NOPR Collection:

Effects of silicon and chromium additions on glass forming ability and microhardness of Co-based bulk metallic glasses

2014-02-01T00:00:00Z

Title: Effects of silicon and chromium additions on glass forming ability and microhardness of Co-based bulk metallic glasses Authors: Hitit, Aytekin; Talaş, Şükrü; Kara, Riıza Abstract: Effects of silicon and chromium additions on glass forming ability (GFA) and microhardness of a Co-Fe-Ta-B bulk metallic glass are investigated by using differential scanning calorimetry (DSC), X-ray diffractometry (XRD) and scanning electron microscopy (SEM). It is found that partial substitution of boron by silicon promotes the GFA of the alloy. Fully amorphous rod of 4 mm is fabricated by suction casting Co₄₃Fe₂₀Ta_5.5B_26.5Si₅ alloy. However, partial replacement of cobalt by chromium decreased the GFA significantly. In fact, critical casting thickness of Co₃₉Cr₄Fe₂₀Ta_5.5B_26.5Si₅ alloy is determined as 2 mm. It is also determined that microhardness values of the amorphous alloys are about 1200HV₃₀₀. This value is lower than the hardness of the base alloy,1455HV₃₀₀, and it is believed that decrease in hardness results from the reduction in boron contents of the alloys. Page(s): 111-115

Diamond like carbon coating of ball bearings for raceway surface by triboadhesion

2014-02-01T00:00:00Z

Title: Diamond like carbon coating of ball bearings for raceway surface by triboadhesion Authors: Rodríguez, J A; Rodríguez, J M; García, J C; Arellano, J A; Maldonado, J L Abstract: This paper presents a comparison of performance of rolling bearings coated with diamond like carbon (DLC) by triboadhesion and without any coating. The bearings are coated only in the inner raceway. The performance evaluation is three fold: (i) an analysis of the vibration signal, (ii) an analysis of the relationship between tangential force and normal force determined like friction coefficient as an indication of the wear resistance of the surface, and (iii) a microscopic analysis of the rolling bearings surface. Four types of rolling bearings are tested: (a) lubricated and uncoated; (b) unlubricated and uncoated; (c) coated with DLC, no lubrication and normal load of 0.35 N and (d) coated with DLC, no lubrication and normal load of 0.5 N. It is found from the friction coefficient that bearings coated with DLC have a higher wear resistance than those without coating. Page(s): 104-110

Simulation and experimental validation of AC motor and PMDC motor pumping system fed by photovoltaic cell

2014-02-01T00:00:00Z

Title: Simulation and experimental validation of AC motor and PMDC motor pumping system fed by photovoltaic cell Authors: Chandrasekaran, N; Thyagarajah, K Abstract: Solar water pumping is a promising renewable alternative to conventional water pumping for large, medium and small power applications. This system is also useful in remote areas where electricity is not available and it is very expensive to lay long transmission lines. This paper deals with basics of solar powered water pumping system and the comparison of performance between AC motor and PMDC motor pumping systems. In this work, the MATLAB based modelling of a PV array, single-phase induction motor and permanent magnet DC motor are studied and developed. The photovoltaic is used to feed power to the water pumping systems. The performance characteristics of single-phase induction motor and permanent magnet direct current motor are obtained by using MATLAB simulation and are validated with experimental results. From the experimental results, it is found that the permanent magnet direct current motor is best suitable for photovoltaic water pumping than the single-phase induction motor in low power applications. Page(s): 93-103

Burst pressure estimation of reworked nozzle weld on spherical domes

2014-02-01T00:00:00Z

Title: Burst pressure estimation of reworked nozzle weld on spherical domes Authors: Lal, G Jegan; Jayesh, P; Thyagarajan, K Abstract: Propellant tanks of rockets or launch vehicles have nozzles welded to their domes as interfaces for valves or pressurisation/vent lines. These nozzle welds are critical since more often the failure happens here when the tank is pressurised. The considerable difference between the yield and ultimate strength of weld as compared to the parent material is the reason for the low burst pressure of the nozzle welds. To eliminate unacceptable weld defects like porosities, cracks etc., the defective portions are rewelded and are called weld reworks. Residual stress present because of rework, further reduces the burst pressure. In this study, burst pressure estimation of a typical nozzle welded to the dome is analysed by finite element method. The effect of geometric non-linearity of the structure in the prediction of burst pressure is clearly brought out. Also, the burst pressure reduction when weld reworks are carried out in a portion of the weld length and reduction in burst pressure when this rework length increases is demonstrated using finite element analysis. Page(s): 88-92