The geometric burning law of gun propellants is widely used in computer codes used for the simulations of the internal ballistics of guns. However, the results of closed vessel tests prove that the burning process of some propellants deviates from the geometric law. Validation of the hypothesis that observed deviations can be attributed to the cracking of propellant grains was the aim of this work. In order to verify the hypothesis, three types of gun propellants were chosen with considerably differing mechanical strengths: a single-base propellant, a double-base propellant, and a composite propellant. The mechanical properties of the gun propellants were tested using a quasi-static compression method with strain rate values of the order of 0.001 s⁻¹ and the Split Hopkinson Pressure Bar technique with the strain rate in the range of 1000–6000 s⁻¹. The mechanical responses of the propellants were assessed on the basis of the true stress–strain curves obtained and from the point of view of the occurrence of cracks in the propellant grains specimens. Moreover, closed vessel tests were performed to determine experimental shape functions for the considered gun propellants. Juxtaposition of the stress‒strain curves with the experimental shape functions proved that the observed deviations from the geometrical burning law can be attributed mainly to the cracking of propellant grains. The results obtained showed that the rheological properties of propellants are important not only from the point of view of logistical issues but also for the properly controlled burning process of propellants during the shot.

Numerical and experimental investigations of armament systems are an important part of modern design processes. The presented paper reports problems that were encountered on the theoretical analysis of the performance of 35 mm anti-aircraft cannon and the way in which they were solved. The first problem concerns the application of results of closed vessel tests of used propellant in interior ballistics simulations. The use of a nonstandard form of the gas generation rate equation solved this problem. The second problem concerned the assessment of projectile–barrel interaction. The barrel resistance was estimated making use of finite element analysis. The third problem arose from the need to determine the heat transfer from propellant gases to the barrel. The employed formula for the heat exchange coefficient and 2D modelling of the heat conduction in the barrel provided the solution. Selected elements of the theoretical model were validated by shooting range experiments and data provided by the ammunition producer. Using the considered approach, crucial ballistic parameters (maximum propellant gas pressure and muzzle velocity) were estimated with an error of less than 6.0%, without application of additional fitting coefficients. The numerical estimation of the barrel external surface temperature provided a relative discrepancy with the experimental data lower than 6% and enabled the estimation of the critical burst length, equal to 14 shots.

The most widely used experimental method for determination of dynamic characteristics of gun propellant combustion is burning a specific amount of a propellant in a closed chamber (vessel) and measuring the resulting pressure versus time profile. The aim of this work is to conduct experimental investigations at different conditions of propellant ignition, which permit to verify the view on legitimacy of standard conditions of closed-vessel tests. This paper considers first of all the influence of conditions of propellant ignition during closed-vessel tests on possible deviations in determination of the burning rate. For this purpose, experimental tests of a fine-grained, single-base propellant are carried out in a conventional closed vessel and a micro-closed vessel, applying different ignition methods for the same loading density. The results of experimental tests and calculations show significant influence of the ignition system type used on determined values of the burning rate and other dynamic characteristics of propellant combustion, such as dynamic vivacity, absolute quickness, and relative quickness.

The paper presents the results of computer simulations of unidentified transient heat transfer in the wall of a 35 mm cannon barrel for a single shot and for a sequence of seven shots with a subsequent firing break. The cannon barrel was made of 32CrMoV12-28 steel. For the phenomenon modelling, it was assumed that the material of the barrel wall is uniform and the barrel’s inner surface does not feature a protective coating of galvanic chrome or a nitrided casing. Calculations were performed for two input data variants: (i) for constant values of thermophysical parameters and (ii) for a temperature-dependent specific heat. The barrel with an overall length of 3150 mm was divided into 6 zones. On the inner surface of the barrel in each zone there were assumed various values of heat flux density expressed as rectangular functions in the range from 0 to 10 ms (with the start of ti of the function shifted in the subsequent zones). The calculation time for a single shot was assumed as equal to 100 ms. The calculations were performed with a finite element method in COSMOS/M software.

This paper presents the method of determining the burning rate of fine-grained propellants based on the results of closed vessel tests. It is shown that in the case of fine-grained propellants, the standard methods of determining the burning rate fail. There are two reasons for this: imperfections of the grain shapes and the prolonged process of ignition due to a more developed surface than that of coarse grains at the same mass of the propellant. The value of the exponent in the burning law is estimated by the use of the so-called experimental form–function. The upper and lower limits of the value of the coefficient in the burning law are estimated. The accuracy of the proposed method is analyzed. Its validity is assessed by comparing the results of closed vessel tests analysis with accessible literature data.