Flat Pad Research Articles

Dynamic behavior of hydrostatic squeeze film dampers fed through four capillary restrictors with micropolar lubricant

PurposeThe purpose of this research is to study the dynamic behavior of hydrostatic squeeze film dampers made of four hydrostatic pads, fed through four capillary restrictors with micropolar lubricant.Design/methodology/approachThe modified version of Reynolds equation is solved numerically by the finite differences and the Gauss–Seidel methods to determine the pressure field generated on the hydrostatic bearing flat pads. In the first step, the effects of the pad dimension ratios on the stiffness and damping coefficients are investigated. In the second step, the damping factor is evaluated with respect to the micropolar properties.FindingsThe analysis revealed that the hydrostatic squeeze film dampers lubricated with micropolar lubricants produces the maximum damping factor for characteristic length of micropolar lubricant less than 5, while the same bearing operating with Newtonian lubricants reaches its maximum damping factor at eccentricity ratios larger than 0.4.Originality/valueThe results obtained show that the effects of micropolar lubricants on the dynamic performances are predominantly affected by the pad geometry and eccentricity ratio.

PO-04-041 EFFICACY OF BALLOON EXPANDABLE EXTREME-LOW TEMPERATURE "XLT" VENTRICULAR EPICARDIAL CRYOABLATION: A PRE-CLINICAL DOSE RANGING STUDY

Lack of transmural lesion formation with catheter or surgical ablation for ventricular tachycardia (VT) can be an important determinant of arrhythmia recurrence. The aim of this study was to evaluate the feasibility and efficacy of a novel balloon expandable extreme-low temperature (XLT) cryoablation device for epicardial ventricular ablation. A total of six healthy Yorkshire swine (63 ± 6 kg) underwent surgical epicardial access. Four-to-five right (RV) and left (LV) ventricular epicardial targets were identified: anterior (1-2), lateral (1-2), summit (1-2). Ablation was performed with the novel 'XLT-cryo' device (HeartPad®Mini, Corfigo, Montclair, NJ), a balloon-expandable epicardial device that circulates extremely cold helium (∼ -253C) at a high flow rate through a flat pad with dimensions of ∼15 x 15mm. It is mounted onto the surface of an ∼30mm insulation balloon with blunted ends for fixation and parietal pericardial protection. At the end of each timed ablation, a thaw cycle was initiated to warm the device and allow repositioning to the next target. Ablation lesion size was measured using TTC staining. A total of 27 epicardial lesions were created (RV: n=2; LV: n = 25). The average lesion depth increased with time and reached complete transmurality with a plateau at 1 minute (time [T; sec] and mean depth±stdv [mm]; T15=11±0.5, T30=12±1, T60=15±1, T120=16±0.5, T240=17±0.5; Figure). Lesion transmurality was achieved in all lesions with ablation time ≥2 min. Lesion geometry was similar across different RV/LV locations, including the LV summit. Ventricular fibrillation (which is common in Yorkshire swine) occurred during/following 3 applications out of 27. Our results indicate that epicardial cryoablation using the novel balloon expandable HeartPad® device with extremely low temperature applications can efficiently produce transmural ventricular lesions in different epicardial locations. This technology holds potential for both surgical and catheter-based VT ablation in humans.

Mechanical Performance Analysis of Hydrostatic Thrust Bearing under Microbevel Parameters

Background: Heavy-duty hydrostatic bearings of the original parallel friction pair are prone to hydrostatic loss problems during operation. Aims: To solve the failure problem, the original hydrostatic oil pad was designed as a micro-inclined plane, and the dynamic pressure caused by the micro-wedge of the oil pad at a higher speed was used to compensate for the static pressure loss of the bearing. objective: For a new type q1-205 microbevel double rectangular cavity hydrostatic bearing. Objective: This study aims to design a new type of q1-205 micro bevel double rectangular cavity hydrostatic bearing. Method: The mathematical model of oil film theoretical analysis of hydrostatic bearing with the micro-inclined surface was established, including the flow equation of a double rectangular cavity with a micro-inclined surface and static and dynamic bearing capacity equation. result: The oil film lubrication performance of the bearing with the wedge parameters of 0mm, 0.02mm, 0.04mm, 0.06mm, 0.08mm and 0.10mm was simulated by the finite volume method, the comprehensive influence law of the wedge-shaped parameters on the vorticity and flow rate of the oil cavity pressure fluid was revealed. Finally, the oil cavity pressure changes of oil films with different wedge parameters under certain load and speed were tested by design experiments, and the theoretical analysis and simulation were verified. Result: In this paper, the mechanical properties of oil film with tilt height between 0 and 0.1mm were simulated with variable viscosity, and the distribution law of pressure field under different working conditions was obtained. Through the experimental study, the pressure data of parallel flat pads and tilting pads under different working conditions are measured and compared with the simulation data. Conclusion: The pressure loss value of the oil pad designed in this paper is relatively small under extreme working conditions. The overall loss rate is about 10% ~ 20%, and the dynamic pressure compensation rate is about 16%. The dynamic pressure generated by the slight inclination Angle can well compensate for the static pressure loss.

A Fully Integrated Solid-State Charge Detector with through Fused Silica Glass via Process

A charge detector is a vital component in neutrino and dark matter detection. The integration of a charge collector in the form of flat pads and readout modules has been proposed as an optimization method as it can reduce noise and installation complexity. As a substrate, fused silica glass has attracted considerable attention due to its low radioactive background properties. In this research, based on the application requirements of a high charge collection rate and low noise, the structure of the charge detector was designed using calculation and simulation methods. The entire manufacturing process is described. In addition, a novel through glass via (TGV) structure composed of a conformal metal layer and a photosensitive material that is easy to fabricate and has high morphological compatibility with via filling is proposed. The curing property of the new material was characterized. A fully integrated solid-state charge detector with 32 groups of TGVs was realized. Additionally, the electrical properties of key structures were tested and analyzed.

Conservative Treatment for Primary Metatarsalgia

Metatarsalgia is one of the most common causes of forefoot pain, and it is characterized by pain in the front part of the foot under the head of the metatarsal bones. Primary metatarsalgia is idiopathic, but it has been suggested to be related to forefoot plantar compression. Because of the various causes of metatarsalgia, there is the need to thoroughly consider the etiology of metatarsalgia to find novel, effective, and conservative treatments for metatarsalgia to avoid surgical treatment. Pressure reduction or redistribution can be achieved using toe exercise, flat shoe inserts, metatarsal pads, custom-molded inserts, and rockerbars. There was no need for one treatment. If toe function was poor, toe exercises were recommended. If dorsiflexion of the ankle joint was limited, the Achilles tendon was stretched. If the pain was localized to the plantar aspect of the 2nd MTP, a decompression insole was applied. If the pain was limited to the plantar aspect of the 2nd MTP, a decompression insole was worn. If swelling occurred, anti-inflammatory drugs were indicated to reduce inflammation. The combination of the two was appropriate for this condition. Toe exercises can improve balance and are worth trying. An in-depth understanding of the various etiologies of metatarsal and toe deformities is essential for successful treatment.

An efficient numerical strategy to predict the dynamic instabilities of a rubbing system: application to an automobile disc brake system

This paper deals with the modelling and the prediction of the dynamic instabilities for a rubbing system. Two hybrid approaches are introduced for dynamic instability analysis and applied to a reduced disc brake system. The methods are based on stochastic algorithms coupled with the finite element method (FEM) using the complex eigenvalue analysis technique. By considering the input parameters as random variables, the uncertainty analysis is performed through two approaches to predict the unstable frequencies of a braking system (1) Monte-Carlo (MC) using Mersenne-Twister (MT19937) algorithm and (2) periodic sampling technique. Since the mechanism of brake squeal involves many design parameters, stochastic finite element approaches will be coupled with sensitivity algorithms, e.g. Variance-Based Sensitivity Analysis and Fourier Sensitivity Analysis Test, to analyze the contribution of each random variable on the dynamic instabilities. First, a comparison between the two stochastic algorithms is performed on standard analytical models. The objective is to validate the accuracy and to assess the numerical efficiency that FAST presents to (1) propagate the uncertainties upstream of the model and (2) to compute the partial variances of the model output. Secondly, the coupling of the previous stochastic algorithms with FEM is carried out and tested through a reduced brake system consisting of a rotating disc with two flat pads. Results show that the hybrid approach FAST-FE is more robust and computationally more efficient compared to the widely used MC-FE for these types of problems. FAST-FE solver converges, within a reasonable computing time, either to approximate the probability density function of the random variables or to compute the partial variances of the dynamic instabilities. Hence, it can be considered as an efficient numerical method for squeal instability analysis in order to reduce squeal noise of such a mechanical system.

Effect of Taper on Shear Stiffness of Steel-Reinforced Neoprene Bearing Pads

Steel-reinforced elastomeric bearing pads are widely used in bridge construction to vertically support girders on piers while also accommodating translational and rotational girder deformations caused by live loads and temperature changes. To support sloped girders, flat bearing pads of uniform thicknesses are typically used with either tapered steel shim plates or an inclined concrete bearing seat. The use of tapered pads has the potential to reduce both construction time and cost by eliminating the need for tapered plates or seats to match the girder slope. However, limited research has been performed to investigate the effect of introducing taper on relevant design properties of bearing pads. In this paper, results are presented from experimental testing that was performed to quantify the effect of taper on shear stiffnesses of pads having varied geometric characteristics (plan view dimensions, elastomer thicknesses, and slope angles). An experimental bearing pad test device was designed and utilized to impose shear loads in accordance with ASTM standards, while simultaneously maintaining a constant axial load. Bearing pads chosen for testing were tapered variations of standard flat bridge bearing pads used in the state of Florida, U.S. Results obtained from the study revealed that shear stiffness was not significantly influenced by the introduction of taper angle, the direction of shear along the length of pads, or axial load level. The shear stiffness of tapered pads remained within approximately 10% of the shear stiffness of corresponding flat pads.

Film Thickness and Friction of ZDDP Tribofilms

Tribofilm formation by several zinc dialkyl- and diaryldithiophosphate (ZDDP) solutions in thin film rolling-sliding conditions has been investigated. A primary, a secondary alkyl and a mixed alkyl ZDDP show similar rates of film formation and generate films typically 150 nm thick. Another secondary ZDDP forms a tribofilm much faster and the film is partially lost after extended rubbing. An aryl ZDDP forms a tribofilm much more slowly. The films all have a pad-like structure, characterised by flat pad regions separated by deep valleys. Three different techniques have been used to analyse the thickness and morphology of the tribofilms: spacer layer imaging (SLIM), scanning white light interferometry (SWLI) of the gold-coated film and contact mode atomic force microscopy (AFM). The SLIM method measures considerably thicker films than the other two techniques, probably because of lack of full conformity of a glass disc loaded against the rough tribofilm. No evidence of a highly viscous layer on top of the solid tribofilm is seen. SWLI and contact mode AFM measure similar film thicknesses. The importance of coating the tribofilm with a reflective layer prior to using SWLI is confirmed. As noted in previous work, the formation of a ZDDP tribofilm is accompanied by a marked shift in the Stribeck friction curve towards higher entrainment speed. For a given ZDDP this shift is found to correlate with the measured tribofilm roughness, proving that it results from the influence of this roughness on fluid entrainment in the inlet.

Pressure distribution in orifice-compensated turbulent hydrostatic bearing with fluid inertia effects using numerical simulations via Navier-Stokes

Significant progress in turbo-machinery’s speed is made recently. To cope with that; many fluids having large differences in rheological properties are introduced as lubricant in hydrostatic bearing systems. The present study aims to improve the understanding of the pressure patterns within hydrostatic bearing flat pads according to different parameters. The main ones are the squeeze film velocity, the feeding pressure and the fluid viscosity. To consider efficiently, the influence of the turbulent and inertia effects numerical simulation are based on transient Navier-Stokes equations. The results of the present study confirm many patterns already mentioned by other authors, and also showed different flow behaviour in terms of vortex evolution according to the studied parameters combinations.

Modeling for optimization of circular flat pad aerostatic bearing with a single central orifice-type restrictor based on CFD simulation

For a circular flat pad aerostatic bearing with a single orifice-type restrictor, flow field in the air film is numerically investigated. The formation process of sonic region and shock waves is studied and formation mechanism of the vortex is revealed. Based on flow analysis, the maximum Mach number is taken as the benchmark of bearing dynamic stability and used as a constraint in the optimization modeling, for which the rationality is verified through transient flow calculations. The mathematical model for optimization considering both stiffness and dynamic stability is established, and several cases of optimization are performed under different given loads. The results are compared and benefits of the design optimization are demonstrated.

3D Numerical investigation of pressure field of an orifice compensated hydrostatic bearing

In recent years, much attention has been given to hydrostatic/hybrid journal bearings in research due to their wide spread engineering applications, such as: high speed turbomachinery, machine tools spindles, cryogenic equipment, and precision grinding. However, the activity toward improved understanding of the flow regimes and the associated pressure pattern in the recess flow phenomena is still needed. The objective of this work is to provide an understanding of the influence of regime flow in recess on the pressure field of hydrostatic bearing flat pad fed by orifice restrictor and orifice inertia. 3D Reynolds averaged Navier Stokes equations with the SST-k ω turbulence model are applied in order to investigate the effects of pressure supply, dynamic viscosity and recess depths on the pressure profile. The finite volume method implemented in the ANSYS-CFX software is used. To prove the robustness of CFD code, a comparison of the numerical results and the Reynolds equation is performed at very deep recess. The results exhibit very good agreements between CFD and Reynolds equation methods. On the other hand, the several cases treated in this work contribute also to analyze and to explain the main reasons providing the inertia and the Rayleigh effect in recess flow.

Research of the Process of Shaping Folded Filler of Sandwich Panels from Cardboard

Sandwich panels with the corrugated filler made of composite cardboard are used in building constructions, road sound dampening screens, etc. Taking into account that in industries applying sandwich panels, the demand for such filler is relatively high, the competitiveness of the product must be at a high level. This requires developing a high-performance industrial technology to produce it. These production processes include rotary shaping. The well-known technology for manufacturing corrugated cardboard from thin paper does not allow making very high products. The article considers the possibility of producing relatively high corrugated filler by creasing and folding. The important point here is to make a flat pad, as one of the elements of the corrugation, at the point of its contact with the skins of the panel. We studied two schemes of folding a preliminarily creased cardboard web and evaluated the advantages of these schemes. We suggested the creaser shape and structure, which allow making high-quality connect pads on the corrugated cardboard within a wide range of sizes.

A Scott bench with ergonomic thorax stabilisation pad improves body posture during preacher arm curl exercise

We assessed whether the use of an ergonomic thorax stabilisation pad, during the preacher arm curl exercise, could significantly reduce the excessive shoulder protraction and thoracic kyphosis induced by the standard flat pad built into the existing preacher arm curl equipment. A 3D motion capture system and inclinometers were used to measure shoulder protraction and thoracic kyphosis in 15 subjects performing preacher arm curl with a plate-loaded machine provided with the standard flat pad. The same measures were repeated after replacing the flat pad with a new ergonomic pad, specifically designed to accommodate the thorax profile and improve body posture. Pad replacement significantly (p < 0.001) reduced shoulder protraction (from to ) and thoracic kyphosis (from to ), enabling postural and functional improvements within the entire spine, shoulder girdle and rib cage. The ergonomic pad may potentially allow a more effective training, prevent musculoskeletal discomfort and reduce the risk of injury.Practitioner summary: We have designed an ergonomic thorax stabilisation pad for the preacher arm curl exercise. The new ergonomic pad improves the poor posture conditions induced by the standard flat pad and may potentially allow a more effective training, prevent musculoskeletal discomfort, improve the breathing function and reduce the risk of injury.

Computational fretting fatigue maps for different plasticity models

ABSTRACTThis paper presents qualitative elastoplastic simulations and analyses of fretting fatigue. Three hardening constitutive models are considered, and their effects on stick–slip conditions and lifetime prediction are compared. The computational analysis consists of the estimation of the shakedown limit cycle and the fatigue prediction using Dang Van or Crossland criterion.A particular configuration, the interaction of a flat pad with rounded corners in contact with a flat substrate made, respectively, of Inconel In718 and Titanium Ti64 alloys, is studied. The shakedown state is analysed using the cyclic and ratcheting equivalent strain concepts already discussed in the literature.In the paper, different fretting maps, based on slip, shakedown and fatigue regimes, are numerically produced and analysed. A new variable, the global slip percentage, is proposed for the characterization of the stick–slip regimes. Analyses of a series of slip maps show that the different hardening models do not introduce significant changes in the stick–slip conditions. Using finite element method simulations combined with fatigue limit criteria (Dang Van and Crossland), fretting fatigue maps are qualitatively reproduced. The main contribution of this work is a comparative discussion on the influence of the hardening models complexity on such maps.

Numerical Investigation into the Effect of Contact Geometry on Fretting Fatigue Crack Propagation Lifetime

Fretting fatigue is a phenomenon in which two contact surfaces undergo a small relative oscillatory motion due to cyclic loading. There is a need to analyze the effects of contact geometry on crack propagation under fretting fatigue conditions. In this investigation, a finite element modeling method was used to study the effects of different contact geometries along with crack–contact interaction on crack propagation lifetime. Different contacts geometries—that is, cylindrical on flat and flat on flat—along with different contact span widths were analyzed. In addition, the effects of different contact spans on stress distribution at the contact interface were investigated. The computed crack propagation life was compared with experimental results. It was found that the crack initiated near the contact trailing edge for all contact geometries, which agreed with experimental observations. In terms of crack propagation for different contact spans, the fretting fatigue life for a two-based cylindrical pad was shorter than that for a two-based flat pad. By increasing the contact span width for both flat and cylindrical pads, the crack propagation lifetime increased. A comparison between the experimental and numerical results demonstrated a difference of about 18% in crack propagation lifetime.

Performance of inherently compensated flat pad aerostatic bearings subject to dynamic perturbation forces

The importance of air bearing design is growing in engineering. As the trend to precision and ultra precision manufacture gains pace and the drive to higher quality and more reliable products continues, the advantages which can be gained from applying aerostatic bearings to machine tools, instrumentation and test rigs is becoming more apparent. The inlet restrictor design is significant for air bearings because it affects the static and dynamic performance of the air bearing. For instance pocketed orifice bearings give higher load capacity as compared to inherently compensated orifice type bearings, however inherently compensated orifices, also known as laminar flow restrictors are known to give highly stable air bearing systems (less prone to pneumatic hammer) as compared to pocketed orifice air bearing systems. However, they are not commonly used because of the difficulties encountered in manufacturing and assembly of the orifice designs. This paper aims to analyse the static and dynamic characteristics of inherently compensated orifice based flat pad air bearing system. Based on Reynolds equation and mass conservation equation for incompressible flow, the steady state characteristics are studied while the dynamic state characteristics are performed in a similar manner however, using the above equations for compressible flow. Steady state experiments were also performed for a single orifice air bearing and the results are compared to that obtained from theoretical studies. A technique to ease the assembly of orifices with the air bearing plate has also been discussed so as to make the manufacturing of the inherently compensated bearings more commercially viable. (c) 2012 Elsevier Inc. All rights reserved.

Measurement of Tangential Contact Stiffness in Frictional Contacts: The Effect of Normal Pressure

The tangential contact stiffness of frictional interfaces affects both the vibration response and structural integrity of structures comprising frictional joints. Vibration and structural response of monolithic structures can be predicted very accurately; however, when assemblies of components involve frictional interfaces, additional damping and compliance are present due to these interfaces. These features make it more challenging to predict the vibration characteristics of assemblies with the same degree of accuracy as can be achieved for single components. If these interface properties can be determined, it should then be possible to significantly enhance current models of the vibration of engineering assemblies. Measurements of both force and displacement in the tangential direction are obtained from a series of in-line fretting tests involving flat pads with rounded corners clamped against the flat surface of a specimen which is oscillated by a hydraulic tensile testing machine. In order to measure the local displacement field very close to the contact interface, the digital image correlation (DIC) method is employed. The effect of normal contact pressure on tangential contact stiffness is investigated. Multiple experiments with the same parameters show good repeatability given the number of variables involved.

Finite Element Analysis of Fretting Fatigue Using Different Pad‘s Geometries and Compression Forces

In this paper, a finite element sub-modelling method is used to estimate the stress distribution and the crack propagation lifetime in Aluminium alloy, Al7075-T6 specimens. Different contact geometries, i.e. cylinder-on-flat and flat-on-flat, and different contact span width’s with different pad’s compression forces are analysed. It is found that fretting fatigue life for two based cylindrical pads is shorter than that for two based flat pads and in two based flat pads is shorter than that for perfectly flat pads. In the case of two based flat pads, stress distribution in the pad with width of 3.1 mm is about 14% higher than that in the pad with the width of 6.2 mm and about 21% higher than that in the pad with the width of 9.3 mm. Similarly, stress in cylindrical pads with width of 3.1 mm is 36% higher than that in the pad with width of 6.2 mm and 130% higher than that in the pad with width of 9.3 mm. Stresses increased by 21% for pad force of 1800 N and around 40% for pad force 2400 N compared with 1200 N pad force. Also it is observed that by increasing pad width for both flat and cylindrical pads, crack propagation lifetime increased. Furthermore, fretting fatigue crack growth rate raises when pads compression force increases.

Performance analysis of Pareto optimal bearings subject to surface error variations

A Pareto optimization study was carried out on a flat pad aerostatic bearing design. Some of the Pareto optimal configurations were then subjected to surface profiling errors including tilt, concavity, convexity and waviness and key performance parameters such as load capacity, stiffness and flow rate determined. From these studies it was concluded that multi-orifice aerostatic flat pad bearings are highly sensitive to surface profile variations and these surface profile variations are inherent limitations of the current manufacturing techniques. A technique to account for the sensitivity to manufacturing tolerance within air bearing optimization studies is also proposed.

The Analysis of Slurry Flow on Quartz Glass Polishing

CMP (Chemical Mechanical Polishing) attracts attention as a technology polishing the glass base of the photo mask used for the liquid crystal products. The quartz glass is rubbed up by polishing pad that the chemical liquid slurry is soaked. The slurry has important roles on CMP because it promotes polishing and removing rubbish by flowing between the polishing pad and quartz glass. However, slurry flow can't be observed easily, numerical analysis is useful tool to clarify the slurry flow phenomenon. The lattice grooved pad is paid attention in this study as a basic grooved pad to make the slurry flow efficiency. None grooved pad and the lattice grooved pad are analyzed, and the feature of each pad is clarified. The analysis results show the slurry isn't replaced easily near the pad center under the square quartz glass on flat pad. On the other hand, it becomes easy for the slurry to be transported on lattice grooved pad by the grooves, and it flows to the whole uniformly. When this analysis results are compared with experimental results, they agree qualitatively. Therefore, to supply the slurry uniformly, and to polish efficiently, it has been understood that the lattice grooved pad is excellent.