Groove Geometry Research Articles

Determination of fundamental parameters for the cross-hatched cylinder liner micro-geometry

This paper is part of a project aiming at optimizing the cylinder-liner/piston-ring contact performance: oil consumption, friction and wear. The surface micro-geometry has a major influence on these characteristics. Classical cylinder-liners display cross-hatched patterns. Grooves modify contact pressure distributions and act as lubricant reservoirs and pipes redistributing oil. The load-carrying capacity is greatly influenced by the number of grooves and their geometry. An automatic groove geometry identification (depth, width, angle) is performed on cylinder-liner surface measurements. The surfaces were measured at two instants: new and after a fired engine test. The micro-geometry evolution is discussed.

Effect of Tool Geometry on Material Flow Behavior of Refill Friction Stir Spot Welding

Using LY12 aluminum alloy as the research object, material flow behavior of refill friction stir spot welding process is simulated. The simulation results are investigated by studying the macrostructure and microstructure of the refill friction stir spot welding joints. Effects of tool geometries on material flow are mainly discussed. Results show that bonding ligament and grains in different regions of the stir zone are affected by the material flow behavior. Rational groove on the sleeve can increase the material flow velocity. From the viewpoint of reducing the unfavorable bonding ligament, the groove on the sleeve inner wall is better than the smaller width groove on the sleeve outer wall. Compared with the concentric circle grooves on the sleeve bottom, the scrolled groove is more beneficial to decrease the bonding ligament thickness and increase the welding spot area. Disregarding the higher heat input, sleeve with bigger outer diameter greatly increases the flow velocity and the welding spot area compared to changing the groove geometry.

Performance Evaluation of Bidirectional Dry Gas Seals with Special Groove Geometry

ABSTRACTThere are a very few studies of bidirectional gas seals, particularly those with certain profiles used in the industry. A parametric study of the performance of bidirectional dry gas seals under a set of operating conditions is presented. The expounded approaches use solution of 3D Navier-Stokes momentum and continuity equations for various forms of grooved gas seals, particularly for the trapezoidal shape variety for which there has been a particular dearth of in-depth analyses. It is shown that such groove geometries enhance the load-carrying capacity of the seal through increased hydrodynamic lift. This is as the result of enhanced localized wedge flow, particularly with a reduced seal gap. Therefore, there is the opportunity of gap minimization while reducing leakage rate and power loss. For given operating loading, kinematic and thermal conditions, as well as seal geometry and topography, the operating minimum film thickness may be considered the main design parameter.

Laser-Assisted Waterjet Microgrooving of Silicon Nitride Ceramics with near Damage-Free

A new processing technology is used in micromachining silicon nitride ceramics for improving the processing efficiency. Laser-assisted waterjet machining technology with near damage-free plays an important role in reducing the heat-affected zone (HAZ). In order to understand the effects of process parameters, such as pulse energy, waterjet offset distance and water pressure, on microgrooving of silicon nitride ceramics and the machining performance, a full-factorial experiment with the comparison experiment has been carried out in this study for analyzing and discussing the groove geometry, the surface quality and HAZ width. It can be concluded that the laser-assisted waterjet processing technology can expel more material removal with near damage-free.

Shear-Friction Behavior of Groove Interface in Concrete Bridge Rehabilitation

AbstractThis study focuses on the shear-friction behavior of a groove interface with transverse reinforcement between existing concrete and newly poured concrete, which has been adopted in the rehabilitation project of three prestressed concrete box girder bridges in China. A series of push-off specimens with groove interfaces was tested with parameters of concrete strength, groove geometry, and reinforcement ratio. For comparison purposes, monolithic specimens and roughened specimens with or without transverse reinforcement were also tested to failure. Cracking loads, ultimate loads, residual strengths, cracking patterns, and failure modes were recorded. Load-slip curves, load-dilation behaviors, and load-strain relationships in steel reinforcement have been investigated. The groove on the surface of the existing concrete can significantly enhance shear-friction capacity of the interface between new and existing concrete. The transverse reinforcement can improve deformation capacity and residual resistan...

Differential sensitivity to methylated DNA by ETS-family transcription factors is intrinsically encoded in their DNA-binding domains.

Transactivation by the ETS family of transcription factors, whose members share structurally conserved DNA-binding domains, is variably sensitive to methylation of their target genes. The mechanism by which DNA methylation controls ETS proteins remains poorly understood. Uncertainly also pervades the effects of hemi-methylated DNA, which occurs following DNA replication and in response to hypomethylating agents, on site recognition by ETS proteins. To address these questions, we measured the affinities of two sequence-divergent ETS homologs, PU.1 and Ets-1, to DNA sites harboring a hemi- and fully methylated CpG dinucleotide. While the two proteins bound unmethylated DNA with indistinguishable affinity, their affinities to methylated DNA are markedly heterogeneous and exhibit major energetic coupling between the two CpG methylcytosines. Analysis of simulated DNA and existing co-crystal structures revealed that hemi-methylation induced non-local backbone and groove geometries that were not conserved in the fully methylated state. Indirect readout of these perturbations was differentially achieved by the two ETS homologs, with the distinctive interfacial hydration in PU.1/DNA binding moderating the inhibitory effects of DNA methylation on binding. This data established a biophysical basis for the pioneering properties associated with PU.1, which robustly bound fully methylated DNA, but not Ets-1, which was substantially inhibited.

The effect of surface grooves on film breakdowns in point contacts

Surface roughness plays an important role in transition from full to mixed elastohydrodynamic regime. One kind of features appearing on a real rough surface are grooves longer than contact diameter. It has already been reported that these grooves cause a local film reduction or a complete collapse. In this study, a ball-on-disc optical tribometer was used to quantitatively study the effect of grooves on film thickness in a point contact. It was observed that the main dependence on speed, the so-called lift-off curve, generally follows the logarithm function. The effects of build-up material, load, slide/roll ratio and groove geometry are presented. These results were fitted to the analytical description, which enables the estimation of groove effects on point contact lubrication.

Fabrication of biomimetic superhydrophobic surfaces by a simple flame treatment method

A simple flame treatment method was explored to construct micro/nanostructures on a surface and then fabricate a biomimetic superhydrophobic surface at a relatively low cost. SiO2-containing polydimethylsiloxane (PDMS) was used as a substrate. The PDMS replicas with various micropatterned surfaces were fabricated using grass leaf, sand paper, and PET sheet with parallel groove geometry as templates via PDMS replica molding. The PDMS replica surfaces with micron structures and the surface of a flat PDMS sheet as a control sample were further treated by flame. The fabricated surfaces were characterized by scanning electron microscopy and water contact angle measurements. The effect of surface microstructures on the transparency of PDMS was also investigated. The studies indicate that the fine nanoscale structures can be produced on the surfaces of PDMS replicas and a flat PDMS sheet by a flame treatment method, and that the hierarchical surface roughness can be adjusted and controlled by varying the flame treatment time. The flame-treated surfaces of PDMS replicas and a flat PDMS sheet possess superhydrophobicity and an ultra-low sliding angle reaching a limiting value of 1°, and the anisotropic wettability of the PDMS replica surface with oriented microgroove structures can be greatly suppressed via flame treatment. The visible light transmittance of the flame-treated flat PDMS surface decreases with prolonged flame treatment times. Copyright © 2016 John Wiley & Sons, Ltd.

Metallurgical response of weld metal to different filler metal and joint design combinations of laser-arc hybrid welded lean duplex and novel ferritic stainless steels

Laser and laser-arc hybrid welding of duplex and ferritic stainless steels is demanding, because microstructure of the welds tends to be highly ferritic. Therefore, filler metal must be used for maintaining corrosion and mechanical properties of the welds. In this study, different filler metals including duplex, basic, and overalloyed austenitic grades were used with laser-arc hybrid method to weld lean duplex 1.4162 and novel ferritic stainless steels grades 1.4622 and 1.4509. Several sets of joint design and welding parameter combinations were used to adjust the amount of filler metal in the weld. The purpose of the trials was to evaluate whether weld metal microstructures (grain morphology, austenite/ferrite balance, etc.) can be modified by using an applicable joint preparation and an “overmatched” filler metal addition. Weld characterization included several research methods such as: Macro- and microscopic examination using light microscope¸ cross-sectional dilution ratio determination from the metallographic cross sections, electron backscatter diffraction method in order to assess austenite, and ferrite phase proportions in the test welds. The effects of used groove geometry, filler metal composition, and content on resulting metallurgical features of the welds are discussed in detail.

A Comparative Study on the Performance of Typical Types of Bionic Groove Dry Gas Seal based on Bird Wing

A series of bionic grooves based on bird wing, such as cluster spiral groove, multi-array spiral groove and flow-split spiral groove, are introduced to improve the film stiffness and sealing properties of dry gas seal. A theoretical model solved with Finite Difference Method (FMD) is developed to study the static sealing performance, such as film stiffness and leakage rate of these bionic groove dry gas seals. Then, a performance comparative study between the bionic groove dry gas seals and common spiral groove dry gas seal with different groove geometry parameters such as groove depth ratio, spiral angle and micro groove number under different average linear velocity at seal ring face and seal pressure is carried out. The closing force, film thickness and leakage rate of dry gas seals with bionic grooves and common spiral groove are measured experimentally. Results show that cluster spiral groove and multi-array spiral groove dry gas seals have superiority in the film stiffness and stiffness-leakage ratio compared with common spiral groove under the condition of high-speed and low-pressure, while flow-split spiral groove dry gas seal has no obvious advantages of performance. Film stiffness of cluster spiral groove dry gas seal and stiffness-leakage ratio of multi-array spiral groove dry gas are 20% and 50% larger than that of common spiral groove dry gas seal, respectively, which are verified by the experimental results.

Joint Strength Optimization of Bi-Adhesively Bonded Composite-Aluminum Sandwich Structure

Adhesively bonded joint strength optimization can be obtained through the modification of the overlap length and bi-adhesively bonded technique. In this technique, the joints have two different types of adhesive in the overlap length. In the present paper, the effects of bi-adhesively bondline on the shear stress, peeling stress and von-Mises stress of tongue and groove joints were investigated by using finite element analysis. The joint models were consisted of thick woven E-glass/vinyl ester laminate composite groove geometry together with aluminum 5083 tongue geometry. Finite element analyses were performed for three different tongue lengths (75, 150, 225 mm). The distribution of shear and peeling stresses were investigated on adhesively bonded tongue and groove joints subjected to longitudinal tensile loads. The results indicated that the joint strength can be improved by selecting appropriate design parameter values with bi-adhesive bonded technique.

Ultrasonic-assisted underwater laser micromachining of silicon

Underwater laser machining process can offer a clean cut with less thermal damage and material deposition on and nearby the cut region. However, the performance of this process is limited by the cut debris and bubble which can significantly disturb the laser beam during the ablation in water. In this study, the ultrasonic-assisted underwater laser ablation has been comprehensively examined to overcome the limitations of the existing process. The presented technique uses ultrasound to vibrate water while a workpiece is being ablated by a laser beam in water. This can atomize the bubble and energize the cut debris to be flushed away from the laser-ablated region. Silicon was selected as a work material in this study, where it was grooved by a nanosecond-pulse laser in water. The effects of ultrasonic parameters and water flow rate on the groove geometry and cut surface morphology were experimentally investigated and analyzed to understand the process performance. By using this technique, a clean and deep groove can be made on silicon wafer. The reactions between silicon–oxygen and silicon–carbon on the cut surface were also characterized and comparatively discussed with the other underwater laser ablation methods. According to the findings of this study, the ultrasonic-assisted underwater laser micromachining technique could be an alternative micromachining process to gain a higher material removal rate and a better cut surface quality than the other methods.

Effect of pass schedule and groove design on the metal deformation of 38MnVS6 in the initial passes of hot rolling

The deformation behaviour of a hot rolled micro-alloyed steel bar of grade 38MnVS6 was examined using an FEM model during the initial passes in a blooming mill, as a function of three different pass schedules, roll groove depth, collar taper angle and corner radius. The simulations predicted the effective strain penetration, load, torque, fish tail billet end shapes, and metal flow behaviour at a chosen temperature, mill rpm and draft. The model predictions were validated for typical groove geometry and a typical pass schedule. Lower collar taper angle, lower corner radius and higher depth of groove in hot rolling enabled achievement of higher strain penetration, higher mill load and lower fish tail formation. The present study establishes the capability of the model to improve the internal quality of the rolled billet as measured by effective strain which was corroborated to the rolled bar macrostructure and microstructure. The model enables yield improvement by the choice of draft to minimise fish tail losses. The surface quality is improved by the ability to avoid fin formation that occurs at certain conditions of rolling. Thus, the groove geometry, roll pass schedule and rolling mill parameters and temperature can be optimised for best product quality and yield.

Gas-tight Thermally Joined Metal-thermoplastic Connections by Pulsed Laser Surface Pre-treatment

Thermal joining of laser-structured metals and thermoplastics has been proven to deliver a high joint strength. A novel idea is to apply this process onto metal-thermoplastic joints in order to produce gas-tight hybrid connections which can be used in several technical applications.The surface pre-treatment of aluminum by infrared pulsed laser radiation was focused in this study. Depending on different cumulative energies two main surface topologies, stochastic and deterministic groove structures, were manufactured. Consequently, heat conduction joining by infrared laser radiation was used to join the metal with polypropylene. The influence of laser structuring on surface roughness and groove geometry was analyzed by scanning electron and laser scanning microscopy. The wetting of the thermoplastic was investigated by optical microscopy. The gas-tightness was identified by a helium leak test and climate testing was performed to analyze the long-term durability. The results indicate that depending on the surface morphology of the metal, durable gas-tight connections can be created by thermal joining.

Laser Marking of Titanium Coating for Aerospace Applications

In the aerospace industry, in order to ensure the identification and the traceability of the products, high repeatability, non-invasive and durable marking processes are required. Laser marking is one of the most advanced marking technologies. Compared to traditional marking processes, like punches, microdot, scribing or electric discharge pencil etcher, laser marking offers several advantages, such us: non-contact working, high repeatability, high scanning speed, mark width comparable to the laser spot dimension, high flexibility and high automation of the process itself. In order to assure the mark visibility for the component lifetime, an appropriate depth of the mark is required. In this way, a stable behaviour is ensured also when the component operates in aggressive environments (i.e. in presence of oxidation, corrosion and wear phenomena). The mark depth is strongly affected by the laser source kind and by the process parameters, such us average power, pulse frequency and scanning speed. Moreover, an excessive mark penetration could cause stress concentrations and reduce the fatigue life of the component. Consequently, an appropriate selection of the process parameters is required in order to assure visibility and to avoid excessive damage. Cold Spray Deposition (CSD) is a relative new technology that allows to produce surface coatings without significant substrate temperature increasing. In aeronautics fields this technology is useful to coat materials sensible to temperature, such as solution tempered aluminum alloy, with a titanium layer. Aim of the work is to characterize the laser marking process on CSD Ti coating, in order to study the influence of the laser marking process parameters (pulse power and scanning speed), on the groove geometry of the marking. The experimental marking tests were carried out through a 30W MOPA Q-Switched Yb:YAG fibre laser; under different process conditions. The groove geometry was measured through a HIROX HK9700 optical microscope. The results showed the effectiveness of the laser process to produce high quality marks on the titanium layer. Moreover, a correlation between the process parameters and the mark's geometry was clearly observed.

Gas Seal Performance and Start up Condition Enhancing with Different Seal Groove Geometries

New dry gas seal “DGS” groove geometry has been developed, using a verified three dimensional simulations. The effect of the various groove profiles; standard spiral, tapered-spiral, spiral with an annulus and tapered-spiral with an annulus were studied at wide range of operating speed. The results indicate that, tapered type spiral groove causes a reduction in opening force and in the leakage rate. In addition, increasing the taper angle reduces the temperature distribution inside the gas film and reduces the thermal stresses on the seal mating rings. The combined use of annuals and taper spiral groove decrease the leakage rate for spiral DGS with annular groove only. The final optimized spiral tapered seal with annuals reduces the leakage rate by 18.5% from standard seal, ensures uniform pressure distribution and hydrostatic lift at low speeds, resulting in low torque and reliable operating at start-up condition.

On-line monitoring and control of thermal stresses in steam turbine rotors

The requirement of high operational flexibility of utility power plants creates a need of using on-line systems for monitoring and control of damage of critical components, e.g. steam turbine rotors. Such systems make use of different measurements and mathematical models enabling calculation of thermal stresses and their continuous control. The paper presents key elements of the proposed system and discusses their use from the point of view of thermodynamics, heat transfer and solid mechanics. Thermodynamic relationships, well proven in design calculations, are applied to calculate on-line the steam temperature at critical locations using standard turbine measurements as input signals. The model predictions are compared with operational data from a real power plant during a warm start-up and show reasonably good accuracy. The effect of variable heat transfer coefficient and material properties on thermal stresses is investigated numerically by finite element method (FEM) on a cylinder model, and a concept of equivalent Green's function is introduced to account for this variability in thermal stress model based on Duhamel's integral. This approach was shown to produce accurate results for more complicated geometries by comparing thermal stresses at rotor blade groove computed using FEM and Duhamel's integral. Finally, the applicability of Neuber's and the Glinka–Molski rule with ideal elastic and bilinear material model to estimating elasto-plastic strains at the rotor groove was investigated by FEM. For the considered groove geometry, Neuber's rule with bilinear material model resulted in most accurate strain predictions.

Enhanced quantum efficiency of photoelectron emission, through surface textured metal electrodes

It is predicted that the quantum efficiency (QE) of photoelectron emission from metals may be enhanced, possibly by an order of magnitude, through optimized surface texture. Through extensive computational simulations, it is shown that the absorption enhancement in select surface groove geometries may be a dominant contributor to enhanced QE and corresponds to localized Fabry–Perot resonances. The inadequacy of extant analytical models in predicting the QE increase, and suggestions for further improvement, are discussed.

Influence of electrode groove geometry on the passive control of the depletion layer in microfluidic fuel cells

Mitigation of the concentration boundary layer is an essential requirement to improve the power density of microfluidic fuel cells. In this study, the formation of a groove shape in the surface of the electrodes, located in parallel on the bottom of the channel, is proposed for the passive control of the depletion layer. The flow field inside the channel is numerically simulated and cell performance is experimentally measured for the various groove formation patterns (converging, parallel, or diverging) and tilt angles (30, 45, or 60°). Experimentally measured cell performance also shows superior results at the best conditions as determined by numerical modeling, where the interdiffusion zone at the fuel-oxidant interface is not significantly expanded and the flow in the direction normal to the electrode surface is large. Our results show that the depletion region is well-controlled when the groove angle is large and when the groove pattern is not parallel, due to the increase in chaotic mixing. At these conditions, with formic acid as the fuel and a platinum electrode, the maximum current density and peak power density are increased by 38.42% and 38.09%, respectively, compared to the values for flat electrodes. Even better cell performance is expected if the optimum design of the groove shape is determined using flow analysis.

리니어 압축기에서 그루브 형상 변화에 따른피스톤의 동특성 해석

It is possible to prevent a piston from contacting the cylinder by changing the shape of the piston or by applying micro-textures, such as micro-grooves or micro-holes, over the piston surface. Usually, the minimum radial clearance reaches its minimum value at the beginning of the suction stroke because the pressure around the piston is low and almost axisymmetric such that the net pressure force on the piston is not sufficiently high to support the piston from touching the cylinder. In this study, we apply a series of saw-tooth-shaped grooves on the piston surface, and numerically investigate the effects of groove depth, groove angle, and the number of grooves with radial clearance variations using a finite difference method. We conduct a dynamic analysis of the piston for various changes in groove geometries to obtain the minimum radial clearance variation for the entire compression cycle. The minimum radial clearance increases while friction loss decreases when we apply the series of saw-tooth-shaped grooves on the piston. In addition, we analyze the impact of the change in the groove shape variable due to changes in radial clearance. Leakage variations are relevant to radial clearance, but have almost no effect on the groove parameters.