Experimental Study on the Mechanical Behavior of Orthodontic Arches Exposed to the Environment in the Oral Cavity

Background. The arches used in orthodontic therapy are subject to increasing physical and chemical stresses. Purpose of the study: This in vitro experimental study aims to highlight and compare the main mechanical properties of orthodontic arches. Materials and Methods: We used 40 springs, 2 materials, 20 of Ni-Cr and 20 of Co-Cr, of different diameters, 0.7 mm 0.8 mm and 1.2 mm, subjected to the environment of artificial saliva and artificial saliva with cola for one month and two months, respectively. Five springs of each material were tested at different times: T0, before application in the oral cavity, then at time T1, T2, T3, T4. Three lengths of the lever arm were considered for bending forces acting on the springs (dental wires). These lengths were 15, 10 and 5 mm. The wires were tested under the action of bending forces on a Hans Schmidt HV 500N stand, obtaining the characteristics of the wires: deformation-force-time. Results: Graphical determinations show that the degree of deformation of the wires is influenced by the applied force, diameter and obviously by the immersion time, respectively by the type of solution in which the springs were immersed. Conclusions: The final degree of bending is higher for Co-Cr arcs than for Ni-Cr at all three dimensions.

Results verification of numerical simulation of the side impact of a vehicle in a three-point bending test

The research objective was to use numerical simulation to verify safety characteristics of deformation zone reinforcements subjected to bending, obtained from experimental results of the stretch-bending test. The methodology proposed for result verification by means of numerical simulation using a three-point bending test was verified on a sheet metal strip made of micro alloyed steel H 220 PD and a two-phase ferritic-martensitic steel DP 600. Material data for the material model according to Krupkovsky were determined in the tensile test. The measured data were processed tabularly and graphically. A comparison of the deformation work constant and the stiffness and deformation force constants shows that a very good match between the measured and the calculated characteristics has been achieved. Based on the data obtained, it can be assumed that it is possible to reduce the weight of deformation elements while maintaining the required safety characteristics by replacing micro alloyed steel H 220PD with the two-phase DP steel.

MODEL AND METHOD FOR CALCULATING THE RESOURCE OF REINFORCED CONCRETE ELEMENTS AND STRUCTURES

The article classifies, identifies and analyzes in detail the main disadvantages of existing models and methods for calculating the resource of building structure elements. A universal model and method for calculating the general and residual resources of reinforced concrete elements and structures that are under prolonged influence to operational loads are proposed. The generalized deformation-force model of the reinforced concrete elements and structures resistance to force effects is represented by an extended system of equations of the deformable solid mechanics. It is shown that the most important force and deformation parameters of the reinforced concrete elements state diagrams at all stages are functionally interconnected not only by rigidity, but by the potential energy of deformation. Therefore, due to the application of the hypothesis of invariability in a unit of volume and independence from the loading mode of the potential energy of their limiting deformation, this model has been developed to the energy level. The main advantages of the developed model of the reinforced concrete elements to force effects resistance in comparison with the existing force and deformation models in determining the resource of such elements are demonstrated. The methodology for calculating the general and residual life of reinforced concrete elements and structures is proposed to be built according to the deflections directly measured during field surveys or the step and width of the opening of normal cracks. In practice, they can be determined by geodetic, photogrammetric or any other means. The combination of the deformation-force model and the energy criterion makes it possible to calculate the general and residual resources of reinforced concrete elements and structures from a unified methodological standpoint. Therefore, the proposed "energy" hypothesis is recommended to be used as a universal energy criterion not only for the bearing strength exhaustion of the reinforced concrete elements, but also for limiting their deflections, as well as the width of the normal cracks opening under the action of any duration loads.

ЗНИЖЕННЯ МЕТАЛОМІСТКОСТІ РОТАЦІЙНО-ПРОФІЛЬОВАНИХ КОЛІСНИХ ОБОДІВ РІЗНИХ ТИПІВ І ТОВЩИНИ

The research carried out made it possible to develop a new scheme for the process of rotary profiling of wheel rims, which allows to reduce the specific quantity of metal for parts. The essence of the solution lies in the fact that at the second step the jet central section is additionally made more powerful. This allows to change the nature of the deformation after the second step and to eliminate unnecessary thickening of the jet base. With an increase in the jet depth the edge sections are subjected to insignificant tensile stresses, while the stress-strain state of the part remains symmetric and constant at each point. The worked out sequence of calculating a new technological process allows calculating all technological parameters: width and length of a flat workpiece; maximum permissible stress in the workpiece material; a profiling route; as well as to identify deformations and stresses for edge elements and in hazardous areas. Further, taking into account the elastic deformations of the workpiece, the profile of the rollers was built, and then optimal deformation force along the transitions was calculated, then feed and the number of revolutions of the rollers were assigned. The new scheme made it possible to reduce metal consumption for parts and obtain a significant economic effect. Ovality of the part and multiple repeated deformation of the same sections of the workpiece are eliminated, and the degree of strengthening of the material is also reduced.

Plastic flow of isotropic rigid body at uniform deformation

The mathematical analysis of plastic flow processes under uniform plane, axisymmetric and volumetric deformation is carried out. The analysis is based on the external shape change of the body, which determines the movement of material points. It is shown that the plastic flow of an isotropic rigid-plastic body under plane deformation obeys the hyperbolic law, and for axisymmetric and volumetric deformations – the inverse square law. Spatial-geometric expressions of these laws made it possible to reveal and explain in a new way the physical essence of plastic shear. It is proved that the stressed state of a body under uniform tension-compression deformation is complex and cannot be defined as “linear”. The normal stress, which coincides with the direction of the resulting deformation force, is not the main one, since in the areas perpendicular to this direction, the shear stresses are not equal to zero. Examples of solving technological problems are given: extrusion of cylindrical billets and wire drawing, rolling of a wide strip of rectangular profile. It is shown that the problems of determining the stress-strain state of isotropic rigid-plastic bodies along the known trajectories of movement of material points are statically definable.

Mechanics of Screw Joints Solved as Beams Placed in a Tangential Elastic Foundation

This article deals with a new original analytical solution of deformation, force and stress states in wood screw joints up to the limit values of pulling out/breaking the screw. The screws are under tension. The wood-to-screw interaction is effectively simplified by introducing several physical model variants using a tangential elastic non-linear foundation. The experimental verification of the proposed models using pull-out tests (i.e., pulling out screws from dry spruce wood in laboratory conditions) confirms the correctness of the proposed models of the elastic linear/non-linear foundation. The validity of the model is also analytically and experimentally verified in the biomechanical model of pulling out screws from the femur of a bovine/human cadaver, which confirms and expands the validity of newly designed screw joint models outside the timber structure area.

NONLINEAR DEFORMATION-FORCE MODEL OF A CONCRETE BAR WITH NON-METALLIC COMPOSITE REINFORCEMENT IN THE GENERAL CASE OF A STRESSED STATE

The article discusses a nonlinear deformation-force model of a concrete bar structure with a non-metallic composite reinforcement (NKA-FRP) in the general case of a stressed state, when all four internal force factors from an external load (namely, bending and twisting moments, transverse and longitudinal forces). A sufficiently deep and meaningful analysis of well-known studies on the selected topic is given. It has been established that the proposed nonlinear deformation-force model of a bar structure with FRP in the general case of a stressed state can be practically useful due to the possibility of its application in the design or reinforcement of beams, girders, columns and elements of rosette trusses of rectangular cross-section, which are operated under aggressive environmental conditions. This model can also be used to check the bearing capacity of existing FRP concrete bar structures, which operate not only under the influence of an aggressive environment, but also under conditions of a complex stress-strain state. In the course of the research, an algorithm was developed for determining the bearing capacity of the design section of a concrete rod with FRP under its complex stress state. General physical relations for the design section are given in the form of a stiffness matrix. The algorithm for calculating a concrete bar with FRP consists of a block for inputting the initial data, the main part, auxiliary subroutines for checking the conditions for increasing the load vector and depletion of the bearing capacity, as well as a block for printing the calculation results. At each stage of a simple static stepwise increasing load, the calculation is carried out by performing a certain number of iterations until the accuracy of determining all components of the deformation vector satisfies a certain predetermined value. The features and patterns of changes in normal and tangential stresses, generalized linear and angular deformations, as well as the equations of equilibrium of a concrete bar with FRP, which operates under the influence of an aggressive environment under conditions of a complex stress state, are also considered.

Investigation of Energy-Absorbing Properties of a Bio-Inspired Structure

Numerous engineering applications require lightweight structures with excellent absorption capacity. The problem of obtaining such structures may be solved by nature and especially biological structures with such properties. The paper concerns an attempt to develop a new energy-absorbing material using a biomimetic approach. The lightweight structure investigated here is mimicking geometry of diatom shells, which are known to be optimized by nature in terms of the resistance to mechanical loading. The structures mimicking frustule of diatoms, retaining the similarity with the natural shell, were 3D printed and subjected to compression tests. As required, the bio-inspired structure deformed continuously with the increase in deformation force. Finite element analysis (FEA) was carried out to gain insight into the mechanism of damage of the samples mimicking diatoms shells. The experimental results showed a good agreement with the numerical results. The results are discussed in the context of further investigations which need to be conducted as well as possible applications in the energy absorbing structures.

Calculation of the force field required for nucleus deformation during cell migration through constrictions

During cell migration in confinement, the nucleus has to deform for a cell to pass through small constrictions. Such nuclear deformations require significant forces. A direct experimental measure of the deformation force field is extremely challenging. However, experimental images of nuclear shape are relatively easy to obtain. Therefore, here we present a method to calculate predictions of the deformation force field based purely on analysis of experimental images of nuclei before and after deformation. Such an inverse calculation is technically non-trivial and relies on a mechanical model for the nucleus. Here we compare two simple continuum elastic models of a cell nucleus undergoing deformation. In the first, we treat the nucleus as a homogeneous elastic solid and, in the second, as an elastic shell. For each of these models we calculate the force field required to produce the deformation given by experimental images of nuclei in dendritic cells migrating in microchannels with constrictions of controlled dimensions. These microfabricated channels provide a simplified confined environment mimicking that experienced by cells in tissues. Our calculations predict the forces felt by a deforming nucleus as a migrating cell encounters a constriction. Since a direct experimental measure of the deformation force field is very challenging and has not yet been achieved, our numerical approaches can make important predictions motivating further experiments, even though all the parameters are not yet available. We demonstrate the power of our method by showing how it predicts lateral forces corresponding to actin polymerisation around the nucleus, providing evidence for actin generated forces squeezing the sides of the nucleus as it enters a constriction. In addition, the algorithm we have developed could be adapted to analyse experimental images of deformation in other situations.