Contact Strength Research Articles

Tooth Surface Contact Strength of Cycloid Internal Gear Pair with High Contact Ratio

Tooth Surface Contact Strength of Cycloid Internal Gear Pair with High Contact Ratio

Genetic Approach for Multiobjective Optimization of Epicyclical Gear Train

The determination of optimal design of the planetary gear train with a lightweight, a short center distance, and a high efficiency is an important issue in the preliminary design of power transmission systems. Conventional and traditional methods have been widely used in optimization. They are deterministic and limited to solve some mechanical problems with several variables and constraints. Therefore, some optimization methods have been developed, such as the nonconventional method, the genetic algorithm (GA). This paper describes a multiobjective optimization for the epicyclical gear train system using the GA. It is aimed to obtain the optimal dimensions for epicyclical gear components like a module, number of teeth, the tooth width, the shaft diameter of the gears, and a performed efficiency under the variation of operating mode of PGT system. The problem is formulated under the satisfaction of assembly and balance constraints, bending strength, contact strength of teeth, and other dimension conditions. The mathematical model and all steps of the GA are presented in detail.

Contact strength of C-S-H cement phase

The object of the study was the cement phase C-S-H – X-ray amorphous calcium hydrosilicates, obtained by steaming at 80°C together limestone and silica at different molar ratios CaO/SiO2 = 0.5; 1.0; 1.5. The contact strength of the C-S-H phase with additions of portlandite, silica and alumina zols, high-aluminate slag was estimated by hyper-pressing method with subsequent destruction. It was established that the contact strength of the cement phase increases in proportion to the specific pressing pressure, the age of samples and inversely the phase basicity reaching 12 MPa. It was evidenced that additives increase the contact strength of the C-S-H stone. The features of the phase formation during the hydration of calcium aluminates were considered. It was established that there is no negative effect of additional porosity on the strength of the stone, because the restructuring of calcium hydroaluminates takes place during hyper-pressing. The specific behavior of low-basic calcium aluminates in a mixture with the C-S-H phase was established in the case of using high-aluminate slag, which consists in additional formation Al(OH)3 gel during the hydration, that is provide an increase in the contact strength of the compositions.

Research on Hydrogeological and Geological Conditions of the Slatinice Dump Base

The aim of this article is to clarify the geological structure of the area of interest (in particular the atmospheric water supply area), the assessment of hydrogeological conditions (determination of dominant collectors, flow directions of shallow and deep groundwater flows). From the aspect of the future process of the bordering Vršany quarry, part of the Slatinice dump will be extracted in the future. Since the basic factors that predispose to sliding (slope of the base, the orientation of the base, the character and nature of the deposited soil, etc.) cannot be influenced at the present or in the future, the only way to improve stability of the dump and to minimize the possibility of larger slope deformations, the long-term improvement of the shear contact strength at the interface of the dump with its subsoil.

СONTACT INTERACTION OF A SLOTTED CYLINDRICAL SHELL WITH A DEFORMABLE FILLER ALLOWING FOR DRY INHOMOGENEOUS FRICTION

The statement of the mixed problem on frictional interaction in the system which consists of cylindrical slit shells, divided by a deformable filler, is realized. Using one-dimensional shell and filler models, the integral equation for finding the contact is constructed. On the basis of numerical solutions the effect of mechanical, geometric and tribologic parameters of contacting pairs on nature of distribution of contact pressure, rigidity and strength of the system is investigated.

Ground-state properties of dipolar Bose polarons

We consider a quantum impurity immersed in a dipolar Bose–Einstein condensate and study the properties of the emerging polaron. We calculate the energy, effective mass and quasi-particle residue of the dipolar polaron and investigate their behaviour with respect to the strength of zero-range contact and a long-range dipolar interactions among the condensate atoms and with the impurity. While quantum fluctuations in the case of pure contact interactions typically lead to an increase of the polaron energy, dipole–dipole interactions are shown to cause a sign reversal. The described signatures of dipolar interactions are shown to be observable with current experimental capabilities based on quantum gases of atoms with large magnetic dipole moments such as Erbium or Dysprosium condensates.

EVALUATION OF THE DYNAMICS OF OCCLUSION RATIO DURING ORTHODONTIC TREATMENT OF PATIENTS WITH PERMANENT BITE.

The unity of the tooth-jaw system is ensured by the close interaction of dental rows, jaws, chewing and facial muscles, temporomandibular joint. Surgical anomalies of bite are often accompanied by significant changes in occlusion ratio of the tooth-jaw system, which significantly affects the quality of life of patients [1, 2, 3]. Significant influence on occlusion ratio has orthodontic treatment. Introduction of high technologies into the practice of prevention and treatment of abnormalities of the zygomatic system contributes to the improvement of dental health, however, the problem of violation of occlusive ratio in dental anomalies and deformations persists in connection with the increase in the prevalence of bite pathology among the population of Ukraine [4, 5].
 Investigation of violations of occlusion of dentitions is an integral part of the complex functional analysis of the dental maxillary apparatus. The most common clinical technique for the analysis of occlusive ratio is the technique of occlusion through articulation paper. However, this method does not meet current requirements, because it reflects neither such parameters as the strength and timeliness of tooth contacts, nor contains information about the nature of occlusive violations. Checking only the static parameters of occlusion is not a complete objective method of assessing the quality of treatment. With a sufficient number and correctly placed occlusal contacts, adequate interposition of the components of the temporomandibular joint, the formation of physiological occlusion will be the basis for the uniform distribution of functional loads. In order to solve the problems, a comprehensive study of the parameters of dynamic occlusion is necessary [6, 7].
 Up to date, an objective criterion for evaluating occlusion is the use of computerized analysis of occlusion with the help of T-Scan. The results obtained during this study can be used to control the quality of performed orthodontic treatment [6, 7, 8, 9].
 Purpose. Determination of the dynamics of occlusal ratio for 117 people of different age groups with sagittal malocclusions during orthodontic treatment generally and specific methods.
 Materials and methods of research. Occlusion contacts were assessed using a computerized occlusion analysis of T-Scan III (USA). Depending on the type of pathology of the occlusion, patients were divided into two groups: A (patients with distal occlusion) and B (patients with mesial occlusion), which depended on the method of orthodontic treatment, and were further divided into 2 subgroups.
 In the subgroups A1 (33 patients) and B1 (28 patients), the treatment was performed with the help of individual myofunctional apparatus - Elastoelainers, in group II patients of subgroup A2 (35 patients), and patients of subgroup B2 (21 patients) - treatment was carried out using fixed dentistry (bracket system).
 The control group consisted of 20 people of the same age with physiological bites and intact dentition.
 Results. Studies have shown that people with sagittal malocclusions expressed disturbances of occlusal ratio (presence premature occlusal contacts on the natural teeth, changes in the direction of the trajectory of the total vector occlusion load) experienced significant changes in the dynamics of the proposed orthodontic treatment, and closer to those of the control group immediately after treatment.
 Conclusions. The effectiveness of orthodontic treatment of patients with sagittal anomalies of occlusion with the help of individually myofunctional devices has been proved, which is confirmed by the data of the dynamics of indices of computer occlusion.

Toughening Nanoparticle Films via Polymer Infiltration and Confinement.

Disorderednanoparticle filmshave significant technological applications as coatings and membranes. Unfortunately, their use to date has been limited by poor mechanical properties, notably low fracture toughness, which often results in brittle failure and cracking. We demonstrate that the fracture toughness of TiO2 nanoparticle films can be increased by nearly an order of magnitude through infiltration of polystyrene into the film. The fracture properties of films with various polymer volume fractions were characterized via nanoindentation pillar-splitting tests. Significant toughening is observed even at low volume fractions of polymer, which allows the nanoparticle packing to be toughened while retaining porosity. Moreover, higher-molecular-weight polymers lead to greater toughening at low polymer volume fractions. The toughness enhancement observed in polymer-infiltrated nanoparticle films may be attributed to multiple factors, including an increase in the area and strength of interparticle contacts, deflection and blunting of cracks during failure, and confinement-induced polymer bridging of nanoparticles. Our findings demonstrate that polymer infiltration is a highly effective route for reinforcing nanoparticle packings while retaining porosity.

In situ testing of barrette foundations for a high retaining wall in molasse rock

Barrettes are common foundations for high-rise buildings, especially because of their high bearing capacity, for vertical as well as for lateral loads. In this paper, it is shown how these were adopted and tested for anchoring a 27 m high retaining wall in rock on a slope located in the centre of Zurich. The monolithic 10 × 1 × 25 m deep barrettes, excavated and built in layered rock (Upper Freshwater Molasse), are also intended to stabilise the slope. The main contribution to their bearing capacity is given by the contact strength between the reinforced concrete and the rock. Two full-scale pull-out tests, instrumented by distributed fibre-optical measurements, are carried out to investigate the contact strength between rock and reinforced concrete. The results show that dilatancy at the contact caused by the irregular excavated surface has a strong influence on the bearing capacity. Additionally, the distributed fibre-optic instrumentation allowed progressive crack propagation of the reinforced concrete in the barrettes to be detected during the test. Inverse analysis of the rock and concrete tensile properties are obtained within a finite-element calculation, which takes into account the non-linear properties of the reinforced concrete and the rock.

The Sun and Planetary Gear Design of a 1.5-MW Wind Turbine

In this paper, a 1.5-MW wind turbine design process is proposed. A hybrid transmission type with single planetary gear connected to two-stage parallel shaft cylindrical gear is designed and some main relevant parameters are calculated. The contact and bending fatigue strength of the sun gear and planetary gear are checked separately in the design process, to verify the calculation results. At last the modeling and finite element analysis method is used to analyze the designed gearbox. The first 3-order vibration modes and the first 8-order mode frequencies of the main components are listed in the final analysis, which proved the validity and rationality of the design.

BACKGROUND TO THE ARRANGEMENT OF AUTOMATING AND VOLVOUS PROCESSES IN THE FORM-FORMING MACHINES WHEN TREATING THE PREPARATIONS AND DETAILS BY THE PLASTIC DEFORMATION METHOD

Purpose. Analysis of surface-hardening technology for cold processing of metals, taking into account the deformation-wave processes occurring in the area in front of the shaping tool. Methodology. To establish the reasons for obtaining finished products with increased roughness, insufficient contact strength, fracturing and peeling of the surface layers, as well as the occurrence of significant dynamic loads in the mechanisms of machines for machining parts using plastic deformation, a two-mass design model is used in which the working tool is connected by friction with the moving processed workpiece. Findings. The results of determining the conditions for the occurrence of self-oscillations in the system “workpiece - tool” are presented. Based on the analysis of the friction characteristics as a function of the mutual slip rate between the workpiece and the shaping tool, the range of slip speeds is set, at which the self-oscillating processes for the friction pair can be excited: "tool - workpiece". Originality consists in the fact that the influence of the variable friction force on the occurrence of sustained self-oscillations between the workpiece being processed and the tool in the machines for “cold” plastic deformation of the metal has been established. The conditions for the occurrence and absence of self-oscillations in the zone of contact between the tool and the workpiece are found. Practical value lies in the fact that the modes of operation of machines for processing products by plastic deformation have been revealed under which unregulated roughness, fracturing and “peeling” of the parts being machined can occur, as well as a high dynamic background during the operation of the shaping tool of driving and power mechanisms. Practical recommendations are given to improve the performance of finished products and reduce vibroactivity in the drive. Keywords: running in, dragging, knurling, plastic deformation, elastic deformation wave, roller, tool, blank.

The Role of a Community Police Officer in Shaping the Security of Local Communities — Considerations in the Context of the First National Surveys of Community Police Officers (2017)

The article is devoted to the discussion of selected results of the nationwide community police officers research conducted by the authors in January 2017. This research is a part of the ongoing project of the Ministry of Internal Affairs and Administration „Community police officer closer to us”. The analysis was based on the answers provided by 5,400 respondents from all over the country to the following questions: Should the role of community police officers be to carry out social prevention tasks? Are community police officers satisfied with their job as community police officers? How do they assess their interpersonal communication skills? Do they think they have prestige in the local community? Do they participate in meetings with the local community and how do they characterize the police mission? The results will be processed in 17 reports from the national community police officers research. The application of conclusions from the results of qualitative and quantitative research conducted all over Poland in 17 garrisons will have a significant impact on the dialogue between the authorities and community police officers, determining the expectations of first contact officers, their problems, strengths and weaknesses. The research carried out will increase the effectiveness of the “Community police officer closer to us” programme, one of the basic programmes of the Ministry of Internal Affairs and Administration implemented in order to build trust between the authorities and a citizen. The research also resulted in two monographs on the functioning of the district division in Poland. The authors’research focuses on the partnership of community police officers services with the local community for internal security, taking into account the role of community police officers social and educational activities, and on drawing a professional portrait of the community police officer who is closer to people, solves problems of local communities and carries out activities in the social and educational area.

Reliability optimization design of bevel gear drive system based on large-scale double-toothed roll crusher

In this paper, a program for calculating contact strength of tooth surface and dedendum bending fatigue strength of bevel gear is developed. Based on genetic algorithm, the gear reliability is taken as the constraint condition. The global optimization design model of bevel gear reliability is established with the optimization objective on minimum total volume of bevel gear. Taking the large-scale double-toothed roll crusher as an example, the application of the reliability optimization program combined with the discrete element is introduced in detail. Finally, the optimization results that accord with the actual working conditions are obtained.

Contact Friction in Metal Drawing and Upsetting. Part 2

A new method is proposed for determining the frictional index by repeated wire extension. The frictional conditions are investigated with change in the extension, the drawplate taper, and other parameters. A general formula for the frictional characteristics and the drawing stress is proposed. The influence of the lubricant on the friction in deformation of the forgings is shown. Formulas for the frictional characteristics as a function of the form factor are derived. These formulas yield accurate results for the mean normal contact strength.

CONTACT PROBLEM FOR A TWO-LAYERED CYLINDER

Introduction. The investigation of the contact problems for cylindrical bodies is urgent due to the engineering contact strength analysis on shafts, cores and pipe-lines. In the present paper, a new contact problem of elastostatics on the interaction between a rigid band and an infinite two-layered cylinder, which consists of an internal continuous cylinder and an outer hollow one, with a frictionless contact between the cylinders, is studied. The outer cylindrical band of finite length is press fitted. By using a Fourier integral transformation, the problem is reduced to an integral equation with respect to the unknown contact pressure.Materials and Methods. Different combinations of linearly elastic materials of the composite cylinder are considered. Asymptotics of the symbol function of the integral equation kernel at zero and infinity is analyzed. This plays an important role for the application of the analytical solution methods. A key dimensionless geometric parameter is introduced, and a singular asymptotic technique is employed to solve the integral equation.Research Results. On the basis of the symbol function properties, a special easily factorable approximation being applicable in a wide variation range of the problem parameters is suggested. The Monte-Carlo method is used to determine the approximation parameters. The asymptotic formulas are derived both for the contact pressure, and for its integral characteristic. Calculations are made for different materials and for various relative thickness of the cylindrical layer including thin-walled layers.Discussion and Conclusions. The asymptotic solutions are effective for relatively wide bands when the contact zone length is bigger than the diameter of the composite cylinder. It is significant that the method is applicable also for those cases when the outer cylindrical layer is treated as a cylindrical shell. The asymptotic solutions can be recommended to engineers for the contact strength analysis of the elastic barrels with a flexible coating of another material.

Calculation of toothed gear mechanisms in machines and assemblies considering the effect of lubricants

The basic criteria of operational efficiency of most toothed gear mechanisms is the contact endurance of the conjugated surfaces of the teeth and the flexural endurance of teeth legs. In this case, the calculation based on contact stresses is the principal one in terms of determining the geometrical dimensions of toothed gear mechanisms, while the calculation of tooth bending is performed for validation.It is known that in order to prolong longevity and improve operational efficiency and load capacity of toothed mechanisms, different lubricants are used. However, given the insufficient body of research into the influence of a lubricant on contact endurance of the active surfaces of teeth, traditional methods for the calculation of toothed gears (for example, GOST 21354-87) equate a lubricant influence coefficient to unity, that is, a perfect case is considered when friction is absent. Such an approach leads to the inaccurate evaluation of load capacity of toothed gears that can be a reason for both their premature failure and the overestimation of their geometrical dimensions.In this work, we have solved the contact problem on a contact between two bodies of arbitrary shape, close to half-planes, at the finite friction coefficient; it was found that the value of the resulting contact stress exceeds the stress, calculated according to the known Hertz solution, by 6 %.The proposed procedure for the calculation of toothed gears in terms of contact strength at the finite friction coefficient, without assumptions about the smallness of the contact area and the shape of borders, makes it possible to estimate load capacity of the toothed gears considering the influence of lubrication and the existence of friction between the conjugated surfaces of the teeth.We have derived the analytical expression for a lubricant influence coefficient based on the solution to the contact problem of pressure from a rigid stamp on the elastic half-plane in terms of the coefficient of friction between the conjugated surfaces of toothed gears. That allows the estimation of the true load capacity of toothed gears under the influence of various lubricants, which is of great theoretical and practical importance when designing machines and assemblies

The Contact Mechanics of Novikov’s Surface-Hardened Gearing during Running-in Process

The article is devoted to the analysis of the state of the contact surfaces of the higher kinematic pair in the general case of relative motion, that is, in the presence of rolling, sliding, and twisting, which is characteristic of Novikov’s circular-screw gears. The purpose of the work is to assess the impact of friction forces, the state of contact surfaces after tool processing, and the localization of the instantaneous contact spot on the level of contact—fatigue durability of gears. Power contact in the presence of geometric slippage of the mating surfaces leads to a significant change in the initial geometry and the mechanical properties of surface layers. In the existing methods of calculations of contact strength, the effect of running-in is investigated insufficiently, which leads to an incorrect result, especially for gear with high hardness of the teeth. In this work, the conditions of contact interaction close to the real requirements are studied on the basis of experimental material, numerical solution of the contact problem, determination of the terms of the contact areas of slip, and adhesion within the instantaneous spot. The shape of the instant contact spot has asymmetry and can be approximated by an ellipse with the introduction of a correction factor. The running-in period is of a plastic nature with cold deformation and reduction of the roughness of surfaces. As a result of the run-in period, the area of actual contact (tooth height) is increased by 2 or more times. It is not desirable to spread the area of contact at the area of adhesion that initiates the formation of pitting. The presence of defective surface area on the level of contact strength does not have significant influence, because of the running-in period, but increases the risk of spalling and brittle fracture.

Laser sintering process of ceramic powders: The effect of particle size on the mechanical properties of sintered layers

Selective Laser Sintering (SLS) of ceramic powders is studied in order to understand how the initial material properties and the process conditions affect the degree of sintering/melting and the mechanical properties of the sintered material. Unimodal powder samples of different narrow particle size distributions between 16 and 184 μm were sintered with a 40 W CO2 laser, using laser scan speeds of either 50 or 100 mm s−1 and, in both cases, a scanning energy of 160 J m−1. The sintered material was studied by means of optical and SEM microphotography and characterized in terms of bulk density and tensile strength. The Rumpf approach to relate interparticle forces to the strength of powder agglomerates was used in this work to estimate the average strength of the sintered interparticle contacts starting from the tensile strength of specimens. In turn, the average strength of the neck contact was used to estimate the size of the neck of fused material between two sintered particles. These data coupled with the Frenkel model for particle sintering allowed an estimate of the sintering temperature for the different experimental conditions tested. The temperatures found are consistent with the glass transition temperature of the material used. The effect of particle size and scanning speed is assessed and discussed.

An Approximate Solution Method of Dynamic Reliability for Wind Turbine Gear Transmission with Parameters of Uncertain Distribution Type

The reliability evaluation of wind turbine system is the theoretical basis for engineering design, and how to deal with its complex wind loads is the technical challenge for it. Considering the distribution type of wind loads is uncertain, the stress-strength interference model based on the assumption of normal distribution can’t be applied to the reliability of wind turbine gear transmission. For this, the dynamic reliability model for wind turbine transmission with uncertain distribution parameters is established firstly with the deterioration of gear contact stress and strength degradation being considered. Then, the dynamic reliability is solved by approximate expansion of the model function into standard normal distribution function based on the stochastic perturbation theory and the Edgeworth series method. In the absence of experimental data, the first four moments of the random parameters with uncertain distribution are obtained by Monte Carlo method. Meanwhile, the dynamic reliability sensitivity to gear parameters is derived by the same method and the sensitivity variation is given which effectively reflecting the influence of gear parameter changes on the system reliability of wind power gear drive, and providing an accurate theoretical basis for the optimal design of the project.

Gathering Point-Aided Viral Marketing in Decentralized Mobile Social Networks

Viral marketing is a technique that spreads advertisement information through social networks. Recently, viral marketing through online social networks has achieved huge commercial success. However, there are still very little research reported on viral marketing in decentralized mobile social networks (MSNs). Comparing with online viral marketing, viral marketing in decentralized MSNs faces many challenges, such as unreliable information diffusion and limited network knowledge. To address these problems, we propose the gathering point-aided mobile viral marketing ( GP-MVM ) scheme, which contains two major components, i.e., seed selection and information diffusion . Seed selection is responsible to select a set of seed nodes from which information diffusion begins. Based on a new metric called integrated contact strength (ICS), we propose two distributed seed selection schemes, i.e., ratio seeding and threshold seeding , while, for information diffusion, we propose the GP-aided diffusion algorithm, which utilizes user GPs to promote information propagation. Continuous-time Markov chain-based analytical model shows that GP-MVM has a good scalability. Simulations indicate that GP-MVM outperforms two state-of-the-art information diffusion methods designed for MSNs, in terms of both diffusion proportion and diffusion speed.