Military Technical Institute Belgrade (Serbian Latin: Vojnotehnički Institut Beograd; abbr. VTI) is a major Serbian aircraft and weapons designer, headquartered in Belgrade, Serbia and governed by the Serbian Ministry of Defence. VTI is a top-level military scientific research institution in Serbia, dealing with research and development (R&D) of new weaponry and military equipment as well as with upgrade of the inventory for all three services of the Army: Land Forces, Air Force and River flotilla.
ABSTRACT While rice husk silica has been explored as a low‐cost filler for conventional epoxies, the synergistic effect of complementary organosilanes—an epoxy‐functional GLYMO and an amino‐functional APTMS—on biogenic silica tailored for a partially bio‐based epoxy matrix has not been systematically investigated. Here, b‐Epoxy composites were prepared in three variants (unmodified b‐Epoxy/SiO 2 , amino‐functionalized b‐Epoxy/SiO 2 ‐AM, and epoxy‐functionalized b‐Epoxy/SiO 2 ‐EP) and characterized through a concerted FTIR/NMR/SEM/TEM/DMTA analytical sequence. Three advances emerge: (i) systematic benchmarking of GLYMO versus APTMS chemistry on the same biosilica source; (ii) identification of 5 wt% as the optimal filler loading for simultaneous tensile and stiffness reinforcement; and (iii) direct correlation of interfacial chemistry with thermomechanical stability. The GLYMO‐functionalized b‐Epoxy/SiO 2 ‐EP system delivered the most balanced performance—tensile strength ≈58 MPa at 5 wt% (significantly higher than 52 MPa for b‐Epoxy/SiO 2 ‐AM, and 46 MPa for the unmodified composite), Young's modulus up to ≈740 MPa, microhardness of 395 MPa (vs. 175 MPa for the neat bio‐matrix), and a T g shift from 96.17°C to 108°C–110°C. The same bio‐resin platform was extended to alkali‐treated flax‐fabric laminates (flexural strength 146.4 MPa) and validated by a cradle‐to‐functionalized‐silica E‐factor of 3.19–4.12 kg/kg—one‐to‐two orders of magnitude lower than conventional fumed silica—establishing silane‐functionalized biosilica as a tunable, circular route to high‐performance bio‐based composites.
Chromium-molybdenum steel group SA 387 Gr. 91 is the latest from the generation of steels designed to operate under high temperature, elevated pressure, and corrosive environments. The most important characteristics of this steel, compared to previously used steels for high-temperature applications, are its high yield strength, good corrosion resistance, significant oxidation resistance, and excellent creep resistance. The latter property enables engineers to design components with significantly thinner walls compared to other types of steels (material savings). In addition to its good mechanical properties at elevated temperatures, weldability is also important for this steel and, in general, for the entire group of such steels. It is crucial that welding does not affect their resistance to corrosion, creep, or their overall mechanical properties, thus extending the remaining lifespan of the structure, which, together with material savings, fits into the concept of sustainable development. This paper will present the characteristics of the behavior of Cr-Mo steels during welding, based on experimental testing (macro and microstructural examination of the welded joint, technological tests – bend testing, hardness testing).
This paper presents a finite element modeling procedure to determine of crack growth behaviour of butt welded joints under the subject of load for mode I. This paper presents a computation procedure to determine the ratio of fatigue crack growth in butt welded plates for mode I fracture mechanics loading conditions. The presence of residual stresses in welded structures can significantly affect the material’s resistance to fatigue under cyclic loading. The presence of tensile residual stresses adversely affects the fatigue crack growth rate increased it. Change of microstructure and hardening material as a result of the welding process also has a negative impact on the growth of the crack. Accurate prediction and reliable assessment of the residual stress are important for the structural integrity and residual life assessment of welded parts design. Although there are several techniques for the determination of residual stresses, the finite element method (FEM) is one of the most convenient and useful. This paper presents a finite element modeling procedure to determine of crack growth behaviour of butt welded joints under tensile load for mode I. Keywords: Welding, Residual stress, Residual life, Crack growth, FEM, Butt welded joint
In this paper, an optimization method for a rocket-refurbishing project is presented. While considering the technical solution the level of reconstruction needs to be decided, from which refurbishment costs are dependent, as well as eventual increase of rocket performances. The idea of rocket motor refurbishment is to extend the life cycle and eventually increase performances for a minimum of an investment. The design shown in this paper is supposed to be an economic solution for the M63 "PLAMEN" 128 mm caliber artillery rocket, resulting in the increase in performance, without significant changes to the construction.
The research presented in this paper focuses on take-off and landing performance of a single pusher-propelled Tactical unmanned aerial vehicle. The analysis presented includes flight test verification of estimated UAV characteristics. The study proposes a possible approximated method for estimating UAV characteristics. Flight test results have been conducted to verify the estimated results, and the calculated and measured results show good agreement.
