Papers by Keyword: Metallic

Abstract: The tight binding linear muffin-tin-orbital (TB-LMTO) method within the local density approximation (LDA) is used to study the electronic structure and high pressure behaviour of thulium compounds TmX (X= P, As, S, and Se). We also predict a structural phase transition from NaCl to CsCl-type structure. The transition pressures were found to be 40.0, 31.0, 58.0 and 49.0 GPa, for TmP, TmAs, TmS and TmSe respectively. Apart from this, the lattice parameter (a₀), bulk modulus (B₀), band structure and density of states are calculated. From energy band diagram, it is observed that these compounds exhibit weak metallic character. The calculated values of lattice parameters and bulk modulus are of reasonable agreement with available data.

Abstract: The electronic structure and high pressure structural phase transition of SmTe and SmPo have been studied by using tight binding linear muffin-tin-orbital (TB-LMTO) method within the local density approximation (LDA). The total energy as a function of volume is obtained and it is found that these compounds are stable in NaCl-type (B₁-phase) structure and transform to CsCl-type (B₂-type) structure. The transition pressure of SmTe and SmPo are found to be 6.6 GPa and 8.6 GPa respectively. We have also calculated lattice parameter (a₀), bulk modulus (B₀), band structure (BS) and density of states (DOS). From energy band diagram, we observed that these compounds exhibit weakly metallic behaviour. The calculated values of lattice parameter and bulk modulus agree well with the available data.

Abstract: The ground state and electronic properties of americium pnictides (AmY, Y=N, P) has been calculated with the help of tight binding linear muffin-in-orbital (TB-LMTO) method within the local density approximation (LDA). From present study it is found that AmN and AmP are stable in NaCl – type structure under ambient pressure. The structural stability of AmN and AmP changes under the application of pressure. We predict a structural phase transition from NaCl-type to CsCl-type structure for these Am-pnictides in the pressure range of 36.0 – 47.0 GPa (AmN-AmP). Optimized lattice parameters, transition pressures and bulk modulus were obtained for the first time and analyzed in comparison with the available theoretical and experimental data.

Abstract: In this study parts having Open Cell Porous Regular Interconnected Metallic Structure (OCPRIMS) of cubic unit cell and OCPRIMS with inner solid core were fabricated through developed process of Rapid Manufacturing (RM) process. Two approaches were used to fabricate inner solid core i,e one by using metallic phosphor bronze powder and other by using solid phosphor bronze rod. The specimens were fabricated in accordance with ISO 3928: 1999 and subjected to tension-tension and compressive-compressive fatigue testing. The endurance limit of OCPRIMS with solid rod cored structure was found to be on the higher side in comparison to other types of specimens. The results of Scanning Electron Microscopy (SEM) and images of fractured surfaces showed the presence of voids, shrinkage cavities and pointed edges on the designed pores. They acted as stress raisers and facilitated crack initiation and propagation in the specimens.

Abstract: We have investigated the pressure induced structural and electronic properties of plutonium pnictides (PuY, Y= P, As, Sb). The total energy as a function of volume is obtained by means of self-consistent tight binding linear muffin-in-orbital (TB-LMTO) method within the local spin density approximation (LSDA). From present study with the help of total energy calculations (spin polarized) it is found that PuP, PuAs and PuSb are stable in NaCl – type structure under ambient pressure. The structural stability of PuP, PuAs and PuSb changes under the application of pressure. We predict a structural phase transition from NaCl-type (B₁-phase) to CsCl-type (B₂-phase) structure for these Pu-pnictides in the pressure range of 20.8 – 42.0 GPa. We also calculate the lattice parameter, bulk modulus, band structure and density of states. From energy band diagram it is observed that all the three compounds exhibit metallic behaviour. The calculated equilibrium lattice parameters and bulk modulus are in good agreement with available experimental data.

Abstract: We report ab initio calculations of pressure induced structural phase transition and electronic properties of thulium nitride (TmN). The total energy as a function of volume is obtained by using the self-consistent tight binding linear muffin-tin-orbital (TB-LMTO) method within the local density approximation (LDA). It is found that TmN is stable in NaCl – type structure under ambient pressure. We predict a structural phase transition from NaCl-type (B₁-phase) structure to CsCl-type (B₂-phase) structure of this compound at a high pressure of 68 GPa. We also calculate the lattice parameter (a₀), bulk modulus (B₀), band structure and density of states. From energy band diagram it is observed that TmN exhibit metallic behaviour. The calculated values of equilibrium lattice parameter and bulk modulus are in general good agreement with available experimental data.

Abstract: The tight-binding linear muffin-tin orbital (TB-LMTO) with in the local density approximation is used to calculate total energy, lattice parameters, bulk modulus, density of states and energy band structures of americium monochalcogenides at ambient as well as high pressure. It is found that AmX (X=S, Se, Te) compounds are stable in NaCl – type structure under ambient pressure. We predict a structural phase transition from NaCl-type (B₁-phase) structure to CsCl-type (B₂-phase) structure for these compounds in the pressure range of 26.0 – 15.0 GPa (AmS to AmTe). From energy band diagram it is observed that AmX compounds exhibit metallic behaviour. The calculated ground state properties such as lattice parameters and bulk modulus are in general good agreement with available experimental and theoretical data.

Abstract: The present study is a preliminary effort which investigates the effect of different sequences of composite materials on the Von Mises stress and stress concentration factor on a simple thin cracked plate. Our approach is to reduce the design of cylinder under internal pure pressure to that of a cracked metal plate reinforced by different sequences layers of composite subjected to a tensile loading. Four reports of the length of the crack front (a) with respect to the thickness (t) of the structure were analyzed. The increased ratio (a/t) from 10% to 40% positively influences the values of stress intensity factors and the Von Mises stress. Finally, the numerical results show that the reinforced the cracked structure with composite layers has greatly reduced the stress intensity factor at the crack tip based on fiber orientations.

Abstract: This study clarifies the fatigue properties using global signal statistical approach during the crack initiation stage for metallic component. Strain loading and acoustic emission (AE) signatures are captured simultaneously in the form of signal waves recorded by strain gauge and AE transducer. An initial study was carried out in the laboratory on medium carbon AISI 1045 steel specimens at constant amplitude cyclic loading condition, which lead to the fatigue failure characteristics. This study was carried out to investigate the relationship between strain and AE signals in order to make sure that AE technique also can be used as a detecting and monitoring crack initiation in metallic specimens. To achieve the goal, three different loads were applied on three specimens to capture the differences of the signals. The specific data acquisition systems were used to collect strain and AE signatures. For the purpose of analysis, the method of root mean square (r.m.s) and the kurtosis were used. The r.m.s value was used to quantify the overall vibrational energy content whereas the kurtosis was then used because of its sensitivity to high amplitude events. Based on these statistical approaches, the correlation patterns between both signals are expected to give a meaningful baseline to predict and monitor crack initiation of a metallic specimen.