Local Pressurization Research Articles

Effect of Local Pressurization on Microstructure and Mechanical Properties of Aluminum Alloy Flywheel Housing with Complex Shape.

In this work, squeeze casting experiments of flywheel housing components with a large wall thickness difference and a complex shape were carried out with AlSi9Mg aluminum alloy. The defects, microstructures, and mechanical properties under different process parameters were investigated. Furthermore, the local pressurization process was applied to the thick-walled positions to force-feed the cast defects. The mechanical properties and microstructures at these positions were analyzed. The results showed that the surface quality of formed components was good and that local pressurization could effectively reduce the shrinkage cavity and shrinkage porosity in thick walls, but the scope and effect of forced feeding were limited. The optimum process parameters were a pouring temperature of 650 °C, a specific pressure of 48 MPa, a mold temperature of 220 °C, a local pressurization of 800 MPa, and pressure delay times of 15 s (side A) and 17 s (side B). The ultimate tensile strength, yield strength, and elongation of the formed component under validation experiments of the optimum process parameters were 201 MPa, 103 MPa, and 5.1%. Meanwhile, the fine grains of primary α-Al were mainly rosette and equiaxed grains, and the average grain size was about 40 μm. The microstructure of the eutectic silicon was acicular and was prone to segregation under pressure. According to profile morphology, the positions after pressurization were divided into a deformation zone, a direct action zone, and an indirect action zone. The coexistence of as-cast and plastic deformation microstructures was observed. The effect of local pressurization mainly involved a change in the solidification process, plastic deformation, and forced feeding.

Low resistance electrical contacts to few-layered MoS2 by local pressurization

The performance of electronic and optoelectronic devices is dominated by charge carrier injection through the metal–semiconductor contacts. Therefore, creating low-resistance electrical contacts is one of the most critical challenges in the development of devices based on new materials, particularly in the case of two-dimensional semiconductors. Herein, we report a strategy to reduce the contact resistance of MoS2 via local pressurization. We fabricated electrical contacts using an atomic force microscopy tip and applied variable pressure ranging from 0 to 25 GPa. By measuring the transverse electronic transport properties, we show that MoS2 undergoes a reversible semiconducting-metallic transition under pressure. Planar devices in field effect configuration with electrical contacts performed at pressures above ∼15 GPa show up to 30-fold reduced contact resistance and up to 25-fold improved field-effect mobility when compared to those measured at low pressure. Theoretical simulations show that this enhanced performance is due to improved charge injection to the MoS2 semiconductor channel through the metallic MoS2 phase obtained by pressurization. Our results suggest a novel strategy for realizing improved contacts to MoS2 devices by local pressurization and for exploring emergent phenomena under mechano-electric modulation.

Flash Heating and Local Fluid Pressurization Lead to Rapid Weakening in Water‐Saturated Fault Gouges

AbstractCoseismic fault displacement is quite large at shallow depths in some earthquakes, and it implies that fault gouges and sediments have extremely low dynamic friction during seismic slip. However, the dynamic weakening mechanisms of gouges under wet conditions are still not well constrained. Here we present direct evidence for the occurrence of flash heating and local fluid pressurization in water‐saturated gouges, by performing low‐ to high‐velocity (V = 10 μm/s to 1 m/s) friction experiments in a pressure vessel, under conditions specially designed to suppress weakening effects of bulk thermal and compaction‐induced pressurization. The tested gouges exhibit transition from velocity strengthening to drastic velocity weakening as slip rates increase. Strong dynamic weakening starts to occur at V ≥ 0.04 m/s at the initiation of sliding (<~0.1 m), which is much more efficient than previously reported in terms of the weakening velocity and distance. Furthermore, the onset of weakening is always accompanied by an instantaneous dilatancy (10–25 μm), which is much larger than that observed in dry tests and in contrast with gradual changes displayed in the wet tests without dynamic weakening. Numerical modeling integrated with microstructural observation reveals that bulk thermal pressurization cannot explain the experimental results, while flash weakening triggered by vaporization of water layers on/around asperity contacts and the resultant local fluid pressurization may be responsible for the observed rapid weakening concomitant with instantaneous dilatancy. Given high efficiency of such weakening process, fluid‐infiltrated faults could be weakened more rapidly than previously recognized during seismic slip.

Clinical efficacy of posterior component separation with Sublay mesh repair for complex abdominal incisional hernia

Objective To explore the clinical efficacy of posterior component separation (PCS) with Sublay mesh repair for complex abdominal incisional hernia. Methods The retrospective crosssectional study was conducted. The clinical data of 30 patients with complex abdominal incisional hernia who were admitted to the Beijing ChaoYang Hospital of Capital Medical University from July 2016 to March 2017 were collected. Patients intraoperatively received PCS with Sublay mesh repair. Observation indicators: (1) intra- and post-operative situations: defect area of incisional hernia, operation time, volume of intraoperative blood loss, time of postoperative drainage-tube removal, postoperative complications and duration of postoperative hospital stay; (2) followup situation. Followup using outpatient examination and telephone interview was performed to detect recurrence of hernia and mesh-related complications up to July 2017. Outpatient examination was done once at postoperative month 1, 3 and 6 and telephone interview was done at 1 year postoperatively. Measurement data with normal distribution were represented as ±s and measurement data with skewed distribution were described as M (range). Results (1) Intra- and post-operative situations: 30 patients received successful PCS with Sublay mesh repair for complex abdominal incisional hernia. Defect area of incisional hernia, operation time, volume of intraoperative blood loss and time of postoperative drainage tube removal were respectively (222±124)cm2, 100 minutes (range, 40-235 minutes), 80 mL (range, 50-200 mL) and 5 days (range, 2-15 days). Of 7 patients with postoperative complications, 3 were complicated with shallow surgical site infection, including 1 with wound healing by vacuum sealing drainage and 2 with delayed healing by debridement and drainage; 2 with postoperative seroma were improved by aspiration and local pressurization after 1 months; 1 with fat liquefaction of abdominal incision was improved by symptomatic treatment; 1 with postoperative active hemorrhage was confirmed with arteriolar hemorrhage of muscular layer and then received hemostasis by ligation. Time of postoperative hospital stay of 30 patients was 15 days (range, 10-57 days). (2) Follow-up situation: 30 patients were followed up for (7±3)months, without occurrences of hernia recurrence, intestinal fistula and mesh-related complications. Conclusion PCS with Sublay mesh repair for complex abdominal incisional hernia is safe and feasible, with good clinical efficacies. Key words: Incisional hernia; Retrorectus hernia repair; Component separation; Mesh

Treatment for early postoperative esophageal fistula complicated with anterior cervical surgery.

To investigate the efficacy of debridement, open drainage, and early feeding to treat early esophageal fistula complicated with anterior cervical surgery. Retrospective analysis was conducted on data from 3154 patients who had undergone anterior cervical surgeries for cervical vertebra diseases between January 2006 and January 2013, in which eight patients had esophageal fistula with five males and three females. Four patients had cervical spinal injuries and four patients had cervical spondylosis. All of whom had postoperative esophageal fistulas and underwent debridement and drainage. The wounds were left open for natural drainage. No drainage devices were placed in surgical sites, and no gastric tubes were placed after surgeries. Such normal food as rice balls but not liquid or semiliquid diet was recommended. Local pressurization was conducted with fists during feeding to prevent food overflowing from orificium fistulae. Healed esophageal fistulas were achieved in all of the patients after 1-2 weeks treatment. There weren't recurrent esophageal fistulas and delayed infection found during 2-5 years follow-up. Good swallowing functions and stable cervical vertebrae were achieved in all of the patients. The satisfactory therapeutic effects were achieved in patients with previous neck diseases. Frankel classifications were increased by 1-2 grades in patients with cervical spinal injuries. JOA scores were increased from 9.5 before surgery to 15.5 after surgery in patients with cervical vertebra diseases. Early postoperative esophageal fistula complication after anterior cervical surgery can successfully be treated by debridement, drainage without gastric tube, and with early oral postoperative feeding but without fluids.

Optimization of Local Pressurization Conditions for Compact Die Casting System

Optimization of Local Pressurization Conditions for Compact Die Casting System

Earthquake friction

Laboratory friction slip experiments on rocks provide firm evidence that the static friction coefficient μ has values ∼0.7. This would imply large amounts of heat produced by seismically active faults, but no heat flow anomaly is observed, and mineralogic evidence of frictional heating is virtually absent. This stands for lower μ values ∼0.2, as also required by the observed orientation of faults with respect to the maximum compressive stress. We show that accounting for the thermal and mechanical energy balance of the system removes this inconsistence, implying a multi-stage strain release process. The first stage consists of a small and slow aseismic slip at high friction on pre-existent stress concentrators within the fault volume but angled with the main fault as Riedel cracks. This introduces a second stage dominated by frictional temperature increase inducing local pressurization of pore fluids around the slip patches, which is in turn followed by a third stage in which thermal diffusion extends the frictionally heated zones making them coalesce into a connected pressurized region oriented as the fault plane. Then, the system enters a state of equivalent low static friction in which it can undergo the fast elastic radiation slip prescribed by dislocation earthquake models.

Mechanical Properties and Fracture Behavior of Indirect Squeeze-Cast A354 Alloy Using Local Pressurization

The effect of local pressurization on mechanical properties and fracture behavior of indirect squeeze-cast A354 alloy has been investigated. As compared to conventional process, the porosity and shrinkage cavity for heavy sectioned squeeze castings were improved by the indirect squeeze casting, while its tensile properties were inferior to other parts of the casting. That is mainly due to that inhomogeneous eutectic Si particles within strip, angular and fragment shapes distribute in bulky α-Al cells, which is caused by slower solidification rate. After T6 treatment, the fragmentation and spheroidization of the eutectic silicon happened. Under this situation, the effect of fragmentation on α-Al matrix reduced. Tensile properties of the casting (both local pressurization part and non-local pressurization part) were enhanced greatly, by 36.8% and 25.4%, respectively. Fracture analysis results show that the type of fracture morphology is changed from mixed mode of brittle cleavage and ductile to ductile mode after T6-treatment.

Study of Firemen Respirator Fixed Inflatable Device Rapid Inflation Methods Optimization

The use of air pressure pump for local pressurization in pressure air system is an important application of energy saving technology of pneumatic. The firemen respirator fixed inflatable this basic principle device utilization system design. Due to the different inflation affects firefighters respirator fixed inflatable device energy consumption and filling speed, in this paper, the energy consumption by comparing different charging mode , and the charging mode is optimized to achieve rapid fire breathing bottle inflated and improve firefighter respirator fixed inflatable device efficiency.

Simulation Analysis and Studying of Die Casting Forming Process for Crankcase

In recent years, with the rapid development of automobile, the production of complex parts adopt the die casting process such as crankcase box. the stress of market competition make greater demand on Casting Products quality, such as the organizational structure of products has no shrinkage porosity defect and has good mechanical properties. this articles simulation analysis of die casting forming process for Box are based on software AnyCasting, analyzing the reasons of air trapping from the filling process, Solidification sequence, Residual melt modulus. and it can conduct local extrusion feeding towards location of shrinkage porosity. By analyzing the metallographic structure we known that Local pressurization could refine Casting organization grain and make the grain more dense.

Coupled seismo-hydromechanical monitoring of inelastic effects on injection-induced fracture permeability

We present in situ measurements of fluid pressure, deformation and seismicity in natural fractures together with coupled hydromechanical simulations. We conducted a step-rate water injection (~3.5MPa and 1200 s) to induce the local pressurization of a critically stressed fractured carbonate reservoir layer located at 250m-depth in the Low Noise Underground Laboratory (LSBB), southern France. An observed factor-of-3 increase in the fracture permeability was associated with the injection-induced fluid pressure increase and about 100 triggered seismic events. Both normal opening (a few microns) of the fluid-injected fracture and the associated tilt (<1 micro-radian) of the fracture near field displayed inelastic behavior highlighting an irreversible fracture shear and dilatant failure, amounting to about 1/3–1/2 of the maximum measured deformations.Using a plane-strain finite-difference coupled hydromechanical model, our calculation shows that tensile failure first occurred in the injection zone and then shear failure spread along fractures into the surrounding unsaturated rock through stress transfer from the injection zone. The most striking result of these model simulations is that the mechanical weakening of the fractures in the near field induced a 2–5×105Pa release of the normal stress across the fluid-injected fracture that provoked fracture slip and increase in permeability. A geological exploration of the fracture zone after the experiment showed that no major failure had occurred, and we therefore relate these strength and permeability variations to the slight reactivation (~microns) of pre-existing fractures.

Flow Behavior and Copper Segregation of Al-Si-Cu Alloys in Local Pressurization

Flow Behavior and Copper Segregation of Al-Si-Cu Alloys in Local Pressurization

Solidification Analysis of Hypoeutectic Aluminum Alloy under Local Pressurization

Solidification Analysis of Hypoeutectic Aluminum Alloy under Local Pressurization

On the Microstructure and Impact Properties of Slow Injection A356 Die Castings with Local Pressurization

Microstructure and impact properties of slow injection A356 die castings with local pressurization have been investigated. The microstructure in the casting different regions were analyzed and compared. The casting impact absorbed energy varies from 1.17 to 2.35J, and is higher than that of other pressure die casting process. Furthermore, fracture mechanisms of different regions in castings are discussed. The results show that, the impact absorbed energy decreases with increase in SDAS. Also significant fluctuations of the impact properties in the thick-walled and local pressurization regions are found.

Noninvasive measurement of instantaneous, radial artery blood pressure

A new prototype system for the noninvasive measurement of instantaneous blood pressure (BP) in the human radial artery has been developed. The system is based on the volume-compensation method, but several components were newly designed, namely, a disk-type cuff for local pressurization and a nozzle-flapper-type electro-pneumatic converter (EPC) for the cuff-pressure control. Results of experiments indicated that, using the disk-type cuff, the radial artery could be completely compressed, and the newly devised EPC had sufficient frequency response for BP measurement in humans. It was also found that the prototype system comprising these components was capable of noninvasively measuring instantaneous BP in the human radial artery, not only under rest conditions but also in a stressful condition, such as during the cold pressor test. In conclusion, the newly developed local pressurization technique appears promising as a useful and helpful means for instantaneous BP monitoring over longer periods of time than have previously been possible. Using this method, it is possible to construct an instrument that is more compact and more comfortable for the subject to use than a conventional commercial instrument. Finally, it has been reported that it may be possible to monitor cardiac output continuously by BP waveform analysis. Thus, continuous cardiac output monitoring might be another potential and important application of the newly designed instrument.

Combustion characteristics of ethanol in a porous ceramic burner and ignition improved by enhancement of liquid-fuel intrusion in the pore with ultrasonic irradiation

Porous burner has a potential of lower-emission in a combustion of liquid fuels. However, it would be less attractive owing to its complexity and inefficiency in operations of the fuel vaporizing, in view of a practical application. To solve the problem described above, an ignition promoted system is proposed with taking advantages of characteristics of the porous burner. In this research, a fuel-vaporizing combustor equipped with porous burner made of Al 2O 3 and 1.7 MHz-ultrasonic oscillator was manufactured based on the calculating of a rate of fuel-penetration through the porous media. It was supposed that the fuel-penetration was derived from a capillary effects and the local pressurization of ultrasonic influenced by pore size and ultrasonic propagation. Combustion characteristics of ethanol fuel with manufactured combustor were investigated experimentally. At a term of startup, it is confirmed that vaporization of ethanol was promoted by ultrasonic and instantaneous ignition was achieved. Vaporizing combustion was sustained with recovering a part of its thermal radiation heat through the porous burner because Al 2O 3 had transparency for light which had near IR wavelength. Complete combustion was achieved within Al 2O 3 burner under the equivalence ratio ranged from 0.63 to 0.80, which showed that the combustion mode was similar to a premixing combustion. However, NO x concentration was comparatively high value, 59–97 ppm (O 2 0% base) in the stable combustion region because a heat value per surface area of the flame was increased due to a local high temperature zone caused by a shortened flame.

Modeling of Melt Droplet Fragmentation Following Vapor Film Destabilization by a Trigger Pulse

In hypothetical Severe Accident studies for a PWR, a large amount of molten corium may be poured into water. There is then a risk of Steam Explosion. After the premixing sequence in which the melt is more or less dispersed into water, a fine fragmentation process may start, which can lead to an escalation. Such an event is generally triggered by the destabilization of the vapor film surrounding the hot melt droplets. In this paper, an attempt to describe all the successive processes leading to this fine fragmentation is presented.First, a critical analysis of previous models is performed, allowing us to propose a new sequence of events. As in the previous models, the film destabilization leads to the growth of cold liquid peaks induced by Rayleigh Taylor instability. As these peaks have a smaller density than the drop, they do not penetrate into the hot drop. At the cold liquid-hot liquid contacts, transient heat transfer leads to the explosive boiling of a small amount of coolant. The generated local pressurization deforms the hot melt interface. This can produce fine fragments from the filaments issued from the melt. Some of them may reach the vapor-coolant interface where intense and rapid vaporization occurs. A large bubble then develops, and a new fragmentation sequence may again appear at the bubble collapse. The present model is supported by experimental results.

Local pressurization during solidification of Al-Si-Cu alloys

Local pressurization is a squeeze method for eliminating the shrinkage porosity. In this study, local pressurization was carried out with a specially designed permanent mold to examine the effect of pressurization on the shrinkage porosity through the investigation of macrostructure, partial density variation under the pin tip for two types of aluminium alloys of hypoeutectic (AC4B) and eutectic (ADC12). Then copper concentration at the different positions in AC4B casting was analysed in order to investigate segregation. And in order to estimate the flow of liquid or solid-liquid zone by local pressurization, the ratio of flowing volume of two alloys was measured with varied pressurization timing and different pressures. The solid fraction of flowing zone was calculated by the use of both the solidification simulation and the characteristic macrostructure change of flowing zone. The solid fraction indicates the fraction within which the present pressurization can induce interdendritic liquid flow.The results showed that the partial density of two alloys cannot be affected within the certain limits of pressurization timing for a given pressure and pressurizing speed, and does not increase obviously even if pressure increases, such as 64 to 128MPa for ADC12 casting. It was also found that the negative segregation of copper in AC4B casting occurred under the pin tip. The concentration of copper varied with distance from the pin tip. The degree of segregation was severe in the position 15mm distant from the pin tip. Opposite to the negative segregation, the positive segregation occurred in the upper zone around the pin. From the simulation, the maximum solid fraction of flowing zone, where interdendritic liquid moves, is shown to be about 0.46 and 0.53 for AC4B casting with pressure of 32 and 64Mpa, respectively.

Flame-Spreading Phenomena in Fin Slots of a Solid Rocket Motor

Flame-spreading processes in thee n-slot regions of solid-propellant motor grains have the potential to ine uence thebehavioroftheoverallignitiontransient.Theresearchconductedinthisinvestigationisaimedatobtainingabetter understanding of the e ame-spreading processes in rocket motors with aft-end e n slots. Nonintrusive optical diagnosticmethodswereemployedtoacquiree ame-spreadingmeasurementsinthee n-slotregionofasubscalerocket motor. Highly nonuniform e ame-spreading processes wereobserved in both the deep and shallow e n regions of the test rig. The average e ame-spreading ratesin thee n-slot region werefound to betwo ordersofmagnitudeless than those in the circularport region of a typical rocket motor. The e ame-spreading interval was found to correlatewell with the local pressurization rates. A higher pressurization rate produces a shorter e ame-spreading time interval.

Transient Boiling Heat Transfer in a Narrow Channel : Fluctuation Phenomena in the Channel Due to Bubble Growth and Collapse

A transient boiling and a two-phase flow in a narrow channel were experimentally investigated under the condition of step-wise heat input in our previous reports. A periodic pulsating flow due to bubble growth and collapse was observed under relatively low heat input. In the present report, such two-phase flow characteristics in the channel have been analyzed, considering the bubble growth and collapse process based on the transient heat conduction in the surrounding liquid layer in a fluctuating pressure field. The calculation results agree qualitatively with the fluctuation period and the voiding dynamics in the channel obtained by the experiment. It has been confirmed that the change of void fraction distribution along the channel with time is realized by such pressure feed-back effects on the transient boiling as boiling suppression due to local pressurization and boiling promotion due to local depressurization in the channel.