Experimental Study on the Tribological Performance of Shark Denticle-Inspired Texture for Roller Cone Bit Bearings

Abstract

During drilling in complex formations, the sliding bearings of roller cone bits are continuously subjected to low-speed, heavy-load, and boundary lubrication conditions, under which adhesive failure readily occurs, severely limiting drilling efficiency. To enhance their wear resistance, a bionic texture inspired by shark denticles was designed and compared with conventional rectangular and circular textures. An equivalent pin–disk contact model was established based on Hertzian contact theory, and tribological experiments were conducted under typical formation conditions using a friction and wear testing machine. The friction coefficient, friction torque, and wear volume of different textures were measured under both lubricated and dry contact conditions, and the underlying mechanisms were elucidated through three-dimensional surface morphology analysis. The results show that the shark denticle-inspired texture reduced the friction coefficient and wear volume by 33.3% and 35%, respectively, under lubrication, while suppressing debris intrusion at the frictional interface under dry contact, thereby providing a degree of surface protection. This study offers theoretical guidance and experimental evidence for advancing the engineering application of bionic tribology in the petroleum industry.

1. Introduction

Deep oil and gas development has become a strategic focus for future energy exploration. During deep drilling operations, roller cone bits operate under extreme conditions, including high temperatures, high pressures, and heavy loads. As the critical load-bearing and transmission component, their sliding bearings are highly prone to adhesive wear failure [1], which severely limits both drilling efficiency and bit service life. Therefore, extending the service life and enhancing the reliability of roller cone bits is essential to overcoming the bottlenecks in deep oil and gas resource development.

Surface texturing, as an advanced approach to improving friction and wear resistance, has attracted widespread attention in recent years. Numerous studies have demonstrated that introducing textures on contact surfaces can effectively enhance hydrodynamic lubrication, generate secondary lubrication effects, reduce friction coefficients, and suppress wear [2,3,4,5,6]. Xie et al. [7] revealed through hydrodynamic simulations that micro-dimple textures outperform smooth surfaces in terms of load-carrying capacity and friction reduction. Song et al. [8] reported that the arrangement and geometry of textures have a significant influence on lubrication regimes. Rao et al. [9,10] verified through mathematical modeling that textured bearings can improve load capacity and reduce friction. Etsion et al. [11] found that the shape and depth of textures strongly affect fluid flow and sealing performance. Niu et al. [12] conducted stiffness and stability tests on textured bearings, confirming their role in enhancing operational reliability. Yang et al. [13] performed ball-on-disk tests under dry friction to examine the influence of groove width on friction and wear behavior. Zhong and Wang [14,15,16] applied surface texturing to roller cone bit bearings and showed that properly designed texture parameters significantly enhance lubrication performance and reduce wear.

Bionics provides a new paradigm for surface texture design, as many organisms in nature possess microstructural features that effectively regulate the interactions among fluids, solids, and contact surfaces [17,18,19]. Long et al. [20] designed vein-inspired textured bearings using leaf morphology as a model, achieving up to 16.23% reduction in wear and a 15.79% decrease in friction under dry sliding. Zhang et al. [21] developed a temperature-controlled microtexture system inspired by the unidirectional liquid transport mechanism of pitcher plants, which offered a new approach to debris removal and friction regulation. Gao et al. [22] designed a bio-inspired plunger modeled on maggots, finding that the textured plunger exhibited more uniform contact pressure and higher oil-film pressure than the standard one. Zhang et al. [23] mimicked pangolin scales to design rotary tillage blades, which improved anti-adhesion and drag-reduction performance by 18.81% compared with conventional blades. Shark-skin-inspired textures have often been employed in studies on fluid drag reduction and surface self-cleaning [24]. Xue et al. [25] fabricated elastic bearings with sharkskin textures via 3D printing and demonstrated enhanced oil-film load capacity and reduced friction. Niu et al. [26] developed shark denticle-inspired rotary tillage blades, which reduced horizontal and vertical resistance during tillage by 21.3% and 24.8%, respectively. Carman et al. [27] achieved drag reduction of up to 85% on ship hulls using sharkskin-inspired surface textures. Despite these advances, systematic experimental data on bionic surface textures for roller cone bit bearings under low-speed, heavy-load, and boundary lubrication conditions remain scarce, and the performance of shark denticle-inspired textures under such conditions requires further validation.

In this study, an equivalent frictional contact model for roller cone bit bearings was developed based on Hertzian contact theory. Femtosecond laser processing was used to fabricate shark denticle-inspired, rectangular, and circular textures on specimen surfaces. Systematic experiments were conducted under representative conditions, including soft, medium-hard, and hard rock formations, as well as dry friction. The friction coefficient, friction torque, wear volume, and surface morphology evolution were measured and analyzed to compare the tribological performance of different textures and to elucidate the wear-reduction mechanisms of shark denticle-inspired textures. The findings provide both theoretical guidance and experimental support for the optimized surface texture design of roller cone bit bearings.

2. Methods

2.1. Equivalent Working Condition Transformation of Roller Cone Bit Bearings

During rock-breaking operations, the drilling weight exerted on roller cone bits can reach several tens of tons, with the large journal at the bearing position bearing the majority of the radial load. The resulting actual contact stress far exceeds the capacity of conventional laboratory equipment. To enable tribological investigations under controllable laboratory conditions, an equivalent transformation of the actual working conditions is required.

In this study, the curved surface contact between the journal and the bearing sleeve was approximated and equivalently transformed based on Hertzian contact theory [28], yielding the pin–disk friction pair model illustrated in Figure 1a. By ensuring equivalence between the actual and experimental contact stresses, the real drilling load could be represented by the normal load applied in laboratory tests. The converted experimental parameters are summarized in

Table 1. Bearing surface load distribution.

Rock Stratum	Soft Rock Layer	Medium-Hard Rock	Hard Rock Layer	Ultra-Hard Rock
Total radial force on bearing (kN)	7.4~19.8	19.8~39.6	39.6~59.4	59.4~74.2
Large journal radial force (kN)	6.7~17.4	17.4~35.6	35.6~53.4	53.4~66.8
Small journal radial force (kN)	0.7~2.4	2.4~4.0	4.0~6.0	6.0~7.4

.

According to the material properties of roller cone bits, the disk specimen, shown in Figure 1b, simulated the surface of the bearing sleeve and was made of beryllium bronze with a diameter of 31.7 mm and a height of 10 mm. After heat treatment, its hardness reached 55 HRC. The pin specimen, shown in Figure 1c, simulated the surface of the journal and was fabricated from 20CrNiMo alloy steel with dimensions of Φ6 mm × 15 mm. The lower end was machined into a circular arc segment, and its hardness reached 60 HRC after heat treatment.

The commonly used load data on the bearing surface of the tooth wheel, which is subjected to the largest load among the commonly used three-tooth wheel drills, are shown in Table 1. In conducting the experimental design, the real load can be equated to the experimental normal load by keeping the actual contact stresses equivalent to the experimental contact stresses [29,30].

The geometric parameters of the tooth wheel drill bit plain bearing are shown in Figure 2, O₁ is the bearing center; O₂ is the journal center; U is the relative sliding speed of the bearing and the journal; the eccentricity angle Ψ is the angle between O₁O₂ and the vertical line; R₁ is the radius of the bearing; R₂ is the radius of the journal; the eccentricity (e is the eccentricity distance, c is the radius gap); h is the thickness of the oil film; θ is the load F deflection angle, and B is the width of the bearing. In this paper, we choose a 12 1/4HJ 636Y three-tooth wheel drill bit as an example, a tooth wheel drill bit large shaft diameter with radial sliding bearing main parameters, such as in

Table 2. Parameters of sliding bearing of tooth wheel drill bit.

Name	Sizes
Bearing radius R1 (mm)	41.5
Bearing radius R2 (mm)	41.25
Bearing width L (mm)	45
Grease dynamic viscosity μ(Pa·s)	0.1281

. According to the sliding bearing internal contact, when

$${\displaystyle \frac{1}{R}}=({\displaystyle \frac{1}{R_2}}-{\displaystyle \frac{1}{R_1}})$$

(1)

$${\displaystyle \frac{1}{E^{\prime }}}={\displaystyle \frac{1-{{\upsilon }_1}^2}{E_1}}+{\displaystyle \frac{1-{{\upsilon }_2}^2}{E_2}}$$

(2)

In the above equation, R₁ and R₂ are the radius of curvature of the bearing and journal, respectively, and E₁ and E₂ represent the modulus of elasticity of the bearing and journal, respectively.

Different drilling pressure contact surface loads for the concentrated load, using Hertz’s theory for the calculation, need to convert the concentrated load into a distributed load, and assuming that the load is uniformly distributed in the bearing width L, it can be obtained for the distribution of the bearing surface load q:

$$q={\displaystyle \frac{F}{L}}$$

(3)

According to Hertz’s theory, when a pair of cylinders with parallel axes come into contact and are subjected to pressure, the contact surface changes from line contact to face contact, the contact surface is a narrow rectangle, and the half-width of the contact surface B is calculated by the formula:

$$B=2\sqrt{{\displaystyle \frac{Rq}{\pi L{E}^{\prime }}}}$$

(4)

In the above equation, R denotes the integrated radius of curvature, E′ is denoted as the equivalent modulus of elasticity, and q is the transformed distributed load.

The maximum contact stress (Hertzian stress) on the contact surface is calculated as shown in Formula (5) should be kept constant when carrying out the equivalent transformation of the ${\sigma }_{\max }$ contact surface to calculate the equivalent surface-acting load F’.

$${\sigma }_{\max }={\displaystyle \frac{2F^{\prime }}{\pi BL}}$$

(5)

The linear velocity of the tooth wheel bit bearing in the actual working condition is 0.16~0.44 m/s, the pin-disc experiment selects the linear velocity equal to the actual working condition, and the rotational speed ranges from 60~300 rmp. The lubrication medium for the friction experiment selects the RB-type bearing grease of the tooth wheel bit when it is actually working, and the experimental models are all started from the initial processing state, to ensure that the medium conditions are consistent with the starting conditions. The selection of experimental working condition parameters follows the working characteristics of the tooth wheel drill: high speed and low pressure, low speed and high pressure. The selection table of experimental parameters is shown in

Table 3. Experimental conversion parameters.

Rock-Breaking Condition	Actual Drilling Pressure (t)	Actual Radial Load (kN)	Actual Linear Velocity (m/s)	Experimental Radial Force (N)	Experimental Rotational Speed (r/min)
Soft formation	5	20.9	0.4346	20	200/300
Medium-hard formation	12	30	0.3477	50	120/180
Hard formation	20	45.9	0.2608	100	60/100

.

2.2. Surface Texture Design and Fabrication

Shark denticles possess groove-like structures that exhibit excellent drag-reduction performance, as shown in the scanning electron microscopy image in Figure 3a [31]. Inspired by this bionic feature and considering the actual contact area dimensions, three textures—shark denticle-inspired, circular, and rectangular—were designed on the disk specimen surface. The distribution of shark denticle-inspired textures is shown in Figure 3b, with a texture area ratio of 30%. The geometry of a single texture unit is presented in Figure 3c, where the depth c and length b were variable, with c/b set to 0.2. The detailed dimensions are listed in

Table 4. Geometrical parameters of shark denticle-inspired texture.

Parameter	a	b	c	d	e
Value (mm)	0.24	0.6/0.4	0.12/0.08	0.01	0.1

. Based on the principles of equal area ratio and equal volume, the radius and depth of circular dimples were determined as 0.33 mm and 0.052 mm, respectively, while the rectangular grooves were designed with the same depth (0.052 mm) as the shark denticle-inspired textures.

Before laser machining, the disk specimens were sequentially ground with sandpaper of grit sizes ranging from 800# to 2000#, followed by polishing with a metallographic polishing machine to achieve a mirror finish. The surface roughness was controlled to Ra ≤ 0.8 μm to minimize the influence of initial asperities. Subsequently, a three-axis ultrafast laser microfabrication system (Xi’an, China) was employed to process the shark denticle-inspired, circular, and rectangular textures on the disk specimens.

Due to the small dimensions of the morphology of the bionic sharkscale shield fabrics, the processing accuracy requirements are high, and the internal depth transformation of the fabrics is linearly proportional. Femtosecond laser processing (pulse width of 100 fs, power of 15 W) is used to achieve micron-level morphology of the bionic sharkscale shield fabrics through the hierarchical scanning strategy (depth of each layer is 0.01 mm), and the processing process follows the surface texture specification to ensure the geometrical consistency of the fabrics. The fabricated shark denticle-inspired texture is shown in Figure 3d.

2.3. Equivalent Friction Tests of Roller Cone Bit Bearings

The equivalent friction tests of roller cone bit bearings were performed on an MMW-1A computer-controlled universal friction and wear tester (MMW-1A, Jinan, China), as shown in Figure 4a. Prior to testing, the machined pin–disk specimens were ultrasonically cleaned in petroleum ether to remove residual particles and machining debris, dried, and weighed using an electronic balance with a precision of 0.1 mg. The specimens were then mounted in the fixture of the tester, shown in Figure 4b, ensuring a contact misalignment ≤ 0.1 mm. The pin–disk module allowed a rotational speed range of 1–2000 r/min, an axial load range of 10–1000 N, and a maximum friction torque of 2500 N·m.

After installation, the test parameters were set through the control interface of the testing machine. The experiment was initiated, and the friction coefficient and torque were recorded in real time. Each load condition was maintained for 30 min at the given rotational speed, followed by stepless adjustment to the next speed level for another 30 min.

Upon completion, the specimens were immediately disassembled, cleaned, dried, and reweighed to determine wear mass loss. The worn disk surfaces were then examined using a non-contact 3D profilometer (MSK-2000, Xi’an, China), as shown in Figure 4c, to measure maximum and average wear depths, as well as to characterize the surface morphology. Wear scar features and failure mechanisms were subsequently analyzed.

Upon completion, the specimens were immediately disassembled, cleaned, dried, and reweighed to determine wear mass loss. The worn disk surfaces were then examined using a non-contact 3D profilometer (MSK-2000, Xi’an, China), shown in Figure 4c, to measure maximum and average wear depths, as well as to characterize the surface morphology. Wear scar features and failure mechanisms were subsequently analyzed.

3. Results and Discussion

3.1. Effect of Texture on Friction Coefficient

Figure 5 shows how the friction coefficient evolves for textured specimens under three representative rock-formation loads. Under low load (Figure 5a), at 200 and 300 r/min, the specimens show marked differences in the friction coefficient. The shark denticle-inspired texture showed a stable curve, maintaining values around 0.094 and 0.090, corresponding to reductions of 19.2% and 19.6% compared with the untextured specimen. The circular texture gives the lowest values but with large fluctuations, indicating poor stability. By contrast, the rectangular texture is slightly higher than the untextured sample, likely because it disrupts lubricant flow and hinders film formation.

As shown in Figure 5b, with the load increased to 50 N, the friction-reducing advantage of the shark denticle-inspired texture became more pronounced. At 120 r/min and 180 r/min, its average friction coefficients were 0.093 and 0.085, respectively—significantly lower than those of circular and rectangular textures and representing reductions of 26.7% and 33.1% compared with the untextured specimen.

Under heavy load conditions, where lubricating films are prone to collapse, the regulation effect of textures on interfacial friction became even more significant. As shown in Figure 5c, the shark denticle-inspired texture exhibited coefficients of 0.104 and 0.094 at 60 r/min and 100 r/min, respectively, representing decreases of 14.1% and 24.1% compared with the untextured specimen. By contrast, the circular texture performs worse than the untextured specimen, likely because edge stress concentrations promote film rupture.

The friction coefficient under dry sliding is displayed in Figure 6. Compared with the untextured specimen, the shark denticle-inspired texture produced no significant change in the overall trend, but the average value in the steady state was 0.633, which is 7.6% lower than the 0.685 measured for the untextured specimen.

In summary, the experimental results coincide with the theoretical analysis, and the shark-like shield-scaled fabric has achieved continuous and stable friction reduction under different loading conditions, with a maximum reduction of up to 33.1%, showing excellent lubrication adaptability. Especially under lubrication conditions, the shark-like shield-scaled structure significantly reduces the coefficient of friction by optimizing the thickness of the oil film, storing the lubricant medium, and improving the surface characteristics of the friction sub-surface. Under heavy load conditions, the shark-like shield scale fabric shows strong friction control ability, effectively reducing the risk of oil film rupture, thus further improving the friction reduction effect. In contrast, the circular fabric has some friction reduction advantages under low load conditions, but degrades under heavy load conditions, indicating that its structure is prone to lubricant film rupture under high loads. In contrast, the rectangular weave has a better friction reduction effect under heavy load conditions, but performs poorly under low load conditions, suggesting that its structure disturbs the lubricant film more, which affects the lubrication effect.

Overall, with its unique geometry, the shark-like shield scale weave exhibits superior friction reduction performance under different working conditions, especially under boundary lubrication and dry friction conditions, which prolongs the wear life of the material through the abrasive grain storage and surface protection mechanisms, further verifying its potential for application in the field of tribology.

3.2. Effect of Texture on Friction Torque

Figure 7 shows friction torque, a key indicator of shear resistance variations at sliding interfaces, under three load conditions. Under light load, Figure 7a shows that at 200 r/min and 300 r/min, the shark denticle-inspired specimen exhibited average torque values of 27.1 N·mm and 25.8 N·mm, representing reductions of 20.4% and 20.1% relative to the untextured specimen. The circular texture gave the lowest torques but showed large fluctuations, while the rectangular texture had slightly higher torques, indicating insufficient lubricant film and higher shear resistance.

At medium load, the superiority of the shark denticle-inspired texture became clearer, as seen in Figure 7b. The average torques at 120 r/min and 180 r/min were 55.8 N·mm and 50.3 N·mm, which are 32% and 38% lower than the untextured surface, respectively. This suggests the shark-denticle geometry promotes localized hydrodynamic pressure, increases film thickness, and reduces shear resistance. The circular texture exhibited weakened drag-reduction capability, with initially lower torques but larger fluctuations at later stages.

Figure 7c demonstrates that under heavy load, the superiority of the shark denticle-inspired texture became more evident. At 60 r/min and 100 r/min, its average torques were 124.3 N·mm and 112.3 N·mm, compared with 149.9 N·mm and 147.8 N·mm for the untextured specimen, representing reductions of 17.1% and 23.7%. These results show that hydrodynamic lubrication from shark-denticle textures remains effective under heavy load. Conversely, the circular texture lost effectiveness quickly, with large fluctuations and torques near or higher than the untextured specimen, indicating stress concentration and film rupture under high contact stress. The rectangular texture showed slightly improved performance compared with the untextured specimen but with limited reduction capability overall.

The friction torque under dry sliding is compared in Figure 8. The shark denticle-inspired specimen yielded an average torque of 749.29 N·mm, 7.9% lower than the 813.59 N·mm recorded for the untextured surface.

In summary, the experimental results show that the shark-like shield-scaled fabrics show significant friction moment reduction under different rock load conditions, with the maximum reduction up to 38.3%, showing excellent lubrication stability and structural adaptability, which is especially suitable for sliding contact systems under complex working conditions of medium and heavy loads. Shark-like scale fabrics achieve significant friction reduction under lubricated conditions by optimizing the lubricant film thickness, storing the lubricant medium, and regulating the shear resistance. Under dry friction conditions, although the friction reduction is reduced, the abrasive storage and surface protection mechanisms are still effective in reducing the frictional torque and improving the wear resistance of the material. In contrast, the circular weave has an advantage in low-load lubrication-dominated conditions, but the performance degradation is significant under heavy load conditions, while the rectangular weave has a limited friction reduction due to the poor lubrication stability caused by the structural design which is not conducive to the continuous establishment of the lubrication film.

3.3. Wear Characteristics

3.3.1. Wear Volume Comparison

Figure 9 compares the wear volumes of disk specimens under different conditions. In soft formation, the untextured specimen exhibited the highest wear, while the shark denticle-inspired texture reduced wear to 4.6 mg, a decrease of 24.6%. Circular and rectangular textures also reduced wear compared to the untextured surface, indicating enhanced wear resistance from texture design.

In medium-hard formation, wear on the shark denticle-inspired specimen decreased further to 3.4 mg, 32% lower than the untextured specimen, demonstrating superior wear resistance. Circular and rectangular textures showed slightly higher wear than the shark-denticle design, confirming its optimal performance under moderate loading.

In hard formation, the shark denticle-inspired specimen reduced wear to 1.3 mg, representing a 35% decrease relative to the untextured surface. The rectangular texture also reduced wear to 1.8 mg, slightly lower than the untextured case, whereas the circular texture exhibited increased wear, suggesting failure of its protective mechanism due to stress concentration or film rupture.

Under dry sliding, wear increased significantly. The untextured specimen lost 26 mg, compared with 23.6 mg for the shark denticle-inspired specimen, a modest reduction of 9.2%, indicating that texture effectiveness is limited without lubrication.

Under different rock formation conditions, the shark-like shield-scaled weaving structure exhibits significant anti-wear performance. In soft rock formations, wear was reduced by 24.6%; in medium-hard rock formations, by 32%; and in hard rock formations, by 35%. These results indicate that the shark-like shield scale fabric effectively reduces wear by optimizing lubricant film thickness, storing lubricant media and providing secondary lubrication support. Under dry friction conditions, wear was reduced by 9.2%, indicating that it is effective in reducing wear by storing and retaining abrasive debris, despite its limited ability to resist wear in an unlubricated condition. Overall, the Shark Shield Scale Woven Structure demonstrated excellent wear resistance in all conditions, with the best results in medium to heavy-duty conditions.

3.3.2. Wear Depth Comparison

Wear depths under different lubrication conditions are summarized in Figure 10. Under grease lubrication, the shark-denticle specimen’s maximum wear depth was 12.28 μm, 32% lower than the untextured surface’s 18.1 μm. The circular and rectangular textures had depths of 21.3 μm and 20.2 μm, 17.7% and 11.8% higher than the untextured specimen.

The shark-denticle specimen’s average wear depth was 2.76 μm, 25.6% lower than the untextured surface’s 3.71 μm. The circular and rectangular textures recorded 3.16 μm and 3.39 μm, corresponding to reductions of 14.8% and 8.6%, respectively. These results confirm the superior surface protection mechanism of the shark denticle-inspired texture under grease lubrication.

In dry sliding, however, the maximum and average wear depths of the shark denticle-inspired specimen increased sharply to 60.25 μm and 40.35 μm, both higher than those of the untextured surface. This suggests that lubrication failure and texture-induced stress concentrations exacerbate wear and may trigger localized spalling.

In summary, under the grease lubrication condition, the maximum wear depth of the imitation sharkscale shield fabric samples is 32% lower than that of the non-weave samples, and the average wear depth is 25.6% lower, which is significantly better than that of the circular and rectangular fabric samples. The wear reduction effect is due to the wedge-shaped micro-bearing effect formed by the weave to enhance the fluid dynamic pressure bearing, and at the same time, it has the function of oil storage and secondary lubrication to maintain the stability of the oil film, and reduce the secondary wear through the abrasive particles trapping effect, which significantly improves the anti-wear performance. In dry friction, the lubrication film failure leads to the disappearance of the dynamic pressure and oil storage function of the fabric, and the stress concentration at the edges leads to the spalling of the material, which in turn increases the wear depth. In conclusion, the shark-like shield fabric has significant wear reduction and surface protection effects under sufficient lubrication conditions, but the fabric parameters need to be optimized to suppress the stress concentration effect in lubrication failure conditions.

To provide a clearer comparison of the tribological performance between the shark denticle-inspired specimen and the untextured specimen, the key experimental results are summarized in

Table 5. Comparison of tribological performance parameters between shark denticle-inspired and untextured specimens under different working conditions.

Loading Conditions	Loading Conditions	RPM Working Conditions	Friction Coefficient Reduction	Friction Torque Reduction	Amount of Wear Reduction	Depth of Wear Reduction
Grease-lubricated condition	Low-load conditions	200 rpm	19.2%	20.4%	24.6%	25.6%
		300 rpm	19.6%	20.1%
	Medium-load conditions	120 rpm	26.7%	32%	32%
		180 rpm	33.1%	38%
	Heavy-duty conditions	60 rpm	14.1%	17.1%	35%
		100 rpm	24.1%	23.7%
Dry friction state			7.6%	7.9%	9.2%	−184.1%

. This summary includes the measured values of friction coefficient, friction torque, and wear rate under both lubricated and dry conditions, offering a direct overview of the overall performance improvement achieved by the biomimetic texture.

3.4. Surface Morphology Analysis

Figure 11 illustrates the surface morphologies of different specimens after testing under hard rock conditions. The untextured specimen, shown in Figure 11a, displayed wide, continuous annular wear scars, indicating that abrasive particles were difficult to expel and plowing dominated. Moreover, the absence of microstructural regulation prevented stable lubricant retention, concentrating wear in the main sliding zone. In contrast, the shark denticle-inspired specimen, shown in Figure 11b, exhibited no obvious scars, with texture boundaries remaining distinct. The rectangular texture, shown in Figure 11c, showed less severe wear than the untextured specimen but still revealed evident wear paths. The circular texture, shown in Figure 11d, presented severe scratches and pronounced edge wear around dimples.

Three-dimensional surface morphologies are presented in Figure 12. The untextured specimen, shown in Figure 12a, exhibited typical abrasive plowing damage, characterized by continuous grooves coupled with discrete pits. The shark denticle-inspired specimen, shown in Figure 12b, retained a relatively intact distribution of asperities without evident surface destruction, confirming that it enhanced hydrodynamic lubrication and suppressed abrasive intrusion, thereby protecting surface integrity. Although the circular-textured specimen shown in Figure 12c also exhibited a certain degree of wear resistance, its performance was relatively inferior. This difference can be clearly observed from the corresponding SEM micrographs.

Under dry friction, as depicted in Figure 13, the untextured specimen, shown in Figure 13a, showed severe adhesive and tearing damage, with uneven scar distribution, large-scale material pile-up and spalling, and pronounced height differences, indicative of adhesion- and tearing-dominated wear mechanisms. In contrast, the shark denticle-inspired specimen, shown in Figure 13b, exhibited comparatively milder damage, with more dispersed scars and limited spalling. The 3D morphology showed shallower pits and partial retention of asperities, suggesting the textures aided stress dispersion and contact regulation. Though unable to maintain a stable lubricant film, the grooves likely acted as buffers and debris traps, reducing local stress concentration. This difference can be clearly observed from the corresponding SEM micrographs.

Under dry friction, the shark-denticle texture still offered superior surface protection and wear resistance compared to the untextured specimen. Although the overall wear mitigation was weaker than under lubrication, its geometric guidance and contact regulation contributed to interface protection, demonstrating practical applicability for roller cone bit bearings in extreme service conditions.

4. Conclusions

This study conducted tribological experiments to address severe wear in roller cone bit sliding bearings under low-speed, heavy-load, and boundary lubrication conditions. An equivalent pin–disk model was used to evaluate the tribological performance of shark-denticle, rectangular, circular, and untextured specimens under lubricated and dry conditions, focusing on the friction coefficient, torque, wear, and surface morphology. The main conclusions are as follows:

• The shark denticle-inspired texture exhibited pronounced friction- and wear-reduction advantages under complex loading conditions. Compared with the untextured specimen, the maximum reductions in friction coefficient, friction torque, and wear volume reached 33.1%, 38.3%, and 35%, respectively. In contrast, the rectangular and circular textures showed poor adaptability, with lubrication instability under some conditions.
• Under dry friction, the shark denticle-inspired texture still retained a certain degree of friction-reducing capability. Although its wear depth was relatively high, the friction coefficient and torque decreased by 7.6% and 7.9%, respectively, compared with the untextured specimen, and the surface integrity was better preserved in the absence of lubrication.
• The shark denticle-inspired texture provided a degree of surface protection. Under lubricated conditions, it facilitated the formation of a regular lubrication interface, effectively reducing abrasive intrusion and plowing. During lubrication failure, it guided debris away from the contact zone, suppressing adhesive delamination and plastic deformation.

The findings confirm the potential of shark denticle-inspired textures in improving the tribological performance of roller cone bit bearings and provide valuable insights for advancing the engineering application of bionic tribology in petroleum equipment. Moreover, the results offer important theoretical guidance for the design and optimization of surface textures in fluid-lubricated contact systems, demonstrating how biomimetic microstructures can effectively regulate stress distribution, promote hydrodynamic pressure generation, and mitigate wear evolution. Although the present study demonstrates that such textures can significantly reduce friction, torque, and wear under both lubricated and dry conditions, certain limitations remain. The current experiments were conducted under relatively short-duration and controlled laboratory conditions. Future work will focus on evaluating the long-term tribological behavior and durability of these textures under extended dry sliding and cyclic loading conditions, as well as optimizing texture geometry and scale to further enhance bearing performance in actual drilling environments.