Sumesh Narayan

Strain hardening behaviour in sintered Fe—0.8%C—1.0%Si—0.8%Cu powder metallurgy preform during cold upsetting

Abstract Cold upsetting experiments were performed on sintered Fe—0.8%C—1.0%Si—0.8%Cu steel preforms in order to evaluate the strain hardening characteristics. Powder preforms of 86 per cent theoretical density and an initial aspect ratio of 0.4 were prepared using a suitable die and a 1 MN capacity hydraulic press. Sintering was carried out in an electric muffle furnace for a period of 90 min at 1150 °C. Each sintered compact was subjected to an incremental compressive loading of 0.04 MN until fractures appeared on the free surface. Experiments were performed with no lubricant and using graphite as a lubricant. The behaviour of the applied stress as a function of both strain and densification level exhibits a continuous enhancement over three different response modes. The first and third stage responses offer a high resistance to deformation, whereas the second stage shows virtually steady-state behaviour. The instantaneous strain hardening exponent ni and strength coefficient Ki of the steel preforms were calculated and found to continuously increase with an increase in the deformation and densification levels.

Workability Studies in Forming of Sintered Fe-0. 35C Powder Metallurgy Preform During Cold Upsetting

An experimental investigation on the workability behaviour of sintered Fe-0. 35C steel preforms under cold upsetting, have been studied in order to understand the influence of aspect ratio and lubrication condition on the workability process. The above mentioned powder metallurgy sintered preform with constant initial theoretical density of 84% of different aspect ratios, namely, 0. 4 and 0. 6 respectively were prepared using a suitable die-set assembly on a 1 MN capacity hydraulic press and sintered for 90 min at 1 200°C. Each sintered preform was cold upset under nil/no and graphite frictional constraint, respectively. Under the condition of triaxial stress densification state, axial stress, hoop stress, hydrostatic stress, effective stress and formability stress index against axial strain relationship was established and presented in this work. Further more, attained density was considered to establish formability stress index and various stress ratio parameters behaviour.

Influence of Carbon Content on Strain Hardening Behaviour of Sintered Plain Carbon Steel Preforms

Complete experimental investigation on the instantaneous strain hardening behaviour of powder metallurgy (P/M) preforms of pure iron, Fe-0. 35%C, Fe-0. 75%C and Fe-1. 1%C was carried out. The strain hardening behaviour of the above-mentioned P/M sintered steel preforms with aspect ratio of 0. 4 under triaxial stress state condition was determined by cold upsetting under nil/no and graphite lubricant conditions. The instantaneous strain hardening value (ni), strength coefficient (Ki), and the stress as a function of strain and densification were obtained and analyzed. Furthermore, a relation was obtained from a semi-log plot of stress against relative density and analyzed to study the hardening behaviour owing to densification as stress was a function of induced strain as well as densification in the P/M materials.

Phenomenon of Instantaneous Work Hardening Characteristics of Sintered Cold Deformed Cu Alloy Preforms

Work hardening behavior is an important phenomenon especially when a material is subjected to cold work. The two important parameters that expose this study are strain hardening exponent, n, and strength coefficient, K, according to ludwik equation, σ=Kε^n. In addition to strain as influencing factor for work hardening behavior, the attained density during deformation is also considered in the present investigation; a rational approach and its characteristic evaluation has been proposed. Thus a copper alloy preforms of three different aspect ratios prepared using conventional powder metallurgy method and a secondary deformation such as cold deformation were carried out till maximum density or fracture appears at the outer surface of deforming preforms. The dimensional and density measurements were carried out carefully and the same is utilized to explain the instantaneous work hardening behavior with respect to induced strain and attained density.

Strain hardening behaviour in forming of sintered iron-0.35% carbon powder metallurgy preform during cold upsetting

A complete experimental investigation on the instantaneous strain-hardening behaviour of powder metallurgy preforms of Fe-0.35%C was carried out. The strain hardening behaviour of the above-mentioned P/M sintered steel preforms with aspect ratio of 0.4 and 0.6, respectively, under triaxial stress state condition was determined by cold upsetting under nil/no and graphite lubricant conditions. The instantaneous strain hardening value (ni), strength coefficient (Ki), and the stress as a function of strain and densification were obtained and analyzed. Further, a relation is obtained from a semi-log plot of stress against relative density. This was analyzed to study the hardening behaviour due to the densification as applied stress is a function of induced strain as well as of densification in the powder metallurgy materials.

Forming Limit Analysis of Molybdenum Reinforced Carbon Steels

The occurrence of ductile fracture during the plastic deformation of powder metallurgy materials is adverse and damaging and the prediction of fracture is very important in the early stages as early modifications will prevent failure. This will tend to save a lot of money and forming limit studies in many metal forming processes is up most important. Forming limit analysis on the cold forged molybdenum reinforced carbon steels were carried out in this work. In this study two key strain hardening parameters are used to study the formability characteristics. This analysis is effectively used for design of powder metallurgy parts and most importantly the die design as repressing needs to be employed before pores appear as cracks on the free surface. The cold forging was carried out on Fe-0.8%C, Fe-0.8%C-1%Mo, Fe-0.8%C-1.5%Mo and Fe-0.8%C-2.0%Mo and the formability behavior of the same is presented.

Workability studies of sintered aluminium composites during hot deformation

Experimental investigation has been carried out to evaluate the effect of titanium carbide (TiC), molybdenum carbide (Mo2C), iron carbide (Fe3C) and tungsten carbide (WC) addition on the composite aluminium preforms. The hot upsetting of the composite aluminium preforms with various carbide contents, namely, Al-4% TiC, Al-4% WC, Al-4% Fe3C and Al-4% Mo2C, and different aspect ratios, namely, 0.4 and 0.6, was carried out and the workability behaviour of the same was determined. The influence of carbide addition in the aluminium composite and initial preform geometry on the relative density (R), stress ratio parameters, σ θ / σ eff , σ m / σ eff and σ z / σ eff , and formability stress index was studied.

Design of a Ducted Cross Flow Turbine for Fiji

Marine current energy is clean and reliable energy source. It can be alternative energy source to produce electricity if tapped with a suitable marine current energy converter. Pacific Island countries (PIC) like Fiji can reduce the amount of Fossil fuel used. However for most energy converters designed perform well at marine current velocities above 2m/s and it needs to be installed at depths of 20 – 40m also installation and the maintenance cost of such devise will be quite high if it needs to be installed in Fiji. Therefore a ducted cross flow turbine was designed, which can give desired output at minimum installation and maintenance cost. A dusted cross flow turbine has been design taking into account for its operating condition. The turbine was modelled and analyzed in commercial; Computational Fluid dynamic (CFD) code ANSYS-CFX. The code was first validated and with experiment results and finally performance analysis of full scale turbine was carried out. The designed turbine can have maximum efficiency of 56% producing rated power of 21kW; it produces 0.77kW at cut in speed of 0.65m/s.

Design of a Gorlov Turbine for Marine Current Energy Extraction

As fossil fuels near depletion and their detrimental side effects become prominent on ecosystems, the world searches renewable sources of energy. Marine current energy is an emerging and promising renewable energy resource. Marine current energy can be alternative energy source for electricity production. Many marine current converters are designed to tap marine current energy; however, Gorlov turbine proves to have minimum manufacturing and maintenance cost, hence giving desired power output. A 0.3m diameter and 0.6m long 3 bladed Gorlov turbine was designed, fabricated and test to analyse its performance. The turbine produces average power 15 W and proves to be quite efficient for marine current energy extraction.

Workability Behaviour of Powder Metallurgy Aluminium Composites

An efficient way to find the workability limit for powder metallurgy parts has been suggested. Compacts of Al-4%TiC, Al-4%WC, Al-4%Fe3C, and Al-4%Mo2C were produced to the relative density of 0.82 and 0.86 with three different geometries through primary operations of powder metallurgy routes. Each sintered compact was hot deformed to various strain levels till a visible crack appeared at the free surface. Oyane’s fracture principle was used to develop a theory to study powder metallurgy compacts. A least square technique was used to determine the constants in fracture criteria and these equations were finally used to find workability limit. It is found that the projected technique was well in agreement with the experimental values.