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Item Influence of die angle on containerless extrusion of CP titanium rods(2005) Srinivasan, K.; Venugopal, P.As the name implies containerless extrusion is done without container and the total force consists of three individual terms namely ideal force, shear force and die friction force. Container wall billet friction is absent. The shear force varies directly with die angle, die friction force varies inversely with Sine of twice the die angle and ideal force is independent of angle. At a particular angle the total force is minimum. This is termed as optimum die angle. This can be understood from slab analysis of the process. Theoretically the optimum die angle varies only with extrusion strain and friction factor. It is found to change from 25° at a strain of 0.15 to 30° at a strain of 0.42. Experimentally the optimum angle is found to be independent of strain and at all strains it is found to be 25° at a constant friction factor of 0.14. More over the experimental pressure is less than that-predicted by theory. This is attributed to the temperature rise in the deformation zone and a consequent decrease in flow stresses of titanium.Item Local stress and strain variations in the deformation zone can be ascertained by measuring hardness. Hardness is correlated with strain and stress. The expressions discussed later are useful in determining the local variations in stress and strain from hardness measurement. It is a simple method compared to visioplasticity. One can estimate the forces required for a forming process. It helps in the choice of equipment, design of tooling and selection of lubricant for the particular process.(Indian Academy of Sciences, Hardness-stress-strain correlation in aluminium - A simpler alternative to visioplasticity in metal forming) Dharmaveera, N.; Srinivasan, K.1996Item A simple method of characterizing local stress and local strain variation in metal working is suggested. It is an alternative to complex and time consuming visioplastic technique. A power law expression exists for hardness and strain similar to that of stress and strain. A linear expression relating hardness and stress has been estahlished. These are valid not only for pure metals but also for their alloys. © Meshap Science Publishers.(Hardness-stress-strain correlation in copper and brass through compression testing) Dharmaveera, N.; Srinivasan, K.1996Item This paper deals with an experimental investigation concerning the open die extrusion (ODE) of three materials of varying physical properties and mechanical properties. Two geometrical configurations (solid and tube) and two methods (by direct and indirect techniques) were considered to examine the influence of these variables in the generation and retention of heat in the deformation zone with the objective of ensuring a greater achievable strain. Studies reveal that solid configuration supports the retention of heat as against tubular configuration. Low thermal conductivity, density, specific heat and high flow stress which characterise 99Ti make this material an excellent candidate for ODE as opposed to AISI 1020 steel and aluminium, which fail to meet all the above physical and mechanical properties. The indirect technique reduces the friction factor and thus enables greater strains to be achieved. © 1997 Elsevier Science S.A.(Elsevier BV, Adiabatic and friction heating on the open die extrusion of solid and hollow bodies) Srinivasan, K.; Venugopal, P.1997Item A heterogeneous process such as open die extrusion has been done on CP titanium and the extent of heterogeneity has been determined. The pressure for carrying out the process has been calculated theoretically, measured experimentally and calculated indirectly from hardness measurement in the deformation zone. Hardness-stress-train correlation is very useful here. A nomogram has been given so that knowing, ?, ?, ? and hardness, the punch pressure can be read off. It is a steady-reckoner that is very relevant for the shop floor in industry or the laboratory.(Elsevier Science S.A., Hardness-stress-strain correlation in titanium open die extrusion: an alternative to visioplasticity) Srinivasan, K.; Venugopal, P.1999Item CP aluminium was subjected to axysymmetric compression testing at 303, 373, 473, 573 and 673 K. Strength coefficient and strain hardening exponent were determined from log-log plot of true stress and true strain at different temperatures. True stress vs temperature at different strains indicated that dynamic strain ageing (DSA) occurred between 473 and 673 K. Warm working is to be done between 423 K and 473 K, so that optimum substructure hardening and strain hardening can be achieved during mechanical processing. © Indian Academy of Sciences.(Indian Academy of Sciences, High temperature compression testing and determination of warm working temperature for commercial purity aluminium) Rao, B.K.; Khadar, M.S.A.; Srinivasan, K.1999Item The precipitation hardening of a Al-Zn-Mg-Al2O3(p) composite is explored. It is found that the peak hardness achieved is almost double that of precipitation hardening of Al-Zn-Mg alloy or dispersion strengthening of Al-Zn-Mg with 5% Al2O3(p). Toughness is marginally improved and tensile strength is one and half times that of precipitation hardened Al-Zn-Mg alloys. The ageing time for peak hardness is reduced due to acceleration of formation of precipitate. © Indian Academy of Sciences.(Indian Academy of Sciences, Precipitation hardening in Al-Zn-Mg-Al2O3(p) composite) Kiran, K.S.; Srinivasan, K.1999Item Open die extrusion (ODE) has been done on AISI 1020 steel, commercial purity aluminium and commercial purity titanium, in both direct and inverted modes. It was found that inverted extrusion requires lesser forces than direct extrusion. Limit strains are more for the former than for the later as measured experimentally and as calculated theoretically. Theoretical limit strains are lesser than experimental ones in both the case of rods and tubes. ODE is only for shorter components due to unsupported billet and interference from buckling. It is also only for smaller strains due to interference from upsetting of unsupported billet above the die rather than extrusion through the die. © 2004 Elsevier B.V. All rights reserved.(Direct and inverted open die extrusion (ODE) of rods and tubes) Srinivasan, K.; Venugopal, P.2004Item Friction factor of CP aluminium and aluminium-zinc alloys(2006) Vidhya Sagar, N.; Anand, K.S.; Mithun, A.C.; Srinivasan, K.Friction factor has been determined for CP aluminium and aluminium-zinc alloys using ring compression test at different temperatures from 303 K to 773 K. It is found that CP aluminium exhibits sticking whereas Al-Zn alloys do not exhibit sticking at elevated temperatures. Hot working of Al-Zn alloy is easier than that of CP aluminium at 773 K. As zinc content increases up to 10 wt% the friction factor decreases up to 0.02. © Indian Academy of Sciences.Item Influence of die angle on containerless extrusion of commercially pure titanium tubes(2007) Srinivasan, K.; Venugopal, P.Containerless tube extrusion has been investigated with commerically pure titanium at room temperature and a strain rate of 0.07 s-1 using 20 conical dies of five different strains and four different angles with MoS2 lubricant. Theoretical punch pressures have been calculated using appropriate equations from slab analysis of the process and compared with experimentally determined punch pressures. It is found that there exists an optimum angle at which the punch pressure is the least at a given strain.