Mechanical behaviour of aluminium-lithium alloys

Aluminium-lithium alloys hold promise of providing a breakthrough response to the crying need for lightweight alloys for use as structurals in aerospace applications. Considerable worldwide research has gone into developing a range of these alloys over the last three decades. As a result, substantial understanding has been developed of the microstructure-based micromechanisms of strengthening, of fatigue and fracture as well as of anisotropy in mechanical properties. However, these alloys have not yet greatly displaced the conventionally used denser Al alloys on account of their poorer ductility, fracture toughness and low cycle fatigue resistance. This review aims to summarise the work pertaining to study of structure and mechanical properties with a view to indicate the directions that have been and can be pursued to overcome property limitations

Synthesis of Polycarbosilane, Polymer Impregnation Pyrolysis based C SiC Composites and Prototype Development

Due to some extraordinary thermo-mechanical properties, silicon carbide is considered one of the best materials used for high temperature applications in defence and aerospace. Polycarbosilane (PCS) has been widely used as SiC precursor. This paper describes the research and development work undertaken to establish the technologies for synthesis and characterisation of PCS, fabrication process and characterisation of Carbon fibre reinforced SiC matrix (C/SiC) composite laminates and shaped articles. The molecular weight and softening point of the PCS was found to be 1400-1800 Mn and 140-150 °C respectively. Flexural stress of the unidirectional (UD) C/SiC composites and bidirectional (2D) C/SiC composites was found to be 400-450 MPa and 300-350 MPa respectively. Tensile stress of the 2D C/SiC composite was found to be around 200 MPa. Coefficient of thermal expansion and thermal diffusivity of the 2D C/SiC composites at RT- 1000 °C were found to be in range of 0.3-2.2×10-6/ °C and 32-6 mm2/s respectively. The fabrication process developed for the UD and 2D C/SiC composites using the indigenous PCS has been also demonstrated to fabricate typical size divergent rocket nozzle and hot structure. Fabrication process of the SiC fibre has also been described in brief

Synthesis of Silver Nanostructures and their Application in Highly Sensitive SERS Sensors

A comparison of Surface Enhanced Raman Scattering (SERS) activity of chemically synthesised silver nanostructures with different shapes is reported. The silver nanostructures of cubical, prism and wire like morphology were synthesised using chemical synthesis route and utilised as SERS substrates. The sensors were fabricated by spin coating these materials over a Silicon or glass substrate. The fabricated sensors were used to analyse response with two different analytes, 4-Mercaptobenzoic acid and Rhodamine 6G under different concentrations. The signal enhancement was compared with a silver coated thin film over glass substrate and it was observed that the enhancement of the order of 103 is achieved. The nanowire performed better than the other forms of silver and gave a higher signal enhancement for all the analytes as compared to other nanostructures. The fabricated sensors may be useful for various applications including explosive and biowarfare agent detection

Concurrent Development and Certification of SOFTCOMAG 49AA Alloy for Aeronautical Applications

Softcomag 49AA alloy consisting of 49 wt per cent Fe, 49 wt. per cent Co and 2 wt per cent V is a soft magnetic alloy with a combination of very high saturation magnetisation and high magnetostriction and used for several aeronautical applications such as generators (stators and rotors), fixed iron moving armature units etc. Though this alloy is brittle in nature, it can be formed into hot rolled bars and cold rolled sheets by adopting suitable thermo mechanical treatments. In order to indigenise and subsequent type certification for aeronautical applications, the alloy was produced using 100 per cent virgin raw materials in a vacuum induction melting (VIM) furnace which not only ensures substantial reduction of inclusions, but also the production of homogeneous alloy as a result of induction stirring. The chemical composition was examined and hot working parameters of the alloy were so optimised that they would result in the best combination of magnetic, physical and mechanical properties for the end use, which forms the central theme behind the developmental activity that was simultaneously covered by a comprehensive certification process. The material thus produced is subjected to stringent quality control checks in accordance with stipulated airworthiness norms. The paper discusses in detail the indigenisation efforts and airworthiness certification of the alloy Softcomag 49AA and its comparison with equivalent grades, namely PERMENDUR 49 and VACOFLUX 50.Defence Science Journal, 2012, 62(1), pp.67-72, DOI:http://dx.doi.org/10.14429/dsj.62.1093

Flexing behaviour of high strength coated fabrics

381-387Flexing characteristics of three varieties of thermoplastic polyurethane (TPU) coated high strength fabrics (nylon 6,6, polyester and kevlar) have been evaluated by subjecting them to 5000 cycles in a De-Mattia flex tester. The flexing damage is assessed in terms of % loss of strength by evaluating the residual tensile strength of flexed fabrics. Statistical analysis has been carried out at 95% significance level for assessing the influence of flexing cycles and variation in thermoplastic polyurethane concentration on the residual strength of coated kevlar fabrics. Accordingly, the specific trend exhibited is established. The study shows that the coated kevlar fabric has suffered with maximum strength loss, while nylon and polyester show excellent flex damage resistance with negligible strength loss. Further, the sensitivity to damage of kevlar fabric has been studied by varying the number of flex cycles from 1000 to 5000 and the extent of damage that happened within the structure is thoroughly analyzed using field emission scanning electron microscope. Finally, the possible mean of improving strength retention (22%) of coated kevlar fabric subjected to repeated flexing by the application of a proprietary high viscosity polymer coating has been proposed

Flexing behaviour of high strength coated fabrics

Flexing characteristics of three varieties of thermoplastic polyurethane (TPU) coated high strength fabrics (nylon 6,6, polyester and kevlar) have been evaluated by subjecting them to 5000 cycles in a De-Mattia flex tester. The flexing damage is assessed in terms of % loss of strength by evaluating the residual tensile strength of flexed fabrics. Statistical analysis has been carried out at 95% significance level for assessing the influence of flexing cycles and variation in thermoplastic polyurethane concentration on the residual strength of coated kevlar fabrics. Accordingly, the specific trend exhibited is established. The study shows that the coated kevlar fabric has suffered with maximum strength loss, while nylon and polyester show excellent flex damage resistance with negligible strength loss. Further, the sensitivity to damage of kevlar fabric has been studied by varying the number of flex cycles from 1000 to 5000 and the extent of damage that happened within the structure is thoroughly analyzed using field emission scanning electron microscope. Finally, the possible mean of improving strength retention (22%) of coated kevlar fabric subjected to repeated flexing by the application of a proprietary high viscosity polymer coating has been proposed

MHD and rotation effects on flow past an accelerated vertical plate with variable temperature and mass diffusion in the presence of chemical reaction

An exact analysis of rotation effects on an unsteady flow of an incompressible and electrically conducting fluid past a uniformly accelerated infinite isothermal vertical plate, under the action of a transversely applied magnetic field is presented. The plate temperature is raised linearly with time and the concentration level near the plate is also raised to C’w. The dimensionless governing equations are solved using the Laplace-transform technique. The velocity profiles, temperature and concentration are studied for different physical parameters such as the magnetic field parameter, chemical reaction parameter, thermal Grashof number, mass Grashof number, Schmidt number, Prandtl number and time. It is observed that the velocity increases with increasing values of the thermal Grashof number or mass Grashof number. It is also observed that the velocity increases with decreasing values of the magnetic field parameter or rotation parameter Ω

MHD and rotation effects on flow past an accelerated vertical plate with variable temperature and mass diffusion in the presence of chemical reaction

An exact analysis of rotation effects on an unsteady flow of an incompressible and electrically conducting fluid past a uniformly accelerated infinite isothermal vertical plate, under the action of a transversely applied magnetic field is presented. The plate temperature is raised linearly with time and the concentration level near the plate is also raised to C’w. The dimensionless governing equations are solved using the Laplace-transform technique. The velocity profiles, temperature and concentration are studied for different physical parameters such as the magnetic field parameter, chemical reaction parameter, thermal Grashof number, mass Grashof number, Schmidt number, Prandtl number and time. It is observed that the velocity increases with increasing values of the thermal Grashof number or mass Grashof number. It is also observed that the velocity increases with decreasing values of the magnetic field parameter or rotation parameter Ω