V.M.J. Sharma

Experimental Investigations on Tensile Strength of Flux Bounded TIG Welds of AA2219-T87 Aluminum Alloy

Limitation in depth of penetration is a concern in conventional tungsten inert gas (TIG) welding process. To improve penetration capability of TIG process, flux bounded TIG (FBTIG) has been recently developed. Tensile strength of FBTIG welds of aluminum alloy AA2219-T87 is investigated in the present study and compared with that of conventional TIG welds and base metal. Tensile strength of FBTIG weld was found to be better than conventional TIG weld due to fine grain structure of FBTIG welds.

Study of LCF Behavior of IN718 Superalloy at Room Temperature

nconel 718 is an age hardenable nickel base supper alloy with high strength at elevated temperatures, and excellent creep properties. It is used extensively in turbine discs, blades where components experience elevated temperatures for prolonged duration, leading to coarsening of the microstructure. To evaluate the life of such components after prolonged exposure to service conditions, LCF properties at such large grain sizes are essential. For this purpose, low cycle fatigue (LCF) behavior of forged Inconel 718 turbine rotor disc having large grain size was studied at room temperature. Total strain controlled fatigue tests were conducted in air at ambient temperature on this alloy in solution treated and aged condition. The results indicated that the material exhibits cyclic strain softening and the cyclic yield strength is lower by 40% compared to the monotonic yield strength. The deformation takes place by multiple planar slip.

On the Measurement of Dynamic Elastic and Internal Friction Properties of Nickel Based Super Alloys up to 650°C Temperature

Elastic constants are the fundamental key parameters to understand the mechanical behaviour of engineering materials under stressed condition. This paper explains the test methodology and provides results of experiments carried out using resonance based high temperature impulse excitation technique test facility for the measurement of technical elastic moduli i.e., Young’s modulus (E), Shear modulus (G), Poisson’s ratio (ν) and internal friction (Q-1) of two nickel-base polycrystalline super alloys IN718 and Haynes 214 from ambient to 650°C temperature in argon environment during heating and cooling.

Local Deformation Behavior of Inconel 718 TIG Weldment at Room Temperature and at 550°C

The weld portion will have different mechanical properties in weld bead, HAZ and fusion boundary due to variation in the microstructure, chemistry and internal stresses that arise in the welding process. Inconel 718 TIG welded samples are tested to study the deformation behavior of the weld constituents with the help of non contact laser extensometer. Stress-strain curves for the individual constituents of weld, parent, fusion boundary and HAZ are evaluated at room temperature and at 550°C. Test results show that the welded samples exhibited 50% lower tensile properties compared to the parent material. Parent metal remains elastic through out the test. The proof stress of the weld alone is 100 MPa lower than the average proof stress of the welded sample when considered standard gauge length.

Effect of Tempering Temperature on Strength and Fracture Toughness of 0.3C-CrMoV(ESR) Steel

0.3C-CrMoV(ESR) steel is an ultra-high strength low alloy steel indigenously developed by ISRO for space applications. The steel is used in the form of rings of 2.8 m diameter also. In this paper, the effect of tempering temperature on ring rolled steel for the best combination of fracture toughness and strength properties is studied. The tensile properties and fracture toughness of the steel were evaluated in the as quenched and tempered conditions through the specimens drawn in radial direction of the ring segment. Five tempering temperatures were used in the study: 200, 450, 475, 500 and 510°C. Tensile strength of the steel showed continuous decrease with increasing tempering temperature, but yield strength increased reaching maximum when tempered at 450°C and further decreased with increasing tempering temperature. The elongation was higher for higher tempering temperature. The strain hardening exponent decreased with increasing tempering temperature. The fracture toughness test results showed that tempering between 475 and 510°C exhibited better combination of fracture toughness and strength.

Axial and Bending Fatigue Testing of AISI 304 L Plumbing Tubes Used for Launch Vehicles Control System

Gimbaling the engine nozzle within a specified angle through hydraulic actuator modules is commonly used to control the trajectory path of satellite launch vehicles. During one of the hot test of a liquid engine stage, a drop in system pressure in actuator module was noticed due to cracking of case drain plumbing inside the ferrule. The tensile and fatigue (axial and bending) test of the tube material was carried out to understand the cause of failure, simulating the actual service conditions such as strength and bending moment in assembled tube. Findings of the metallurgical investigation along with the fatigue test results were presented in this paper.

FAILURE OF AUSTENITIC STAINLESS STEEL COMPONENTS USED IN NITROGEN OXIDE PLANT

Austenitic stainless steel components of a nitrogen oxide plant have been found to leak in service. The failed components, namely pipe-to-pipe joints and pipe-to-flange joints, have been studied through standard metallographic techniques to analyse the cause of the failure. In case study I, involving the failure of pipe-to-flange joints, cracking was observed in the pipe wall next to the pipe-to-flange weld. In case study II, involving the failure of a sight port flange, cracking was observed in the flange adjacent to the pipe-to-flange weld. In both cases, cracking was by an intergranular mechanism, and carbon contents were much higher than permitted for “L” grades of austenitic stainless steel.