Finite Element Analysis of Optimum Back Pressure during Equal Channel Angular Pressing

Titanium is a hard metal with good mechanical properties, corrosion resistant and biocompatibility which makes it have a wide range of applications (biomedical and aerospace). Severe plastic deformation (SPD) is employed to produce Ultrafine Grained (UFG) structures. UFG structures have better mechanical properties due to their compaction. Equal Channel Angular Pressing (ECAP) is adapted to produce a UFG structure in Titanium. In this process, titanium sponge powder is filled in the aluminium shell by intermediate tapping to fill the volume of the shell. The shell is then closed with an Al cap and ECAP is done with continuous back pressure at 300°C. The test specimen has undergone four passes in route BC at different back pressure (50, 100 and 150 MPa) where titanium is consolidated without any crack. Titanium showed decreased grain size and porosity with increasing backpressure. In particular, it is seen that the sample ECAPed by 100 MPa backpressure showed a relative density of about 98% with a hardness of 37 HRC. It is seen that ECAP is more economical and the product obtained by the ECAP process has better properties.

Experimental and numerical investigation on inner flow and spray characteristics of elliptical GDI injectors with large aspect ratio

Equal channel angular pressing (ECAP) is used to consolidate particles of nano and micro levels at a shorter time and lower temperature. This process is more convenient than the conventional sintering process. In the conventional route, the sintered density obtained is 2.36 g/cc (89% relative density). Whereas, in ECAP, the theoretical density of 93% is observed after the first pass which is higher than the conventionally sintered sample. The relative density increases with an increase in the number of passes and it reached a maximum of 98.5% after 3 passes in route BC. The microstructure of the conventionally sintered sample showed coarse grains with the presence of porosity. Whereas, the samples compacted by ECAP had fine and elongated grains along with a low amount of porosity. Hardness showed a similar pattern to that of density. In ECAP, a hardness of 81 HRB was obtained after three passes in route BC. Al-5083 alloy was compacted by ECAP at 150°C with back pressure (50 MPa). No surface and internal defects were observed. The relative density of 98.5% without any surface cracks was obtained after three passes in route BC when processed through ECAP.

<div class="htmlview paragraph">The tightening legislation in the on-road heavy-duty diesel area means that pollution control systems will soon be widely introduced on such engines. A number of different aftertreatment systems are currently being considered to meet the incoming legislation, including Diesel Particulate Filters (DPF), Diesel Oxidation Catalysts (DOC) and Selective Catalytic Reduction (SCR) systems.</div> <div class="htmlview paragraph">Relatively little is known about the interactions between lubricant-derived species and such aftertreatment systems. This paper describes the results of an experimental program carried out to investigate these interactions within DPF, DOC and SCR systems on a state-of-the-art 9 litre engine.</div> <div class="htmlview paragraph">The influence of lubricant composition and lube oil ash level was investigated on the different catalyst systems. In order to reduce costs and to speed up testing, test oil was dosed into the fuel. Tests without dosing lubricant into the fuel were also run.</div> <div class="htmlview paragraph">Driving distances of up to 115,000 km (based on oil consumption) were simulated in these experiments. Following such treatments, no significant change in the activity of the CR-DPF oxidation catalyst, Diesel Oxidation Catalysts or SCR catalysts were observed. In each case, the distribution of oil-derived species was studied as a function of distance down the catalyst. It was found that the Ca, Zn and P were generally present in higher concentrations at the front of the catalyst, decreasing down the unit. In contrast, sulfur is distributed evenly throughout the length of each catalyst. This is because sulfur can be deposited from the gas phase and is more mobile on the catalyst surface.</div> <div class="htmlview paragraph">Interestingly, when doping high ash oil into the fuel it was found that the back pressure of the DPF system increased rapidly. This is particularly important since it is known that used engine oil is sometimes poured back into the fuel tank for disposal. These results imply that this practice may strongly affect the efficiency of DPF devices.</div> <div class="htmlview paragraph">This rapid increase in back pressure is a consequence of doping the fuel with the high ash oil, since operation of the engine with the high ash oil without doping, or with a low ash oil with doping, resulted in only a gradual increase in back pressure. In addition, the distribution of the ash in the filter was strongly affected when doping the high ash oil into the fuel, in that the ash was uniformly distributed down the length of the filter. In the other experiments carried out here, and in measurements of field-aged filters, the ash thickness increases with distance into the filter. These observations reveal that care needs to be taken when doping oil into the fuel to accelerate the observation of oil-derived effects in DPF systems.</div>

Microstructural modelling of equal channel angular pressing for producing ultrafine grained materials

This paper examines the effect of friction and back pressure on the formability of superplastically formed aluminium alloy AA7475 sheet at the temperature of 517 °C. Several experiments with lubrication and back pressure are performed using a simple box shape tool cavity. The coefficient of Coulomb friction between the formed sheet and tool has been determined indirectly using a finite element model to simulate superplastic forming of the box shape. Typical values determined for all lubricant conditions tested are in the range 0.1 < μ < 0.2. The void growth with strain was determined directly from measurements as a function of back pressure. The results show the application of back pressure at 1 MPa reduces the growth of voids from 7% to 0.3% void volume fraction at a logarithmic thickness strain of 0.65. This paper reports back pressure has a significantly greater role than friction in enhancing the formability of the alloy.

Study of channel angle influence on material flow and strain inhomogeneity in equal channel angular pressing using 3D finite element simulation

The grain structure of coarse-grained Cu of different degrees of purity was modified by plastic deformation by , 4 and 8 passes of equal channel angular pressing (ECAP) at an ambient temperature with and without back pressure. The effect of this modification on deformation resistance was tested in rate change tests in compression at elevated temperatures up to 473. Electron microscopy and compressive strength evolution with strain confirmed that static recrystallization leads to grain coarsening during heating to test temperatures of 423 for and 473 for and that discontinuous grain coarsening by dynamic recry- stallization sets in already at . The influence of the grain structure on the deformation resistance is discussed in terms of a control loop considering generation and loss of free dislocations. The magnitude and rate dependence of the maximal deformation resistance of unrecrystallized ECAPed Cu were explained in terms of dynamic recovery at low- and high-angle boundaries as proposed previously. The interpretation sheds doubt on the common interpretation of rate change experiments in terms of thermally activated glide.

The production yield and clean coal quality in dense-medium coal washing equipment such as three-product cylindrical separators are mainly controlled via the back-pressure adjustment at the sink port. However, the role of the back pressure in the fluid flow in such separators has been previously assessed only to a very limited extent. This study was undertaken to investigate the effect of back pressure on the flow pattern in a 70-mm three-product cylindrical separator. Accordingly, a time-dependent, three-dimensional numerical study was conducted based on computational fluid dynamics (CFD) in a two-phase system. The turbulence was simulated by the Reynolds stress model (RSM) whereas the volume of fluid (VOF) method was used to model the water–air interface. The simulation results were validated using the experimental data. The sensitivities of the flow fields and some other hydrodynamic characteristics to the increase of back pressure were different in the first and second stages of separator. Increase in the tangential velocity, the suppression of the air core and the improvement of medium recovery were some of the consequences of increasing the back pressure.

Copper-based powder materials have found their application in many industries. These include classical powder metallurgy, automotive and aviation industries, microelectronics, instrument engineering, and nanotechnology. In this paper, the processes of forming and sintering copper powders obtained by various methods are considered. The main part of the research was carried out on powders of the PMS-1 brand obtained by electrolysis. Four batches of samples (18 pieces each) were pressed at different pressures. Based on the results of the research, a molding mode was proposed, which should ensure the density of blanks not less than 70 % of the density of compact material. To find the simplest and most rational modes of sintering blanks, the process was carried out in air and in dissociated ammonia. The parameters of the samples were calculated after each technological operation, and the volume shrinkage of the samples was calculated depending on the initial density. Draft tests were carried out. Sediment tests were performed up to a maximum pressure of 400 MPa. Despite the fact that the degree of high-altitude deformation was 37–40 %, none of the samples collapsed during the tests, and no visible cracks were observed. Based on preliminary experiments, the masses and forming modes of rectangular blanks that were used for equal channel angular pressing were calculated. Equal channel angular pressing was performed for two samples parties obtained using different sintering modes. When pressing the first samples party, the lack of the required level of back pressure led to either a complete or significant violation of the material integrity. Before pressing the samples of the second party, a copper sample was previously placed into the channel to create a natural backpressure. It was also possible in principle to carry out the process of equal channel angular pressing of porous sintered workpieces without violating the integrity of the material.

A two‐step process consisting of modified equal channel angular pressing (ECAP) and subsequent isothermal rolling (IR) was developed to produce thin sheets of aluminum alloys with ultra‐fine grained (UFG) structure. Significant increase in the efficiency of ECAP was attained by using flat billets and a back pressure system. The incorporation of final IR into technologic route provides a reduced strain which is necessary to impose for the fabrication of thin sheets with UFG structure. In addition, it allows producing relatively “long billets.” In order to demonstrate the feasibility of this technique an Al–5.1Mg–2.1Li–0.17Sc–0.08Zr (wt %) alloy was subjected to ECAP at 325 °C to a total strain of ∼8 using processing route CX. The operation time of this processing did not exceed 15 min. Subsequent IR at the same temperature with a total reduction of 88% was applied to produce thin sheets with a 1.8 mm thickness and an average size of recrystallized grains of ∼1.6 µm. These sheets exhibit extraordinary high superplastic ductilities. In addition, this material demonstrated almost isotropic mechanical behavior at room temperature. The maximum elongation‐to‐failure of ∼2700% was attained at a temperature of 450 °C and an initial strain rate of 1.4 × 10−2 s−1. Thus it was demonstrated that the two‐step processing consisting of ECAP with a back pressure followed by IR was a simple technique providing potential capability for the fabrication of superplastic sheets from an Al–Mg–Li–Sc alloy on a commercial scale.

Activation of the prismatic and pyramidal slip systems, along with the twinning as the secondary deformation mechanism, assists in the accommodation of a larger plastic strain during the deformation of magnesium alloys. In this paper, deformation mode activity and texture evolution of the WE43 magnesium alloy were investigated during core-sheath equal channel angular pressing (ECAP) at room temperature. Texture studies and transmission electron microscopy inspections suggest that the mechanisms behind the ECAP at room temperature assisted by back pressure were activation of (101¯0) prismatic slip (as the primary mechanism), as well as extension and contraction twinning.

Whereas there are case reports of laparoscopy in patients with ventriculoperitoneal shunts, there are no studies assessing the potential failure of shunt valves with the increased intra-abdominal pressure of laparoscopy. This study aims to assess this factor. An in vitro model was used to assess the potential for retrograde failure of ventriculoperitoneal shunt valves in a commonly used shunt. Nine shunts were subjected to graded increases in back pressure and observed for retrograde valve leak. None of the shunts tested showed any signs of leak associated with the increased back pressure. However, disruption of shunt seals was noted in seven of the nine shunts, occurring at the minimal pressure of 80 mmHg. There appears to be minimal risk of retrograde failure of the valve system in the ventriculoperitoneal shunt tested. However, tests on different types of ventriculoperitoneal shunts would be needed to confirm these results if laparoscopy is to be considered safe in patients with ventriculoperitoneal shunts in situ.

Petroleum fuel consign has been lessening at a very high proportion. Almost all automobiles depend upon an IC engine driven by petroleum fuels. As much as the number of automobiles is developing in this modern world, it is obligated to reduce fuel expenditure. One of the ways to do this is to diminish the car's drag. Among a manifold process of reducing drag, using Vortex Generators is one. Delta-shaped vortex generators are used at the rear trunk of the range rover, where the flow separates. K-epsilon turbulent model in ANSYS-Fluent 19.2 software is used to imitate the airflows. This work observed the number and spacing between successive vortex generators based on comparing drag coefficient values. The contours of static pressure and velocity magnitude were also observed for each model. When the vortex generators were attached, the pressure coefficients at the rear trunk began to increase, confirming the increment in back pressure. Hence, the increase in back pressure indicates a reduction in the drag coefficient. It has been found that a combination of 7 vortex generators is the optimum solution. The devices work better at a higher velocity than the lower velocity without affecting vehicle stability. The vortex - 4 model's drag coefficient was found to be significantly lower than that of the standard model vehicle, which is 0.42877. The Base Model of Range Rover (2020) is my sense of humor, the highest drag coefficient. So vortex generators are commonly used on automobile vehicles to prevent downstream flow separation and improve their overall performance by reducing drag.

Objectives In wells which are producing on intermittent gas lift (IGL), the injected gas cannot sweep the entire liquid volume to the surface from the bottom of the tubing as there is continuously some fluid falling back in the tubing. The fallback can be described as the difference between the volume of the slug at the start of the gas injection and the volume of the actual produced slug at the surface. This fallback of liquid happens due to the fact that the gas has a tendency to flow through the liquid slug and letting the liquid to fall. The intensity of the liquid fallback increases more when there is increase in back pressure at wellhead. In order to minimize this liquid falling back in wells on intermittent gas lift, the sweeping pipe bend technology has been used in the various onshore fields operated by ONGC which has resulted in substantial gains and has been brought out in the paper. Process Gas break through and fallback are affected by three factors including the development of the gas bubble, the velocity of the slug flowing upward in the tubing, and wellhead restrictions caused due to presence of many 90-degree bends. To prevent gas breakthrough and to optimize the liquid fallback to minimum 5-7 % per 1000 feet of lift, it is recommended to maintain 1000 feet/min of minimum velocity of slug. Slower is the velocity of the slug which is moving up in the tubing, the longer time it takes for the gas to break through the liquid. At 1000 feet/min velocity, the wellhead restrictions can result in fallback losses due to breakthrough of gas in the well. In general, the flow path through the Christmas tree into the flowline is rather tortuous, moving first through a tee to the wing valve, then through other 90-degree ells before finally reaching the flowline. These restrictions further result in slowdown of the velocity of the slug thus resulting in more liquid to fallback and subsequently in significant production losses. Results In order to overcome the aforementioned problem and to reduce fallback in an intermittent gas lift well, sweeping pipe bend technology was considered and in the first phase implemented in 5 identified wells of different fields of ONGC Assets. With the help of sweeping pipe bend, the flow pattern becomes streamlined and number of 90-degree bends reduces or eliminates resulting in substantial reduction in the back pressure thus reducing the fall back. The implementation of the technology has resulted in an average liquid gain of 20.3% per well. Various guidelines for successful application of sweeping pipe bend have also been brought out in the paper. Additive Information 650 candidate wells operating on intermittent gas lift have been identified for the implementation of Sweeping Pipe Bends. As per the analysis, the implementation of Sweeping Pipe Bend is likely to result in a liquid gain of about 1000 m3/day from these wells.