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Shekhar H.,Explosives Research & Development Laboratory
Central European Journal of Energetic Materials | Year: 2013

The velocity of detonation (VOD) of polyurethane (PU) based binary explosive compositions is assessed by Kamlet's method and compared with experimental results for a few compositions. These compositions are used as booster compositions for the initiation of main charges and the velocity of detonation is determined empirically for compositions with explosives like RDX, HMX, TATB, FOX-7, CL-20. For some of the compositions, the VOD was determined experimentally and found to match the predicted values. For RDX/PU (95/5) explosive composition, the experimental and estimated VODs at 1.66g/cm3 bulk charge density, are 8211 and 8224 m/s respectively. For CL-20/PU (95/5) composition, at a charge density of 1.82 g/cm3, the calculated VOD was 8775 m/s against the experimental value of 8943 m/s. The applicability of Kamlet's method for the prediction of the VOD for 95/5 Explosive/PU compositions was also established. These findings contradict an earlier hypothesis concerning the weight average estimation of Kamlet's parameter Φ and establish closer estimates of the VOD using the weight average assessment of the parameters 'N', 'M' and 'Q'. Source


Shekhar H.,Explosives Research & Development Laboratory
Defence Science Journal | Year: 2011

Dual-thrust mode is adopted in solid propellant rocket propulsion through tailoring of burning area, nozzle, rocket motor chamber, propellant type, multiple propellant blocks. In the present study, mathematical formulation has been evolved for generation of burning surface area with web burnt for a simple central blind hole in a solid cylindrical propellant geometry with proper partial inhibition on external and lateral surfaces. The burn-back equation has been validated by static firing and parametric study was conducted to understand effect of various control geometrical parameters. The system is utilised for high volumetric loading, single propellant, single composition, single-chamber, single nozzle dual-thrust mode of burning profiles in rocket application. © 2011, DESIDOC. Source


Shekhar H.,Explosives Research & Development Laboratory
Central European Journal of Energetic Materials | Year: 2012

Linear variation of burning rate with pressure (burning rate, r = H + Sp), referred in the literature as Muraour's law, is adopted as the burning rate law for solid rocket propellants. The two constants 'H' and 'S' are the vacuum burning rate and the slope of burning rate variation, respectively. The conventional power law of the burning rate, r = apn, is also analyzed and its practical, anomalous behaviour such as zero burning rate at zero pressure, the reduction in pressure sensitivity of the burning rate at higher pressures, the lower burning rate for the high pressure index in typical situations etc, are explained with illustrations. Like the conventional power law of burning rate, the linear burning rate law considered here is also empirical but mathematically simpler than the power law. Using burning rate and pressure data from various literature sources similar regression coefficients are observed for the conventional power law as well as for the alternative linear burning rate law. The mathematical concept for the evolution of the pressure time profile with the considered linear burning rate law is developed and validated practically with the actual firing of rocket propellants as uninhibited, tubular configurations in a ballistic evaluation motor (BEM). Close matching of the firing curve, predicted by the conventional power law and by the proposed linear burning rate law validates the mathematical formulation. The considered linear burning rate law is simple, easy to apply and gives a better representation of the burning rate behaviour of solid rocket propellants. Source


Shekhar H.,Explosives Research & Development Laboratory
Defence Science Journal | Year: 2012

Mechanical property evaluation of composite solid rocket propellants is used as a quick quality control tool for propellant development and production. However, stress-strain curves from uni-axial tensile testing can be utilised to assess the shelf-life of propellants also. Composite propellants (CP) of two varieties cartridge-loaded (CLCP) and case-bonded (CBCP) are utilized in rocket and missile applications. Both classes of propellants were evaluated for mechanical properties namely tensile strength, modulus and percentage elongation using specimens conforming to ASTM D638 type IV at different ageing time. Both classes of propellants show almost identical variation in various mechanical properties with time. Tensile strength increases with time for both classes of propellants and percentage elongation reduces. Initial modulus is also found to decrease with time. Tensile strength is taken as degradation criteria and it is observed that CLCP has slower degradation rate than CBCP. This is because of two facts-(i) higher initial tensile strength of CLCP (1.39 MPa) compared to CBCP (0.665 MPa) and (ii) lower degradation rate of CLCP (0.0014 MPa/day) with respect to CBCP (0.0025 MPa/day). For the studied composite propellants, a degradation criterion in the form of percentage change in tensile strength is evaluated and shelf life for different degradation criteria is tabulated for quick reference. © 2012, DESIDOC. Source


Shekhar H.,Explosives Research & Development Laboratory
Defence Science Journal | Year: 2011

Mechanical properties of solid rocket propellants are dependent on temperature. Any change in temperature brings significant change in the tensile strength, percentage elongation, and elastic modulus of the propellant. Different classes of operational solid rocket propellants namely extruded double-base propellants, composite, extruded composite and nitrarte ester polyester propellants were evaluated at different temperatures in the operating range of the rockets and missiles preferably in the range of-50 °C to +55 °C It was observed that for each class of propellant, as temperature reduces, propellant becomes hard. This is depicted by increase in elastic modulus and tensile strength of the material. However, trend of percentage elongation is not very uniform. Extruded double-base propellants show less percentage elongation (around 1 per cent) at reduced temperature (-50 °C) probably due to brittleness. So is the trend with case-bonded composite propellants. However, reverse trend is exhibited by cartridge-loaded composite propellants and nitrate ester polyester propellants. Such propellants show higher percentage elongation (6 per cent for CLCP and 35 per cent for NEPE) at reduced temperature (-50 °C). This makes such propellants tough and more area under stress-strain curve at reduced temperature is observed. © 2011, DESIDOC. Source

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