Biomimetic Non-smooth Surface Research Articles

Simulation Study on Bearing Lubrication Mechanism and Friction Characteristics of the Biomimetic Non-Smooth Surface of a Cross-Scale, Second-Order Compound Microstructure

The reasonable design of biomimetic non-smooth surfaces is a novel and effective way to solve problems such as the poor lubricity and serious friction and wear of friction pairs of seawater axial piston pumps. Inspired by cross-scale, second-order compound microstructures on the surfaces of some living organisms, a hydrodynamic lubrication model of a slipper pair with a surface featuring spherical pits containing spherical convex hulls was built. This study analyzed the bearing lubrication mechanism and friction characteristics of cross-scale, second-order compound microstructure from the microflow perspective via the CFD method and optimized the working and geometric parameters using a hybrid orthogonal test scheme. The study’s results show that the cross-scale, second-order compound microstructure can produce a superimposed hydrodynamic pressure effect to improve the bearing capacity of the lubrication film of a slipper pair, reducing the friction coefficient. The orders of factors (the working parameter and geometric parameters) under multiple indices (the total pressure-bearing capacity and the friction coefficient) were found. The optimal combination is a spherical pit with a first order diameter of 0.7 mm, a first order depth-to-diameter ratio of 0.1, an area rate of 20%, an arrangement angle of α/3 and a spherical convex hull with a second order diameter of 0.13 mm, and a second order depth-to-diameter ratio of 0.3. Compared to a smooth surface and a first-order, non-smooth microstructure, the cross-scale, second-order compound microstructure has an 11.0% and 8.9% higher total pressure-bearing capacity, respectively, and the friction coefficient decreased by 9.5% and 5.4%, respectively.

Transpiration cooling with bio-inspired structured surfaces

Transpiration cooling is considered to be one of the most effective cooling methods for protecting components from ablation in extremely high temperature environments, so improving transpiration cooling efficiency is quite useful in practical applications. Living creatures always have the optimal properties for cooling after long-term evolution. This study proposes a novel transpiration cooling concept using a biomimetic non-smooth surface inspired by the earthworm’s rough skin. The transpiration cooling efficiencies of porous plates with three different bio-inspired non-smooth surfaces - isosceles-trapezoid, right-angled-trapezoid and parallelogram grooves -are numerically investigated. The numerical model is validated by experimental data. The structure of the non-smooth surface dramatically affects the film thickness and surface heat convection intensity of transpiration cooling. The cooling efficiency is significantly improved by the parallelogram style non-smooth surface. The bio-inspired non-smooth surface successfully thickens the protective film and achieves a significantly better cooling performance. The protective film of transpiration cooling is thickened 22.7% while the transpiration cooling efficiency is significantly increased by 12% with the assistance of the bio-inspired non-smooth surface.

Effect of Composition on the Mechanical Properties and Wear Resistance of Low and Medium Carbon Steels with a Biomimetic Non-Smooth Surface Processed by Laser Remelting

To study the effect of laser biomimetic treatment on different material compositions, five kinds of steels with different carbon element contents were studied by laser remelting. The characteristics (depth, width), microstructure, hardness, tensile properties, and wear resistance of the samples were compared. The results show that when the laser processing parameters are fixed, the characteristics of the unit increase with an increase of carbon element content. Moreover, the hardness of the unit also increases. Compared with the untreated samples, when the carbon content is 0.15–0.45%, the tensile strength of the laser biomimetic samples is higher than that of the untreated samples. For the biomimetic samples with different carbon content, with an increase of carbon content, the tensile strength increases first and then decreases, while the plasticity of the biomimetic samples decreases continuously. The bionic samples have better wear resistance than that of the untreated samples. For bionic specimens with different carbon elements, wear resistance increases with an increase of carbon element content.

Friction and Wear Study on Friction Pairs with a Biomimetic Non-smooth Surface of 316L Relative to CF/PEEK under a Seawater Lubricated Condition

Current studies of a seawater axial piston pump mainly solve the problems of corrosion and wear in a slipper pair by selecting materials with corrosion resistance, self-lubrication, and wear resistance. In addition, an appropriate biomimetic non-smooth surface design for the slipper pair can further improve the tribological behavior. In this paper, 316L stainless steel and CF/PEEK were selected to process the upper and bottom specimens, and the biomimetic non-smooth surface was introduced into the interface between the friction pair. The friction and wear tests were performed on a MMD-5A tester at a rotation speed of 1000 r/min and load of 200 N under seawater lubricated condition. The results indicate that the main friction form of the smooth surface friction pair corresponds to abrasive wear and adhesive wear and that it exhibits a friction coefficient of 0.05–0.07, a specimen temperature of 56 °C, a high wear rate, and surface roughness. Pits on the non-smooth surface friction pairs produced hydrodynamic lubrication and reduced abrasive wear, and thus the plowing effect is their main friction form. The non-smooth surface friction pairs exhibit a friction coefficient of 0.03–0.04, a specimen temperature of 48 °C, a low wear rate, and surface roughness. The study has important theoretical significance for enriching the lubrication, friction, and wear theory of a seawater axial piston pump, and economic significance and military significance for promoting the marine development and the national defense military.

Simulation on Wear-Resisting of Biomimetic Brake Disc/Pad Coupling System

Based on design dimensions for particular concaves distributed non-smooth surface, the biomimetic brake disc/pad coupling system model is established, and the wear resistant performance of biomimetic non-smooth surface brake disc/pad coupling system is simulated using finite element analysis, then compared with analysis result of smooth model. Result shows the Von Mises stress of biomimetic non-smooth sample is less than that of smooth sample, and the concaves improve the contact stress distribution in the contact area of brake disk and brake pad. Analysis results show that wear resistant performance of biomimetic non-smooth sample is better than that of smooth specimen.

The comparative study of thermal fatigue behavior of H13 die steel with biomimetic non-smooth surface processed by laser surface melting and laser cladding

According to previous studies, the thermal fatigue behavior of hot-work tool steel with biomimetic non-smooth surface treated by laser surface melting (LSM) gets a significant improvement. However, the properties of LSM non-smooth unit degenerate during thermal cycles. In order to improve the properties of non-smooth unit during thermal cycles, laser cladding (LC) was employed to fabricate the non-smooth unit. Before and after thermal fatigue testing, the microstructure and microhardness of non-smooth unit treated by LSM and LC have been investigated. The results showed that the non-smooth sample processed by LC is more effective to improve thermal fatigue behavior than that treated by LSM. During the thermal fatigue testing, LC non-smooth unit had better resistance to thermal cycles softening compared with LSM non-smooth unit. After thermal fatigue testing, a distinct change of the microstructure of LSM non-smooth unit was detected, i.e., the grains of the non-smooth unit became coarsening obviously. However, the microstructure of LC non-smooth unit was not changed significantly after thermal fatigue testing.

Effects of striated laser tracks on thermal fatigue resistance of cast iron samples with biomimetic non-smooth surface

In order to enhance the thermal fatigue resistance of cast iron materials, the samples with biomimetic non-smooth surface were processed by Neodymium:Yttrium Aluminum Garnet (Nd:YAG) laser. With self-controlled thermal fatigue test method, the thermal fatigue resistance of smooth and non-smooth samples was investigated. The effects of striated laser tracks on thermal fatigue resistance were also studied. The results indicated that biomimetic non-smooth surface was benefit for improving thermal fatigue resistance of cast iron sample. The striated non-smooth units formed by laser tracks which were vertical with thermal cracks had the best propagation resistance. The mechanisms behind these influences were discussed, and some schematic drawings were introduced to describe them.

Effects of pre-placed coating thickness on thermal fatigue resistance of cast iron with biomimetic non-smooth surface treated by laser alloying

In order to enhance the thermal fatigue resistance of gray cast iron with biomimetic non-smooth surface further, studies on laser alloying of Cr powder with different pre-placed coating thickness were performed to change both the composition and the microstructure of non-smooth unit. Additionally, the optimization of coating thickness was done based on the content of Cr in alloyed zone and the thermal fatigue behaviors of non-smooth samples. The results indicated that there was a critical coating thickness which corresponded to the increase of Cr content in alloyed zone under a definitive laser processing conditions, and the critical thickness was 0.3 mm in this paper. Any coating thicker than 0.3 mm would lead to the waste of alloying powder. The thermal fatigue resistance of non-smooth samples was better than that of smooth sample. In addition among all the non-smooth samples, the sample which was treated by the laser alloying of Cr had superior resistance to thermal fatigue compared with laser melting treated samples. And the thermal fatigue resistance increased with increasing of Cr content in alloyed zone which was caused by pre-placed coating thickening.

Study on preheating and annealing treatments to biomimetic non-smooth cast iron sample with high thermal fatigue resistance

According to the previous studies, biomimetic non-smooth samples fabricated by laser melting had superior resistance to thermal fatigue compared with smooth sample. In order to improve the treating technology for biomimetic non-smooth surface of cast iron samples so as to enhance their thermal fatigue resistance further, preheating and annealing were applied in the procedure. Moreover, the effects of preheating and annealing treatments on the microstructure and microhardness of the biomimetic non-smooth units were also investigated. The results indicated that the cracks and holes in non-smooth units caused by laser processing could be avoided by preheating at an appropriate temperature, and the residual stresses in non-smooth units were eliminated largely through annealing. Of all samples tested, those preheated at 250 °C during laser processing and then annealed had the best thermal fatigue resistance.

Effect of units in different sizes on thermal fatigue behavior of 3Cr2W8V die steel with biomimetic non-smooth surface

Aiming to deeply research the thermal fatigue behavior of 3Cr2W8V die steel with biomimetic surface, the specimens with different sizes of concave-shape and striation-shape units were processed by laser technique. By establishing cross-section model of the units and by calculating their volume, the size of the units was quantitatively expressed, and its effect on thermal fatigue behavior of 3Cr2W8V die steel was investigated and compared. The results showed that the units in different sizes have different degrees of effects on resisting the thermal fatigue cracks; especially those in the larger size can play a greater role in preventing the crack initiation and blocking the crack propagation; and further the influence of the size of the units on thermal fatigue behavior is more sensitive to resist the crack propagation. Based on the self-strengthening of the units, the increased resistance of the units in the larger size to crack initiation can be attributed to the crack prevention mechanism owing to the reduced probability of crack nucleation and the enhanced resistance to plastic deformation on the biomimetic surface, while the enhanced resistance to crack propagation is due to the crack blocking mechanism that results in the slow crack growth rate.

Effects of graphite shape on thermal fatigue resistance of cast iron with biomimetic non-smooth surface

In order to improve thermal fatigue resistance of cast iron and further study the effects of graphite shape on it, samples with different graphite shapes were processed by laser to create a biomimetic non-smooth surface. The results indicated that laser processed zone caused the longer crack initiation life and the slower crack propagation rate, which endowed biomimetic non-smooth surface with a beneficial effect on improving thermal fatigue behavior of iron with flake, vermiform or nodular graphite. Thermal fatigue resistance of samples with the same kind of surface (smooth or non-smooth) all were sorted as nodular graphite iron > vermicular graphite iron > flake graphite iron.

Thermal fatigue behavior of gray cast iron with striated biomimetic non-smooth surface

In order to enhance thermal fatigue resistance of brake drum materials, gray cast iron samples with biomimetic non-smooth surface were processed by laser to imitate the alternately soft and hard structure of shell nacreous layer. The key feature of this biomimetic non-smooth surface is that some parallel striations with various spacing distribute on the smooth surface of sample. With self-controlled thermal fatigue test method, the thermal fatigue behaviors of smooth and non-smooth samples were investigated and compared. The results indicated that biomimetic non-smooth surface had a beneficial effect on improving thermal fatigue resistance of samples, and the resistance of non-smooth sample which has smaller spacing of striations is the best in the experiment. Function of non-smooth unit such as the resistance to initiation and propagation of thermal crack is the main reason for improved thermal fatigue property of gray cast iron.

Effects of C content on the thermal fatigue resistance of cast iron with biomimetic non-smooth surface

In order to improve thermal fatigue resistance of brake drum materials, cast iron samples with biomimetic non-smooth surface were processed by laser to imitate the alternately soft and hard structure of nacreous layer. In addition, C contents were adjusted for further investigating the effect on thermal fatigue resistance of non-smooth sample. The results indicated that biomimetic non-smooth surface had a beneficial effect on improving thermal fatigue behavior of samples with different C contents, and non-smooth sample with 3.7% C contents had the best enhanced degree of thermal fatigue resistance comparing with smooth sample which has the same C content.

Effects of surface shape on thermal fatigue resistance of biomimetic non-smooth cast iron

According to the principle of bionics, the experimental samples with a biomimetic non-smooth surface were manufactured using a laser. Three kinds of shapes including ‘spot’, ‘striation’ and ‘lattice’, were chosen for forming the non-smooth surface. With the self-controlled thermal fatigue test method, the thermal fatigue behavior of smooth and non-smooth samples was investigated and compared. The results indicated that the biomimetic non-smooth surface had a beneficial effect on improving the thermal fatigue behavior of gray cast iron, and that the non-smooth sample with the lattice shape had the highest resistance to thermal fatigue. Compared to the base material, the non-smooth unit zone was characterized by the alteration of microstructure. The lack of the graphite phase, the enhancing of mechanical properties in the unit zone and the effects of thermal crack deflection are the main reasons for improving the thermal fatigue resistance of gray cast iron with the biomimetic non-smooth surface.

The thermal fatigue resistance of cast iron with biomimetic non-smooth surface processed by laser with different parameters

Thermal fatigue cracks occur frequently on the brake drums’ surface, and this phenomenon leads to their premature failure. In order to improve their thermal fatigue resistance, according to the principles of biomimetic non-smooth surface, through processing striate units on the surface of cast iron samples by laser with different parameters, the thermal fatigue performances of smooth and non-smooth samples were investigated, respectively. The rules which laser parameters effected thermal fatigue resistance of non-smooth samples were analyzed. The results indicated that non-smooth surface could decrease thermal crack quantity and their propagation rates; thermal fatigue resistance was improved by processing non-smooth units on sample's surface. Different sizes of non-smooth units were obtained by adjusting laser parameters. The bigger non-smooth units resulted in better thermal fatigue resistance. Furthermore, the mechanisms of enhanced thermal fatigue resistance were studied.