THEORETICAL BASIСS OF PROVIDING THE TECHNICAL CHARACTERISTICS OF MILITARY AND CIVIL VEHICLES BY JUSTIFICATION OF THE FORM AND PROPERTIES OF THE MATERIALS OF CONTACTING ELEMENTS

Elements of constructions of modern military and civil vehicles usually work in conditions of high contact loads. Аt the stage of their creation, strength studies are carried out using traditional models of contact of bodies of nominal shape. Нowever, the real structural elements have deviations from such models, which are due to design and technological factors: macrodeviation of the shape, surface roughness, strengthening etc. Such perturbations of nominal parameters have a significant effect on the distribution of contact pressure between the elements of military and civil vehicles, however, traditional methods for studying the stress-strain state of contacting bodies do not make it possible to take such factors into account fully, collectively and exhaustively. To eliminate the existing contradiction, a semi-analytical method is proposed, which is based on the development of variational principles and boundary-element sampling. The created models make it possible to take into account the regularities of the influence of shape perturbations and properties of the surface layers of contacting bodies on the stress-strain state. As a result, it becomes possible to justify favorable perturbations by strength criteria. Such models and methods are offered to the work, and on their basis it’s proposed the implementation of research elements of military and civil vehicles for appointment to ensure world class the technical and tactically technical characteristics. Ключові слова: military and civilian vehicles; design and technological factor; stress-strain state; contact interaction; strength

Optimization of Exposed Concrete Pigmented with FexOy

Lately concrete has been used not only as backbone of structure but as esthetic construction art. The challenge is to combine these two parameters and predict concrete behavior. The target of this paper is to successfully develop easily controllable, visually attractive concrete that provides with necessary compressive strength criteria. Two mix designs with Fe2O3 and Fe3O4 pigments were tested for 1, 3, 7, 14, 28-day compressive strength. Concrete samples were left indoors and outdoors to investigate migration of salts also called as efflorescence. Concrete mix designs without pigment additive showed higher compressive strength as well as density compering to pigmented concrete. Pigmented concrete outdoor specimens showed increased migration of salts on surface comparing to indoor specimens.

Coupling-Strength Criteria for Sequential Implicit Formulations

Sequential Fully Implicit (SFI) schemes have been proposed as an alternative to the Fully Implicit Method (FIM). A significant advantage of SFI is that one can employ scalable strategies to the flow and transport problems. However, the primary disadvantage of using SFI compared with FIM is the fact that the splitting errors induced by the decoupling operator, which separates the pressure from the saturation(s), can lead to serious convergence difficulties of the overall nonlinear problem. Thus, it is important to quantify the coupling strength in an adaptive manner in both space and time. We present criteria that localize the computational cells where the pressure and saturation solutions are tightly coupled. The approach is using terms in the FIM Jacobian matrix, we quantify the sensitivity of the mass and volume-balance equations to changes in the pressure and the saturations. We identify three criteria that provide a measure of the coupling strength across the equations and variables. The standard CFL stability criteria, which are based entirely on the saturation equations, are a subset of the new criteria. Here, the pressure equation is solved using Algebraic MultiGrid (AMG), or a multiscale solver, such as the Multiscale Restricted-Smooth Basis (MsRSB) approach. The transport equations are then solved using a fixed total-velocity. These ‘coupling strength’ criteria are used to identify the cells where the pressure-saturation coupling is strong. The applicability of the derived coupling-strength criteria is tested using several test cases. The first test is using a gravitational immiscible dead-oil lock-exchange under a unit mobility ratio and large differences in density. For this case, the SFI algorithm fails to converge to the fully coupled solution due to the large splitting errors. Introducing a fully coupled solution stage on the local subdomains as an additional correction step restores nonlinear convergence. Detailed analysis of the ‘coupling strength’ criteria indicates that the criteria related to the sensitivity of the mass balance to changes in the pressure and the sensitivity of the volume balance to changes in the saturations are the most important ones to satisfy. Other test cases include an alternate gas-water-gas injection in a top layer of the SPE 10 test case and an injection-production scenario in a three-dimensional reservoir with layered lognormally distributed permeability. We propose novel criteria to estimate the strength of coupling between pressure and saturation. These CFL-like numbers are used to identify the cells that require fully implicit treatment in the nonlinear solution strategy. These criteria can also be used to improve the nonlinear convergence rates of Adaptive Implicit Methods (AIM).

Study on Properties of Automatically Designed 3D-Printed Customized Prosthetic Sockets

This paper presents the results of experiments conducted on a batch of additively manufactured customized prosthetic sockets for upper limbs, made of thermoplastics and designed automatically on the basis of a 3D-scanned limb of a 3-year-old patient. The aim of this work was to compare sockets made of two different materials—rigid PLA and elastic TPE. Two distinct socket designs with various mounting systems were prepared. To find a reliable set of parameters for cheap and stable manufacturing of usable prostheses using 3D printers, realizing the fused deposition modeling (FDM) process, sets of sockets were manufactured with various process parameters. This paper presents the methodology of the design, the plan of the experiments and the obtained results in terms of process stability, fit and assessment by patient, as well as strength of the obtained sockets and their measured surface roughness. The results are promising, as most of the obtained products fulfil the strength criteria, although not all of them meet the fitting and use comfort criteria. As a result, recommendations of materials and process parameters were determined. These parameters were included in a prototype of the automated design and production system developed by the authors, and prostheses for several other patients were manufactured.