Silica-Based Composites with Enhanced Rheological Properties Thanks to a Nanosized Graphite Functionalized with Serinol Pyrrole

Silica-based rubber composites have tremendous importance, as they allow the reduction in hysteresis in demanding dynamic-mechanical applications such as tire compounds and hence have a lower environmental impact. However, they also present drawbacks such as poor rheological behavior. In this work, an innovative silica-based hybrid filler system was developed, obtaining a rubber composite with an improved set of properties. A nanosized high surface area graphite (HSAG) was functionalized with 2-(2,5-dimethyl-1H-pyrrol-1-yl)propane-1,3-diol, serinol pyrrole (SP), through a simple process characterized by a high carbon efficiency. The HSAG-SP adduct, with about nine parts of SP per hundred parts of carbon filler, was used to form a hybrid filler system with silica. An elastomeric composite, with poly(styrene-co-butadiene) from anionic polymerization and poly(1,4-cis-isoprene) from Hevea brasiliensis was prepared with 50 parts of silica, which was replaced in a minor amount (15%) by either pristine HSAG or HSAG-SP. The best set of composite properties was obtained with HSAG-SP: the same dynamic rigidity and hysteresis and tensile properties of the silica-based material and appreciably better rheological properties, particularly in terms of flowability. This work paves the way for a new generation of silica-based composites, with improved properties, based on a hybrid filler system with a nanosized edge functionalized graphite.

NEW MODEL OF MACHINE FOR PROCESSING SURFACES OF LARGE-SIZED PARTS HAVING THE SHAPE OF BODIES OF ROTATION

During long-term operation of rotating parts of technological machines, which include tires and support rollers of rotary kilns, rolling surfaces lose their shape accuracy and quality. Built-in machine modules are used to restore large-sized parts in the form of bodies of revolution. Such repair work requires special technological approaches and careful preparation before starting. It is necessary to take into account the real geometry of the surface of the part being repaired, which may have shape errors in the longitudinal and cross section due to wear, and conduct a preliminary analysis of the state of the part. It is also necessary to take into account the large dimensions and weight of the workpiece, and the inconsistent position of its axis during rotation. The technologies used and mobile machines for carrying out these repairs still have drawbacks that do not allow for efficient processing and affect the accuracy and quality of the resulting surface. The solution to this problem can be the development of new models of machine tools for processing large-sized bodies of revolution, the design of which will be more perfect in comparison with the previous models. To achieve this goal, it is necessary to study and analyze the existing domestic and foreign models of mobile machines and the principle of their operation. The proposed new machine model should have sufficient static and dynamic rigidity, as well as have a module responsible for adaptive control of the machining process, which will compensate for unstable positioning of parts during machining.

Experimental Dynamic Rigidity of an Elastic Coupling with Bolts

The paper presents an elastic coupling with bolts and intermediary non-metallic elements, which allows for radial and axial deviation and can absorb shocks and torsional vibrations. The designed bolts have a particular shape of a circular area of a length equal to the width of the non-metallic element, a cylindrical area larger than the diameter of the cylindrical groove where the non-metallic elements are mounted, and a cylindrical area smaller than the threaded area to avoid stress concentrators and bolt breakage. The coupling represents a symmetrical piece, having two planes of symmetry. Therefore, the study of such a mechanical system can be considerably simplified considering the design and description of the repeating elements. The novelty of this coupling consists in the existence of an intermediate disc between two half-couplings (driving and driven half-coupling). The non-metallic elements with different shapes are made of different types of rubber, mounted on cylindrical bolts fixed by the driving half-coupling, transmitting the motion in both directions.

Structural dynamics of a 3 DOF parallel kinematic machine

Milling is an intrinsically interrupted cutting operation; therefore, vibrations occur. There are both self-excited (chatter) and forced vibration. Vibrations in milling appear due to the lack of dynamic stiffness of some components in the machine tool-tool-workpiece system. If the vibrations are excessive, the machine stability is negatively affected. In this paper a parallel kinematic machine is modelled and structurally analyzed, considering vibrational parameters (mass, inertia, stiffness, and damping). Theoretical results are used to verify the model. The proposed model provides an effective guide to design milling machines with the best structural arrangement (architecture) and enhancing performance. The value of this finding is in answering the research question: ""Should the machine tool-tool-workpiece system be kept decoupled to mitigate the vibration generated during a cutting operation?"". Two approaches were proposed to determine which option (coupled or decoupled bases) provides greater dynamic rigidity. The evidence shows that the decoupled base proposal maintains a cutting operation without displacement peaks due to greater operation times and better damping response.

Research and improvement of methods of testing machines for geometric and kinematic accuracy

Purpose. To analyze and check for adequacy the known calculation formulas in determining the geometric and kinematic accuracy, statistical and dynamic rigidity and testing the machine for technological reliability. To carry out comparative calculations to simplify the methodology of complex tests of metal-cutting machines of the universal group. To select and improve the measuring equipment during the complex tests of the milling machine. Methodology. The research is based on the use of analytical methods for calculating the static rigidity coefficient, additional calculation of the measuring instrument design due to the gear ratio, the angle of rotation of the lever and the theoretical error of the displacement mechanism based on the known probability distribution theorem. Findings. The formulas of researches of the coefficient of static rigidity, the mechanism of the measuring device, the angle of rotation of the lever, the theoretical error of the mechanism of movement and the density of probability of distribution of the angle of the lever mechanism of the indicator of tangent type has been obtained. Originality. The research has been carried out and the parametric relationship between the static rigidity coefficient in the design of the spindle assembly of the vertical milling machine with the error of the calculations of the design, the departure of the spindle cone and the location between the supports has been established. The values and functional dependences of the amplitude of oscillations on the maximum allowable spindle speeds and feed rates at which the surface roughness of the workpiece reaches the specified geometric limits has been obtained. It is experimentally confirmed that the parameters of the system of pre-planned repairs are directly related to the reliability of the machine. The resource on the accuracy of the machine determines the need for overhaul, and the repair period depends on the service life of parts and elements of the machine. The actual service life should be a multiple of the repair period, as the restoration of the part is planned during the current repair. Practical value. The practical achievement of the obtained results is to confirm the adequacy of the known calculation formulas in determining the geometric and kinematic accuracy, statistical and dynamic rigidity and testing the machine for technological reliability. On the basis of the received analytical and settlement data was made the simplified complex technique of test of the metal-cutting machine during the: testing the machine at idle; testing of the machine when working under load; testing of the machine for geometric and kinematic accuracy; determination of statistical and dynamic rigidity; research of vibration-resistant vertical milling machine; testing of the machine for technological reliability.

INCREASING THE DYNAMIC RIGIDITY OF BORING BARS

The article presents the design of an anti–vibration holder, the use of which in the processing of materials by cutting will reduce the level of self–generated vibrations that occur in tool systems. The advantages of the holder are the simplicity of construction and installation of the damping element; the ability to install various types of cutting heads on the holder. As an example, the possibility of using a holder when boring a hole in a thin–walled part is considered. A fragment of the part drawing and the boring scheme is shown. The influence of processing conditions on the tool deviation from the processed surface is studied. Graphs of the dependencies of the deflection of the forming point on the radial component of the cutting force, the departure of the holder, the diameter of the holder, and the elastic modulus of the holder material are constructed. Conclusions are made about the applicability of such holders.

Forced Vibration Numerical Analysis of Reticulate Systems by Dynamic Finite Element Method

This work is devoted to forced vibration numerical analysis of reticulate bar systems. The dynamic finite element method was used for determination of frequencies, displacement amplitudes, rotation angles and the dynamic effort factors. By this method the components of the dynamic rigidity matrix and inertia matrix depend on applied external excitation frequency. Obtained results are compared with those calculated by the classical finite element method as well as by analytical method. It is shown that the dynamic finite element allows for exact solutions to the problems in forced vibration of structures. Accuracy of dynamic finite element solution is verified through obtaining analytical solutions on simple systems. In case of complex systems where analytical calculations are complicated the dynamic finite element can become a universal tool for dynamic analysis.

A novel technique for hypersonic vehicle control

A novel control technique is investigated for hypersonic aerial vehicles. The technique is based on the use of active shock bumps (SBs) as a form of control device. The SBs deflect to create shockwaves on–demand, at specific locations around the aerial vehicle. As a result, a force is applied on the aerial vehicle, which in turn is used to provide the necessary moment for pitch and roll manoeuvres. In this work, a preliminary aerodynamic analysis of the SB device technique is made by means of CFD. For this purpose, and taking the large corresponding Reynolds numbers of the flow into consideration, the two–dimensional Euler equations are solved. A parametric investigation is carried out, by examining the effect of key parameters, namely the Mach number (M) and device deflection angle (δSB) on the produced force acting on the vehicle, serving as a proof of concept. Using a specific interpolation method, the resultant force is presented as a function of the Mach number and the device deflection angle, on three–dimensional charts, where the effect of each parameter is shown (force–Mach–deflection maps). Furthermore, a preliminary feasibility study is performed, including a kinematic analysis and some key material considerations. Additionally, a kinetic analysis is also conducted to secure the dynamic rigidity of the actuating mechanism and provide an initial estimation concerning weight and basic geometrical parameters of the SB mechanism components.