A Semi-analytical Method for Analys of Contact Interaction Between Structural Elements Along Aligned Surfaces

A significant share of structures includes the components that are in contact with each other. These include, for example, stamps, molds, machine tools, technological equipment, engines, etc. They are characterized by a varied load mode. Therefore, an important aspect in studying the stressed-strained state of such structures is to determine the dependence of contact pressure on the external forces applied to them. A superposition principle for contact problems is not applicable in a general case. However, for this type of structures, the linear dependence of contact pressure on the load level has been established. In this case, the contact area does not depend on the load level. It has been demonstrated that this pattern holds not only for a one-component but also for the multi-component load. As a result, the possibility for rapid determining the stressed-strained state of such structures is ensured, while maintaining the accuracy of the results obtained.The applicability of the constructed method has been demonstrated by using the machine tools' clamping accessories as an example. The established patterns are important when estimating the designs of structures. The derived direct proportional dependence of the solution on the applied loads makes it possible to shorten the design time of structures with the elements that interact when they are in contact at surfaces of the matching shape. In this case, we have considered different sets of loads, as well as the various varying variants of these loads. The examined cases have confirmed the direct proportionality of the components of the stressed-strained state of the magnitude of the applied forces for the case of their coordinated change. It has been also shown under an uneven change in the individual components of loads the dependence of contact pressure and components of the stressed-strained state of the examined objects on the applied forces demonstrates a complex character different from the directly proportional relation. The established dependences underlie the substantiation of the design and technological parameters of the structures that are designed, as well as their operational mode

Substantiating the Requirements to Functional Indicators for the Manipulators of Mobile Robotic Demining Complexes

It has been proposed that humanitarian demining should involve mobile robotic complexes equipped with manipulators based on mechanisms with parallel kinematic structures. The features of design and characteristics of the manipulators have been considered. We have established special features in equipping the manipulators, used to directly manipulate objects. The geometrical and strength parameters for the threaded connection between a fuse and a mine shell have been determined. A scheme of efforts interaction in the threaded connection has been substantiated. We have found patterns in the emergence of the thread force reactions under a gravitational load of the fuse and at thread tightening. The efforts that arise at unscrewing the fuse of an anti-tank mine by the manipulator have been experimentally determined. The measurements employed specialized equipment in the form of a set of special grips. The result of measurements is the established effort of thread tightening and the momentum loads required for unscrewing the fuse. We have substantiated the rational kinematic and dynamic algorithms of the manipulator operation in the process of unscrewing the fuse. To this end, we measured the displacements of the fuse under the action of asymmetrical force and momentum loads. The measurements of parameters have been performed of cyclic loads necessary to unfix the threaded connection between the fuse and a mine. A special algorithm of dynamical loads on the fuse has been suggested, which ensures rational conditions for its unscrewing. The paper reports results from experimental study into remotely-controlled disposal of explosive objects and unexploded ammunition using an example of an anti-tank mine. We have shown feasibility of the proposed technology of humanitarian demining of territories containing explosive objects

Investigation of Multiple Contact Interaction of Elements of Shearing Dies

When justifying the design parameters, it is necessary to carry out the analysis of the strain-strain state of individual elements of technological systems, which are sets of parts under contact interaction conditions. These problems are nonlinear, and the principle of superposition does not apply to them. For this reason, the amount of calculations increases dramatically. To overcome this drawback, methods and models for the rapid and precise study of the strain-strain state of complex objects, taking into account contact interaction are developed. The feature of the problem statement is that the solution of contact problems under certain conditions linearly depends on the load. The patterns of contact pressure distribution are determined. It is concentrated in the areas of constant shape and size. Only the scale of contact pressure distribution varies.This gives an opportunity to significantly accelerate design studies of die tooling while preserving the accuracy of numerical modeling of the stress-strain state.The developed approach involves a combination of advantages of numerical and analytical models and methods for analyzing the stress-strain state of elements of shearing dies, taking into account contact interaction. This concerns the possibility to solve problems for a system of complex-shaped contacting bodies, which is impossible with the use of analytical models. On the other hand, the possibility of scaling the solutions of these problems with the stamping force is substantiated, which is generally not performed for nonlinear contact problems. So, it is sufficient to solve the problem of determining the strain-strain state of elements of such a shearing die. For the other value of stamping force, the proportionality rule is applied. Thus, the efficiency of research sharply increases and high accuracy of the obtained results is ensured

Devising an Engineering Procedure for Calculating the Ductility of a Roller Bearing Under a No-central Radial Load

Known theoretical approaches to calculating the ductility of rolling bearings include rather complicated analytical dependences and require cumbersome computation. That makes it a relevant task to undertake a research aimed at the development of an engineering approach to the calculation of radial ductility of bearings.The current study proposes an engineering method for determining radial ductility using cylindrical roller bearings as an example. It accounts for the radial gap, contact deformation of parts, the deformations of bending and misalignment of rings for cases when a bearing is exposed to the action of a central radial load and a radial load with eccentricity. The adopted simplified linear calculation model for determining the angle of rings misalignment is valid for small angles when contact is maintained over the entire length of the roller. Computation of radial ductility of roller bearings under a no-central radial load is based on determining the sum of variable elastic deformations in a contact between rings and the most loaded roller. The values for elastic deformations are determined from known formulae for solving the contact problem in elasticity theory taking into consideration a mismatch between the geometric centers of outer and inner rings.Adequacy of the proposed engineering procedure has been confirmed by results from calculating the specific ductility of the cylindrical roller bearing 2211 with a central radial load. By using the proposed methodology, we have derived values for specific ductility that are 3...4 % lower compared to similar results obtained from a known procedure. By using the cylindrical roller bearing 42726 as an example, we have investigated structural parameters considering a no-central radial load. A decrease in the bearing 42726 ductility with an increase in the number of rollers and rigidity of the outer ring has been shown, as well as with a decrease in the eccentricity of a radial load.The ductility of rolling bearings must be known when constructing dynamic models of certain machines: machine tool spindles, shaft-gears at large-size reducers, crane structures. Therefore, the proposed engineering procedure for determining the ductility of roller bearings at small angles of rings misalignment could be applied in the practice of designing machines and mechanisms for which the elastic characteristics of all their components are important