Low Internal Pressure Research Articles

Magnetization of sinking porous diapirs in planetesimal cores

Magnetization by core dynamo activity in large asteroids and planetesimals is suggested by the remnant magnetization of many achondritic meteorites. However, the conditions for a sustained dynamo in such small bodies is problematic for several reasons. Such bodies may not have the energy budget or size to achieve a sufficient dynamo. Moreover, given their low internal pressures, planetesimal cores likely freeze from the top down, wherein the gravitationally unstable solid in the freezing front has high viscosity and is not easily destabilized. The solid may delaminate in intermittent pulses, which can lead to ephemeral intervals of vigorous convection sufficient to drive dynamo activity, although they may be too short lived to fully magnetize the planetesimal. However, delaminated diapiric downwellings from the solidification front are likely to be partial melts or mushes and thus porous, two-phase bodies. Percolative flow or seepage through the diapir can potentially induce magnetization in the diapir quickly, possibly allowing rapid triggering of dynamo activity. We build on our recent two-phase magnetohydrodynamic theory to examine the magnetization of a porous metallic diapir sinking through a liquid metal in the presence of an imposed background field. Without seepage of liquid through the diapir (i.e., if it were rigid and impermeable), the background magnetic field is distorted by flow around the diapir, as expected. Some of the field distortion is offset with the addition of seepage through the diapir. However, fast seepage can establish a dipole moment inside the diapir, which points opposite the direction of diapiric descent. Wide-spread delamination and diapirism could therefore rapidly establish a multi-polar poloidal field whose field lines extend outside the core, thereby allowing remanent magnetization of the solid and solidifying material above it.

Restricted Mobility and Jamming of Densely Packed DNA Pulled Out from Phage Phi29 Virus Capsids

Many viruses, such as dsDNA bacteriophages, contain DNA packed to such high density that the mobility of the DNA inside the capsid is severely restricted, which can significantly affect the processes of motor-driven DNA packaging and ejection. We use single-molecule optical tweezers measurements to probe the dynamics and mobility of the tightly confined DNA by rapidly removing ATP near the end of packaging, which releases the motor's grip, and applying constant force to pull out the DNA. We find that, on average, the speed of DNA exit is significantly slowed when the DNA is packed at a density greater than ∼0.3 g/ml, consistent with decreased molecular mobility. Significant heterogeneity in the dynamics and long pauses are observed, which we attribute to nonequilibrium DNA conformations arising during DNA packaging and/or exit. Addition of Mg 2+ ions, which electrostatically screen DNA interactions, decrease exit velocity and increase pause durations, consistent with lower internal pressure and increased DNA intra-strand friction. Preliminary measurements with varying applied and internal forces suggest that, contrary to a prior hypothesis, exit velocity may not be linearly proportional to driving force as expected for a process governed only by simple viscous friction.

A numerical analysis on microtube hydroforging

ABSTRACT High-pressure tube hydroforming is a promising method to deform the tubes in various shapes by bulging the tube by applying high internal pressure. However, the challenges lie in the process itself, i.e., requires an expensive pump system and brings excessive thinning in the deformed part section. One option is to reduce the required pressure to solve these difficulties, and the other is to provide the axial feed to the tube in the deformation zone to reduce the thinning. However, due to the higher axial load, the tube buckles. This study is taking advantage of this buckling mechanic to convert it into a successful shaping option. This process is named as tube hydroforging. In this process, the tube was first bulged to a level using internal pressure in an open die without axial feed. Then a minimum pressure was applied, and dies were displaced to shape the tube. The paper studies the process for the microtube. The results noted that lower internal pressure is required to bulge the tube and either no internal or a minimum constant pressure to hydroforge the tube depending on the opening section and thickness of the tube.

Impact of hydrogen on rupture behaviour of Zircaloy-4 nuclear fuel cladding during loss-of-coolant accident: a novel observation of failure at multiple locations

To establish the exclusive role of hydrogen on burst behaviour of Zircaloy-4 during loss-of-coolant accident transients, an extensive single-rod burst tests were conducted on both unirradiated as-received and hydrogenated Zircaloy-4 cladding tubes at different heating rates and internal overpressures. The visual observations of cladding tubes during bursting as well as post-burst are presented in detail to understand the effect of hydrogen concentration, heating rate, and internal pressure. Impact of hydrogen on burst parameters—burst stress, burst strain, burst temperature—during loss-of-coolant accident transients are compared and discussed. Rupture at multiple locations for hydrogenated cladding at lower internal pressure and higher heating rate is reported for the very first time. A novel burst criterion accounting hydrogen concentration in nuclear fuel cladding is proposed.

Low Velocity Impact and Internal Pressure Behaviors of Unaged E-Glass and S-Glass/Epoxy Composite Elbow Pipe Joints

AbstractThis experimental analysis studies the consequences of impact loading on the impact performance and monotonic burst pressure on the level of leakage after impact of E- and S-glass/epoxy com...

Void-interface wetting to crossing transition owing to bubble to void transformation

Understanding cavity-interface interaction is crucial in designing high-strength, radiation-tolerant nanocomposites. Here, bubbles near the Cu–Nb interface in Nb could be absorbed by Cu voids wetting the interface due to the high system energy difference produced by the huge pressure difference between the bubbles and voids and high mobility of bubbles, and no bubble-denuded zone forms owing to fast Brownian motion of bubbles, which keeps bubbles distributed homogeneously. However, owing to the low system energy difference generated by the low internal pressure difference and low mobility, voids near the Cu–Nb interface in Nb would simply coalesce with Cu voids wetting the interface, leading to the void-interface wetting to crossing transition and the formation of void-denuded zones due to the negligible migration of internal Nb voids.

Prediction of thermal performance of vacuum insulation panels (VIPs) with micro-fiber core materials

Compared with traditional insulated materials, vacuum insulation panels (VIPs) are developed to achieve the better insulated performance. Understanding the heat transfer of VIPs is a crucial issue for the purpose of predicting thermal conductivity. To investigate the thermal conductivity, VIPs with micro-fiber core material were prepared and five typical VIPs at different internal pressure varied from 0.1 Pa to 1000 Pa were fabricated. The microstructure of micro-fiber has been measured to for exploring the mechanism of heat transfer. This paper emphasized on thermal conductivity of the porous core material, gases thermal conductivity and thermal radiation to evaluate the performance of VIPs. A validated heat transfer model was applied to analyze the performance of VIPs. The results indicated that the model could predict the thermal conductivity with satisfactory accuracy. Lower mean diameter and internal pressure would result in a deduction of thermal conductivity. However, extra low mean diameter and internal pressure would increase the cost. Reasonable mean diameter and internal pressure should be considered carefully in building applications. Finally, this research provides data reference for studying the heat transfer of micro material, which also discloses the behavior of heat transfer.

A method for predicting the blasting pressure of balloons using the surface strain in low pressure

Balloons made by cut fabric pieces are widely used in space research. To predict the blasting pressure of a balloon, we propose a novel method based on the non-contact test strain at a low internal pressure. The three-dimensional digital image correlation technique is introduced to measure the surface strain of the balloon. Representative regions of the balloon are selected as the test regions. A correction factor is proposed that accounts for the relationship between the internal pressure and the surface strain for the actual and the ideal balloon. By combining the maximum surface strain at a given internal pressure and the correction factor, we can predict the blasting pressure of the balloon. A blasting test is carried out to verify the feasibility of the predictive method. When the value of the ratio of the maximum test strain to the limiting strain reaches about a reference value, the absolute value of the deviation percentage between the predicted blasting pressure and the actual blasting pressure is less than 10%. The blasting pressure for balloon can be predicted accurately. This method does not require the balloon to be inflated to a high internal pressure, which improves the practicality of the prediction.

Giant impacts stochastically change the internal pressures of terrestrial planets.

Pressure is a key parameter in the physics and chemistry of planet formation and evolution. Previous studies have erroneously assumed that internal pressures monotonically increase with the mass of a body. Using smoothed particle hydrodynamics and potential field method calculations, we demonstrate that the hot, rapidly rotating bodies produced by giant impacts can have much lower internal pressures than cool, slowly rotating planets of the same mass. Pressures subsequently increase because of thermal and rotational evolution of the body. Using the Moon-forming impact as an example, we show that the internal pressures after the collision could have been less than half that in present-day Earth. The current pressure profile was not established until Earth cooled and the Moon receded, a process that may take up to tens of millions of years. Our work defines a new paradigm for pressure evolution during accretion of terrestrial planets: stochastic changes driven by impacts.

Hermetic Sealant Material Possibilities for IR Sensor Packaging

Hermeticity is one of the most critical issues for infrared (IR) sensor packages, since any leakage will impair the functionality of the device. The issues associated with the premature failure of hermetic sealants were studied in detail, both by simulation as well as by experimentation. Alternate prospective hermetic sealant candidates for transistor outline IR sensor packages were identified and evaluated. Hermetic sealant options for wafer-level IR sensor packaging were also investigated, which involves wafer-level hermetic cum vacuum packaging. Metallic hermetic sealant is preferred for this approach, since it facilitates integration with the getter material. However, the primary challenge encountered here is the requirement of high processing temperature for the getter activation. An activated getter adsorbs active gases inside the volume of the packages, resulting in lower internal pressure. It was determined that appropriate micro-alloying of the getter is required to minimize the getter activation temperature. This is achieved by selective micro-alloying of the getter material, which induces more grain boundaries and thereby promotes in-depth diffusion even at lower activation temperature. Integration of getter material with all three different types of metallic wafer-level bonding mechanisms was investigated. This includes eutectic, diffusion and transient liquid-phase bonding mechanisms. Selection of an appropriate bonding mechanism and integration scheme depends on the corresponding structure, layout and temperature rating of the specific IR sensor devices.

A numerical study of the response of buried steel pipelines undergoing strike-slip fault

Sudden ground motions resulting from seismic events can cause severe damage to buried pipelines resulting in fuel supply disruption and significant economic losses. The objective of this numerical study is to model and analyze the response of a buried pipeline in a strike-slip fault movement. Here, the interaction of the pipeline with the surrounding soil due to sudden ground movement has been studied by taking into account the contact between the pipeline and the soil, the nonlinear response of soil, and the material and geometrical non-linearities. The pipeline is assumed to be made of APIX65 grade steel. The material behavior is assumed to be governed by J2, rate-independent plasticity theory with strain-hardening included. The onset of buckling-mode failure in the pipeline has been studied for different pipe diameter-to-thickness ratios, the internal pressure, the fault displacement and fault offset rates to better understand the pipeline response due to seismic loads. Study predicts a systematic pre-buckling pattern of a pipe undergoing fault. This study also shows that fault resistance increases with higher diameter to thickness ratio and lower internal pressure. Moreover, the fault resistance counter-intuitively increases with an increase in fault offset rate.

Development of Alloyed Pipe Steel Composition for Oil and Gas Production in the Arctic Region

Gas and oil pipelines for the Arctic region must sustain low temperatures and high internal pressures of a corrosive active medium. Generation of new steel compositions for oil and gas pipelines is an urgent issue in order to ensure their high reliability. Low-carbon steels with a ferritic–pearlitic structure are normally used in pipe production, but they are unable to cope with increased market demands. The main objective of this study is to investigate the influence of the cooling rate on the structure and morphological characteristics of bainite, which determines the exploitation properties of the pipe steels. Dilatometric tests were carried out using a Gleeble 3500 complex. Optical microscope and scanning electron microscope analysis, with the computer image analysis system Thixomet PRO, were used to study the microstructure of steel. Hardness was measured in accordance with ASTM E-384. Morphological characteristics of bainite components that were formed at various cooling rates from 0.05 to 100 °C/s were defined. The novel result of this study is the continuous cooling transformation diagram of undercooled austenite of the steel containing 0.062% C; 1.80% Mn; 0.120% Mo; 0.032% Cr, 0.90% Ni and other elements (Al, Cu, V, Nb, Ti).

Low-cycle fatigue issue of steel spiral cases in pumped-storage power plants under China's and US's design philosophies: A comparative numerical case study

This study focuses on the low-cycle fatigue issue of steel spiral cases (SSCs) in pumped-storage power plants considering their frequent operation-mode switches. First, a finite element (FE) analysis of a composite SSC-concrete structure was performed with an improved ABAQUS-based complete simulation procedure, which has been validated in the authors' previous work. Both low and high temporary internal water pressure (IWP) were considered following the China's and US's design philosophies, respectively. It has identified an association between the untimely and delayed gap-closing phenomenon and the high stresses in the SSC. Then the FE results were imported into the DesignLife software to carry out a fatigue analysis. The results show that the low-cycle fatigue issue of the SSC might not be totally out of the question even only considering routine operation-mode switching frequency of the pump-turbine set. The temporary IWP at different levels has a significant impact on the fatigue life of the SSC.

(Invited) Operando Investigation of All-Solid-State-Batteries Using Li3PS4 Solid Electrolyte

All-solid-state batteries have been presented as the ideal solution to address i) the safety limitations of conventional Li-ion batteries by suppressing the flammable organic electrolytes and ii) the problem of insufficient energy densities. To date, two types of solid Li-ion electrolytes have been mainly studied, namely, sulfur-based and ceramic-based materials. Despite the progress in the development of superionic conductor, many aspects of their reaction mechanisms and stability upon cycling still remain non-elucidated. In order to get a better insight about their stability upon cycling, the development of a reliable electrochemical cells is thus of a prime importance when studying battery materials in operando mode during cycling. This is never an easy task, since the design of such cells has to be adequate to the technique of a choice and meet all necessary requirements. However, once a proper design is found, the surface, the bulk, the interfaces, and finally the combination of those can be studied and lead to the elucidation of the reaction mechanisms, thus further improving the battery technology. Unfortunately, in most cases the electrochemical cells used for operando measurement are not ideal and suffer from low internal pressure (i.e. poor contact between the electrodes). It shorts the lifespan of the cell, especially in the case of all-solid-state-batteries. Herein we present different cell designs developed in our laboratory and used for operando studies. Through this presentation, we will use bulk, surface and imaging techniques to better understand the limitation of all solid state batteries. As an example, Operando neutron imaging has been employed to understand the Li diffusion within the electrode and inside an all-solid state batteries employing Li3PS4 as solid electrolyte whereas operando X-ray microscopic tomography was employed to follow the possible electro-mechanical fracture occurring during cycling and the possible impact on the electrochemical performance.

Jet properties and mixing chamber flow in a high-pressure abrasive slurry jet: part II—machining rates and CFD modeling

Part I of this two-part paper presented mixing chamber conditions and jet characteristics in a high-pressure abrasive slurry jet micro-machining (HASJM) system. The present paper describes the modeling of the slurry entrainment process within the mixing chamber and mixing tube of the nozzle using computational fluid dynamics (CFD) and shows how the results can be used to explain and predict machining performance. The slurry flow rate into the mixing chamber was found to have a large impact on the performance of the jet due to differences in the momentum of the high-velocity water and low-velocity slurry. The erosive efficacy of the jet was assessed by machining channels and blind holes in aluminum 6061-T6. Differences in the centerline erosion rates of holes and channels for a given jet showed clear evidence of incubation and stagnation zone effects. The CFD models simulated various slurry flow rates entering the mixing chamber as a result of the low pressure created by the central high-velocity jet of water. They predicted correctly an experimentally observed flooding condition in which slurry completely filled the mixing chamber and mixing tube. The models could also identify the transient conditions leading to the onset of this flooding as the chamber first began to fill, which could not be identified experimentally. Flooding was found to significantly reduce the jet velocity, thus diminishing its erosive efficacy. The models also identified the operating conditions within the mixing chamber that produced boiling due to the low internal pressure generated by the central high-velocity jet of water. This boiling condition was found in part I to result in a wider jet exiting the mixing tube.

Bending and buckling of internally-pressurized steel lined pipes

During offshore installation, steel lined pipes are subjected to severe plastic bending, resulting in detachment of the thin-walled liner pipe from the outer pipe and eventually, the formation of local buckling in the form of short-wave wrinkles that menace the structural integrity of the pipeline. The paper focuses on the mechanical behaviour of mechanically lined pipes subjected to monotonic bending, considering for the presence of low and moderate levels of internal pressure, aimed at preventing or delaying wrinkle formation, and improving structural performance. The problem is solved numerically, accounting for geometric non-linearities, local buckling phenomena and elastic-plastic material behaviour for both the liner and the outer pipe. Two types of lined pipes are examined, with and without mechanical bonding between liner and outer pipe referred to as tight-fit and snug-fit lined pipe, respectively. The results demonstrate that the bending performance of lined pipes, under low or moderate internal pressure levels, is significantly improved. The influence of initial geometric imperfections on liner pipe buckling is also examined, showing the imperfection sensitivity of bi-material pipe bending behaviour.

Elastic–plastic solutions for a circular hydraulic pressure tunnel based on the D–P criterion considering the fluid field

This work provides new findings on the theory of the Drucker–Prager (D–P) failure criterion applied to study the analytical solutions of the radius and stress of a plastic zone and the displacement at the periphery of a hydraulic pressure tunnel under a uniform ground stress field considering fluid. This work focuses on the elastic–plastic rock mass during the stages of construction and operation. The obtained results are compared to other calculation techniques and show that the elastic–plastic solution calculated based on the D–P criterion is more conservative than that based on the Mohr–Coulomb (M–C) model. The first principal stress varies with the internal water pressure, which first decreases to zero and then gradually increases in the plastic zone. As the value of the water head difference is large enough, there will be a threshold radius in the elastic zone, at which the maximum principal stress changes from the radial stress to the tangential stress with increasing distance from the tunnel, ultimately reaching the in situ stress, and the threshold radius is related to the magnitude of the water head difference. Considering the effect of seepage, the radial stress and tangential stress are not symmetrical about the axis of in situ stress within the elastic zone. In addition, the degree of deviation from the in situ stress increases with the increasing value of water head difference. Under the low internal water pressure condition, an increase in the osmotic pressure will further develop the plastic zone; however, under the high internal water pressure condition, an increase in the osmotic pressure will slow the development of the plastic zone.

Resin Viscosity Influence on Fiber Compaction in Tapered Resin Injection Pultrusion Manufacturing

Viscosity of the liquid resin effects the chemical and mechanical properties of the pultruded composite. In resin injection pultrusion manufacturing the liquid resin is injected into a specially designed tapered injection chamber through the injection slots present on top and bottom of the chamber. The resin is injected at a pressure so as to completely wetout the fiber reinforcements inside the tapered injection chamber. As the resin penetrates through the fibers, the resin also pushes the fibers away from the wall towards the center of chamber causing compaction of the fiber reinforcements. The fibers are squeezed together due to compaction, making resin penetration more difficult; thus higher resin injection pressures are required to efficaciously penetrate through the compacted fibers and achieve complete wetout. The impact of resin viscosity on resin flow, fiber compaction, wetout and on the final product is further discussed. Injection chamber design predominantly effects the resin flow inside the chamber and the minimum injection pressure required to completely wet the fibers. Therefore, a desirable injection chamber design is such that wetout occurs at lower injection pressures and at low internal pressures inside the injection chamber.

Friction models for evaluating dynamic stresses in non-bonded flexible risers

This paper addresses friction models used for evaluating dynamic stresses in non-bonded flexible risers. A review of the most commonly used methods to model friction between layers in such structures was performed. Four models for calculating friction under dynamic contact pressure and constant shear interaction stick stiffness conditions were then formulated to enable stress calculation of cross-sections exposed to variable tension and bending loads. The friction models were implemented into a computer code used for numerical studies. A sensitivity study was carried out to determine the optimum shear interaction stick stiffness parameter, K0, with respect to representing the plane surfaces remain plane assumption. This was followed by an investigation of the performance of the developed models with respect to the tendon axial force next to the outermost fibre position. The proposed friction models were also verified against full scale tests in terms of bending moment-curvature data. As the test data indicated less bending stiffness in the stick domain than that can be obtained by the plane surfaces remain plane assumption, a method to estimate the parameter K0 was proposed, which accounted for the shear deformation of the plastic layers. The initial strain concept was further applied to deal with the significant hysteresis observed in the test data for low internal pressures pointing the way forward with respect to dealing with this effect in stress analysis. Furthermore, a friction model comparison study was carried out for investigating the static friction effect on the axial force at the outermost fibre position and the bending moment-curvature relationship.

Process and loading path design for hydraulic compound forming of rectangular tubes

Tubes with various cross-sectional shapes are widely used in automotive and bicycle manufacture for lightweight considerations. This study proposes a compound forming process for hydroforming a rectangular cross-sectional tube of aluminum alloys AA6061-O. The compound forming process is divided into crushing, hydroforming, and calibration. The finite element simulation software DEFORM was used to analyze the plastic deformation pattern of the tube during the compound forming processes and determine feasible loading paths that can generate a uniform thickness distribution, a lower internal pressure, and a smaller clamping force. The effects of varied internal pressures on the product shapes, thickness distributions, and forming loads are discussed. A self-designed hydroforming test machine with an internal pressure capacity of 30 MPa and axial feeding force of 40 tons was used to conduct hydroforming experiments. The experimental results of the product thickness distributions and dimensions were compared with simulation results, and the validity of the FE modeling is confirmed. Sound products with the required shape and dimensions can be obtained using the proposed hydraulic compound forming process with a low internal pressure of 8 MPa.