Effect of Grain Size, Grain Shape and Subgrain Size on High Temperature Creep Behaviour

Several strengthening machanisms, namely solute strengthening, precipitation and fine particle strengthening, grain size as well as shape control and substructure strengthening, have been utilised in the development of creep resistant alloys. Of these, the effect of polycrystal grain size, grain shape and subgrain size on viscous as well as power-law (climb) creep processes are considered here. Viscous creep processes include Nabarro-Herring (N-H), Coble and Harper-Dorn (H-D) creep. N-H and Coble creep processes are strongly influenced by grain size whereas creep rates under H-D creep are independent of grain size. Though it is usually assumed that power-law creep is independent of grain size, in practice it is not so. Several investigations have revealed that power-law creep does depend on grain size. There are detailed and well understood results pertaining to the role of grain size in viscous creep. On the other hand, subgrain size has been seen to have effect only on the climb creep behaviour which is yet to be clearly understood

Correlations of projectile like fragments in heavy ion reactions at Fermi energy

Correlations between pairs of projectile-like fragments, emitted by the system ${^{16}O}+{^{197}Au}$ at the laboratory bombarding energy of 515 MeV, have been studied under two stipulated conditions: (1) at least one member of the pair is emitted at an angle less than the grazing angle for the system, (2) both the members of the pair are emitted at angles larger than the grazing angle. A surprisingly large difference, by more than an order of magnitude, is found between the correlations for the two cases. This observation could be explained on the basis of a simple semi-classical break up model. Further analysis of the variation of the charge correlation function with the difference in the nuclear charges of the correlated pair showed trends which are consistent with an "inelastic break up process", in which the projectile breaks up at the radius of contact, in such a way that, one fragment (preferably the lighter) is emitted to one side within the grazing angle, while the other orbits around the target nucleus for a while and emerges on the other side, at a negative scattering angle, much like in a deep inelastic scattering.Comment: 19 pages, 12 figures accepted by Eurp. Physics Journal

Carbon Carbon Composites: An Overview .

Carbon carbon composites are a new class of engineering materials that are ceramic in nature but exhibit brittle to pseudoplastic behaviour. Carbon-carbon is a unique all-carbon composite with carbon fibre embeded in carbon matrix and is known as an inverse composite. Due to their excellent thermo-structural properties, carbon-carbon composites are used in specialised application like re-entry nose-tips, leading edges, rocket nozzles, and aircraft brake discs apart from several industrial and biomedical applications. The multidirectional carbon-carbon product technology is versatile and offers design flexibility. This paper describes the multidirectional preform and carbon-carbon process technology and research and development activities within the country. Carbon-carbon product experience at DRDL has also been discussed. Development of carbon-carbon brake discs process technology using the liquid impregnation process is described. Further the test results on material characterisation, thermal, mechanical and tribological properties are presented

PHARMACEUTICAL STANDARDIZATION OF JATIPHALADYA VATI

Standardization is the process of developing and agreeing upon technical standards. A standard is a document that establishes uniform engineering or technical specifications, criteria, methods, processes or practices. Many drugs are described in Ayurvedic classical texts for the treatment of various disorders. Jatiphaladya Vati is one such Kharaliya Rasayana mentioned in Rasendra Saara Samgraha, indicated in Arshas (Haemorrhoids). Jatiphala (Myristica fragrans Houtt.), Lavanga (Syzygium aromaticum), Pippali (Piper longum), Saindhava lavana (Rock salt), Shunthi (Zingiber officinale Roxb), Dhattura beeja (Datura metel Linn.), Hingula (Cinnabar) and Tankana (Borax) are the main ingredients. Shodhana (Purification), Churna nirmana (Preparation of powder), Bhavana (Soaking with liquid and triturating till drying) and Mardana (Trituration) are the important steps involved in preparation of Jatiphaladya Vati. Shodhana of Hingula, Tankana and Dhattura beeja was carried out by classical method to remove the impurities. Churna of all above ingredients were prepared by subjecting it to grinding in Khalwa yantra and filtering through cloth. All ingredients were mixed properly to make homogenous mixture; later on it was triturated with Nimbu swarasa to obtain 250 mg tablets (brick red in colour) in tablet compression machine. The present study has been planned to standardize the method of preparation of an important Herbo-mineral formulation i.e. Jatiphaladya Vati

Dynamic Time Slice Calculation for Round Robin Process Scheduling Using NOC

Process scheduling means allocating a certain amount of CPU time to each of the user processes.  One of the popular scheduling algorithms is the “Round Robin” algorithm, which allows each and every process to utilize the CPU for short time duration.  Processes which finish executing during the time slice are removed from the ready queue.  Processes which do not complete execution during the specified time slice are removed from the front of the queue, and placed at the rear end of the queue. This paper presents an improvisation to the traditional round robin scheduling algorithm, by proposing a new method. The new method represents the time slice as a function of the burst time of the waiting process in the ready queue. Fixing the time slice for a process is a crucial factor, because it subsequently influences many performance parameters like turnaround time, waiting time, response time and the frequency of context switches.  Though the time slot is fixed for each process, this paper explores the fine-tuning of the time slice for processes which do not complete in the stipulated time allotted to them

STANDARDIZATION OF YOGAAMRUTO RASA BY USING MODERN ANALYSIS TECHNIQUES

Rasa Shastra is a partially independent branch of Ayurvedic medicine, which deals with preparation of the drugs with metals and minerals to produce the drugs with higher efficacy in lower dose with good palatability. Yogaamruto Rasa (YMR) is one such Rasoushadhi mentioned in Rasa Kamdhenu indicated for all types of Kushta. Parada, Gandhaka, Tamra churna, Vatsanabha, Vacha, Trikatu, Musta and Vidanga are the main ingredients of YMR. Shodhana, Mardana, Murchchana, Pishti nirmana, Aagni paaka are the important steps involved in preparation of YMR. Till date no standards are available for the above drug. Need of the hour is to revalidate the safety and efficacy of the above said formulation. In the current study of YMR it was subjected to analysis through X-ray diffraction (XRD), Scanning electron microscope (SEM), Energy dispersive X-ray spectroscopy (EDX) and Zeta potential (ZP). XRD of YMR reveals that major peaks are of Cu20 (Cuprite) and minor peaks of HgS (Meta Cinnabar), Cu2S (Cuprous Sulphide). SEM study found the smallest grain size ranging between115nm at 5Kx magnification to 82.11 nm at 7Kx magnification. EDX study reveals that YMR contains significant percentage of O-25.96%, Cu-22.82%, C-20.41%, Hg- 12.84 %, S- 9.8%. w/w. ZP mean value for YMR is 51.4 mV which indicates moderate colloidal stability.

Experimental Studies of Resin Systems for Ablative Thermal Protection System

The present work was initiated to finalise resin for the development of thermal protection system (TPS) for the external surface of a polymeric composite rocket motor case made up of Carbon roving and Epoxy resin. The temperature on the outer surface of the composite case increases due to kinetic heating caused by aerodynamic drag and vehicle velocity. These rocket motor casings are functionally required only in the ascent phase of missile trajectory till motor action time and stage separation. Due to which the experienced heat flux is relatively less, and the temperature on the external composite case is in order of 250 °C - 300 °C depending on missile configuration and trajectory, unlike extreme thermal conditions on ablative nozzle liners exposed to rocket motor exhaust. The maximum allowable temperature in the present study for the Carbon-Epoxy case is 100 °C due to degradation in mechanical properties. The thermal protection system on the external surface will function as a heat-insulating layer based on the working mechanism of ablation. The resin of the thermal protection layer has a substantial impact on the manufacturing process and curing aspects, especially compatibility with the pre-cured carbon epoxy case layer. The generation of test results for thermal stability, cure characteristics and Tg for Epoxy resin has also been included in present studies as an additional objective that provides significant inputs for process development. The test results for Epoxy resin is also used as a basis for the finalisation of resin for the thermal protection layer for processing aspects apart from its basic thermal stability characteristics. The ablative thermal protection working mechanism is based on the ablation phenomenon. In the case of ablation, resin plays a vital role due to pyrolysis and other thermal characteristics. In the present experimental studies, the Phenolic resin and Silicone resin are considered as candidate resin materials for ablative thermal protection system based on available literature and in house experience. The main objective of the present studies is to evaluate thermal stability, char yield after final decomposition through DSC and TGA techniques for both resins as these are fundamental characteristics needed for the present specific application. The test results for specific grades (formulation) of phenolic and Silicone resins are generated and compared. In the present work, the experimental studies to evaluate glass transition temperature (Tg), thermal stability, and cure characteristics for Epoxy resin is also carried through DSC. The test results of specific grade Epoxy resin provides a basis to assess thermal margins for resins selected for ablative thermal protection system and inputs for process development and design requirements. The scope of the present studies is aimed to finalise the resin system for external thermal protection of composite rocket motor case based on thermal characteristics test results and other compatibility aspects with the structural layer