Rohit Kumar Gupta

Vestibular evoked myogenic potentials in children with sensorineural hearing loss

OBJECTIVE OF THE STUDYnTo assess the saccular function using the vestibular evoked myogenic potential (VEMP) test in children with severe to profound sensorineural hearing loss.nnnMETHODSn15 children (12 males and 3 females) with severe to profound sensorineural hearing loss in the age range of 4-12 years constituted the study group. 10 children (6 males and 4 females) with normal hearing constituted the control group. All the children were evaluated for saccular function by using the vestibular evoked myogenic potentials (VEMP).nnnRESULTSnFor study group the mean P1 and N1 latencies values were 15.12ms and 23.86ms, respectively. For control group the mean P1 and N1 latencies were 15.39ms and 23.68ms. The comparison of mean P1 and N1 latencies values between study and control groups revealed no significant difference (p>0.05). Furthermore, the mean amplitude values of VEMP responses for study and control groups were 75.78μV and 160.51μV, respectively. The comparison mean amplitude values between study and control groups revealed statistically significant difference (p<0.05). Out of 15 children in the study group 2 children had the absent VEMP response in both the ears.nnnCONCLUSIONnBecause the vestibular function plays an important role in gross motor development in children, audiologists and otologist should recognize and understand the vestibular dysfunction in hearing impaired children and be prepared to undertake appropriate evaluations. However, additional research is needed on a larger sample size to determine the value of routine vestibular evaluation in children with sensorineural hearing loss and its potential benefit on the clinical outcome of these patients along with VEMP testing.

Effect of Pressure and Temperature on Phase Transformation and Properties of Titanium Aluminide Obtained through Reaction Synthesis

Reaction synthesis process has been used to develop γ titanium aluminide using elemental powders. Powder mixture of Ti-48 at. pct Al was prepared in ball mill and reaction synthesis was carried out in hot press with varying temperature and pressure. Titanium aluminide synthesized under high pressure and temperature resulted in better properties with respect to densification, homogenization response, mechanical properties and oxidation resistance as compared to that synthesized under low pressure and temperature. Al rich phases were observed in as-synthesized condition in all the experiments. However, some Ti rich phases were also found in high pressure-temperature synthesized samples. Density, hardness and tensile strength have been correlated with applied pressure through empirical relations. Variation in density with pressure is found to be logarithmic whereas hardness and tensile strength variation with pressure is polynomial.

Aging Behavior in 15-5 PH Precipitation Hardening Martensitic Stainless Steel

15-5 PH stainless steel is strengthened by precipitation of copper rich phases in a low carbon body centred cubic (b.c.c) lath martensitic matrix. Microstructures developed in aerospace grade 15-5PH precipitation-hardened stainless steel with different aging heat treatments have been studied. An attempt has been made to correlate the microstructural observations with the mechanical properties in different aging regimes. The overaging treatment imparts excellent ductility with a compromise in strength in peak aged condition to overaged condition the tune of 300 MPa in both tensile and yield strength. Hardness and tensile strength showed a similar decreasing trend with increase in aging temperature.

Equal Channel Angular Pressing of Aluminum-Alumina In Situ Metal Matrix Composite

The present investigation is on synthesis of in situ Al-alumina composite and to evaluate the effect of equal channel angular pressing on the refinement of the grain structure and enhancement in the hardness and the strength. The billets pressed in as cast condition has shown cracks during first pass. The billets pressed immediately after solution treatment for one pass and followed by ageing treatment immediately after pressing exhibited very high hardness of 125BHN against 95 BHN to that of the T6 condition of 6061 aluminium alloy. The microstructural refinement from 35 µm to 11 µm is obtained in annealed and ECAP 2 pass condition.

Electron Beam Welding Studies on Nb-Hf-Ti Refractory Alloy

Niobium, a refractory metal is mainly used as alloying addition in steels, superalloys, titanium and copper alloys. Being lightest refractory metal with high melting temperature, niobium based alloys are developed for high temperature applications of aerospace systems. However, poor oxidation resistance at elevated temperature limits its fabrication options and also requires oxidation protection in service. Among the fabrication methods, electron beam welding has been found to be a realistic option and the same has been studied in the present work. The paper presents the details of the Electron Beam Welding study carried out in developing the welding procedure for this alloy. An attempt has been made to correlate the weldment microstructure with the mechanical properties.

Development of Titanium Alloy Hemispherical Forging for Pressure Vessel of Launch Vehicle

Titanium alloy Ti6Al4V is used for manufacturing pressure vessels of launch vehicle in view of its excellent corrosion resistance and fabrication characteristics. This material also offers advantage of good strength to weight ratio necessary for space application. This paper describes the experience gained in the technology development of hemispherical forgings of titanium alloy Ti6Al4V. To achieve α-β microstructure and mechanical properties in the final product, hot working of the alloy from the stage of forging of cast ingots to finish working was carried out in the (α-β) region. The manufacturing parameters are established through state-of-the-art technology and capabilities. Process technology for processing of the hemispherical dome has been established and the same has been presented here.

Processing and Characterization of Superinvar for Space Application

Material with ultra-low coefficient of thermal expansion (CTE) is required for mounting camera and other optical elements in satellite systems. Invar (64 Fe 36Ni) has been the work-horse material for this purpose. In recent years, modified version of conventional invar i.e. Superinvar with 5% cobalt (replacing 5% nickel) is being used to further bring down the errors in camera mountings due to thermal expansion. Processing of this alloy poses many challenges due to its requirement of ultra-low CTE. In the present work, melting and thermomechanical processing parameters were selected to meet the specified requirement of the alloy. The alloy was melted through vacuum induction melting process to obtain uniform and homogeneous chemistry and properties. Virgin raw material was used to achieve lowest carbon and manganese contents. Chemical composition thus obtained is found to be within the specification. Material was hot worked to refine the microstructure. Three different sizes of forged blocks were produced. Hot worked material was heat treated to obtain desirable and stable microstructure. Heat treatment cycle for stabilization was selected and used to retain carbon in the solution and minimize temporal growth. Mechanical properties (tensile strength and modulus of elasticity) and physical properties (CTE, thermal conductivity) were evaluated. Properties were found to be meeting the specification. It is observed that the material shows uniform single phase austenitic microstructure. The paper presents details of the process selection and challenges in processing of this alloy to obtain the targeted CTE < 0.6x10-6 per °C in the temperature range of 25°C to 150°C along with other desired mechanical properties.

Effect of Ti Particle Size on Reaction Synthesis of Ti Aluminide

Titanium aluminide intermetallic was made through reaction synthesis (RS) process using elemental powders. Pressure assisted synthesis was carried out at high temperature under vacuum. Ti powder with two different particle sizes (200μm and 30μm average) were used in RS. Synthesized blocks were homogenized and characterized for chemical homogeneity, density, phase formation and microstructure evolution. Products near to theoretical density have been obtained with uniform chemistry after homogenization. Al3Ti as a major phase along with TiAl as minor phase was confirmed after RS and TiAl along with Ti3Al was observed after homogenization. Homogenization cycle was found to be different for the alloys made through different Ti particle sizes. Significant role of Ti particle size has been observed in this pressure assisted RS process.

Comparative Study on Tempering Response of Martensitic Grade AISI-420 Stainless Steels with Varying Carbon Content

Martensitic grade stainless steels are being extensively used in aerospace, defence and nuclear sectors for structural applications. Specialized applications require close control in chemistry and heat treatment parameters. Control of carbon in AISI-420, alloying content has typical service advantages. To study the effect of tempering temperature with carbon content on mechanical properties, various heat treatment cycles were devised, avoiding the regime of temper embrittlement. This paper presents the tempering response of medium carbon stainless steel AISI-420 grade with respect to change in carbon content from 0.2% to 0.3%. It is observed that, by varying the tempering temperature, the grade can be tailored to obtain wide range of mechanical properties. With increasing carbon content, martensite is found to be changing in morphology from lath to lath & plate (mixed) and the amount of retained austenite also increases. An attempt has been also made to arrive at a structure-property correlation in this grade of stainless steel.

Development and Characterization of 15Cr-5Ni-1W Martensitic Precipitation Hardening Stainless Steel for Aerospace Applications

15Cr-5Ni-1W precipitation hardening (PH) stainless steel is a martensitic PH stainless steel finding extensive use in semi-cryo engine applications. The alloy was developed through Vacuum Induction Melting (VIM) + Electro slag refining (ESR) under argon cover route. The alloy contains heavy elements like Mo, Nb, V and W totalling ~ 2 % by weight. Since the alloy is martensitic, stringent gas levels were also specified. Hence it was a challenging task to realise it without any segregation and stringent gas levels. The alloy was successfully melted through two different melt routes – (C). Electric Arc melting followed by Vacuum Oxygen decarburization (VOD) - vacuum degassing (VD) followed by secondary melting by ESR and also by melt route (V) vacuum induction melting (VIM) + ESR route. It was then forged into bars, rods and rings. The samples from the alloy were subjected to two different heat treatment cycles. Both the heat treatment cycles involved hardening at 1000°C for 2 hrs followed by air cooling to room temperature. In one of the cycle, sub-zero heat treatment at-70 °C was done prior to tempering while in the other cycle; direct tempering was carried out after hardening operation. Tempering was carried out at 2 different temperatures of 490 and 500 °C to achieve the specified mechanical properties. It was found that the alloy could meet the specified strength and ductility with both the heat treatment cycles mentioned above. However samples subjected to subzero heat treatment showed marginally higher strength with slight compromise in ductility. The alloy also exhibited similar impact toughness in both the heat treatment conditions. Delta ferrite was also found to be within 2% for both the heat treatment cycles employed in this study. The alloy also exhibited excellent strength and ductility at elevated temperature of 500 °C with just 25% reduction in yield strength compared to room temperature yield strength without much change in ductility.