Multi Pass Research Articles

Processing and characterization of nanostructured Grade 2 Ti processed by combination of warm isothermal ECAP and extrusion

In this study, combined multi pass equal channel angular pressing (ECAP), and subsequent warm extrusion at different temperatures are performed on commercial purity titanium. Mechanical and microstructural evolutions are then investigated. Since it was observed that the four passes ECAP processed sample showed the best strength and reasonable elongation, this sample was selected for studying the extrusion temperature effects on the structure and mechanical properties of Grade 2 titanium. Therefore, the 4th passes ECAP processed sample was extruded at different temperatures of 300°C, 350°C, 400°C, 450°C and 500°C. The result revealed that the best mechanical properties were achieved from the specimen processed by four passes ECAP followed by warm extrusion at 300°C. The strength, and hardness of this sample were considerably improved in comparison with that of the unprocessed sample. Also, its ultra-fine grained and nanograined microstructure were homogeneous, with a grain size ranged from 40 to 200nm with an average grain size of about 123nm. It was seen that the mechanical properties of some samples after applying this combined process (ECAP + warm extrusion) are comparable with those of Grade 5 titanium which is commonly used in medical applications but contains alloying elements that are toxic to human health.

Shell side plain tube bundle performance of a multi-pass direct expansion evaporation of ammonia at various degrees of exit superheat

This paper presents the experimental results of shell side dry expansion evaporation characteristics of ammonia on a triangular pitch plain tube bundle in a multi pass cross flow configuration evaporator. Heat exchanger had 4 passes with 3 plain tubes in each pass. The average bundle heat transfer coefficient showed better performance at −1.7 °C versus −20 °C. Heat transfer performance of individual passes were studied at saturation temperature of −1.7 and −20 °C, heat flux range of 5 to 45 kW m−2 and exit superheat temperature of 2 to 10 °C. Present data suggest that variation in bundle performance is less significant at lower heat fluxes with low degree of exit superheat. Top pass with maximum quality along the bundle height showed the least performance with increase in the degree of exit superheat.

Influence of heat treatment on mechanical properties and microstructure of the Al2024/SiC composite produced by multi–pass friction stir processing

Abstract Aluminium matrix nano-composites were produced by friction stir processing of an Al-Cu alloy at different number of passes with pre-inserted SiC particles. The metal matrix composites were supplementary heat treated to elucidate the effect of heat treatment on microstructural changes and mechanical properties. The samples were fabricated by two and four passes. The supplementary heat treatment consisted of annealing at 590 °C for 1 h and artificial aging at 180 °C for 8 h. Microstructural studies showed that fine and co-axial grains along with uniform distribution nano-particles were formed in the stir zone (SZ). The agglomerated nano-scale particles were also observed in the samples. Micro-hardness results presented that in the SZ-region, hardness decreased with increasing the number of passes in the samples that were not heat treated. However, hardness uniformly increased about 70 HV in the heat-treated samples. Wear mechanism in all of the samples was adhesive mechanism and the value of wear resistance increased about 170% in the heat-treated samples. The obtained results showed that the improvement of hardness and wear resistance in the heat-treated sample was related to the change in size and distribution of the S-phase precipitates in microstructure.

Twinning and detwinning behaviors of Mg–3Al–1Zn sheets subjected to different loading paths

Abstract Twinning and detwinning are the important deformation modes in magnesium alloys during different deformation processes. To analyze the interaction of two deformation mechanisms under different loading paths, firstly, compression–tension experiments are performed on rolled sheet along the rolling direction. Quasi in-situ electron backscatter diffraction (EBSD) method is used to track the evolution of twinning fraction and texture at exactly observed region. The influence of Schmid factor (SF) value on choosing of twinning and detwinning variants during the above deformation is analyzed, and it is found that twinning and detwinning behaviors are mainly controlled by the variants with maximum SF value. Then, the twinning and detwinning behaviors under multi passes and directions compression are also investigated, which reveal that the secondary twinning can impede the following detwinning.

Phase sensitive chirped laser dispersion spectroscopy under high absorbance conditions

A whole-fiber methane sensor under high absorbance based on phase sensitive chirped laser dispersion spectroscopy is presented in this paper. The laser source of the sensor is a tunable distributed feedback diode laser with a frequency of 1653.7 nm. A telecom-based electro-optical intensity Mach-Zehnder modulator working in carrier suppression mode is adapted to modulate the single frequency laser beam for generating a dual-sideband spectrum beside the carrier wave. Unlike previous proposed phase sensitive chirped laser dispersion spectroscopy scheme, the beatnote signal generated by the two sidebands is detected experimentally. The refractive index fluctuation around the 23 transition of methane is measured by detecting the phase variation of the dual-sideband beatnote signal through using the heterodyne interferometric method. A lock-in amplifier is employed in the phase demodulation process. By connecting the refractive index (the real part of the complex refraction index) and the absorption coefficient (the imaginary part of the complex refraction index) via Kramers-Kroning relation, the gas concentration information is retrieved from the optical dispersion measurement. Absorption-based wavelength modulation spectroscopy measures the gas concentration encoded in the optical intensity based on Beer-Lambert's law. However, the signal sensitivity of wavelength modulation spectroscopy decreases, and the signal even decreases while the gas concentration is raised in high absorbance condition, which leads to an uncertainty in concentration measurement. Experimental results demonstrate that wavelength modulation spectroscopy has better performance in low absorbance condition. The detection limit is about 38.1 ppmm. However, because the sensitivity decreases in high absorbance conditions, the upper detection limit of wavelength modulation spectroscopy is only 1500 ppmm. The dynamic range is defined through dividing the upper detection limit by the detection limit. Therefore, the wavelength modulation spectroscopy obtains a linear measurement dynamic range of 16 dB. Nevertheless, under the same experimental condition, the phase sensitive chirped laser dispersion spectroscopy has a much larger linear measurement range from 47.3 ppmm to 174825 ppmm with a dynamic range higher than 35 dB. Absorption-based gas measurement technique such as wavelength modulation spectroscopy can achieve a low detection limit by using long optical path at the expense of lower upper limit concentration. Phase sensitive chirped laser dispersion spectroscopy appears to be effective in high absorbance condition, which may be caused by high concentration or long optical path. Furthermore, by combining phase sensitive chirped laser dispersion spectroscopy and long optical path technique such as multi pass cell in sensor design, large linear measurement dynamic range and low detection limit can be obtained at the same time.

Applications of Performance Tables on Steady State Analysis of Multipass Parallel Cross Flow Heat Exchanger

In this paper, steady state sensible performance analysis on multi pass parallel cross flow exchanger was considered. The inputs to the heat exchanger were described through meaningful physically significant parameters such as number of transfer units, capacity rate ratio and dimensionless input temperature. The inputs to the heat exchager were varied systematically and a parametric study was conducted to determine the thermal performance at each individual pass of the heat exchanger. Heat exchanger’s thermal performance was described through the discharge temperatures that were expressed in a dimensionless form. The results from the study were presented in the form of performance tables. The performance tables employed meaningful and industry recognized dimensionless input parameters and the heat exchanger‘s performance was described through dimensionless discharge temperatures at every pass of the heat exchanger. The developed performance tables shall serve two critical aspects. First, it will help the heat exchanger designers to readily choose an optimum heat exchanger. An undersized heat exchanger shall not deliver the requirements and likewise an oversized heat exchanger shall add unnecessary weight and cost. This aspect was clearly observed in this study as indefinetly increasing the number of transfer units (or surface area) beyond a threshold value didn’t enhance the heat transfer. By employing the performance tables as a guide, the heat exchanger designers can quickly ascertain the performance of the heat exchanger without having to perform simulations and/or lengthy calculations. Second, during operational phase of the heat exchanger, the performance tables can be used to understand the performance variation of the heat exchanger with respect to mass flow rates and/or can help the engineers to choose appropriate mass flow rates for the required heat transfer. The highest heat exchanger performance was observed at the lowest capacity rate ratio and likewise the lowest heat exchanger performance was observed at the highest capacity rate ratio. In-addition, during the operational phase, the performance tables can help to detect an underperforming heat exchanger and can help the engineers to schedule maintenance activity on the heat exchanger equipment.

Study on Laser Cladding of Heat Resisting Steel Using EuTroLoy 16006 Powder(II) - Characteristics of Alloying Elements Distribution of Multi Pass Clad Layer -

Study on Laser Cladding of Heat Resisting Steel Using EuTroLoy 16006 Powder(II) - Characteristics of Alloying Elements Distribution of Multi Pass Clad Layer -

Weld Residual Stress Analysis of Low Alloy Steel Multi Pass Bead on Plate Specimen by Considering Phase Transformation Strain Characteristics and Using Shell Element

Weld Residual Stress Analysis of Low Alloy Steel Multi Pass Bead on Plate Specimen by Considering Phase Transformation Strain Characteristics and Using Shell Element

멀티패스 레이저 클래딩에 있어서 중첩률의 기준에 따른 클래드 층의 특성 비교

멀티패스 레이저 클래딩에 있어서 중첩률의 기준에 따른 클래드 층의 특성 비교

Rotating Heat Transfer Measurements on Realistic Multi-pass Geometry

In this contribution, a novel rig was used to assess the heat transfer coefficients on a full internal multi pass cooling scheme.Transient liquid crystal technique was used for the measurement of the heat transfer coefficient (HTC) on channel's internal surfaces.A first set of experiments were performed at engine similar conditions of Re=21000 and Ro=0.074. In order to assess the reliability of the measurement methodology and to explore the thermal behavior at higher rotation numbers, tests were also carried out at Re=17000 and Ro=0.074-0.11. From the spatially resolved HTC maps made available, it is possible to characterize the thermal performances of the whole passage and to highlight the effect of rotation.

Analysis method for Thomson scattering diagnostics in GAMMA 10/PDX.

We have developed an analysis method to improve the accuracies of electron temperature measurement by employing a fitting technique for the raw Thomson scattering (TS) signals. Least square fitting of the raw TS signals enabled reduction of the error in the electron temperature measurement. We applied the analysis method to a multi-pass (MP) TS system. Because the interval between the MPTS signals is very short, it is difficult to separately analyze each Thomson scattering signal intensity by using the raw signals. We used the fitting method to obtain the original TS scattering signals from the measured raw MPTS signals to obtain the electron temperatures in each pass.

Multi Pass Optimization of Cutting Conditions by Using the Genetic Algorithms

Production of high-quality products with lower cost and shorter time is an important challenge to face of increasing global competition. Determination of optimal cutting parameters is one of the most important elements in any planning process of metal parts. In this study we present a multi-optimization technique based on genetic algorithms and dynamic programming, to search for optimal cuttings parameters such as cutting depth, feed rate and cutting speed of multi-pass turning processes. Two conflicting objectives, the production cost and operation time are simultaneously optimize under a set of practical of machining constraints. The proposed model deals with multi-pass turning processes in which the cutting operations are divided into multi-pass rough machining and finish machining. Results obtained from Genetic algorithms method are used to define the optimum number of machining passes by dynamic programming; such technique helps us in the decision making process. An example is presented to develop the procedure of this technique.

A novel laboratory procedure for predicting continuous centrifugal gravity concentration applications: The gravity release analysis

A novel procedure, Gravity Release Analysis (GRA), is introduced for performance prediction of continuous centrifugal concentration, using lab-scale batch tests. Also, linked with the GRA, the Gravity Release Index (GRI) was developed for ranking the ore amenability to centrifugal gravity concentration. Ore samples from the flotation circuit of Myra Falls concentrator were subjected to Multi Pass Test and Gravity Amenability Test for comparison with GRA. Recovery kinetics of batch centrifugal concentration was analysed to establish the Gravity Release Index (GRI). Both Gravity Amenability Test and Multi Pass Test failed to cover the broader mass yield range of continuous centrifugal concentration and this was the main drawback in performance prediction of larger units from lab-scale data. GRA covered a wider mass yield range, yielding better performance prediction of larger continuous units. From the gravity recovery kinetics of the batch unit, varying GRI values for Au, Fe, Zn, Fe and S were obtained, with Au having the highest- GRI and amenability to centrifugal gravity concentration. Varying amenabilities for different Au forms (free Au particles, Au bearing sulphides) to centrifugal gravity concentration could also be distinguished. SEM analysis on recovered gold entities justified the prediction by the GRI. Overall, GRA could effectively predict continuous centrifugal concentration using small amounts of feed with lab-scale batch units. Determination of the GRI for targeted metals would provide further precision for bench-marking and scaling-up of continuous centrifugal concentration.

Microstructure and mechanical properties of thin ZK61 magnesium alloy sheets by extrusion and multi–pass rolling with lowered temperature

Thin Mg—6.63wt.%Zn—0.56wt.%Zr (ZK61) magnesium alloy sheets with fine-grain structure were successfully fabricated by extrusion and multi–pass rolling with lowered temperature from 653K to 523K. Relationships between grain size, texture and mechanical properties of as–rolled ZK61 magnesium alloy were investigated. Microstructure homogeneity as well as planar texture anisotropy was strikingly improved by hot rolling deformation via multiple dynamic recrystallization. A uniform fine–grained structure of 6.1μm in average grain size and a {0002} basal texture were obtained. These led to better strength isotropy in the plane, and high yield strengths of ∼200MPa, which was related to pyramidal (<c+a>) slip. Enhanced ductility more than 20% in fracture elongation was composed of uniform elongation strongly correlated with basal texture, especially along TD, and post–necking elongation enhanced by grain refinement.

Influence of multi-pass friction stir processing on wear behaviour and machinability of an Al-Si hypoeutectic A356 alloy

A356 is a widely used Al-Si alloy in automotive and aerospace industries for its good combination of mechanical and tribological properties. When these materials are to be considered for advanced engineering applications, machining becomes inevitable. However, presence of coarse and non-uniformly distributed silicon particles greatly influence the material properties imposing great challenge to its machinability. Our present work is focussed to improve the wear resistance and machinability of this alloy using multi pass friction stir processing (FSP). The wear behaviour of FSPed materials is characterised against metallic and abrasive medium and the machining studies are done by drilling experiments in dry condition. Under metallic wear condition, the wear resistance is maximum for the material subjected to 3 pass FSP and in case of abrasive wear, the maximum wear resistance is observed in 2 pass FSPed material. A decrease in both drilling force and surface roughness is observed with increase in FSP passes upto 2 pass beyond which they increased. Study on edge burr formation during drilling suggests that the entry and exit burrs are minimal for 3 pass FSPed material. A detailed investigation on the observed results is done in correlation with the microstructural evolution and mechanical properties.

Implementation of a Dual Mesh Method for Longitudinal Rolling in QForm V8

Numerical modeling of longitudinal rolling usually requires high computational power meanwhile it still takes long time to simulate multi pass process. Different methods for increasing of accuracy and speed of rolling simulation have being proposed recently. One of them is simultaneous use of two finite element meshes of different density, i.e. dual mesh method. The article is dedicated to solving of important problems of rolling technology and presents several examples of rolling simulation in QForm V8 based on dual mesh method.

Particle refinement and fine-grain formation leading to enhanced mechanical behaviour in a hypo-eutectic Al–Si alloy subjected to multi-pass friction stir processing

The present research aims at studying the synergetic effect of pre-process thermal treatment and multi pass friction stir processing (FSP) on microstructure and mechanical properties of a hypo-eutectic Al–Si automotive alloy. The effect of FSP with and without pre-process thermal treatment is studied up to 3 passes and it is found that both the size of silicon particles and aluminium grains become finer with increasing FSP passes. Maximum particle and grain refinement is observed in the material subjected to 3 passes of FSP with pre-process thermal treatment. The thermal treatment prior to FSP led to spheroidization of silicon particles which influenced the particle and grain refinement during FSP to a great extent. The effect of microstructural modification by FSP on the mechanical properties has been studied by micro-hardness and tensile testing. The 3 pass FSPed material without thermal treatment showed maximum ductility of 36.5%. However, maximum tensile strength of 251MPa is obtained in the 3 pass FSPed material with pre-process thermal treatment. The various mechanisms involved in enhancing the mechanical properties are explained by means of fractography results and the microstructural evolution during multiple FSP passes.

Evaluation of the effects of melting phenomenon on the residual stress formation in ferritic pipeline multi pass girth-weld joints

Coupled thermo-metallurgy-mechanical (TMM) analysis using FEM was carried out to represent a girth welding in ferritic pipeline steel. One of the crucial points to predict residual stress especially in multi pass welding is how to model material behaviour when melting takes place. When elements melt, they lose stiffness and also remaining plastic strain. Based on literature, it is suggested that this stiffness and plastic strain mitigation occurs even below melting temperature, known as annealing temperature. In this paper three FEM models are evaluated: 1) model without omitting stiffness and plastic strain; 2) with mitigating stiffness and plastic strain at melting point (1,400°C); 3) with mitigating stiffness and plastic strain at annealing temperature (970°C). Residual stress of two specimens was measured to validate the FEM models where model with 970°C of omitting stiffness and plastic strain showed best matching results.

Effect of phase transformation strain on residual stress analysis results of multi pass bead on plate specimen

Effect of phase transformation strain on residual stress analysis results of multi pass bead on plate specimen

Experimental Investigation Of Heat Transfer Characteristics Of Nanofluid Using Parallel Flow, Counter Flow And Shell And Tube Heat Exchanger

Abstract Cooling is indispensable for maintaining the desired performance and reliability over a very huge variety of products like electronic devices, computer, automobiles, high power laser system etc. Apart from the heat load amplification and heat fluxes caused by many industrial products, cooling is one of the major technical challenges encountered by the industries like manufacturing sectors, transportation, microelectronics, etc. Normally water, ethylene glycol and oil are being used as the fluid to carry away the heat in these devices. The development of nanofluid generally shows a better heat transfer characteristics than the water. This research work summarizes the experimental study of the forced convective heat transfer and flow characteristics of a nanofluid consisting of water and 1% Al2O3 (volume concentration) nanoparticle flowing in a parallel flow, counter flow and shell and tube heat exchanger under laminar flow conditions. The Al2O3 nanoparticles of about 50 nm diameter are used in this work. Three different mass flow rates have been selected and the experiments have been conducted and their results are reported. This result portrays that the overall heat transfer coefficient and dimensionless Nusselt number of nanofluid is slightly higher than that of the base liquid at same mass flow rate at same inlet temperature. From the experimental result it is clear that the overall heat transfer coefficient of the nanofluid increases with an increase in the mass flow rate. It shows that whenever mass flow rate increases, the overall heat transfer coefficient along with Nusselt number eventually increases irrespective of flow direction. It was also found that during the increase in mass flow rate LMTD value ultimately decreases irrespective of flow direction. However, shell and tube heat exchanger provides better heat transfer characteristics than parallel and counter flow heat exchanger due to multi pass flow of nanofluid. The overall heat transfer coefficient, Nusselt number and logarithmic mean temperature difference of the water and Al2O3 /water nanofluid are also studied and the results are plotted graphically.