Showing papers by "Defence Research and Development Laboratory published in 2000"

Microstructural changes during welding and subsequent heat treatment of 18Ni (250-grade) maraging steel

Abstract: Sheet material specimens from 18Ni (250-grade) maraging steel were gas tungsten-arc welded using two different filler wires: one matching the base material in composition and the other with higher cobalt but lower molybdenum and titanium contents. Welding was carried out both in constant-current and pulsed modes. Post-weld aging was performed at three different temperatures, viz., 425, 480 and 520°C. Metallographic characterization revealed pronounced segregation, presumably of Ti and Mo, along interdendritic and intercellular boundaries in the weld metal produced with filler of matching composition. This led, during subsequent aging, to austenite reversion at temperatures much lower than in wrought (unwelded) material. Segregation and austenite reversion were not noticed when Ti and Mo contents were reduced in the filler wire, except at the highest aging temperature used. The use of pulsed welding resulted in some grain refinement, but the effect was not considerable.

Tensile properties and fracture toughness of 18Ni (250 grade) maraging steel weldments

Abstract: Gas tungsten arc welding was performed on 18Ni (250 grade) maraging steel sheet using two different filler wires: one of the same composition as the base material and the other containing more cobalt and aluminium and less molybdenum and titanium. Weld specimens were then aged under four different sets of conditions. After metallographic characterisation, mechanical properties including hardness, tensile strength and ductility, and fracture toughness were evaluated. Results showed that use of the matching filler material led to lower strength but higher ductility than in the other case; this was attributed to the presence of reverted austenite in the former (caused by segregation, especially of molybdenum) at the fusion zone substructure boundaries. In both types of weld metal, a re-solution treatment followed by aging at 480°C resulted in optimum tensile properties. Fracture toughness of the aged weldments was in general close to that of the parent material aged at 480°C; some deterioration occur...

Guided Missile with an Intelligent Agent

Abstract: Guided missiles involve the use of a conventional deviated pursuit course like proportional navigation algorithm and its variants, which is optimal when the speed advantage of the guided missile is very high and the target maneouvering is minimal. Against the present-day aircraft, which employs fly-by-wire technology for high maneouverability and high speed, missiles need to have a much higher speed advantage or to use a combination of artificial intelligence and modern control algorithms. Results of Simulation of pursuit and evasion with an autonomous intelligent agent incorporated in the control loop are presented.

Information management/librarian to knowledge manager: change of role

Abstract: Many organizations world over are embracing knowledge management systems for survival and to retain profitability. This trend is visible in the technology intensive businesses like biotechnology, computers and telecommunications and also in professions like legal, accountancy and management consultancy. A new breed of managers called " Knowledge Manager " has emerged to put the new system in place in the organizations. Information Managers and Librarians are increasingly drafted to fill the post of Knowledge Managers as their work is nearest to the job. This article covers the broad classification of knowledge and the mechanisms of its transmission and transformation. Finally the importance of human element in the Knowledge Management System is highlighted for the benefit of Information Managers and Librarians.