Pressure Path Research Articles

Groundwater changes in relation to seismic activity: a case study from Eskipazar (Karabuk, Turkey)

The reported study contributes to research on earthquake prediction. Between 2007 and 2009, changes were observed in two geothermal and mineral springs located in Eskipazar (∼3–5 km to the north of the North Anatolian Fault Zone) in Turkey, in relation to small-magnitude earthquakes. During pre-seismic and post-seismic activities, variations were observed in the hydrogeological parameters of the spring waters. Temperature increases of 0.4–1°C were measured in one of the springs prior to three different earthquakes. There was a slight increase in the spring discharge with respect to the first earthquake, which occurred closest to the spring. This led to a reduction in electrical conductivity (EC), total dissolved solids (TDS), Ca, HCO3, δ13C, Al, Mn, and Fe concentrations in the spring water, whereas tritium and Se values increased. Several days before the third earthquake, which occurred at a shallower depth, a decrease was observed in the discharge, which led to a reduction in tritium, δ13C and Si concentrations. These variations could be explained by changes in the mixing ratio of waters of different genesis, depending on changes in permeability, pore pressure, and flow paths of the aquifer due to regional stress changes.

Predictors of single‐leg standing balance in individuals with medial knee osteoarthritis

To identify factors related to single-leg standing balance in individuals with medial compartment knee osteoarthritis (OA). This cross-sectional study assessed clinical, demographic, and biomechanical measures in 57 individuals and their relationships with single-leg standing balance. Differences in age, mass, symptoms, knee pain, radiographic severity, lower extremity alignment, and hip and knee extension as well as hip abduction torques were compared between those who could and could not perform 3 trials of single-leg standing balance. Multiple regression was used to identify predictors of center of pressure (COP) path length in those who could complete the task. Thirty-four individuals (60%) successfully completed all 3 single-leg standing balance trials and were significantly younger (P = 0.003) than those who could not. No other variable was significantly different between the groups. Disease severity, number of painful knees, lower extremity alignment, pain intensity, and quadriceps torque were all significant predictors of COP path length. Specifically, better single-leg standing balance (smaller COP path length) was related to more severe radiographic changes and stronger quadriceps, those with bilateral symptoms, and to less varus malalignment and knee pain. Single-leg standing balance in those with medial knee OA is related to the modifiable factors lower extremity alignment, knee pain, and quadriceps strength. Given the reduced balancing ability in this patient population, interventions targeting these factors are necessary.

Evaluation of Shear Modulus and Damping Ratio of Granular Materials Using Discrete Element Approach

In this paper, an attempt has been made to highlight the influence of different parameters such as number of cycles, confining pressure, void ratio, gradation, initial anisotropy and stress path on the dynamic properties of granular materials using Discrete Element Method (DEM). A series of strain controlled cyclic triaxial numerical simulations using three dimensional DEM have been carried out on an assembly of spheres. Dynamic properties such shear modulus (G) and damping ratio (D) were determined from the typical hysteresis loop obtained during cyclic triaxial test simulation. It has been observed from the test results that the numerical simulation using DEM has captured the variation of dynamic properties over a wide range of shear strain values for different parameters considered for the current investigation. Maximum shear modulus (Gmax) was found to be influenced by initial confining pressure, void ratio, gradation and initial anisotropy. Whereas, the damping ratio (D) was found to be influenced by number of cycles, initial confining pressure, gradation and stress path. Further it has been shown that the variation of shear modulus with shear strain can be divided into three distinct zones such as Isotropic Zone (IZ), Anisotropic Zone (AZ) and Stable Anisotropic Zone (SAZ). A drastic reduction of shear modulus with shear strain has been observed in the Anisotropic Zone (AZ). In addition, the results obtained using numerical simulations have been compared with the laboratory experimental values.

Pressure-volume-temperature relationship of Fe72Pt28 alloy under high pressure and temperature

The pressure-volume relationship of Fe72Pt28 alloy was investigated at 300, 500, 700, 900, 1100, and 1300 K by performing energy-dispersive X-ray diffraction measurements using a white X-ray beam produced from synchrotron radiation at the High Energy Accelerator Organization, Japan. The pressure-volume relationship measurements were performed only along the decreasing the pressure path. Below 700 K and 3.5 GPa, the compressibility of Fe72Pt28 alloy increased with the pressure. Above 900 K, the pressure-volume relationship was almost linear. Further the temperature-volume relationship at high pressures was linear. An abrupt decrease in the volume or a thermal expansion coefficient anomaly, which was observed in the case of Fe69Ni31 alloy in previous experiments, was not observed in the case of Fe72Pt28 alloy,

Buckling and postbuckling of radially loaded microtubules by nonlocal shear deformable shell model

This paper presents an investigation on the buckling and postbuckling of microtubules (MTs) subjected to a uniform external radial pressure in thermal environments. The microtubule is modeled as a nonlocal shear deformable cylindrical shell which contains small scale effects. The governing equations are based on higher order shear deformation shell theory with a von Kármán–Donnell-type of kinematic nonlinearity and include the extension-twist and flexural-twist couplings. The thermal effects are also included and the material properties are assumed to be temperature-dependent. A singular perturbation technique is employed to determine the buckling pressure and postbuckling equilibrium paths. The small scale parameter e 0 a is estimated by matching the buckling pressure of MTs measured from the experiments with the numerical results obtained from the nonlocal shear deformable shell model. The numerical results show that buckling pressure and postbuckling behavior of MTs are very sensitive to the small scale parameter e 0 a. The results reveal that the 13_3 microtubule has a stable postbuckling path, whereas the 13_2 microtubule has an unstable postbuckling behavior due to the presence of skew angles.

Orientation mapping applied to the study of ferroelectric ceramic

Orientation imaging microscopy (OIM) is a technique which allows crystallographic information to be obtained from samples both in scanning and transmission electron microscopes (SEM/TEM). Microstructure can be quantitatively characterized, different phases identified, and grain boundary character and morphology described. This technique based on electron backscatter diffraction (EBSD) in the SEM has shown in the last decade a spectacular advance in speed and quality of the data as well as post-processing procedures. In most cases the investigated samples are conductive and one encounters no problems connected with specimen charging. Controlling the charge and quality of the surface are the challenges for the operator running experiments on insulators. Specimen charging obscures both the forward scatter electron image and decreases the EBSD pattern quality making its analysis difficult or even impossible. Also final steps of sample preparation largely determine whether or not the pattern quality is sufficient for indexing. The influence of gas pressure and gas path length on the image quality of diffraction pattern is illustrated with the results of experiments carried out on the (PbLa)(ZrTi)O3 ceramics. Ferroelectric domains in the PLZT grains have been identified both by EBSD in the SEM and BF images in the TEM. Domains in particular grains have the same crystal orientations but different polarisation directions.

Study of Forming Parameters in Hydroforming of a Thin-Walled ASTM C11000 Copper Tube

Tube hydroforming technology is still considered a new technique growing fast in automotive and aircraft industries. Many researches on all aspects of this process are still required. Contact friction is one of the most effective parameters on tube wall thinning. To successfully fulfill the process without any common defects, it is very important to determine the proper internal pressure and axial feeding loading paths. In this paper, the effect of lubrication on tube wall thinning on ASTM C11000 copper alloy is discussed as well as the effect of internal pressure and axial feeding. An axisymmetric bulged tube is investigated using theoretical, numerical and experimental methods. Improved linear and non-linear pressure and feeding loading paths are applied and the predicted results are experimentally proved. It is observed that non-linear pressure application gives smoother results. Also proper lubrication plays an important role in success of the process.

Laboratory Study of the Effective Pressure Law for Permeability of the Low‐Permeability Sandstones from the Tabamiao Area, Inner Mongolia

AbstractLaboratory experiments with two modified factorial designs were performed to determine the effective pressure law for permeability of two low permeability sandstone samples from the Tabamiao area, Inner Mongolia. Two modified factorial schemes were adopted for the experiments. The first included three cycles, of which each run through loading and unloading confining pressure (Pc) in a constant‐pore‐pressure condition. The second scheme has four cycles, of which each run through raising and lowering pore pressure (Pp) in a constant‐confining‐pressure condition. Permeability data were collected by the steady‐state method. The response‐surface method was used which supposed that nothing was known about the material behavior, and a model was built empirically by matching an approximate k – Pc – Pp surface to the data. The coefficients describing the surface reflected information about material behavior and were transformed into κ – Pc – Pp response surface. The κ – Pc – Pp surfaces show that at intervals along the pressure path the κ values in the effective pressure law (Peff = Pc – κPp) varied with pore and confining pressure. At the highest confining pressure 44 MPa in the test, the values of κ of two samples were all significantly less than 1.0 and even below zero at some low pore pressure. The data suggest that values decrease with increasing confining pressure and lowering pore pressure, and are very small at high confining pressure and low pore pressure. This can be interpreted in terms of the changes in the geometry of the micro‐cracks during closure and the deformation of the rock particles after the closure of micr‐cracks with increasing confining pressure and lowering pore pressure.

Nonlinear Buckling and Postbuckling Behavior of 3D Braided Composite Cylindrical Shells Under External Pressure Loads in Thermal Environments

Nonlinear buckling and postbuckling behavior for a 3D braided composite cylindrical shell of finite length subjected to lateral pressure, hydrostatic pressure, or external liquid pressure in thermal environments have been presented in this paper. Based on a new micromacromechanical model, a 3D braided composite may be treated as a cell system and the geometry of each cell is deeply dependent on its position in the cross section of the cylindrical shell. The material properties of the epoxy are expressed as a linear function of temperature. The governing equations are based on Reddy’s higher order shear deformation shell theory with a von Kármán–Donnell type of kinematic nonlinearity and including thermal effects. A singular perturbation technique is employed to determine the buckling pressure and postbuckling equilibrium paths. The numerical illustrations concern the postbuckling behavior of perfect and imperfect braided composite cylindrical shells with different values of geometric parameter and of fiber volume fraction in different cases of thermal environmental conditions. The results show that the shell has lower buckling pressures and postbuckling paths when the temperature-dependent properties are taken into account. The results reveal that the temperature changes, the fiber volume fraction, and the shell geometric parameter have a significant effect on the buckling pressure and postbuckling behavior of braided composite cylindrical shells.

Novel combined standard hydromechanical sheet hydroforming process

Sheet hydroforming techniques are widely used in industries for the production of different components with specific characteristics. Despite the advantages of the conventional sheet hydroforming techniques, they have their own limitations. In this paper, to increase the application and to overcome the limitations of conventional deep drawing, a new sheet hydroforming technique is proposed that is a combination of the standard and the hydromechanical sheet hydroforming processes. The proposed method has the advantages of conventional processes but eliminates their limitations. This technique is used in forming a cylindrical cup and a complex industrial part. After applying the appropriate pressure path, the products are formed successfully in one stage without any defects. It is also shown that the required forming pressure in the proposed process is low compared with other sheet hydroforming processes. It is demonstrated that because of the low internal pressure required in the present method, pre-bulging does not have any significant effect on the thickness distribution of the product. It is concluded that in this process increasing the friction coefficient between punch and blank can reduce the sheet thinning.

Non-linear buckling and postbuckling of shear deformable anisotropic laminated cylindrical shell subjected to varying external pressure loads

Abstract Non-linear buckling and postbuckling of a moderately thick anisotropic laminated cylindrical shell of finite length subjected to lateral pressure, hydrostatic pressure and external liquid pressure has been presented in the paper. The material of each layer of the shell is assumed to be linearly elastic, anisotropic and fiber-reinforced. The governing equations are based on a higher order shear deformation shell theory with von Karman–Donnell-type of kinematic non-linearity and including the extension/twist, extension/flexural and flexural/twist couplings. The non-linear prebuckling deformations and initial geometric imperfections of the shell are both taken into account. A singular perturbation technique is employed to determine the buckling pressure and postbuckling equilibrium paths. The numerical illustrations concern the postbuckling response of perfect and imperfect, moderately thick, anisotropic laminated cylindrical shells with different values of shell parameters and stacking sequence. The results confirm that there exists a circumferential stress along with an associate shear stress when the shell is subjected to external pressure.

Numerical and experimental investigation of the effect of the pressure path on forming metallic bellows

Tubular metal bellows have wide applications in different industries. They are mainly manufactured in the open die hydroforming process, which comprises two stages of bulge and closing (final forming). In this paper, the effect of pressure path on forming bellows in both stages was studied by finite element simulation and experiment. The results obtained from simulation illustrated that the pressure path influences the production of the desired parts, or the occurrence of bursting or wrinkling defects in the products. Experiments were carried out to verify the simulation results. By using the simulation and experimental results a comprehensive forming window for bellows was presented. Based on this forming window, the wrinkling and bursting defects for bulge and closing stages, and the safe zone for producing the desired part were determined. The study also showed that the number of convolutions does not influence the internal pressure and maximum forming load, but affects the forming energy.

Integration of gradient based and response surface methods to develop a cascade optimisation strategy for Y-shaped tube hydroforming process design

In the last years a strong research effort was produced in order to develop and design new forming technologies able to overcome the typical drawbacks of traditional forming operations. Among such new technologies, hydroforming proved to be one of the most promising. The design of tube hydroforming operations is mainly aimed to prevent bursting or buckling occurrence and such issues can be pursued only if a proper control of both material feeding history and internal pressure path during the process is performed. In this paper, a proper optimisation strategy was developed on Y-shaped tube hydroforming process which is characterized by a quite complex process mechanics with respect to axi-symmetric tube hydroforming operations. The design procedure was aimed to properly calibrate the internal pressure histories. The basic idea, in this paper, is to integrate a steepest descent method with a moving least squares approach in order to reach the optimal internal pressure curve in the hydroforming of an Y-shaped steel tube. Thus, a cascade optimisation procedure was implemented which consisted of two optimisation steps: the former is focused on the application of a steepest descent method, the latter is based on a response surface approach utilising a moving least squares approximation. The cascade procedure was driven by the will to reduce the total number of numerical simulations necessary to reach the optimum with respect to other optimisation methods.

Effect of tibial re-alignment surgery on single leg standing balance in patients with knee osteoarthritis

Background Standing balance is impaired in individuals with knee osteoarthritis and is associated with disease severity. The effects of surgical interventions on standing balance have received little attention. The purpose of the present study was to examine measures of balance during tests of single-limb standing before and after medial opening wedge high tibial osteotomy – a lower limb re-alignment procedure for those with varus alignment and knee osteoarthritis. Methods Standing balance was assessed in 49 individuals prior to and 12 months following medial opening wedge high tibial osteotomy. Participants performed three trials of single-limb balance lasting 10 s each while standing on a force platform. Anteroposterior and mediolateral coordinates of the centre of pressure were obtained from the force platform and used to calculate the total centre of pressure path length as well as the range and variability (standard deviation) of the anteroposterior and mediolateral coordinates. Findings Though all centre of pressure measures were lower following high tibial osteotomy, none reached statistical significance ( P > 0.05) and effect sizes were small ( d < 0.34). The largest mean improvement was 7.6% (95% confidence interval: −0.7–15.8%). Interpretation Results indicate that standing balance in individuals with knee osteoarthritis is not significantly different following high tibial osteotomy surgery. Standing balance in this patient population is a complex process not entirely dictated by disease symptoms or structural factors such as alignment.

Experimental Study of Lubrication Influence in the Production of Hydroformed T-Joint Tubes

THF process is a forming technique that consists of tube deformation by means of hydraulic pressure and punches which guarantee the tube ends feeding and sealing. In the last years, this technique found a large and rapid diffusion thanks to its many advantages with respect to conventional processes: parts weight reduction, tighter dimensional tolerances, lower costs or fewer secondary assembly operations. Besides, many lacks in the process knowledge still represent an obstacle and they are usually bypassed by trial and error methods. Therefore, lot of studies were conducted to better understand the influence of the process parameters, such as pressure path, punch stroke or material behaviour. In this paper, an experimental study of tubular T-joints made of copper manufactured by means of THF process is described. The aim of this work is to analyze the tube-die interface friction condition effects on the final part. In fact, material flow during the process is greatly influenced by the friction conditions between tube and die especially due to the high pressure acting inside the tube. Different lubrication types were considered: dry, oil, Teflon, Teflon with oil, Teflon spray and Graphitic oil. Two different experimental campaigns were performed in this investigation. The first one was carried out in order to estimate the lubricant friction coefficients using a Pin on Disk tribometer. The second one was performed to study the effects of the lubrication on the process and the tests were conducted hydroforming T-joints under the different lubrication conditions considered. The collected data allowed to identify how the different lubrication conditions affect the final workpiece geometry. Moreover, a critical aspect of the process related to the tube wrinkling was identified and a solution was proposed.

A gradient-based decomposition approach to optimize pressure path and counterpunch action in Y-shaped tube hydroforming operations

In tube hydroforming, the concurrent actions of pressurized fluid and mechanical feeding allows obtaining tube shapes characterized by complex geometries such as different diameters sections and/or bulged zones. Main process parameters are material feeding history (i.e., the punches velocity history), internal pressure path during the process, and (in T- or Y-shaped tube hydroforming) counterpunch action. What is crucial, in such processes, is the proper design of operative parameters aimed to avoid defects (for instance underfilling or ductile fractures). Actually, the design of tube hydroforming operations is mainly aimed to prevent bursting or buckling occurrence and such issues can be pursued only if a proper control of process parameters is performed. In this paper, a design procedure for Y-shaped tube hydroforming operations was developed. The aim of the presented approach is to calibrate both internal pressure history during the process and counterpunch action in order to reach a sound final component. The approach utilized to optimize the aforementioned parameters is founded on gradient-based techniques and the optimization problem here addressed depends on a considerable number of design variables. In order to reduce the total number of numerical simulations/experiments necessary to reach the optimal values of the design variables, the basic idea of this paper is to develop a sort of decomposition approach aimed to take into account subsets of design variables in the most effective way. The proposed decomposition approach allows avoiding about 50% of the numerical simulations necessary to solve the same problem by traditional gradient technique.

Absorption of Photo‐Ionizing Radiation of Corona Discharges in Air

AbstractThe absorption characteristics of photo‐ionizing VUV radiation emitted by corona discharges in the pressure range from 20 to 750 Torr in dry and humid air were measured. The experimental results are compared with data and approximation formulae obtained by others. For a wide region of pressure and absorption path length, the formula proposed by Zheleznyak et al. (Teplofiz. Vysokih Temp. 1982, 20, 423) seems to be the most reliable for approximation of our results for dry air. We propose a modification of that formula for humid air. The obtained results are suitable for modelling of discharge development in ambient air.magnified image

Technology for two-sided processing of high-accuracy lenses with a thin center

This paper presents the layout of the technological equipment for simultaneous two-sided processing of high-accuracy lenses with a thin center. A mathematical model of the process of shaping spherical surfaces under free-lapping conditions is created, and an analytical expression is obtained for determining the friction and pressure paths in the contact zone of the tool and the workpiece. A technique is proposed for carrying out numerical studies to detect the optimum setup parameters of the machine, taking into account the technological inheritance of the blank from the viewpoint of the distribution of the allowance to be removed.

On the pressure evolution of dynamic properties of supercooled liquids

A pressure counterpart of the Vogel–Fulcher–Tammann (VFT) equation for representingthe evolution of dielectric relaxation times or related dynamic properties is discussed:τ(P) = τ0Pexp[DPΔP(P0−ΔP)], whereΔP = P−PSL,P0 is the ideal glasspressure estimation, DP is the pressure fragility strength coefficient, and the prefactorτ0P is related to the relaxation time at the stability limit(PSL)in the negative pressure domain. The discussion is extended to the Avramov model (AvM) relationτ(T,P) = τ0exp[ε(Tg(P)/T)D],supplemented with a modified Simon–Glatzel-type equation for the pressure dependence of the glasstemperature (Tg(P)), enabling an insight into the negative pressure region. A recently postulated (Dyre 2006Rev. Mod. Phys. 78 953) comparison between the VFT and the AvM-type descriptions isexamined, for both the temperature and the pressure paths. Finally, we address thequestion ‘Does fragility depend on pressure?’ from the title of Paluch M et al (2001J. Chem. Phys. 114 8048) and propose a pressure counterpart for the ‘Angellplot’.

Experimental validation of optimisation strategies in hydroforming of T-shaped tubes

For three dimensional tube hydroforming operations (i.e. T or Y shaped tubes) the calibration of both material feeding history and internal pressure path during the process is crucial and many approaches to such optimization were presented; the authors developed some procedures to optimize pressure paths and punch velocity histories with the application of an integrated method FEM - Gradient based optimization tools. In this paper, an experimental validation campaign of the utilized optimization strategies is presented with the aim to assess the effectiveness of the developed procedures. An optimization procedure (gradient based techniques) was applied on the process parameters leading to the determination of an optimal pressure path. Finally, a testing machine was set up to carry out hydroforming operations on T-shaped tubes. The developed equipment allows a computer assisted control of both the internal fluid pressure paths and the punches actions (material feeding paths). The experimental evidences validated the results obtained by the optimization strategies utilized to design the process parameters.