Density Of Dimples Research Articles

Effect of different laser texturing patterns on rolling contact surface and its tribological & fatigue life behavior on 100Cr6 bearing steel

The effects of laser texturing technology on the tribological performance of tapered roller bearings in terms of fatigue life, friction, and wear are studied for the first time. The influence of diameter, height and density of the circular-shaped dimples is thoroughly analyzed, first on flat samples, and the most encouraging results are upscaled to components. This research demonstrates the advantages that surface texturing can bring to the most demanding applications involving rolling surfaces under lubrication regime. The experiments show a torque reduction up to 18% and very promising results in fatigue life tests.

Development of energy efficient structured plates with zigzag arrangement of multirow inclined oval trench dimples

A numerical study of the anomalous intensification of the turbulent heat transfer is performed for the initial hydrodynamic section of a long flat plate with a single row dense package of 16 inclined Oval Trench Dimples (OTD). Multiblock overlapping grids are used to solve Reynolds-Averaged Navier-Stokes (RANS) equations in the framework of VP2/3 in-house code. Firstly, applicability of RANS approach is confirmed by thorough comparison against the experimental measurements of the pressure distributions for a single inclined OTD mounted on a flat plate. Then, the dense package of OTD with the inclination angle of 60° is compared against Spherical Dimple (SD) at the same Reynolds number of 6000 based on the trench width and for the same trench depth and relatively high density of dimples. For OTD a progressive increase of the pressure drop is observed between the zone of deceleration of the free flow and the zone of low pressure near the inlet of spherical segments, where a tornado-like vortex is developed. Moreover, a gradual amplification of the reverse secondary flow is observed for OTD resulting in the minimum relative friction coefficient of −4 and the maximum relative Nusselt number of 4.4. Finally, acceleration and substantial thinning of the boundary layer above the upstream part of the OTD are observed. A new type of energy-efficient structured surfaces ready for additive technologies is proposed and justified for heat exchangers.

Effect of Textured Dimples on the Tribological Behavior of WC/Co Cemented Carbide in Dry Sliding with Al2O3/WC Ceramic

Micro-dimples were fabricated on the surface of WC/Co cemented carbide disks by laser, and dry friction tests were carried out by sliding with Al2O3/WC ceramic balls. Results show that the textured cemented carbide can reduce the average friction coefficient by about 30% compared to the smooth sample, while the textured cemented carbide with solid lubricants can reduce the average friction coefficient by about 50%. The density of textured dimples has no obvious influence on the friction coefficient. The wear rates of worn ceramic balls continue to decline with the increase in sliding speeds. The wear rates of the ceramic balls can be reduced by 40~50% for textured samples and about 65% for textured samples with solid lubricants compared to the untextured ones. The mechanism for improving the tribological properties of cemented carbide materials is that the textured dimples can store lubricants and capture wear debris, which would play an important role in promoting the engineering application of surface texturing in cemented carbide materials.

Effect of layered heterogeneous microstructure design on the mechanical behavior of medium carbon steel

A heterogeneous microstructure composed of multiscale ferrite (spanning ultrafine, fine, and coarse grains) and granular or short rod cementite was obtained by warm rolling pseudoeutectoid microstructure. Combined with the short-time annealing process, the deformation tendency of ferrite grains and the dissolution and precipitation of cementite were adjusted. The mechanical properties of medium carbon steel are close to that of low alloy high strength steel. It was found that the GNDs are distributed in a gradient at the interface of the soft domain, and the closer to the boundary the higher the density, which contributes to the occurrence of the hetero-deformation induced (HDI) hardening mechanism and provides additional strength and plasticity. The increase in elongation of the annealed samples is due to the recrystallization of ferrite and the redistribution of cementite, which realizes the combination of HDI mechanism, Orowan strengthening and annealing softening mechanism. Additional strengthening mechanisms are calculated and a physical model of cementite ripening during annealing is proposed. The tensile fracture shows that the cracks mainly propagate along the grain boundaries of the layered microstructure, and the high density of dimples can make the propagation path of the cracks tortuous and increase the elongation.

Response of Ti6321 titanium alloy at different strain rates under tensile loading

To investigate mechanical properties of Ti6321 titanium alloy, tensile tests at different strain rates are carried out. The changes of microstructure and properties at the range of 10−3 s−1–105 s−1 have been studied. Lower density and larger size of dimples produce when stretched at high strain rates of 103 s−1 compared to quasi-static stretching. The yield strengths of the alloy are 805, 1096 and 2440 MPa at strain rates of 10−3 s−1, 2 × 103 s−1 and 105 s−1, respectively with obvious strain rate strengthening effect. At 105 s−1 strain rate, parallel twins generate at grain boundaries to coordinate the deformation when dislocations cannot meet indicating the twinning mechanism comes into play.

Critical assessment of the strain-rate dependent work hardening behaviour of AISI 304 stainless steel

Abstract In the present work, the effect of strain rate on the micro-mechanism of plastic deformation and ensuing work hardening behaviour of AISI 304 stainless steel has been critically investigated. The defining role of the early stage of deformation ( γ → α ′ in 3% strained specimen at HSR was higher contributing to lower transition strain from stage 1 to 2 of work hardening compared to SSR, the extent of work hardening was higher in the latter case during the stage 2 due to a combined effect of extensive twinning and deformation induced martensite formation, which was limited in HSR due to occurrence of cross-slip. These differences in the work hardening mechanisms were manifested as an improvement in UTS/YS ratio from 2.66 to 2.99 in HSR and SSR specimens, respectively. Furthermore, changes in the mechanism of plastic deformation was also reflected as ~4 fold increase in dislocation density for SSR specimen compared to HSR specimen at any given strain level and nearly 27% increase in hardness at the point of fracture. A significant improvement in UTS/YS ratio and ductility for SSR specimen left its signature on the fracture surface in form of three-fold increase in the number density of finer dimples compared to HSR specimen.

Effect of Shape, Density, and an Array of Dimples on the Friction and Wear Performance of Laser Textured Bearing Steel under Dry Sliding

The present study is directed to reveal the effect of density and shape of the dimples on the friction and wear characteristics of textured bearing steel (100Cr6) under dry sliding conditions. One untextured and four laser-textured disks of 100Cr6 steel with circular and bi-triangular dimples having 7 and 20% density, respectively, in the spiral layout were tested using a pin-on-disk unidirectional tribometer against a 100Cr6 pin having a flat surface with rounded corners under flat-on-flat configuration. The tests were carried at different speeds of 0.2, 0.6, and 1 m/s at a constant load of 15 N. The results indicate that a higher density of bi-triangular dimples had less wear and a lower coefficient of friction compared to untextured disk or disk with circular dimples, particularly at a relatively higher speed. This has been attributed to a relatively higher number of dimples in the contact zone in case of a spiral array, which increases the entrapment of more wear particles leading to a reduction in wear. The friction coefficient had a relatively higher value at a relatively lower speed but decreased at the highest speed of 1.0 m/s used in the present study. The results suggest that dimples may not be too effective under dry contact because they lose their effectiveness to trap wear debris after getting filled.

High‐Temperature Tensile Fractography of Zr‐, Ni‐, and Mn‐Containing Al‐Si‐Cu‐Mg Cast Alloys

This study investigated the fracture behavior of 0.3% Zr‐containing 354 alloy following the addition of 0.75% Mn or 2%Ni. The examined surfaces were obtained from tensile testing of the bars at 250°C. For each alloy, the test bar samples were examined in the T6‐treated conditions after being exposed to 250°C for 1 and 200 hours. The fracture surface of the base alloy (0.3% Zr‐containing 354 alloy) after stabilization for one hour at 250°C reveals a dimpled structure throughout, indicating the ductile nature of the fracture mode. The Alx (Zr, Ti)Si complex compound is observed with star‐like and blocky morphologies, with cracks appearing in various particles of this compound. By increasing the stabilization time up to 200 hours, coarser and deeper dimples are formed, highlighting the increased ductility of the alloy due to the softening behavior associated with the prolonged exposure at 250°C. In the one‐hour stabilized T6‐treated condition alloy containing 2% Ni tested at 250°C, the appearance of microcracks in the Ni‐rich phases and the lower density of dimples on the fracture surface compared to those observed in the base alloy emphasize the low ductility of alloy due to Ni‐containing intermetallics. Examination of the fracture surface of Mn‐containing alloys revealed the advantageous role of sludge particles in resisting the propagation of cracks that developed in many intermetallic phases.

Design and Development of Surface Texture for Tribological Application

Surface texturing is a process of fabricating specific patterns on a surface to enhance surface properties such as friction, contact area, air aspiration, wear, hydrophobicity, etc. Fabricating surfaces with planned micro features is an effective method to improve tribological performance of the interacting surfaces. Laser surface texturing process is one of the best suitable processes for producing micro-patterns. Micro textures are imparted on HSS discs using CO2 laser, varying the shape and dimensions of the resulting dimples affecting the frictional coefficient and wear. Experiments have been accomplished to determine effects of textural variations such as areal density of dimples, dimple shape, area of dimples and depth of dimples on the Coefficient of Friction (COF) and Wear. Effects of lubrication conditions (Dry and Wet), pin material (MS, SS, EN31), applied load (25N, 50N, 75N) and Sliding velocity (400 rpm, 800 rpm and 1200 rpm) are evaluated on COF and Wear. Tests have been performed on pin-on-disk apparatus along guidelines of Taguchi L18 Orthogonal Array, keeping constant sliding distance of 940 m (about 10,000 cycles). Experimentally, it is found that wet lubricated, circular shaped dimples, with areal density 7.5%, dimple area 0.09 mm2 with MS material pin provides best results. This experimental analysis has been performed to test the applicability, efficiency and reliability of the textured surfaces.

Effect of local laser surface texturing on tribological performance of injection cam

The camshaft is a crucial component of an engine’s valve train. This paper devotes to the experimental studies of the performance of laser surface textured (LST) camshaft. The first part experiment was carried out on the block-on-ring tester to investigate the tribological behaviors of textured surface in line contact. The area density of the textured dimples was in the range 3–40% with depths 5–24 μm and diameter 70 μm. The friction coefficient and wear tracks were analyzed to confirm the optimum textured patterns. After that, the local LST cams (textured on the lifting region) were further tested in a single-cylinder diesel. It was found that after 300 h durability test at the rated speed and load, the total lifting loss of cams decreased nearly 34.4% in maximum. In addition, the performance of the engine was not affected evidently. The enhanced lubricity and local hardening were two mechanisms for highly promoting the anti-wear property of the LST cams.

Characterization and friction behavior of LST/PEO duplex-treated Ti6Al4V alloy with burnished MoS2 film

Laser surface-textured Ti6Al4V substrate was treated by plasma electrolytic oxidation process to prepare an oxide ceramic coating and then burnished with a thin MoS2 film. The area densities of textured dimples and the surface roughness of oxide ceramic underlay which affected the longevity of MoS2 films were thoroughly investigated. The results showed that a mixed surface pattern combining large textured dimples (diameter 150μm) with small discharged dimples (diameter 5–17μm) was fabricated by the LST/PEO duplex treatment and it contributed to prolonging the lubricating life of MoS2 film in comparison to the LST or PEO treatment. Wherein, the mixed dimples acted as lubricant reservoirs and the hard oxide coatings provided high load supports for the lubricating films. A much longer life of low friction was provided by the LST/PEO/MoS2 coatings with higher density of textured dimples (S=55%) and lower roughness of LST/PEO surface (Ra=1.0μm).

An overview of geometrical parameters of surface texturing for piston/cylinder assembly and mechanical seals

Surface texturing has been effectively used to improve tribological performance of sliding surfaces. Reduction in friction, increase in hydrodynamic load carrying capacity, reduction in wear and increase in fluid film stiffness are few examples of the benefits that can be obtained by surface texturing. In order to obtain these benefits, several researchers have investigated the effects of surface texturing geometrical parameters on the performance of different applications. If these geometrical parameters are not optimized for each application, they may have detrimental effects on their performance. These geometrical parameters in case of micro dimples include depth, diameter, depth to diameter ratio, shape and density of dimples. In this paper, the author reviews the effects of these geometrical parameters on the performance of two applications piston ring/cylinder assembly and mechanical seals.

Numerical Analysis the Tibological Performance of a Laser Surface Textured Mechanical Seal

This paper presents a numerical study of the effects of surface structure geometrical parameters on the tribological performance of a laser surface textured mechanical seal. Seal performance such as seal clearance which is corresponding to hydrodynamic effect and friction torque is calculated for a range of sealed pressures, dimples area density and dimple depth over dimple diameter ratio. The results indicated that laser surface textured mechanical seals substantially improve the tribological performance in the lower sealed pressure than in high pressure. Area density of dimples has little effect on the tribological performance, however, dimple depth over dimple diameter ratio has significant effect on the tribological performance.

Evolution of Surface Morphology in Ni(γ)/Ni<sub>3</sub>Al(γ´) Two-Phase Foil during Electrochemical Etching

Evolution of surface morphology in Ni(γ)/Ni3Al(γ´) two-phase foil of binary Ni-18 at.%Al was examined during the electrochemically selective etching in the electrolyte of distilled water including 1 wt.% (NH4)2SO4 and 1 wt.% citric acid. In the early stage (0.5 h), only the γ matrix was etched and the outmost γ´ particles were protected by a preexisting surface product. As the γ matrix was etched more, the side surfaces of the outmost γ´ particles and the γ´ particles that were located inside were exposed in the electrolyte. They were dissolved, and had a high density of fine dimples. However, the dissolution rate of the γ´ particles was slower than that of the γ matrix and thus the selective etching was retained in this stage. Finally, at 5h, more γ´ particles were exposed and the flat and smooth surfaces of the outmost γ´ particles were completely eliminated by the dissolution on the side surfaces. From these observations plus the saturation of the current density observed in the electrochemical test, we concluded that the change in the surface morphology was finished at this stage. Thus, the surface became more rough and irregular, which resulted from the original two-phase microstructure and the fine dimple structure by transpassivation.

An experimental study on the dynamic fracture of extruded AA6xxx and AA7xxx aluminium alloys

The dynamic fracture behaviour of extruded AA6xxx and AA7xxx aluminium alloys is investigated using an instrumented Charpy test machine and V-notch specimens. The specimens are made from extruded flat profiles with a rectangular cross-section of 10 mm thickness and 83 mm width. The material is in T6 temper, i.e. the peak hardness condition. The alloys have either recrystallized or fibrous grain structure. For each alloy six different Charpy impact tests are carried out in two series. In Series 1, the notch is parallel to the thickness direction of the profile (i.e. through the thickness), while the notch is perpendicular to the thickness direction in Series 2 (i.e. lying in the plane of the flat profile). In each series, the longitudinal direction of the specimen is parallel, 45° or 90° to the extrusion direction. Comprehensive fractographic investigations are carried out for the different tests and alloys. It is found that the dissipated energy is practically invariant to specimen orientation and notch direction for the recrystallized alloy. For the fibrous alloys the dissipated energy is lower when the longitudinal direction of the specimen is 90° to the extrusion direction, i.e. when the notch is parallel with the fibrous grain structure. Further, the energy dissipation is higher for Series 2 than for Series 1 due to substantial delamination and secondary cracking in Series 2. The precipitate-free zones (PFZs) formed adjacent to the grain boundary are weak areas, preferable for crack initiation and growth. This is seen in the fracture surface as facets with high density of small dimples and is more pronounced for specimens with the notch parallel to the fibre direction.

Effect of hot plastic deformation on microstructure and mechanical property of Mg-Mn-Ce magnesium alloy

Hot plastic deformation was conducted using a new solid die on a Mg-Mn-Ce magnesium alloy. The results of microstructural examination through OM and TEM show that the grain size is greatly refined from 45 μm to 1.1 μm with uniform distribution due to the occurrence of dynamic recrystallization. The grain refinement and high angle grain boundary formation improve the mechanical properties through tensile testing with the strain rate of 1.0 × 10−4 s−1 at room temperature and Vickers microhardness testing. The maximum values of tensile strength, elongation and Vickers microhardness are increased to 256.37 MPa, 17.69% and HV57.60, which are 21.36%, 133.80% and 20.50% more than those of the as-received Mg-Mn-Ce magnesium alloy, respectively. The SEM morphologies of tensile fractured surface indicate that the density and size of ductile dimples rise with accumulative strain increasing. The mechanism of microstructural evolution and the relationship between microstructure and mechanical property of Mg-Mn-Ce magnesium alloy processed by this solid die were also analyzed.

Plastic deformation and fracture response of 304 stainless steel subjected to dynamic shear loading

This paper describes an experimental investigation into the effect of strain rate on the plastic and fracture response of 304 stainless steel subjected to dynamic shear deformation by a torsional split Hopkinson bar in the strain rate range 102 s-1 to 3 × 103 s-1. Results indicate that dynamic shear response and fracture characteristics of 304 stainless steel depend strongly on applied strain rate. The yield and failure strength as well as the fracture strain increase with strain rate. It is also found that increasing strain rate increases work hardening, strain rate sensitivity, and deformation heat. However, the inverse tendency is observed for activation volume. The observed shear response can be described by the Kobayashi-Dodd constitutive relation. Good agreement is found between predicted and measured data. Fractographic analysis shows that localised shearing failure is predominant under all deformation conditions. The fracture surface consists of dimples, typical of ductile materials. Increasing the strain rate increases both density and depth of dimples, verifying that the fracture strain increases with strain rate. The presence of deformed shear bands confirms the existence of instability in the form of unstable flow due to flow localisation. Within the deformed shear bands, the deformation is not homogeneous and the grains are heavily distorted, resulting in enhancement of microhardness.