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Additive manufacturing, as a production technology and a scientific field, offers a lot of potential for new research, attracts the attention and interest of manufacturing companies and the academic community. With a new approach in product design, a digital connection chain, and the possibility of producing final products with complex configurations, it has significant advantages in relation to conventional production. However, the initial investment and production costs make this technology still inaccessible to a certain number of users, with the tendency for this to change. In this sense, great attention has been paid to additive manufacturing planning, cost analysis and the possibility of optimizing structural and process parameters of production and processes. This paper is intended to explain, in a clear and concise manner, the basic assumptions of the technology, its advantages and certain disadvantages, ongoing and future trends in development as well as current areas of research (cost estimation, multi criteria decision making (MCDM), topology optimization) and applied methods and concepts. The authors believe that this paper will provide additional help in process planning for additive manufacturing as well as promote the necessity for introducing and application of different optimization techniques when designing technology for additive manufacturing.

At the beginning of the 21st century, integrated management systems (IMS) are the key for quality management, in order to meet customer needs, restructuring the organization, reducing costs, increasing productivity and profit, and the long-term sustainable development of the organization. ISO 9001 forms the backbone of an integrated management system, as it establishes a systematic approach keeping in mind risk in business. Risk-based thinking is already a part of the process approach. This approach establishes a link between the likelihood of a particular danger and the seriousness of the consequences. The paper presents the principles of risk management that are embedded in the integrated quality management system at the Military Technical Institute. The specificity of the development of armament and military equipment requires an integrated approach to risk management. The presented structure of the IMS enables a simple extension with the requirements of the new standards that are planned for implementation in the future.

Rocket motor propellant grain, cast or bonded into the motor chamber or solid coating, is exposed to various loads during its service life. Rocket propellant is a viscoelastic material, whose mechanical properties strongly depend on temperature and strain rate. Application of cyclic loads, primarily thermal, onto a rocket motor on the field stock, may cause an undesirable mechanical damage of the grain. Over time, after long storage, it may grow up and lead to the grain failure. One of the ways for evaluation of this phenomenon is to determine a cumulative damage law. In this example, this law has been evaluated for hydroxy terminated polybutadiene (HTPB) composite rocket propellant by exposing a number of specimens to different long term stress levels. Using this law, it is possible to calculate a probability of failure and time distribution of the structural reliability of the grain in order to determine the useful life. Besides, the analysis has shown that there is a possible correlation between tensile strength of the propellant and the cumulative damage law. This fact can be used instead of carrying a longterm experiment for the exact determination of the law.

Dispersion of the impact points of the unguided rockets is a consequence of disturbances, such as thrust misalignments, rocket asymmetry, manufactoring inacuracy, etc. Influence of some disturbances are most significant in the initial phase of flight when the rocket leaves the launcher due to the small velocity. This influence is minimized by rotation of the rockets in the launcher tube which in practice is realized by the guide pin connected to the rocket and groove in the launcher tube or by canted nozzles. Also the rotation of the rocket in the launching tube and in flight can be realized by canted fins foled in the nozzle when the rocket is in the launcher tube. These fins are deployed when the rocket leaves the tube and creates rocket rotation in free flight. The rolling moments of the rocket in the launcher tube and during free flight are calculated by CFD simulation. The CFD simulation is also used for calculation of the fin hinge moment generated by exaust gases from rocket motor which is required for deployement of the fins when the rocket leaves the launcher tube. The roll rate required for minimization of the rocket dispersions and roll rate in the launcher tube for various cant angle of the fins are calculated by 6DOF numerical simulation. The results of simulation are used to select the best value of the fins cant angle.

The main propulsive group of anti-armor guided missile is reinforced by additional propulsive group with the aim to increase the range. Final concept of the propulsion has been adopted after consideration of several proposed solutions. Two additional motors are made and they are currently under development. The first results were obtained, and the additional motors at this stage are refined through the static tests as well as through the correction of the composition and the design of the propellant grains. An overview of the common procedure is described on the way to winning the final solution for rocket propulsion.

The paper discusses the influence of ignition mixture granulation onto the regime of rocket motor ignition. Igniter tests were performed in manometric bomb and pressure distribution was measured. In each test different granulations of the same mixture in powder form were tested. After that, two different ignition mixture compositions in the form of pressed tablets were tested. Total masses of ignition mixtures were equal in all the tests. In the first series of the igniter tests, very carefully chosen different granulation of the powder was used in each test, with the particles in a narrow range. From one to another test, only the granulation of the mixture was changed. The purpose was to determine if there exists an influence of the mixture granulation onto the pressure gradient and thus also onto the regime of the rocket motor ignition. It turned out, surprisingly, that there were no visible differences in the regimes of pressure increase due to the different granulation of the ignition mixtures. In another series of tests the mixture was prepared in the form of pressed tablets, with various sizes from test to test. Two different mixtures were tested, and the mass of each single charge of the igniter was the same as in the first series of tests. It is shown that the form of the pressed tablets, as well as their composition, may considerably affect the mode of rocket motor ignition.

A case-bonded solid propellant rocket grain is subjected to many stress-inducing loads during the service life, due to temperature, extended polymerization, transportation, vibration, acceleration, aerodynamic heating etc. and finally due to the operating pressure in the rocket motor. Composite propellant is a viscoelastic material whose mechanical properties highly depend on temperature and strain rate and sometimes may vary in the range of use of rocket motors for several orders of magnitude. Relationships between stresses and strains are much more complex than for the elastic material. Therefore, the stress and strain analysis and estimation of safety factor under the action of each individual load is quite complex and sometimes impossible. An even greater problem occurs when multiple different types of loads act simultaneously. An extreme case occurs in the moment of rocket motor ignition. Then, the very fast load acts due to the pressure, at which the propellant tensile strength is high. At the same time, the very slow thermal load acts on the grain, and in these conditions the propellant tensile strength is low. The vector addition of the stresses and strains due to different loads is not possible. It is also not possible to define the equivalent or resultant values of tensile strength and allowable strain. The principle of adding the current damage is applied here, similar to the model of cumulative damage. In addition, due to the large variations in mechanical properties of the rocket propellant, it is necessary to apply the methods of mathematical statistics for assessing the propellant grain reliability and service life.

An artillery projectile in flight produces a low pressure area immediately behind the projectile which creates a force called base drag which lessens the velocity of the projectile. It is known that theoretically this base resistance can be reduced or even eliminated by allowing a stream of hot gas to flow out of the base surface of the projectile in a suitable manner. The effect produced by this stream of hot gas is called base-bleed effect. The internal ballistic calculation of existing base bleed configuration is presented in the paper. A numerical simulation of axisymmetric body projectiles was obtained with the Reynolds Averaged Navier-Stokes (RANS) computational fluid dynamics software (CFD). Also, two turbulence models were tested and validated with the semi empirical prediction. The realizable k-ɛ turbulence model was chosen for calculation of aerodynamic drag of the projectile with and without base bleed effect. Computed result show a drag reduction with base bleed of about 12% in supersonic flow regime.

In order to achieve very strong inter-ballistic requirements, a unusual free standing rocket motor propellant grain was designed, with variable channel diameter. Due to its very high length, it was expected for the grain to be exposed to dangerous combination of different loads during the design phase. Structural analysis of viscoelastic propellant grain is always very complex and it differs substantially from an elastic analysis, because the propellant mechanical properties depend on temperature and strain rate. The most complex case in the analysis occurs when multiple loads operate simultaneously. In this paper, the structural analysis has been done during the initial period of rocket flight, when the grain is under very fast load due to acceleration and at the same time under a slow load due to surface pressure, created as a result of temperature dilatation. In the absence of data on mechanical properties of the new propellant composition, the properties over the whole time-temperature range were estimated comparing by a similar composition that have been completely tested earlier. Using finite element method (ANSYS program) two different design solutions were examined and the more reliable one was adopted.

Uniaxial tensile tests of different composite solid rocket propellant compositions, based on hydroxyl-terminated polybutadiene (HTPB), have shown that mechanical properties extensively change after curing, up to 100% of their initial values, during the first few months. After that period, they stabilize and start to return slowly in the opposite direction. Careful measurements of these features are necessary in order to control the production quality of the propellant and for a comparison of different propellant compositions or batches. Furthermore, time distributions of the mechanical properties in the initial period after production and short-time aging should not be neglected, because they strongly affect the propellant grain structural analysis and a correct estimation of rocket motor reliability.

During the design and development of a solid rocket motor, intensive irregular burning appeared in the area of high initial temperatures. The cylindrical propellant grain was designed for approximately neutral burning, with a hollow tube and both burning ends as well as with the outer surface inhibited. A simple grain configuration and a propellant with plateau burning were selected, and the operating pressure of the rocket motor was chosen to be in the area of the plateau. Unfortunately, the special conditions of the gas flow through the propellant grain port, caused by the central tube passing through the grain channel, as well as high propellant temperature sensitivity, led to an increased turbulence and a very strong irregular burning occurrence at high temperatures (+50oC). In these conditions the combustion went out of the plateau regime and the pressure exponent rapidly grew up. The problem was solved without changing the double-based propellant composition. The high burning surface to nozzle throat area ratio was decreased below the critical threshold appearance of irregular burning, without significantly affecting the motor performances. The rocket motor nozzle and the propellant grain were redesigned. Despite the limited possibilities of changing the propellant grain geometry, an uncommon solution was found, opening a part of the inhibitor at the outer surface of the grain.