Analysis of the Operation of an Arched Elastomeric Shock Absorber Under Two-Axial Loading

Elastomeric shock absorbers are used in various technical fields to protect equipment from impacts. Elastomers made in an arched shape have complex nonlinear force characteristics due to large deformations, loss of stability of working elements and closing of surfaces. In this regard, obtaining the power characteristics of arched elastomeric shock absorbers is a complex computational problem. It is noteworthy that, in the literature, these characteristics are given only for the case of normal compression. However, when assessing the possibility of using a shock-absorbing system based on arched elastomeric shock absorbers, it is necessary to take into account their lateral force. The study proposes to solve the problem of determining the elastic force characteristics of a shock absorber while operating in the normal and lateral directions in the system of finite element analysis in a flat formulation. Analytical expressions are obtained for the normal and transverse static reactions of the shock absorber under simultaneous loading in the normal and transverse directions. Analytic expressions can be used to simulate complex shock-absorbing systems with a large number of such shock absorbers.

Designing a detachable body with sliding side walls and a roof

Objective: Selection of technical solutions for designing a covered detachable body fence with sliding side walls and a roof. Methods: A detachable body with sliding side walls and a roof was designed in accordance with several technical and regulatory documents using the KOMPAS-3D design software. Results: The covered detachable body with sliding side walls and a roof designed for the carriage of goods that require protection from atmospheric precipitation has been proposed. A scheme of a lock for side sliding doors and a linkage scheme of the doors’ middle part have been developed. Drawings of the main load-bearing elements of the car body are presented, including the underframe with three longitudinal and several transverse and auxiliary beams. The diagram of fastening the sliding door roller assemblies on the car body to the lower longitudinal beams and to the upper beam is given. Practical importance: The covered detachable body with sliding side walls and a roof allows reducing the time and human effort of loading and unloading the car, provides simultaneous loading and unloading of goods both from the side and from the top of the body using various hoisting devices.

Rhodium(I)-Catalyzed CO-Gas-Free Arylative Dual-Carbonylation of Alkynes with Arylboronic Acids via the Formyl C–H Activation of Formaldehyde

The rhodium(I)-catalyzed reaction of alkynes with aryl­boronic acids in the presence of formaldehyde results in a CO-gas-free arylative dual-carbonylation to produce γ-butenolide derivatives. The simultaneous loading of phosphine-ligated and phosphine-free rhodium(I) complexes is required for efficient catalysis. The former complex catalyzes the abstraction of a carbonyl moiety from formaldehyde through the activation of its formyl C–H bond (decarbonylation) and the latter catalyzes the subsequent dual-incorporation of the resulting carbonyl unit (carbonylation). The use of larger amounts of the phosphine-ligated rhodium(I) complex generates more carbonyl units, leading to the formation γ-butenolides via the dual-incorporation of the carbonyl unit.

PRECISION OF PRODUCTION CROWN MANUFACTURING USING 3D-PRINTING TECHNOLOGY. IMMEDIATE TEMPORARY RESTORATION AFTER DENTAL IMPLANTATION

Subject. Currently, tooth loss prosthetics using implants are widely used. An important problem is the loss of bone tissue due to infections around the implant. Micro-gaps at the implant-abutment interface can contribute to infection with microorganisms.The aim of this study was to investigate the precision of connecting the implant-abutment components with simultaneous loading and temporary restoration. Methodology. The precision of the "implant – abutment – artificial crown" connection was studied on a clinical case with simultaneous removal of a tooth root, followed by implant placement and temporary restoration. Before installing the implant, specialized programs combined a three-dimensional CT model of the jaw with a 3D model of the dentition obtained as a result of scanning. To study precision, a duplicate plastic crown was made according to this virtual plan and fixed in a similar implant. The "implant-crown" model was fixed in plaster and a section was made up to the level of the "implant-abutment-artificial crown" connection, which was studied using electron microscopy at magnification of 50, 100 and 200 times. Results. Electron microscopy data showed that the junction of the internal surface of the implant with the plastic "abutment" had a gap width in the range of 54-77 microns. Conclusion. The exact fit of the restoration on the implant was confirmed by electron microscopy. In the presented example, due to the production of temporary restoration, it was possible to reduce the number of manipulations with the implant-abutment components. Modern milling and 3D printing technologies show high precision.

Three-Component Wear-Resistant PEEK-Based Composites Filled with PTFE and MoS2: Composition Optimization, Structure Homogenization, and Self-lubricating Effect

The aim of this work was to design and optimize compositions of three-component composites based on polyetheretherketone (PEEK) with enhanced tribological and mechanical properties. Initially, two-component PEEK-based composites loaded with molybdenum disulfide (MoS2) and polytetrafluoroethylene (PTFE) were investigated. It was shown that an increase in dry friction mode tribological characteristics in metal-polymer and ceramic-polymer tribological contacts was attained by loading with lubricant fluoroplastic particles. In addition, molybdenum disulfide homogenized permolecular structure and improved matrix strength properties. After that, a methodology for identifying composition of multicomponent PEEK-based composites having prescribed properties which based on a limited amount of experimental data was proposed and implemented. It was shown that wear rate of the “PEEK + 10% PTFE + 0.5% MoS2” composite decreased by 39 times when tested on the metal counterpart, and 15 times on the ceramic one compared with neat PEEK. However, in absolute terms, wear rate of the three-component composite on the metal counterpart was 1.5 times higher than on the ceramic one. A three-fold increase in wear resistance during friction on both the metal and ceramic counterparts was achieved for the “PEEK + 10% PTFE + 0.5% MoS2” three-component composite compared with the “PEEK + 10% PTFE”. Simultaneous loading with two types of fillers slightly deteriorated the polymer composite structure compared with neat PEEK. However, wear rate was many times reduced due to facilitation of transfer film formation. For this reason, there was no microabrasive wear on both metal and ceramic counterpart surfaces.