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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.

The paper points out to the differences of the First order theory and Second order theory and of the significance in practical calculations. The paper presents theoretical foundations and expressions of calculations of impacts on the stability of structure, that is, review of the Second order theory in a bridge with members semi-rigid connections in joints. In the real structures in general and the especially in the prefabricated structures the connection of members in the nodes can be partially rigid which can be very significant for the changes in tension and deformation. If the influence of the normal forces is significant and the structure is slender then it is necessary to carry out a calculation according to the Second order theory because the balance between internal and external forces really established on the deformed configuration and displacements in strict formation are also unreal. The importance and significance of the calculations and distribution of impact according to the Second order theory were presented in numerical examples as well as the calculation of critical load as well as the buckling length of members with semi-rigid connections in joint.

Actual vapor pressure (VP) is an important parameter that is used in many evapotranspiration equations. However, vapor pressure is difficult to measure accurately. In the humid climate, the actual vapor pressure can be derived from minimum air temperature. The objectives of this study were: first, to estimate errors that can arise if VP data are not available and have to be estimated; second, to compare the Priestley-Taylor ET0 values computed under various levels of VP data availability; and third, to evaluate the reliability of Priestley-Taylor equation as compared to the FAO-56 Penman-Monteith method. The following main conclusions can be drawn: Estimated VP values generally were in closest agreement with measured VP values. The measurements of air humidity at humid locations are not indispensable for estimating reference evapotranspiration. The Priestley-Taylor method (with measured or estimated VP) provides the very good agreement with the evapotranspiration obtained by the FAO-56 Penman-Monteith method except windless locations.

In modern timber structures a large number of beams are loaded with bending Contemporary engineering practice has shown that the effect of tangential stress and deflection of beams are not controlled during the design of this kind of beams. This could produce negative consequences in structure behavior during the exploitation. Using optimal design procedure in this article, the member is designed for bending in two planes. The following criteria must be observed: normal bending stress, shear stress and maximal deflection.

In the modern civil engineering design, especially in the field of machine foundations, the dynamic actions in the form of the impulse load that is short-term, high intensity loads are very frequent. When an acting force during a short time interval remains constant, the impulse is of a rectangular form, as opposed to the trapezoid, triangular, parabolic and sinusoid form, with defined time of increase and decrease of the load. This paper considers the influence of the form of the impact impulse load on the dynamic response of the foundation structure, without changing the remaining parameters.

New trends in technological systems in terms of processing processes have also placed new demands on the measuring technique. The application of conventional metrology systems and the procedures that support them have become a limiting factor in terms of flexibility and measurement accuracy. The main problem problem is the rapid metrological identification of complex metrological tasks, such as, for example, shape and position tolerances for parts of medium and high accuracy. In addition to metrological identification, the problem is also the connection of metrological databases, which has a direct impact on the obtain results accuracy. In order to solve these problems, this paper presents an approach to modeling a digital measuring twin based on a numerically controlled measuring machine. In a broader sense, the developed model integrates machine and computer technologies and was applied in the field of metrology, that is, the examination of achieved tolerances on machine parts using CMM. The benefits are reflected in the fact that it is not necessary to construct expensive prototypes, it saves time, avoids collision and the most important thing in the world of industry, it saves money.

The flow field phenomena that occur as a result of thrust vector control (TVC) system activity on a missile with lateral jets are very complex and influence all other components of the missile. Influence is more significant when TVC is generating commands, when jets are asymmetrically directed. The main goal of these study was to determine the influence of of the hot rocket motor's combustion products on the basis of the CFD model proven with the cold-jet simulation. Based on obtained experimental aerodynamic coefficients for the cold-jet simulation the preliminary aerodynamic CFD model was designed. Three-dimensional Reynolds averaged Navier-Stokes numerical aerodynamic and hot-jet simulations were carried out to predict the aerodynamic loads of the missile based on the finite volume method. The study resulted in the definition of a methodology for the investigation of the jet reaction effects in a wind tunnel. A method for determining of the TVC system interference on the aerodynamic characteristics, as a basic prerequisite for structural, stability and performance analysis, was proposed. Mutual verification and validation process was carried out through experiment and proper application of the commercial CFD software code for calculation aerodynamic effects of the hot gases lateral jets on the performance of a guided missile. Experimental and computational results of the pitching moment coefficients are presented and agreed well with.

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.

This paper presents a theoretical investigation of elastic and inelastic buckling of thin-walled beam with initial imperfections. The main aim of this paper is to show that the fracture of beams varies from brittle to extremely ductile depending on the imperfections. Elastic solution for estimation of initial imperfections against the limit load capacity in the elastic range is well known. However, the elastic solution can be applied only to the line of limit load capacity. Examination of the limit load capacity of structure is very complicate problem of material non-linearity, because this problem must includes the plastic mechanism of failure. In this paper the limit load capacity of beam is analyzed using the reological-dynamical analogy (RDA) [4]. In order to demonstrate the ability of RDA, the comparison with experimental and numerical results of one steel beam from Ref [1] by Murray, is done.

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.

This paper shows contemporary issues related to unfavorable effects of concrete alkali-aggregate reaction (AAR) on concrete bridge structures (CBS). Although AAR unfavorable effects on CBS were identified in 1930s, it was much later that AAR was acknowledged as one of the most pronounced deterioration processes in concrete that results in damages to concrete structures. There are two basic forms of AAR: alkali-silica reaction (ASR) and alkali-carbonate reaction (ACR). Compared to ACR, ASR is more prominent, especially in certain geographic parts of the world. Damages to concrete caused by the ASR have negative effect primarily on usability and durability of CBS, what is followed by the decrease in load bearing capacity of structural components and reliability of the whole structure, shortening of service life (SL) and costly repairs. For CBS, simultaneous occurrence of ASR and other degradation processes in concrete, such as those caused by the presence of moisture, water, temperature variations and use of deicing salt during winter, are especially damaging. Based on review of the most relevant literature, this paper is focused on mechanisms and mechanisms factors of the ASR, related contemporary research and reliability design guidelines for CBS that are based on prevention of the initiation and development of ASR.

Replacing or upgrading software packages requires a detailed analysis and testing. This is especially important for software modules that are part of the production process. Machining of free-form surfaces always requires using of a five-axis milling machine. Tool path post-processing for these machines always attracts special attention. The most important part of the postprocessor is implemented IKS (Inverse Kinematic Solver). Implemented IKS in the postprocessor must accurately describe the kinematics of milling machine in the production plant. Military Technical Institute performed parallel testing of two postprocessing modules of CAD/CAM system Siemens PLM NX: and old GPM (Graphics Postprocessor Module and a new module MOM (Manufacturing Output Manager). Complete analysis was sent to the NX support center and application engineers confirmed that the old and new postprocessors do not behave identically. The paper describes in detail the analysis and explains the solution of the presented problem.

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.

This paper presents the design of the steel water tower with spherical water tank height H = 44m. Spherical tank is located at the top of the steel tubular column, with diameter F = 128cm. The construction of the water tower was modeled using the ABAQUS software package, to give a realistic picture of the stress-strain states in all points of the tank shell and the tubular column. Analysis of the load of construction was carried out based on European standards, with special attention to the influence of the earthquake on the spherical tank.

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.

Program Manufuture Vision 2020 was developed as a Strategic Research Agenda and Road Maps, as a basis for EU research within Horizon 2020. This document is a response to the challenges of global competitiveness and sustainable development, seeking to EU industry as many turns, innovative production based to create additional value for the customer and the use of ICT technologies. Somewhat later also made public a document - Manufuture a strategic research agenda '2020-2030' and Roadmaps, to support structural changes industry, which should be orjetisana high automation, effectiveness and flexibility. Technological developments driven by technological advancement potential in a process chain, from raw materials to the exclusion of the product from use, through continuous improvement of additional value for the customer. These documents Program Manufacture represent a proactive action and collaborative research for 40 industrial sectors. Key areas of this research are: the factory of the future - the Factory of the Future (FOF), and digital production - Digital Manufacturing as well as digital quality.

Wind tunnel cold flow tests were conducted, using the convergentdivergent two-dimensional nozzle, with a tab as the obstacle at the nozzle exit area. This geometry is applied in thrust vector control systems for missiles. During the variation of some of the most influential geometry parameters in the flow domain, the nozzle surface pressure distribution is measured, and the Schlieren photos are recorded. Using those experimental results, CFD modeling is conducted, and four turbulence models are compared. After comparison, the advantage is given to transitional k-w turbulent models, regarding results concurrence and computational cost. These results can be used as a guideline for further three-dimensional CFD researches of real thrust vector control geometries, and also for a better understanding of flow processes in those applications.

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.

Five axis milling technology has been in use nearly 25 years in VTI Belgrade. Primarily it is used in the production process of wind tunnel models. For generating tool path and the post-processing paths, used postprocessor generated on Siemens PLM NX. Producer of CAD/CAM software, in newer versions, the old concept of post processing GPM (Graphics Postprocessor Module) replaced it with a new, improved, module MOM (Manufacturing Output Manager). The VTI are identified in the CNC code for five axes milling, generated using the MOM module, some errors. Product support application engineer confirmed all the allegations VTI. This was the reason for the development of its own postprocessor for five axes milling machines with double rotating head. The paper gives a detailed overview of the development based on the kinematic model of the five-axes milling machine in VTI Belgrade.