Actual Pressure Distribution Research Articles

Pressure Distribution Control on Surface Conformable Polishing in Chemical Mechanical Planarization

An original polishing mechanism with a triple layer pad was developed as a surface conformable polishing mechanism in CMP (Chemical Mechanical Planarization). According to the polishing mechanism, removal profile can be controlled by base plate curvature through an assist pad made of elastic material. A pad system supported by an envelope plane composed of five wafers contributes to make a wafer level paralleled to a pad level relatively during polishing. As the result, a static pressure distribution can be transferred precisely to a dynamic polishing profile regardless of strong shearing force by polishing. In order to verify the polishing removal controllability, an original pressure distribution analysis was developed by an actual pressure distribution measurement around an entire pad surface. The analyzed pressure distribution profile was in good agreement with the actual polishing profile. From the result that the static pressure profile can be transferred to the polishing profile precisely, it was verified that the polishing mechanism is reasonable for surface conformable polishing system in CMP.

Influence of the Swirling Flow in the Side Cavities of a High-Pressure Centrifugal Compressor on the Characteristics of Excited Acoustic Modes

Previous experimental investigations revealed the existence of acoustic modes in the side cavities of a high-pressure centrifugal compressor. These modes were excited by pressure patterns which resulted from rotor/stator-interactions (often referred to as Tyler/Sofrin-modes). The acoustic modes were significantly influenced by the prevailing flow in the side cavities. The flow field in such rotor/stator-cavities is characterized by a high circumferential velocity component. The circumferential velocity of the flow and the phase velocity of the acoustic eigenmode superimpose each other, so that the frequencies of the acoustic eigenmodes with respect to the stator frame of reference follow from the sum of both velocities. In the previous study the circumferential velocity was estimated based on existing literature and the phase velocities of the acoustic modes were calculated via an acoustic modal analysis. Based on these results the rotational speeds of the compressor, where acoustic modes were excited in resonance, were determined. The present paper is based on these results and focuses on the influence of the swirling flow and the coupling of the excited acoustic modes between the two side cavities. Such a coupling has been predicted in previous numerical studies but no experimental evidence was available at that time. In this study the circumferential velocities of the flow are determined by measuring the actual radial pressure distribution in the side cavities and assuming radial equilibrium. The determined values are directly used for the prediction of the rotational speeds at resonance. The values for the rotational speeds at resonance predicted that way are compared to the resonance speeds found in the experiments. Further on, simultaneously measured pressure fluctuations in the shroud and hub side cavities with respect to the rotor frame of reference give evidence about the coupling of the acoustic modes between the two side cavities in case of resonance. If the experimentally determined swirling flow velocity is accounted for in the prediction of acoustic resonances, the calculated rotational speeds of resonance are in good agreement with the experimental findings in most cases. Neglecting the flow in the cavities, however, leads to large deviations between calculated and experimentally determined rotational speeds. Varying the operating point of the compressor results in changes of the circumferential velocities in the side cavities and, therefore, in changes of the rotational speeds of resonance. Contrary to the acoustic modes calculated via a finite element analysis by the authors of this paper in previous studies the excited acoustic modes in the experiments are mostly not coupled between the two side cavities, but are localized to one of both cavities. This finding is assumed to be caused by the flow field in the compressor.

Groundwater inflow rate estimation considering excavation-induced permeability reduction in the vicinity of a tunnel

본 연구에서는 절리 암반 내 터널굴착 시 지하수 유출량 예측량이 실제 계측치와 큰 차이가 나는 이유 중 하나인 터널주변 절리암반의 투수계수의 감소 현상에 대해 논의하였다. 현재 터널 설계 시 일반적으로 사용되고 있는 지하수 유출량 산정식은 터널주변 암반이 등방, 균질하고 일정한 투수계수를 유지한다고 가정한다. 하지만, 실제로는 터널주변 절리암반의 투수계수는 터널주변 유효응력 상태에 따라 변화하며, 절리 내 지하수 흐름에 따라 다시 터널주변 유효응력 분포가 영향을 받는 수리-역학적 상호거동을 보인다. 터널굴착 직후 터널 접선방향 유효응력이 응력집중과 간극수압 감소로 인해 급증하고 그에 따라 절리의 닫힘현상이 발생하며, 결과적으로 터널인접 절리암반 링 구간에서 투수계수가 급격히 감소하게 된다. 이러한 터널인접 링 구간 내에서 상당히 큰 간극수압 감소가 발생하게 되어 터널주변 간극수압 분포는 등방 균질의 절리암반으로 가정한 산정식과 큰 차이를 보인다. 본 연구에서는 절리암반의 수리-역학적 상호거동의 개념을 도입하여 터널주변 간극수압 분포와 터널 내 지하수 유입량 산정방법을 제안하고 이를 수치해석을 통해 검증하였다. This paper discussed about the effect of permeability reduction of the jointed rock mass in the vicinity of a tunnel which is one of the reasons making large difference between the estimated ground-water inflow rate and the measured value. Current practice assumes that the jointed rock mass around a tunnel is a homogeneous, isotropic porous medium with constant permeability. However, in actual condition the permeability of a jointed rock mass varies with the change of effective stress condition around a tunnel, and in turn effective stress condition is affected by the ground water flow in the jointed rock mass around the tunnel. In short time after tunnel excavation, large increase of effective tangential stress around a tunnel due to stress concentration and pore-water pressure drop, and consequently large joint closure followed by significant permeability reduction of jointed rock mass in the vicinity of a tunnel takes place. A significant pore-water pressure drop takes place across this ring zone in the vicinity of a tunnel, and the actual pore-water pressure distribution around a tunnel shows large difference from the value estimated by an analytical solution assuming the jointed rock mass around the tunnel as a homogeneous, isotropic medium. This paper presents the analytical solution estimating pore-water pressure distribution and ground-water inflow rate into a tunnel based on the concept of hydro-mechanically coupled behavior of a jointed rock mass and the solution is verified by numerical analysis.

Load Capacity of Partially Textured Slip Parallel Slider and Concentric Journal Bearing Using Narrow Groove Theory

Load capacity of partially textured slip parallel slider and concentric journal bearing is estimated using narrow groove theory (NGT). The overall pressure distribution in a hydrodynamic bearing using NGT provides a good approximation to the actual pressure distribution around bearing with large but finite number of grooves. The non-dimensional pressure expressions are derived based on one-dimensional analysis. The partially textured slip parameters used in the analysis are: non-dimensional texture length; land with slip to recess region ratio; non-dimensional slip coefficient; and non-dimensional depth of recess. Partially textured slip is effective in the case of parallel slider and concentric journal bearing to yield load capacity.

The point and area-averaged wind pressure influenced by conical vortices on saddle roofs

This paper investigates the point pressure and area-averaged wind pressure distributions on saddle roofs occurring below conical vortices. A wind tunnel study was firstly conducted to obtain the actual wind pressure distribution under different wind attack angles. The mean pressure distribution is used to identify the flow conditions that favor the formation of conical vortices. The vortex strength is compared under different wind directions. Suction and correlation coefficients beneath vortex cores were analyzed to identify the most unfavorable wind direction for saddle roofs, i.e. along the connection of the roof points with the highest elevations. The non-Gaussian distributions of pressure fluctuation on saddle roofs exposed to conical vortices are presented. Exponential decay function representing the suction decay throughout the influence area of conical vortices on saddle roofs is proposed. Second, the area-averaged pressures are calculated by averaging all pressure taps within the area at each instant of time. A relationship between peak loads over various tributary zones and increasing tributary areas is presented, fitted, and verified by comparing with the probability density curve of single point pressures. The Non-Gaussian feature of the area-averaged pressure time series is compared with that of point pressures using higher order moments (i.e. skewness and kurtosis). Results indicate that area-averaged pressures, whose uniform fluctuations concentrate on low-frequency ranges, are more normally distributed than individual pressures.

Measurement of the clamping pressure distribution in polymer electrolyte fuel cells using piezoresistive sensor arrays and digital image correlation techniques

A combined method for the simultaneous measurement of the clamping pressure distribution and endplates deformation in polymer electrolyte fuel cells (PEFC) is presented. The proposed approach, which allows overcoming some important limitations associated with the use of conventional pre-scaled pressure films, is used to investigate the correlation between the actual pressure distribution on the membrane electrode assembly (MEA), the endplate out-of-plane deformation and the applied clamping torque, for two single fuel cells assembled with either copper or aluminium/copper endplates. Results proved that, in point-load design PEFCs, both pressure magnitude and distribution are affected by endplates deformation and thickness mismatching between the sealing gasket and the MEA. Moreover, while the average pressure on the MEA displays a slight increase (+25%) as the clamping torque is raised from 5 to 10Nm, it increases monotonically on the sealing gasket, with local peaks that exceed the saturation level of the sensor array (20.7MPa). A dimensionless uniformity index has been introduced to assess the uniformity of the pressure distribution, allowing an easy comparison of different fuel cell assembly configurations. The proposed methodology might assist the design of next-generation fuel cells or could be used as a powerful validation tool for detailed finite element models. It can also be applied to study other kind of fuel cells and batteries as well.

Can we predict outcome of surgical reconstruction of Charcot neuroarthropathy by dynamic plantar pressure assessment?—A proof of concept study

The joint deformity that arises as a result of Charcot neuroarthropathy, leads to gait modification. Ulceration risk associated with the deformity is generally assessed by measuring plantar pressure magnitude (PPM). However, as PPM is partially dependent on gait speed and treatment interventions may impact speed, the use of PPM to validate treatment is not ideal. This study suggests a novel assessment protocol, which is speed independent and can objectively (1) characterize abnormality in dynamic plantar loading in patients with foot Charcot neuroarthropathy and (2) screen improvement in dynamic plantar loading after foot reconstruction surgery. To examine whether the plantar pressure distribution (PPD) measured using EMED platform, was normal, a customized normal distribution curve was created for each trial. Then the original PPD was fitted to the customized normal distribution curve. This technique yields a regression factor (RF), which represents the similarity of the actual pressure distribution with a normal distribution. RF values may range from negative 1 to positive 1 and as the value increases positively so does the similarity between the actual and normalized pressure distributions. We tested this novel score on the plantar pressure pattern of healthy subjects ( N = 15), Charcot patients pre-operation ( N = 4) and a Charcot patient post-foot reconstruction ( N = 1). In healthy subjects, the RF was 0.46 ± 0.1. When subjects increased their gait speed by 29%, PPM was increased by 8% ( p < 10 −5), while RF was not changed ( p = 0.55), suggesting that RF value is independent of gait speed. In preoperative Charcot patients, the RF < 0, however, RF increased post-surgery (RF = 0.42), indicating a transition to normal plantar distribution after Charcot reconstruction.

The Lubrication Regime at Pin-Pulley Interface in Chain CVTs

This paper deals with the strongly nonstationary squeeze of an oil film at the interface between the chain pin and pulley in chain belt continuously variable transmission. We concentrate on the squeeze motion as it occurs as soon as the pin enters the pulley groove. The duration time to complete the squeeze process compared with the running time the pin takes to cover the entire arc of contact is fundamental to understand whether direct asperity-asperity contact occurs between the two approaching surfaces to clarify what actually is the lubrication regime (elastohydrodynamic lubrication (EHL), mixed, or boundary) and to verify if the Hertzian pressure distribution at the interface can properly describe the actual normal stress distribution. The Hertzian pressure solution is usually taken as a starting point to design the geometry of the pin surface; therefore, it is of utmost importance for the designers to know whether their hypothesis is correct or not. Taking into account that the traveling time, the pin spends in contact with the pulley groove, is of about 0.01 s, we show that rms surface roughness less than 0.1 μm, corresponding to values adopted in such systems, guarantees a fully lubricated EHL regime at the interface. Therefore, direct asperity-asperity contact between the two approaching surfaces is avoided. We also show that the Hertzian solution does not properly represent the actual pressure distribution at the pin-pulley interface. Indeed, after few microseconds a noncentral annular pressure peak is formed, which moves toward the center of the pin with rapidly decreasing speed. The pressure peak can grow up to values of several gigapascals. Such very high pressures may cause local overloads and high fatigue stresses that must be taken into account to correctly estimate the durability of the system.

An artificial intelligence approach for measurement and monitoring of pressure at the residual limb/socket interface – a clinical study

A good-fitting prosthetic socket requires the pressure between the stump and socket to be distributed to ensure the load is carried by pressure tolerant regions of the limb. Transducers and Finite Element Analysis have been utilised to measure and monitor these pressures. However, it has been recognised that both techniques have limitations, making them impractical for everyday clinical use to aid the prosthetist in the socket fitting process. This paper details the design of a Hybrid Inverse Problem Engine (HIPE) which combines Artificial Intelligence (AI) and experimental/numerical data to create a less invasive and passive approach to develop a practical clinical tool for predicting the pressure distribution at the limb/socket interface. Testing and validation of the HIPE under laboratory conditions showed that the technique was able to predict the location and magnitude of pressures applied manually to the socket. A comparison of the predicted pressure distribution found using the HIPE, at the limb/ socket interface of a patient in a clinical environment with photoelastic data of the actual pressure distribution, further indicated the technique's potential benefits. It is hoped that the HIPE will eventually become a general tool suitable for monitoring the fit of a prosthesis in a clinical environment.

Simultaneous subsurface defect detection and contact parameter assessment in a wheel–rail system

In the last few years, a non-conventional ultrasonic approach has been proposed by the authors to experimentally assess the main contact parameters in wheel–rail systems. This technique, which is based on the analysis of the reflection of high frequency ultrasonic waves from the wheel–rail interface, makes it possible to obtain graphic maps from which we can observe the shape of the contact area, measure its size, and also collect qualitative information about contact pressure distribution. Furthermore, ultrasonic waves are quite well known as one of the primary non-destructive testing techniques useful in checking the presence of cracks in wheels, rails and axles. Thus, it was thought to combine these two approaches to obtain a single tool capable of supplying at the same time information about wheel–rail contact and the possible presence of subsurface cracks, which are typically located a few millimeters below the surface. This study reports the results of a series of experiments, performed on realistic wheel–rail couplings, in which the wheel was characterized by the presence of subsurface defects of known geometry. For each case tested, the whole ultrasonic waveform (which contains information about both the contact interface and a certain thickness of the wheel to investigate) was acquired and analyzed with dedicated software. The original data, expressed in terms of amplitude of reflected peaks, have been processed to obtain a number of graphic maps which, layer by layer, starting from the surface, give an idea first of all of contact conditions and, at the same time, of what kind of anomalies are present below it. These data are potentially useful in supporting numerical studies on the propagation of rolling contact fatigue (RCF) subsurface cracks by providing both actual contact pressure distribution and geometry of the cracks.

Application of an Ultrasonic Technique to Assess Contact Performance of Bolted Joints

Bolted joints are a widespread type of connection used in mechanical engineering, but their performance, in terms of contact area size and shape and pressure distribution, is not easy to verify due to the nature of closed contact, which makes it difficult to investigate them with most experimental techniques. This study proposes the application of an ultrasonic method (through immersion scans of the potential contact region between the members of a bolted joint) aimed at obtaining both graphical maps of contact conditions and, after a calibration process, actual contact pressure distributions. The analysis is carried out on a number of joints characterized by different values of plate thickness and applied load. Moreover, to evaluate the quantitative accuracy of the ultrasonic technique, the results have been compared to those of another experimental technique (pressure-sensitive film) and numerical findings obtained by a finite element model of the experimental setup.

Three-dimensional dynamic hip contact area and pressure distribution during activities of daily living

Estimation of the hip joint contact area and pressure distribution during activities of daily living is important in predicting joint degeneration mechanism, prosthetic implant wear, providing biomechanical rationales for preoperative planning and postoperative rehabilitation. These biomechanical data were estimated utilizing a generic hip model, the Discrete Element Analysis technique, and the in vivo hip joint contact force data. The three-dimensional joint potential contact area was obtained from the anteroposterior radiograph of a subject and the actual joint contact area and pressure distribution in eight activities of daily living were calculated. During fast, normal, and slow walking, the peak pressure of moderate magnitude was located at the lateral roof of the acetabulum during mid-stance. In standing up and sitting down, and during knee bending, the peak pressures were located at the edge of the posterior horn and the magnitude of the peak pressure during sitting down was 2.8 times that of normal walking. The peak pressure was found at the lateral roof in climbing up stairs which was higher than that in going down stairs. These results can be used to rationalize rehabilitation protocols, functional restrictions after complex acetabular reconstructions, and prosthetic component wear and fatigue test set up. The same model and analysis can provide further insight to soft tissue loading and pathology such as labral injury. When the pressure distribution on the acetabulum is inverted onto the femoral head, prediction of subchondral bone collapse associated with avascular necrosis can be achieved with improved accuracy.

Film pressure distributions in point contacts predicted by thermal EHL analyses

In general, lubricated rolling/sliding contact fatigue problems have been investigated by assuming Hertzian contact pressure distributions. In this paper, thermal EHL analyses in consideration of the variations in oil properties in all directions within the film have been carried out under conditions of circular and elliptical contacts. It has been found that the actual film pressure distributions differ markedly from the Hertzian pressure distribution depending on the thermal conductivities of both contacting surfaces, slide–roll ratios and viscosity–pressure coefficients.

Thermo-mechanical model with adaptive boundary conditions for friction stir welding of Al 6061

Thermo-mechanical simulation of friction stir welding can predict the transient temperature field, active stresses developed, forces in all the three dimensions and may be extended to determine the residual stress. The thermal stresses constitute a major portion of the total stress developed during the process. Boundary conditions in the thermal modeling of process play a vital role in the final temperature profile. The heating and cooling rates with the peak temperature attained by the workpiece determine the thermal stress. Also, predicting realistic peak temperature becomes important as the operating temperature at the interface of tool-workpiece is very close to the solidus temperature of the aluminum workpiece. The convection heat-transfer coefficients of the surfaces exposed to air can be theoretically determined using Newton's law of cooling. Contact conductance depends on the pressure at the interface and has a non-uniform variation. The actual pressure distribution along the interface is dependent on the thermal stress from local temperature and non-linear stress–strain state. Therefore, applying an adaptive contact conductance can make the model more robust for process parameter variations. A finite element thermo-mechanical model with mechanical tool loading was developed considering a uniform value for contact conductance and used for predicting the stress at the workpiece and backplate interface. This pressure distribution contours are used for defining the non-uniform adaptive contact conductance used in the thermal model for predicting the thermal history in the workpiece. The thermo-mechanical model was then used in predict stress development in friction stir welding.

Analyses of the fuel cell stack assembly pressure

A proper stacking design and cell assembly are important to the performance of fuel cells. The cell assembly will affect the contact behavior of the bipolar plates with the membrane electrode assembly (MEA). Not enough assembly pressure may lead to leakage of fuels, high contact resistance and malfunctioning of the cells. Too much pressure, on the other hand, may result in damage to the gas diffusion layer and/or MEA. The stacking design may affect the pressure distribution within the fuel cell stack and thus the interfacial contact resistance. Uneven distribution of the contact pressure will result in hot spots which may have a detrimental effect on fuel cell life. In this study, finite element analysis (FEA) procedures were established for a PEM single cell with point stack assembly method. The mechanical properties and geometrical dimensions of all the fuel cell components, such as bipolar plates, membrane, gas diffusion layer and end plates were collected for accurate simulation. From the FEAs, the compliance as well as the pressure distribution of the single cell was calculated. In order to verify the results of the analysis, experimental tests, with a pressure film inserted between the bipolar plates and the MEA, were conducted to establish the actual pressure distribution. Color variations of the pressure film could be calibrated to obtain pressure distribution. Compliance of the gas diffusion layer was also measured. The analysis procedures for the fuel cell stacking assembly were established by comparing the simulation results with those of the experimental data at various levels of assembly pressures. They can help determine the proper stacking parameters such as stacking design, bipolar plate thickness, sealing size and assembly pressure, and are important in obtaining a consistent fuel cell performance.

Measurement of bite force variables related to human discrimination of left–right hardness differences of silicone rubber samples placed between the incisors

This study was designed to examine human subjects' ability to discriminate between spatially different bite pressures. We measured actual bite pressure distribution when subjects simultaneously bit two silicone rubber samples with different hardnesses using their right and left incisors. They were instructed to compare the hardness of these two rubber samples and indicate which was harder (right or left). The correct-answer rates were statistically significant at P < 0.05 for all pairs of different right and left silicone rubber hardnesses. Simultaneous bite measurements using a multiple-point sheet sensor demonstrated that the bite force, active pressure and maximum pressure point were greater for the harder silicone rubber sample. The difference between the left and right was statistically significant (P < 0.05) for all pairs with different silicone rubber hardnesses. We demonstrated for the first time that subjects could perceive and discriminate between spatially different bite pressures during a single bite with incisors. Differences of the bite force, pressure and the maximum pressure point between the right and left silicone samples should be sensory cues for spatial hardness discrimination.

圧力分布測定用ロードセルに関する研究(J14-2 人体計測と制御,J14 ヒューマン・ダイナミクス)

A system to measure the pressure distribution that acts on a surface of a structure is investigated. This system has some difficulties owing to the change of the boundary conditions in the contact area if sensors are directly put on the surface. In order to overcome the difficulties, an alternative method is proposed. In the present system, the strain informations are measured apart from the contact area, and inverse analysis is applied to obtain pressure distribution acting on the surface of the structure using supplementary information of the strains. On the process of the inverse analysis, some regularization technique, Tikhonov method and truncating singular value decomposition (TSVD), are employed to avoid the instability of the numerical solutions. A simple experimental study is performed to confirm the validity of the present method, where a load cell is made to measure the actual foot pressure distribution.

Actual extreme pressure distributions and LRC formula

This paper discusses the conditionally sampled actual wind pressure distributions causing peak quasi-static internal forces in the structural frames of a low-rise building model with a square plan. The actual extreme pressure distributions are compared with Kasperski's load–response-correlation (LRC) formula and the quasi-steady pressure distributions. The validity of Kasperski's LRC formula is proved to estimate the actual extreme wind load for the general location of the frame including the separation bubble region. The only exception was where the frame was immersed in the vicinity of the leading edge, where the non-Gaussian characteristics are predominant. The reason for the discrepancy in the LRC pressure distribution and the actual extreme pressure distribution is attributed to the intermittent characteristics of the fluctuating pressure field in the vicinity of the leading edge, which cannot be represented by the temporal average characteristics.

Optical Pedobarography for Assessing Neuropathic Feet in Diabetic Patients—A Review

The use of optical pedobarography is presented in this article. The limitations of the analytical methods using peak pressures as a parameter for assessment of foot at risk of plantar ulcers are indicated. A new method, which takes into consideration the actual plantar pressure distribution using the power ratio PR (the ratio of high-frequency power to the total power in the walking foot pressure image distribution)and relates it to 3 levels of sensation loss is described. PR is able to detect early loss of foot sensation characterized by a loss of sensation level of 4.5 gm. The methods available in the literature for management of foot ulcers by proper footwear design, and their limitations, are discussed. A new method of individualized footwear based on matching the softness of the footwear insole with the softness of normal foot sole soft tissue (having durometer reading of 20 degrees Shore) and optimum insole thickness (12 mm) is helpful in the prevention of plantar ulcers.

Simulation of non-Gaussian wind pressures on a 3-D bluff body and estimation of design loads

In some previous research works, the authors have discussed the determination of the actual wind pressure distribution on the surfaces of 3-D irregular buildings of large size [see the papers by Borri and Facchini, In: Proceedings of the 10th International Conference on Wind Engineering, Balkema Publishers, 1995; 8th ASCE Specialty Conference on Probabilistic Mechanics and Structural Reliability, 2000; Structural Dynamics, vol. 1, Balkema Publishers, 1999, p. 3; and by Bartoli et al., In: 4th International Colloquium on Bluff Body Aerodynamics & Applications, 2000]. Owing to the complex shape of the buildings, experimental campaigns in boundary layer wind tunnel (BLWT) are usually carried out, with the aim of determining the dynamic wind pressures: the evaluation of their time and space correlation structure and the characterization of the stochastic properties of pressure fields. The present paper focuses on the computational aspects for determining the actual design loads leading to effects, which are equivalent to the dynamic action, caused by turbulent wind.