Large Expansion Ratio Research Articles

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.

The Thermal Response of Intumescent Coating Under Different Combinations of External Heat Fluxes

In this study, the heat-blocking performance of intumescent coating under various combinations of external radiative and convective heat fluxes is investigated numerically. The results show that the temperature distribution and heat fluxes near the coating surface are significantly affected by the heat-source combination, and consequently, the thermal responses of coating are different. For the same magnitude of convective heat source, the higher flame temperature (lower heat convection coefficient) has larger thermal effect on coating response. For the same magnitude of heat source, the radiative heat source generates more thermal response of coating than the convective one. Moreover, if the external heat flux is not intense enough to cause large expansion ratio (2 < xL/L < 11) in 3600 s, the combination of heat source can significantly affect the substrate temperature and the total heat flux at the coating surface. However, if the expansion ratio is sufficiently large (xL/L > 11) at the quasi-steady-state (3600 s), the substrate temperature and the total heat flux are independent of the combination of heat source, which only affects the temperature and the radiative and convective heat fluxes near the coating surface (∼3 mm in this study).

Polyamide 6 modified polypropylene with remarkably enhanced mechanical performance, thermal properties, and foaming ability via pressure‐induced‐flow processing approach

AbstractPressure‐induced‐flow (PIF) processing has been considered as an efficient approach to prepare high‐performance polymer materials. In this study, the effects of PIF processing on various properties of PP/PA6 blend, including the microstructure, thermal, and mechanical properties, as well as foaming behavior, were investigated. The results showed that PIF processing had a significant effect on the microstructure of PP/PA6 blend. Meanwhile, the thermal stability of PP/PA6 blend was greatly improved. Compared to its counterparts without PIF processing, the mechanical strength of PIF PP/PA6 blend was remarkably enhanced, which was even higher than that of PIF PP (Polypropylene). PIF processing could both strengthen and toughen PP/PA6 blend. Dynamic mechanical analysis (DMA) results also indicated that PIF PP/PA blend had higher strength under dynamic mechanical conditions. Furthermore, the PP/PA6 foams with and without PIF processing were fabricated using a batch foaming method. With PIF processing, the resultant PP/PA6 blend displayed a significantly enhanced foaming ability with higher cell density and larger expansion ratio.

A Fundamental Study for Next Generation Heat Engines

To generate electric power from unused heat, realization of heat engines that can work under small temperature difference during the heat exchange processes are required. Trilateral cycle can maximize the exergy recovery from waste heat. The working fluid is maintained in a liquid phase during the heating process and it expands in the expander in gas-liquid two phase. In the present study, a novel reciprocating positive displacement expander for two phase expansion which can achieve large expansion ratio, high airtightness and low vibration is proposed. And issues for practical application is discussed.

An experimental study on the detonation transmission behaviours in acetylene-oxygen-argon mixtures

Accidental explosions/detonations preventions and control are practical as well as scientific issues. Although numerous research have been carried out to examine the combustion characteristics in acetylene mixtures, very limited studies focused on detonation transmission behaviours in a finite expansion space, which is of vital importance for the explosion safety assessment. This paper reports the detonation transmission behaviours through a confined sudden expansion in stoichiometric acetylene-oxygen mixtures diluted with varying amount of argon. Detonation velocity measurement and soot film visualization were used to characterize the detonation behaviour. The experimental results indicate that the initial over-driven degree of re-initiated detonation decreases with the increase of argon dilution in the expanded tube. Two transmission modes with distinct detonation cellular structures are experimentally observed. For the large expansion ratio, localized explosions followed by fine-scale detonation structures are observed in the expanded tube. As the initial pressure approaches the limiting transmission pressure, the re-initiation distance remarkably increases. For the small expansion, the near-limit detonation waves are observed to transmit to the expanded tube successfully without detonation re-initiation. A dimensionless cell size Λ is introduced to correlate with the re-initiation distance of transmitted detonation in acetylene-oxygen-argon mixtures, and a unified curve can be obtained.

Gyrofluid Model of Plasma Expansion in a Diverging Magnetic Field

The gyrofluid equations for electrons and for ions are used to model the acceleration of plasma from a source region of high magnetic field to a region of lower field. The model includes a source term for plasma generation, a self-consistent electric field, nonzero ion temperature, plasma acceleration by the mirror force, and the reduction in density from the diverging flow. The model is applicable to plasma experiments with helicon sources, ion engines for spacecraft, and some plasma processing configurations. The ion flux from the source region is found to be approximately the Bohm flux and the downstream ion flux density scales with the magnetic field. The downstream flow is determined by the conversion of upstream thermal energy in both electrons and ions into kinetic energy in flow speed. For large expansion ratios, the final speed approaches 1.5 times the ion sound speed.

Carbon nanotubes in microwave foaming of thermoplastics

In this work, we introduce the use of selective microwave heating to solve the problems of conventional heating systems, such as non-uniformity and thickness restriction, in classical thermoplastic foaming methods. To do so, carbon nanotubes (CNTs) are used as microwave absorbers in a transparent polymer media. When irradiated, CNTs are responsible for a local temperature increase in the polymer/gas solution, allowing local polymer softening and increased blowing agent super-saturation, in turn inducing bubble nucleation and growth. The huge number of active sites (CNTs) for both heating and bubble nucleation and the possibility to fine-tune the heating energy provide large uniformity and an extra control over the bubble growth, to generate well-expanded, fine-celled, uniform, relatively thick foams. As a model system, we successfully foamed 1 cm-thick polystyrene/CNT nanocomposites with CO2, and achieved uniform morphologies and large expansion ratios (over 22 folds). For proper comparison, we also utilized conventional foaming methods such as water bath and fast pressure drop, both resulting in denser and less uniform foams. Here, for the first time, a single particle type, CNTs, is used as a “nucleating agent”, a “heating agent” and, as it will be seen in the following, a “collapse-preventing agent”.

Appropriate size, spacing, expansion ratio, and location for clickable elements on smart TVs with remote motion control

Motion control based on gyroscopes and/or accelerometers is a promising technique that can replace a typical television (TV) remote control. In this study, we investigated the effects of the size, spacing, expansion ratio, and location of clickable elements on the usability of remote motion control for smart TVs. Seven different target sizes, four expansion ratios, and 25 locations on a TV were examined in an experiment. Twenty-four people performed the task of pointing at and clicking on a single target on the TV with remote motion control. The results revealed that the target size of 80 mm exhibited the best performance in terms of the task completion time, pointing errors, and pointing convenience. A larger expansion ratio was better, particularly when the target size was smaller than 80 mm. Further, the usability of target locations was statistically analyzed. Then, the usability of 12 numeric keypads consisting of four different spacings among buttons and three button sizes were examined in another experiment. The results showed that a larger spacing among the buttons was worse, but the spacing of 10 mm was suitable for reducing errors with appropriate task completion time.

Experimental Study on the Effect of an Expanding Conjunction Between a Spilling Basin and the Downstream Channel on the Height After Jump

In order to study the impact of an expanding conjunction (with a divergent conjunction or with an abruptly expanding conjunction) between a stilling basin and the downstream channel on the height after jump, systematic experimental studies were carried out with different divergent angles and different abrupt expansion ratios at the conjunction. The link between the conjunction type and the height after jump is explored. The height after jump without an expanding conjunction is larger than that with a divergent conjunction, while the height after a jump without an expanding conjunction is larger than that with the abrupt expanding conjunction. Furthermore, with a larger divergent angle or larger expansion ratio, the impact on the height after jump becomes more variable. It is proposed that the existing formula which is used to calculate the height after jump in a straight channel is not appropriate for a jump with an expanding conjunction. This paper proposes a corrected formula to calculate the height after jump with an expanding conjunction, which is suggested for application in the engineering design process.

Ultra-tough and super thermal-insulation nanocellular PMMA/TPU

Nanocellular polymers have been considered promising multifunctional materials with unique properties. The key challenge is to fabricate nanocellular polymers with adequate cell sizes and densities. Herein, we report a novel method to prepare nanocellular polymethylmethacrylate (PMMA)/thermoplastic polyurethane (TPU) with tunable structures. The nanocellular PMMA/TPU displays a ductile fracture behavior while the microcellular PMMA shows a brittle fracture behavior. The nanocellular PMMA/TPU presents a tensile toughness and an impact toughness which are respectively 180-fold and 762% higher than the microcellular PMMA. The nanocellular structure combined with the nanostructured TPU greatly promotes the movement, shear slip and nano-fibrillation of the polymer chains, thus leading to this remarkably enhanced toughness. The nanocellular PMMA/TPU with an average cell size of 205nm and an expansion ratio of 8.0 displays a thermal conductivity of 24.8mW/m·K and a high compressive strength, which is to the best of our knowledge for the first time to achieve this superinsulating performance with porous polymers. The reduced air’s thermal conductivity due to the Knudsen effect combined with the reduced polymer’s thermal conduction due to the large expansion ratio are responsible for this superinsulating performance. The multifunctional nanocellular material offers a promising solution for advanced thermal insulation applications.

Performance evaluation of organic Rankine cycle systems utilizing low grade energy at different temperature

In order to effectively utilize low grade energy at different temperatures, this paper presents three systems using liquefied nature gas (LNG) as cold source. 16 potential applicable organic working fluids are selected for different cycles and systems. In the meantime, thermodynamic and thermal-economic analysis and comparison based on a multi-objective optimal model has been done. The results indicate that, when the temperature of low grade energy is below 370 K, the single-system has the best performance, and the tripartite-system has the best performance when the temperature is above 370 K. Propane emerges as the most suitable working fluid for single-system and R245fa for tripartite-system. Meanwhile, best work conditions have been calculated for single-system and tripartite-system. Moreover, the turbine's cost is the largest for both systems because of the large expansion ratio.

Numerical Characterisation of Supersonic Exhaust Diffusers

<p>Rocket motors that are designed to operate at high altitudes need a nozzle with a large expansion ratio to maximize the thrust at much lower atmospheric pressure than that of the sea level pressure. Accurate performance of these nozzles cannot be obtained when static tested on ground. Computational fluid dynamics (CFD) analyses have been performed to characterise the supersonic exhaust diffuser (SED). The results obtained from the CFD analyses have been found to be in good agreement with experimental and numerical values reported in the published literature. Started and un-started regions of the SED have been identified with the CFD results.</p>

Study of Large-Expansion-Ratio Tube Hydroforming with Movable Dies

In this paper, finite element codes LS-DYNA and DYNAFORM are used to analyze the plastic flow pattern of a tube hydroforming into a product with large expansion ratio and eccentric axes. Tube hydroforming with a movable die is proposed to enhance the forming capacity of tube hydroforming technology. The relative speed of the axial feedings to the movable die for obtaining a sound product is determined by a geometric analysis. The whole forming processes are divided into two stages. At the first stage, an internal pressure is applied on the inner surface of the tube and two axial feedings and a movable die move forward simultaneouly. At the second stage, one of the axial feedings keeps moving forward, whereas, the movable die moves backward. With this forming schedule for the axial feedings and movable die, products with more uniform thickness distributions are obtained. Finally, experiments of tube hydroforming with a movable die are conducted. Low-carbon steels are used as the tube specimen in the experiments. The simulation results of the product shape and thickness distributions are compared with experimental results to verify the validity of the finite element modeling and the proposed forming schedules.

Development and experimental study on a single screw expander integrated into an Organic Rankine Cycle

Expander is a key components in Organic Rankine Cycle (ORC) system. In order to improve the performances of single screw expander in large expansion ratio conditions and give consideration to normal conditions, a new idea called ‘increasing the built-in volume ratio appropriately and converting single screw expander into double-stage machine in large expansion conditions by utilizing the discharge velocity of screw grooves was proposed. By implementing this idea, a new prototype of single screw expander was designed and manufactured. Then the prototype was integrated into an experimental ORC system with R123. Experiments were carried out to analyze the characteristics of the developed single screw expander and the ORC system. The results show that the maximum expander shaft power, shaft efficiency, isentropic efficiency, volume efficiency and expansion ratio were 8.35 kW, 56%, 73%, 83% and 8.5, respectively. In addition, under expansion losses seem to be eliminated by the new structure of the expander. It was also found that 12–17% of the expander power was consumed by the circulation pump, of which the measured efficiency was between 20% and 31%. A maximum ORC efficiency of 7.98% was achieved.

Combined Turbine and Cycle Optimization for Organic Rankine Cycle Power Systems—Part B: Application on a Case Study

Organic Rankine cycle (ORC) power systems have recently emerged as promising solutions for waste heat recovery in low- and medium-size power plants. Their performance and economic feasibility strongly depend on the expander. The design process and efficiency estimation are particularly challenging due to the peculiar physical properties of the working fluid and the gas-dynamic phenomena occurring in the machine. Unlike steam Rankine and Brayton engines, organic Rankine cycle expanders combine small enthalpy drops with large expansion ratios. These features yield turbine designs with few highly-loaded stages in supersonic flow regimes. Part A of this two-part paper has presented the implementation and validation of the simulation tool TURAX, which provides the optimal preliminary design of single-stage axial-flow turbines. The authors have also presented a sensitivity analysis on the decision variables affecting the turbine design. Part B of this two-part paper presents the first application of a design method where the thermodynamic cycle optimization is combined with calculations of the maximum expander performance using the mean-line design tool described in part A. The high computational cost of the turbine optimization is tackled by building a model which gives the optimal preliminary design of an axial-flow turbine as a function of the cycle conditions. This allows for estimating the optimal expander performance for each operating condition of interest. The test case is the preliminary design of an organic Rankine cycle turbogenerator to increase the overall energy efficiency of an offshore platform. For an increase in expander pressure ratio from 10 to 35, the results indicate up to 10% point reduction in expander performance. This corresponds to a relative reduction in net power output of 8.3% compared to the case when the turbine efficiency is assumed to be 80%. This work also demonstrates that this approach can support the plant designer in the selection of the optimal size of the organic Rankine cycle unit when multiple exhaust gas streams are available.

Possible user-dependent CFD predictions of transitional flow in building ventilation

A modified backward-facing step flow with a large expansion ratio of five (5) was modeled by 19 teams without benchmark solutions or experimental data for validation in an ISHVAC-COBEE July 2015 Tianjin Workshop, entitled as “to predict low turbulent flow”. Different computational fluid dynamics (CFD) codes/software, turbulence models, boundary conditions, numerical schemes and convergent criteria were adopted based on the own CFD experience of each participating team. The largest coefficient of variation is larger than 50% and the largest relative maximum difference of penetration length is larger than 150%. The predicted non-dimensional penetration lengths as a function of the Reynolds number (1–10,000) are found to be significantly diverse among different teams. Even when the same turbulence model or even the laminar model is used, the difference in the predicted results is still notable among different teams. It indicates that the combined effects of a lack of general turbulence model, and possible errors in multiple decisions based on users' experience may have caused the observed significant difference. Prediction of transitional flows, as often observed in building ventilation, is shown to be still a very challenging task. This calls for a solid approach of validation and uncertainty assessment in CFD “experiments”. The users are recommended to follow an existing guideline of uncertainty assessment of CFD predictions to minimize the errors and uncertainties in the future.

Synthesis and Design of a One Degree-of-Freedom Planar Deployable Mechanism With a Large Expansion Ratio

This paper presents a new design of a deployable one degree-of-freedom (DOF) mechanism. Polygonal rigid-link designs are first investigated. Then, belt-driven links are considered in order to maximize the expansion ratio while avoiding flattened ill-conditioned parallelogram configurations. The planar basic shape of the proposed design is a triangle. Hence, virtually any planar or spatial surface can be created by assembling such faces. For architecture and telescopic applications, the cupola assembly is investigated. The advantages of this approach are discussed, and the scalability is demonstrated. Finally, a prototype is built for illustration purposes.

On the performance analysis of AHSS with an application to SET technology – FEM simulations and experimental measurements

Solid expandable tubular (SET) is an innovative breakthrough in the petroleum industry that aims to resolve issues associated with deep wells. It consists of in-place plastic deformation of tubular diameter resulting in larger conduit size that allows drilling deeper. However, due to volume constancy, increasing the tubular diameter results in a decrease in its wall-thickness, and hence even an initially thick-walled tubular may convert into thin-walled; especially at high expansion ratios. Extending the frontier of expandable applications require larger expansion percentage and enhanced tubular integrity after expansion, which exceed the capability of current tubular material. Therefore, the current study aims to investigate new alternative materials to be used as tubular for SET technology. Selected AHSS grades including TRIP, TWIP, and DP steels are analyzed numerically using FEM. Experimental validation of the FEM model was carried out using full-scale expandable tubular testing facility available at Sultan Qaboos University (Muscat, Oman). Interesting results in terms of stress, strain, expansion force, burst and collapse pressures, length shortening and wall-thickness reduction were obtained. Bauschinger effect arises at the collapse pressure rating has been considered in the study. It was found that materials with high true uniform elongation (and therefore with large strain hardening capability) are more capable of counteracting strain intensifications caused by plastic deformation, allowing either larger expansion ratio or larger safety margin for the deformation capability of the material at a given expansion ratio.

Pixel Grafting

Split-thickness skin grafting is the gold standard for treatment of major skin loss. This technique is limited by donor-site availability in large burn injuries. With micrografting, a technique where split-thickness skin graft is minced into 0.8 × 0.8-mm pieces, the authors have demonstrated an expansion ratio of 1:100 and healing comparable to that achieved with split-thickness skin grafting. In this study, the authors explore the regenerative potential of a skin graft by cutting split-thickness skin grafts to pixel size (0.3 × 0.3 mm) grafts. Wound healing was studied in full-thickness wounds in a porcine model by creating an incubator-like microenvironment using polyurethane wound chambers. Multiple wound healing parameters were used to study the outcome of pixel grafting and compare it to micrografting and nontransplanted wounds. The authors' results show that 0.3 × 0.3-mm pixel grafts remain viable and contribute to skin regeneration. The pixel graft-transplanted wounds demonstrated a faster reepithelialization rate, decreased wound contraction, and increased mechanical stability compared with nontransplanted wounds. The reepithelialization rates of the wounds were significantly increased with pixel grafting at day 6 after wounding compared with micrografting. Among the other wound healing parameters, there were no significant differences between wounds transplanted with pixel grafts and micrografts. Pixel grafting technique would address the most commonly encountered limitations of the split-thickness skin graft with the possibility of an even larger expansion ratio than micrografting. This technique is simple and fast and can be conducted in the operating room or in the clinic.