Large Expansion Ratio Research Articles

Multi-scale elastoplastic mechanical model and microstructure damage analysis of solid expandable tubular**Project supported by the National Major Science & Technology Project of China (Grant No. 2016ZX05020-003).

We present an in-depth study of the failure phenomenon of solid expandable tubular (SET) due to large expansion ratio in open holes of deep and ultra-deep wells. By examining the post-expansion SET, lots of microcracks are found on the inner surface of SET. Their morphology and parameters such as length and depth are investigated by use of metallographic microscope and scanning electron microscope (SEM). In addition, the Voronoi cell technique is adopted to characterize the multi-phase material microstructure of the SET. By using the anisotropic elastoplastic material constitutive model and macro/microscopic multi-dimensional cross-scale coupled boundary conditions, a sophisticated and multi-scale finite element model (FEM) of the SET is built successfully to simulate the material microstructure damage for different expansion ratios. The microcrack initiation and growth is simulated, and the structural integrity of the SET is discussed. It is concluded that this multi-scale finite element modeling method could effectively predict the elastoplastic deformation and the microscopic damage initiation and evolution of the SET. It is of great significance as a theoretical analysis tool to optimize the selection of appropriate tubular materials and it could be also used to substantially reduce costly failures of expandable tubulars in the field. This numerical analysis is not only beneficial for understanding the damage process of tubular materials but also effectively guides the engineering application of the SET technology.

A cylindrical mixing chamber ejector analysis model to predict the optimal nozzle exit position

By introducing the theory of an annular mixing-layer, a new model to predict the optimal nozzle exit position (ONXP) is established and verified for ejectors with a cylindrical mixing chamber. Furthermore, the optimal entrainment ratio, area ratio and dimensionless optimal nozzle exit position (DONXP) of ejectors under different working conditions are analysed by this model. Compared with the experimental data of R141b, R245fa, R134a and R600a ejectors, the entrainment ratio error is within ±10.70%, and the critical backpressure is within ±7%. The introduced theory can accurately predict the ONXP of the R245fa ejectors (within an error of ±15.85%) and the DONXP distribution of the R141b ejectors, and can properly predict the performance of the R134a ejectors under the same dimensions. With an increasing compression ratio, the DONXP decreases, and the rate of decrease is faster when the compression ratio exceeds the value of the inflection point. The compression ratio corresponding to the inflection point is higher for an ejector with a large expansion ratio than that with a small expansion ratio. In addition, the DONXP decreases when the expansion ratio increasing under a small compression ratio while increases when the expansion ratio increasing under a large compression ratio.

Study of the thermal stability of foam of different expansion ratio

Introduction. Currently, the industry produces a wide range of foam generators to produce fire-extinguishing foams, and the foams they produce differ significantly in their expansion ratio and, consequently, fire resistance. Since heat fluxes have the main destructive effect on the foam, the purpose of this paper is to establish the patterns of destruction of foam of different expansion ratio when heated.Methods of research. The foam with expansion ratio from 7.5 to 80 was used for the tests. It was obtained by mechanical beating of 6 % solution of foaming agent PO-6RZ. The thermal stability of the foam was studied when the heat flow from the gas burner flame affects the foam layer. During the experiment, the change in the height of the foam column in time was recorded.Results and Discussion. The results of measurements, presented in the form of dependence of foam layer destruction rate on time, quantity of released liquid phase on 1 m2·s, dependence of foam layer destruction rate on its density allowed revealing a number of patterns. The destruction rate of foam with an expansion ratio of up to 30 remains constant throughout the entire duration of thermal exposure. As the foam expansion ratio increases, the rate of destruction at the initial stage of heat flux exposure increases. With a foam expansion ratio of more than 50, there is initially a sharp increase in the rate of destruction, which subsequently decreases as the foam column decreases. In the conditions of the experiment, the best characteristics were shown by the foam with an expansion ratio of 50, because in the foam with a smaller expansion ratio the syneresis makes a significant contribution to its destruction, and the foams with a larger expansion ratio are destroyed by the mechanical effect of convective flame flows.Conclusion. The study of the foam destruction patterns under thermal impact allowed establishing the fact that its destruction is limited by the rate of impoverishment of the upper layers with liquid.

Dynamic self generation of hydrogen bonding and relaxation of polymer chain segment in stabilizing thermoplastic polyurethane microcellular foams

Cell stabilization of TPU foams made from supercritical CO2 (scCO2) foaming remains a huge challenge and significantly limits TPU foams’ applications. One key point is the absence of molecular mechanism during TPU foam shrinkage and not to mention the solution. In this work, the interactions within/among TPU macromolecular chain(s) are investigated in-depth via several in-situ characterization methods, hence clarified the molecular mechanism during TPU foam shrinkage and uncovers the direction to achieve cell stabilization. It is revealed that dynamical self-generation of hydrogen bonding and polymer chain segments’ relaxation after foaming play significant roles in cell stabilization. Base on this molecular mechanism, strategies of strengthening and accelerating hydrogen bonding, inducing another primary bonding besides hydrogen bonding among molecular chains, fixing hard segments while relaxing soft segments are proposed. Consequently, this work guides the direction to produce thermoplastic elastomer foams of large expansion ratio with less shrinkage via scCO2 foaming.

Strong and super thermally insulating in-situ nanofibrillar PLA/PET composite foam fabricated by high-pressure microcellular injection molding

Strong, thermally insulating and biological PLA foams derived from cost-effective and environmentally friendly process are needed for saving resources and improving energy efficiency. PLA’s brittle feature and poor foaming ability are currently the major challenges which strongly restrict developing high-performance PLA foams. Herein, a scalable, cost-effective and environmentally friendly route by combining in-situ nanofibril reinforcement with high-pressure microcellular injection molding (HPMIM) was developed for producing high-performance PLA foams. Nanofibrillar PLA/PET composite was prepared by coupling twin-screw compounding and melt spinning. The presence of PET nanofibrils with an average diameter of 114.8 nm greatly improve PLA’s crystallization, viscoelasticity and melt strength, thereby enhancing its foaming ability. Thus, sub-microcellular nanofibrillar PLA/PET composite foam with an average cell size of 322.8 nm was produced using HPMIM, which shows dramatically enhanced mechanical properties than the pure PLA foam. Remarkably, the Izod and Gardner impact strengths of the HPMIM-fabricated PLA/PET foam are respectively more than 7-fold and 6-fold higher than those of the PLA foam fabricated by regular microcellular injection molding. Moreover, nanofibrillar PLA/PET composite foams with expansion ratio varying from 3.8-fold to 26.2-fold were fabricated. Thanks to the unique nanostructured cell walls with numerous micro/nano fibrils and voids, these nanofibrillar PLA/PET composite foams with large expansion ratios show outstanding thermally insulating properties. The 26.2-fold PLA/PET composite foam exhibits a thermal conductivity of 26.8 mW/m·K, much better than that of current polymer foams. The scalable and environmentally friendly method combined with the unique foam structure opens up new perspectives for developing high-performance multifunctional porous materials.

Progress on rapid hot gas forming of titanium alloys: mechanism, modelling, innovations and applications

The variable cross-section thin-walled hollow components of titanium alloys are increasingly used in the power and fuel systems of aerospace vehicles, which play an important role in reducing the weight of the structure, improving the service performance and reliability, etc. However, the formability of titanium alloys is very poor at room temperature, so it is very difficult to manufacture the complex thin-walled hollow components. Hot gas forming is an efficient strategy to form integral hollow components of titanium alloys. In this paper, some progress on this forming technology from the author’s lab is presented, which includes the deformation mechanisms, constitutive equations, process simulation, technological innovations and typical applications. Based on the research about the deformation mechanisms, the unified constitutive model was developed. Then the deformation process and microstructure evolution of gas forming could be predicted numerically. According to the difficulties of different components with different materials and geometries, new forming process with non-uniform temperature field, new heating system and new tooling strategy were presented. The new technologies were applied to form the components with irregular cross sections and components with large expansion ratios, meeting the application demand of aerospace industry, etc.

Multistage axial hydro-forging sequence of double-stepped tube with large expansion ratio

In order to manufacture the double-stepped tube with large expansion ratio, a multistage axial hydro-forging sequence was proposed by combination of hydroforming with movable dies in this paper. The new forming process is divided into four stages. In the second stage, hydro-forging stage, the thickness will be increased and the thinning ratio will be decreased due to the axial compression deformation, then the forming capacity of the tube will be improved. Experiments and finite element simulation were conducted to verify the feasibility of the proposed multistage axial hydro-forging sequence process. Experimental and simulation results showed that double-stepped tube with large expansion ratio can be produced with movable die design. At the same time, a better thickness distribution could be achieved. This investigation demonstrates that multistage axial hydro-forging sequence is a potential forming approach for manufacturing of large-expansion-ratio double-stepped tubes with high reliability.

Stiff Composite Cylinders for Extremely Expandable Structures

The realization of concurrently largely expandable and selectively rigid structures poses a fundamental challenge in modern engineering and materials research. Radially expanding structures in particular are known to require a high degree of deformability to achieve considerable dimension change, which restrains achievable stiffness in the direction of expanding motion. Mechanically hinged or plastically deformable wire-mesh structures and pressurized soft materials are known to achieve large expansion ratios, however often lack stiffness and require complex actuation. Cardiovascular or drug delivery implants are one example which can benefit from a largely expandable architecture that is simple in geometry and intrinsically stiff. Continuous shell cylinders offer a solution with these properties. However, no designs exist that achieve large expansion ratios in such shells when utilizing materials which can provide considerable stiffness. We introduce a new design paradigm for expanding continuous shells that overcomes intrinsic limitations such as poor deformability, insufficient stiffness and brittle behaviour by exploiting purely elastic deformation for self-expandable and ultra-thin polymer composite cylinders. By utilizing shell-foldability coupled with exploitation of elastic instabilities, we create continuous cylinders that can change their diameter by more than 2.5 times, which are stiff enough to stretch a confining vessel with their elastic energy. Based on folding experiments and analytical models we predict feasible radial expansion ratios, currently unmatched by comparable cylindrical structures. To emphasize the potential as a future concept for novel simple and durable expanding implants, we demonstrate the functionality on a to-scale prototype in packaging and expansion and predict feasible constellations of deployment environments.

Multistage Axial Hydro-Forging Sequence: A New Forming Approach for Manufacturing of Double-Stepped Tubes

To manufacture the large-expansion-ratio double-stepped tube without thinning, a new approach known as multistage axial hydro-forging sequence has been proposed in this study. The whole forming process is divided into five stages. Compared with traditional tube hydroforming, the thickness can be increased by axial compression deformation to reduce the thinning ratio and enhance the forming capacity of the tube in hydro-forging stage and double-stepped hydro-forging stage, respectively. The proposed multistage axial hydro-forging sequence process was implemented by experiments along with the finite element simulation to validate its feasibility. The suitable loading path to prevent defects such as wrinkle and thinning was discussed. The results showed that double-stepped tube with large expansion ratio can be produced successfully with movable dies’ design. There is no thinning in the final tube, particularly in all stepped area, and a better thickness distribution could be achieved. As a result, the proposed multistage axial hydro-forging sequence can be a feasible forming approach for the fabrication of large-expansion-ratio double-stepped tubes with high reliability.

Acoustic Length Sensor for Soft Extensible Pneumatic Actuators With a Frequency Characteristics Model

In this study, we present a length sensor that can be used for extensible soft pneumatic actuators. Conventional length sensors detect the changes in electrical resistance and capacitance owing to the deformation of the actuator; hence, deterioration and destruction occur when they are used with an actuator that has a large expansion ratio. In addition, their low resolution and linearity makes them unsuitable for use in actuator control. Our proposed sensor comprises only a speaker and a microphone installed at one end of the actuator. We propose a method to deterministically measure the length of a tube by generating a broadband acoustic signal in a tube and measuring the resonance characteristics determined by the shape of the tube. Our experimental results demonstrate that the error in the measurement with our sensor is not more than 4% with a strain up to 200%. Unlike conventional acoustic sensing methods that measure the time of flight by using ultrasound, our proposed method yields accurate results even when the tube is bent. Therefore, the proposed method can be applied to various types of pneumatic actuators.

Failure analysis and solution study of 203 mm solid expandable tubular

The solid expandable tubular technology (SETT) is a permanent radial plastic deformation of the casing, which serves to block the leaking section and subsidize the casing. The difficulty of the SETT lies mainly in the material selection of the solid expandable tubular (SET) and the design of the expansion cone structure. The 20G steel casing pipe with 203 mm × 10 mm specification in dagang oilfield is subject to an expansion test with a variable-diameter expansion cone (an expansion rate of 20.2%), during which the casing pipe ruptured and failed. In this paper, the microstructure is analyzed by scanning electron microscope (SEM) and the failure analysis of SET is studied macroscopically by finite element analysis method, and the corresponding solution is proposed. The research shows that when the expansion ratio is 20.2% and the 20G steel casing is used as the material of SET, the maximum stress of SET during the expansion process exceeds the ultimate tensile strength of the material, the SET fracture fails, and 20G steel pipe is not suitable for use as materials of SET in the case of a large expansion ratio (20.2%). In this paper, the expansion cone is continuously optimized. It is found that the single-stage expansion cone is more conducive to the expansion operation than the variable-diameter expansion cone. The expansion cone chamfer and friction coefficient have a significant influence on the driving force, and should be fully lubricated during the expansion operation. In addition, this paper also prefers 316L steel material with better plasticity and toughness. It is found that 316L can expand successfully without failure at large expansion ratio. The research results provide a theoretical basis for the material selection of SET and the structural design of the expansion cone, and have important significance for ensuring the success of the expansion work.

Plasma Actuator–Assisted Rocket Nozzle for Improved Launcher Performance

The need to avoid unstable separations and side loads during low-altitude operations imposes a strict limit on the nozzle expansion ratio of launchers propulsion systems. Remarkable performance losses are consequently induced. An innovative concept is here presented that overcomes this limit. Plasma actuators are proposed as a means to stabilize separation in highly overexpanded conventional bell-shaped nozzles. A larger expansion ratio can thus be adopted in boosters and first-stage engines, and their vacuum specific impulse is increased. The concept is here assessed by means of Reynolds-averaged Navier–Stokes simulations. The effects of the plasma actuators are described by average body force and heat source terms. The potentialities of this concept, adaptable to any bell-shaped nozzle, are assessed evaluating the possible payload gain for a representative case. The results show that the proposed concept allows for suitable payload growth and engine flexibility.

Thermal‐Insulation, Electrical, and Mechanical Properties of Highly‐Expanded PMMA/MWCNT Nanocomposite Foams Fabricated by Supercritical CO2 Foaming

AbstractFoaming behavior of poly(methyl methacrylate) (PMMA)/multi‐walled carbon nanotubes (MWCNTs) nanocomposites and thermally‐insulating, electrical, and mechanical properties of the nanocomposite foams are investigated. PMMA/MWCNT nanocomposites containing various amounts of MWCNTs are first prepared by combining solution and melt blending methods, and then foamed using CO2. The foaming temperature and MWCNT content are varied for regulating the structure of PMMA/MWCNT nanocomposite foams. The electrical conductivity measurement results show that MWCNTs have little effect on the electrical conductivity of foams with large expansion ratio. Thermal conductivities of both solid and foamed PMMA/MWCNT nanocomposites are measured to evaluate their thermally insulating properties. The gas conduction, solid conduction, and thermal radiation of the foams are calculated for clarifying the effects of cellular structure and MWCNT content on thermal insulation properties. The result demonstrates that MWCNTs endowed foams with enhanced thermal insulation performance by blocking thermal radiation. Moreover, the compressive testing shows that MWCNTs improve the compressive strength and rigidity of foams. This research is essential for optimizing environmentally friendly thermal insulation nanocomposite foams with enhanced thermal‐insulation and compressive mechanical properties.

Computational study of axisymmetric divergent bypass dual throat nozzle

A bypass dual throat nozzle (BDTN) is a fluidic thrust-vectoring nozzle (FTVN) that is based on the conventional dual throat nozzle (DTN). The BDTN provides high thrust vectoring (TV) efficiency with low thrust loss and does not consume additional secondary flow. A fixed-geometry axisymmetric divergent BDTN (ADBDTN) that has flow adaptive capability and can provide high TV efficiency in the pitch and yaw directions without substantially changing the working state of the engine is investigated in this study. In addition, the TV mechanism and the effects of the expansion ratio, bypass width, and rounding radii at the nozzle throat and cavity bottom on the nozzle performance under the vectored state are presented in detail. Results show that the TV mechanism of the ADBDTN is similar to that of the DTN, which deflects the primary flow through the separation zone inside the recessed cavity. Larger expansion ratios and rounding radii at the nozzle throat contribute to the large pitch thrust-vector angle and high discharge coefficient. Decreasing the expansion ratio and increasing the rounding radius at the nozzle throat can improve the thrust coefficient. As the bypass width increases, the thrust and discharge coefficients increase and the pitch thrust-vector angle reaches its maximum. The effect of the rounding radius at the cavity bottom on the nozzle performance is relatively small. For the configuration with flow adaptive capability, the largest pitch thrust-vector angle is 25.37∘ and the highest thrust and discharge coefficients are 0.957 and 0.983, respectively.

Strategy to control CO2 diffusion in polystyrene microcellular foaming via CO2-philic additives

The introduction of suitable CO2-philic additives, enabling high CO2 concentration retained in the polymer matrix, might be a promising strategy to obtain foams with small cell size and large volume expansion ratio. The effect of molecular weight (Mn) (2000–17000 g/mol) of CO2-philic additives (PDMS and PVAc) on the diffusion of supercritical CO2 into and out of polystyrene (PS) was investigated via experiments and dissipative particle dynamics simulations. The CO2 diffusion coefficient increased with the presence of additives especially with PDMS (2000 g/mol, from 1.2 × 10−9 m2/s to 2.8 × 10−9 m2/s). Meanwhile, the saturation solubility of CO2 increase with the incorporation additives. Compared with high Mn additives, the slower CO2 desorption rate with additives with Mn of 2000 g/mol enabled higher amount of CO2 retained in PS, resulting in higher cell density. The incorporation of PDMS (2000 g/mol) decreased the cell size (from 11.67 to 7.57 μ m) and increased volume expansion ratio of PS foams.

Effects of Expansion Ratio and Reynolds Number on Backward-Facing Step Flow with Large Expansion Ratio

Effects of Expansion Ratio and Reynolds Number on Backward-Facing Step Flow with Large Expansion Ratio

Fluid Flow and Heat Transfer Characteristics of Backward-Facing Step Flow with Large Expansion Ratio

Fluid Flow and Heat Transfer Characteristics of Backward-Facing Step Flow with Large Expansion Ratio

Pressure and heat transfer characteristics in a backward-facing step flow with a large expansion ratio

Pressure and heat transfer characteristics in a backward-facing step flow with a large expansion ratio

Effects of mechanical property parameters on wrinkling behavior of thin-walled tubes in hydroforming process

In tube hydroforming, some controllable wrinkles can be used to improve the formability of tubes, so as to obtain the tubular parts with large expansion ratio and relatively uniform wall thickness. In this paper, finite element analysis and experimental research with 5052 aluminum alloy and 304 stainless steel tubes are used to investigate the effects of mechanical property parameters on wrinkling behavior of thin-walled tubes for hydroforming application. The numerical simulation results show that the effect of elastic modulus is very small and ignorable, but the initial yield stress and tangent modulus of tubes have an obvious effect on their wrinkling behavior. Tubes with higher initial yield stress and lower tangent modulus tend to possess three axisymmetric wrinkles within the lower internal pressure range. Moreover, it is found that the ratio of initial yield stress to flow stress of the tubes, σs/σf, is a significant factor to their wrinkling behavior. Three axisymmetric wrinkles could be produced on the tubes with higher σs/σf under a lower internal pressure. All of these were verified by the experimental results of 5052 aluminum alloy and 304 stainless steel tubes, whose wrinkles obtained under wrinkling internal pressure of 1.8 ps and 1.2 ps can be flattened completely in the calibration stage. These research findings are extremely meaningful to get controllable wrinkles for different kinds of tubes.

Estimation of Frictional Coefficient between Punch and Billet at Back-Stroke in Backward Can Extrusion Test of Steel

A backward can extrusion test provides severe tribological conditions because high pressure, high temperature, and large surface expansion ratio affect the lubricant. During the forward stroke these conditions intensify with increasing cup depth of the extruded workpiece; additionally, the back-stroke force during retraction of the punch rises to a significant level under a poor-lubricated condition. This study estimates the coefficient of friction μp between punch and workpiece during the back-stroke by combining experiments using conventional soap-phosphate coated steel and numerical analysis by FEM. The values of μp were estimated to be 0.09 and 0.03 in case of small and large workpiece depth, respectively. Friction decreased with elevating temperature.