Successive Passes Research Articles

Effect of ECAP process on the Microstructure and Mechanical Properties of Al6061-Gr Composites

In the present study, Aluminium metal matrix composite with Al6061 matrix and Graphite (5-20µm) particulate reinforcement of varying composition (2-8wt.%) were prepared by stir casting technique. Significant improvement in tensile strength and ductility was noticed as the weight percent of Gr increases in as cast Al6061- Gr composites. The cast composites have been subjected to annealing treatment at a temperature of 400°C for 4 hours to homogenize the microstructure. The specimens have been prepared from these composites for Equal Channel Angular Pressing (ECAP). The ECAP process was carried out at room temperature using a die with channel angle of 120o and Bc route was adopted for successive passes. The effect of ECAP on the microstructure and mechanical properties of Al6061 –Gr composites were evaluated. After ECAP process, the sizes of the reinforcement particles are not changed but they were distributed uniformly in the matrix. In addition, a significant reduction in the grain size of the matrix alloy was observed. The hardness and tension tests were conducted at room temperature as per ASTM standards. The results are compared with the base Al6061 material and as cast Al6061-Gr composites. There is a significant improvement in the hardness and the Ultimate tensile strength of ECAP processed composites.

An evaluation of multipass narrow gap laser welding as a candidate process for the manufacture of nuclear pressure vessels

Nuclear pressure vessels are currently fabricated using arc welding processes. Recently, considerable effort has been directed at the development of electron beam welding as an alternative fabrication technique owing to the substantial productivity gains it would offer. However, little attention has been directed at laser-based techniques. In this work we evaluate the potential for applying multipass narrow-gap laser welding (NGLW) to the fabrication of nuclear pressure vessels, based on the characterization of a 30 mm thick weld in SA508 steel. Although still a multipass process, the number of passes is reduced in comparison to an arc weld of the same thickness, and the deposition of successive passes provides a degree of tempering to previously deposited weld metal in a way that the electron beam welding process does not. Principal engineering challenges for the implementation of multipass NGLW include the achievement of appropriate joint fit-up, and the shielding of a molten pool at the base of a deep and narrow weld groove.

Digital signal processing of acoustic emission signals using power spectral density and counts statistic applied to single‐point dressing operation

Dressing is an important operation for the grinding process. Its goal is to recondition the wheel tool to re-establish its cutting characteristics, owing to the wear produced after successive passes. Monitoring systems that use acoustic emission (AE) have been studied to correlate the signals with several tool conditions. This study brings a new approach of processing AE signals with the purpose of identifying the correct moment to stop the dressing, which is essential in an automatic control system. From the AE signals collected in dressing tests with aluminium oxide grinding wheel and single-point dresser, spectral analysis was made through power spectral density, selecting frequencies bands that best characterise the process. The statistical parameter ‘counts’ was applied to the raw signal unfiltered and filtered in the selected bands in order to identify the tool condition and, in turn, towards a monitoring system implementation. Results showed an expressive relation between tool cutting conditions and processed signals in the selected bands. There was a great disparity of the filtered signals in the selected bands and signals unfiltered, reflecting that the filtered ones were more efficient in terms of process automation.

Stressors, Difficult Situations and Their Relationship with Emotional and Habitual Overeating and Its Consequences in a Group of Truck Drivers

Truck drivers are one of the professional groups that due to the nature of their work is particularly exposed to numerous risks and difficult situations. At the same time it is one of professional groups, in which the level of overweight and obesity is very high in comparison with the rest of society, what can be caused by both: habitual and emotional overeating. The aim of the study was to examine and describe the stressors and difficult situations in the work of truck drivers and their relationship with emotional and habitual consumption of excessive amounts of food. A group of subjects consisted of 250 drivers (M=42, SD=19). The study was conducted at car parks located near to the major roads of Poland in the time off from work – usually in the intervals between successive passes. The results indicate that in a group of truck drivers habitual eating is more frequent than emotional overeating. Habitual consumption of excessive amounts of food is strongly associated with the occurrence of excessive weight gain in this occupational group.

Waterjet and laser etching: the nonlinear inverse problem.

In waterjet and laser milling, material is removed from a solid surface in a succession of layers to create a new shape, in a depth-controlled manner. The inverse problem consists of defining the control parameters, in particular, the two-dimensional beam path, to arrive at a prescribed freeform surface. Waterjet milling (WJM) and pulsed laser ablation (PLA) are studied in this paper, since a generic nonlinear material removal model is appropriate for both of these processes. The inverse problem is usually solved for this kind of process by simply controlling dwell time in proportion to the required depth of milling at a sequence of pixels on the surface. However, this approach is only valid when shallow surfaces are etched, since it does not take into account either the footprint of the beam or its overlapping on successive passes. A discrete adjoint algorithm is proposed in this paper to improve the solution. Nonlinear effects and non-straight passes are included in the optimization, while the calculation of the Jacobian matrix does not require large computation times. Several tests are performed to validate the proposed method and the results show that tracking error is reduced typically by a factor of two in comparison to the pixel-by-pixel approach and the classical raster path strategy with straight passes. The tracking error can be as low as 2–5% and 1–2% for WJM and PLA, respectively, depending on the complexity of the target surface.

Influence of multi-pass friction stir processing on microstructure and mechanical properties of 7B04-O Al alloy

Three-pass friction stir processing (FSP) with different moving distances of the stirring tool between the two successive passes, 50% diameter of the pin (traditional way) and 50% diameter of the shoulder (novel way), was conducted on 7B04-O Al alloy. The result shows that an improvement in the mechanical properties of the processed zone is accomplished due to grain and second phase particles refinement. The hardness of the multi-pass FSP (M-FSP) sample is about HV 40 higher than that of the base metal. And the tensile strength of the M-FSP specimens is also significantly increased to about 1.4 times that of the base metal. Besides, the weak region of the processed zone is mainly dependent on the moving distance, where it is the previous pass stir zone in the traditional way and the transitional zone in the novel way. Increasing the rotational speed narrows the weak region in the novel way, while it does not in the traditional way.

Differences in Kernel Shape, Size, and Density between Healthy Kernels and Mold Discolored Kernels and their Relationship to Reduction in Aflatoxin Levels in a Sample of Shelled Corn

Abstract. Unacceptably high levels of aflatoxin in shelled corn drastically reduce its market value and result in substantial economic losses. This study looked at the reduction in aflatoxin levels that could be achieved by removal of kernels discolored by mold and presumed to contain aflatoxin. The study related kernel physical characteristics to the reduction achieved using screening and density separation techniques which are currently in use in the grain industry. Physical properties of corn kernels discolored by mold and healthy corn kernels were determined in a sample taken from a 737 kg corn lot known to have relatively high levels of aflatoxin. Properties measured included kernel diameters, sphericity, and kernel density. Differences between discolored and healthy kernels in major diameter, minor diameter, sphericity, and density were statistically significant. Tests were also conducted at a commercial inbred seed corn processing facility using a screen cleaner and a gravity table. Removal of fine material (approximately 10% by weight) reduced aflatoxin levels by 84%. In two successive passes through a screen cleaner, removal of smaller kernels and kernel pieces with a round-hole sieve further reduced aflatoxin levels by 1.8% and 9.4%, respectively. After the smaller kernels and kernel pieces were added back to the lot, two successive passes through a gravity table reduced aflatoxin levels by 12.6% and 16.4%, respectively. Kernel density distributions of a sample taken before gravity table density sorting, and of samples of the higher and lower density fractions after sorting, were also determined. The effect of screening with a slotted sieve was studied by screening a 3 kg sample from the corn lot using a table top Clipper cleaner. This 3 kg sample had been previously screened to remove fines. The results indicate that, at least for some corn lots, aflatoxin levels can be reduced using a screen cleaner and a gravity table. The authors also concluded that insight into the effectiveness of aflatoxin reduction in corn by size and density sorting could be gained by conducting a size and density analysis on a representative sample of kernels taken from the corn being sorted. Keywords: Aflatoxin, Corn, Density, Gravity table, Physical properties, Screening, Sieves.

Об одном частном случае синтеза системы управления процессом обработки металлов точением

Introduction . One of the widely accepted methods of the precision metal turning provided a fairly complex shape of the workpiece is the method of multiple repetitions of turning. The principle of this method is cutting an extra thin layer of the work material. At that, the required operating depth is obtained through the successive passes of the cutting tool along the workpiece. An essential fault of this method of complex parts processing is low efficiency due to the long processing time. Materials and Methods . The improvement of efficiency is possible through the introduction of new modern methods of the treatment process control. Modern approaches to the analysis and synthesis of the control systems of complex operating procedures based on the development of the synergetic concept of management could be used as such methods. A special feature of this approach is the identification and control of the inherent feedbacks stabilizing the treatment process. On the basis of the analysis conducted, the control that is a new nonlinear degenerative feedback is synthesized. Its task is to assure adequate quality and efficiency of the processing under the asymptotic stability of the required attractors. Research Results . A fundamentally new mathematical model considering non-linear processes of the force changes is developed to simulate the system and allowance for the effect of the engine parameters. The analysis of the dynamics of the metal turning control system with the evaluation of the process quality is carried out. A synergistic approach to the construction of the optimal production control system considering the interconnectivity of the actuators providing the workpiece rotation and supply is used. The analysis of the synthesized system dynamics with the comparative evaluation of the quality growth is conducted. Discussion and Conclusions . The synthesized synergetic control law changes fundamentally the properties of the metal turning control system. A comparative analysis of the obtained dependences allows observing a substantial increase in the processing accuracy. At that, a synthesized system control asymptotically approaches the deviation of the allowance to the value specified as one of the constants on the control channel of the feed velocity.

Thermal design of liquid cooled charge air cooler: A computational approach

Successive advent of vehicle emissions norms & strong emphasis on fuel efficiency have enforced vehicle manufactures to deploy turbo charging of intake air prior to intake manifold. However introduction of turbochargers also signify need of a heat exchanger called charge air cooler or intercooler to reduce the temperature of turbocharged air to optimum limit prior to intake manifold of engine. The major limitation of conventional air to air charge air coolers is that they yield low heat transfer rate to weight ratio & low heat transfer rate to frontal area ratio characteristics. Beside this at higher boost pressure and higher temperature conditions there are metallurgical challenges for conventional air to air charge air coolers. Therefore; design optimization aimed at improved heat transfer from charge air is the need of strict environmental norms (Euro V onward). Rapid growth of automobile sector coupled with cutting edge technology development is also leading demand for highly efficient as well as compact solutions for charge air cooler. This provide motivation and challenge to design highly optimized new technology based system, which can provide increased rate of heat transfer with lesser pressure drop & overall compact size. To overcome discussed limitations of conventional air to air charge air cooler; the present research explores thermal design of liquid cooled charge air cooling device with unique charge air flow mechanism. The new design of liquid cooled charge air cooler provides multiple flow passes in order to achieve advantages of both cross flow as well as counter flow type heat exchangers. Multiple flow passes basically ensure maximum interaction of two heat exchanging fluids; hence heat exchanger effectiveness gets improved. Charge air is introduced to the heat exchanger with the help of an inlet tank header. The flow of charge air around the heat exchanger is precisely controlled by a casing, which ensures a uniform guided flow to successive passes of heat exchanger. An outlet tank header serves the purpose of supplying charge air to the engine intake manifold. A Computational Fluid Dynamics (CFD) methodology is used to optimize flow dynamics of two working fluids, namely liquid water and charged air coming out of turbocharger.

Dynamic precipitation behavior and mechanical property of an Mg94Y4Zn2 alloy prepared by multi-pass successive equal channel angular pressing

After sixteen successive passes of equal channel angular pressing (ECAP), kinked 18R-LPSO phase and refined DRX grains were developed in Mg94Y4Zn2 alloy. Simultaneously, nano-sized 14H micro cells and Mg24Y5 particles were dynamically precipitated. Owing to the above microstructure characteristics, the 16p-ECAP alloy exhibited outstanding mechanical property with compressive strength and fracture strain of 611MPa and 20.1%, respectively.

Experimental study of a six new ball-burnishing strategies effects on the Al-alloy flat surfaces integrity enhancement

In the literature, the most studies conducted on the flat surface ball-burnishing process have been focused on the most important classical factors like burnishing speed, lateral feed, and the ball-burnishing load or pressure on the treated surfaces integrity enhancement. In this research, ball-burnishing strategies are studied as a new ball-burnishing factor. The aim of this research is to show the improvement of the flat surface integrity of 2017A-T451 aluminum alloy using six new ball-burnishing strategies. Ball-burnishing tests were conducted in two passes using the recommended values of the ball-burnishing factors (the penetration depth a b is 40 μm, the linear ball-burnishing speed V b is 500 mm/min and a lateral feed f of 0.2 mm). Two ball-burnishing strategies in two successive and perpendicular passes to the machining direction and four ball-burnishing strategies in two crossed passes have been designed and tested to improve the flat surfaces integrity of the samples. The characterization and the micrographic observations of the ball-burnished surfaces show that using the best ball-burnishing strategy leads to a great enhancement in surface quality. The latter is predicted by a gain in average roughness Ra of 81 %, an improvement in the mean spacing of profile irregularities Sm of 34 %, an enhancement in surface Nano-hardness HIT of 17 %, and sub-layer hardness betterment up to a depth of 500 μm.

Effect of Equal Channel Angular Pressing on the Microstructure and Mechanical Properties of Hybrid Metal Matrix Composites

Objectives: The objective of the present study is to prepare Al6061-Gr-SiChybrid composites by stir casting route and the effect of Equal Channel Angular Pressing (ECAP) on the microstructure and mechanical properties of Al6061-Gr-SiC hybrid composites will be evaluated. Methods: In the present study, Al6061 is selected as matrix material. The reinforcement materials chosen are graphite (Gr) and Silicon carbide (SiC) particles of 10-30 μm size. The hybrid composites have been prepared by stir casting route in which the amount of Gr particles are kept at 3wt% and SiC particles are varied from 2-10wt% in steps of 2wt% . The cast hybrid composites are subjected to annealing treatment at 400oC for 4 hours and specimens have been prepared from these composites for ECAP process. The ECAP process was carried out at room temperature using a die with channel angle of 120o and Bc route was adopted for successive passes. The influence of ECAP on microstructure and mechanical properties of Al-Gr-SiC hybrid composite was evaluated. Findings: The microstructural study revealed that the composites are free from defects and also the distribution of reinforcement particles in the matrix are fairly uniform. Significant improvement in micro hardness and tensile strength was observed as the wt% of SiCp increases in as cast Al6061-Gr- SiC hybrid composites. After ECAP process, the size and distribution of the reinforcement particles are not changed but significant reduction in the grain size of the matrix alloy was observed. The micro hardness and tensile test results revealed that, there is a significant improvement in the micro hardness and the Ultimate tensile strength of ECAP processed hybrid composites. The enhancement in mechanical properties are mainly attributed to the grain refinement of the matrix alloy and strain hardening of hybrid composite materials by ECAP process. Applications: The ECAP process had a profound effect in enhancing the mechanical properties of hybrid composites. These composite materials have great impact in automobile, military and aerospace industries.

Microstructure and superior mechanical properties of a multi-axially forged WE magnesium alloy

A magnesium alloy containing rare earth elements (Y and mish metals) was severely deformed through multi-axial forging (MAF) at 400 °C and the obtained microstructure, texture, and mechanical properties were characterized after applying successive MAF passes. The results showed that the volume fraction of the recrystallized grains was noticeably increased by increasing the MAF passes, where a homogeneous microstructure with a mean grain size of 4.8 μm was obtained after five MAF passes. A strengthened basal texture was developed after the first MAF pass. Further deformation to three and five MAF passes resulted in a texture weakening, where pyramidal planes tend to rotate parallel to the forging direction. The contribution of particle stimulated nucleation (PSN) was suggested to play an effective role in the texture weakening. The basal texture and grain refinement, which were achieved after applying one pass MAF, led to a combined improvement in strength and ductility, including 460 MPa ultimate strength and 12.4% ductility. As the number of deformation passes increased to three and five, the flow stress of the material was reduced, while the ductility considerably enhanced. The latter findings were discussed relying on the fact that the texture weakening after multi-pass MAF could make the deformation easier through activating more slip systems.

Compressive Deformation Behavior of an Ultrafine/Nano Grained AZ31 Magnesium Processed by Accumulative Back Extrusion

Abstract An AZ31magneium alloy was processed through accumulative back extrusion (ABE) process at 280 °C up to six passes. Compressive deformation behavior of the processed materials was studied by employing uniaxial compression tests at room temperature. The results indicated that grains of 80 nm to 1 µm size were formed during accumulative back extrusion, where the mean grain size of the experimental material was reduced by applying successive ABE passes. A deformation texture characterizing with the basal plane mainly lie inclined to the deformation axis was developed. Compressive yield and maximum compressive strengths were measured to increase by applying successive extrusion passes, while the strain-to-fracture dropped. The evolution of mechanical properties was explained relying on the grain refinement effect as well as texture change. It was described that the share of different deformation mechanisms and developing of shearing regions near the grain boundaries may influence the deformation behavior of the ultrafine/nano grained AZ31 alloy.

Effect of Equal Channel Angular Pressing on the Microstructure and Mechanical Properties of Al6061-SiCp Composites

In the present study, Aluminium metal matrix composite with Al6061 matrix and SiC (10-30μm) particulate reinforcement of varying composition (2-10wt.%) were prepared by stir casting technique. Significant improvement in tensile strength and hardness was noticed as the wt.% of SiCp increases in as cast Al6061- SiC composites. The cast composites have been subjected to annealing treatment at a temperature of 400oC for 4 hours to homogenize the microstructure. The specimens have been prepared from these composites for Equal Channel Angular Pressing (ECAP). The ECAP process was carried out at room temperature using a die with channel angle of 120° and Bc route was adopted for successive passes. The effect of ECAP on the microstructure and mechanical properties of Al6061 -SiC composite is evaluated. After ECAP process, the size and distribution of the reinforcement particles are not changed but there is a significant reduction in the grain size of the matrix alloy was observed. The hardness and tension tests were conducted at room temperature as per ASTM standards. The results were compared with the base Al6061 material and as cast Al6061-SiC composites. There is a significant improvement in the hardness and the Ultimate tensile strength of ECAP processed composites.

The impact of solvent characteristics on performance and process stability of printed carbon resistive materials

Carbon conductive pastes deposited by screen printing are used in many commercial applications including sensors, PCB, batteries, and PV, and as such represent an important value-added coating. An experimental investigation was carried out into the role of the solvent on the drying characteristics, conductivity, and process consistency in screen printed carbon pastes. Four materials with solvent boiling points between 166 and 219°C were deposited at film thickness between 6 and 16 μm, and the sheet resistance and film thickness were measured after successive passes through an industrial dryer operating with an air temperature of 155°C. Sheet resistances of 14 Ω/sq. were obtained with the thicker films while thinner films produced a sheet resistance of 46 Ω/sq. Thinner films achieved a stable resistivity within a 2.5-min residence time, while the thicker films required a residence time in excess of 12.5 min to achieve a stable resistivity. As well as prolonging drying times, the higher boiling point increased the resistivity of the cured film. It is postulated that the lower resistance of the faster drying materials is a result of film stressing increasing inter particle contact. Process models indicate that multiple thin layers are a more efficient means of manufacture for the process parameters examined.

Investigation of Microstructure and Mechanical Properties of ECAP-Processed AM Series Magnesium Alloy

Magnesium alloy Mg-Al-Mn (AM70) was processed by equal channel angular pressing (ECAP) at 275 °C for up to 4 passes in order to produce ultrafine-grained microstructure and improve its mechanical properties. ECAP-processed samples were characterized for microstructural analysis using optical microscopy, scanning electron microscopy, and transmission electron microscopy. Microstructural analysis showed that, with an increase in the number of ECAP passes, grains refined and grain size reduced from an average of 45 to 1 µm. Electron backscatter diffraction analysis showed the transition from low angle grain boundaries to high angle grain boundaries in ECAP 4 pass sample as compared to as-cast sample. The strength and hardness values an showed increasing trend for the initial 2 passes of ECAP processing and then started decreasing with further increase in the number of ECAP passes, even though the grain size continued to decrease in all the successive ECAP passes. However, the strength and hardness values still remained quite high when compared to the initial condition. This behavior was found to be correlated with texture modification in the material as a result of ECAP processing.

Aluminium-steel lap joining by multipass friction stir welding

The use of a multipass welding strategy for increasing the bonding area in the dissimilar friction stir lap welding (FSLW) of aluminium to steel is analysed in current work. In order to minimize tool wear, the pin penetration into the lower plate, the steel plate, was set to a minimum. By performing partially overlapped welding passes it was possible to analyse the quality of the bonding across the multipass weld. The microstructural analysis of the bonding interface, after weld collapse in tensile-shear testing, enabled to conclude that by minimizing the pin penetration in the steel plate, the formation of intermetallics in the bonding interface is supressed and base materials joining results from mechanical bonding and solid state solution. However, for each welding pass, the bonding is not uniform/continuous across the pin trajectory. The deleterious effect of the bonding discontinuities on the monotonic weld strength may be limited by overlapping the successive weld passes, in order to maximize the bonding area. Improving the fatigue strength requires optimizing the welding parameters and/or pin positioning relative to the lower plate in order to avoid the occurrence of micro-cavities at the bonding interface.

Students' Perceptions on an Interprofessional Ward Round Training - A Qualitative Pilot Study.

Introduction: Ward rounds are an essential activity for interprofessional teams in hospital settings and represent complex tasks requiring not only medical knowledge but also communication skills, clinical technical skills, patient management skills and team-work skills. The present study aimed to analyse final year students’, nurses’ as well as physiotherapists’ views on a simulation-based interprofessional ward round training.Methods: In two successive passes a total number of 29 final year students, nursing students and physiotherapy students (16 in the first run, 13 in the second) volunteered to participate in two standardized patient ward round scenarios: (1) patient with myocardial infarction, and (2) patient with poorly controlled diabetes. Views on the interprofessional ward round training were assessed using focus groups.Results: Focus group based feedback contained two main categories (A) ward round training benefits and (B) difficulties. Positive aspects enfolded course preparation, setting of the training, the involvement of the participants during training and the positive learning atmosphere. Difficulties were seen in the flawed atmosphere and realization of ward rounds in the daily clinical setting with respect to inter-professional aspects, and course benefit for the different professional groups.Conclusion: The presented inter-professional ward round training represents a well received and valuable model of interprofessional learning. Further research should assess its effectiveness, processes of interprofessional interplay and transfer into clinical practice.

Effect of Copper Addition to Aluminum on its Metallurgical, Mechanical Characteristics and Surface Roughness after Rolling

Aluminum and its alloys are widely used materials in industrial and engineering applications. They are second in use after steel due to their attractive properties e.g. strength-to-weight ratio, their electrical and thermal conductivities, and corrosion resistance. However, against these attractive properties commercially pure aluminum has certain limitations in the cast condition because it solidifies in large grain size columnar structure which reduces its mechanical strength and surface quality. It is, therefore, always alloyed with other elements to reduce or eliminate these defects. In this paper, the effect of copper addition at a rate of 4% Wt. to commercially pure aluminum both in the cast and after rolling conditions is investigated. Aluminum sheets and aluminum-4% copper sheets were cold rolled in three successive passes, from 4 mm to 3mm to 1.3 mm. After each pass, the grain size, Vickers micro-hardness and surface roughness were determined and discussed. It was found that addition of 4% Cu to commercially pure Al in the cast condition resulted in refining its microstructure both in the cast and after rolling conditions. Furthermore, the rolling process resulted in enhancement of the surface quality only after the first and second passes.