homogeneous distribution; however, the effect of glass and carbon fibers helped to reduce the negative effects of agglomeration, keeping the mechanical properties at an acceptable level.

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Received: 2025-01-18
Revised: 2025-03-29
Accepted: 2025-06-12
Published Online: 2025-07-28

© 2025 the author(s), published by De Gruyter

This work is licensed under the Creative Commons Attribution 4.0 International License.

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https://doi.org/10.1515/eng-2025-0125
Keywords for this article
wear resistance; friction coefficient; journal bearing; chopped fibers; nano-WC
Creative Commons
BY 4.0

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  32. Use of modeling, BIM technology, and virtual reality in nondestructive testing and inventory, using the example of the Trzonolinowiec
  33. Tunable terahertz metasurface based on a modified Jerusalem cross for thin dielectric film evaluation
  34. Integration of SEM and acoustic emission methods in non-destructive evaluation of fiber–cement boards exposed to high temperatures
  35. Non-destructive method of characterizing nitrided layers in the 42CrMo4 steel using the amplitude-frequency technique of eddy currents
  36. Evaluation of braze welded joints using the ultrasonic method
  37. Analysis of the potential use of the passive magnetic method for detecting defects in welded joints made of X2CrNiMo17-12-2 steel
  38. Analysis of the possibility of applying a residual magnetic field for lack of fusion detection in welded joints of S235JR steel
  39. Eddy current methodology in the non-direct measurement of martensite during plastic deformation of SS316L
  40. Methodology for diagnosing hydraulic oil in production machines with the additional use of microfiltration
  41. Special Issue: IETAS 2024 - Part II
  42. Enhancing communication with elderly and stroke patients based on sign-gesture translation via audio-visual avatars
  43. Optimizing wireless charging for electric vehicles via a novel coil design and artificial intelligence techniques
  44. Evaluation of moisture damage for warm mix asphalt (WMA) containing reclaimed asphalt pavement (RAP)
  45. Comparative CFD case study on forced convection: Analysis of constant vs variable air properties in channel flow
  46. Evaluating sustainable indicators for urban street network: Al-Najaf network as a case study
  47. Node failure in self-organized sensor networks
  48. Comprehensive assessment of side friction impacts on urban traffic flow: A case study of Hilla City, Iraq
  49. Design a system to transfer alternating electric current using six channels of laser as an embedding and transmitting source
  50. Security and surveillance application in 3D modeling of a smart city: Kirkuk city as a case study
  51. Modified biochar derived from sewage sludge for purification of lead-contaminated water
  52. Special Issue: AESMT-7 - Part II
  53. Experimental study on behavior of hybrid columns by using SIFCON under eccentric load
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