Defence Research Agency

About: Defence Research Agency is a based out in . It is known for research contribution in the topics: Synthetic aperture radar & Radar. The organization has 1211 authors who have published 1109 publications receiving 31542 citations.

Microstructural control in a gamma-tial alloy by ma and hiping

Abstract: The ψ-TiAl-based alloys are potentially very attractive low-density materials for use at elevated temperatures. In this article, a novel method of controlling the grain size of these alloys using mechanical alloying and hot isostatic pressing is presented.

Modelling of hole mobilities in heavily doped strained SiGe

Abstract: Low-field hole mobilities have been calculated for heavily relaxed and strained doped SiGe alloy layers with Ge contents varying from 0 to 50%, using a novel semi-analytical bandstructure model which incorporates the effects of strain on the valence band of the alloy We obtain poor results compared with experiment for mobilities in heavily doped Si, and attribute this to (i) a failure of the Born approximation at low carrier energies and (ii) the omission of additional effects associated with heavy doping and high carrier concentrations For the strained doped and intrinsic alloy we observe that both the in-plane and out-of-plane hole drift mobilities increase with increasing Ge content relative to those for Si These enhancements are due mainly to the effects of strain, and to a lesser extent due to alloying with Ge, but are offset by the presence of alloy scattering Our results are sensitive to the details of the models used for scattering by ionized impurities; however, the large uncertainties and scatter of the experimental data preclude accurate estimates of the alloy potential We find that an alloy potential of 20 eV gives an in-plane mobility consistent with experimental data for intrinsic material Our calculations for heavily doped layers are affected by uncertainties in the value of the alloy potential and highlight a need for a better quantitative understanding of the scattering processes which are important in heavily doped alloy layers

Changes in strength and power performance and serum hormone concentrations during 12 weeks of task‐specific or strength training in conscripts

Abstract: The purpose of this study was to investigate the effects of two different training programs on strength and power performance and serum hormone concentrations. A total of 104 male soldiers volunteered and took part in the 12-week training period with baseline, mid-, and post-measurements of body composition, muscle strength, lower and upper body power, and blood samples to determine serum hormone concentrations. The mean (±SD) age of subjects was 20 ± 1 years, height 180 ± 6 cm and body mass 72.4 ± 8.8 kg. The subjects were divided into three different training groups: soldier task-specific training (TS), strength training (ST), and control (CON). Each group had a total of 18 training sessions during the 12-week study. In the muscle strength tests, most improvements could be observed in the TS and ST groups, especially, during the first weeks of the training period. Maximal isometric leg extension force increased significantly by 7.9 ± 12.2% (p < .05) in the TS and 7.1 ± 12.6% (p < .05) in the ST groups between the PRE and MID, as well as between the PRE and POST measurements by 8.1 ± 12.4% (p < .05) in TS and 12.3 ± 15.3% (p < .01) in ST. Serum TES concentration increased significantly in TS between the PRE and MID (16.8 ± 33.9%) and PRE and POST (11.2 ± 16.7%) measurements. Serum COR concentrations decreased in TS between the MID and POST (-7.8 ± 10.9%) and PRE and POST (-11.0 ± 14.3%) measurements. Although the differences observed were rather minor in magnitude, training in the TS and ST groups led to greater improvements in muscle strength and power performance compared to the training in the CON group. The development of strength and/or power of the lower and upper body was greater in the TS and ST groups, which is crucial for warfighter's performance. Therefore, it is important to have a structured resistance-training program during military training to optimize the strength, power, and military-specific performance.

Ageing and toughness of silicon carbide particulate reinforced Al-Cu and Al-Cu-Mg based metal-matrix composites

Abstract: Metal-matrix composites (MMC) comprising powder aluminium alloys reinforced by particulate ceramic are being developed for widespread aerospace structural applications ranging from fuselage and missile components to undercarriage parts. Most interest is centred on MMCs with an Al-Cu-Mg (2124) matrix alloy. These MMCs possess high levels of specific stiffness with high specific strengths but can exhibit lower ductility and toughness than conventional unreinforced aluminium alloys.

Method of treatment of metal matrix composites

Abstract: A treatment process for a composite comprising a matrix of a precipitation hardenable aluminum alloy and a particulate or short fiber ceramic reinforcement. The process includes hot and/or cold working the composite, subjecting the composite to a controlled heating step in which the composite is raised from ambient temperature to a temperature of from 250 to 450° C. at a rate of temperature increase less than 1000° C. per hour, and subjecting the resulting heat treated composite to a solution treating step.