An experimental analysis of upset forging of aluminium cylindrical billets considering the dissimilar frictional conditions at flat die surfaces

Friction plays a major role in all bulk metal forming processes, except in a few isolated cases such as die-less wire drawings, etc. In upset cold forging, the existence of frictional constraints between the dies and the work-piece directly affect the plastic deformation of the latter. When a solid cylinder is compressed axially between the top and bottom platen, the work piece material in contact with their surfaces undergoes heterogeneous deformation resulting in “barrelling” of the cylinder. The friction at the faces of contact retards the plastic flow of metal on the surface and in its vicinity. A conical wedge of a relatively undeformed metal is formed which suffers high strain hardening and bulges out in the form of a barrel. This experimental work has been undertaken to study the bulging effect of aluminium solid cylinders, varying the frictional conditions at the flat die surfaces. Flat dies of different surface finish were produced by different machining processes like grinding, milling, electro-spark machining, and lathe turning and finishing with ‘0’ grade emery paper. Experiments were conducted for two aspect ratios. The radius of curvature of bulge was measured and found to conform to the calculated bulge using experimental data. The calculations are made with the assumption that the curvature of the bulge followed the form of a circular arc. A relationship was established between the various bulge parameters including new hoop strain, hydrostatic stress, geometrical shape factor, and stress ratio factor, considering the dissimilar frictional conditions.     

An experimental investigation on barreling of aluminium alloy billets during extrusion forging using different lubricants

The paper reports on an investigation of extrusion forging during cold upsetting using a suitable die of aluminium alloy (H9-6063) solid cylinders subjected to different geometrical conditions such as approach angles namely, 15°, 30°, 40° and 50°, with two different initial protrusion heights namely 10 mm and 12 mm. During experiments three geometries namely barreled cylinder, truncated cone part and protruded part or extruded part were observed. The calculations were made on the assumption that the curvatures of the barrel were in the form of a circular arc and volume constancy principle. The relationship was also established among the various parameters namely the hoop stress, the hydrostatic stress, the new geometrical shape factor, and the radius of curvature of the bulge. An attempt has been made to establish the relationship between the approach angle and extrusion height and found that the extrusion height increases with the increase in the approach angle for any given extrusion load.     

Effect of carbon content on workability of powder metallurgy steels

Workability behaviour of steel powder metallurgy performs containing 0%, 0.4% and 0.8% of carbon were completely investigated experimentally. Cold upsetting of abovementioned powder metallurgy sintered steels preforms with two different aspect ratios namely 0.39 and 0.59 was carried out with graphite as lubricant and the formability behaviour of the preforms under triaxial stress state condition was determined. The formability stress parameter was evaluated for all the above said preforms and its variation with respect to axial strain was plotted, studied and discussed relative to their as sintered microstructures. Also the characteristics of various stress ratio parameters with respect to axial strain were analyzed and presented.     

Tribological behaviour of powder metallurgy-processed aluminium hybrid composites with the addition of graphite solid lubricant

The tribological behaviour of powder metallurgy-processed Al 2024–5 wt% SiC–x wt% graphite (x=0, 5, and 10) hybrid composites was investigated using a pin-on-disc equipment. An orthogonal array, the signal-to-noise ratio and analysis of variance were employed to study the optimal testing parameters using Taguchi design of experiments. The analysis showed that the wear loss increased with increasing sliding distance and load but was reduced with increased graphite content. The coefficient of friction increased with increasing applied load and sliding speed. The composites with 5 wt% graphite had the lowest wear loss and coefficients of friction because of the self-lubricating effect of graphite. Conversely, due to the effect of the softness of graphite, there was an increase in wear loss and the coefficient of friction in composites with 10 wt% graphite content. The morphology of the worn-out surfaces and wear debris was examined to understand the wear mechanisms. The wear mechanism is dictated by the formation of both a delamination layer and mechanically mixed layer (MML). The overall results indicated that aluminium ceramic composites can be considered as an outstanding material where high strength and wear-resistant components are of major importance, particularly in the aerospace and automotive engineering sectors.     

Analysis of workability behavior of Al–SiC P/M composites using backpropagation neural network model and statistical technique

This paper presents an artificial neural network (ANN) model for predicting and analyzing the workability behavior during cold upsetting of sintered Al–SiC powder metallurgy (P/M) metal matrix composites (MMCs) under triaxial stress state condition which is the multifaceted technological concept, depending upon the ductility of the material and the process parameters. The input parameters of the ANN model are the preform density, the particle size, the percentage of reinforcement and the applied load. The output parameters of the model are the axial stress, the hoop stress, the axial strain, the hoop strain, the instantaneous strain hardening index, and the instantaneous strength coefficient. This model is a feed forward backpropagation neural network and is trained and tested with pairs of input/output data. A very good performance of the neural network, in terms of good agreement with the experimental data has been achieved. As a secondary objective, quantitative and statistical analyses were performed in order to evaluate the effect of the process parameters on the workability and the plastic deformation behavior of the composites.     

Studies on void coalescence analysis of nanocrystalline cryorolled commercially pure aluminium formed under different stress conditions

Cryorolling was performed on commercially pure aluminium sheet from an initial thickness of 7 mm to 0.25 mm with a total true strain of around 3.33. Cryorolling was performed in many passes with only 5% reduction in each pass to avoid adiabatic heating during rolling process. Detailed Transmission Electron Microscopic studies showed increased dislocation density and distributed dislocation cell structure. Streaks along with ring pattern in selected area electron diffraction of transmission electron microscopy evidenced the existence of texture component on the surface of rolled sheet along with nanocrystalline sub-structure. Studies on fracture behavior of the cryorolled sheets were performed using specimen of double edge-notch tensile geometry. Compared to the conventionally rolled sheet metal, the strain triaxiality ratio value in the case of cryorolled sheets is insensitive to the void growth analysis due to the presence of nano-sized grains. The ratio of length to the width of voids varies from 1.6 to 2.4 in the case of conventionally rolled sheet. In contrast, length to width ratio is very close to 1.0 in the case of cryorolled sheet. Thus no oblate or prolate voids were observed during cryorolling compared with conventionally rolled sheets and it is observed the formation of equiaxed nanostructured grains. In the case of cryorolled sheets, minimal variation in length to width ratio was observed with the variation in the shear strains, due to the presence of nanostructured grains. Whereas, in the case of conventionally rolled material, wide variation in the length to width ratio with the variations in the shear strains was observed.     

Trust-based evolutionary game model assisting AODV routing against selfishness

Self-organizing networks such as wireless ad hoc networks present a number of problems and paradoxes towards trustworthiness and consistency of the network. Lack of cooperation between nodes drastically brings down the throughput of the network. Selfish behavior of the nodes is one of the issues, which deter the trust among them. This paper explores the multiple modes to build trust and proposes an effective, dynamic and distributed framework using evolutionary game theory. Strategic, non-cooperative and evolutionary game theory has been utilized to model the dynamic behavior of selfish nodes in a self-policing ad hoc network. AODV routing assisted by the proposed game model enlightens a cogent scenario, which demonstrates that it can stimulate cooperation among selfish nodes, albeit without negotiations. The proposed model encompasses two distinct modes to learn and predict the behavior of neighbors namely deterministic and random. Deterministic mode is a generic one which helps to analyze the behavior of the network for standard strategic patterns whereas the random strategy profiles are explored using randomized analysis based on genetic algorithm. This paper investigates the simulated results for the two methods and asserts that if nodes use evolved strategies and trust evaluation mechanism, then the model supports in accomplishing the cooperation level to reach the maximum possible.     

Some aspects of workability studies on sintered high strength P/M steel composite preforms of varying TiC contents during hot forging

Workability is a measure of the extent of deformation that powder metallurgy materials can withstand prior to fracture occurred in the forming or upsetting processes. Workability of a material is obtained from several parameters namely strain, strain rate and temperature. Hot upsetting of the composite steel preforms with varying TiC contents, namely, 3% and 4%, and aspect ratios, namely, 0.45, 0.71 and 1.25, was carried out at a temperature of 1120 °C and the formability behaviour of the same under triaxial stress state condition was determined. The curves plotted for different preforms were analysed and a relationship was established between the axial strain and the formability stress index (β). The influence of TiC addition, in the steel composite, on the formability stress index, the relative density (R) and various stress ratio parameters, namely, (σ_θ/σ_eff), (σ_m/σ_eff) and (σ_z/σ_eff) were studied. An attempt is also made to relate the fracture strain of the preforms with the formability stress index (β) under triaxial stress state condition.     

Study of Dissimilar Header Welding Between 2.25Cr–1Mo Steel and 9Cr–1Mo Steel with 9018 B9 Electrode Under Various Conditions of Post Weld Heat Treatment

Headers are an integral part of the power plant equipment which serves as junction for receiving and distribution of fluid. Headers are routinely used in high temperature applications in which various combinations of steels are used to achieve weight and cost savings thus optimising the use of steels. This paper intends in studying the evolution of microhardness and microstructure in a dissimilar header fillet welding between the base materials 2.25Cr–1Mo steel and 9Cr–1Mo steel when welded using 9018 B9 electrode and a constant preheat of 220 °C. The post weld heat treatment (PWHT) is varied at temperatures from room temperature to 770 °C and the soaking duration is kept at 1 h. The changes in microstructure and microhardness are examined with the help of micrographs, electron dispersive spectrum and scanning electron microscopy analysis. As the PWHT temperatures changes, the variation in microstructure and microhardness becomes very much evident which is detailed out in this paper. Also, carbon migration phenomena and its relation with the PWHT temperatures has been studied in this paper.     

Influence of ZrO2, SiO2, Al2 O3 and TiO2 nanoparticles on maize seed germination under different growth conditions

The focus of this investigation is to evaluate the phytotoxicity of selected metal oxide nanoparticles and microparticles as a function of maize seed germination and root elongation under different growth conditions (Petri plate, cotton and soil). The results of seed germination and root elongation experiments reveal that all the growth conditions show almost similar results. Alumina (Al₂ O₃) and titania (TiO₂) nanoparticles significantly reduce the germination percentage, whereas silica (SiO₂) nanoparticles and microparticles enhance the same. The results of nanoparticles and microparticles of zirconia (ZrO₂) are found to be same as those of controls. Root elongation is enhanced by SiO₂ nanoparticles and microparticles treatment, whereas inhibition is observed with Al₂ O₃ and TiO₂ nanoparticles and microparticles. The X‐ray fluorescence spectrometry data of the treated and control seed samples show that seeds uptake SiO₂ particles to a greater extent followed by TiO₂, Al₂ O₃ and ZrO₂. In addition, the uptake of nanoparticles is found to be greater than that of microparticles. Thus, the tested metal oxides penetrated seeds at the nanoscale as compared with the microscale. This study clarifies phytotoxicity of nanoparticles treated in different growth substrates and highlights the impact of nanoparticles on environment and agricultural systems.Inspec keywords: zirconium compounds, silicon compounds, aluminium compounds, titanium compounds, nanoparticles, nanobiotechnology, botany, toxicologyOther keywords: metal oxide nanoparticles, maize seed germination, phytotoxicity, microparticles, root elongation, growth conditions, Petri plate, cotton, soil, X‐ray fluorescence spectrometry, environment systems, agricultural systems, ZrO₂ , SiO₂ , Al₂ O₃ , TiO₂