Concave Dimples Research Articles

Effect of surface patterning on frictional heating of vitamin E blended UHMWPE

Friction between articulating surfaces cause temperature rise in the acetabular cup and femoral head. This heating may influence the rate of wear, fatigue, creep and oxidative degradation of bearing materials. The objective of this study is to determine the effect of surface patterning on frictional temperature rise of the articulating surfaces of vitamin E blended ultra-high molecular weight polyethylene acetabular component paired with a cobalt–chromium (CoCrMo) femoral component. For this reason concave dimples were formed on inner surface of the acetabular cup with 0.5mm diameter and 0.5mm depth. Temperature rise between the bearing surfaces was measured under different loading conditions. Frictional measurements of the joints were carried out on a custom made hip joint friction experimental set up. The prostheses were of 28mm diameter. Applied static loads were changed from 200N to 1500N. In the flexion–extension plane, a simple harmonic oscillatory motion between ±24° was applied to the ultra high molecular weight polyethylene acetabular component. The frequency of motion was 1Hz and the tests were run up to 11,000 cycles. Temperature rise in acetabular and femoral component was recorded with embedded thermocouples. Lower temperature rise in patterned sample pairs were measured than unpatterned samples. So it can be said that the surface patterning contributes to reduction of frictional heating of sliding surfaces.

Self-assembled porous templates allow pattern transfer to poly(dimethyl siloxane) sheets through surface wrinkling

Euler buckling forms surface microwrinkles ranging in size from sub-micrometers to tens of micrometers as a result of the modulus difference between the surface of the material and the material itself. When the buckling occurs in the limited areas smaller than the wrinkle wavelength, the shape of the buckled surface deforms into concave dimples or convex lenses. The shape of the buckled surface can be controlled by changing the modulus of poly(dimethylsiloxane). Hierarchical patterning by using a photomask was also achieved. This process provides a novel way to pattern soft substrates, including elastomers and gels.

The influence of concave dimples on the metallic counterface on the wear of ultra-high molecular weight polyethylene

The aims of this study were to investigate how the dimples on a metallic counterface affect the wear rate of ultra-high molecular weight polyethylene (UHMWPE) in a multi-directional reciprocating pin-on-plate machine. The plates were high nitrogen stainless steel, representing the femoral head material. The pins used in this study were of ultra-high molecular weight polyethylene GUR 1120, which represents the material used in an acetabular cup. Three different cases were investigated: a smooth surface without dimples as a reference case, a surface with medium dimples with an average valley of 2.3 µm and a surface with large dimples with an average valley of 5.9 µm. It was found that all the dimples investigated did not improve the lubrication, but instead increased the surface roughness; consequently, the wear of UHWMPE was slightly increased.

Measurements of the Effectiveness of Concave Spherical Dimples for Enhancement Heat Transfer

Measurements of the Effectiveness of Concave Spherical Dimples for Enhancement Heat Transfer

Biomimetic Anti-Abrasion Surfaces of a Cone Form Component Against Soil

The geometrical surfaces of soil-burrowing animals were imitated and modeled on a cone component, the measuring tip part of a soil cone penetrometer. These biomimetic surfaces are concave dimples, convex domes and two wavy forms. The conventional cone surface and the biomimetic cone surfaces were analyzed in ANSYS 11.0 program to estimate cone equivalent stress and soil equivalent stress. Results show that biomimetic surfaces with the geometrical structures have lower cone equivalent stresses and soil equivalent stresses than that with conventional (smooth) surface. The least maximum cone equivalent stress and least maximum soil equivalent stress were recorded for biomimetic surfaces with concave dimples and wavy form-2 respectively. The two-body abrasive wear of biomimetic cone surfaces and conventional (smooth) cone surface were run on a rotary disk type of abrasive wear testing machine. The biomimetic cone surfaces were found to have lower abrasive wear than the conventional surface. It was found that and biomimetic cone surface with concave dimples has the lowest abrasive wear among the all tested surfaces.

내부 냉각유로에서 열전달 강화와 압력손실 감소를 위한 표면 형상체의 개발

A new surface shape of an internal cooling passage which largely reduces the pressure drop and enhances the surface heat transfer is proposed in the present study. The surface shape of the cooling passage is consisted of the concave dimple and the riblet inside the dimple which is protruded along the stream-wise direction. Direct Numerical Simulation (DNS) for the fully developed turbulent flow and thermal fields in the cooling passage is conducted. The numerical simulations for five different surface shapes are conducted at the Reynolds number of 2800 based on the mean bulk velocity and channel height and Prandtl number of 0.71 . The driving pressure gradient is adjusted to keep a constant mass flow rate in the x direction. The thermoaerodynamic performance for five different cases used in the present study was assessed in terms of the drag, Nusselt number, Fanning friction factor, volume and area goodness factor in the cooling passage. The value of maximum ratio of drag reduction is -22.86 % , and the value of maximum ratio of Nusselt number augmentation is 7.05% when the riblet angle is 60°. The remarkable point is that the ratio of Nusselt number augmentation has the positive value for the surface shapes which have over 45° of the riblet angle. The maximum volume and area goodness factors are obtained when the riblet angle is 60°.

Laser trapping of deformable objects

We report the trapping and manipulation of bubbles in viscous glass melts through the use of a laser. This phenomenon is observed in bubbles tens of micrometers in diameter under illumination by low numerical aperture (NA = 0.55). Once the bubble was centered on the optical axis, it was trapped and followed a lateral relocation of the laser beam. This phenomenon is explained by modifications of the bubble's shape induced by axial heating and a decrease in surface tension. It is shown that formation of a concave dimple on the bubble's front surface explains the observed laser trapping and manipulation. This mechanism of laser trapping is expected to take place in other deformable materials and can also be used to remove bubbles from melts or liquids. For this technique to be effective, the alteration of the bubble's shape should be faster than its expulsion out of the laser's point of focus.

Heat transfer of impinging jet array over concave-dimpled surface with applications to cooling of electronic chipsets

Heat transfer measurements over the impinging surface roughened by concave dimples for a 4 × 3 in-line jet array with jet Reynolds number ( Re) and separation distance ( S/ D j) varying in the ranges of 5000 ⩽ Re ⩽ 15,000 and 0.5 ⩽ S/ D j ⩽ 10 are performed. For each tested Re and S/ D j combination, the heat transfer data acquired from three eccentricities ( E) between jet-centre and dimple-centre of 0, 1/4 and 1/2 dimple-pitch ( H) is analyzed. A set of selected experimental data illustrates the isolated and interactive influences of surface topology, Re, S/ D j and E/ H ratio on local and spatially averaged heat transfers. In conformity with the experimentally revealed heat transfer physics, the empirical heat transfer correlations that permit the evaluation of spatially averaged Nusselt number over the central jet region of the concave-dimpled surface with E/ H ratios of 0, 1/4 and 1/2 are generated.

Reduction of polyethylene wear by concave dimples on the frictional surface in artificial hip joints

For the purpose of reduction of polyethylene wear generated in artificial hip joints, concave dimples were formed on the surface of the metal femoral head by electrical discharge etching with the constant diameter of 0.5 mm, pitch of 1.2 mm, and depth of 0.1 mm. Using a hip joint simulator, the total amount of polyethylene wear was 7.2 mg in the concave-patterned condition and 23.1 mg in the nonpatterned condition. The reasons for the reduction of polyethylene wear by the concave pattern may be i) a reduction of abrasive wear by providing escape dimples for wear particles and ii) an improvement in the lubricity on the frictional surface by the supply of lubricant that is stored in dimples.