Vikas Verma

Design of a lead-lag compensator for position loop control of a gimballed payload

In the last few years Digital controllers are widely used because of their excellent qualities of simplicity, effectiveness and they are applicable for broad class of systems. At present their involvement in industrial processes is more than 95%. They generally relate to accuracy, relative stability and speed of the response so as to yield an optimal control system for the given purpose. In this paper, the control of gimbal has been stated for the defence application mounted on the tank. A gimbal is a mechanical arrangement, which is used to isolate the payload from the moving vehicle. This is particularly used in line of stabilization systems and inertial guidance systems [1]. These systems require very fast and accurate control within a particular bandwidth. In the present problem, the digital controller is implemented using frequency domain approach in order to control the rate of motion of platform, meeting the stringent requirements of disturbance attenuation and robust stability.

Analysis of powder metallurgy process parameters for mechanical properties of sintered Fe–Cr–Mo alloy steel

ABSTRACT The present work involves an investigation to find out the best combination of process parameters for a Fe–Cr–Mo alloy with the help of Design of Experiments (DOE) tool. The Fe–Cr–Mo alloy containing 0, 0.4 and 0.8 wt.% carbon is compacted at 650 MPa pressure and sintered at 1120°C and 1200°C temperature, respectively, with 3.5 or 6°C/minute cooling rate. Quality characteristics like hardness and tensile strength are analyzed for various combinations of graphite weight %, sintering temperature, and cooling rate. The conducted experimental trials are based on the design matrix obtained from general factorial design. Significant regression models are developed from the above mentioned process parameters to predict the quality characteristics using DOE tool. The developed mathematical model during the course of research helped in investigating best combination of process parameters for powder processing. The desirability test showed its usefulness in finding out the number of optimization strategies to achieve the optimum values of hardness and tensile strength. The observed results are correlated with the microstructure. Diffusion of carbon during sintering decides the optimum amount of carbon. Higher carbon addition results in residual graphite which weakens the sintered alloy.

Processing of alumina-based composites via conventional sintering and their characterization

ABSTRACT The present work relates to the processing of dense alumina-based composites, their microstructural characterization and study of mechanical properties. Alumina ceramic material and alumina-based composites with m-Zirconia and Ceria addition are sintered at 1600°C, 1650°C and 1700°C temperatures via conventional sintering. Solid-state diffusion during sintering led to volume diffusion in alumina, and volume and grain boundary diffusion in alumina composite. In the present sintering conditions alumina is found to be the least dense as improper solid-state diffusion resulted in porosity, whereas alumina–zirconia composite achieved the highest density of 97%. Scanning electron microscope (SEM) micrograph shows homogeneous distribution of fine zirconia particles inside the alumina matrix, filling the voids of the alumina skeletal structure. Zirconia connects to alumina particles, restricting its abnormal grain growth. It results in strong bonding and grain refinement. Alumina–zirconia composite exhibits the highest hardness and fracture toughness of 14.37 GPa and 4.6 MPa · m1/2 at 1700°C. Alumina suppresses the transformation of m-t zirconia, resulting in high toughness of alumina composites. Alumina–zirconia–ceria composite revealed the presence of porosity, which led to less densification and low mechanical properties.

Studies on induction hardening of powder-metallurgy-processed Fe–Cr/Mo alloys

Induction hardening of dense Fe–Cr/Mo alloys processed via the powder-metallurgy route was studied. The Fe−3Cr−0.5Mo, Fe−1.5Cr−0.2Mo, and Fe−0.85Mo pre-alloyed powders were mixed with 0.4wt%, 0.6wt%, and 0.8wt% C and compacted at 500, 600, and 700 MPa, respectively. The compacts were sintered at 1473 K for 1 h and then cooled at 6 K/min. Ferrite with pearlite was mostly observed in the sintered alloys with 0.4wt% C, whereas a carbide network was also present in the alloys with 0.8wt% C. Graphite at prior particle boundaries led to deterioration of the mechanical properties of alloys with 0.8wt% C, whereas no significant induction hardening was achieved in alloys with 0.4wt% C. Among the investigated samples, alloys with 0.6wt% C exhibited the highest strength and ductility and were found to be suitable for induction hardening. The hardening was carried out at a frequency of 2.0 kHz for 2–3 s. A case depth of 2.5 mm was achieved while maintaining the bulk (interior) hardness of approximately HV 230. A martensitic structure was observed on the outer periphery of the samples. The hardness varied from HV 600 to HV 375 from the sample surface to the interior of the case hardened region. The best combination of properties and hardening depth was achieved in case of the Fe−1.5Cr−0.2Mo alloy with 0.6wt% C.

Microstructure and mechanical behaviour characterisation of Al-Al2O3 MMC processed by DIMOX and Al-Al2O3/MnO2 MMC processed via stir casting route

In the present study two types of composite were developed - Al-Al2O3 composite by direct metal oxidation (DIMOX) and by reinforcements using both ex situ and in situ approaches together by a dispersing powder mixture of Al2O3 and MnO2 in a ratio of 1:1, through stir casting route in aluminium matrix. Al-Al2O3 composites were synthesised successfully under ambient conditions and it was found that the particles increased as the holding time and the number of stirrings was increased resulting in improved mechanical properties. Generation of Al2O3 particles in the matrix was confirmed by X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS) examination. Hence, oxidation, which is known as a major problem in composite preparation by liquid metallurgy route, can be used for preparation of composites and for improving the properties. In Al-Al2O3/MnO2 composites the mechanical properties as well as particle distribution improved as Al2O3 + MnO2 were introduced and also with their increasing weight percent.

Study of Microstructure, Impact Strength on Manual Metal Arc Welding Of Gray Cast Iron Using Enife-Ci Filler Metal

The effect on the microstructure obtained in the heat-affected zone (HAZ) and the carbide zone in the weld metal properties of Casted grey cast iron plates (grade-GJLEN 1561) are used as base material. The welding was carried out with manual shielded metal arc welding using ENiFe-CI filler metal. The welds were prepared by using the arc welding process and filler Nickel base filler materials are used in welding as electrode, which is ductile in nature 85 ENiFe-CI is the grade of nickel base filler electrode. For knowing the effect of preheat treatment, the plates were firstly heated to near about 400- 450˚C by the help of gas cutting torch and the post weld heat treatment (PWHT) was limited only for 45 minute at 810 o C. The welds were characterized by micro structural analysis, impact test, and tensile test. The Charpy-impact properties of the weldment specimens improved with the PWHT and were somewhat lower than previously developed data on the wrought material. Keyword: - gray cast iron, impact test, microstructure, post weld heat treatment (PWHT), tensile test. I. INTRODUCTION Weld ability of cast iron has been found to be very poor due to the heterogeneity of matrix phase and non-wet ability of the graphite phase. These phases undergo a series of microstructure changes in the HAZ during weld repairing by fusion welding the project discusses the nature of these changes occurring in the vicinity of the weld zone as well as method of controlling these to get satisfactory weldment. It further discusses the practical aspect of weld joint preparation, the selection of welding process and procedure, the choice of filler metal-composition etc. and degree of pre as well as post weld heat-treatment to obtain defect and stress free welding. The welding of ductile cast iron is not normally practiced in the foundry industry for the reclamation or fabrication of castings, due to the inconsistency of the mechanical and physical properties achieved. Grey irons contain higher amounts of carbon compared to steels which diffuses into the austenite during welding, forming hard brittle phases, namely martensite and carbides at the weld interface. These give rise to poor elongation properties and high hardness values. Weldability of ductile cast iron depends on its original matrix, chemical composition mechanical properties and structure of welding process and working condition. The preheating temperature range depends on the hardenability of the iron chemical composition or carbon equivalent, the size and complexity of the weld and the type of filler materials.